ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 44,Issue 4,2018 Table of Contents
TIAN Fuyou
,
ZHENG Yongguang
,
ZHANG Xiaoling
,
ZHANG Tao
,
LIN Yinjing
,
ZHANG Xiaowen
,
ZHU Wenjian
2018, 44(4):469-484.
DOI: 10.7519/j.issn.1000-0526.2018.04.001
Abstract:
A very extreme rainfall event occurred on 7 May 2017 in Xintang Town, Zengcheng District of Guangzhou with maximum hourly precipitation exceeding 180 mm and 3 h rainfall exceeding 330 mm (shortly “the 5·7 extreme rainfall event”), causing severe economic damages. The rainfall process can be divided into two stages: Huadu rainfall stage and Zengcheng rainfall stage. The severe rainfall was mainly concentrated in two or three hours. The maximum minutely rainfall was high up to 5.0 mm. About 120 mm of the rain poured between 05:30 and 06:00 BT for the extreme hourly precipitation of 184.4 mm in Xintang Town of Zengcheng. Some negative lightning was observed during the Huadu rainfall stage and only several lightning occurred during the Zengcheng convection stage. Both radar reflectivity and satellite images show that the severe convective rainfall system was characterized by smallscale and rapid developing. The radar vertical profiles show the convection featured lowechocentroid warmcloud precipitation. There was remarkable spatial inconsistency between radar maximum reflectivity and minimum TBB of satellite image during the mature stages of the convection. The strong updraft was the cause of the spatial inconsistency between radar maximum reflectivity and minimum TBB. The topographic radiation cooling formed the surface cold center near Huadu. The terrain combined with largescale weak cold air blocked the northmoving warm, moist flow, and the convection was finally triggered near Huadu. The continuously transport of warm, moist air and blocking of Huadu terrain maintained the mesoscale convective system (MCS) during 01:00-03:00 BT in Huadu. The southmoving largescale weak cold air enhanced the cold pool, and pushed the MCS to move southward rapidly in 03:00-04:00 BT. The combination of southmoving MCS and local convection enhanced the convection over Zengcheng Region. The cold pool driven theory can explain the longtime maintenance and development of the MCS over Zengcheng. Both weak ambient flow and southward surface flow made the MCS slowly move during the two heavy rainfall stages. Thus, the extremely severe rainfall over Huadu and Zengcheng of Guangzhou took place.
A very extreme rainfall event occurred on 7 May 2017 in Xintang Town, Zengcheng District of Guangzhou with maximum hourly precipitation exceeding 180 mm and 3 h rainfall exceeding 330 mm (shortly “the 5·7 extreme rainfall event”), causing severe economic damages. The rainfall process can be divided into two stages: Huadu rainfall stage and Zengcheng rainfall stage. The severe rainfall was mainly concentrated in two or three hours. The maximum minutely rainfall was high up to 5.0 mm. About 120 mm of the rain poured between 05:30 and 06:00 BT for the extreme hourly precipitation of 184.4 mm in Xintang Town of Zengcheng. Some negative lightning was observed during the Huadu rainfall stage and only several lightning occurred during the Zengcheng convection stage. Both radar reflectivity and satellite images show that the severe convective rainfall system was characterized by smallscale and rapid developing. The radar vertical profiles show the convection featured lowechocentroid warmcloud precipitation. There was remarkable spatial inconsistency between radar maximum reflectivity and minimum TBB of satellite image during the mature stages of the convection. The strong updraft was the cause of the spatial inconsistency between radar maximum reflectivity and minimum TBB. The topographic radiation cooling formed the surface cold center near Huadu. The terrain combined with largescale weak cold air blocked the northmoving warm, moist flow, and the convection was finally triggered near Huadu. The continuously transport of warm, moist air and blocking of Huadu terrain maintained the mesoscale convective system (MCS) during 01:00-03:00 BT in Huadu. The southmoving largescale weak cold air enhanced the cold pool, and pushed the MCS to move southward rapidly in 03:00-04:00 BT. The combination of southmoving MCS and local convection enhanced the convection over Zengcheng Region. The cold pool driven theory can explain the longtime maintenance and development of the MCS over Zengcheng. Both weak ambient flow and southward surface flow made the MCS slowly move during the two heavy rainfall stages. Thus, the extremely severe rainfall over Huadu and Zengcheng of Guangzhou took place.
2018, 44(4):485-499.
