ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 48,Issue 12,2022 Table of Contents
2022, 48(12):1497-1511.
DOI: 10.7519/j.issn.1000-0526.2022.072701
Abstract:
Targeting the severe torrential rain process in Henan Province on 20 July 2021, this paper focuses on revealing the features of the water vapor transport, the budget of water vapor flux and the transformation of water vapor as well as the associated impact on the variation of local precipitation based on FNL reanalysis data, gauge precipitation data and high-resolution simulation results. The results show that the water vapor over the ocean was continuously transported to the severe precipitation area by the water vapor channel built by the synergistic effect between the powerful and quasi-stationary Typhoon In-Fa over the East Sea and the stable atmospheric circulation pattern in the middle and high latitude zone. Then the local water vapor constrained within the extreme precipitation area was further transported from the low level to the middle and high level depending on the dynamical convergence mechanism in the low-level troposphere, which was dominated by the mesoscale synoptic system and the blocking effect of the windward slope. The vertical transport of the water vapor was indeed favorable for the reinforcement of the convection in the extreme precipitation area. Finally, under the synergistic effect of the convective ascending motion and the orographic lifting mechanism of the windward slope, more water vapor was vertically transported to the middle and higher troposphere by the reinforced vertical airflow, which stimulated the desublimation process between the water vapor and the ice-phase particles, resulting in the remarkable increase of the precipitation efficiency. The remarkable increase of the precipitation efficiency within the windward slope region was directly responsible for the occurrence of the severe torrential rain in the perspective of microphysical processes. This paper not only comprehensively reveals the main source and the consumption process of the local water vapor dominated by the muti-scale synoptic system in the extreme precipitation event, but also advances the understanding to the occurrence mechanism of the extreme precipitation.
Targeting the severe torrential rain process in Henan Province on 20 July 2021, this paper focuses on revealing the features of the water vapor transport, the budget of water vapor flux and the transformation of water vapor as well as the associated impact on the variation of local precipitation based on FNL reanalysis data, gauge precipitation data and high-resolution simulation results. The results show that the water vapor over the ocean was continuously transported to the severe precipitation area by the water vapor channel built by the synergistic effect between the powerful and quasi-stationary Typhoon In-Fa over the East Sea and the stable atmospheric circulation pattern in the middle and high latitude zone. Then the local water vapor constrained within the extreme precipitation area was further transported from the low level to the middle and high level depending on the dynamical convergence mechanism in the low-level troposphere, which was dominated by the mesoscale synoptic system and the blocking effect of the windward slope. The vertical transport of the water vapor was indeed favorable for the reinforcement of the convection in the extreme precipitation area. Finally, under the synergistic effect of the convective ascending motion and the orographic lifting mechanism of the windward slope, more water vapor was vertically transported to the middle and higher troposphere by the reinforced vertical airflow, which stimulated the desublimation process between the water vapor and the ice-phase particles, resulting in the remarkable increase of the precipitation efficiency. The remarkable increase of the precipitation efficiency within the windward slope region was directly responsible for the occurrence of the severe torrential rain in the perspective of microphysical processes. This paper not only comprehensively reveals the main source and the consumption process of the local water vapor dominated by the muti-scale synoptic system in the extreme precipitation event, but also advances the understanding to the occurrence mechanism of the extreme precipitation.
2022, 48(12):1512-1524.
DOI: 10.7519/j.issn.1000-0526.2022.101001
Abstract:
Based on surface conventional meteorological data, hourly observation data from regional meteorological stations and ERA5 reanalysis data, the evolution characteristics and formation mechanism of mesoscale low-level jet and mesoscale vortex during the severe torrential rain process in Henan Province from 19 to 20 July 2021 are analyzed. The results show that the process of this extreme precipitation was directly related to the formation and development of the low-level jet and mesoscale vortex. The establishment and development of low-level jet was synchronized with the occurrence and enhancement of precipitation, while the mesoscale vortex appeared about 10 hours later than the establishment of low-level jet, and the low-level jet developed strongly with the enhancement of low-level vortex development. The strengthening and westward extension of the western Pacific subtropical high and eastward movement of the low pressure on the southeast of the Hetao Area increased the geostrophic wind, which was the main reason for the formation of the low-level jet. The existence of allobaric wind was the main reason for the easterly jet. The horizontal convergence and torsion in the lower troposphere caused by low-level jet were the main reasons for the development of mesoscale vortex in the middle and lower troposphere. The vertical vorticity advection caused by the vertical motion was the main reason for the enhancement of the voriticy in the middle troposphere. The condensation latent heat in the middle troposphere was another important reason for the vortex development.
