ISSN 1000-0526
CN 11-2282/P
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    2021,47(6):645-654, DOI: 10.7519/j.issn.1000-0526.2021.06.001
    Abstract:
    Developments of operational global medium range forecast system of National Meteorological Centre are reviewed. The topics focus on the advances in science and technology in National Meteorological Centre since the setup of global forecast system. The improvements in localization, operational application and further development of sequence of spectral model series are summarized, and those in progress of self developed global medium range forecast system, GRAPES_GFS, are described in detail.
    2021,47(6):655-670, DOI: 10.7519/j.issn.1000-0526.2021.06.002
    Abstract:
    Quantitative precipitation forecast (QPF) is the traditional and critical forecasting operation of National Meteorological Centre (NMC). With the rapid development of society and economy and its increasing demand in the fineness of various meteorological products, developing the fine gridded QPF has become the primary task of NMC. A fine gridded QPF product system with a spatial resolution of 5 km and 1 h 〖JP2〗interval for 3 d lead time and 3 h interval for 3-10 d lead time has been built, which covers rain, sleet, freezing rain, snow and depth of new snowfall forecast. This paper presents the progress of the related technology development in high resolution numerical weather forecast model, fine gridded QPF, gridded precipitation type and depth of new snowfall forecast and refined QPF verification. Finally, the existing problems and future developments of the current fine gridded QPF technology are discussed.
    2021,47(6):671-684, DOI: 10.7519/j.issn.1000-0526.2021.06.003
    Abstract:
    The forecasting operation of quantitative hydrometeorology with accurate spatio temporal distribution is to meet the demands of the national disaster prevention and mitigation, major projects support, expanding impacted forecasting and risk warning. Although great progresses in the hydrometeorological forecasting have been made in National Meteorological Centre in the recent years, there are still many gaps compared with the advanced forecasting technology in foreign countries. The current development of technique and operation status of the hydrometeorological forecasting was reviewed in this paper. In addition, the current challenges facing China were summarized and the corresponding measures and further development plans were proposed. At present, the main techniques on hydrometeorological forecasting can be classified as two types: the rainfall threshold model based on statistical theory and the distributed hydrological model. Moreover, the atmospheric hydrological geological model based on big data analysis and artificial intelligence technique will play important roles in the hydrometeorological forecasting. Hydrometeorological monitoring with satellite, radar and gauge observations is the foundation of hydrometeorological forecasting. Hydrometeorological forecasting based on seamless fine intelligent and grid QPF and hydrometeorological ensemble forecasting model will be the important development directions of the hydrological forecasting in the future.
    2021,47(6):685-692, DOI: 10.7519/j.issn.1000-0526.2021.06.004
    Abstract:
    This article reviews the three decade development of the typhoon numerical forecast operational system in the National Meteorological Centre (NMC) of China Meteorological Administration since the beginning of the Eighth Five Year Plan, including its first generation typhoon track numerical prediction system using regional model, a typhoon track numerical prediction system developed on the basis of the global spectral model, and the global and regional tropical cyclone (TC) forecast system independently developed by the China Meteorological Administration. It summarizes the key technologies and forecast performance of these systems, with a focus on the main technical achievements of GRAPES_TYM. It also puts forward some views on the development of the national typhoon numerical prediction system in the next five years.
    2021,47(6):693-702, DOI: 10.7519/j.issn.1000-0526.2021.06.005
    Abstract:
    In recent 10 years, the refinement level and dynamic, quantitative capacity of agrometeorological disaster forecasting and assessment have been promoted accompanied with the development of the agrometeorological disaster monitoring and assessment theory, the comprehensive use of numerical simulation technology, remote sensing monitoring technology, and modern information technology, as well as the application of intelligent grid meteorological element prediction in agrometeorological disaster monitoring and forecasting operation. All these have played an important role in agricultural disaster prevention and reduction and in yield improvement. In this paper, the main research and service achievements of dynamic, quantitative and refined agrometeorological disaster forecasting and assessment in recent 10 years are introduced, and the future development trend is looked forward to so as to provide a reference for the further development of agrometeorological disaster forecasting and assessment services.
    2021,47(6):703-716, DOI: 10.7519/j.issn.1000-0526.2021.06.006
    Abstract:
    An X-band dual-polarization phased array radar (XPAR) network is being set up in the Guangdong-Hong Kong-Macao Greater Bay Area (GBA) to improve observation accuracy and enhance low-altitude observation capability. In order to solve the raindrop attenuation problem of X-band radar and meet the requirements of observation and networking, self-consistent algorithm for attenuation correction is introduced and localized. The results show that the correction amplitude of reflectivity factor reaches 6 dB, and the negative 〖JP2〗value of differential reflectivity is also effectively constrained. Scatter analysis and quantitative statistical results of adjacent XPARs show that the spatial and intensity distributions of the two groups of data after quality control have a high consistency. Compared with S-band radar data which are taken as the truth value, the XPAR intensity of reflectivity factor is weak before attenuation correction, but enhanced to the equivalent strength of the S-band radar after correction, which is stronger locally and the accuracy is significantly improved. Differential reflectivity is corrected to some extent, the scatter distribution of corrected differential reflectivity and reflectivity factor is more concentrated and related coefficient is higher. It can be seen that this algorithm solves well the rain area attenuation problem of X-band phased array radar, and provides early data quality assurance for the promotion and application of X-band phased array radar network data and product development in the GBA.
    2021,47(6):717-726, DOI: 10.7519/j.issn.1000-0526.2021.06.007
    Abstract:
    By using the daily data from 50 stations and ERA-Interim reanalysis data in Qinghai Plateau during 1980-2018, and the methods of linear regression, Pearson correlation analysis and probability density distribution, this paper analyzed the spatio-temporal characteristics of hail frequency, hail diameter, hail duration, and the effects of elevations, special layer heights, and surface temperature on hail. The results demonstrate that the mean hail frequency in Qinghai Plateau has decreased significantly in the recent 39 years, especially since 2000. Hail events are most seen in June and July, with a fast decline rate in a year. The mean single time hail duration has decreased significantly, while the occurrence of large hail events has increased since the middle-late of 1990s. From the spatial distribution, the high value areas of hail frequency and duration are in the south part of Qinghai Plateau with high elevation, while the high value areas of mean hail diameter are in the eastern part of Qinghai Plateau with lower altitudes. The hail diameter in 3-5 mm〖JP〗 and duration 2-3 min of hail events have the highest frequeney. The lower 0℃ and -20℃ isotherm heights are favorable for hail formation and prolonging the hail duration. The higher 0℃ and -20℃ isotherm heights play an important role in supporting the collision and growth of hail in the air. The decreases of hail frequency and hail duration are related to the significant increase in mean surface air temperature and decrease in diurnal temperature range as well as the rising of 0℃ and -20℃ layer heights.
    2021,47(6):727-736, DOI: 10.7519/j.issn.1000-0526.2021.06.008
    Abstract:
    A list control method is proposed, which considers the acquisition rate, acquisition punctuality rate, quality control accuracy rate and model consistency rate of observation data. The wind observation data of 120 radiosonde stations in 2019 are used to validate the method, and analyze the quality of observation data. The results are as follows. The stations with observation data problems can be effectively checked out by the list control method. Compared with the model data, the observation data of the list stations have obvious systematic deviation, and the bias and root mean square error (RMSE) are significantly larger than the national averages. The quality of radiosonde wind observation data is good, and the wind direction and wind speed observation data are relatively consistent with the model data in all the four seasons with the biases are within ±1° and ±1.5 m·s-1, respectively. The wind direction consistency in autumn is the highest, and the wind speed consistency in summer and winter is lower than that in spring and autumn. The wind direction consistency first decreases and then increases with the decrease of pressure in spring and summer, while it is opposite in autumn and winter. The wind speed consistency basically changes in a three peak pattern with the decrease of pressure.
