ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 38,Issue 5,2012 Table of Contents
2012, 38(5):513-525.
DOI: 10.7519/j.issn.1000-0526.2012.05.001
Abstract:
The feasibility and availability of applying ensemble Kalman filter (EnKF) technique in convective scale systems were demonstrated by an observation system simulation experiment (OSSE) in this paper, which assimilates simulated radial velocity and reflectivity of one Doppler radar with an EnKF assimilation system based on WRF model. The experiment shows: the assimilation system has the ability to accurately analyze the detailed characters of flow fields, thermodynamic and microphysical fields of the storm, forecast and analysis errors of almost all variables decrease significantly after assimilation cycles, and forecast fields of all levels can be improved by assimilation, especially on levels of larger errors. Reliable correlativity between radar reflectivity, radial velocity observations and forecast fields can be established after 8 assimilation cycles, and the background error covariance has a complex structure and is highly inhomogeneous, anisotropic and flowdependent. Determinate forecast of ensemble mean field can keep the detail characters of truth storm in short period but errors grow fast.
The feasibility and availability of applying ensemble Kalman filter (EnKF) technique in convective scale systems were demonstrated by an observation system simulation experiment (OSSE) in this paper, which assimilates simulated radial velocity and reflectivity of one Doppler radar with an EnKF assimilation system based on WRF model. The experiment shows: the assimilation system has the ability to accurately analyze the detailed characters of flow fields, thermodynamic and microphysical fields of the storm, forecast and analysis errors of almost all variables decrease significantly after assimilation cycles, and forecast fields of all levels can be improved by assimilation, especially on levels of larger errors. Reliable correlativity between radar reflectivity, radial velocity observations and forecast fields can be established after 8 assimilation cycles, and the background error covariance has a complex structure and is highly inhomogeneous, anisotropic and flowdependent. Determinate forecast of ensemble mean field can keep the detail characters of truth storm in short period but errors grow fast.
2012, 38(5):526-532.
DOI: 10.7519/j.issn.1000-0526.2012.05.002
Abstract:
The average bias of T639 model forecast fields for 1-10 d forecast in 2009-2010 was evaluated. Forecast fields were included 500 hPa geopotential height, 850 hPa temperature and 2 m temperature. The result showed that T639 model has obviously forecast system errors for the three fields. The decaying averaging method was trying to correct forecast system errors. Corrected result showed that the decaying averaging method has positive correction skill, but correction skill was decreased with lead time. System errors of East Asia were less than the Northern Hemisphere and the correction skill of decaying averaging method for East Asia was also less than the Northern Hemisphere. Through evaluating correction skill of cold season and warm season respectively it is found that the correction skill has no obvious difference for 500 hPa geopotential height and 850 hPa temperature, but for 2 m temperature, the correction skill of cold season was higher than warm season. In addition, the test on different weight of “decaying averaging method” showed that the correction skill was best when weight was round about 0.1 for 850 hPa temperature and 2 m temperature and round about 0.06 for 500 hPa geopotential height.
The average bias of T639 model forecast fields for 1-10 d forecast in 2009-2010 was evaluated. Forecast fields were included 500 hPa geopotential height, 850 hPa temperature and 2 m temperature. The result showed that T639 model has obviously forecast system errors for the three fields. The decaying averaging method was trying to correct forecast system errors. Corrected result showed that the decaying averaging method has positive correction skill, but correction skill was decreased with lead time. System errors of East Asia were less than the Northern Hemisphere and the correction skill of decaying averaging method for East Asia was also less than the Northern Hemisphere. Through evaluating correction skill of cold season and warm season respectively it is found that the correction skill has no obvious difference for 500 hPa geopotential height and 850 hPa temperature, but for 2 m temperature, the correction skill of cold season was higher than warm season. In addition, the test on different weight of “decaying averaging method” showed that the correction skill was best when weight was round about 0.1 for 850 hPa temperature and 2 m temperature and round about 0.06 for 500 hPa geopotential height.
2012, 38(5):533-542.