Based on surface conventional meteorological data, hourly observation data from regional meteorological stations and ERA5 reanalysis data, the evolution characteristics and formation mechanism of mesoscale low-level jet and mesoscale vortex during the severe torrential rain process in Henan Province from 19 to 20 July 2021 are analyzed. The results show that the process of this extreme precipitation was directly related to the formation and development of the low-level jet and mesoscale vortex. The establishment and development of low-level jet was synchronized with the occurrence and enhancement of precipitation, while the mesoscale vortex appeared about 10 hours later than the establishment of low-level jet, and the low-level jet developed strongly with the enhancement of low-level vortex development. The strengthening and westward extension of the western Pacific subtropical high and eastward movement of the low pressure on the southeast of the Hetao Area increased the geostrophic wind, which was the main reason for the formation of the low-level jet. The existence of allobaric wind was the main reason for the easterly jet. The horizontal convergence and torsion in the lower troposphere caused by low-level jet were the main reasons for the development of mesoscale vortex in the middle and lower troposphere. The vertical vorticity advection caused by the vertical motion was the main reason for the enhancement of the voriticy in the middle troposphere. The condensation latent heat in the middle troposphere was another important reason for the vortex development.
2022, 48(12):1525-1538.
DOI: 10.7519/j.issn.1000-0526.2022.081501
Abstract:
In order to improve the precipitation forecasting skill of CMA-MESO (China Meteorological Administration Mesoscale Model) at 3 km resolution, three different horizontal correlation characteristic scales of background error covariance are obtained with 2-D discrete cosine transform filter from three months’ (2 June to 31 August 2018) background error samples. The three horizontal co-correlation scales are fitted and implemented in CMA-MESO operational testing system with recursive filter of three different scales, so as to replace the single-scaled recursive filtering. The results show that the profiles of three horizontal co-correlation scales with height are similar, with tens to hundreds km apart. The analysis qualities and verification of precipitation forecasting between the control experiments (single-scaled recursive filterings) and sensitivity experiments (three different scaled recursive filterings) with CMA-MESO system at 3 km resolution are compared. The numerical results indicate that the wind and relative humidity analyses are more close to observation in sensitivity experiments. The increment difference of temperature analysis is very small. In addition, the precipitation forecast skill is improved in sensitivity experiments. The first 6 h precipitation forecast TS value over 1-31 July 2018 with cold start is higher and the bias value is more close to 1 in sensitivity experiments. Meanwhile, the TS value of every 6 h precipitation in 24 h forecasting term with warm start is improved too.
In order to improve the precipitation forecasting skill of CMA-MESO (China Meteorological Administration Mesoscale Model) at 3 km resolution, three different horizontal correlation characteristic scales of background error covariance are obtained with 2-D discrete cosine transform filter from three months’ (2 June to 31 August 2018) background error samples. The three horizontal co-correlation scales are fitted and implemented in CMA-MESO operational testing system with recursive filter of three different scales, so as to replace the single-scaled recursive filtering. The results show that the profiles of three horizontal co-correlation scales with height are similar, with tens to hundreds km apart. The analysis qualities and verification of precipitation forecasting between the control experiments (single-scaled recursive filterings) and sensitivity experiments (three different scaled recursive filterings) with CMA-MESO system at 3 km resolution are compared. The numerical results indicate that the wind and relative humidity analyses are more close to observation in sensitivity experiments. The increment difference of temperature analysis is very small. In addition, the precipitation forecast skill is improved in sensitivity experiments. The first 6 h precipitation forecast TS value over 1-31 July 2018 with cold start is higher and the bias value is more close to 1 in sensitivity experiments. Meanwhile, the TS value of every 6 h precipitation in 24 h forecasting term with warm start is improved too.