    2021,47(6):737-745, DOI: 10.7519/j.issn.1000-0526.2021.06.009
    Abstract:
    From 20:00 BT 9 to 20:00 BT 13 August 2020, due to the combined effects of the westerly trough and the Typhoon Lichma, large scale severe precipitation occurred in Shandong Province. The center of the severe precipitation was at Zhangqiu Station. In order to use multi source data to study the microphysical structure characteristics of heavy rainfalls in the typhoon rain belt, this paper analyzes the data of minutely precipitation, raindrop spectrum, dual polarization Doppler radar, wind profiler radar, etc. during the severe rainfall process at Zhangqiu Station. The results show that there was an obvious cold cloud precipitation mechanism at the beginning of this precipitation process. During the precipitation, the scale spectrum of raindrops changed significantly with time. During the period of severe precipitation, the spectrum of raindrops was broad, showing an obvious bimodal structure. The correlation coefficient between the sequence of raindrop numbers with a diameter greater than 1 mm and the sequence of minutely precipitation reached 0.956 〖KG-*5〗8. However, during periods of weakening precipitation, the spectrum of raindrops gradually narrowed, showing a single peak structure clearly, and the number of raindrops with a diameter greater than 1 mm decreased. When the radar echo height was high, the proportion of raindrops with a diameter greater than 1 mm increased, the raindrop spectrum was wider, and the multimodal distribution appeared. Strong wet turbulence clusters formed a large value area of the differential reflectance factor (ZDR), which neither corresponded to severe convection nor to surface heavy raindrops. This was caused jointly by the deformation of the wet turbulence resulting from updraft, downdraft and other reasons. During heavier precipitation, a thin layer structure with abrupt changes in wind direction and wind speed appeared in the time cross section of wind profile in the 0.9-1.4 km height. Corresponding to the thin layer, the minutely rainfall was the heaviest, and the proportion of raindrops with a diameter greater than 1 mm was obviously biased. The phenomenon revealed by the analysis results could provide a reference for understanding the droplet spectrum characteristics and microphysical structure of typhoon heavy rainfall.
    2021,47(6):746-754, DOI: 10.7519/j.issn.1000-0526.2021.06.010
    Abstract:
    Based on the hourly 2 m temperature, relative humidity, surface pressure and visibility data of 158 stations in Sichuan Province during the period 1967-2008, the monthly sunny global horizontal irradiation (GHI) was calculated and integrated by using simple model for atmospheric transmission of sunshine (SMARTS). The relationship between sunny GHI and altitude was established, which was applied to the correction of GHI interpolation during the period 1990-2019, and the correction effect was verified. The results show that the sunny GHI increases logarithmically with altitude, and the higher the altitude is, the smaller the increase of sunny GHI with altitude becomes. In terms of radiation correction, the correction range of Sichuan Basin with low altitude and flat terrain is the smallest, the high-altitude plateau in western Sichuan is in the middle, the transition zone between high and low altitudes is the largest. The results of cross validation show that the annual mean absolute error of the seven stations is reduced from 182.77 kW·h·m-2 to 145.48 kW·h·m-2, while the relative error is reduced from 13.41% to 10.24%.
    2021,47(6):755-766, DOI: 10.7519/j.issn.1000-0526.2021.06.011
    Abstract:
    In this study, instrument measured evaporation and conventional meteorological observations from 80 stations in Heilongjiang Province from 1961 to 2017 were collected. Using these data, methods such as linear trend estimation, cumulative anomaly, Mann Kendal mutation analysis, mathematical statistics and Marr’s wavelet analysis were employed to analyze the annual and seasonal characteristics of the spatio temporal evolution of instrument measured evaporation in Heilongjiang Province. Additionally, the relationships of the characteristics with climate factors were analyzed. The results show that the geographical correlation of annual evaporation is significant. Annual evaporation decreases as latitude, longitude and altitude increased. The decreasing rates are 55.4 mm/°N, 45.2 mm/°E and 88.8 mm/(100 m), respectively. From 1961 to 2017, annual evaporation in Heilongjiang Province showed a significant downward trend, decreasing at 13.7 mm/(10 a). Annual evaporation had 8 a and 24 a cycles. Statistics show that at up to 70.0% of the stations, the annual pan evaporation show a downward trend, of which 62.5% of the stations have passed the significance test at 0.05 level, which means there is “evaporation paradox” in Heilongjiang Province. Exploring seasonal pan evaporation trend shows that evaporation decreased significantly in spring, having 24 a and quasi 2 a cycles, and 67 stations show a downward trend, 44 of which show a significant downward trend (P<0.05). However, the magnitude of this decrease in summer and fall is relatively small with non significant changes, with 7 a cycles. In winter, evaporation increase slightly having 24 a, 11 a, and 2 a cycles and 23 stations show a significant rising trend. Mutation test shows that there is a significant mutation time of evaporation in year, spring and winter, but no significant mutation in summer and autumn. Additionally, it is found that changes in annual and seasonal pan evaporation are positively correlated with average temperature and wind speed, and negatively correlated with humidity. Our analysis indicates that a significant decrease in wind speed is the dominant factor leading to the decrease in evaporation throughout the year, and the superposition effect of a significant decrease in wind speed and obvious humidification makes the decrease trend of spring evaporation more significant. The higher temperature and lower relative humidity climate may be the cause of the slight increase in evaporation in winter.
    2021,47(6):767-772, DOI: 10.7519/j.issn.1000-0526.2021.06.012
    Abstract:
    The main characteristics of the general atmospheric circulation in March 2021 are as follows. There were two polar vortex centers in the Northern Hemisphere, the 500 hPa geopotential height presented the distribution of a three wave pattern in the mid high latitude of Northern Hemisphere. The strength of Western Pacific subtropical high was closed to that in normal years, and the south branch though was a little weaker. The national average temperature in March was 6.6℃, 2.5℃ higher than the normal (4.1℃) and recorded the second highest in the same period since 1961. The monthly mean precipitation amount was 27.8 mm, 6% less than in normal period (29.5 mm). There were three large scale sand dust weather processes in March, which were more and stronger than the usual, of which the sand dust weather in 13-18 was the strongest sand dust weather process in the past 10 years. A severe convective weather process occurred in the Yangtze River Basin at the end of the month, causing severe weather such as hail and thunderstorm. During this month, cold airs were weak, and only one moderate cold wave process appeared in 15-17. The droughts continued in Yunnan Province, droughts appeared and developed in South China.
