2015 Vol. 21, No. 1
2015, 21(1): 1-13.
Abstract:
Based on the data (including radius of maximum winds) from the JTWC (Joint Typhoon Warning Center), the tropical cyclones’(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the Black Body Temperature (TBB) of the Japanese geostationary meteorological satellite M1TR IR1, and combining 13 tropical cyclones which landed in China again after visiting the island of Taiwan during the period from 2001 to 2010, we analyzed the relationship between the number of convective cores within TC circulation and the intensity of TC with the method of convective-stratiform technique (CST) and statistical and composite analysis. The results are shown as follows. (1) The number of convective cores in the entire TC circulation is well corresponding with the outer spiral rainbands and the density of convective cores in the inner core area increases (decreases) generally with increasing (decreasing) TC intensity. At the same time, the number of convective cores within the outer spiral rainbands is more than that within the inner core and does not change much with the TC intensity. However, the density of convective cores within the outer spiral rainbands is lower than that within the inner core. (2) The relationship described above is sensitive to landing location to some extent but not sensitive to the structure of TC. (3) The average value of TBB in the inner core area increases (decreases) generally with increasing (decreasing) of TC intensity, which is also sensitive to landing situation to some extent. At the same time, the average value of TBB within the outer spiral rainbands is close to that within the entire TC circulation, and both of them are more than that within the inner core. However, they do not reflect TC intensity change significantly. (4) The results of statistical composite based on convective cores and TBB are complementary with each other, so a combination of both can reflect the relationship between TC rainbands and TC intensity much better.
Based on the data (including radius of maximum winds) from the JTWC (Joint Typhoon Warning Center), the tropical cyclones’(TCs) radii of the outermost closed isobar, TCs best tracks from Shanghai Typhoon Institute and the Black Body Temperature (TBB) of the Japanese geostationary meteorological satellite M1TR IR1, and combining 13 tropical cyclones which landed in China again after visiting the island of Taiwan during the period from 2001 to 2010, we analyzed the relationship between the number of convective cores within TC circulation and the intensity of TC with the method of convective-stratiform technique (CST) and statistical and composite analysis. The results are shown as follows. (1) The number of convective cores in the entire TC circulation is well corresponding with the outer spiral rainbands and the density of convective cores in the inner core area increases (decreases) generally with increasing (decreasing) TC intensity. At the same time, the number of convective cores within the outer spiral rainbands is more than that within the inner core and does not change much with the TC intensity. However, the density of convective cores within the outer spiral rainbands is lower than that within the inner core. (2) The relationship described above is sensitive to landing location to some extent but not sensitive to the structure of TC. (3) The average value of TBB in the inner core area increases (decreases) generally with increasing (decreasing) of TC intensity, which is also sensitive to landing situation to some extent. At the same time, the average value of TBB within the outer spiral rainbands is close to that within the entire TC circulation, and both of them are more than that within the inner core. However, they do not reflect TC intensity change significantly. (4) The results of statistical composite based on convective cores and TBB are complementary with each other, so a combination of both can reflect the relationship between TC rainbands and TC intensity much better.
2015, 21(1): 14-22.
Abstract:
During the developing phase of central Pacific El Niño (CPEN), more frequent TC genesis over the northwest quadrant of the western North Pacific (WNP) is attributed to the horizontal shift of environmental vorticity field. Such a northwestward shift resembles the La Niña composite, even though factors that cause the shift differ (in the La Niña case the relative humidity effect is crucial). Greater reduction of TC frequency over WNP happened during the decaying phase of eastern Pacific El Niño (EPEN) than CPEN, due to the difference of the anomalous Philippine Sea anticyclone strength. The TC genesis exhibits an upward (downward) trend over the northern (southern) part of the WNP, which is linked to SST and associated circulation changes through local and remote effects.
During the developing phase of central Pacific El Niño (CPEN), more frequent TC genesis over the northwest quadrant of the western North Pacific (WNP) is attributed to the horizontal shift of environmental vorticity field. Such a northwestward shift resembles the La Niña composite, even though factors that cause the shift differ (in the La Niña case the relative humidity effect is crucial). Greater reduction of TC frequency over WNP happened during the decaying phase of eastern Pacific El Niño (EPEN) than CPEN, due to the difference of the anomalous Philippine Sea anticyclone strength. The TC genesis exhibits an upward (downward) trend over the northern (southern) part of the WNP, which is linked to SST and associated circulation changes through local and remote effects.