2022, 48(12):1539-1549.
DOI: 10.7519/j.issn.1000-0526.2022.082201
Abstract:
The multi-model integration test of the Bayesian model averaging (BMA) method is carried out for the forecast after correcting the errors of 2 m temperature, 10 m wind speed, and 2 m relative humidity from 1 December 2020 to 15 March 2021 in the Beijing-Tianjin-Hebei Region based on the four models （CMA-GFS, CMA-REPS, CMA-MESO 〖KG-*5〗3 km, and CMA-MESO 〖KG-*5〗1 km）. The results show that the root-mean-square error of each model’s element is significantly reduced after error calibration. The prediction effect of the BMA multi-model blending is much better than that of calibrated output of every participant model. Compared with the original errors of several models, the improvement of the 2 m temperature integration forecast is between 0.5-1.4℃, and the improvement rate of the root-mean-square error is about 20%-40%. In the meantime, the root-mean-square error of 10 m wind speed and 2 m relative humidity improved by 12%-45% and 25%-35%, respectively. The horizontal root mean square error distribution of each element is significantly different at different terrain heights, and the error distribution of different elements has been significantly reduced throughout the region. In addition, BMA can obtain the full probability density function, which can quantitatively predict the uncertainty of each element.
The multi-model integration test of the Bayesian model averaging (BMA) method is carried out for the forecast after correcting the errors of 2 m temperature, 10 m wind speed, and 2 m relative humidity from 1 December 2020 to 15 March 2021 in the Beijing-Tianjin-Hebei Region based on the four models （CMA-GFS, CMA-REPS, CMA-MESO 〖KG-*5〗3 km, and CMA-MESO 〖KG-*5〗1 km）. The results show that the root-mean-square error of each model’s element is significantly reduced after error calibration. The prediction effect of the BMA multi-model blending is much better than that of calibrated output of every participant model. Compared with the original errors of several models, the improvement of the 2 m temperature integration forecast is between 0.5-1.4℃, and the improvement rate of the root-mean-square error is about 20%-40%. In the meantime, the root-mean-square error of 10 m wind speed and 2 m relative humidity improved by 12%-45% and 25%-35%, respectively. The horizontal root mean square error distribution of each element is significantly different at different terrain heights, and the error distribution of different elements has been significantly reduced throughout the region. In addition, BMA can obtain the full probability density function, which can quantitatively predict the uncertainty of each element.
2022, 48(12):1550-1564.
DOI: 10.7519/j.issn.10000526.2022.033101
Abstract:
A comparison of two rainstorms that ocurred in June 2001 and July 1986 (hereafter “01·6” and “86·7”) related to distant typhoons affecting Jiangsu 〖JP2〗Province during Meiyu period shows that for “01·6”,〖JP〗 the precipitation duration is shorter, the precipitation area is not changed, and the rainfall intensity is stronger, while for “86·7”, the precipitation duration is longer, the precipitation area moves from north to south, and the rainfall intensity is weaker. In terms of atmospheric circulations, during the “01·6” process, the subtropical high extends significantly to the north, the northward extending inverted trough of typhoon and the lowlevel jet jointly form the lowlevel convergence and transport the warm and moist air together, the lowpressure troughs at middle and upperlevel are stable, and the influence of upperlevel cold air is weaker. Comparatively during the “86·7” process, the northward extension and impact of typhoon’s inverted trough are weaker， the convergence of lowlevel wind and the transportation of warm and humid air flow rely more on lowlevel jet than on the inverted trough of typhoon, the lowpressure troughs at middle and upper level both move eastward and southward quickly, and the influence of upperlevel cold air is strong. In terms of dynamical analysis, the highlevel divergence and lowlevel convergence of the “01·6” process are more intense, the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep, the nongeostrophic wet 〖WTHX〗Q〖WT5BZ〗 vector convergence is stronger, and all these dynamic processes stay over the southeastern part of Jiangsu. However, for “86·7”, the dynamic processes are weaker, the coupling of divergence and vertical vorticity move from northcentral Jiangsu to the southeastern part of Jiangsu, and the nongeostrophic 〖WTHX〗Q〖WT5BZ〗 vector convergence zone covers eastern part of Jiangsu. Compared with “86·7”, the lowlevel water vapor flux convergence of “01·6” is stronger, the air over the rainstorm area of “01·6” is more saturated, and the deep saturated layer “01·6” is formed earlier and maintain longer. In terms of thermodynamical analysis, the convective instability of middle and lowerlevel atmosphere is stronger, but the E index and its increment of “01·6” are greater, which demonstrates that the middle 〖JP2〗and lowlevel atmosphere contains more energy and more water vapor.