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    Available online:  July 19, 2021 , DOI:
    Abstract:
    The vertical distribution of aerosol and atmospheric meteorological conditions during haze and heavy haze from 2007 to 2017 are analyzed by utilizing date of CALIPSO(The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) and NCEP FNL(Final Operational Global Analysis)1°×1° reanalysis data.The results show that aerosol particles in haze and heavy haze mainly concentrate below 2.7km and 1.5km in the lower troposphere.With 0.9, 1.66 and 1.34km as the critical height, the extinction coefficient (EC,Extinction Coefficient) of cleaning days, haze days and heavy haze days decreases exponentially above the critical height and logarithmically below.The average annual Paraticulate Deploarization Ratio (PDR,Particulate Deploarization Ratio) and color ratio (CR,Color Ratio) range of haze days and severe haze days are 0.1-0.3 and 0.5-0.9.In heavy haze, aerosol particles below 2km are relatively regular and small in size, and their irregularity and size increase sharply between 2-4km.PDR increases gradually with height below 7km and decreases gradually above 7km.Different from the cleaning day, CR basically increases with the height in haze.The contribution of polluted dust aerosol to near-ground EC in heavy haze days and haze days is 0.58km-1 and 0.35km-1, respectively.The second is the polluted continental type, 0.27km-1 and 0.20km-1 respectively.In addition, at 2-4km, the dust type has a certain effect on the EC of haze, while the elevated smoke type has a certain effect on the EC of haze.In the heavy haze days, the average wind speed and relative humidity were low below 1.5km, which is conducive to the increase of EC.In haze days, low average wind speed and high relative humidity are maintained at a higher height, making the height of aerosol high concentration layer up to 2.7km.During haze, the sources of near-surface pollutants are long-distance transmission from Mongolia, Inner Mongolia and the neighboring provinces.In heavy haze days, the transport of pollutants in the direction of Mongolia and Henan accounted for more, up to 25.26% and 31.58% respectively.The proportion of multi-layer inversion corresponding to heavy haze is close to 50%, and the proportion of Ground+low-suspended type and Ground+high-suspended type are the largest.Since these two types of inversion correspond to smaller outflow below the inversion layer, the atmosphere is more stable,and aerosol particles are concentrated in the lower layer when there is heavy haze.
    Available online:  July 09, 2021 , DOI:
    Abstract:
    In this study, the key area of upstream southwest wind speed was established, which is closely associated with Spring Persistent Rains in Hunan (SPRH). The starting date, ending date, rainfall, rainy period and intensity index of SPRH were defined from 1980 to 2014. The temporal and spatial patterns of SPRH rainfall were analyzed. The anomaly of the atmospheric circulations during the strong/weak SPRH period and sea surface temperature (SST) during the early period were discussed. Results showed that: The climate average of SPRH occurred from the 13 pentads to the 27 pentads, whereas the starting date and ending date of SPRH varied in different years. The rainfall of SPRH was exceeded normal conditions during the periods of before the mid-1980s and after 2014, whereas it was lower than normal conditions during the periods of the mid-1980s to 2014. The strong years of SPRH in whole province were found in 1981, 1992, 2014 and 2016. By contrast, the weak years of SPRH in whole province occurred after 1990 including 1991, 1994, 2008 and 2011. In the strong SPRH years in whole province, the western pacific subtropical high (WPSH) remarkably became stronger and westward; the Indo-Burmese trough tended to become weaker; and an anomalous anticyclone existed in the southern Yangtze River regions in low-level wind field. Hunan was located in the center of anomalous anticyclone, which led to strong SPRH. However, in the weak SPRH years, WPSH evidently became weaker; the Indo-Burmese trough tended to become stronger; and an anomalous cyclone was found in southern China. Additionally, Hunan was located in the center of anomalous water vapor divergence, resulting in weaker SPRH in whole province. In the following year of the occurrence of El Nino events, SPRH started earlier, longer rainy period, more intensive rainfall amount compared with the normal years. On the contrary, during the following year of the occurrence of La Nina, SPRH started later, shorted rainy periods, lower rainfall amount and weaker rainfall intensity compared with the normal years.
    Available online:  July 08, 2021 , DOI:
    Abstract:
    The radar reflectivity assimilation using 3DVAR method can not improve the water vapor and temperature conditions in the background field, and the spin up problem exists in the model. Based on ARPS 3DVAR system, a pseudo observation assimilation method for retrieving water vapor and in-cloud temperature based on radar reflectivity is proposed. This paper discusses the influence of assimilating radar radial wind and reflectivity, pseudo observation on precipitation, gale and hail, and discusses the influence of different cold start time on precipitation forecast for a squall line event occurred in the south of the Yangtze River on May 4, 2020. The results indicate that: (1) assimilating the pseudo water vapor and in-cloud potential temperature at the cold start time, the water vapor was increaded in the observed strong echo area., while the negative water vapor increment mainly appears in the spurious convection of background, the potential temperature increase mainly concentrates in the area where the observed echo is larger than the background simulated echo. (2) Compared with only assimilating radar data after assimilating pseudo-water vapor and pseudo- in- cloud potential temperature, the analyses and forecasts of squall line events are qualitatively and quantitatively improved, including: the simulated 2-5 km updraft helicity is more consistent with the location of damage wind and hail disaster;the FSS score at 1,5,10 mm threshold of 1haccumulated precipitation in 0-12 h is significantly improved. (3) Different cold start-up time experiments show that After the background field was updated at 1200 UTC, the precipitation FSS score was significantly improved compared with 0500 UTC, while assimilating pseudo observation data has a positive contribution to improving precipitation both experiments..
    Available online:  July 05, 2021 , DOI:
    Abstract:
    Abstract: To investigate the influence of Stochastically Perturbed Parametrization Tendencies (SPPT) on convective Scale Ensemble Prediction under complex topography conditions, sensitivity experiments were conducted on three parameters of sppt random disturbance field, including time scale, spatial scale and grid standard deviation, to explore its prediction effect. The results show that in the 90 km spatial scale of, the 3 h time scale and the 0.525 grid standard deviation in SPPT are best in this case. The spreads of upper-air physical quantities (zonal wind field, temperature field and humidity field) and surface layer physical quantities (10 m wind and 2 m temperature) increase rapidly. The spread/ RMSE considering the prediction error is better than other experiments. Although the ensemble mean of 3 h accumulated precipitation is not significantly improved in all grade compared with other experiments, the ETS scores of precipitation grades ≥10 mm, ≥25 mm and ≥50 mm are close to or higher than those of the control experiment, and the probability prediction skills are better. On the whole, the influence on spread of spatial scale parameter is more obvious than that of time scale, and the increase of perturbation amplitude also plays a positive role in the increase of spread. At the same time, it can improve the probability prediction skills of precipitation of different magnitudes.. Key words: Ensemble forecast, convective scale, uncertainty, Stochastically Perturbed Parameterization Tendencies, SPPT
    Available online:  July 05, 2021 , DOI:
    Abstract:
    Based on WRFV3.9 mode, the Stochastic Perturbed Parameterization was used to perturb MYNN boundary layer and RUC land surface process scheme parameters to simulate a severe rainstorm in southwest Mountains of China. The optimal settings for parameter perturbations of MYNN boundary layer and RUC land surface process in mountain rainstorm ensemble forecast were explored.The main conclusions are as follows:In the random disturbance MYNN boundary layer scheme (SPPM) and RUC land surface process scheme (SPPR) parameters, the disturbance is mainly influenced the variables at the ground and lower level, and the disturbance energy gradually develops from the lower level to the higher level in the mode, and the SPPM can get greater disturbance energy then SPPR. The SPPM scheme is more sensitive to the variation of temporal correlation parameters than the spatial correlated parameters. However, the perturbation energy of SPPR scheme is generally small, and the variation of spatial and temporal correlation parameters has relatively little influence on its ensemble prediction performance. In SPPM scheme, a better ensemble prediction skill can be obtained by the temporal correlation selection for 6h and the spatial scale selection for 70km, and in SPPR scheme, relatively speaking, a better ensemble prediction skill can be obtained by the temporal correlation for 6h and the spatial scale for 50km.
