Abstract:The climatological characteristics of seasonal, monthly and pentad mean air temperatures in the springs of 1981-2010 are analyzed and compared with those in the springs of 1951-1980 by using the daily air temperatures from observing stations of China and the monthly NCEP/NCAR atmospheric reanalysis data of the United States. The variation characteristics of air temperature and seasonal process in spring after 1980s are also investigated. The possible causes for temperature change in spring are preliminarily discussed. The results show that except the Southwest China, most regions of China experience warming temperature in spring and the situation of temperature “increasedecrease” is presented from Northeast to Southwest after 1980s. The air temperature rises by 0-1℃ in most regions of China except some parts of Southwest China in March, April and May. The seasonal process from March to May speeds up in the region to the south of Yangtze River and the eastern part of Southwest China, while it slows down in northeast China, the southern part of Southwest China and the northern part of Northwest China. The seasonal process in Inner Mongolia and the southern part of South China goes from fast to slow. On the whole, under the background of global warming, the onset and end dates of spring become earlier in East China, while the change is indistinct in West China. Compared with the condition in 1951-1980, the Ural blocking high and East Asian trough have weakened, while the zonal circulation over Asia in the middle and high latitudes, the subtropical high in western Pacific Ocean, and the subtropical westerly jet over East Asia have strengthened since 1980s. Those are disadvantageous to the influence of cold air from polar region and high latitude areas in the Northern Hemisphere on the climate of China. Therefore, temperatures are high over most of China, especially Northeast China in spring. However, the strengthen of the middle east jet and the southward of the East Asian jet are in favor of the cold air from the centraleastern part of Europe influencing Southwest China and resulting in low air temperature there. In the meantime, the weakened southern branch trough goes against the warm and wet flows from the Indian Ocean and Bay of Bengal influencing the Southwest China, which easily results in low temperature in these areas.

Abstract:Based on the NCEP/NCAR reanalysis data, sea surface temperature (SST) of NOAA, index of 74term circulation characteristics and weather observation data from 34 stations of Chongqing over 1961-2012, the climatic characteristics of spring continuous rain in Chongqing, the climate impact factors of the same period such as atmospheric circulation, the West Pacific subtropical high and early winter impact factors like SST, OLR, atmospheric circulation and the West Pacific subtropical high were analyzed. The results indicated that the spring continuous rain has so high frequency that Chongqing suffers serious spring continuous rain easily in March, followed by May. During the serious continuous rain period, the impacted range and the maintained time expanded. Furthermore, the probability of low temperature increases obviously. From the spatial distribution, the frequency of the spring continuous rain is high in Southeast China, but is relatively less in the northeastern and western parts. The spatial distribution of the continuous rain include two types: consistency in all areas and contrary in the west and east parts. In spring, lower 500 hPa geopotential heights are on the lower side in Barents Sea and the Tibetan Plateau region, higher in the east of Baikal Lake region, the general circulation anomalies over Eurasia midhigh latitude is beneficial to southward movement of cold air, and the West Pacific subtropical high weakens and retreats to east and south, which are the main factors for the occurrence of continuous rain in Chongqing. In early winters, the occurrence of the La Nina event, the development of the convection in the 150°E equator region, the establishment of high pressure ridge in the upper atmosphere in Okhotsk Sea area are conducive to the occurrence of spring continuous rain in Chongqing.

Abstract:Based on conventional and automatic weather station observation data, satellite, lightning location, radar data and NCEP reanalysis data, this paper analyzed the mesoscale convection condition and evolution characteristics of convective system in the disastrous rainstorm that happened in the west of Jiangxi from 24 to 25 May 2014. The conclusions are as follows. (1) Synoptic background of this rainstorm consists of eastward the movement of upper trough, strengthening of warm wet air in the edge of subtropical high, and the effect of cold air. (2) Surface mesoscale convergence line contributes to development and strengthening of MβCS. The longtime lasting of many dense MβCSs with smooth boundary in western Jiangxi leads to continuous heavy rainfall in the corresponding region. The cold cloud’s position and intensity of TBB≤-62℃ are good indicators for surface precipitation, especially the center of TBB≤-72℃ coincides with the rainfall center best. (3) In this rainstorm, distribution of 5 min rainfall is almost in accord with distribution of CG lightning number, which happends 10 min earlier than jump of surface precipitation. (4) Mesoscale vortex in radar radial velocity graph is one of the most important factors for this rainstorm. Western Jiangxi presents notable wind convergence and wind speed divergence. Lowlevel strong southwest jet’s overlying deep “radial wind convergence zone” helps the strengthening and maintaining of the rain. In addition, with the help of dynamic convergence and mountainous topography, strong southerly jet with abundant water vapor meets in the west of Jiangxi, causing continuous heavy rainfall. (5) The change of biggest radar echo intensity assists estimating the change of 5 min rainfall intensity, but it is not a good indicator. Radar wind profile products are good indicators of heavy rainfall on the surface, which forecasted this heavy rainfall seen in western Jiangxi 2 h in advance.

