2023 Vol. 29, No. 1
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2023, 29(1): .
Abstract:
2023, 29(1): 1-15.
doi: 10.46267/j.1006-8775.2023.001
Abstract:
Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration and the Chinese Academy of Meteorological Sciences jointly set up the Longmen Cloud Physics Field Experiment Base, China Meteorological Administration. This paper introduces the instruments and field experiments of this base, provides an overview of the recent advances in retrieval algorithms of microphysical parameters, improved understanding of microphysical characteristics, as well as the formation mechanisms and numerical prediction of heavy rainfalls in south China based on the field experiments dataset.
Aiming at the needs of mechanism analysis of rainstorms and development of numerical prediction models in south China, the Guangzhou Institute of Tropical and Marine Meteorology of China Meteorological Administration and the Chinese Academy of Meteorological Sciences jointly set up the Longmen Cloud Physics Field Experiment Base, China Meteorological Administration. This paper introduces the instruments and field experiments of this base, provides an overview of the recent advances in retrieval algorithms of microphysical parameters, improved understanding of microphysical characteristics, as well as the formation mechanisms and numerical prediction of heavy rainfalls in south China based on the field experiments dataset.
2023, 29(1): 16-25.
doi: 10.46267/j.1006-8775.2023.002
Abstract:
An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage (June 13-15) was the frontal heavy rainfall caused by cold air (brought by an East Asian trough) from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet (SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage (June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet (BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.
An extreme monsoonal heavy rainfall event lasted for nine days and recurred in the interior of northern south China from June 13 to 21, 2022. Using regional meteorological stations and ERA5 reanalysis data, the causes of this extreme monsoonal rainfall event in south China were analyzed and diagnosed. The results are shown as follows. A dominant South Asian high tended to be stable near the Qinghai-Tibet Plateau, providing favorable upper-level dispersion conditions for the occurrence of heavy rainfall in south China. A western Pacific subtropical high dominated the eastern part of the South China Sea, favoring stronger and more northward transport of water vapor to the northern part of south China at lower latitudes than normal. The continuous heavy precipitation event can be divided into two stages. The first stage (June 13-15) was the frontal heavy rainfall caused by cold air (brought by an East Asian trough) from the mid-latitudes that converged with a monsoonal airflow. The heavy rains occurred mostly in the area near a shear in front of the center of a synoptic-system-related low-level jet (SLLJ), and the jet stream and precipitation were strongest in the daytime. The second stage (June 16-21) was the warm-sector heavy rainfall caused by a South China Sea monsoonal low-level jet penetrating inland. The heavy rainfall occurred on the windward slope of the Nanling Mountains and in the northern part of a boundary layer jet (BLJ). The BLJ experienced five nighttime enhancements, corresponding well with the enhancement of the rainfall center, showing significant nighttime heavy rainfall characteristics. Finally, a conceptual diagram of inland-type warm-sector heavy rainfall in south China is summarized.
2023, 29(1): 26-38.
doi: 10.46267/j.1006-8775.2023.003
Abstract:
Composite radar reflectivity data during April - September 2011-2015 are used to investigate and classify storms in south China (18-27°N; 105-120°E). The storms appear most frequently in May. They are either linear; cellular or nonlinear systems, taking up 29.45%, 24.51% and 46.04%, respectively, in terms of morphology. Linear systems are subdivided into six morphologies: trailing stratiform precipitation (TS), bow echoes (BE), leading stratiform precipitation (LS), embedded line (EL), no stratiform precipitation (NS) and parallel stratiform precipitation (PS). The TS and NS modes have the highest frequencies but there are only small samples of LS (0.61%) and PS (0.79%) modes. Severe convective wind (≥17m s-1 at surface level) accounts for the highest percentage (35%) of severe convective weather events produced by cellular systems including individual cells (IC) and clusters of cells (CC). Short-duration heavy rainfall (≥50 mm h-1) and severe convective wind are the most common severe weather associated with TS and BE modes. Comparison of environmental physical parameters shows that cellular convection systems tend to occur in the environment with favorable thermal condition, substantial unstable energy and low precipitable water from the surface to 300 hPa (PWAT). However, the environmental conditions favoring the initiation of linear systems feature strong vertical wind shear, high PWAT, and intense convective inhibition. The environmental parameters favoring the initiation of nonlinear systems are between those of the other two types of morphology.