DOI: 10.7519/j.issn.1000-0526.2018.04.002
Abstract:
Based on the conventional observation data and the Guangzhou Doppler weather radar data, this article analyzed the synoptic background, mesoscale systems and predictability of the torrential rain process which occurred in Guangzhou on 7 May 2017. By contrasting the members of ECMWF ensemble forecast which successfully forecasted the local heavy precipitation on 7 May 2017 with the failed member, key triggering factor affected this process was investigated. The results show that the ambient condition and dynamic forcing were weaker on 7 May 2017. In the context of weak wind field, a convergence line formed between the warm flow from the sea and the cold downslope wind in the front of mountain, combined with the intense temperature gradient, initially triggering the generation of convective storms. Subsequently, the outflow of the preexisting thunderstorms impacted the warm, moist flow at boundary layer, inducing new convergence lines continually. Therefore the weakened storm-cells enhanced again and aroused the second stage of heavy rainfall. The first stages of the local torrential rain on 7 May 2017 was induced by short-lived severe local storm with a meso-vortex evolved from the steady and strong block-shaped echo. The second stage of this torrential rain was caused by long-lived heavy precipitation (HP-type) supercell storm. However, the band echo merging from a mass of new-born convective cells and moving eastward with the short-wave trough was responsible for the third stage of this torrential rain. The radar echo had the low-quality core vertical structure and warm cloud precipitation character during all the three stages. It has turned out that more enhanced temperature gradient and surface wind convergence might be the important triggering factors for local severe precipitation. This finding is based on the member comparison of ECMWF ensemble forecast that successfully forecasted the local heavy and weak precipitation on 7 May 2017. Now, it is still difficult for numerical models to forecast the extremely heavy rains in short lead-time forecast under the condition of warm sector and, especially, the weak wind field. The main method for this is to enhance rainstorm disaster monitoring and early warning.
Based on the conventional observation data and the Guangzhou Doppler weather radar data, this article analyzed the synoptic background, mesoscale systems and predictability of the torrential rain process which occurred in Guangzhou on 7 May 2017. By contrasting the members of ECMWF ensemble forecast which successfully forecasted the local heavy precipitation on 7 May 2017 with the failed member, key triggering factor affected this process was investigated. The results show that the ambient condition and dynamic forcing were weaker on 7 May 2017. In the context of weak wind field, a convergence line formed between the warm flow from the sea and the cold downslope wind in the front of mountain, combined with the intense temperature gradient, initially triggering the generation of convective storms. Subsequently, the outflow of the preexisting thunderstorms impacted the warm, moist flow at boundary layer, inducing new convergence lines continually. Therefore the weakened storm-cells enhanced again and aroused the second stage of heavy rainfall. The first stages of the local torrential rain on 7 May 2017 was induced by short-lived severe local storm with a meso-vortex evolved from the steady and strong block-shaped echo. The second stage of this torrential rain was caused by long-lived heavy precipitation (HP-type) supercell storm. However, the band echo merging from a mass of new-born convective cells and moving eastward with the short-wave trough was responsible for the third stage of this torrential rain. The radar echo had the low-quality core vertical structure and warm cloud precipitation character during all the three stages. It has turned out that more enhanced temperature gradient and surface wind convergence might be the important triggering factors for local severe precipitation. This finding is based on the member comparison of ECMWF ensemble forecast that successfully forecasted the local heavy and weak precipitation on 7 May 2017. Now, it is still difficult for numerical models to forecast the extremely heavy rains in short lead-time forecast under the condition of warm sector and, especially, the weak wind field. The main method for this is to enhance rainstorm disaster monitoring and early warning.
2018, 44(4):500-510.
