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doi: 10.11676/qxxb0.20230120
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doi: 10.11676/qxxb2024.20230096
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doi: 10.11676/qxxb2024.20230095
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doi: 10.11676/qxxb2024.20230083
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doi: 10.11676/qxxb0.20230006
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doi: 10.11676/qxxb0.20230030
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doi: 10.11676/qxxb0.20230094
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doi: 10.11676/qxxb0.20230053
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doi: 10.11676/qxxb0.20230079
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doi: 10.11676/qxxb2023.20220187
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doi: 10.11676/qxxb2023.20230050
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doi: 10.11676/qxxb2023.20220217
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doi: 10.11676/qxxb2023.20230031
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doi: 10.11676/qxxb2023.20230067
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doi: 10.11676/qxxb2023.20230038
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doi: 10.11676/qxxb2023.20230010
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doi: 10.11676/qxxb2023.20220188
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doi: 10.11676/qxxb2023.20220163
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doi: 10.11676/qxxb2023.20230041
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2023, 81(4): 531-546.
doi: 10.11676/qxxb2023.20220157
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A spring rainstorm which was underestimated by subjective quantitative precipitation forecast struck southern North China on 21 April 2018. The mesoscale and large scale dynamic processes of the backdoor cold front and associated mesoscale convective system (MCS) were studied using high spatial and temporal resolution observations, the fifth generation of the European Centre for Medium-Range Weather Forecasts atmospheric reanalysis and high-resolution numerical simulations. Results showed that the rainstorm was produced by the backdoor cold front. The backdoor cold front consisted of two sections, and the western one was oriented along the south-north direction while the eastern one was oriented along the east-west direction. Cold air was concentrated below 1.5 km. With the strengthening of northeasterly or easterly winds behind the front, the front moved southward, the height of cold air dam on the east side of Taihang mountain increased, and the front intensified. The rainstorm was brought by the MCS, which occurred in the horizontal wind convergence region ahead of warm air climbing along the backdoor front. The formation and maintenance of MCS occurred near the backdoor front accompanied by frontogenesis. The enhancement of the northeasterly winds behind the front resulted in rapid southward movement of the front and higher cold air dam, while the MCS was enhanced and the convective center also moved southward. The ascending motion favorable for MCS formation was mainly contributed by the resultant force of vertical pressure gradient force and buoyancy. Diagnostic analysis showed that the large value center of the resultant force was ahead of the warm and moist air climbing along the front, corresponding to the region of large horizontal equivalent potential temperature gradient. These results explain the southward movement of the convective center and the development of MCS. This work reveals the key mesoscale dynamic processes of the MCS and backdoor cold front in spring rainstorm in North China, and sheds light on the improvement of related numerical model physical processes and forecasting techniques in the future.
A spring rainstorm which was underestimated by subjective quantitative precipitation forecast struck southern North China on 21 April 2018. The mesoscale and large scale dynamic processes of the backdoor cold front and associated mesoscale convective system (MCS) were studied using high spatial and temporal resolution observations, the fifth generation of the European Centre for Medium-Range Weather Forecasts atmospheric reanalysis and high-resolution numerical simulations. Results showed that the rainstorm was produced by the backdoor cold front. The backdoor cold front consisted of two sections, and the western one was oriented along the south-north direction while the eastern one was oriented along the east-west direction. Cold air was concentrated below 1.5 km. With the strengthening of northeasterly or easterly winds behind the front, the front moved southward, the height of cold air dam on the east side of Taihang mountain increased, and the front intensified. The rainstorm was brought by the MCS, which occurred in the horizontal wind convergence region ahead of warm air climbing along the backdoor front. The formation and maintenance of MCS occurred near the backdoor front accompanied by frontogenesis. The enhancement of the northeasterly winds behind the front resulted in rapid southward movement of the front and higher cold air dam, while the MCS was enhanced and the convective center also moved southward. The ascending motion favorable for MCS formation was mainly contributed by the resultant force of vertical pressure gradient force and buoyancy. Diagnostic analysis showed that the large value center of the resultant force was ahead of the warm and moist air climbing along the front, corresponding to the region of large horizontal equivalent potential temperature gradient. These results explain the southward movement of the convective center and the development of MCS. This work reveals the key mesoscale dynamic processes of the MCS and backdoor cold front in spring rainstorm in North China, and sheds light on the improvement of related numerical model physical processes and forecasting techniques in the future.
