ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 49,Issue 9,2023 Table of Contents
2023, 49(9):1029-1044.
DOI: 10.7519/j.issn.1000-0526.2023.050602
Abstract:
Affected by the strong cold air in 19-24 February 2022, an extreme cold event occurred in Yunnan, which was characterized by sharp drop in temperature， affecting large areas and lasting a long time. In this paper, the extreme characteristics of the cold event and the evolution characteristics of the upper and lower atmospheric circulation during the process are analyzed by using the data of 124 meteorological observation stations in Yunnan, the reanalysis data of NCEP/NCAR and ERA5 atmospheric circulation. The results show that this cold event was very extreme, and was the second strongest cold wave weather event in Yunnan in recent ten years. The cold air intensity at 69 stations reached the cold wave standard, of which the daily average temperature at 10 stations reached or broke the lowest temperature record in February. During the cold event, the rainy and snowy weather was prominent, the accumulated precipitation in the process was close to the climatological precipitation in February, and the scope of a single day snowfall was the largest in recent 20 years. The factors that affected the strong cold event were extremely complex. The cold air activity was closely related to the strengthening and evolution of the atmosphere circulation system in midhigh latitudes, such as the Ural high ridge, the East Asia trough, the Asian upperair westerly jet, the Siberian high, and was also associated with the eastward propagation of the subtropical abnormal Rossby wave train which was originated from the North Atlantic Region. This abnormal Rossby wave train played an important role in guiding the southward dispersion of wave energy and the southward movement of cold air in the Tibetan Plateau, and had a certain impact on the strengthening of southwest water vapor transport in front of the south branch trough. Meanwhile, the convective activities in the tropics also had a certain impact on the strengthening of cold air in East Asia. During the cold event, the cold air flew southward along the northeast path, influencing Yunnan. The intersection of cold and warm air in Yunnan was very prominent, resulting in significant cooling, rain and snow during the cold event.
Affected by the strong cold air in 19-24 February 2022, an extreme cold event occurred in Yunnan, which was characterized by sharp drop in temperature， affecting large areas and lasting a long time. In this paper, the extreme characteristics of the cold event and the evolution characteristics of the upper and lower atmospheric circulation during the process are analyzed by using the data of 124 meteorological observation stations in Yunnan, the reanalysis data of NCEP/NCAR and ERA5 atmospheric circulation. The results show that this cold event was very extreme, and was the second strongest cold wave weather event in Yunnan in recent ten years. The cold air intensity at 69 stations reached the cold wave standard, of which the daily average temperature at 10 stations reached or broke the lowest temperature record in February. During the cold event, the rainy and snowy weather was prominent, the accumulated precipitation in the process was close to the climatological precipitation in February, and the scope of a single day snowfall was the largest in recent 20 years. The factors that affected the strong cold event were extremely complex. The cold air activity was closely related to the strengthening and evolution of the atmosphere circulation system in midhigh latitudes, such as the Ural high ridge, the East Asia trough, the Asian upperair westerly jet, the Siberian high, and was also associated with the eastward propagation of the subtropical abnormal Rossby wave train which was originated from the North Atlantic Region. This abnormal Rossby wave train played an important role in guiding the southward dispersion of wave energy and the southward movement of cold air in the Tibetan Plateau, and had a certain impact on the strengthening of southwest water vapor transport in front of the south branch trough. Meanwhile, the convective activities in the tropics also had a certain impact on the strengthening of cold air in East Asia. During the cold event, the cold air flew southward along the northeast path, influencing Yunnan. The intersection of cold and warm air in Yunnan was very prominent, resulting in significant cooling, rain and snow during the cold event.
LIU Jing
,
LIU Zhaoxu
,
YANG Lianmei
,
LI Jiangang
,
ZENG Yong
,
TONG Zepeng
,
JIANG Yufei
,
ZHOU Yushu
2023, 49(9):1045-1062.