A comparison of two rainstorms that ocurred in June 2001 and July 1986 (hereafter “01·6” and “86·7”) related to distant typhoons affecting Jiangsu 〖JP2〗Province during Meiyu period shows that for “01·6”,〖JP〗 the precipitation duration is shorter, the precipitation area is not changed, and the rainfall intensity is stronger, while for “86·7”, the precipitation duration is longer, the precipitation area moves from north to south, and the rainfall intensity is weaker. In terms of atmospheric circulations, during the “01·6” process, the subtropical high extends significantly to the north, the northward extending inverted trough of typhoon and the lowlevel jet jointly form the lowlevel convergence and transport the warm and moist air together, the lowpressure troughs at middle and upperlevel are stable, and the influence of upperlevel cold air is weaker. Comparatively during the “86·7” process, the northward extension and impact of typhoon’s inverted trough are weaker， the convergence of lowlevel wind and the transportation of warm and humid air flow rely more on lowlevel jet than on the inverted trough of typhoon, the lowpressure troughs at middle and upper level both move eastward and southward quickly, and the influence of upperlevel cold air is strong. In terms of dynamical analysis, the highlevel divergence and lowlevel convergence of the “01·6” process are more intense, the coupling of positive vorticity at lower level and negative vorticity at upper level is more stable and deep, the nongeostrophic wet 〖WTHX〗Q〖WT5BZ〗 vector convergence is stronger, and all these dynamic processes stay over the southeastern part of Jiangsu. However, for “86·7”, the dynamic processes are weaker, the coupling of divergence and vertical vorticity move from northcentral Jiangsu to the southeastern part of Jiangsu, and the nongeostrophic 〖WTHX〗Q〖WT5BZ〗 vector convergence zone covers eastern part of Jiangsu. Compared with “86·7”, the lowlevel water vapor flux convergence of “01·6” is stronger, the air over the rainstorm area of “01·6” is more saturated, and the deep saturated layer “01·6” is formed earlier and maintain longer. In terms of thermodynamical analysis, the convective instability of middle and lowerlevel atmosphere is stronger, but the E index and its increment of “01·6” are greater, which demonstrates that the middle 〖JP2〗and lowlevel atmosphere contains more energy and more water vapor.
2022, 48(12):1565-1576.
DOI: 10.7519/j.issn.1000-0526.2022.072101
Abstract:
Since the 21st Century, Fujian Province has witnessed several severe or relatively severe drought events. Especially in recent years, drought has still been an important part of disaster prevention and mitigation in Fujian Province. According to the daily meteorological comprehensive index (MCI) of 66 national meteorological stations in Fujian from January 1961 to December 2020, the drought processes of the regional and 66 meteorological stations in Fujian are identified by referring to the local algorithm and the “Regional Drought Process Monitoring and Evaluation Method”. Besides, the Copula function is used to reveal the characteristics of drought process change and return period in Fujian. The results show that the variation trend of drought duration and intensity in Fujian is basically consistent. The drought processes are mainly single-season drought and two-season consecutive drought. The two-season consecutive drought mainly covers summer and autumn and the three-season conscutive drought only occurred from summer to winter. There are 1-3-year recurrence periods for most drought processes, and fewer return periods for severe drought processes. The worst droughts with a return period of more than 50 years were the summer-autumn-winter droughts in 1967 and 2003. The droughts with short return periods have long durations and strong intensities along the central and southern coastal areas, becoming gradually shortened and weakened northward. The central and southern coastal areas are still the areas suffering from the droughts with longer durations and stronger intensity, but the inland mountainous areas in the north of the province once had droughts with long duration and strong intensity simultaneously. In the past 60 years, there were 9 years with no drought, 18 years with the drought recurrence period reaching more than 100 years in some regions, and other 33 years with the drought return period not exceeding 50 years.