2015, 21(1): 23-33.
Abstract:
Based on the Tropical Cyclone (TC) Yearbooks data and JRA-25 reanalysis data from the Japan Meteorological Agency (JMA) during 1979-2008, dynamic composite analysis and computation of kinetic energy budget are used to study the intensifying and weakening TCs during Extratropical Transition over China. The TCI shows strong upper-level divergence, strengthened low-level convergence and significantly enhanced upward motion under the influence of strong upper-level troughs and high-level jets. The TCI is correspondingly intensified after Extratropical Transition (ET); TCW exhibits strong upper-level divergence, subdued low-level convergence and slightly enhanced upward motion under the influence of weak upper-level troughs and high-level jets. It then weakens after ET. The increase (decrease) of the generation of kinetic energy by divergence wind in TCI (TCW) at low level is one of the major reasons for TCI's intensification (TCW's weakening) after transformation. The generation of kinetic energy by divergence wind is closely related to the development of a low-level baroclinic frontal zone. The growth of the generation of kinetic energy by rotational wind in TCI at upper level is favorable for TCI's maintenance, which is affected by strong upper-level troughs. The dissipation of the generation of kinetic energy by rotational wind in TCW at upper level is unfavorable for TCW's maintenance, which is affected by weak upper-level troughs.
Based on the Tropical Cyclone (TC) Yearbooks data and JRA-25 reanalysis data from the Japan Meteorological Agency (JMA) during 1979-2008, dynamic composite analysis and computation of kinetic energy budget are used to study the intensifying and weakening TCs during Extratropical Transition over China. The TCI shows strong upper-level divergence, strengthened low-level convergence and significantly enhanced upward motion under the influence of strong upper-level troughs and high-level jets. The TCI is correspondingly intensified after Extratropical Transition (ET); TCW exhibits strong upper-level divergence, subdued low-level convergence and slightly enhanced upward motion under the influence of weak upper-level troughs and high-level jets. It then weakens after ET. The increase (decrease) of the generation of kinetic energy by divergence wind in TCI (TCW) at low level is one of the major reasons for TCI's intensification (TCW's weakening) after transformation. The generation of kinetic energy by divergence wind is closely related to the development of a low-level baroclinic frontal zone. The growth of the generation of kinetic energy by rotational wind in TCI at upper level is favorable for TCI's maintenance, which is affected by strong upper-level troughs. The dissipation of the generation of kinetic energy by rotational wind in TCW at upper level is unfavorable for TCW's maintenance, which is affected by weak upper-level troughs.
2015, 21(1): 34-42.
Abstract:
In this paper, we first analyzed cloud drift wind (CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, conducted contrast numerical experiments of assimilating the CDW data before and after reassignment to examine the impacts on the forecast of the track of Typhoon Chanthu (1003) from 00:00 (Coordinated Universal Time) 21 July to 00:00 UTC 23 July, 2010. The analysis results of the CDW data indicate that the number of CDWs is mainly distributed in the mid- and upper-troposphere above 500 hPa, with the maximum number at about 300 hPa. The height reassigning method mentioned in this work may update the height effectively, and the CDW data are distributed reasonably and no obvious contradiction occurs in the horizontal direction after height reassignment. After assimilating the height-reassigned CDW data, especially the water vapor CDW data, the initial wind field around Typhoon Chanthu (1003) became more reasonable, and then the steering current leading the typhoon to move to the correct location became stronger. As a result, the numerical track predictions are improved.
In this paper, we first analyzed cloud drift wind (CDW) data distribution in the vertical direction, and then reassigned the height of every CDW in the research domain in terms of background information, and finally, conducted contrast numerical experiments of assimilating the CDW data before and after reassignment to examine the impacts on the forecast of the track of Typhoon Chanthu (1003) from 00:00 (Coordinated Universal Time) 21 July to 00:00 UTC 23 July, 2010. The analysis results of the CDW data indicate that the number of CDWs is mainly distributed in the mid- and upper-troposphere above 500 hPa, with the maximum number at about 300 hPa. The height reassigning method mentioned in this work may update the height effectively, and the CDW data are distributed reasonably and no obvious contradiction occurs in the horizontal direction after height reassignment. After assimilating the height-reassigned CDW data, especially the water vapor CDW data, the initial wind field around Typhoon Chanthu (1003) became more reasonable, and then the steering current leading the typhoon to move to the correct location became stronger. As a result, the numerical track predictions are improved.