Abstract:The torrential rainfall in the middle and northern parts of Zhejiang Province on 7 June 2013 was diagnosed based on the latest ECMWF ERAInterim global reanalysis data with 0.75°×0.75° resolution. The results show that the torrential rain was caused by two developing eastwardmoving systems-an upperlevel shortwave trough and a lowlevel southwest vortex, and the torrential rainfall area over the middle and northern of Zhejiang are located in the coupling area of the upperlevel and lowlevel jet streams. A large amount of instability energy was stored below 700 hPa before the occurrence of rainstorm, which was triggered by the southwest vortex close to the torrential rainfall area. The analysis of environmental fields by means of physical decomposition of atmospheric variables shows that background ambient was in favor of this regional rainstorm, causing the instantaneous anomaly field to trigger the torrential rainfall at last. The torrential rainfall is obviously located in the anomalous warm convergence shear line at 850 hPa.

Abstract:By using the observation data, operational model data and NCEP reanalysis data (1°×1°), the characteristics and forecasting difficulties of severe Typhoon Fitow (No.1323) and the cause for the strong wind and heavy rainfall are analyzed synthetically. The results show that Fitow moves westward suddenly and intensifies near the offshore, and these are the major forecasting difficuties in operation and reasons of the big forecasting errors. The subtropical jet over East Asia intensifies rapidly and the subtropical high extends westward, causing Fitow to move westward suddenly. The strong divergence in the right side of the subtropical jet’s entrance is an important dynamic mechanism for Fitow to intensify near the offshore and for the heavy rainfall and strong wind in Fitow’s north side. Danas (No.1324) provides plentiful water vapor transport, bringing the heavy rainfall and causing Fitow’s intensity to sustain near offshore. In addition, Danas makes the subtropical high extend westward. Therefore, the existence of Danas is also an important factor causing Fitow to move westward suddenly. When forecasters failed to pay enough attention to the upperlevel fields, especically subtropical westerly jet, which is likely the main reason of the bigger forecasting errors of the track, intensity, rainfall and gale of Fitow. Finally, when the tracks of the ensemble prediction systems have large divergence or the different models produce greatly different forecast results, the ammending technique based on multimodel ensembles is an effective method to improve the accuracy of typhoon track forecasting.

Abstract:Based on WRF mesoscale model which couples CAMS cloud scheme with cloud microphysics process, a low trough cold front precipitation process that occurred on 25 September 2012 in Shanxi Province was simulated. According to the simulation results, the macro and micro cloud structure and supercooled water distribution were analyzed combining with other data, such as aircraft detection, satellite, radar and ground rainfall observations. The structure and physical condition of supercooled water were studied so that seeding suggestions could be provided in this kind of cloud system. The simulated weather situation, precipitation, cloud top temperature, radar echo distribution, and hydrometeors evolution are basically consistent with the observations. The main results are as follows. This precipitation process was influenced by a low trough cold front system in front of which high and cold cloud was composed of ice particles. The cloud top temperature was about -40℃, and no precipitation on surface. Near the front, clouds were mixed by warm and cold particles. The cold cloud zone was made up of small amount of supercooled water and large quantity of ice particles, with heaviest precipitation on the surface. Behind the front, high and cold cloud had a small amount of ice particles, no supercooled water. The cloud top temperature was about -30℃ and the surface rain was light. The supercooled water was mainly distributed in the -5℃ layer in front of the front. Showing the characteristic of lower height and smaller content, the supercooled water was hold by water vapor through the vertical updraft on one hand, and consumed by ice particles sublimation growth process on the other hand. The updraft condition, which in and under supercooled water layer was weak and over it was strong, was not beneficial to the maintenance of large amount of liquid water, but promoted ice particles to develop quickly. In this area, water vapor is not saturated with respect to liquid water but saturated to ice. The water vapor was consumed by a lot of ice particles, not favorable for the existence of supercooled water, so only a small amount of supercooled water stay in cloud. During this process, along with the increase of concentration ice nuclei, the concentration of ice crystals got increased, but the snow and graupel content and supercooled water in the -5 to 0℃ layer was not affected.