Since the 21st Century, Fujian Province has witnessed several severe or relatively severe drought events. Especially in recent years, drought has still been an important part of disaster prevention and mitigation in Fujian Province. According to the daily meteorological comprehensive index (MCI) of 66 national meteorological stations in Fujian from January 1961 to December 2020, the drought processes of the regional and 66 meteorological stations in Fujian are identified by referring to the local algorithm and the “Regional Drought Process Monitoring and Evaluation Method”. Besides, the Copula function is used to reveal the characteristics of drought process change and return period in Fujian. The results show that the variation trend of drought duration and intensity in Fujian is basically consistent. The drought processes are mainly single-season drought and two-season consecutive drought. The two-season consecutive drought mainly covers summer and autumn and the three-season conscutive drought only occurred from summer to winter. There are 1-3-year recurrence periods for most drought processes, and fewer return periods for severe drought processes. The worst droughts with a return period of more than 50 years were the summer-autumn-winter droughts in 1967 and 2003. The droughts with short return periods have long durations and strong intensities along the central and southern coastal areas, becoming gradually shortened and weakened northward. The central and southern coastal areas are still the areas suffering from the droughts with longer durations and stronger intensity, but the inland mountainous areas in the north of the province once had droughts with long duration and strong intensity simultaneously. In the past 60 years, there were 9 years with no drought, 18 years with the drought recurrence period reaching more than 100 years in some regions, and other 33 years with the drought return period not exceeding 50 years.
2022, 48(12):1577-1589.
DOI: 10.7519/j.issn.1000-0526.2022.081101
Abstract:
Based on rainfall observation and EAR5 reanalysis data, 19 cases of extreme rainstorms induced by southwest vortex and seen in Sichuan Basin from 1981 to 〖JP2〗2020 are statistically analyzed, and the dynamic〖JP〗 synthesis analysis on the circulation background and the structural characteristics of the southwest vortex are carried out. The results show that the life time of the southwest vortex lasts for 48-132 h, and the extreme rainstorm generally breaks out within 18 hours 〖JP2〗after the southwest vortex is formed. The circulation〖JP〗 background of southwest vortex can be divided into two types: the east high west low type and the low trough type. The South Asian high and the subtropical high are strong in the east high west low type. The southern end of the 500 hPa Lake Baikal low trough is superimposed with the plateau low trough to form a deep low trough. Sichuan Basin is located in front of the trough and on the west side of the subtropical high. The low trough type is located in the east of 140°E of the subtropical high, and the South Asian high is more westward and southward than the east high west low type. Sichuan Basin is affected by the eastward shift of the low trough of the Qinghai-Tibetan Plateau. The both types have the water vapor transport channel from the Bay of Bengal to South China Sea to Sichuan Basin, and the water vapor transport of the east high west low type is much stronger. Under the background of east high west low type, the southwest vortex is stronger in intensity and larger in scope, having a deep warm core structure in the vertical direction, and a deep asymmetric distribution of the wind field. Under the background of the low trough type, the southwest vortex has a temperature anomalous distribution of “cold in the upper part-warm in the middle-cooler in the lower part”, and the asymmetry of the wind field is only maintained at the lower level. The common features of the two types are the high energy and high humidity in the lower layer, and the positive vorticity column has a “convergence in the lower layer and divergence in the upper layer” dynamic structure.