DOI: 10.7519/j.issn.1000-0526.2012.05.003
Abstract:
Using the observational data， intensive surface observation data, TBB data and NCEP reanalysis data, the synoptic and dynamic diagnosis and mesoscale characteristics of a continued strong convection weather process are analyzed. The results show that: (1) the Continuous downslide cold troughs, from Mongolia cold vortex, are its impact systems. High cold trough, lowlevel warm temperature ridge, and wet tongue overlapping are conducive to the establishment and development of convective instability. (2) The warm dry lid formed by the inversion layer near 850 hPa at the lower troposphere is more conducive to the occurrence of deep convective activity. The larger the air temperature lapse rate is, the easier the occurrence of thunderstorm and gale is. And there is a good correspondence between magnitude of the CAPE, vertical wind shear and the strength of convection weather. (3) The strong convection weather process in 23-24 June 2006 is caused by mesoβ scale hailstorm cloud with a 6 h life time, but the violent weather in the 25th is caused by mesoα scale squall line cloud with a 10 h life time. (4) The surface convergence line or dry line is one of the factors which trigger the strong convection; and the convective cells or cloud cluster are generally generated close to the surface convergence line.
Using the observational data， intensive surface observation data, TBB data and NCEP reanalysis data, the synoptic and dynamic diagnosis and mesoscale characteristics of a continued strong convection weather process are analyzed. The results show that: (1) the Continuous downslide cold troughs, from Mongolia cold vortex, are its impact systems. High cold trough, lowlevel warm temperature ridge, and wet tongue overlapping are conducive to the establishment and development of convective instability. (2) The warm dry lid formed by the inversion layer near 850 hPa at the lower troposphere is more conducive to the occurrence of deep convective activity. The larger the air temperature lapse rate is, the easier the occurrence of thunderstorm and gale is. And there is a good correspondence between magnitude of the CAPE, vertical wind shear and the strength of convection weather. (3) The strong convection weather process in 23-24 June 2006 is caused by mesoβ scale hailstorm cloud with a 6 h life time, but the violent weather in the 25th is caused by mesoα scale squall line cloud with a 10 h life time. (4) The surface convergence line or dry line is one of the factors which trigger the strong convection; and the convective cells or cloud cluster are generally generated close to the surface convergence line.
2012, 38(5):543-551.
DOI: 10.7519/j.issn.1000-0526.2012.05.004
Abstract:
Based on the high resolution NCEP reanalysis data the helicity, moist potential vorticity (MPV) and some other essential physical quantities were computed, and then combined with Doppler Radar products, the associated thermodynamic and dynamic mechanisms for the occurrence and evolution of an extremely heavy rain in eastern Guangdong caused by the tropical storm (0903) Linfa were analyzed. The results suggested that the southwesterly jet in the periphery of typhoon trough provided abundant moisture and thermodynamic conditions. At midlow levels over the rainfall region, the equivalent potential temperature (θse) surfaces were steep and decreased with increasing altitudes, i.e. θse/p＞0. Meanwhile at low levels over the same area, the MPV was remarkably high negative. These two conditions indicated a strong convectional instability. Strong convergence at low levels and divergence at high levels, mesoscale circulation and intense rotational ascending motion provided the dynamic conditions. It was also shown that the location and time of high θse tongue and low MPV tongue overlapped agreed with those of the heavy rain, and the positive center at midlow levels and negative center at high levels of the vertical helicity were coincided with the rainfall center. Additionally, heavy precipitation tended to take place during the period when the rotational ascending motion rapidly intensified; and the echo characteristics also showed that the extremely heavy rain is produced by the high precipitation rate with long duration of precipitation.
Based on the high resolution NCEP reanalysis data the helicity, moist potential vorticity (MPV) and some other essential physical quantities were computed, and then combined with Doppler Radar products, the associated thermodynamic and dynamic mechanisms for the occurrence and evolution of an extremely heavy rain in eastern Guangdong caused by the tropical storm (0903) Linfa were analyzed. The results suggested that the southwesterly jet in the periphery of typhoon trough provided abundant moisture and thermodynamic conditions. At midlow levels over the rainfall region, the equivalent potential temperature (θse) surfaces were steep and decreased with increasing altitudes, i.e. θse/p＞0. Meanwhile at low levels over the same area, the MPV was remarkably high negative. These two conditions indicated a strong convectional instability. Strong convergence at low levels and divergence at high levels, mesoscale circulation and intense rotational ascending motion provided the dynamic conditions. It was also shown that the location and time of high θse tongue and low MPV tongue overlapped agreed with those of the heavy rain, and the positive center at midlow levels and negative center at high levels of the vertical helicity were coincided with the rainfall center. Additionally, heavy precipitation tended to take place during the period when the rotational ascending motion rapidly intensified; and the echo characteristics also showed that the extremely heavy rain is produced by the high precipitation rate with long duration of precipitation.