    Available online:  July 05, 2021 , DOI:
    Abstract:
    Based on the precipitation data from China meteorology administrator, ERA5 (the fifth generation of European Centre for Medium-Range Weather Forecasts Reanalysis) reanalysis data and the TBB (Black-Body Temperature) data from FY-4A, the factors of heavy rain causing landslide on July 23, 2019 were investigated. The results are listed as follows: it was found that the strongest precipitation at 22 BJT was caused by the convective cloud belt with TBB below -82℃, its weather systems were 700-750hPa low trough and the cold front in the north of Sichuan basin. Before the rainstorm, the cold front in the north of Sichuan basin forced the air with large energy flowing from the basin to northwestern Guizhou. With the development of southern airflow in the south of Jichang Town, Shuicheng County, sufficient water vapor conditions were provided for the occurrence of heavy rainfall. Meanwhile, the enhancement of warm and humid airflow made the convective instability in the lower layer of Jichang town increase. At the beginning of the precipitation period (20BJT), the upward movement was mainly below 700 hPa, which was related to the influence of the easterly airflow that encountered the topographic obstruction and climbed along the slope of the terrain at Jichang town. As the weather-scale cyclonic circulation extended into Guizhou, widespread precipitation should occur as a result of the enhanced upward motion at the middle and lower layers, but the actual precipitation areas occurred only in the narrower zones of the cyclonic circulation. After Barnes band-pass filter analysis, it was found there were a number of small-scale cyclones and anticyclones in the weather-scale cyclonic flow field, and there were two small cyclone circulation on the west side of Jichang town, and the strong convergence zone on the north side of them was just the precipitation zone。At the same time, Jichang town was also located in a small-scale saddle-shaped field region, which was obviously favorable to the convergence at low and middle level, superimposing with topographic upward motion, the sudden heavy rainfall occurred, which caused the formation of landslides.
    Available online:  July 01, 2021 , DOI:
    Abstract:
    A total of 29 typhoons generated over Western North Pacific and South China Sea in 2019, 2 more than the average of 27 in the same period of many years, and 56 typhoons landed in China, 21 less than the average of 7.0 in the same period of many years. The overall typhoon intensity is relatively weak, with the peak intensity averaging 37.8 m/s (level 13), which is weaker than the perennial average. The overall strength of the landfall typhoon is weak, but the landfall intensity of "Lekima" is strong and the impact is heavy. Autumn typhoon generation is obviously more. There were 6 typhoons in November, which were the most typhoons in November since 1949. Compared with Japan JMA and the JTWCUnited States, CMA China is in the leading position in the prediction level of 24h and 96-120h, the prediction error of 48-72 hours is slightly higher than that of JMAJapan, but lower than that of the United StatesJTWC.
    Available online:  June 29, 2021 , DOI:
    Abstract:
    Based on the models of decision tree and Bayesian, the progressing of decision making in the meteorological service for the extreme thunderstorm in Beijing on 21 July 2012 has been simulated and analyzed in scenario. Thorough the diagnosis of decision makings in the typical thunderstorm, it will prove whether it is possible of applying for the supporting decision making model to attain the optimal decision in solving the uncertainties problems of decision making, under the current condition of data resources( e.g., the mesoscale NWP system and observation data) and technology standards. Using the grid data of NWP on that day, the risks of floods and debris flow have been assessed to be high, respectively. Considering the threshold rainfalls of causing floods in the historical flooding events and the predicted rainfall distribution on that day, the high risk of thunderstorms also could be recognized simultaneously. The posteriori probability deduced using the Bayesian model is only 23.1%. However, considering the difference of expected losses in predicting severe weather and non-severe weather, the expected losses of predicting non-severe weather can be obviously greater than that of predicting severe weather. Therefore, it would be advisable of predicting severe weather and pick the pessimistic scheme in the meteorological service, which was the optimal decision making in that situation. The simulation of the meteorological service during the thunderstorm on that day reveals that (1) it should be more tolerable to the uncertainty in severe weather forecasting and warning to relieve the necessary pressure to forecasters risen from the afraid of false forecasting and warning, and (2) it should provide the public with the uncertainty information, which will be useful in the decision making of the actual meteorological information users, in the weather forecasting.
    Available online:  June 29, 2021 , DOI:
    Abstract:
    It is still extremely difficult and challenging for accurate prediction of convective weather systems. In order to improve the service ability in strong weather monitoring and prediction, the following studies have been carried out recently: (1) The new mesocyclone and tornado vortex feature recognition algorithms are developed and proved to be successfully in identifying tornado vortex characteristics in more than a dozen tornado cases. Extracted from Doppler radar volume scan data, more than thirty parameters have been used in the study on the automatic recognition and warning technology of classified severe convective weather (downburst, tornado, hail and short-time strong precipitation).. (2) Rapid update cycle forecast system can effectively improve the quality of model initial values that is very suitable for short-time forecast application. For the sake of improving severe thunderstorm prediction, a novel pseudo-observation and assimilation approach involving water vapor mass mixing ratio is proposed to better initialize numerical weather prediction (NWP) at convection-resolving scales. (3) The blending technology which is expected to overcome the deficiency of the quantitative precipitation forecast (QPF) by a mesoscale NWP model for the short term at convective scales and the rapidly descending skill of rainfall forecast based on radar extrapolation method beyond the first few hours is under development, and also has potential in enhancing the ability of rainfall forecast within the nowcasting period.
    Available online:  June 28, 2021 , DOI:
    Abstract:
    Based on the datasets of Meiyu monitoring and observation of precipitation and NCEP atmosphere reanalysis and sea surface temperature, the abnormal characteristics of Meiyu over the Yangtze–Huai River Basin (YHRB) in 2019 and its causes of large-scale circulation are analyzed. The results are as follows: (1) The abnormal characteristics obviously showed that the Meiyu onset date was later than normal compared with a shorter duration, the Meiyu precipitation presented a distribution pattern of the more in the south and the less in the north of the Yangtze River over YHRB which was less than normal in overall in the Meiyu season of 2019. Among the three subareas, the Meiyu period of the subarea of the middle and lower reaches of Yangtze River was almost simultaneous with that of Jiangnan subarea, and the Meiyu of the Jianghuai subarea was not obviously. (2) Due to the periodical enhancement of the cold air between June 8 to 15 it was impeded and delayed that the seasonal northward of East Asian summer monsoon, which lead to the conversion later from winter to early summer of the circulation pattern in East Asian and Meiyu onset date also later over YHRB. It can be regarded as the precursory signals of Meiyu onset date later over YHRB in 2019 that the sea surface temperature in Indian Ocean was warmer than normal in May-June and the reverse date of MTGMUT was later over 60o~80oE of South Asia. (3) Compared with climate mean state, the eastern ridge of South Asian high and East Asia westerly jet were southward at upper-level, the circulation meridionality in the middle-high latitude in Eurasia was stronger and the western ridge of Northwest Pacific subtropical high was southward and the geopotential height east of Australia was higher at middle-level, the intensity was weaker and the northernmost was southward of the East Asia summer monsoon at low-level. Due to the combined influence of the above-mentioned abnormal characteristic , it was under the control of the strong divergence at upper-level and the strong meridional gradient convergence of vapor flux at low-level in the south of the Yangtze River over YHRB. That is greatly conducive to the development of vertical upward movement and the occurrence of heavy rainfall and cause the distribution pattern of the Meiyu precipitation in 2019 with the more in the south and the less in the north of the Yangtze River over YHRB.