Composite radar reflectivity data during April - September 2011-2015 are used to investigate and classify storms in south China (18-27°N; 105-120°E). The storms appear most frequently in May. They are either linear; cellular or nonlinear systems, taking up 29.45%, 24.51% and 46.04%, respectively, in terms of morphology. Linear systems are subdivided into six morphologies: trailing stratiform precipitation (TS), bow echoes (BE), leading stratiform precipitation (LS), embedded line (EL), no stratiform precipitation (NS) and parallel stratiform precipitation (PS). The TS and NS modes have the highest frequencies but there are only small samples of LS (0.61%) and PS (0.79%) modes. Severe convective wind (≥17m s-1 at surface level) accounts for the highest percentage (35%) of severe convective weather events produced by cellular systems including individual cells (IC) and clusters of cells (CC). Short-duration heavy rainfall (≥50 mm h-1) and severe convective wind are the most common severe weather associated with TS and BE modes. Comparison of environmental physical parameters shows that cellular convection systems tend to occur in the environment with favorable thermal condition, substantial unstable energy and low precipitable water from the surface to 300 hPa (PWAT). However, the environmental conditions favoring the initiation of linear systems feature strong vertical wind shear, high PWAT, and intense convective inhibition. The environmental parameters favoring the initiation of nonlinear systems are between those of the other two types of morphology.
2023, 29(1): 39-54.
doi: 10.46267/j.1006-8775.2023.004
Abstract:
The long-term trends in the occurrence frequency of pre-summer daytime and nocturnal extreme hourly rainfall (EXHR) during 1988-2018 in Hong Kong and their spatial distributions are examined and analyzed. Despite a significant increasing trend observed in the occurrence frequency of pre-summer EXHRs during the investigated period, the increase in daytime and nocturnal EXHRs show distinct spatial patterns. Nocturnal EXHRs show uniform increasing trends over the entire Hong Kong. However, the increase in daytime EXHRs is concentrated over the northern or eastern areas of Hong Kong, indicating a downstream shift of pre-summer EXHRs in Hong Kong with regard to the prevailing southwesterly monsoonal flows in south China. The clustering of weather types associated with daytime and nocturnal EXHRs further reveals that the increase in EXHRs over Hong Kong are mainly contributed by the increase of the events associated with southwesterly monsoonal flows with relatively high speeds. During the past few decades, the southwesterly monsoonal flows at coastal south China have undergone a substantial weakening due to the increased surface roughness induced by the urbanization over the Guangdong-Hong Kong-Macau Greater Bay Area since 1990s, leading to enhanced low-level convergence and thus significant increase in EXHRs at coastal south China. Meanwhile, daytime sea-wind circulation at coastal south China is markedly enhanced during the investigated period, which is the main reason for the northward shift of daytime EXHRs in Hong Kong. In addition, the blocked southwesterly monsoonal flows at coastal south China are detoured eastward, leading to stronger convergence and increase in EXHRs at eastern coast of Hong Kong, especially during daytime, when the easterly sea winds prevail at the region.
The long-term trends in the occurrence frequency of pre-summer daytime and nocturnal extreme hourly rainfall (EXHR) during 1988-2018 in Hong Kong and their spatial distributions are examined and analyzed. Despite a significant increasing trend observed in the occurrence frequency of pre-summer EXHRs during the investigated period, the increase in daytime and nocturnal EXHRs show distinct spatial patterns. Nocturnal EXHRs show uniform increasing trends over the entire Hong Kong. However, the increase in daytime EXHRs is concentrated over the northern or eastern areas of Hong Kong, indicating a downstream shift of pre-summer EXHRs in Hong Kong with regard to the prevailing southwesterly monsoonal flows in south China. The clustering of weather types associated with daytime and nocturnal EXHRs further reveals that the increase in EXHRs over Hong Kong are mainly contributed by the increase of the events associated with southwesterly monsoonal flows with relatively high speeds. During the past few decades, the southwesterly monsoonal flows at coastal south China have undergone a substantial weakening due to the increased surface roughness induced by the urbanization over the Guangdong-Hong Kong-Macau Greater Bay Area since 1990s, leading to enhanced low-level convergence and thus significant increase in EXHRs at coastal south China. Meanwhile, daytime sea-wind circulation at coastal south China is markedly enhanced during the investigated period, which is the main reason for the northward shift of daytime EXHRs in Hong Kong. In addition, the blocked southwesterly monsoonal flows at coastal south China are detoured eastward, leading to stronger convergence and increase in EXHRs at eastern coast of Hong Kong, especially during daytime, when the easterly sea winds prevail at the region.