2012, 38(5):552-560.
DOI: 10.7519/j.issn.1000-0526.2012.05.005
Abstract:
Using MICAPS 3.1, the mesoscale automatic weather stations (AWS) and Doppler radar, the rainstorm in the southeastern Guangdong with the rainfall exceeding 600 mm within 13 hours on June 25, 2010 is analyzed. It is shown that the direct impact system of this extreme precipitation is the deep highaltitude cold vortex which located south and moved slowly; the strong low level jet (LLJ) and LLJ provided sufficient moisture and dynamic conditions; and that the organized arrangement of the multisingle storm activity, the ground quasistationary front and the mesoscale warm shear line which maintained for a long time are the main causes for the formation of “train effect”. The precipitation echoes move along with the total surface center, and the special terrain is also one reason of the “train effect”. The reflectivity images have shown that the banded heavy precipitation echo can be a lowmass center structure and then strong vertical development. The speed image with a “bull eye” structure shows that there was a low level southwest jet. Based on these studies, a “train effect” storm model is proposed.
Using MICAPS 3.1, the mesoscale automatic weather stations (AWS) and Doppler radar, the rainstorm in the southeastern Guangdong with the rainfall exceeding 600 mm within 13 hours on June 25, 2010 is analyzed. It is shown that the direct impact system of this extreme precipitation is the deep highaltitude cold vortex which located south and moved slowly; the strong low level jet (LLJ) and LLJ provided sufficient moisture and dynamic conditions; and that the organized arrangement of the multisingle storm activity, the ground quasistationary front and the mesoscale warm shear line which maintained for a long time are the main causes for the formation of “train effect”. The precipitation echoes move along with the total surface center, and the special terrain is also one reason of the “train effect”. The reflectivity images have shown that the banded heavy precipitation echo can be a lowmass center structure and then strong vertical development. The speed image with a “bull eye” structure shows that there was a low level southwest jet. Based on these studies, a “train effect” storm model is proposed.
2012, 38(5):561-568.
DOI: 10.7519/j.issn.1000-0526.2012.05.006
Abstract:
Using rime and glaze observation data at 142 stations in Hebei Province, surface observation data at 94 stations in the southern Hebei Province and radiosonde data at Xingtai from 1980 to 2009, the spatial and temporal distribution characteristics of rime and glaze are analyzed, and suitable meteorological conditions (temperature, humidity and wind) for rime and glaze are studied by the boxwhisker plot. The results show that： (1) rime and glaze occur mainly in the southern Hebei Province from November to March the following year, and they are more frequent in eastern plains than western mountains; (2) the suitable meteorological conditions for rime are on fog days, and daily mean temperature is between -7.2 and -3.1℃, daily mean humidity ≥92%, daily mean wind speed ≤1.2 m·s-1, and the probability of temperature inversions is about 95% when rime occurs; (3) the suitable meteorological conditions for glaze are rain days and daily mean temperature is between -4.1 and 0℃, daily mean humidity ≥87%, and probability of temperature inversions is 100% when glaze occurs; (4) relative humidity in the high value area of rime and glaze is significantly higher than low value area. Therefore, higher relative humidity is the main cause for the formation of high occurrence area of rime and glaze.
Using rime and glaze observation data at 142 stations in Hebei Province, surface observation data at 94 stations in the southern Hebei Province and radiosonde data at Xingtai from 1980 to 2009, the spatial and temporal distribution characteristics of rime and glaze are analyzed, and suitable meteorological conditions (temperature, humidity and wind) for rime and glaze are studied by the boxwhisker plot. The results show that： (1) rime and glaze occur mainly in the southern Hebei Province from November to March the following year, and they are more frequent in eastern plains than western mountains; (2) the suitable meteorological conditions for rime are on fog days, and daily mean temperature is between -7.2 and -3.1℃, daily mean humidity ≥92%, daily mean wind speed ≤1.2 m·s-1, and the probability of temperature inversions is about 95% when rime occurs; (3) the suitable meteorological conditions for glaze are rain days and daily mean temperature is between -4.1 and 0℃, daily mean humidity ≥87%, and probability of temperature inversions is 100% when glaze occurs; (4) relative humidity in the high value area of rime and glaze is significantly higher than low value area. Therefore, higher relative humidity is the main cause for the formation of high occurrence area of rime and glaze.
2012, 38(5):569-576.