    Available online:  June 17, 2021 , DOI:
    Abstract:
    Using conventional observation data, doppler radar data of Xi’an station, ground weather station observation data and ERA5 reanalysis data (0.25*0.25), the environmental conditions and triggering mechanism of four severe convection weathers in Guanzhong area under the influence of subtropical high from 2015 to 2018 were comparative analyzed. These four cases resulting in local geological disasters and urban flooding, however, the global model failed to forecast a short-term rainstorm. Results show that the severe convection in Guanzhong area under the control of subtropical high often coexists with the hot weather. When severe convection occurs, low-level atmospheric water vapor content is large, the atmospheric precipitable water can be more than 50 mm, relative to the systemic rainstorm occurred in the peripheral of the subtropical high, the water vapor transmission is relatively weak, the strength of the water vapor transmission determines the total rainfall in the severe convection process. Convergence center is located on the ground to 800 hPa, compared with the systemic rainstorm, the convergence center position is lower, and the main role of low-level convergence is to overcome convection suppression, release unstable energy. Favorable environmental conditions for the occurrence of severe convection including strong potential unstable layer, low LFC, medium intensity convective available potential energy and thick warm clouds. The trigger mechanism is mainly cold front and low-level wind convergence line, when there is a cold front in the upstream, the cooling effect of precipitation behind the cold front will increase the temperature gradient to enhance the cold front, cold air in the lower layer invades the atmosphere with high temperature and high humidity controlled by subtropical high, triggering severe convection occurs; The convection in warm regions is usually triggered by ground convergence line, convection induced cold pools can form gust front and trigger new convection. Qinling terrain has a significant impact on the movement and spread of the severe convection. The convective that triggers in north of Guanzhong area and move southward can easily cause heavy rain storm because of the rain belt blocked by Qinling. The new convective occurred along the terrain convergence line in the northern Qinling triggers new convective development in Guanzhong area, as the potential energy is converted to kinetic energy during the descending process, the convection system moves faster and the duration of heavy precipitation is shorter, it is easier to produce large-scale thunderstorm and gale weather.
    Available online:  June 08, 2021 , DOI:
    Abstract:
    For a further study on the usage of ADTD lighting data in rapid refresh assimilation system, this thesis introduces a new relationship between lightning activity and radar echo characteristics in Central China to calculate lighting-proxy reflectivity and conducts three sets of numerical experiments to analyze a strong weather process occurred in Jianli, Hubei Province on 1 June 2015. The influence of lightning data on radar reflectivity, cloud microphysical variables and precipitation forecast calculated by rapid refresh assimilation system was mainly analyzed. Results are as follows. The ADTD lightning data can capture the heavy precipitation signal well. The assimilation of lighting-proxy reflectivity of new relationship can improve the precipitation forecast skill by adjusting the cloud microphysical variables. By comparing the results of precipitation,it can be concluded that after adding lightning-proxy reflectivity obtained by the new relationship,the missing report rate can be effectively reduced,and the model can respond to the precipitation forecast that is more closely to the observation in a short time scale. Finally,the accuracy of short-term prediction is improved.
    Available online:  May 10, 2021 , DOI:
    Abstract:
    Based on hourly and 5-minute observation data of automatic weather station, swan mosaic product of radar combined reflectivity factor in the middle reaches of the Yangtze River and NCEP FNL reanalysis data, the characteristics of four convective storms with low-echo-centroid type of short-term heavy precipitation in Wuhan were analyzed. The results showed that: (1) the characteristics of convective system induced by different weather background were different. Under the background of warm forcing, the environmental conditions were high energy and high humidity, and the accumulation of thunderstorm cold pool was conducted to triggering linear convection in the stable precipitation front; under the baroclinic frontogenesis background, the convergence of cold and warm was intense, and the baroclinic was strengthened; there were more mesoscale cyclone waves on the ground, and the stable precipitation in the front area was often accompanied by a short-term strong drop Under the quasi barotropic background, the baroclinic atmosphere was weak, but the high-energy and high humidity environment as well as the near surface layer flow field forcing and local thermal difference were easy to trigger severe thermal convection activities. (2) According to the radar echo characteristics and precipitation characteristics of convective storms, TS type moved faster, resulting in a small range of short-term heavy rainfall; quasi-stationary type showed that the echo of large-scale stratiform cloud with zonal trend was stable, and there were multiple cumulus convective echoes in the middle. The precipitation enhancement in each stage corresponds to the new convective cell passing through Wuhan station; the consolidation type was in the circulation When the wave merges, it was often accompanied by the occurrence of heavy rainfall, and the echo shape and direction after merging affect the intensity and duration of precipitation. (3) Under different environmental background, trigger inducement and organizational form, the surface meteorological elements before and after the occurrence of short-term heavy rainfall showed different change characteristics; the different front characteristics and convection trigger positions leaded to different temperature changes. (4) Ground mesoscale system played an important role in triggering and organizing the development of MCS. Its generation, elimination and transformation usually heaved a certain advance in time for MCS. Paying attention to the development and evolution of ground mesoscale systems such as ground convergence line and temperature front area was of great significance for predicting the triggering and organizational evolution of MCS.
    Available online:  April 23, 2021 , DOI:
    Abstract:
    Several intense tornadoes (≥EF3) in China in recent years resulted in heavy casualties and serious economic losses. The tornado has a very small scale, and its occurrence frequency in China is extremely low. At present, tornadoes cannot still be forecast in operation in China. However, with the development of observation networks of new-generation weather radar and surface automatic weather stations, damage survey and numerical weather prediction model, remarkable progress in tornado research in China has been made. The climatology, synoptic backgrounds and favorable environmental conditions for tornado in China have been understood, and it has also been found that the favorable environmental conditions for tornado in different synoptic backgrounds are somewhat different. The damage survey process and analysis technology of tornado disaster have been developed and completed. The damage surveys and analyses of several intense tornadoes, such as the 2016 Funing, Jiangsu Province EF4 tornado, have been made in detail. More understandings of meso- and micro-scale characteristics of tornadic convective storms have been got, including the findings of the storm cold pool with appropriate intensity, the bottom of the mesocyclone generally lower than the height of 1 km, the positive intensity correlation between tornado and its parent mesocyclone, slantwise mesocyclone, tornadic debris signature, descending reflectivity core, and multi-vortex structure of some tornadoes. Two tornadoes have successfully been ideally simulated using a fine-resolution cloud model, and the tornado-scale vortices in the convective eyewall of 2005 typhoon Matsa and the multiple vortices of the 2016 Funing tornado have been successfully simulated by using the WRF (Advanced Weather Research and Forecast) model. Future, we still need to further develop tornado detection technology, and to study fine surface meteorological element distribution and structure features, tornado vortex and lightning activity of tornadic convective storms, and close studies on the development mechanisms of tornado are surely needed using finer-resolution observation data and higher-resolution numerical weather simulation, in order to provide more scientific foundations to promote the tornado forecasting and warning ability in China.
    Available online:  January 14, 2021 , DOI:
    Abstract:
    By virtue of the daily temperature observations of 2400 stations in China from 1960 to 2019, the climatological characteristics of the cold event in China are systematically analyzed, and the relationship between cold wave, cold air process and the Arctic Oscillation (AO) is discussed. The results show that the cold wave and cold air process in China mainly occur in autumn, winter and spring, and the frequency and intensity have obvious monthly and seasonal differences. Regional cold wave has the highest frequency in autumn, and national cold wave and all types of cold air have the highest frequency in winter. The average intensity of regional cold event is the largest in February, and the average intensity of national cold event is the largest in November. Based on the analysis of winter temperature in China, the past 60 years can be divided into two stages, that is, the cold period from 1960 to 1986 and the warm period from 1987 to 2019. In the winter of cold period, the frequency of the national cold wave shows a significant decrease trend (-0.57 times/10 years), and the frequency of regional cold air and all-type (the sum of national type and regional type) cold air processes in winter shows a significant upward trend of 1.37 times/10 years and 1.28 times/10 years, respectively. In the warm period, there is a significantly decreasing trend of national cold wave frequency (-0.17 times/10 years) and a significantly increasing trend of regional cold air frequency (0.53 times/10 years) in January. The frequency and intensity of cold wave and cold air over China are closely related to the Arctic Oscillation (AO). On the interannual scale, the frequency (intensity) of various cold wave in various seasons is negatively correlated with the AO index, but the frequency (intensity) of various cold air in winter is positively correlated with AO index. On the interdecadal scale, the frequency of winter regional cold wave, the frequency of national cold wave, and the intensity of national cold wave are significantly positively correlated with the AO index.