Based on rainfall observation and EAR5 reanalysis data, 19 cases of extreme rainstorms induced by southwest vortex and seen in Sichuan Basin from 1981 to 〖JP2〗2020 are statistically analyzed, and the dynamic〖JP〗 synthesis analysis on the circulation background and the structural characteristics of the southwest vortex are carried out. The results show that the life time of the southwest vortex lasts for 48-132 h, and the extreme rainstorm generally breaks out within 18 hours 〖JP2〗after the southwest vortex is formed. The circulation〖JP〗 background of southwest vortex can be divided into two types: the east high west low type and the low trough type. The South Asian high and the subtropical high are strong in the east high west low type. The southern end of the 500 hPa Lake Baikal low trough is superimposed with the plateau low trough to form a deep low trough. Sichuan Basin is located in front of the trough and on the west side of the subtropical high. The low trough type is located in the east of 140°E of the subtropical high, and the South Asian high is more westward and southward than the east high west low type. Sichuan Basin is affected by the eastward shift of the low trough of the Qinghai-Tibetan Plateau. The both types have the water vapor transport channel from the Bay of Bengal to South China Sea to Sichuan Basin, and the water vapor transport of the east high west low type is much stronger. Under the background of east high west low type, the southwest vortex is stronger in intensity and larger in scope, having a deep warm core structure in the vertical direction, and a deep asymmetric distribution of the wind field. Under the background of the low trough type, the southwest vortex has a temperature anomalous distribution of “cold in the upper part-warm in the middle-cooler in the lower part”, and the asymmetry of the wind field is only maintained at the lower level. The common features of the two types are the high energy and high humidity in the lower layer, and the positive vorticity column has a “convergence in the lower layer and divergence in the upper layer” dynamic structure.
2022, 48(12):1590-1607.
DOI: 10.7519/j.issn.1000-0526.2022.040201
Abstract:
All-sky observations of space-based microwave imager contain information of strong meteorological sensitivity related to cloud and precipitation. But the observation error in all-sky data assimilation is apparently non-Gaussian behavior which cannot meet the basic assumption that the observation error is Gaussian in the data assimilation. In this research, a “symmetric cloud” dependent all-sky observation error model developed by European Centre for Medium-Range Weather Forecasts (ECMWF) was used for Fengyun-3C microwave radiation imager (FY-3C MWRI), observations during super typhoons “Maria” and “Lekima” were selected and the all-sky observation error was analyzed after quality control and normalization. The results show that the all-sky first-guess departures normalized by the symmetric error model become to near Gaussian distribution so 〖JP2〗that the data can be used in the data assimilation. In addition, 〖JP〗all-sky approach brings 43.90%-54.63% more data than clear sky, with the biggest increases in the area of the outer spiral cloud band and cloud wall of typhoon. This result preliminarily demonstrates the assimilation potential of FY-3C MWRI all-sky observation data, and the utilization of observation data from the current Fengyun series microwave imagers〖JP2〗 is expected to improve the numerical weather prediction.
All-sky observations of space-based microwave imager contain information of strong meteorological sensitivity related to cloud and precipitation. But the observation error in all-sky data assimilation is apparently non-Gaussian behavior which cannot meet the basic assumption that the observation error is Gaussian in the data assimilation. In this research, a “symmetric cloud” dependent all-sky observation error model developed by European Centre for Medium-Range Weather Forecasts (ECMWF) was used for Fengyun-3C microwave radiation imager (FY-3C MWRI), observations during super typhoons “Maria” and “Lekima” were selected and the all-sky observation error was analyzed after quality control and normalization. The results show that the all-sky first-guess departures normalized by the symmetric error model become to near Gaussian distribution so 〖JP2〗that the data can be used in the data assimilation. In addition, 〖JP〗all-sky approach brings 43.90%-54.63% more data than clear sky, with the biggest increases in the area of the outer spiral cloud band and cloud wall of typhoon. This result preliminarily demonstrates the assimilation potential of FY-3C MWRI all-sky observation data, and the utilization of observation data from the current Fengyun series microwave imagers〖JP2〗 is expected to improve the numerical weather prediction.
2022, 48(12):1608-1616.
DOI: 10.7519/j.issn.1000-0526.2022.042901
Abstract:
Historical similar typhoons are important references for typhoon prediction and decisionmaking besides conventional methods. However, it is timeconsuming and laborious to retrieve similar information from a large number of historical typhoons. In this paper, a similarity retrieval method of subtropical high based on improved visual geometry group model (VGG16) is proposed to query historical similar typhoons based on subtropical high similarity. Through the image extraction, data enhancement, model learning and optimization of 19 〖KG-*5〗736 subtropical high corresponding times in the typhoon season from 1979 to 2020, taking the learned perceptual image patch similarity (LPIPS) as the measurement index of subtropical high similarity, we establish an improved VGG16 model finally. The test results show that greatly similar historical typhoons can be found by using this model. The similarity between the historical similar typhoon ranked first retrieved by this model and the target typhoon is 92.55%, which provides a very meaningful reference for typhoon forecasters. At the same time, compared with the traditional manual recognition, this model takes shorter recognition time and has higher retrieval efficiency, and can be applied in typhoon forecasting and research.