Abstract:The soil moisture and precipitation data of Inner Mongolia of CMA Land Data Assimilation System (CLDAS) were evaluated. The drought that happened in Inner Mongolia in the summer of 2014 was analyzed using CLDAS with RSM and DNP, and the results of dry year (2014) and wet year (2013) were compared with SPI and PDECI. The analysis results revealed that the dynamic variation of daily soil relative moisture and the precipitation area and grade can be reconstructed by CLDAS, which can meet the requirements of drought monitoring. The soil relative moisture index based on CLDAS can monitor the daily and regional changes of drought of quickly and conveniently. The continuous absence of effective precipitation day is relatively valid for estimating longperiod and continuous drought. In brief, CLDAS is able to fulfill the timeliness, resolution and representativeness requirements of meteorological service, and can serve research and operation widely as important supplementary for monitoring data. It is valuable for areas like Inner Mongolia where weather station is relatively scarce in a widespread area.

Abstract:Based on the LDII lightning locator and Lanzhou CINRAD/CC radar datasets, the relationship between the radar echo parameter and lightning activity area was analyzed using the summer precipitation cases in the central of Gansu Province in 2011 and 2012 respectively. Then, the key characteristics of the radar data were summarized and a lightning warning program was established. The results show that the echo top of 35 dBz and 40 dBz reflectivity above the height of -10℃ layer can be used in the lightning warning, which can make the prediction time of lightning warning be 23 and 16 minutes in advance respectively. Vertically integrated liquid (VIL) with values less than 30 kg·m-3 can be utilized as a sufficient condition to judge whether thunderstorm will occur. Generally the warning should be 7 minutes earlier than the ocurrence of lightning when the echo top (ET) exceeds 10 km. The lightning warning program was tested using the cases in 2013, and the result indicates that this program has a good effect on the thunderstorm warning.

Abstract:Three computational schemes for pseudoequivalent potential temperature (PEPT) are compared, the influences of PEPT on the computational accuracy of Showalter index (SI) are analyzed, and highaccuracy computation schemes of SI are proposed. First, the airparcel temperature and pressure at the lifted condensation level are calculated on the basis of the conservation property of potential temperature and mixing ratio during dry adiabatically lifting process. Then, Bolton formula is used to calculate the initial PEPT at 850 hPa. Next, Stackpole iteration algorithm is employed to look for the airparcel temperature at 500 hPa lifted adiabatically from 850 hPa keeping PEPT conservational, and thus SI can be finally solved. It is found that the computational error of PEPT constitutes an important part of the error of SI, therefore it is quite necessary to utilize accurate formula to compute PEPT. Comparison shows that the Bolton formula and LRC formula are more precise than the conventional Rossby formula to calculate PEPT. The PEPT at 850 hPa calculated by the classic Rossby formula is systematically lower than that using the other two formulas, and the error increases with the increasing of air temperature and humidity. Consequently, the mean absolute error of SI decreases from 0.66℃ using Rossby formula to 0.45℃ using Bolton formula. In comparison with the previous studies, the computation scheme proposed in this paper shows improved accuracy, feasibility in programming, and encouraging potential in operational practices of convective weather forecasting.