DOI: 10.7519/j.issn.1000-0526.2023.062801
Abstract:
In this study, NCEP/NCAR FNL 0.25°×0.25° reanalysis data, GDAS 1°×1° reanalysis data, the fused hourly precipitation of satellite and radar, conventional weather data of Xinjiang, FY-2G satellite data, the GPS-observed PWV data and the HYSPLIT trajectory model are used to conduct an in-depth analysis of extreme precipitation events that occurred in the southeastern Hami Area of Xinjiang on 31 July 2018 (hereinafter referred to as the 31 July process) and in the northern Hami Area on 8 August 2016 (hereinafter referred to as the 8 August process). Based on calculations of water vapor transport stream function, potential function, water vapor transport trajectories, water vapor budge, the characteristics of large-scale water vapor transport and convergence during two severe rainfall events are analyzed. The results show that the two events both occurred in the situation of abnormal continental high, which provided a favorable circulation background for long-distance water vapor transport. The water vapor transports in both of the severe rainfall events consisted of three stages, and the Hexi Corridor water vapor transport contributed to the water vapor supply in both events. Before and during the 31 July process, affected by the easterly water vapor transport channel, there was an obviously humidification at stations of Hami Area and Gansu Province from southeast to northwest. The transport and supplement of water vapor from low latitude provided an abundant water vapor supply for the short-time severe rainfall in southeastern Hami Area. Comparatively, before and during the 8 August process, the water vapor transport channel from northern Tibetan Plateau to southern Bazhou Area in Xinjiang was established. The water vapor in Tibetan Plateau was carried toward north, joining in the water vapor taken by southwest airflow in front of the trough. At the same time, with the low-level water vapor from Hexi Corridor, three humidification processes were triggered in northern Hami Area.
In this study, NCEP/NCAR FNL 0.25°×0.25° reanalysis data, GDAS 1°×1° reanalysis data, the fused hourly precipitation of satellite and radar, conventional weather data of Xinjiang, FY-2G satellite data, the GPS-observed PWV data and the HYSPLIT trajectory model are used to conduct an in-depth analysis of extreme precipitation events that occurred in the southeastern Hami Area of Xinjiang on 31 July 2018 (hereinafter referred to as the 31 July process) and in the northern Hami Area on 8 August 2016 (hereinafter referred to as the 8 August process). Based on calculations of water vapor transport stream function, potential function, water vapor transport trajectories, water vapor budge, the characteristics of large-scale water vapor transport and convergence during two severe rainfall events are analyzed. The results show that the two events both occurred in the situation of abnormal continental high, which provided a favorable circulation background for long-distance water vapor transport. The water vapor transports in both of the severe rainfall events consisted of three stages, and the Hexi Corridor water vapor transport contributed to the water vapor supply in both events. Before and during the 31 July process, affected by the easterly water vapor transport channel, there was an obviously humidification at stations of Hami Area and Gansu Province from southeast to northwest. The transport and supplement of water vapor from low latitude provided an abundant water vapor supply for the short-time severe rainfall in southeastern Hami Area. Comparatively, before and during the 8 August process, the water vapor transport channel from northern Tibetan Plateau to southern Bazhou Area in Xinjiang was established. The water vapor in Tibetan Plateau was carried toward north, joining in the water vapor taken by southwest airflow in front of the trough. At the same time, with the low-level water vapor from Hexi Corridor, three humidification processes were triggered in northern Hami Area.
2023, 49(9):1063-1074.
DOI: 10.7519/j.issn.1000-0526.2023.070801
Abstract:
Using conventional observation data, ground automatic weather station data, Doppler weather radar and wind profiler radar data, etc., this paper analyzes the EF2 tornado that occurred in Jinghai, Tianjin at about 17:30 BT 31 August 2018. The focus is on the analysis of environmental background conditions, local instability conditions, trigger uplift conditions and radar echo characteristics, etc. before and after the occurrence of tornado. The results show that this tornado weather occurred when the 500 hPa high-altitude trough moved eastward, the subtropical high strengthened its westward movement and Typhoon Capricorn was moving northward. Before the tornado occurred, the environmental background conditions were obviously unstable, the CAPE value was 1797 J·kg-1 (CIN was 0 J·kg-1) and the wind vector difference in the height of 0-6 km was approximately 14 m·s-1 and there was lower lifting condensation level (LCL). At the same time, there was high CAPE (maximum value exceeded 4000 J·kg-1), lower LCL. Before the tornado occurred, LCL showed a sudden drop (lowest to around 897 hPa). With the occurrence of tornado, the vertical wind shear values near the ground (0-1 km height and below) at both upwind and downwind stations showed the characteristics of rapid increase first and then rapid decrease. The rapid decrease of the vertical wind shear value started from the upper layer and descended rapidly, while the vertical wind shear value above the 0-1 km height did not change significantly. Doppler weather radar observations show that the tornado echo had a small individual scale (with a diameter of about 2 km at the positive and negative velocity centers), a maximum rotational speed of 24 m·s-1 at the positive and negative velocity centers, and a vertical vorticity of 2.4×10-2 s-1. The echo of this tornado had obvious overhanging structure, bounded weak echo zone and tornado vortex. Moreover, the low-level inflow at the rear side was very strong, so it should be a micro supercell tornado. The collision between the sea breeze front moving to the locale and the gust front formed by the upwind thunderstorm cell outflow triggered the vigorous release of unstable energy locally, stimulating the regeneration of thunderstorm cells, and developing into organized strong thunderstorm cells, which should be the direct trigger conditions for the occurrence of this tornado.