2023, 29(1): 55-67.
doi: 10.46267/j.1006-8775.2023.005
Abstract:
While heavy rainfall frequently takes place in southern China during summer monsoon seasons, quantitative precipitation forecast skills are relatively poor. Therefore, detailed knowledge about the raindrop size distribution (DSD) is useful in improving the quantitative precipitation estimation and forecast. Based on the data during 2018-2022 from 86 stations in a ground-based optical disdrometer measurement network, the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution (N(D)), mass-weighted mean diameter (Dm) and other integral DSD parameters such as radar reflectivity (Z), rainfall rate (R) and liquid water content (LWC). In addition, the effects of geographical locations, weather systems (tropical cyclones, frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered. The results are shown as follows. 1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation, and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution. The relationships between the Z and R for stratiform and convective precipitation are also derived for the province, i.e., Z = 332.34 R1.32 and Z = 366.26 R1.42 which is distinctly different from that of the Next-generation Weather Radar (NEXRAD) Z-R relationship in United States. 2) In the rainy season (April-September), the Dm, R and LWC are larger than those in the dry season (OctoberMarch). Moreover the above parameters are larger, especially in mid-May, which is the onset of the South China Sea summer monsoon. 3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dm and a larger normalized intercept parameter (log10Nw), suggestive of maritime-like rainfall. Dm is larger and log10Nw is smaller in the inland area, suggestive of continental-like rainfall. 4) Affected by such weather systems as the tropical cyclone, frontal system and summer monsoon, the DSD shows characteristics with distinct differences. Furthermore, frontal system rainfall tends to present a continental-like rainfall, tropical cyclone rainfall tends to have a maritime-like rainfall, and summer monsoon rainfall characteristic are between maritime- and continental-like cluster (raindrop concentration and diameter are higher than continental cluster and maritime cluster, respectively.)
While heavy rainfall frequently takes place in southern China during summer monsoon seasons, quantitative precipitation forecast skills are relatively poor. Therefore, detailed knowledge about the raindrop size distribution (DSD) is useful in improving the quantitative precipitation estimation and forecast. Based on the data during 2018-2022 from 86 stations in a ground-based optical disdrometer measurement network, the characteristics of the DSD in Guangdong province are investigated in terms of the particle size distribution (N(D)), mass-weighted mean diameter (Dm) and other integral DSD parameters such as radar reflectivity (Z), rainfall rate (R) and liquid water content (LWC). In addition, the effects of geographical locations, weather systems (tropical cyclones, frontal systems and the summer monsoon) and precipitation types on DSD characteristics are also considered. The results are shown as follows. 1) Convective precipitation has a broader N(D) and larger mean particle diameter than the stratiform precipitation, and the DSD observations in Guangdong are consistent with the three-parameter gamma distribution. The relationships between the Z and R for stratiform and convective precipitation are also derived for the province, i.e., Z = 332.34 R1.32 and Z = 366.26 R1.42 which is distinctly different from that of the Next-generation Weather Radar (NEXRAD) Z-R relationship in United States. 2) In the rainy season (April-September), the Dm, R and LWC are larger than those in the dry season (OctoberMarch). Moreover the above parameters are larger, especially in mid-May, which is the onset of the South China Sea summer monsoon. 3) The spatial analysis of DSD shows that the coastal station observations indicate a smaller Dm and a larger normalized intercept parameter (log10Nw), suggestive of maritime-like rainfall. Dm is larger and log10Nw is smaller in the inland area, suggestive of continental-like rainfall. 4) Affected by such weather systems as the tropical cyclone, frontal system and summer monsoon, the DSD shows characteristics with distinct differences. Furthermore, frontal system rainfall tends to present a continental-like rainfall, tropical cyclone rainfall tends to have a maritime-like rainfall, and summer monsoon rainfall characteristic are between maritime- and continental-like cluster (raindrop concentration and diameter are higher than continental cluster and maritime cluster, respectively.)