Abstract:China Meteorological Administration (CMA) commenced building surface automatic weather station (AWS) around 2000. More than 2400 national AWSs have been built to observe precipitation, air temperature, wind direction, wind speed, air pressure, air humidity and soil temperature, etc. Moreover, more than 55000 regional AWSs that are mainly applied to disaster prevention and reduction have been also set up to monitor precipitation, air temperature, wind direction, wind speed, air pressure or humidity. The data quality of the above large number of AWSs could not reach very correct degree. So, at the end of 2009 CMA launched a project named Construction of Quality Control and Comprehensive Evaluation System for Realtime Observation Data of AWS. (1) After analyzing various performance ways and causes of the erroneous meteorological data from AWS, the quality control technique was developed for realtime observed and transmitted hourly data of precipitation, air temperature, wind direction, wind speed, air pressure and air humidity. The quality control method includes climatic range check, internal consistency check, temporal consistency check, spatial consistency check, mancomputer interaction control, etc. Each kind of inspection process contains a number of control modes. (2) Based on the operational process of AWS observation data acquisition, transmission, collection, decode and realtime service, threestep quality control system of AWS realtime observation data was developed. In the system, the nationallevel system is mainly responsible for data quality evaluation, the provincial one including 31 provincial data management departments is in charge of data quality control, and more than 2400 national stations are responsible for data quality monitoring and erroneous data correction. The threestep quality control system operates based on national and provincial realtime databases, organized mainly by one realtime quality control software, mancompute interaction quality monitoring platform, data quality evaluation platform, nationprovincestation threestep quality automatic feedback process for suspect data information. (3) The threestep quality control system of AWS realtime observation data has been installed and operational applied at more than 2400 national AWSs, 31 provincial meteorological information departments and one national meteorological information center. Quality control, quality monitoring, quality feedback and quality evaluation are operated for meteorological data of realtime observation and transmission from above national and regional AWSs. The quality of all AWS observation data is greatly improved year by year. For example, data availability of hourly air temperature and precipitation realtime observed by above AWSs in main flood season increases from 88%, 83% respectively in 2009 to about 98% in 2012 and 2013.

Abstract:Intensity forecast errors are analyzed according to the official forecasts from the Central Meteorological Observatory (CMO) of China Meteorological Administration (CMA) for typhoons in the western North Pacific during 2001-2012. It is shown that no significant improvement can be observed during the 12 years with undulating annual mean errors. The forecast errors are relatively small for steady intensity change process, but large for rapid intensity change process. There is a high probability for the forecasts to be stronger (weaker) than the observations at the leading time of 24, 96 and 120 h (48 and 72 h). It should be noted that the forecast errors are larger at the northeastern part of the South China Sea than other locations. The probability of the forecast intensity being stronger than the observations in 120 h is increased with the increase of typhoon intensity. The threshold error values of 70% accumulated probability are calculated for typhoons in different intensity and moving speed categories and a probability intensity forecast scheme is proposed to provide a guidance with an estimation of the forecast errors.

Abstract:A method of quality detection about ground echo intensity and speed of CINRAD/SC new generation Doppler weather radar is proposed in this paper. First, calibrate all the weather radars by same parameters, and collect ground echo intensity data as a template on clear days. Then compare it with realtime echo intensity data. Through phaseshift, the speed data are automatically tested by the sides of error between measured and theoretical values and the echo intensity and speed data is detected and corrected to achieve high detection precision of weather radar.

Abstract:During the spring of 2015, the air temperature over most China was above normal and the mean precipitation over China was near normal with strong intraseasonal variations in South China. In the early spring (March to April) of 2015, precipitation in South China was below normal, and after the arrival of the prime rainy season in the late spring, precipitation in the region was significantly above normal. Analysis shows that the later arrival of prime rainy season is related to the El Ni〖AKn~D〗o event, which induced the westward extension of the western Pacific subtropical high (WPSH) and prevented the water vapor from transporting to South China. After the arrival of prime rainy season, the transport passage of the water vapor to China via Indian Ocean is built up, accompanying the development of Somali crossequatorial flows, and the transportation has a northward shift resulting from the WPSH in the South China Sea. Moreover, the Indian Ocean is warmer than normal in the late spring, inducing the development of the lowlevel anticyclonic anomaly over South China Sea and the intensification of water vapor transportation. The two elements are likely the causes for the abnormal precipitation in South China.

Abstract:The main characteristics of the general atmospheric circulation in July 2015 are listed as follows: there are several polar vortex centers in the Northern Hemisphere. In the midhigh latitudes, the circulation presents a fivewave pattern. The Northwest Pacific subtropical high is stronger than normal. Meanwhile, the monthly mean precipitation amount is 88.7 mm, which is 26.5% less than its climatological mean, the monthly mean temperature is 22.1℃, 0.2℃ higher than normal. There are 7 severe rainfall events with extreme precipitation records observed at some stations in China. Five tropical cyclones are active over the Northwest Pacific Ocean and the South China Sea, and two of them land China. Longlasting high temperature events occur in Xinjiang, and drought in North China, Huanghuai Area and other places. Meanwhile, 24 provinces suffer from hail disasters.