Using conventional observation data, ground automatic weather station data, Doppler weather radar and wind profiler radar data, etc., this paper analyzes the EF2 tornado that occurred in Jinghai, Tianjin at about 17:30 BT 31 August 2018. The focus is on the analysis of environmental background conditions, local instability conditions, trigger uplift conditions and radar echo characteristics, etc. before and after the occurrence of tornado. The results show that this tornado weather occurred when the 500 hPa high-altitude trough moved eastward, the subtropical high strengthened its westward movement and Typhoon Capricorn was moving northward. Before the tornado occurred, the environmental background conditions were obviously unstable, the CAPE value was 1797 J·kg-1 (CIN was 0 J·kg-1) and the wind vector difference in the height of 0-6 km was approximately 14 m·s-1 and there was lower lifting condensation level (LCL). At the same time, there was high CAPE (maximum value exceeded 4000 J·kg-1), lower LCL. Before the tornado occurred, LCL showed a sudden drop (lowest to around 897 hPa). With the occurrence of tornado, the vertical wind shear values near the ground (0-1 km height and below) at both upwind and downwind stations showed the characteristics of rapid increase first and then rapid decrease. The rapid decrease of the vertical wind shear value started from the upper layer and descended rapidly, while the vertical wind shear value above the 0-1 km height did not change significantly. Doppler weather radar observations show that the tornado echo had a small individual scale (with a diameter of about 2 km at the positive and negative velocity centers), a maximum rotational speed of 24 m·s-1 at the positive and negative velocity centers, and a vertical vorticity of 2.4×10-2 s-1. The echo of this tornado had obvious overhanging structure, bounded weak echo zone and tornado vortex. Moreover, the low-level inflow at the rear side was very strong, so it should be a micro supercell tornado. The collision between the sea breeze front moving to the locale and the gust front formed by the upwind thunderstorm cell outflow triggered the vigorous release of unstable energy locally, stimulating the regeneration of thunderstorm cells, and developing into organized strong thunderstorm cells, which should be the direct trigger conditions for the occurrence of this tornado.
2023, 49(9):1075-1084.
DOI: 10.7519/j.issn.1000-0526.2023.072401
Abstract:
Based on the Shandong S-band dual polarization Doppler weather radar data, sounding data and surface precipitation observation as well as the environmental background features, severe rainstorms are divided into the thunderstorm gale (accompanied by severe precipitation or hail) dominated type (referred to as “mixed type”) and the simple severe precipitation dominated type (referred to as “precipitation dominated type”). Three types of minute precipitation magnitudes are considered for each type of rainstorm, and comparative analysis of the low-level dual polarization parameter characteristics of severe rainstorms in the six different scenarios is conducted in this paper. The results show that as the magnitude of minute precipitation increases, the low-level reflectivity factor (ZH) and specific differential phase (KDP) of both types of severe rainstorms increase. The differential reflectivity (ZDR) and correlation coefflicient (CC) of “precipitation dominated type” rainstorms do not show significant changes, while the ZDR and CC of “mixed type” storms decrease. This indicates that with the increase in magnitude of precipitation, the number of large-size hails in the lower layers of “mixed type” severe rainstorms increases, resulting in the decrease in ZDR and CC. For high-intensity precipitation above 2 mm·min-1， the low-level ZH, ZDR, and KDP of “mixed type” rainstorm are concentrated at 50.5-57.0 dBz, 1.7-2.7 dB, 2.4-4.3°·km-1, and CC is above 0.960， while the low-level ZH, ZDR, and KDP of the “precipitation dominated type” rainstorm are concentrated at 49.5-53.5 dBz，〖JP〗 1.2-2.1 dB, 2.5-3.9°·km-1 with CC above 0.970. This means that most “mixed type” rainstorms contain a large amount of small-size hails around 5-10 mm during high-intensity precipitation. These smaller hailstones tend to melt into larger rain droplets in the lower layers, increasing the ZDR value and also making the echo intensity ZH higher than that of the “precipitation dominated type”. At the same minute precipitation level, the low-level ZH and ZDR of the “mixed type” rainstorm are greater than those of the “precipitation dominated type” storm, and CC is smaller than that of the “precipitation dominated type” storm. This is because the former owns not only more 5-10 mm smaller hailstone but also some large hail particles. The larger KDP in the lower layer of rainstorms has obvious indicative significance for the two types of severe precipitation.