DOI: 10.7519/j.issn.1000-0526.2012.05.007
Abstract:
In this paper, the precipitation data at Beijing Observatory from 1841 to 2008, and the rainfall data at 20 meteorological stations and 82 rainfall stations for nearly five decades, are used to analyze the spatial and temporal variations of the precipitation in Beijing at different subregions, and the rainfall databyminute are used by the Generalized Pareto Distribution (GPD) method to analyze the shortduration rainfall in Beijing at different return periods. The results have shown that: Beijing has two rainy periods of 1871-1894 and 1947-1960 and two dry periods of 1853-1870 and 1992-present. From the 1970s to 1980s, the heavy rainfall in Beijing mainly occurred in urban area. After the 1990s, the short duration of heavy rainfall displayed the local characteristics of the uneven distribution, and heavy precipitation centers roughly changed to a southwestnortheast banded distribution. According to the rainfall spatial distribution and EOF analysis, the rainfall region can be divided into four subregions, i.e. mountain areas, urban centers, northeast mountains and southeast plains. The result of rainfall in different return periods is close to the existing drainage specifications, which means that the simulation results of return period are reliable.
In this paper, the precipitation data at Beijing Observatory from 1841 to 2008, and the rainfall data at 20 meteorological stations and 82 rainfall stations for nearly five decades, are used to analyze the spatial and temporal variations of the precipitation in Beijing at different subregions, and the rainfall databyminute are used by the Generalized Pareto Distribution (GPD) method to analyze the shortduration rainfall in Beijing at different return periods. The results have shown that: Beijing has two rainy periods of 1871-1894 and 1947-1960 and two dry periods of 1853-1870 and 1992-present. From the 1970s to 1980s, the heavy rainfall in Beijing mainly occurred in urban area. After the 1990s, the short duration of heavy rainfall displayed the local characteristics of the uneven distribution, and heavy precipitation centers roughly changed to a southwestnortheast banded distribution. According to the rainfall spatial distribution and EOF analysis, the rainfall region can be divided into four subregions, i.e. mountain areas, urban centers, northeast mountains and southeast plains. The result of rainfall in different return periods is close to the existing drainage specifications, which means that the simulation results of return period are reliable.
2012, 38(5):577-584.
DOI: 10.7519/j.issn.1000-0526.2012.05.008
Abstract:
The Urumqi Institute of Desert Meteorology under the China Meteorological Administration (CMA) launched a scientific experiment with the radar wind profiler at the Tazhong Station—an experimental site for atmospheric environment observations in the hinterland of the Taklimakan Desert in July-October 2010. This study uses high temporal resolution data from the experiment to analyze the turbulence development of boundary layer, vertical velocity and atmospheric virtual temperature of typical clearair day. The results show that: (1) The turbulence refractive index structure constant (C2n) can reflect in detail the development of turbulence, and the height of turbulence development bloom area in summer days may be reached at 4000 m. (2) RASS system has good credibility for atmospheric virtual temperature detection, and its near boundary layer is generally in line with the daily temperature variation. (3) The clearair days in Taklimakan Desert are mainly controlled by east and northeast winds, the wind speed is relatively small and changes within 2.0-6.0 m·s-1. The atmospheric vertical velocity change of the desert hinterland fits in with the static equilibrium theory, the vertical velocity is very weak, generally in the -1.0 to 1.0 m·s-1 range fluctuations.
The Urumqi Institute of Desert Meteorology under the China Meteorological Administration (CMA) launched a scientific experiment with the radar wind profiler at the Tazhong Station—an experimental site for atmospheric environment observations in the hinterland of the Taklimakan Desert in July-October 2010. This study uses high temporal resolution data from the experiment to analyze the turbulence development of boundary layer, vertical velocity and atmospheric virtual temperature of typical clearair day. The results show that: (1) The turbulence refractive index structure constant (C2n) can reflect in detail the development of turbulence, and the height of turbulence development bloom area in summer days may be reached at 4000 m. (2) RASS system has good credibility for atmospheric virtual temperature detection, and its near boundary layer is generally in line with the daily temperature variation. (3) The clearair days in Taklimakan Desert are mainly controlled by east and northeast winds, the wind speed is relatively small and changes within 2.0-6.0 m·s-1. The atmospheric vertical velocity change of the desert hinterland fits in with the static equilibrium theory, the vertical velocity is very weak, generally in the -1.0 to 1.0 m·s-1 range fluctuations.