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      2012,38(12):1482-1491, DOI: 10.7519/j.issn.1000-0526.2012.12.005
      Abstract:
      By using the conventional meteorological data, Doppler radar data and NCEP/NCAR reanalysis data, the characteristics of Doppler radar’s reflectivity, environmental condition and trigger mechanism of the heavy rain are analyzed and compared between two abrupt heavy rain processes occurring in Sichuan Basin on 3 July (7.3) and 23 July (7.23) 2011. The results show that: the “7.3” heavy rain happened under a typical circulation background, and moisture transporting to the heavy rain area from the South China Sea was smoothly, thus the heavy rainfall maintained so long, but the “7.23” heavy rain occurred behind the upper cold vortex, and convective unstable energy was abundant and vertical wind shear was strong, thus this heavy rain process happened with hail and thunderstorm weather accompanied, its radar reflectivity was 5 dBz stronger than “7.3” case and had the characteristics of severe storms such as the low level weak reflectivity and the upper echo overhang. As a whole, the non equilibrium force is contributed to the occurrence of heavy rain and it is the excited mechanism of the two heavy rainfalls, and the change of the divergence evolvement is consistent with the strength and the position of the heavy rain which would happen 6 hours later.
      2006,32(10):64-69, DOI: 10.7519/j.issn.1000-0526.2006.10.010
      Abstract:
      Based on the data of CINRAD Doppler Radar which located at Xinle of Hebei Province,the hail,strong wind and heavy rainfall weather events in mid-south Hebei in 2004 are statistically analyzed.The routine radar products,such as echo reflectivity,radial velocity,Vertically Integrated Liquid(VIL)Water,hail index,mesocyclone,velocity azimuth display wind profile,etc.are used in this statistics.The results show that hail's VIL value is larger than generic thunder storm's.At the same time,greater VIL value and longer sustaining will bring about greater diameter hail and larger effect area.It is the very useful index to indicate strong wind in mesocyclone products and the wind direction sudden change in radial velocity products.A reference based on analyzing this type synoptic forecast with radar system in future is proposed.
      2008,34(12):27-35, DOI: 10.7519/j.issn.1000-0526.2008.12.004
      Abstract:
      Cloud macro and micro physical characteristic parameters play an important role not only in the field of the analysis and forecast of the weather and climate, but also in the field of weather modification to identify the seeding c ondition. Based on the data from FY-2C/D stationary satellite and SBDART radiati on transfer model, associated with the sounding data and surface information, a method retrieving cloud macro and micro physical parameters is established in th is research. These parameters include cloud top height, cloud top temperature, d epth of super-cooled layer, depth of warm layer, cloud bottom height, depth of c loud, cloud optical thickness, cloud effective particle radius and cloud liquid water content. It has been run operationally. In this paper, the correlated info rmation such as physical meaning, retrieving method and technology, retrieving p rocess and data format are simply introduced. Furthermore, comparing with the ob servation of Cloudsat up to the minute, the retrieving results of main cloud par ameters are proved to be reasonable and usable. By contrast with same kind produ cts of MODIS, it also shows good corresponding relationship.
      2013,39(10):1284-1292, DOI: 10.7519/j.issn.1000-0526.2013.10.006
      Abstract:
      Based on the fog observation data during 24-27 December 2006 (advection radiation fog), NCEP NC reanalysis data (2.5°×2.5°) and GDAS global meteorological data (1°×1°), detailed trajectory analysis of the boundary layer characteristics and water vapor transport of the fog is investigated, combined with the weather condition, meteorological elements and physical quantity field. The results show that: (1) there is thick inversion layer, even multi layer inversion throughout the dense fog event. Temperatures of different inversion tops in the middle and high levels are 2-5℃ higher than the surface temperature. The thickness of inversion layer is more than 200 m, and it gets to 500 m at 08:00 BT 26 December, indicating the atmosphere is very stable and conducive to the convergence of water vapor before the fog forms. However, it is not favorable for the divergence of water vapor after the formation of fog, which helps the development and maintenance of the fog, causing the fog to last about 64 hours with dense fog (visibility <50 m) about 37 hours; (2) The divergence of water vapor flux in low level is negative in the advection fog event. The upper air has persistent moisture convergence and the strongest moisture convergence appears at 02:00 BT 25 December, being -30×10-7 g·s-1·cm-2·hPa-1. The accumulation of low level water vapor makes fog form and develop while the divergence of water vapor flux speeds up its dissipation. 〖JP2〗The long lasting advection radiation fog is mainly caused by the continuous water vapor convergence; (3) The water vapor path is from the coastal area in easten China to Nanjing. The water vapor is continuously supplied from sea during the fog event, with the water vapor flux maximum getting to 2 g·s-1·hPa-1·cm-1. The sufficient supply and supplementary of water vapor determines the duration of the fog.
      2017,43(7):769-780, DOI: 10.7519/j.issn.1000-0526.2017.07.001
      Abstract:
      The spatial distributions of severe convective wind (SCW) and nonsevere thunderstorms (NT) over South China, occurring between 08:00 BT and 20:00 BT during spring and summer in 2010-2014, were analyzed by using the observational data from China Meteorological Administration. And then, their environmental characteristics were compared between SCW and NT in spring and summer. It was found that SCW in summer is more frequently than that in spring and that NT in summer is about 3.6 times the counts of NT in spring. SCW events mainly concentrate in the western Guangdong to the Pearl River Delta Region. Compared to NT, SCW is generally associated with stronger baroclinity, instability and stronger dynamic forcing. The precipitable water and averaged relative humidity between 700-500 hPa of SCW tend to be higher than those of NT in spring, while the opposite is the case for the pattern in summer. In conclusion, it is obvious that the dynamic forcing for SCW in spring is much better than these in summer, while the thermal condition is more significant in summer.
      2009,35(1):55-64, DOI: 10.7519/j.issn.1000-0526.2009.1.007
      Abstract:
      A strong rainstorm is analysis which occurred in Xinghua located the north of Ji angsu province on 25 July 2007. Results show that wind disaster originated from two kinds of rainstorm. One kind was the gust front which occurred at the front of the storm. Strong wind of grade 7-9 was attained when it happened. Another ki nd was the downburst arose in the multi cell storm. The original height of refl ectivity core was higher than -20℃ isotherm. It had the characteristics of conv ergence on the mid level and descending of reflectivity core. The strong wind ab ove grade 10 was attained, when the descending airflow diverged strongly on the ground. A new cell was combined with the former storm above the gust front, thus the storm enhanced. When the downburst happened, the storm weakened, and another new cell was combin ed with the former storm. The downburst happened continuously, and the impact of gust front persisted.
      2014,40(2):133-145, DOI: 10.7519/j.issn.1000-0526.2014.02.001
      Abstract:
      By using the NCEP reanalysis data, the vapor budget of the area covered by the severe torrential rain over the northeast of North China on 21 July, 2012 is calculated according to the vapor budget equation. The results show that meridional water vapor transportation is dominant while the extremely heavy rain hits Beijing Region, where most moist vapor comes from the southern boundary below 500 hPa. The low level regional moisture convergence is consistent with the time and space when the torrential rain breaks out and develops. Above the middle level the vertical vapor transport is more prominent. Then the variation features of the vapor transport corridors and their moisture contributions are got through the HYSPLIT mode. The backward trajectory analyses illustrate two major vapor transport corridors. The moistest vapor derived from Yellow Sea and East China Sea along the low level make the main moisture contribution during the heavy precipitation. Moisture from the South China Sea and the Bay of Bengal strengthens the water vapor in the region when the heavy rain starts and develops. Also the drier vapor corridor along the high level from the northwest of China plays an important role in this case.