Based on the Shandong S-band dual polarization Doppler weather radar data, sounding data and surface precipitation observation as well as the environmental background features, severe rainstorms are divided into the thunderstorm gale (accompanied by severe precipitation or hail) dominated type (referred to as “mixed type”) and the simple severe precipitation dominated type (referred to as “precipitation dominated type”). Three types of minute precipitation magnitudes are considered for each type of rainstorm, and comparative analysis of the low-level dual polarization parameter characteristics of severe rainstorms in the six different scenarios is conducted in this paper. The results show that as the magnitude of minute precipitation increases, the low-level reflectivity factor (ZH) and specific differential phase (KDP) of both types of severe rainstorms increase. The differential reflectivity (ZDR) and correlation coefflicient (CC) of “precipitation dominated type” rainstorms do not show significant changes, while the ZDR and CC of “mixed type” storms decrease. This indicates that with the increase in magnitude of precipitation, the number of large-size hails in the lower layers of “mixed type” severe rainstorms increases, resulting in the decrease in ZDR and CC. For high-intensity precipitation above 2 mm·min-1， the low-level ZH, ZDR, and KDP of “mixed type” rainstorm are concentrated at 50.5-57.0 dBz, 1.7-2.7 dB, 2.4-4.3°·km-1, and CC is above 0.960， while the low-level ZH, ZDR, and KDP of the “precipitation dominated type” rainstorm are concentrated at 49.5-53.5 dBz，〖JP〗 1.2-2.1 dB, 2.5-3.9°·km-1 with CC above 0.970. This means that most “mixed type” rainstorms contain a large amount of small-size hails around 5-10 mm during high-intensity precipitation. These smaller hailstones tend to melt into larger rain droplets in the lower layers, increasing the ZDR value and also making the echo intensity ZH higher than that of the “precipitation dominated type”. At the same minute precipitation level, the low-level ZH and ZDR of the “mixed type” rainstorm are greater than those of the “precipitation dominated type” storm, and CC is smaller than that of the “precipitation dominated type” storm. This is because the former owns not only more 5-10 mm smaller hailstone but also some large hail particles. The larger KDP in the lower layer of rainstorms has obvious indicative significance for the two types of severe precipitation.
2023, 49(9):1085-1096.
DOI: 10.7519/j.issn.1000-0526.2023.052501
Abstract:
Long-time series of Doppler radar products of Yinchuan from May to September of 2011-2016 are used to analyze the climatic characteristics of convective storms in northern Ningxia. The results indicate that 77% of all convective storms in northern Ningxia lasted for no more than 30 min and moved at a speed of 9-13 m·s-1. Most of them mainly moved eastward at higher speeds compared to the moving speeds in other directions. The maximum reflectivity factor of convective storms was concentrated between 35-50 dBz, the echo top height was between 5-9 km, and the vertical integrated liquid water content was generally less than 10 kg·m-2. The 500 hPa wind was the steering flow of convective storms. The probability of convective storm occurrence was lower when 500 hPa and 700 hPa were controlled by northerly winds, but relatively high when controlled by southerly winds. July was the peak month for convective storms, and the peak hours were 12:00 BT to 13:00 BT. Helan Mountain was the area with the highest occurrence of convective storms, followed by the sandy areas from the central-north of Lingwu to the north of Otog Front Banner. The distribution of convective storms was not uniform in Helan Mountain, and the most frequent occurrence was in the areas between high mountains and deep valleys.
Long-time series of Doppler radar products of Yinchuan from May to September of 2011-2016 are used to analyze the climatic characteristics of convective storms in northern Ningxia. The results indicate that 77% of all convective storms in northern Ningxia lasted for no more than 30 min and moved at a speed of 9-13 m·s-1. Most of them mainly moved eastward at higher speeds compared to the moving speeds in other directions. The maximum reflectivity factor of convective storms was concentrated between 35-50 dBz, the echo top height was between 5-9 km, and the vertical integrated liquid water content was generally less than 10 kg·m-2. The 500 hPa wind was the steering flow of convective storms. The probability of convective storm occurrence was lower when 500 hPa and 700 hPa were controlled by northerly winds, but relatively high when controlled by southerly winds. July was the peak month for convective storms, and the peak hours were 12:00 BT to 13:00 BT. Helan Mountain was the area with the highest occurrence of convective storms, followed by the sandy areas from the central-north of Lingwu to the north of Otog Front Banner. The distribution of convective storms was not uniform in Helan Mountain, and the most frequent occurrence was in the areas between high mountains and deep valleys.