2023, 29(1): 68-86.
doi: 10.46267/j.1006-8775.2023.006
Abstract:
A heavy rainfall event in south China was simulated by the Weather Research and Forecasting (WRF) model with three microphysics schemes, including the Morrison scheme, Thompson scheme, and Milbrandt and Yau scheme (MY), which aim to evaluate the capability to reproduce the precipitation and radar echo reflectivity features, and to evaluate evaluate their differences in microphysics and the associated thermodynamical and dynamical feedback. Results show that all simulations reproduce the main features crucial for rainfall formation. Compared with the observation, the MY scheme performed better than the other two schemes in terms of intensity and spatial distribution of rainfall. Due to abundant water vapor, the accretion of cloud droplets by raindrops was the dominant process in the growth of raindrops while the contribution of melting was a secondary effect. Riming processes, in which frozen hydrometeors collect cloud droplets mainly, contributed more to the growth of frozen hydrometeors than the Bergeron process. Extremely abundant snow and ice were produced in the Thompson and MY schemes respectively by a deposition process. The MY scheme has the highest condensation and evaporation, but the lowest deposition. As a result, in the MY scheme, the enhanced vertical gradient of condensation heating and evaporation cooling at low levels produces strong positive and weak negative potential vorticity in Guangdong, and may favor the formation of the enhanced rainfall center over there.
A heavy rainfall event in south China was simulated by the Weather Research and Forecasting (WRF) model with three microphysics schemes, including the Morrison scheme, Thompson scheme, and Milbrandt and Yau scheme (MY), which aim to evaluate the capability to reproduce the precipitation and radar echo reflectivity features, and to evaluate evaluate their differences in microphysics and the associated thermodynamical and dynamical feedback. Results show that all simulations reproduce the main features crucial for rainfall formation. Compared with the observation, the MY scheme performed better than the other two schemes in terms of intensity and spatial distribution of rainfall. Due to abundant water vapor, the accretion of cloud droplets by raindrops was the dominant process in the growth of raindrops while the contribution of melting was a secondary effect. Riming processes, in which frozen hydrometeors collect cloud droplets mainly, contributed more to the growth of frozen hydrometeors than the Bergeron process. Extremely abundant snow and ice were produced in the Thompson and MY schemes respectively by a deposition process. The MY scheme has the highest condensation and evaporation, but the lowest deposition. As a result, in the MY scheme, the enhanced vertical gradient of condensation heating and evaporation cooling at low levels produces strong positive and weak negative potential vorticity in Guangdong, and may favor the formation of the enhanced rainfall center over there.
2023, 29(1): 87-100.
doi: 10.46267/j.1006-8775.2023.007
Abstract:
During the April-June raining season, warm-sector heavy rainfall (WR) and frontal heavy rainfall (FR) often occur in the south of China, causing natural disasters. In this study, the microphysical characteristics of WR and FR events from 2016 to 2022 are analyzed by using 2-dimensional video disdrometer (2DVD) data in the south of China. The microphysical characteristics of WR and FR events are quite different. Compared with FR events, WR events have higher concentration of D < 5.3 mm (especially D < 1 mm), leading to higher rain rates. The mean values of Dm and lgNw of WR events are higher than that of FR events. The microphysical characteristics in different rain rate classes (C1: R ~ 5-20 mm h-1, C2: R ~ 20-50 mm h-1, C3: R ~ 50-100 mm h-1, and C4: R > 100 mm h-1) for WR and FR events are also different. Raindrops from C3 contribute the most to the precipitation of WR events, and raindrops from C2 contribute the most to the precipitation of FR events. For C2 and C3, compared with FR events, WR events have higher concentration of D < 1 mm and D ~3-4.5 mm. Moreover, the shape and slope (μ-Λ) relationships and the radar reflectivity and rain rate (Z-R) relationships of WR and FR events are quite different in each rain rate class. The investigation of the difference in microphysical characteristics between WR and FR events provide useful information for radar-based quantitative precipitation estimation and numerical prediction.