      2012,38(1):1-16, DOI: 10.7519/j.issn.1000-0526.2012.1.001
      Abstract:
      In this paper, the modulation of atmospheric MJO on typhoon generation over the northwestern Pacific and its mechanism are first studied by using the MJO index. The results show that the MJO plays an important modulation role in typhoon generation over the northwestern Pacific: The proportion of typhoon number is 21 between active period and inactive period; During the MJO active period, the proportion of typhoon number is also 2:1 between phases 5-6 and phases 2-3 of MJO. The composite analyses of atmospheric circulation show that there are different circulation patterns over the northwestern Pacific in different phases of the MJO, which will affect the typhoon generation. In phases 5-6 (2-3), the dynamic factor and convective heating patterns over western Pacific are favorable (unfavorable) for typhoon generation. Then, the comparing analyses of the 30-60 day low frequency kinetic energy in lower and higher levels of the troposphere show that the atmospheric intraseasonal oscillation over the northwestern Pacific has a clear impact on the typhoon generation. There is an evident positive (negative) anomaly area of 30-60 day low frequency kinetic energy in the more (less) typhoon years over the northwestern Pacific east of the Philippines, which means that strong (weak) atmospheric intraseasonal oscillation (ISO) over the northwestern Pacific is favorable (unfavorable) for typhoon generation. The analyses of 200 hPa velocity potential show that there is a clear divergence (convergence) pattern over the northwestern Pacific in the more (less) typhoon years, which is favorable (unfavorable) for typhoon generation. The modulation of the intraseasonal oscillation on the typhoon tracks over the northwestern Pacific is studied by observational data analyses. We classified the main classes of typhoon tracks into 5 types as straight west moving typhoons (I), northwest moving typhoons (II), recurving to Korea/west of Japan typhoons (III), landing on Japan typhoons (IV) and recurving to the east of Japan typhoons (V). Then the composite analyses of atmospheric low-frequency wind fields at 850, 500 and 200 hPa, corresponding to the typhoon forming date, for every typhoon track are completed. The analysis results of relationships between the low-frequency (ISO) wind fields and typhoon tracks have indicated that the typhoon tracks will be affected by wind pattern of the ISO. The low frequency positive vorticity belt (the maximum value line of cyclonic vorticity) associated with low-frequency cyclone (LFC) at 850 hPa is so closely related to the typhoon track, that the maximum value line (belt) of low frequency cyclonic vorticity can be an important factor to predicate the typhoon tracks over the northwestern Pacific. And the typhoon tracks will be also affected by the ISO circulation pattern at 200 hPa, particularly the strong low frequency wind associated with low frequency anticyclone (LFAC).
      2011,37(10):1262-1269, DOI: 10.7519/j.issn.1000-0526.2011.10.009
      Abstract:
      Based on the daily precipitation data at 110 observational stations during 1961-2008 in South China, the climatic characteristics and variation of torrential rain days, rainstorm intensity and contribution which is in annual, the first and second flood seasons in South China were studied by using statistical and diagnostic methods, such as linear regression analysis, Mann Kendall test, wavelet analysis and the computation of trend coefficients. The results have shown that the annual mean torrential rain days have a decreasing trend from coastal regions to inland in South China in recent 48 years, the highest center is in Dongxing of Guangxi (14.9 d), and the lowest center is in Longlin of Guangxi (3.2 d). About 72% of the total torrential rain days occurred in the flood seasons with about 45% in the first season and 27% in the second season. The mean torrential rain days have increased faintly in annual, the first and second flood seasons in South China, but it is not obvious. There are the characteristics of interannual and interdecadal changes. The mean rainstorm intensity has increased faintly in annual and in the first flood season in South China. However, since 2005 it has become obviously. The mean rainstorm intensity has declined in the second flood season, but it is not obvious. The annual mean rainstorm contribution to the total rainfall has increased obviously, but the mean contribution is not obvious in the first and second flood seasons. The wavelet analysis has shown that the changes of torrential rain days, intensity and contribution which is in annual, the first and second flood seasons in South China have two significant periods of 2-3 a and 3-4 a.
      2011,37(5):599-606, DOI: 10.7519/j.issn.1000-0526.2011.5.012
      Abstract:
      Using the diurnal snow data of 120 meteorological stations in Yunnan Province during 1961-2008, the temporal and spatial distribution characteristics and the trend of climatic change of the annual and monthly snow fall are analyzed. It is pointed out that the total trend of snow frequency and covering stations has been decreasing in Yunnan in the recent 50 years. And the annual snow frequency has declined at a mean rate of 4.5 times per year. The temporal trends of monthly snow frequency and covering stations are all negative. Moreover the reduction of snow frequency in December is the largest in magnitude, therefore, it is the most remarkable. And the reduction of snow stations in April is the largest. As far as the spatial change of the secular trend variation of annual snow frequency is concerned, the reduction of annual snow frequency is larger in Northwest Yunnan than in its northeast and east, where the reduction rate is 0.44 times per year. And the temporal changes of annual snowfall and depth of snow cover are studied, the results show that the secular trends of annual snowfall and the maximum depth of snow cover are all positive. This means that in the nearly 50 years the heavy snow frequency has increased over Yunnan Province.
      2014,40(7):816-826, DOI: 10.7519/j.issn.1000-0526.2014.07.005
      Abstract:
      In term of precipitation data of 2400 stations from 1981 to 2010, annual, seasonal and monthly distribution and evolution characteristics of rainstorm were analyzed. The results show that the processes of rainstorm have been increased evidently since 21 century especially in the south of China, but the duration is relatively short. Rainstorm days have been increased, but the amount of precipitation is not as much as in 1990s. Variation trend of the annual (monthly) precipitation amount is in accordance with that of rainstorm days, but rainfall is averagely more while the rainstorm days are less during spring rainfall phase over the south of Yangtze River. Distribution of the maximum annual rainstorm days is very similar with that of the annual mean rainstorm days, revealing the feature of more in south and east but less in north and west. Maximum annual rainstorm days are more than double of annual average rainstorm days with multi centers due to the effect of topography. The months of maximum monthly rainstorm days over different regions of the same province are incompletely same as the result of the impact of different weather systems. Generally, rainstorm days have been increased since 2000, rainstorm begins earlier, ends latter and lasts longer than before. Nowadays, as the extreme rainfall events and secondary disasters happen frequently, it is conducive for the forecast of quantitative precipitation forecast (QPF) to learn the spatio temporal distribution and evolution features of rainstorm.