2023, 49(9):1097-1107.
DOI: 10.7519/j.issn.10000526.2023.062702
Abstract:
Based on the typhoon data of Shanghai Typhoon Institute and the daily typhoon precipitation data of national stations of China during 1961-2020, the climatic characteristics of different levels of typhoon precipitation caused by typhoon passing though Taiwan Island in southeast coastal of China including Zhejiang, Fujian and Guangdong provinces are statistically analyzed, and the causes for the differences in extreme precipitation are discussed.The study results show that 90% of the typhoons passing though Taiwan Island can bring rainstorms to the southeast coastal area of China. There are 1.6 typhoon rainstrom events every year. The interannual variation of the daily maximum precipitation amount of shows an obvious increasing trend. Especially, the rainstrom extreme events have increased significantly since 2003.The variation of monthly frequency of daily precipitation at different levels shows a single peak pattern, and the peak months are from July to September.The occurrence frequency of the daily maximum precipitation at different levels shows that the frequency of extreme precipitation over 100 mm decreases with the increase of precipitation intensity, and the frequency of extreme precipitation over 300 mm decreases obviously. In terms of spatial distribution, the daily rainstorm frequency shows an uneven and rapid decrease from the coastal areas to the inland areas.The rainstorms from the typhoon through Taiwan Island have most prominent impact on the northern coast of Fujian Province, and Zherong Station in Fujian is the extreme rainstorm center. Based on NCEP reanalysis data, the largescale environmental comparison of the difference between the two similar typhoon groups shows that to the heavy precipitation typhoon group, strong wind speed area on the north side of the typhoon center leads to strong onshore winds. With the effect of mountain terrain, there is stronger convergence and very strong deep vertical upward movement, in front of mountains. With better moisture conditions, theupward motion can take the lowlevel highenergy water vapor to the middlehigh levels. The precipitation dynamics and water vapor conditions are significantly stronger than those of the weak precipitation typhoon group, thus resulting in more typhoon rainstorms.
Based on the typhoon data of Shanghai Typhoon Institute and the daily typhoon precipitation data of national stations of China during 1961-2020, the climatic characteristics of different levels of typhoon precipitation caused by typhoon passing though Taiwan Island in southeast coastal of China including Zhejiang, Fujian and Guangdong provinces are statistically analyzed, and the causes for the differences in extreme precipitation are discussed.The study results show that 90% of the typhoons passing though Taiwan Island can bring rainstorms to the southeast coastal area of China. There are 1.6 typhoon rainstrom events every year. The interannual variation of the daily maximum precipitation amount of shows an obvious increasing trend. Especially, the rainstrom extreme events have increased significantly since 2003.The variation of monthly frequency of daily precipitation at different levels shows a single peak pattern, and the peak months are from July to September.The occurrence frequency of the daily maximum precipitation at different levels shows that the frequency of extreme precipitation over 100 mm decreases with the increase of precipitation intensity, and the frequency of extreme precipitation over 300 mm decreases obviously. In terms of spatial distribution, the daily rainstorm frequency shows an uneven and rapid decrease from the coastal areas to the inland areas.The rainstorms from the typhoon through Taiwan Island have most prominent impact on the northern coast of Fujian Province, and Zherong Station in Fujian is the extreme rainstorm center. Based on NCEP reanalysis data, the largescale environmental comparison of the difference between the two similar typhoon groups shows that to the heavy precipitation typhoon group, strong wind speed area on the north side of the typhoon center leads to strong onshore winds. With the effect of mountain terrain, there is stronger convergence and very strong deep vertical upward movement, in front of mountains. With better moisture conditions, theupward motion can take the lowlevel highenergy water vapor to the middlehigh levels. The precipitation dynamics and water vapor conditions are significantly stronger than those of the weak precipitation typhoon group, thus resulting in more typhoon rainstorms.
2023, 49(9):1108-1118.