DOI: 10.7519/j.issn.1000-0526.2018.04.003
Abstract:
An extremely heavy rainfall event occurred in Guangzhou City on 7 May 2017. The record-breaking heavy precipitation caused severe property damage. To investigate the reasons/mechanisms responsible for the severe rainfall, a detailed observation analysis was performed in this study, based on the dataset collected by ground-based Doppler radars, two-dimensional video disdrometer (2DVD), microwave radio- meter and wind-profiling radar. The research results show that the ambient conditions prior to this event are characterized by small value of convective inhibition (CIN), low lifting condensation level (LCL), moderate convective available potential energy (CAPE), deep warm layer, and moist southerly flow. From midnight to dawn of 7 May 2017, initial convection was generated mainly by the terrain-blocked southerly flow, leading to the formation of quasi-stationary rainbands. From sunrise to early morning, new convective cells were repeatedly triggered along the precipitation-induced outflows boundary (i.e., back building process) and were continuously propagated backward (i.e., “echo training”). The observaiton of 2DVD further suggests that the surface heavy precipitation was composed of a high concentration of small raindrops and a few large raindrops. This microphysical information indicates that the high-precipitation-efficiency warm rain process was the main microphysical mechnism responsible for the heavy rainfall. This argument is supported with the low-centroid cumulonimbus structures observed by Doppler radar. It suggests that the continuously intensifying southerly flow played an important role in sustaining the convective system and producing the local heavy rainfall.
An extremely heavy rainfall event occurred in Guangzhou City on 7 May 2017. The record-breaking heavy precipitation caused severe property damage. To investigate the reasons/mechanisms responsible for the severe rainfall, a detailed observation analysis was performed in this study, based on the dataset collected by ground-based Doppler radars, two-dimensional video disdrometer (2DVD), microwave radio- meter and wind-profiling radar. The research results show that the ambient conditions prior to this event are characterized by small value of convective inhibition (CIN), low lifting condensation level (LCL), moderate convective available potential energy (CAPE), deep warm layer, and moist southerly flow. From midnight to dawn of 7 May 2017, initial convection was generated mainly by the terrain-blocked southerly flow, leading to the formation of quasi-stationary rainbands. From sunrise to early morning, new convective cells were repeatedly triggered along the precipitation-induced outflows boundary (i.e., back building process) and were continuously propagated backward (i.e., “echo training”). The observaiton of 2DVD further suggests that the surface heavy precipitation was composed of a high concentration of small raindrops and a few large raindrops. This microphysical information indicates that the high-precipitation-efficiency warm rain process was the main microphysical mechnism responsible for the heavy rainfall. This argument is supported with the low-centroid cumulonimbus structures observed by Doppler radar. It suggests that the continuously intensifying southerly flow played an important role in sustaining the convective system and producing the local heavy rainfall.
2018, 44(4):511-517.
DOI: 10.7519/j.issn.10000526.2018.04.004
Abstract:
The gradient velocity azimuth display (GVAD) technology has been developed to get over the influence of velocity aliasing in traditional velocity azimuth display (VAD) technology, which can calculate the vertical wind profiler (VWP) above the radar. This paper first introduced the theory of GVAD technology and conducted simulation, and analyzed about the GVAD technology, and then applied it into the case of typhoon and severe precipitation monitored by CINRAD. The simulation result demonstrated that the GVAD technology can overcome the velocity aliasing effectively compared with the traditional VAD technology, and the added noise also can be depressed through lowpass filter. The influence of aliasing velocity was got over in the two cases, but the noise and fluctuation in radial velocity were enlarged by the gradient of radial velocity, which affected the retrieval accuracy of wind although the lowpass filter was adopted, especially, the retrieval accuracy of wind speed was impacted. In the examples, the retrieved wind speed by GVAD technology was 2-3 m·s-1 less than the value by the traditional VAD technology. So, the influence of noise and fluctuation in CINRAD on GVAD technology should be further studied and reduced.
The gradient velocity azimuth display (GVAD) technology has been developed to get over the influence of velocity aliasing in traditional velocity azimuth display (VAD) technology, which can calculate the vertical wind profiler (VWP) above the radar. This paper first introduced the theory of GVAD technology and conducted simulation, and analyzed about the GVAD technology, and then applied it into the case of typhoon and severe precipitation monitored by CINRAD. The simulation result demonstrated that the GVAD technology can overcome the velocity aliasing effectively compared with the traditional VAD technology, and the added noise also can be depressed through lowpass filter. The influence of aliasing velocity was got over in the two cases, but the noise and fluctuation in radial velocity were enlarged by the gradient of radial velocity, which affected the retrieval accuracy of wind although the lowpass filter was adopted, especially, the retrieval accuracy of wind speed was impacted. In the examples, the retrieved wind speed by GVAD technology was 2-3 m·s-1 less than the value by the traditional VAD technology. So, the influence of noise and fluctuation in CINRAD on GVAD technology should be further studied and reduced.
2018, 44(4):518-525.