2023, 81(4): 547-558.
doi: 10.11676/qxxb2023.20220216
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To investigate the climate background for the extreme rainfall anomaly in 2021 over the mid-lower reaches of the Yellow river, this study analyzes the leading mode of autumn rainfall over the mid-lower reaches of the Yellow river during 1951—2021 and its relationship with the extreme rainfall anomaly in 2021. Rainfall data collected at 160 stations in China and NCEP/NCAR atmospheric circulation reanalysis as well as NOAA sea surface temperature (SST) reanalysis are used. The result of Empirical Orthogonal Function analysis reveals a consistent autumn rainfall pattern from the southeast of Gansu province to the west of Shandong province, which covers the mid-lower reaches of the Yellow river. This pattern is regarded as the leading mode of autumn rainfall over the mid-lower reaches of the Yellow river. The time coefficient in 2021 is the maximum since 1951, consistent with the extreme precipitation in 2021 in the region. The extreme event in 2021 is a typical example corresponding to the leading mode. This study uses the time series of Autumn Rainfall over the Yellow river (ARYR) to represent the variability of this leading mode. Analysis reveals that the interannual and interdecadal variations of this mode are affected by El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) with more rainfall during La Niña phase and negative PDO phase. Further, the leading rainfall mode over the mid-lower reaches of the Yellow river is closely related to SST anomalies in the mid-latitude North Pacific with more rainfall under higher SST. The mid-latitude North Pacific SST (MNPSST) index is calculated over the key region in the North Pacific, where the correlation is the most significant. The MNPSST index is the highest in 2021 since 1951. When the MNPSST index is high, the regressed high-level (low-level) anticyclone (cyclonic) shear occurs over the mid-lower reaches of the Yellow river, and strong upward motions develop over the mid-lower reaches of the Yellow river and the Marine Continent (MC) region. In the autumn of 2021, there are strong upward motions in the northern South China Sea, and anomalous easterly winds over the northern Pacific are obviously stronger. As a result, water vapor flux anomalies could split to southern and eastern branches, reaching the mid-lower reaches of the Yellow river basin. The leading mode of autumn rainfall over the mid-lower reaches of the Yellow river is strongly related to the intensity of SST anomaly in the North Pacific. Positive SST anomalies in the mid-latitude North Pacific are one of the most important factors affecting extreme rainfall over the mid-lower reaches of the Yellow river in autumn 2021.
To investigate the climate background for the extreme rainfall anomaly in 2021 over the mid-lower reaches of the Yellow river, this study analyzes the leading mode of autumn rainfall over the mid-lower reaches of the Yellow river during 1951—2021 and its relationship with the extreme rainfall anomaly in 2021. Rainfall data collected at 160 stations in China and NCEP/NCAR atmospheric circulation reanalysis as well as NOAA sea surface temperature (SST) reanalysis are used. The result of Empirical Orthogonal Function analysis reveals a consistent autumn rainfall pattern from the southeast of Gansu province to the west of Shandong province, which covers the mid-lower reaches of the Yellow river. This pattern is regarded as the leading mode of autumn rainfall over the mid-lower reaches of the Yellow river. The time coefficient in 2021 is the maximum since 1951, consistent with the extreme precipitation in 2021 in the region. The extreme event in 2021 is a typical example corresponding to the leading mode. This study uses the time series of Autumn Rainfall over the Yellow river (ARYR) to represent the variability of this leading mode. Analysis reveals that the interannual and interdecadal variations of this mode are affected by El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) with more rainfall during La Niña phase and negative PDO phase. Further, the leading rainfall mode over the mid-lower reaches of the Yellow river is closely related to SST anomalies in the mid-latitude North Pacific with more rainfall under higher SST. The mid-latitude North Pacific SST (MNPSST) index is calculated over the key region in the North Pacific, where the correlation is the most significant. The MNPSST index is the highest in 2021 since 1951. When the MNPSST index is high, the regressed high-level (low-level) anticyclone (cyclonic) shear occurs over the mid-lower reaches of the Yellow river, and strong upward motions develop over the mid-lower reaches of the Yellow river and the Marine Continent (MC) region. In the autumn of 2021, there are strong upward motions in the northern South China Sea, and anomalous easterly winds over the northern Pacific are obviously stronger. As a result, water vapor flux anomalies could split to southern and eastern branches, reaching the mid-lower reaches of the Yellow river basin. The leading mode of autumn rainfall over the mid-lower reaches of the Yellow river is strongly related to the intensity of SST anomaly in the North Pacific. Positive SST anomalies in the mid-latitude North Pacific are one of the most important factors affecting extreme rainfall over the mid-lower reaches of the Yellow river in autumn 2021.