2012, 38(5):585-592.
DOI: 10.7519/j.issn.1000-0526.2012.05.009
Abstract:
In this paper, the 0-36 h downward shortwave flux at ground surface (SWDOWN) forecasting has been simulated by WRFV3 continuously for approximately four months: January, April, August and October in 2009. The hourly total solar radiation (HTSR) forecasting was converted by the 12-36 h SWDOWN output from WRF simulation. And HTSR forecast was compared with the observation of Wuhan Station. The results show that: （1) the simulation of HTSR is interrelated well with observation. Correlation of every month is larger than 0.8 and corresponds to 0.01 significance levels. （2) Each time HTSR mean forecast errors (MFE) in the morning and evening are smaller than in other time, but the maxima of mean absolute percentage errors (MAPE) appear in the morning and evening. MAPEs from 9 AM to 3 PM change a little and their reliability is higher than in other time. （3) WRFV3 model has ability to forecast the total solar radiation in clear, cloudy or overcast weather conditions, especially good performance in clear sky. However, this simulation is not a perfect initial field for power prediction of photovoltaic systems. Our future work is to use some methods for correcting HTSR forecast and improve their practical application.
In this paper, the 0-36 h downward shortwave flux at ground surface (SWDOWN) forecasting has been simulated by WRFV3 continuously for approximately four months: January, April, August and October in 2009. The hourly total solar radiation (HTSR) forecasting was converted by the 12-36 h SWDOWN output from WRF simulation. And HTSR forecast was compared with the observation of Wuhan Station. The results show that: （1) the simulation of HTSR is interrelated well with observation. Correlation of every month is larger than 0.8 and corresponds to 0.01 significance levels. （2) Each time HTSR mean forecast errors (MFE) in the morning and evening are smaller than in other time, but the maxima of mean absolute percentage errors (MAPE) appear in the morning and evening. MAPEs from 9 AM to 3 PM change a little and their reliability is higher than in other time. （3) WRFV3 model has ability to forecast the total solar radiation in clear, cloudy or overcast weather conditions, especially good performance in clear sky. However, this simulation is not a perfect initial field for power prediction of photovoltaic systems. Our future work is to use some methods for correcting HTSR forecast and improve their practical application.
2012, 38(5):593-600.
DOI: 10.7519/j.issn.1000-0526.2012.05.010
Abstract:
The daily meteorological data at 37 stations in Jiangsu Province, the NCEP/NCAR reanalysis data of monthly mean geopotential height and wind fields, and the data of the North Pacific sea surface temperature (SST) from 1980 to 2009 are analyzed by methods of composite and teleconnection. The characteristics of atmospheric circulation and North Pacific SST were studied when comfort index of human body (CIHB) was anomalous in winter and summer. The results indicated that: （1) the cold air force in winter is weaker when the CIHB is higher than that when the CIHB is lower. Because East Asian trough is shallower, winter monsoon is weaker especially the north wind and downdraft are also weaker at the stage of higher CIHB than lower CIHB. In summer, subtropical high was found to be westward and strengtherning and South Asia high lies easterly and northerly and strengtherns in the higher CIHB stage, including the stronger summer monsoon and weaker vertical convection. （2) In winter, SST in the Midwest Pacific at the stage of higher CIHB is warmer than the lower CIHB, particularly in Kuroshio in China eastern offshore. No matter the leading or contemporaneous correlation, the correlation between the West Pacific SST and the CIHB in winter is positive mainly, especially in Kuroshio.
The daily meteorological data at 37 stations in Jiangsu Province, the NCEP/NCAR reanalysis data of monthly mean geopotential height and wind fields, and the data of the North Pacific sea surface temperature (SST) from 1980 to 2009 are analyzed by methods of composite and teleconnection. The characteristics of atmospheric circulation and North Pacific SST were studied when comfort index of human body (CIHB) was anomalous in winter and summer. The results indicated that: （1) the cold air force in winter is weaker when the CIHB is higher than that when the CIHB is lower. Because East Asian trough is shallower, winter monsoon is weaker especially the north wind and downdraft are also weaker at the stage of higher CIHB than lower CIHB. In summer, subtropical high was found to be westward and strengtherning and South Asia high lies easterly and northerly and strengtherns in the higher CIHB stage, including the stronger summer monsoon and weaker vertical convection. （2) In winter, SST in the Midwest Pacific at the stage of higher CIHB is warmer than the lower CIHB, particularly in Kuroshio in China eastern offshore. No matter the leading or contemporaneous correlation, the correlation between the West Pacific SST and the CIHB in winter is positive mainly, especially in Kuroshio.