DOI: 10.7519/j.issn.1000-0526.2018.04.005
Abstract:
Using 60 m base-line binocular visible imager and scanning infrared imager, a dual-band whole sky cloud measurement and control system was built. According to the principle of binocular distance measurement, the binocular visible imager can accurately obtain the height of cloud base, and through comprehensive three-dimensional scanning the whole sky visible light cloud pictures were obtained. The scanning infrared imager can measure the temperature of cloud base and inverse the height of cloud base on the basis of the principle of atmospheric radiation transmission, and through comprehensive three-dimensional scanning, the whole sky infrared cloud pictures were obtained. Combined with the height of cloud base and the real-time correction of atmospheric temperature vertical decline rate, the binocular visible imager could measure the height of cloud base, improve the accuracy of inversion the height of cloud base of the scanning infrared imager, achieving the height of cloud base data fusion. Based on image fusion technology of wavelet multi-resolution analysis, the whole sky visible light and infrared cloud image are fused, improving cloud computing accuracy under the fog-haze conditions. Thus, cloud base height and cloud cover could be observed day and night.
Using 60 m base-line binocular visible imager and scanning infrared imager, a dual-band whole sky cloud measurement and control system was built. According to the principle of binocular distance measurement, the binocular visible imager can accurately obtain the height of cloud base, and through comprehensive three-dimensional scanning the whole sky visible light cloud pictures were obtained. The scanning infrared imager can measure the temperature of cloud base and inverse the height of cloud base on the basis of the principle of atmospheric radiation transmission, and through comprehensive three-dimensional scanning, the whole sky infrared cloud pictures were obtained. Combined with the height of cloud base and the real-time correction of atmospheric temperature vertical decline rate, the binocular visible imager could measure the height of cloud base, improve the accuracy of inversion the height of cloud base of the scanning infrared imager, achieving the height of cloud base data fusion. Based on image fusion technology of wavelet multi-resolution analysis, the whole sky visible light and infrared cloud image are fused, improving cloud computing accuracy under the fog-haze conditions. Thus, cloud base height and cloud cover could be observed day and night.
2018, 44(4):526-537.
DOI: 10.7519/j.issn.1000-0526.2018.04.006
Abstract:
Clear air echo (CAE) helps to understand the structure of wind, temperature and humidity of the atmosphere; dualpolarization Doppler weather radar provides a wealth of information in detecting atmosphere. In this paper, CAE of Nanjing University of Information Science and Techonogy, CPol dualpolarization radar in summer of 2015 is taken as cases to analyze the wind, temperature and humidity structure of atmosphere and the impact factors of CAE, combined with the sounding observations. The characteristics of radar reflectivity factor Z, radial velocity Vr and differential reflectivity factor ZDR of CAE are analyzed. The results show that the uneven distribution of refractive index caused by the temperature, pressure and humidity gradients and the turbulence enhancement induced by the background wind field can cause the clear sky echo. The echo mechanism is turbulent scattering. The differential reflectivity factor is affected by the Doppler effect. The ZDR of CAE has different characteristics in different wind and air turbulence situations. The results are helpful for better understanding the impact of atmospheric wind, temperature and humidity structure on radar electromagnetic scattering and the quality control of radar data.
Clear air echo (CAE) helps to understand the structure of wind, temperature and humidity of the atmosphere; dualpolarization Doppler weather radar provides a wealth of information in detecting atmosphere. In this paper, CAE of Nanjing University of Information Science and Techonogy, CPol dualpolarization radar in summer of 2015 is taken as cases to analyze the wind, temperature and humidity structure of atmosphere and the impact factors of CAE, combined with the sounding observations. The characteristics of radar reflectivity factor Z, radial velocity Vr and differential reflectivity factor ZDR of CAE are analyzed. The results show that the uneven distribution of refractive index caused by the temperature, pressure and humidity gradients and the turbulence enhancement induced by the background wind field can cause the clear sky echo. The echo mechanism is turbulent scattering. The differential reflectivity factor is affected by the Doppler effect. The ZDR of CAE has different characteristics in different wind and air turbulence situations. The results are helpful for better understanding the impact of atmospheric wind, temperature and humidity structure on radar electromagnetic scattering and the quality control of radar data.
2018, 44(4):538-547.