2023, 81(4): 559-568.
doi: 10.11676/qxxb2023.20220196
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Northeast Cold Vortex (NECV) is a deep cold low-pressure system occurring in the troposphere over Northeast Asia, and anomalies of its activity can often bring great uncertainty to summer precipitation prediction. To improve precipitation prediction technology, this article analyzes climatological characteristics of NECV and its influence on summer precipitation in the Haihe river basin based on precipitation data collected at more than 2400 stations in China and NCEP/NCAR reanalysis circulation data for the period 1961−2021. Machine automatic recognition, correlation analysis and regression reconstruction are employed in this study. Major results are as follows: (1) The occurrence time and geographical location of NECV have obvious climatological characteristics. It can appear all year round, and the number of cold vortex days is the largest in summer. From May to September, there are more cold vortex processes, especially in June. In summer, the center of cold vortex is located further south in June, further west in July, and further northeast in August. (2) There is no significant correlation between summer precipitation in the Haihe river basin and the overall number of days of NECV throughout the year or in summer. However, there is a significant positive correlation with the number of days of summer Western Vortex (＜120°E) and a significant negative correlation with the number of days of summer Eastern Vortex (≥120°E). The frequent activities of the Western Vortex in summer are conducive to higher summer precipitation in the Haihe river basin, while the frequent activities of the Eastern Vortex in summer may result in less summer precipitation in the Haihe river basin. (3) NECV can affect summer precipitation in the Haihe river basin through anomalies of dynamic circulation and water vapor transport. Corresponding to the Western Vortex, the westerly jet at 200 hPa is significantly stronger over Haihe river basin, and Haihe river basin at 500 hPa is located in the rising zone in front of the low pressure trough in the blocking circulation pattern of "high in the east and low in the west". Meanwhile, anomalous southerly winds at 850 hPa over East Asia enhance water vapor transport to Haihe river basin. Corresponding to the Eastern Vortex, the westerly jet at 200 hPa shows no obvious anomalies over Haihe river basin, while Haihe river basin at 500 hPa is in the divergence area in front of the high pressure ridge of "low in the east and high in the west" circulation pattern, and there is no obvious water vapor transport anomaly at 850 hPa over East Asia.