Historical similar typhoons are important references for typhoon prediction and decisionmaking besides conventional methods. However, it is timeconsuming and laborious to retrieve similar information from a large number of historical typhoons. In this paper, a similarity retrieval method of subtropical high based on improved visual geometry group model (VGG16) is proposed to query historical similar typhoons based on subtropical high similarity. Through the image extraction, data enhancement, model learning and optimization of 19 〖KG-*5〗736 subtropical high corresponding times in the typhoon season from 1979 to 2020, taking the learned perceptual image patch similarity (LPIPS) as the measurement index of subtropical high similarity, we establish an improved VGG16 model finally. The test results show that greatly similar historical typhoons can be found by using this model. The similarity between the historical similar typhoon ranked first retrieved by this model and the target typhoon is 92.55%, which provides a very meaningful reference for typhoon forecasters. At the same time, compared with the traditional manual recognition, this model takes shorter recognition time and has higher retrieval efficiency, and can be applied in typhoon forecasting and research.
2022, 48(12):1617-1628.
DOI: 10.7519/j.issn.1000-0526.2022.071501
Abstract:
The second generation laser raindrop spectrum data of Parsivel in Xuzhou and Xinyi in Jiangsu〖JP〗 Province are used to analyze the precipitation in different stages caused by typhoons Rumbia and Lekima from 2018 to 2019. The results are as follows. Small- and medium-sized raindrops are with weak rain intensity and when the intensity increases the diameters of raindrops increase. There are more big raindrops in heavy rain. With much more small and medium raindrops， the “Lekima” precipitation event has the low centroid characteristics of precipitation caused by tropical typhoon. Contrarily, with much more big raindrops, the “Rumbia” precipitation event has the characteristic of precipitation caused by extratropical typhoon. During both of the heavy rain events, there are larger average spectrum widths and diameters of raindrops, higher raindrop concerntration, multi-peaks of large raindrops, which accords with the Gamma distribution, showing characteristics of convective precipitation. Large spectrum width and maximum diameter of raindrops are found in weak rain event casued by “Rumbia”, but the average diameter of raindrops is small and there were great differences between large and small drops in diameter, which basically follows the Gamma distribution, being mixed cloud precipitation. On the contrary, in weak rain event by “Lekima”, there is smaller average spectrum width, raindrop diameter and more small raindrops, and the spectral pattern is smooth, in line with the Marshall-Palmer distribution, which are characterized by stratiform cloud precipitation. The radar reflection profiles of the two-typhoon strong and weak precipitation periods also have a certain corresponding relationship with the raindrop spectrum. The higher the echo extension, the wider the 35 dBz effective precipitation echo, and more and larger raindrops are formed at high altitudes. The falling raindrops continue to collide and merge, and with the increase of the number of raindrops, the diameter increases, and the opposite is true for the weak precipitation period. Heavy rain is mainly caused by convective cloud containing more large raindrops, and also by mixed cloud. Small and medium raindrops in mixed cloud precipitation contribute most both in number and precipitation. Although there are more small and medium raindrops in convective cloud precipitation, the raindrops with larger diameters are the major contributors. Compared with the empirical relations, the typhoon precipitation derived from the actual index of Z-R relationship might be underestimated or overestimated. The empirical relations are not applicable to different types of precipitation. It is necessary to summarize the Z-R relationship applicable to different precipitation types in different places and seasons.