DOI: 10.7519/j.issn.1000-0526.2018.04.007
Abstract:
Precise estimation of precipitation in Taihang Mountains is crucial for understanding water cycle and providing support for water management in Haihe River Basin. By using Doppler radar, this study developed the Z-I relationships with different time windows (1-5 h) in three counties in eastern side of Taihang Mountains using radar reflectivity (Z) and rain gauge data (I) from June to September during 2013-2014. By dividing the 45 precipitation events into three categories: Light, moderate and heavy, precipitation was precisely estimated from different Z-I relationships under different categories. Take the rainfall event on 9 July 2013 as an example. It showed that (1) the errors of estimated precipitation from different time windows declined firstly, then rose up as the time windows moved from 1 h to 5 h, and the lowest error appeared in 2 h. (2) The 2 h Z-I relationship greatly improved the precision of moderate rain. (3) The estimation of heavy rain also improved when the 2 h Z-I relationship was applied to the rainfall event that happened on 9 July 2013.
Precise estimation of precipitation in Taihang Mountains is crucial for understanding water cycle and providing support for water management in Haihe River Basin. By using Doppler radar, this study developed the Z-I relationships with different time windows (1-5 h) in three counties in eastern side of Taihang Mountains using radar reflectivity (Z) and rain gauge data (I) from June to September during 2013-2014. By dividing the 45 precipitation events into three categories: Light, moderate and heavy, precipitation was precisely estimated from different Z-I relationships under different categories. Take the rainfall event on 9 July 2013 as an example. It showed that (1) the errors of estimated precipitation from different time windows declined firstly, then rose up as the time windows moved from 1 h to 5 h, and the lowest error appeared in 2 h. (2) The 2 h Z-I relationship greatly improved the precision of moderate rain. (3) The estimation of heavy rain also improved when the 2 h Z-I relationship was applied to the rainfall event that happened on 9 July 2013.
FENG Aiqing
,
ZENG Hongling
,
YIN Yizhou
,
SONG Yanling
,
LIU Yanju
,
WANG Yanjiao
,
WANG Ling
,
WANG Youmin
,
ZHU Xiaojin
,
CAI Wenyue
,
HOU Wei
,
HUANG Dapeng
,
GUO Yanjun
,
ZHANG Yingxian
,
ZHONG Hailing
,
LI Ying
,
SHI Shuai
,
ZHI Rong
,
HONG Jieli
,
WANG Dongqian
2018, 44(4):548-555.
DOI: 10.7519/j.issn.1000-0526.2018.04.008
Abstract:
Climate in China was at a normal level in 2017 and relatively fewer climate disasters occurred. Annual mean temperature 10.39℃ over China was 0.84℃ higher than normal years. In terms of high temperature, July and September had the highest temperature compared to that in the same periods since 1951, and the day highs at 113 stations broke the historical records. The annual mean precipitation over China was 641.3 mm, which increased 1.8% than normal years. Compared with the normal, precipitation was less in winter and more in summer, and approached normal in spring and autumn. The daily rainfall at 31 stations exceeded historical extremes, of which many stations were found in the areas where torrential rain seldom occurs. Besides, the continuous precipitation at 47 stations exceeded historical extremes. Precipitation in the preflood season in South China and in rainy season in Southwest China decreased by 9% and 4%, respectively. Precipitation in Meiyu season increased by 6% but was significantly less than that of 2015 and 2016. The rainy season in North China was shortened by 10 days and the rainfall was 28% less than normal. However, the autumn rainfall in West China increased by 49%, getting to the highest since 1984. The rainy season in Northeast China was short with rainfall 14% less than normal. Moreover, rainstorm processes presented frequently, and extremely severely, resulting in great damages. There were more landing typhoons, which were more frequent, concentrated and regionally overlapping. High temperature occurred for more days in China, appearing early in northern China but more intense in southern China. The effects of other disasters such as drought, freezing, snowstorms, dust in spring and haze were light.