2015, 21(1): 43-54.
Abstract:
This paper attempts to reveal a long-distance-relayed water vapor transport (LRWVT) east of Tibetan Plateau and its impacts. The results show that from August to October, east of Tibetan Plateau, there exists a unique LRWVT, and the water vapor from the South China Sea and the western Pacific can affect the Sichuan Basin, Northwest China and other Chinese regions far from the tropical sea through this way. From August to October, the precipitation of the region east of the Plateau is closely linked both in the intra-annual and inter-annual variations, and the LRWVT from the South China Sea and the western Pacific is an important connection mechanism. The large-scale circulation background of the LRWVT impacting the precipitation of the region east of the Plateau is as follows: At high levels, the South Asian High is generally stronger than normal and significantly enhances with its northward advance and eastward extension over the region east of the Plateau. At mid-level, a broad low pressure trough is over Lake Balkhash and its surroundings, and the Western Pacific Subtropical High (WPSH) is northward and westward located, and the western part of Sichuan Basin and the eastern part of Northwest China are located in the west and northwest edge of WPSH.
This paper attempts to reveal a long-distance-relayed water vapor transport (LRWVT) east of Tibetan Plateau and its impacts. The results show that from August to October, east of Tibetan Plateau, there exists a unique LRWVT, and the water vapor from the South China Sea and the western Pacific can affect the Sichuan Basin, Northwest China and other Chinese regions far from the tropical sea through this way. From August to October, the precipitation of the region east of the Plateau is closely linked both in the intra-annual and inter-annual variations, and the LRWVT from the South China Sea and the western Pacific is an important connection mechanism. The large-scale circulation background of the LRWVT impacting the precipitation of the region east of the Plateau is as follows: At high levels, the South Asian High is generally stronger than normal and significantly enhances with its northward advance and eastward extension over the region east of the Plateau. At mid-level, a broad low pressure trough is over Lake Balkhash and its surroundings, and the Western Pacific Subtropical High (WPSH) is northward and westward located, and the western part of Sichuan Basin and the eastern part of Northwest China are located in the west and northwest edge of WPSH.
2015, 21(1): 55-66.
Abstract:
Based on the daily precipitation and temperature data of 97 stations in Southwest China (SW China) from 1960 to 2009, a dry-wet index is calculated. The spatiotemporal variation characteristics of dry-wet conditions, precipitation and temperature are studied. Then the abnormal atmospheric circulation characteristics are discussed using reanalysis data. The results show that SW China has exhibited an overall trend of autumnal drought since the late 1980s, and this drought trend became more significant early in the 2000s, especially in the eastern SW China. Autumnal dry-wet variation in southwestern China showed two major modes: consistent change across the entire region and opposing changes in the eastern and western regions. The spatial distribution of dry-wet anomalies was more significantly affected by precipitation, while temporal variation in dry-wet conditions was more strongly influenced by temperature. The former mode is affected by the anomalies of the precedent SST near the Western Pacific Warm Pool, the Western Pacific Subtropical High, the East Asian Trough and the South Trough. The latter mode is related to the wind anomalies in the eastern SW China and the vertical movement in the western and eastern SW China. These are the main influencing factors for the autumn dry-wet variation in SW China, which are of great significance to the prediction of drought.
Based on the daily precipitation and temperature data of 97 stations in Southwest China (SW China) from 1960 to 2009, a dry-wet index is calculated. The spatiotemporal variation characteristics of dry-wet conditions, precipitation and temperature are studied. Then the abnormal atmospheric circulation characteristics are discussed using reanalysis data. The results show that SW China has exhibited an overall trend of autumnal drought since the late 1980s, and this drought trend became more significant early in the 2000s, especially in the eastern SW China. Autumnal dry-wet variation in southwestern China showed two major modes: consistent change across the entire region and opposing changes in the eastern and western regions. The spatial distribution of dry-wet anomalies was more significantly affected by precipitation, while temporal variation in dry-wet conditions was more strongly influenced by temperature. The former mode is affected by the anomalies of the precedent SST near the Western Pacific Warm Pool, the Western Pacific Subtropical High, the East Asian Trough and the South Trough. The latter mode is related to the wind anomalies in the eastern SW China and the vertical movement in the western and eastern SW China. These are the main influencing factors for the autumn dry-wet variation in SW China, which are of great significance to the prediction of drought.