2012, 38(5):601-607.
DOI: 10.7519/j.issn.1000-0526.2012.05.011
Abstract:
The climatic characteristics of precipitation over the middle and lower reaches of the Yangtze River Valley (YRV) during early summer of 2011 and associated causes are examined in this study. It is shown that, during May 2011, the precipitation over the middle and lower reaches of the YRV was below normal, but was above normal during June, and then droughtflood alternation occurs. This droughtsflood alternation is mainly influenced by the intensity of the South China Sea summer monsoon and the East Asian summer monsoon, and the abrupt northward shift of the western Pacific subtropical high (WPSH). During June 2011, there are two troughs located in the Arabian Sea and the Sea of Japan respectively, and a ridge located in the Lake Baikal over the middlehigh latitude Eurasian area. The frequent activities of northeast cold vortex (NECV) bring cold air masses to the middle and lower reaches of the YRV. At the same time, the WPSH extends to the west and north of its normal position, and shifts westward several times in June. It is indicated that it is just the interaction between the NECV and WPSH that leads to the reinforcement of the southwest lowlevel jet (LLJ) in the lower troposphere. The convergence between the northward warm and wet southwesterly flow brought by LLJ and the southward dry and cold air by NECV is favorable to the positive precipitation anomaly in the middle and lower reaches of the YRV.
The climatic characteristics of precipitation over the middle and lower reaches of the Yangtze River Valley (YRV) during early summer of 2011 and associated causes are examined in this study. It is shown that, during May 2011, the precipitation over the middle and lower reaches of the YRV was below normal, but was above normal during June, and then droughtflood alternation occurs. This droughtsflood alternation is mainly influenced by the intensity of the South China Sea summer monsoon and the East Asian summer monsoon, and the abrupt northward shift of the western Pacific subtropical high (WPSH). During June 2011, there are two troughs located in the Arabian Sea and the Sea of Japan respectively, and a ridge located in the Lake Baikal over the middlehigh latitude Eurasian area. The frequent activities of northeast cold vortex (NECV) bring cold air masses to the middle and lower reaches of the YRV. At the same time, the WPSH extends to the west and north of its normal position, and shifts westward several times in June. It is indicated that it is just the interaction between the NECV and WPSH that leads to the reinforcement of the southwest lowlevel jet (LLJ) in the lower troposphere. The convergence between the northward warm and wet southwesterly flow brought by LLJ and the southward dry and cold air by NECV is favorable to the positive precipitation anomaly in the middle and lower reaches of the YRV.
2012, 38(5):608-614.
DOI: 10.7519/j.issn.1000-0526.2012.05.012
Abstract:
Based on the precipitation and temperature data at National Climate Centre 723 stations, the JRA25 and NCEP/NCAR I reanalysis data sets and the NOAA Climate Prediction Centre extended reconstructed SST data, using methods of linear trend, dynamical diagnosis, correlation analysis and wavelet analysis, the climate characteristics and variation features of seven great river valleys (SGRV) in July 2011 were researched, and the mechanism of precipitation anomalies of the Yangtze River Valley (YRV) during the dominant flood season was revealed. Results indicated that the precipitations of SGRV were overall less in July 2011, however, the precipitation of YRV was far less than normal; meanwhile, the temperatures of SGRV were characterized by continued climate warming, especially for Songhua River Valley. The linear trend of precipitation changing showed that Zhujiang River Valley and YRV were in a linearly increased trend, Huaihe River Valley maintained an unchanged condition, and Liaohe, Haihe, Huanghe and Songhua River Valleys where in a linearly decreased trend. In addition to the obvious interannual variability, the decadal changes of precipitation in YRV, Huaihe, Haihe and Huanghe River Valleys were also obvious. The main causes for the belownormal precipitation of YRV in July 2011 were as follows: The atmospheric responses to external forcing of equatorial MiddleEastern Pacific were the same as those to La Nina pattern; the subtropical high was abnormal and the East Asian southerly wind circulation intensity index (IES) was weak; besides, the water vapor budget had a deficit and the precipitation efficiency was low.