Climate in China was at a normal level in 2017 and relatively fewer climate disasters occurred. Annual mean temperature 10.39℃ over China was 0.84℃ higher than normal years. In terms of high temperature, July and September had the highest temperature compared to that in the same periods since 1951, and the day highs at 113 stations broke the historical records. The annual mean precipitation over China was 641.3 mm, which increased 1.8% than normal years. Compared with the normal, precipitation was less in winter and more in summer, and approached normal in spring and autumn. The daily rainfall at 31 stations exceeded historical extremes, of which many stations were found in the areas where torrential rain seldom occurs. Besides, the continuous precipitation at 47 stations exceeded historical extremes. Precipitation in the preflood season in South China and in rainy season in Southwest China decreased by 9% and 4%, respectively. Precipitation in Meiyu season increased by 6% but was significantly less than that of 2015 and 2016. The rainy season in North China was shortened by 10 days and the rainfall was 28% less than normal. However, the autumn rainfall in West China increased by 49%, getting to the highest since 1984. The rainy season in Northeast China was short with rainfall 14% less than normal. Moreover, rainstorm processes presented frequently, and extremely severely, resulting in great damages. There were more landing typhoons, which were more frequent, concentrated and regionally overlapping. High temperature occurred for more days in China, appearing early in northern China but more intense in southern China. The effects of other disasters such as drought, freezing, snowstorms, dust in spring and haze were light.
2018, 44(4):556-564.
DOI: 10.7519/j.issn.1000-0526.2018.04.009
Abstract:
The concentration of greenhouse gases continued to increase in 2017, and the global mean temperature was 1.1℃ above the pre-industrial levels, making the year 2017 become the second warmest year on record and the warmest year not influenced by El Nino event. The cryosphere continued its contraction. The maximum sea-ice extent of Arctic sea in winter broke the lowest record while the sea-ice extent of Antarctic was near the record low level throughout the year. Global sea surface temperatures were significantly above the 1981-2010 average, and the global mean sea level kept rising steadily. The ocean heat content reached new record highs due to the intensified impact of ocean acidification. Many significant weather and climate events occurred in 2017, including a very active North Atlantic hurricane season, major monsoon floods in the Indian subcontinent, severe droughts in East Africa as well as some torrential rains, heat waves, cold waves and severe convective weather at regional or local scale worldwide. Econo-mic losses from the weather and climate related disasters set a new record in 2017. This paper summarizes the major events and its impact in 2017, and analyzes the formation causes of typical events including the exceptionally destructive hurricanes that occurred in rapid succession in the North Atlantic and the significant summer heat waves in the United States. Analysis of atmospheric circulation and external forcing shows that the positive SST anomalies of Caribbean and western tropical Atlantic enhanced the convective activity and decreased the vertical shear of wind speed, providing favorable background conditions for the development of hurricanes. In addition, the stage weakening of North American subtropical high caused four destructive hurricanes to make landfall successively in southern United States and the Caribbean region. In early July, the North American subtropical high that was influenced by the eastward extension and enhancement of subtropical westerly jet and the maintaining of Northeast Pacific cut-off low continued controlling the southwestern United States. This was the major reason for the summer heat wave on the west coast of the United States.
The concentration of greenhouse gases continued to increase in 2017, and the global mean temperature was 1.1℃ above the pre-industrial levels, making the year 2017 become the second warmest year on record and the warmest year not influenced by El Nino event. The cryosphere continued its contraction. The maximum sea-ice extent of Arctic sea in winter broke the lowest record while the sea-ice extent of Antarctic was near the record low level throughout the year. Global sea surface temperatures were significantly above the 1981-2010 average, and the global mean sea level kept rising steadily. The ocean heat content reached new record highs due to the intensified impact of ocean acidification. Many significant weather and climate events occurred in 2017, including a very active North Atlantic hurricane season, major monsoon floods in the Indian subcontinent, severe droughts in East Africa as well as some torrential rains, heat waves, cold waves and severe convective weather at regional or local scale worldwide. Econo-mic losses from the weather and climate related disasters set a new record in 2017. This paper summarizes the major events and its impact in 2017, and analyzes the formation causes of typical events including the exceptionally destructive hurricanes that occurred in rapid succession in the North Atlantic and the significant summer heat waves in the United States. Analysis of atmospheric circulation and external forcing shows that the positive SST anomalies of Caribbean and western tropical Atlantic enhanced the convective activity and decreased the vertical shear of wind speed, providing favorable background conditions for the development of hurricanes. In addition, the stage weakening of North American subtropical high caused four destructive hurricanes to make landfall successively in southern United States and the Caribbean region. In early July, the North American subtropical high that was influenced by the eastward extension and enhancement of subtropical westerly jet and the maintaining of Northeast Pacific cut-off low continued controlling the southwestern United States. This was the major reason for the summer heat wave on the west coast of the United States.
2018, 44(4):565-571.