Northeast Cold Vortex (NECV) is a deep cold low-pressure system occurring in the troposphere over Northeast Asia, and anomalies of its activity can often bring great uncertainty to summer precipitation prediction. To improve precipitation prediction technology, this article analyzes climatological characteristics of NECV and its influence on summer precipitation in the Haihe river basin based on precipitation data collected at more than 2400 stations in China and NCEP/NCAR reanalysis circulation data for the period 1961−2021. Machine automatic recognition, correlation analysis and regression reconstruction are employed in this study. Major results are as follows: (1) The occurrence time and geographical location of NECV have obvious climatological characteristics. It can appear all year round, and the number of cold vortex days is the largest in summer. From May to September, there are more cold vortex processes, especially in June. In summer, the center of cold vortex is located further south in June, further west in July, and further northeast in August. (2) There is no significant correlation between summer precipitation in the Haihe river basin and the overall number of days of NECV throughout the year or in summer. However, there is a significant positive correlation with the number of days of summer Western Vortex (＜120°E) and a significant negative correlation with the number of days of summer Eastern Vortex (≥120°E). The frequent activities of the Western Vortex in summer are conducive to higher summer precipitation in the Haihe river basin, while the frequent activities of the Eastern Vortex in summer may result in less summer precipitation in the Haihe river basin. (3) NECV can affect summer precipitation in the Haihe river basin through anomalies of dynamic circulation and water vapor transport. Corresponding to the Western Vortex, the westerly jet at 200 hPa is significantly stronger over Haihe river basin, and Haihe river basin at 500 hPa is located in the rising zone in front of the low pressure trough in the blocking circulation pattern of "high in the east and low in the west". Meanwhile, anomalous southerly winds at 850 hPa over East Asia enhance water vapor transport to Haihe river basin. Corresponding to the Eastern Vortex, the westerly jet at 200 hPa shows no obvious anomalies over Haihe river basin, while Haihe river basin at 500 hPa is in the divergence area in front of the high pressure ridge of "low in the east and high in the west" circulation pattern, and there is no obvious water vapor transport anomaly at 850 hPa over East Asia.
2023, 81(4): 569-579.
doi: 10.11676/qxxb2023.20220202
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Based on "The Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-Ⅲ)" and the routine meteorological operational sounding data, the European Centre for Medium-Range Weather Forecasts Fifth Generation Reanalysis (ERA-5) data, and the ISCCP cloud cover data during the summers (June, July, and August) of 2013—2015, influences of the east-west difference in the convective boundary layer (CBL) height over the Tibetan Plateau (TP) on synoptic-scale atmospheric circulation are analyzed by statistic and physical diagnosis methods. It is found that the east-west difference in CBL shows an obvious diurnal variation. The CBL is high in the west and low in the east from the noon to the late afternoon, which is mainly attributed to the larger rise of the western CBL height. Corresponding to the large east-west difference in the CBL, temporal change of surface virtual potential temperature displays a "high in the west-low in the east" feature and the change in the western TP (WTP) is larger than that in the eastern TP (ETP). Meanwhile, temperature within the CBL increases in the WTP but slightly decreases in the ETP. Pressure decreases in the CBL but increases in higher levels in the WTP. The anomalous low pressure in the WTP is shallow. At the same time, low-level pressure increases in the ETP. The low-level east-west pressure difference may result in east-west pressure gradient anomaly and anomalous southerly winds over the central TP, which is accompanied by low-level convergence and high-level divergence in the WTP. The shallow low pressure anomaly is favorable for the development of low clouds.
Based on "The Third Tibetan Plateau Atmospheric Scientific Experiment (TIPEX-Ⅲ)" and the routine meteorological operational sounding data, the European Centre for Medium-Range Weather Forecasts Fifth Generation Reanalysis (ERA-5) data, and the ISCCP cloud cover data during the summers (June, July, and August) of 2013—2015, influences of the east-west difference in the convective boundary layer (CBL) height over the Tibetan Plateau (TP) on synoptic-scale atmospheric circulation are analyzed by statistic and physical diagnosis methods. It is found that the east-west difference in CBL shows an obvious diurnal variation. The CBL is high in the west and low in the east from the noon to the late afternoon, which is mainly attributed to the larger rise of the western CBL height. Corresponding to the large east-west difference in the CBL, temporal change of surface virtual potential temperature displays a "high in the west-low in the east" feature and the change in the western TP (WTP) is larger than that in the eastern TP (ETP). Meanwhile, temperature within the CBL increases in the WTP but slightly decreases in the ETP. Pressure decreases in the CBL but increases in higher levels in the WTP. The anomalous low pressure in the WTP is shallow. At the same time, low-level pressure increases in the ETP. The low-level east-west pressure difference may result in east-west pressure gradient anomaly and anomalous southerly winds over the central TP, which is accompanied by low-level convergence and high-level divergence in the WTP. The shallow low pressure anomaly is favorable for the development of low clouds.
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ISSN0577-6619
CN11-2006/P
Editor In Chief: Yihui DING