DOI: 10.7519/j.issn.1000-0526.2023.082801
Abstract:
Two extreme heat events, caused sequentially by continental high and subtropical high, occurred in Chongqing in the midsummer of 2022. Based on surface observation data and ERA5 reanalysis data, the differences in high temperature characteristics between the two stages dominated by continental high and subtropical high are compared and analyzed. The results show that during the short stage of continental high domination, the heating process was developing with less intensity, high relative humidity and bigger diurnal temperature range. During the long stage of subtropical high domination, the heat event exhibited great extremity, grew severe with pronounced xerothermic characteristics and nocturnal warming. The diagnosis of thermodynamic equation reveals that when the continental high was dominant, diabatic heating and vertical motion jointly contributed to the warming, while when subtropical high set in, diabatic heating and heat advection became the primary and secondary factors for the diurnal warming, and the contribution of vertical motion became insignificant. At night, as the dry adiabatic or super-adiabatic layer at lower level abated and vanished, the warming effect induced by downward motion on the northern side of Yunnan-Guizhou Plateau drastically intensified. The surface thermodynamic difference suggests that the surface latent heat flux decreased and sensible heat flux increased significantly under the domination of subtropical high than under the continental high. The increasing surface sensible heat directly heated the atmosphere, intensively driving up the surface temperature.
Two extreme heat events, caused sequentially by continental high and subtropical high, occurred in Chongqing in the midsummer of 2022. Based on surface observation data and ERA5 reanalysis data, the differences in high temperature characteristics between the two stages dominated by continental high and subtropical high are compared and analyzed. The results show that during the short stage of continental high domination, the heating process was developing with less intensity, high relative humidity and bigger diurnal temperature range. During the long stage of subtropical high domination, the heat event exhibited great extremity, grew severe with pronounced xerothermic characteristics and nocturnal warming. The diagnosis of thermodynamic equation reveals that when the continental high was dominant, diabatic heating and vertical motion jointly contributed to the warming, while when subtropical high set in, diabatic heating and heat advection became the primary and secondary factors for the diurnal warming, and the contribution of vertical motion became insignificant. At night, as the dry adiabatic or super-adiabatic layer at lower level abated and vanished, the warming effect induced by downward motion on the northern side of Yunnan-Guizhou Plateau drastically intensified. The surface thermodynamic difference suggests that the surface latent heat flux decreased and sensible heat flux increased significantly under the domination of subtropical high than under the continental high. The increasing surface sensible heat directly heated the atmosphere, intensively driving up the surface temperature.
2023, 49(9):1119-1130.
DOI: 10.7519/j.issn.1000-0526.2023.053102
Abstract:
Using the maximum temperature observation data, Meiyu data and NCEP/NCAR reanalysis data, we analyze the interdecadal variation characteristics of high temperature stations in Yangtze River Basin and the corresponding atmospheric circulation anomaly at different periods of summer from 1961 to 2020. The results show that high temperature events mainly occurred in the middle-east part (east of 105°E) of the Yangtze River Basin. There existed an abrupt mutation in the summer high temperature across this basin around 2002. Relative to the 35℃ threshold, the increments of high temperature stations at 37℃ and 40℃ were more obvious before and after the mutation. But interdecadal variation characteristics at different periods of summer were inconsistent, and they can be divided into two categories: the slow increasing periods without significant interdecadal turnings and the quick increasing periods, in which an abrupt mutation occurred around 2002 and the interdacadal relative change rates were higher than that of the whole season of summer. The Eurasian teleconnection, the East Asia-Pacific teleconnection and the end time of Meiyu were the major contributors to the intraseasonal inconsistency. During the quick increasing periods, the significant interdecadal increase of high temperature was always accompanied by abnormal intensification of East Asia-Pacific teleconnection. The circulations in the mid-high latitude over Eurasia were significantly different between the two periods with the largest relative change rates. During the slow increasing periods, however, Eurasian teleconnection strengthened at a lower magnitude, while East Asia-Pacific teleconnection was weakened. The slow increase of high temperature stations in 9-19 July was related to the late end of Meiyu.
Using the maximum temperature observation data, Meiyu data and NCEP/NCAR reanalysis data, we analyze the interdecadal variation characteristics of high temperature stations in Yangtze River Basin and the corresponding atmospheric circulation anomaly at different periods of summer from 1961 to 2020. The results show that high temperature events mainly occurred in the middle-east part (east of 105°E) of the Yangtze River Basin. There existed an abrupt mutation in the summer high temperature across this basin around 2002. Relative to the 35℃ threshold, the increments of high temperature stations at 37℃ and 40℃ were more obvious before and after the mutation. But interdecadal variation characteristics at different periods of summer were inconsistent, and they can be divided into two categories: the slow increasing periods without significant interdecadal turnings and the quick increasing periods, in which an abrupt mutation occurred around 2002 and the interdacadal relative change rates were higher than that of the whole season of summer. The Eurasian teleconnection, the East Asia-Pacific teleconnection and the end time of Meiyu were the major contributors to the intraseasonal inconsistency. During the quick increasing periods, the significant interdecadal increase of high temperature was always accompanied by abnormal intensification of East Asia-Pacific teleconnection. The circulations in the mid-high latitude over Eurasia were significantly different between the two periods with the largest relative change rates. During the slow increasing periods, however, Eurasian teleconnection strengthened at a lower magnitude, while East Asia-Pacific teleconnection was weakened. The slow increase of high temperature stations in 9-19 July was related to the late end of Meiyu.