During the April-June raining season, warm-sector heavy rainfall (WR) and frontal heavy rainfall (FR) often occur in the south of China, causing natural disasters. In this study, the microphysical characteristics of WR and FR events from 2016 to 2022 are analyzed by using 2-dimensional video disdrometer (2DVD) data in the south of China. The microphysical characteristics of WR and FR events are quite different. Compared with FR events, WR events have higher concentration of D < 5.3 mm (especially D < 1 mm), leading to higher rain rates. The mean values of Dm and lgNw of WR events are higher than that of FR events. The microphysical characteristics in different rain rate classes (C1: R ~ 5-20 mm h-1, C2: R ~ 20-50 mm h-1, C3: R ~ 50-100 mm h-1, and C4: R > 100 mm h-1) for WR and FR events are also different. Raindrops from C3 contribute the most to the precipitation of WR events, and raindrops from C2 contribute the most to the precipitation of FR events. For C2 and C3, compared with FR events, WR events have higher concentration of D < 1 mm and D ~3-4.5 mm. Moreover, the shape and slope (μ-Λ) relationships and the radar reflectivity and rain rate (Z-R) relationships of WR and FR events are quite different in each rain rate class. The investigation of the difference in microphysical characteristics between WR and FR events provide useful information for radar-based quantitative precipitation estimation and numerical prediction.
2023, 29(1): 101-114.
doi: 10.46267/j.1006-8775.2023.008
Abstract:
Based on the hourly precipitation data at 176 observational stations over south China and the hourly ERA5reanalysis data during the 40-yr period of 1981-2020, we analyzed the universal characteristics of moisture transport and their associated background circulations for four types of regional extreme precipitation events(REPEs) over south China. Main findings are shown as follow. (ⅰ) The wind that transported moisture for the REPEs over south China featured a notable diurnal variation, which was consistent with the variations of the precipitation. (ⅱ) Four types of REPEs could be determined, among which the southwest type(SWT) and the southeast type(SET) accounted for ~92%and ~5.7%, respectively, ranking the first and second, respectively. (ⅲ) Trajectory analyses showed that the air particles of the SWT-REPEs had the largest specific humidity and experienced the most intense ascending motion, and therefore their precipitation was the strongest among the four types. (ⅳ) South China was dominated by notable moisture flux convergence for the four types of REPEs, but their moisture transport was controlled by different flow paths. (ⅴ) Composite analyses indicated that the background circulation of the four types of REPEs showed different features, particularly for the intensity, location and coverage of a western Pacific subtropical high. For the SWT-REPEs, their moisture transport was mainly driven by a lower-tropospheric strong southwesterly wind band in the low-latitude regions. Air particles for this type of REPEs mainly passed over the Indochina Peninsula and South China Sea. For the SET-REPEs, their moisture transport was mainly steered by a strong low-tropospheric southeasterly wind northeast of a transversal trough. Air particles mainly passed over the South China Sea for this type of REPEs.