2015, 21(1)
Abstract:
Based on the daily mean temperature and 24-h accumulated total precipitation over central and southern China, the features and the possible causes of the extreme weather events with low temperature and icing conditions, which occurred in the southern part of China during early 2008, are investigated in this study. In addition, multimodel consensus forecasting experiments are conducted by using the ensemble forecasts of ECMWF, JMA, NCEP and CMA taken from the TIGGE archives. Results show that more than a third of the stations in the southern part of China were covered by the extremely abundant precipitation with a 50-a return period, and extremely low temperature with a 50-a return period occurred in the Guizhou and western Hunan province as well. For the 24- to 216-h surface temperature forecasts, the bias-removed multimodel ensemble mean with running training period (R-BREM) has the highest forecast skill of all individual models and multimodel consensus techniques. Taking the RMSEs of the ECMWF 96-h forecasts as the criterion, the forecast time of the surface temperature may be prolonged to 192 h over the southeastern coast of China by using the R-BREM technique. For the sprinkle forecasts over central and southern China, the R-BREM technique has the best performance in terms of threat scores (TS) for the 24- to 192-h forecasts except for the 72-h forecasts among all individual models and multimodel consensus techniques. For the moderate rain, the forecast skill of the R-BREM technique is superior to those of individual models and multimodel ensemble mean.
Based on the daily mean temperature and 24-h accumulated total precipitation over central and southern China, the features and the possible causes of the extreme weather events with low temperature and icing conditions, which occurred in the southern part of China during early 2008, are investigated in this study. In addition, multimodel consensus forecasting experiments are conducted by using the ensemble forecasts of ECMWF, JMA, NCEP and CMA taken from the TIGGE archives. Results show that more than a third of the stations in the southern part of China were covered by the extremely abundant precipitation with a 50-a return period, and extremely low temperature with a 50-a return period occurred in the Guizhou and western Hunan province as well. For the 24- to 216-h surface temperature forecasts, the bias-removed multimodel ensemble mean with running training period (R-BREM) has the highest forecast skill of all individual models and multimodel consensus techniques. Taking the RMSEs of the ECMWF 96-h forecasts as the criterion, the forecast time of the surface temperature may be prolonged to 192 h over the southeastern coast of China by using the R-BREM technique. For the sprinkle forecasts over central and southern China, the R-BREM technique has the best performance in terms of threat scores (TS) for the 24- to 192-h forecasts except for the 72-h forecasts among all individual models and multimodel consensus techniques. For the moderate rain, the forecast skill of the R-BREM technique is superior to those of individual models and multimodel ensemble mean.
2015, 21(1): 76-83.
Abstract:
Variations in Guangzhou’s aerosol optical characteristics and their possible causes are studied against the large-scale background of South China Sea summer monsoons (SCSSM) using aerosol data derived from Panyu Atmospheric Composition Watch Station in Guangzhou and the National Centers for Environmental Prediction/National Center for Atmospheric Research (USA). The data is reanalyzed to develop a composite analysis and perform physical diagnoses. Analysis of the results shows that aerosol extinction in Guangzhou first increases then decreases during the active period of a SCSSM, with variations in the stratification of the planetary boundary layer (PBL) and environmental winds playing important roles in affecting Guangzhou’s aerosol optical characteristics. Regional diabatic heating and anomalous cyclonic circulations excited by monsoon convection induce environmental wind anomalies that significantly modify the stratification of the PBL.
Variations in Guangzhou’s aerosol optical characteristics and their possible causes are studied against the large-scale background of South China Sea summer monsoons (SCSSM) using aerosol data derived from Panyu Atmospheric Composition Watch Station in Guangzhou and the National Centers for Environmental Prediction/National Center for Atmospheric Research (USA). The data is reanalyzed to develop a composite analysis and perform physical diagnoses. Analysis of the results shows that aerosol extinction in Guangzhou first increases then decreases during the active period of a SCSSM, with variations in the stratification of the planetary boundary layer (PBL) and environmental winds playing important roles in affecting Guangzhou’s aerosol optical characteristics. Regional diabatic heating and anomalous cyclonic circulations excited by monsoon convection induce environmental wind anomalies that significantly modify the stratification of the PBL.
2015, 21(1): 84-91.