2023, 49(9):1131-1141.
DOI: 10.7519/j.issn.1000-0526.2023.070301
Abstract:
Based on the hourly maximum temperature observations from 19 national meteorological stations during the summers of 2008-2021, this paper analyzes the spatial distribution of high temperature (HT) hours and the features of interdecadal, intraseasonal and diurnal variabilities in Beijing. The results show that the numbers of both HT days and HT hours are much greater in the dountown area and the south of the city, but less in the north and west parts as the result of the combined influences of topography and urban heat island effect. Among them, the Haidian, Fengtai and Changping districts are the most concentrated areas of HT days and hours. On the intraseasonal scale, the HT hours in Beijing are mainly concentrated in the period from late mid-June to early mid-July, which is the period before the beginning of the rainy season in North China. The first dekad of July is the most concentrated period of HT activities. On the diurnal variation, the HT activities can be seen mainly from 09:00 BT to 21:00 BT, particularly concentrated from 14:00 BT to 17:00 BT. In addition, linear regression is also employed in this paper to fit the relationship between maximum temperature and HT hours. The correlation coefficient between the fitting result and the observation reaches as high as 0.82. In Beijing, for each 1℃ increase in maximum temperature over the 35℃ threshold, the HT hours increase by about 1.7 hours. The HT hours in Beijing also exhibits an obvious interdecadal variability. The distribution of the differences of accumulated summer HT hours between 2015-2021 and 2008-2014 is quite different from the spatial distribution of HT hours in climatic state. The area with large interdecadal differences is not located at the central part of HT days or HT hours. Relative to the period of 2008-2014, the HT hours in 2015-2021 are commonly added from 11:00 BT to 19:00 BT, which means the HT periods in Beijing tend to start earlier and end later in the latter period.
Based on the hourly maximum temperature observations from 19 national meteorological stations during the summers of 2008-2021, this paper analyzes the spatial distribution of high temperature (HT) hours and the features of interdecadal, intraseasonal and diurnal variabilities in Beijing. The results show that the numbers of both HT days and HT hours are much greater in the dountown area and the south of the city, but less in the north and west parts as the result of the combined influences of topography and urban heat island effect. Among them, the Haidian, Fengtai and Changping districts are the most concentrated areas of HT days and hours. On the intraseasonal scale, the HT hours in Beijing are mainly concentrated in the period from late mid-June to early mid-July, which is the period before the beginning of the rainy season in North China. The first dekad of July is the most concentrated period of HT activities. On the diurnal variation, the HT activities can be seen mainly from 09:00 BT to 21:00 BT, particularly concentrated from 14:00 BT to 17:00 BT. In addition, linear regression is also employed in this paper to fit the relationship between maximum temperature and HT hours. The correlation coefficient between the fitting result and the observation reaches as high as 0.82. In Beijing, for each 1℃ increase in maximum temperature over the 35℃ threshold, the HT hours increase by about 1.7 hours. The HT hours in Beijing also exhibits an obvious interdecadal variability. The distribution of the differences of accumulated summer HT hours between 2015-2021 and 2008-2014 is quite different from the spatial distribution of HT hours in climatic state. The area with large interdecadal differences is not located at the central part of HT days or HT hours. Relative to the period of 2008-2014, the HT hours in 2015-2021 are commonly added from 11:00 BT to 19:00 BT, which means the HT periods in Beijing tend to start earlier and end later in the latter period.
2023, 49(9):1142-1148.