      2017,43(5):528-539, DOI: 10.7519/j.issn.1000-0526.2017.05.002
      Abstract:
      An extremely severe precipitation event took place in North China in 19-20 July 2016. It was characterized by large rainfall, persistent rainfall, warm cloud rainfall, strong local rainfall intensity and orographic precipitation. Its rainfall was larger than that of the extreme rainfall in 3-5 August 1996, and only next to the amount of the 2-7 August 1963 extreme rainfall event. It occurred under the circulation background of the South Asia high moving eastward, the West Pacific subtropical high moving northwestward and the low vortex in the westerlies developing in mid high latitude. The abnormal development of Huanghuai cyclone, southwest and southeast low level jets, and the abnormally abundant moisture indicates that the dynamic lifting and moisture conditions favored this severe rainfall process significantly. The whole rainfall event presented clearly the phase characteristics, and could be divided into two stages. The first stage was the orographic rainfall caused by the easterly winds ahead of the trough from the early morning to the daytime of 19 July, while the second part was produced by spiral rain bands in the north side of Huanghuai cyclone from the night of 19 to the daytime of 20 July. In the first stage, the easterly low level jet was lifted by the Taihang Mountains, which continuously triggered the convective cells along the east edge of the mountains. The weak dry and cold advection at mid level and the strong warm and wet advection at low level jointly maintained the convective instability. The cold pool generated by heavy rainfall and the mesoscale frontogenesis process created by local orographic effect provided favorable conditions for severe convections to occur continuously. The second stage rainfall was mainly related to the development of cut off vortex and Huanghuai cyclone. The blocking of the high pressure system slowed the steps of Huanghuai cyclone in North China, thus leading to the long lasting rainfall process.
      2010,36(3):9-18, DOI: 10.7519/j.issn.1000-0526.2010.3.002
      Abstract:
      Potential vorticity (PV) is one of the important concepts in advanced synoptic and dynamic meteorology. This paper is a brief introduction to the theory of potential vorticity, including the concept of PV, the conservation and invertibility of PV, PV thinking, moist PV (MPV), and the application of PV theory.
      2007,33(12):116-120, DOI: 10.7519/j.issn.1000-0526.2007.12.018
      Abstract:
      A comprehensive analysis and process system based on ArcGIS, and its chief targ et, its software frame, standardized data, database system, basic functions and its key technique, etc. are are described. The system is professional especially to weather modification, and it mainly applies to comprehensive analysis and pr ocess for weather modification, decision-making of operation schemes, appraisal of operation effectiveness, and services for enhancement precipitation or suppre ssion hail by ways of cannons or rocks, etc. In this system, information collect ion, analysis, management and comprehensive application of the weather modificat ion are realized. It also can be used in other fields in meteorology.
      2013,39(9):1163-1170, DOI: 10.7519/j.issn.1000-0526.2013.09.011
      Abstract:
      Drought and flood have significant impacts on catchment water use and ecological balance. To develop practical drought/flood monitoring indicators that only need a few climate variables, it is fundamentally necessary to explore the relationship between hydrology variables and climate variables for the specific catchment. This study investigates the correlations between lake water level and various time scale climatological indices according to the standardized precipitation index (SPI) and the standardized precipitation evapotranspiration index (SPEI), based on the monthly water level records from Honghu Lake representative gauging stations and the monthly observations of 8 meteorological stations in the Four Lake Basin. The results showed that extreme droughts and floods are primarily controlled by precipitation variability over the Four Lake Basin, and both SPEI and SPI are well related with lake water level of Honghu Lake while the degree of the correlation varies between different seasons and SPEI/SPI time scales, with the highest correlations for rainy summer and autumn months. Generally, the 4-6 month scale SPEI/SPI drought index is most closely correlated with lake water level of Honghu Lake, showing an apparent response of lake water level to the current and former months’ water surplus and deficiency. When compared with the historical time series of monthly average lake water level of Honghu Lake, the 5 month scale SPEI/SPI agrees well with the variability of the lake water level. The response relationship found during the study can not only aid the monitoring and forecasting of flood and drought conditions in the Four Lake Basin based on conventional weather data, but also provides some references for other places of China.
      2011,37(1):122-128, DOI: 10.7519/j.issn.1000-0526.2011.1.017
      Abstract:
      The following are the main characteristics of the general atmospheric circulation in October 2010. There were two polar vortex centers in the Northern Hemisphere. The circulation presents a four wave pattern in middle high latitudes, in which the strong Ural ridge corresponds to a large 40 gpm positive anomaly area. Strength of the Western Pacific subtropical high is weaker than normal years. The monthly mean temperature (10.1 ℃) is 0.5 ℃ higher than the same period of normal years, and the mean precipitation (42.6 mm) is 15.1% above normal. The major weather events include: 8 precipitation processes occuring, in which a rare heavy rain has struck on Hainan in the first and middle dekad of October; two tropical cyclones generated, with one super typhoon (Chaba, numbered 1013) landed in Fujian; in the last dekad of October, strong cold air outbreak across most areas of China; heavy fog aroused in the central and eastern China.
      2013,39(3):281-290, DOI: 10.7519/j.issn.1000-0526.2013.03.002
      Abstract:
      By using conventional observation data and NCEP reanalysis data, diagnostic analysis is performed on a rainstorm process, which occurred on 22-25 July 2010 in the western part of Sichuan Basin. The result shows that the rainstorm was generated under the circulation background that low level southerly airflows had remained over the region from the South China Sea to Sichuan Basin, so this rainstorm was closely related to the evolution of the southerly wind speeds. The rainfall intensity increased as the south winds grew stronger. Speed convergence formed by the enhanced south winds and positive vorticity advections became main dynamic trigger factors for the rainstorm. Therefore, the rainstorm is pretty consistent with the low level convergence and the positive vorticity advection. In addition, the result of WRF numerical simulation further indicates that: the evolution of 3 h wind speed at 850 hPa has good indication for the development of mesoscale convective systems. On the leeward side of the 3 h wind speed increasing area, convective cloud clusters are to develop rapidly in the next 3 hours. Moreover, the topographic influence simulation tests suggest that the airflow convergence generated in the west of the Basin is closely related to the topography of plateau.
      2011,37(2):142-155, DOI: 10.7519/j.issn.1000-0526.2011.2.003
      Abstract:
      Using the Variational Doppler Radar Analysis System (VDRAS) combined with local unconventional observation data, a more in depth contrastive analysis is carried on the initiation mechanism of two storm cases in Beijing, one is 814 (August 14, 2008) case with strong rainfall that we call it as moist storm and the other is 824 (August 24, 2008) case with little rainfall that we call it as dry storm. The results show: (1) The synoptic scale systems of 814 storm were stable Northeast cold vortex low trough at 500 hPa and shear line at 850 hPa, the specific humidity that more than 12 g·kg-1 below 850 hPa and the relative humidity that more than 90% in the surface indicated that the atmosphere was very moist. It had convective instability caused by humidity advection in lower levels. The 824 storm had a prevailing straight west wind in high levels, an anticyclone in lower levels, and a surface cold front moving fast.The specific humidity that less than 6 g·kg-1, and the relative humidity that less than 30% below 850 hPa indicated that the atmosphere was very dry. It had convective instability caused by temperature advection. (2) There was much strong vertical wind shear in the whole vertical layer for 814 storm case, the clockwise wind direction with height within 500-1500 m intensified the warm and humidity inflow of lower layer advantageous to storm initiation and development. While there was weak vertical wind shear and unobvious warm and humidity inflow of lower layer for 824 case, which was not conducive to storm initiation and development. In addition, composited wind of the whole troposphere and storm movement speed were very low for 814 case, but they were very high for 824 case. (3) The 814 storm was formed by the collision and mergence of multi cell storms, a convergence line was formed by the cold pool outflow produced by the precipitation of the upstream of thunderstorm cell and the east wind in low levels which forced the low level warm and moist air to uplift, additionally the strong convective instability and vertical wind shear supported the formation and development of new storm. The interactions (collisions) of gust fronts in the leading edge of cold pool of multi cell thunderstorm group, further exacerbating the low level instability, leading to the regeneration and mergence of new convective thunderstorms. The 824 storm was a line convective system accompanied with cold front that rapid moved eastward and lasted for short time, there was no east wind with warm and moisture air accompanying the cold pool outflow produced by the downdrafts of thunderstorm. The absence of mesoscale lifting mechanism and moisture inflow couldn’t support the formation and development of new storm.

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