Abstract:
The purpose of this study is to select a suitable sea wind retrieval method for FY-3B (MWRI). Based on the traditional empirical model of retrieving sea surface wind speed, and in the case of small sample size of FY-3B satellite load regression analysis, this paper analyzes the channel differences between the FY-3B satellite microwave radiation imager (MWRI) and TMI onboard the TRMM. The paper also analyzes the influence of these differences on the channel in terms of receiving temperature, including channel frequency, sensitivity and scaling precision. Then, the limited range of new model coefficient regression analysis is determined (in which the channel range settings include the information and features of channel differences), the regression methods of the finite field are proposed, and the empirical model of wind speed retrieval applicable to MWRI is obtained, which achieves robust results. Compared to the TAO buoy data, the mean deviation of the new model is 0.4 m/s, and the standard deviation is 1.2 m/s. In addition, the schematic diagram of the tropical sea surface wind speed retrieval is provided.
The purpose of this study is to select a suitable sea wind retrieval method for FY-3B (MWRI). Based on the traditional empirical model of retrieving sea surface wind speed, and in the case of small sample size of FY-3B satellite load regression analysis, this paper analyzes the channel differences between the FY-3B satellite microwave radiation imager (MWRI) and TMI onboard the TRMM. The paper also analyzes the influence of these differences on the channel in terms of receiving temperature, including channel frequency, sensitivity and scaling precision. Then, the limited range of new model coefficient regression analysis is determined (in which the channel range settings include the information and features of channel differences), the regression methods of the finite field are proposed, and the empirical model of wind speed retrieval applicable to MWRI is obtained, which achieves robust results. Compared to the TAO buoy data, the mean deviation of the new model is 0.4 m/s, and the standard deviation is 1.2 m/s. In addition, the schematic diagram of the tropical sea surface wind speed retrieval is provided.
2015, 21(1): 92-100.
Abstract:
An optimization method is based to design a snowfall estimate method by radar for operational snow warning, and error estimation is analyzed through a case of heavy snow on March 4, 2007. Three modified schemes are developed for errors caused by temperature changes, snowflake terminal velocity, the distance from the radar and calculation methods. Due to the improvements, the correlation coefficient between the estimated snowfall and the observation is 0.66 (exceeding the 99% confidence level), the average relative error is reduced to 48.74%, and the method is able to estimate weak snowfall of 0.3 mm/h and heavy snowfall above 5 mm/h. The correlation coefficient is 0.82 between the estimated snowfall from the stations 50 to 100 km from the radar and the observation. The improved effect is weak when the influence of the snowflake terminal velocity is considered in those three improvement programs, which may be related to the uniform echo. The radar estimate of snow, which is classified by the distance between the sample and the radar, has the most obvious effect: it can not only increase the degree of similarity, but also reduce the overestimate and the undervaluation of the error caused by the distance between the sample and the radar. The improved algorithm further improves the accuracy of the estimate. The average relative errors are 31% and 27% for the heavy snowfall of 1.6 to 2.5 mm/h and above 2.6 mm/h, respectively, but the radar overestimates the snowfall under 1.5 mm/h and underestimates the snowfall above 2.6 mm/h. Radar echo may not be sensitive to the intensity of snowfall, and the consistency shown by the error can be exploited to revise and improve the estimation accuracy of snow forecast in the operational work.
An optimization method is based to design a snowfall estimate method by radar for operational snow warning, and error estimation is analyzed through a case of heavy snow on March 4, 2007. Three modified schemes are developed for errors caused by temperature changes, snowflake terminal velocity, the distance from the radar and calculation methods. Due to the improvements, the correlation coefficient between the estimated snowfall and the observation is 0.66 (exceeding the 99% confidence level), the average relative error is reduced to 48.74%, and the method is able to estimate weak snowfall of 0.3 mm/h and heavy snowfall above 5 mm/h. The correlation coefficient is 0.82 between the estimated snowfall from the stations 50 to 100 km from the radar and the observation. The improved effect is weak when the influence of the snowflake terminal velocity is considered in those three improvement programs, which may be related to the uniform echo. The radar estimate of snow, which is classified by the distance between the sample and the radar, has the most obvious effect: it can not only increase the degree of similarity, but also reduce the overestimate and the undervaluation of the error caused by the distance between the sample and the radar. The improved algorithm further improves the accuracy of the estimate. The average relative errors are 31% and 27% for the heavy snowfall of 1.6 to 2.5 mm/h and above 2.6 mm/h, respectively, but the radar overestimates the snowfall under 1.5 mm/h and underestimates the snowfall above 2.6 mm/h. Radar echo may not be sensitive to the intensity of snowfall, and the consistency shown by the error can be exploited to revise and improve the estimation accuracy of snow forecast in the operational work.
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