Based on the precipitation and temperature data at National Climate Centre 723 stations, the JRA25 and NCEP/NCAR I reanalysis data sets and the NOAA Climate Prediction Centre extended reconstructed SST data, using methods of linear trend, dynamical diagnosis, correlation analysis and wavelet analysis, the climate characteristics and variation features of seven great river valleys (SGRV) in July 2011 were researched, and the mechanism of precipitation anomalies of the Yangtze River Valley (YRV) during the dominant flood season was revealed. Results indicated that the precipitations of SGRV were overall less in July 2011, however, the precipitation of YRV was far less than normal; meanwhile, the temperatures of SGRV were characterized by continued climate warming, especially for Songhua River Valley. The linear trend of precipitation changing showed that Zhujiang River Valley and YRV were in a linearly increased trend, Huaihe River Valley maintained an unchanged condition, and Liaohe, Haihe, Huanghe and Songhua River Valleys where in a linearly decreased trend. In addition to the obvious interannual variability, the decadal changes of precipitation in YRV, Huaihe, Haihe and Huanghe River Valleys were also obvious. The main causes for the belownormal precipitation of YRV in July 2011 were as follows: The atmospheric responses to external forcing of equatorial MiddleEastern Pacific were the same as those to La Nina pattern; the subtropical high was abnormal and the East Asian southerly wind circulation intensity index (IES) was weak; besides, the water vapor budget had a deficit and the precipitation efficiency was low.
2012, 38(5):615-622.
DOI: 10.7519/j.issn.1000-0526.2012.05.013
Abstract:
Climate anomaly and atmospheric circulation features were analyzed over China in August 2011. Causation of drought in Southwest China (SWC) and less tropical cyclone (TC) activities over the western North Pacific and the South China Sea (SCS) were studied in this paper. Results showed that anomalous atmospheric circulation including positive 500 hPa geopotential height anomaly, the stronger West Pacific subtropical high (WPSH), weak summer monsoon, weak vapor transportation was the main reason for the SWC drought. Moreover, the SWC drought might be caused by the lag impact of 2010/2011 central Pacific La Nina event and warm mode of the Indian Ocean. In addition, less TC activities were due to the combined impacts of multifactors including weak convection over the SCS, abnormally northward monsoon trough east of Philippines, large vertical shear anomalies and the stronger WPSH.
Climate anomaly and atmospheric circulation features were analyzed over China in August 2011. Causation of drought in Southwest China (SWC) and less tropical cyclone (TC) activities over the western North Pacific and the South China Sea (SCS) were studied in this paper. Results showed that anomalous atmospheric circulation including positive 500 hPa geopotential height anomaly, the stronger West Pacific subtropical high (WPSH), weak summer monsoon, weak vapor transportation was the main reason for the SWC drought. Moreover, the SWC drought might be caused by the lag impact of 2010/2011 central Pacific La Nina event and warm mode of the Indian Ocean. In addition, less TC activities were due to the combined impacts of multifactors including weak convection over the SCS, abnormally northward monsoon trough east of Philippines, large vertical shear anomalies and the stronger WPSH.
2012, 38(5):623-628.
DOI: 10.7519/j.issn.1000-0526.2012.05.014
Abstract:
Based on the observation of webbulb, drybulb, blackglobe temperatures, and the simultaneous air temperature, wind speed and relative humidity records of the adjacent AWS of Guangzhou in September 2009 to March 2010, study is carried out of the features of Wet Bulb Globe Temperature (WBGT) index of Guangzhou and two kinds of forecasting equations-a daytime and nighttime forecasting method and an hourly forecasting method. Then the forecasting errors of the two kinds of methods together with the initial equation imported from Hongkong Observatory are analyzed, and results show that, the initial Hongkong equation has the biggest error, and the hourly forecasting method constructed based on the hourly fitting has the least error; The three methods all have less errors in nighttime than in daytime, and errors of both daytime and nighttime forecasting method and hourly forecasting method are less than 1℃. Compared with the daytime and nighttime forecasting method, the hourly forecasting method has the similar errors in nighttime and much less errors in daytime. Therefore, based on these, the hourly forecasting method is applied in the meteorological service of the equestrianism of Guangzhou 2010 Asian Games. In the end, the forecasting error of WBGT equation is discussed based on the forecast error of temperature and relative humidity.