Based on the hourly precipitation data at 176 observational stations over south China and the hourly ERA5reanalysis data during the 40-yr period of 1981-2020, we analyzed the universal characteristics of moisture transport and their associated background circulations for four types of regional extreme precipitation events(REPEs) over south China. Main findings are shown as follow. (ⅰ) The wind that transported moisture for the REPEs over south China featured a notable diurnal variation, which was consistent with the variations of the precipitation. (ⅱ) Four types of REPEs could be determined, among which the southwest type(SWT) and the southeast type(SET) accounted for ~92%and ~5.7%, respectively, ranking the first and second, respectively. (ⅲ) Trajectory analyses showed that the air particles of the SWT-REPEs had the largest specific humidity and experienced the most intense ascending motion, and therefore their precipitation was the strongest among the four types. (ⅳ) South China was dominated by notable moisture flux convergence for the four types of REPEs, but their moisture transport was controlled by different flow paths. (ⅴ) Composite analyses indicated that the background circulation of the four types of REPEs showed different features, particularly for the intensity, location and coverage of a western Pacific subtropical high. For the SWT-REPEs, their moisture transport was mainly driven by a lower-tropospheric strong southwesterly wind band in the low-latitude regions. Air particles for this type of REPEs mainly passed over the Indochina Peninsula and South China Sea. For the SET-REPEs, their moisture transport was mainly steered by a strong low-tropospheric southeasterly wind northeast of a transversal trough. Air particles mainly passed over the South China Sea for this type of REPEs.
Analysis of Precipitation Anomaly and a Failed Prediction During the Dragon-boat Rain Period in 2022
2023, 29(1): 115-127.
doi: 10.46267/j.1006-8775.2023.009
Abstract:
This study investigates the possible causes for the precipitation of Guangdong during dragon-boat rain period(DBRP) in 2022 that is remarkably more than the climate state and reviews the successes and failures of the prediction in2022. Features of atmospheric circulation and sea surface temperature(SST) are analyzed based on several observational datasets for nearly 60 years from meteorological stations and the NCEP/NCAR Global Reanalysis Data.Resultsshow that fluctuation of the 200-h Pa westerly wind as well as the westerly jet is strengthened due to the propagation of wave energy, leading to strong updraft over southern China. Activities of a subtropical high and a shear line provide favorable conditions for the transport of moisture to Guangdong. With the support of powerful southwest winds, extreme precipitation is induced. ENSO is a good indicator of atmospheric circulation at mid-and high-levels during the DBRP in2022 but it performs badly at low levels. During recent years, the influence of ENSO on precipitation during the DBRP has decreased obviously. The SSTA of tropical southeast Atlantic(SEA) in spring may become the key indicator. During the years with warm SEA, wave trains propagate from northwest to southeast over Eurasia with energy enhancing the westerly jet, conducive to updraft over southern China and the occurrence of heavy precipitation. Meanwhile, the Rossby wave is triggered over Maritime Continent by heat sources of southern Atlantic-western Indian Ocean through the Gill response. Thus, strong transport of moisture and heavy rainfall occur.
This study investigates the possible causes for the precipitation of Guangdong during dragon-boat rain period(DBRP) in 2022 that is remarkably more than the climate state and reviews the successes and failures of the prediction in2022. Features of atmospheric circulation and sea surface temperature(SST) are analyzed based on several observational datasets for nearly 60 years from meteorological stations and the NCEP/NCAR Global Reanalysis Data.Resultsshow that fluctuation of the 200-h Pa westerly wind as well as the westerly jet is strengthened due to the propagation of wave energy, leading to strong updraft over southern China. Activities of a subtropical high and a shear line provide favorable conditions for the transport of moisture to Guangdong. With the support of powerful southwest winds, extreme precipitation is induced. ENSO is a good indicator of atmospheric circulation at mid-and high-levels during the DBRP in2022 but it performs badly at low levels. During recent years, the influence of ENSO on precipitation during the DBRP has decreased obviously. The SSTA of tropical southeast Atlantic(SEA) in spring may become the key indicator. During the years with warm SEA, wave trains propagate from northwest to southeast over Eurasia with energy enhancing the westerly jet, conducive to updraft over southern China and the occurrence of heavy precipitation. Meanwhile, the Rossby wave is triggered over Maritime Continent by heat sources of southern Atlantic-western Indian Ocean through the Gill response. Thus, strong transport of moisture and heavy rainfall occur.