The second generation laser raindrop spectrum data of Parsivel in Xuzhou and Xinyi in Jiangsu〖JP〗 Province are used to analyze the precipitation in different stages caused by typhoons Rumbia and Lekima from 2018 to 2019. The results are as follows. Small- and medium-sized raindrops are with weak rain intensity and when the intensity increases the diameters of raindrops increase. There are more big raindrops in heavy rain. With much more small and medium raindrops， the “Lekima” precipitation event has the low centroid characteristics of precipitation caused by tropical typhoon. Contrarily, with much more big raindrops, the “Rumbia” precipitation event has the characteristic of precipitation caused by extratropical typhoon. During both of the heavy rain events, there are larger average spectrum widths and diameters of raindrops, higher raindrop concerntration, multi-peaks of large raindrops, which accords with the Gamma distribution, showing characteristics of convective precipitation. Large spectrum width and maximum diameter of raindrops are found in weak rain event casued by “Rumbia”, but the average diameter of raindrops is small and there were great differences between large and small drops in diameter, which basically follows the Gamma distribution, being mixed cloud precipitation. On the contrary, in weak rain event by “Lekima”, there is smaller average spectrum width, raindrop diameter and more small raindrops, and the spectral pattern is smooth, in line with the Marshall-Palmer distribution, which are characterized by stratiform cloud precipitation. The radar reflection profiles of the two-typhoon strong and weak precipitation periods also have a certain corresponding relationship with the raindrop spectrum. The higher the echo extension, the wider the 35 dBz effective precipitation echo, and more and larger raindrops are formed at high altitudes. The falling raindrops continue to collide and merge, and with the increase of the number of raindrops, the diameter increases, and the opposite is true for the weak precipitation period. Heavy rain is mainly caused by convective cloud containing more large raindrops, and also by mixed cloud. Small and medium raindrops in mixed cloud precipitation contribute most both in number and precipitation. Although there are more small and medium raindrops in convective cloud precipitation, the raindrops with larger diameters are the major contributors. Compared with the empirical relations, the typhoon precipitation derived from the actual index of Z-R relationship might be underestimated or overestimated. The empirical relations are not applicable to different types of precipitation. It is necessary to summarize the Z-R relationship applicable to different precipitation types in different places and seasons.
2022, 48(12):1629-1636.
DOI: 10.7519/j.issn.1000-0526.2022.111001
Abstract:
The main characteristics of the general atmospheric circulation in September 2022 are as follows. There was a single polar vortex center in the Northern Hemisphere and it was weaker than normal. The circulation at the mid-high latitudes of the Eurasian was mainly dominated by zonal circulation, presenting a weak “two troughs and one ridge” situation. The western pacific subtropical high was stronger than that of the climatological normal, located eastward compared to that in the same period of normal years. The monthly mean temperature was 17.9℃, higher than normal (16.9℃) by 1.0℃. The monthly mean precipitation was 49.4 mm, 24% less than normal (65.3 mm). During this month, China had four torrential rain processes with strong precipitation intensities and at many stations the rainfall surpassed the historical records. Seven typhoons formed over the western North Pacific and the South China Sea in September, but only one of them, i.e., the Severe Typhoon Muifa (No.2212), made landfall four times in China. Then, the Super Typhoon Noru (No.2216) affected the South China Sea and the South China Region. So, the number of generated typhoons was higher than normal, but the landing typhoons were fewer. In addition, the continuous lack of rain in the middle and lower reaches of Yangtze River led to sustained drought above moderate magnitude.
The main characteristics of the general atmospheric circulation in September 2022 are as follows. There was a single polar vortex center in the Northern Hemisphere and it was weaker than normal. The circulation at the mid-high latitudes of the Eurasian was mainly dominated by zonal circulation, presenting a weak “two troughs and one ridge” situation. The western pacific subtropical high was stronger than that of the climatological normal, located eastward compared to that in the same period of normal years. The monthly mean temperature was 17.9℃, higher than normal (16.9℃) by 1.0℃. The monthly mean precipitation was 49.4 mm, 24% less than normal (65.3 mm). During this month, China had four torrential rain processes with strong precipitation intensities and at many stations the rainfall surpassed the historical records. Seven typhoons formed over the western North Pacific and the South China Sea in September, but only one of them, i.e., the Severe Typhoon Muifa (No.2212), made landfall four times in China. Then, the Super Typhoon Noru (No.2216) affected the South China Sea and the South China Region. So, the number of generated typhoons was higher than normal, but the landing typhoons were fewer. In addition, the continuous lack of rain in the middle and lower reaches of Yangtze River led to sustained drought above moderate magnitude.
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ISSN:1000-0526 CN:11-2282/P