DOI: 10.7519/j.issn.1000-0526.2018.04.010
Abstract:
During the summer of 2017 (June to August), the average precipitation over China was 348.6 mm, which is 8.1% more than normal (332.6 mm). Two rainfall bands were observed over eastern China. The East Asian summer monsoon (EASM) was weaker than normal, while the west Pacific subtropical high (WPSH) was significantly stronger than normal with southward ridge position. The “-+-” circulation pattern was located in Eurasian mid-high latitude with positive anomaly over the Lake of Baikal region. The cold SST in the middle-east of equatorial Pacific in the early winter changed to warm phase in the summer of 2017, and the 4th rain pattern, e.g. above normal rainfall in southern China, prevailed, while the blocking high over the Lake of Baikal appeared frequently. The major precursory signals of southward rainband are the weakened cold sea surface temperature (SST) in the middle-east of equator Pacific in early winter 2016, the positive triple SST in the North Atlantic in spring 2017, and the decreased snow cover in Eurasia from autumn to winter in 2016. Their common effects benefit the blocking high formation over the Lake of Baikal.
During the summer of 2017 (June to August), the average precipitation over China was 348.6 mm, which is 8.1% more than normal (332.6 mm). Two rainfall bands were observed over eastern China. The East Asian summer monsoon (EASM) was weaker than normal, while the west Pacific subtropical high (WPSH) was significantly stronger than normal with southward ridge position. The “-+-” circulation pattern was located in Eurasian mid-high latitude with positive anomaly over the Lake of Baikal region. The cold SST in the middle-east of equatorial Pacific in the early winter changed to warm phase in the summer of 2017, and the 4th rain pattern, e.g. above normal rainfall in southern China, prevailed, while the blocking high over the Lake of Baikal appeared frequently. The major precursory signals of southward rainband are the weakened cold sea surface temperature (SST) in the middle-east of equator Pacific in early winter 2016, the positive triple SST in the North Atlantic in spring 2017, and the decreased snow cover in Eurasia from autumn to winter in 2016. Their common effects benefit the blocking high formation over the Lake of Baikal.
2018, 44(4):572-581.
DOI: 10.7519/j.issn.1000-0526.2018.04.011
Abstract:
The stage characteristics of precipitation over China in the autumn of 2017 is obvious, and the significantly above-normal precipitation over northern China from September to October was mainly influenced by the East Asia circulation pattern anomaly. The distribution of 500 hPa height anomaly field in East Asia was “+-+” from high to low latitude. The polar height field was higher than normal, the polar vortex split and inclined to Northeast Asia, the area between Baikal Lake and Balkhash Lake was under a significantly low trough, and the West Pacific subtropical high was stronger, stretching more westward and northward than normal, which is favorable to the intensive autumn rainfall in West China. In addition, anticyclonic circulation anomaly over Korean Peninsula was conducive to guiding the cold and wet airflow along the easterly path to the area between the Yellow River and the Yangtze River, and to converging with the warm and wet airflow from the Bay of Bengal and the South China Sea. The water vapor flux convergence resulted in precipitation anomalies in the Huanghuai and Jianghuai regions. Further diagnosis shows that the tropical Middle East Pacific sea surface temperature turned cold in autumn, and the Walker circulation in the tropical Pacific increased obviously, which is beneficial to the westward and northward extension of the stronger West Pacific subtropical high. The positive phase of the tropical Indian Ocean dipole in September-October was favorable for the formation of anticyclonic circulation anomalies in the Bay of Bengal, and also beneficial to the westward and northward extension of the West Pacific subtropical high. Therefore, the influence of the external forcing signal of sea surface temperature and the circulation anomaly in the middle and high latitudes over East Asia led to more precipitation over northern China.
The stage characteristics of precipitation over China in the autumn of 2017 is obvious, and the significantly above-normal precipitation over northern China from September to October was mainly influenced by the East Asia circulation pattern anomaly. The distribution of 500 hPa height anomaly field in East Asia was “+-+” from high to low latitude. The polar height field was higher than normal, the polar vortex split and inclined to Northeast Asia, the area between Baikal Lake and Balkhash Lake was under a significantly low trough, and the West Pacific subtropical high was stronger, stretching more westward and northward than normal, which is favorable to the intensive autumn rainfall in West China. In addition, anticyclonic circulation anomaly over Korean Peninsula was conducive to guiding the cold and wet airflow along the easterly path to the area between the Yellow River and the Yangtze River, and to converging with the warm and wet airflow from the Bay of Bengal and the South China Sea. The water vapor flux convergence resulted in precipitation anomalies in the Huanghuai and Jianghuai regions. Further diagnosis shows that the tropical Middle East Pacific sea surface temperature turned cold in autumn, and the Walker circulation in the tropical Pacific increased obviously, which is beneficial to the westward and northward extension of the stronger West Pacific subtropical high. The positive phase of the tropical Indian Ocean dipole in September-October was favorable for the formation of anticyclonic circulation anomalies in the Bay of Bengal, and also beneficial to the westward and northward extension of the West Pacific subtropical high. Therefore, the influence of the external forcing signal of sea surface temperature and the circulation anomaly in the middle and high latitudes over East Asia led to more precipitation over northern China.