2023, 29(1): 128-141.
doi: 10.46267/j.1006-8775.2023.010
Abstract:
In south China, warm-sector rainstorms are significantly different from the traditional frontal rainstorms due to complex mechanism, which brings great challenges to their forecast. In this study, based on ensemble forecasting, the high-resolution mesoscale numerical forecast model WRF was used to investigate the effect of initial errors on a warmsector rainstorm and a frontal rainstorm under the same circulation in south China, respectively. We analyzed the sensitivity of forecast errors to the initial errors and their evolution characteristics for the warm-sector and the frontal rainstorm. Additionally, the difference of the predictability was compared via adjusting the initial values of the GOOD member and the BAD member. Compared with the frontal rainstorm, the warm-sector rainstorm was more sensitive to initial error, which increased faster in the warm-sector. Furthermore, the magnitude of error in the warm-sector rainstorm was obviously larger than that of the frontal rainstorm, while the spatial scale of the error was smaller. Similarly, both types of the rainstorm were limited by practical predictability and inherent predictability, while the nonlinear increase characteristics occurred to be more distinct in the warm-sector rainstorm, resulting in the lower inherent predictability.The comparison between the warm-sector rainstorm and the frontal rainstorm revealed that the forecast field was closer to the real situation derived from more accurate initial errors, but only the increase rate in the frontal rainstorm was restrained evidently.
In south China, warm-sector rainstorms are significantly different from the traditional frontal rainstorms due to complex mechanism, which brings great challenges to their forecast. In this study, based on ensemble forecasting, the high-resolution mesoscale numerical forecast model WRF was used to investigate the effect of initial errors on a warmsector rainstorm and a frontal rainstorm under the same circulation in south China, respectively. We analyzed the sensitivity of forecast errors to the initial errors and their evolution characteristics for the warm-sector and the frontal rainstorm. Additionally, the difference of the predictability was compared via adjusting the initial values of the GOOD member and the BAD member. Compared with the frontal rainstorm, the warm-sector rainstorm was more sensitive to initial error, which increased faster in the warm-sector. Furthermore, the magnitude of error in the warm-sector rainstorm was obviously larger than that of the frontal rainstorm, while the spatial scale of the error was smaller. Similarly, both types of the rainstorm were limited by practical predictability and inherent predictability, while the nonlinear increase characteristics occurred to be more distinct in the warm-sector rainstorm, resulting in the lower inherent predictability.The comparison between the warm-sector rainstorm and the frontal rainstorm revealed that the forecast field was closer to the real situation derived from more accurate initial errors, but only the increase rate in the frontal rainstorm was restrained evidently.
2023, 29(1): 142-152.
doi: 10.46267/j.1006-8775.2023.011
Abstract:
The performance of different quantitative precipitation estimation(QPE) relationships is examined using the polarimetric variables from the X-band polarimetric phased-array radars in Guangzhou, China.Three QPE approaches, namely, R(ZH), R(ZH, ZDR) and R(KDP), are developed for horizontal reflectivity, differential reflectivity and specific phase shift rate, respectively.The estimation parameters are determined by fitting the relationships to the observed radar variables using the T-matrix method.The QPE relationships were examined using the data of four heavy precipitation events in southern China.The examination shows that the R(ZH) approach performs better for the precipitation rate less than 5 mm h-1, and R(KDP) is better for the rate higher than 5 mm h -1, while R(ZH, ZDR) has the worst performance.An adaptive approach is developed by taking the advantages of both R(ZH) and R(KDP) approaches to improve the QPE accuracy.
The performance of different quantitative precipitation estimation(QPE) relationships is examined using the polarimetric variables from the X-band polarimetric phased-array radars in Guangzhou, China.Three QPE approaches, namely, R(ZH), R(ZH, ZDR) and R(KDP), are developed for horizontal reflectivity, differential reflectivity and specific phase shift rate, respectively.The estimation parameters are determined by fitting the relationships to the observed radar variables using the T-matrix method.The QPE relationships were examined using the data of four heavy precipitation events in southern China.The examination shows that the R(ZH) approach performs better for the precipitation rate less than 5 mm h-1, and R(KDP) is better for the rate higher than 5 mm h -1, while R(ZH, ZDR) has the worst performance.An adaptive approach is developed by taking the advantages of both R(ZH) and R(KDP) approaches to improve the QPE accuracy.
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