Based on the observation of webbulb, drybulb, blackglobe temperatures, and the simultaneous air temperature, wind speed and relative humidity records of the adjacent AWS of Guangzhou in September 2009 to March 2010, study is carried out of the features of Wet Bulb Globe Temperature (WBGT) index of Guangzhou and two kinds of forecasting equations-a daytime and nighttime forecasting method and an hourly forecasting method. Then the forecasting errors of the two kinds of methods together with the initial equation imported from Hongkong Observatory are analyzed, and results show that, the initial Hongkong equation has the biggest error, and the hourly forecasting method constructed based on the hourly fitting has the least error; The three methods all have less errors in nighttime than in daytime, and errors of both daytime and nighttime forecasting method and hourly forecasting method are less than 1℃. Compared with the daytime and nighttime forecasting method, the hourly forecasting method has the similar errors in nighttime and much less errors in daytime. Therefore, based on these, the hourly forecasting method is applied in the meteorological service of the equestrianism of Guangzhou 2010 Asian Games. In the end, the forecasting error of WBGT equation is discussed based on the forecast error of temperature and relative humidity.
2012, 38(5):629-634.
DOI: 10.7519/j.issn.1000-0526.2012.05.015
Abstract:
The performance of T639, ECMWF and Japan models about their mediumrange forecasting during December 2011 to February 2012 was verified and compared. The results show that the three models all have good performance on predicting the largescale circulation evolution and adjustment over Asian middle and high latitude area and the temperature trends in the lower troposphere. ECMWF model is the best at forecasting westerly wind index and 850 hPa temperature. With respect to forecasting of trough in the Bay of Bengal, ECMWF model has the best performance, while the forecasts by T639 and Japan models are both weaker than their initial fields. The three models predict the weak surface high, and the errors of Japan model is the smallest while those of T639 and EC models are comparatively larger.
The performance of T639, ECMWF and Japan models about their mediumrange forecasting during December 2011 to February 2012 was verified and compared. The results show that the three models all have good performance on predicting the largescale circulation evolution and adjustment over Asian middle and high latitude area and the temperature trends in the lower troposphere. ECMWF model is the best at forecasting westerly wind index and 850 hPa temperature. With respect to forecasting of trough in the Bay of Bengal, ECMWF model has the best performance, while the forecasts by T639 and Japan models are both weaker than their initial fields. The three models predict the weak surface high, and the errors of Japan model is the smallest while those of T639 and EC models are comparatively larger.
2012, 38(5):635-640.
DOI: 10.7519/j.issn.1000-0526.2012.05.016
Abstract:
The characteristics of general circulation of atmosphere in February 2012 are as follows. There were two polar vortex centers in the Northern Hemisphere, which were located at the northeast of Canada and sea of Okhotsk, respectively. The latter has strengthened compared to the mean conditions. The circulation presented meridional patterns at the middle and high latitudes. There were active blocking anticyclones near the Ural Mountains persistently and their strength was higher than the normal. The average south branch trough was located at 90°E nearly, at the general average position, but stronger than the mean conditions. In February, the mean temperature is -3.2℃, warmer than that in January (-7.2℃), but colder than the same month of normal years (-2.0℃). The average precipitation all the country is 14.5 mm, less than that in January (16.8 mm), and less than the same month of normal years (17.6 mm). There were three cold air events affecting most of the country, and three precipitation processes in this month. There were extreme precipitation events happening at south of the Tibet. In Yunnan Province and southwest of Sichuan Province, the meteorological drought was developing. The cold, rainy (snowy), and less sunshine weathers were continuing in southern China.
The characteristics of general circulation of atmosphere in February 2012 are as follows. There were two polar vortex centers in the Northern Hemisphere, which were located at the northeast of Canada and sea of Okhotsk, respectively. The latter has strengthened compared to the mean conditions. The circulation presented meridional patterns at the middle and high latitudes. There were active blocking anticyclones near the Ural Mountains persistently and their strength was higher than the normal. The average south branch trough was located at 90°E nearly, at the general average position, but stronger than the mean conditions. In February, the mean temperature is -3.2℃, warmer than that in January (-7.2℃), but colder than the same month of normal years (-2.0℃). The average precipitation all the country is 14.5 mm, less than that in January (16.8 mm), and less than the same month of normal years (17.6 mm). There were three cold air events affecting most of the country, and three precipitation processes in this month. There were extreme precipitation events happening at south of the Tibet. In Yunnan Province and southwest of Sichuan Province, the meteorological drought was developing. The cold, rainy (snowy), and less sunshine weathers were continuing in southern China.
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ISSN:1000-0526 CN:11-2282/P