2018, 44(4):582-589.
DOI: 10.7519/j.issn.1000-0526.2018.04.012
Abstract:
Operational positioning, track, intensity and landfall point forecast errors of tropical cyclones (TCs) over Western North Pacific in 2016 are evaluated on the basis of CMA/STI’s “Best-track” dataset. The results show that the performance of TC positioning is a little larger than that in last year, with an average error by all methods is 24.9 km. The track forecast errors of both subjective and objective methods do not continue to decrease, which means the overall forecast performance in 2016 is slightly lower than that in the previous two years. The ECMWF-EPS, NCEP-GEFS and UKMO-EPS have better performance in track prediction than other ensemble prediction systems. No significant improvement in TC intensity prediction by subjective methods has been seen compared with previous years. However, the subjective methods have very small prediction error for the 24 h landfall point of Super Typhoon Sarika in Wanning, Hainan, and the errors are less than 15 km. The landfall prediction performance of global models is better than that of regional models.
Operational positioning, track, intensity and landfall point forecast errors of tropical cyclones (TCs) over Western North Pacific in 2016 are evaluated on the basis of CMA/STI’s “Best-track” dataset. The results show that the performance of TC positioning is a little larger than that in last year, with an average error by all methods is 24.9 km. The track forecast errors of both subjective and objective methods do not continue to decrease, which means the overall forecast performance in 2016 is slightly lower than that in the previous two years. The ECMWF-EPS, NCEP-GEFS and UKMO-EPS have better performance in track prediction than other ensemble prediction systems. No significant improvement in TC intensity prediction by subjective methods has been seen compared with previous years. However, the subjective methods have very small prediction error for the 24 h landfall point of Super Typhoon Sarika in Wanning, Hainan, and the errors are less than 15 km. The landfall prediction performance of global models is better than that of regional models.
2018, 44(4):590-596.
DOI: 10.7519/j.issn.1000-0526.2018.04.013
Abstract:
The main characteristics of the general atmospheric circulation in January 2018 are as follows. There were two polar vortex centers in the Northern Hemisphere. The circulation presented a four-wave pattern in middle-high latitudes. The East Asian trough behaved strongly. The monthly mean precipita-tion was 19.6 mm, 48.4% more than normal. Besides, the activities of cold air strengthened, causing the monthly mean temperature (-5.3℃) to turn from higher than normal to lower, and the mean temperature became 0.3℃ lower than normal (-5.0℃). In this month, precipitation was strengthened with more rainfall than normal, and freezing rain and snow weather occurred in southern China and Shaanxi Province, similar to the freezing disaster in southern China in 2008. Fog-haze event appeared in this month only once, from 13 to 22 January 2018, but was characterized by the widest range, the longest duration and the maximum intensity in the winter of 2017.
The main characteristics of the general atmospheric circulation in January 2018 are as follows. There were two polar vortex centers in the Northern Hemisphere. The circulation presented a four-wave pattern in middle-high latitudes. The East Asian trough behaved strongly. The monthly mean precipita-tion was 19.6 mm, 48.4% more than normal. Besides, the activities of cold air strengthened, causing the monthly mean temperature (-5.3℃) to turn from higher than normal to lower, and the mean temperature became 0.3℃ lower than normal (-5.0℃). In this month, precipitation was strengthened with more rainfall than normal, and freezing rain and snow weather occurred in southern China and Shaanxi Province, similar to the freezing disaster in southern China in 2008. Fog-haze event appeared in this month only once, from 13 to 22 January 2018, but was characterized by the widest range, the longest duration and the maximum intensity in the winter of 2017.
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ISSN:1000-0526 CN:11-2282/P