DOI: 10.7519/j.issn.1000-0526.2023.042002
Abstract:
In 2022, the global mean temperature was about 1.15℃ (±0.13℃) above pre-industrial levels, making it the fifth warmest year. Sea level continued to rise in an upward trend. Arctic Sea ice was below normal and Antarctic Sea ice reached a record low. Pakistan, South Korea, India, Bangladesh, eastern Australia, Brazil, and central and southern Africa suffered rainstorm and floods. The Sahel Region and most of East Africa experienced severe drought. Europe, China, United States, Japan, Pakistan and India experienced record-breaking heat waves. North America and Europe were hit by cold surges and snow storms. Severe convective weather frequently hit parts of the world. A total of 40 tropical cyclones were generated around the world, the number and intensity of which were both lower than the climatic average. Causal analysis indicates that in July, the abnormally strong subtropical high belt in the Northern Hemisphere, along with the persistent and intense warm high-pressure system over Europe, resulted in prevailing subsiding air currents throughout the European Region’s troposphere. This led to record-breaking heat waves across multiple areas in Europe. From July to August, the abnormally strong and westward-shifted western Pacific subtropical high system, along with a redirection of moisture transport from the eastern part of the Bay of Bengal towards northern India and Pakistan, led to intense lower-level moisture convergence with the combined action of the South Asian and East Asian summer monsoons. This prolonged the maintenance of extreme precipitation events and led to the occurrence of severe flood disasters.
In 2022, the global mean temperature was about 1.15℃ (±0.13℃) above pre-industrial levels, making it the fifth warmest year. Sea level continued to rise in an upward trend. Arctic Sea ice was below normal and Antarctic Sea ice reached a record low. Pakistan, South Korea, India, Bangladesh, eastern Australia, Brazil, and central and southern Africa suffered rainstorm and floods. The Sahel Region and most of East Africa experienced severe drought. Europe, China, United States, Japan, Pakistan and India experienced record-breaking heat waves. North America and Europe were hit by cold surges and snow storms. Severe convective weather frequently hit parts of the world. A total of 40 tropical cyclones were generated around the world, the number and intensity of which were both lower than the climatic average. Causal analysis indicates that in July, the abnormally strong subtropical high belt in the Northern Hemisphere, along with the persistent and intense warm high-pressure system over Europe, resulted in prevailing subsiding air currents throughout the European Region’s troposphere. This led to record-breaking heat waves across multiple areas in Europe. From July to August, the abnormally strong and westward-shifted western Pacific subtropical high system, along with a redirection of moisture transport from the eastern part of the Bay of Bengal towards northern India and Pakistan, led to intense lower-level moisture convergence with the combined action of the South Asian and East Asian summer monsoons. This prolonged the maintenance of extreme precipitation events and led to the occurrence of severe flood disasters.
2023, 49(9):1149-1156.
DOI: 10.7519/j.issn.1000-0526.2023.081701
Abstract:
The main characteristics of atmospheric circulation in the Northern Hemisphere exhibited a multipolar distribution of polar vortices in June 2023. The 500 hPa geopotential height field over the Ural Mountains was significantly weaker than the climatological average for the same period. The Western Pacific subtropical high was located more northward and westward than the normal situation. The average precipitation in June was 86.7 mm, which is 16% less than normal; and the least rainfall amount for the same period since 2005. The national average temperature was 21.1℃, showing a positive anomaly of 0.7℃, the second-highest since 1961. During this month, there were five regional torrential rain events mainly in Southwest China and the areas south of the Jianghuai Region. During this month, five large-scale high-temperature processes influence the western and northern parts of China. Moreover, seven severe convective weather events occurred in the provinces of Liaoning, Jilin, Jiangsu, Anhui, Guangdong and Guangxi. In terms of typhoon, there was only one generated in June, the least in June on record. What’s more, the decreased precipitation and higher temperature worsened the drought condition in the northern part of China.
The main characteristics of atmospheric circulation in the Northern Hemisphere exhibited a multipolar distribution of polar vortices in June 2023. The 500 hPa geopotential height field over the Ural Mountains was significantly weaker than the climatological average for the same period. The Western Pacific subtropical high was located more northward and westward than the normal situation. The average precipitation in June was 86.7 mm, which is 16% less than normal; and the least rainfall amount for the same period since 2005. The national average temperature was 21.1℃, showing a positive anomaly of 0.7℃, the second-highest since 1961. During this month, there were five regional torrential rain events mainly in Southwest China and the areas south of the Jianghuai Region. During this month, five large-scale high-temperature processes influence the western and northern parts of China. Moreover, seven severe convective weather events occurred in the provinces of Liaoning, Jilin, Jiangsu, Anhui, Guangdong and Guangxi. In terms of typhoon, there was only one generated in June, the least in June on record. What’s more, the decreased precipitation and higher temperature worsened the drought condition in the northern part of China.
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ISSN:1000-0526 CN:11-2282/P