ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 39,Issue 8,2013 Table of Contents
2013, 39(8):945-954.
DOI: 10.7519/j.issn.1000-0526.2013.08.001
Abstract:
One long lasting squall line storm that struck North China severely in the afternoon of 23 June 2008 is analyzed based on various observation and analysis data collected by radar, satellite, and auto weather stations, etc. This servere convection developed in the background of cold vortex in summer, and an isolated MCS evolved near the sub cold front. Strong convective cells and several super cell storms were active in premature period of the squll line, and the organization of convection is attributed to the surface wind convergence line or front. After the main cold front left at the night of 22 June, the easterly and southerly wind rearside of the high pressure transported warm moist air into the increasing intensity of the frontal zone. On the other hand, from the afternoon of 23 June, a short wave trough near the Hetao Area with high relative humidity developed in the mid and lower levels of troposphere, corresponding to the sub cold front moving towards North China and conecting to the initiation of the convection, and the updraft motion due to the front was diagnosed by the secondary circulation equations. In the rearside of the cyclone, the dry and cold air with obvious subsiding made strong potential instability which is favorable for the convection initiation and formation of strong surface wind. By analyzing the vertical wind profile and the movement of squall line, it is indicated that the boundary moves approximately at the same speed as the lower level vertical shear, so MCS maintains the strength and the lasting time.
One long lasting squall line storm that struck North China severely in the afternoon of 23 June 2008 is analyzed based on various observation and analysis data collected by radar, satellite, and auto weather stations, etc. This servere convection developed in the background of cold vortex in summer, and an isolated MCS evolved near the sub cold front. Strong convective cells and several super cell storms were active in premature period of the squll line, and the organization of convection is attributed to the surface wind convergence line or front. After the main cold front left at the night of 22 June, the easterly and southerly wind rearside of the high pressure transported warm moist air into the increasing intensity of the frontal zone. On the other hand, from the afternoon of 23 June, a short wave trough near the Hetao Area with high relative humidity developed in the mid and lower levels of troposphere, corresponding to the sub cold front moving towards North China and conecting to the initiation of the convection, and the updraft motion due to the front was diagnosed by the secondary circulation equations. In the rearside of the cyclone, the dry and cold air with obvious subsiding made strong potential instability which is favorable for the convection initiation and formation of strong surface wind. By analyzing the vertical wind profile and the movement of squall line, it is indicated that the boundary moves approximately at the same speed as the lower level vertical shear, so MCS maintains the strength and the lasting time.
2013, 39(8):955-964.
DOI: 10.7519/j.issn.1000-0526.2013.08.002
Abstract:
Based on the NCEP FNL data, the mesoscale model WRF is used to simulate the process of a cold air snowstorm occurred in Shandong Peninsula during 29-30 December 2010. High spatiotemporal resolution data from model output are adopted to analyze mesoscale and microphysical characteristics of the cold air snowstorm. The results indicate that this snowstorm occurs under the background of significant air sea temperature differences, furthermore heat and moisture are transported from the sea surface of Bohai sea to cold air, which is caused by turbulence. Vapor from the central part of Bohai Sea are transported to the northeast of Shandong Peninsula, where the moisture convergence layer is thin, below 800 hPa. The duration of the maximum value of specific humidity and the saturated layers of relative humidity is corresponding to the heavy snowfall period. The frontogenesis of mesoscale costal front, which shows a strong convergence zone of northerly and westerly winds in the horizontal structure, plays a significant role in the heavy snow process. The ascending motions in the local circumfluence of the costal front directly decide the area and intensity of the snowstorm. In addition, the updraft is the trigger of instable energy and the mechanism of shallow convective snow. The droplets distribute mainly below 600 hPa and their maximum appears in the 850-900 hPa, respectively, which agrees with the structure of the shallow convection. In addition, the contents of droplets are different from each other, among which the contents of snow and graupel are the most.
Based on the NCEP FNL data, the mesoscale model WRF is used to simulate the process of a cold air snowstorm occurred in Shandong Peninsula during 29-30 December 2010. High spatiotemporal resolution data from model output are adopted to analyze mesoscale and microphysical characteristics of the cold air snowstorm. The results indicate that this snowstorm occurs under the background of significant air sea temperature differences, furthermore heat and moisture are transported from the sea surface of Bohai sea to cold air, which is caused by turbulence. Vapor from the central part of Bohai Sea are transported to the northeast of Shandong Peninsula, where the moisture convergence layer is thin, below 800 hPa. The duration of the maximum value of specific humidity and the saturated layers of relative humidity is corresponding to the heavy snowfall period. The frontogenesis of mesoscale costal front, which shows a strong convergence zone of northerly and westerly winds in the horizontal structure, plays a significant role in the heavy snow process. The ascending motions in the local circumfluence of the costal front directly decide the area and intensity of the snowstorm. In addition, the updraft is the trigger of instable energy and the mechanism of shallow convective snow. The droplets distribute mainly below 600 hPa and their maximum appears in the 850-900 hPa, respectively, which agrees with the structure of the shallow convection. In addition, the contents of droplets are different from each other, among which the contents of snow and graupel are the most.
2013, 39(8):965-974.
DOI: 10.7519/j.issn.1000-0526.2013.08.003
Abstract:
Super Typhoon Muifa (1109) got enhanced and weakened twice during its 12 d lifetime. The intensity was predicted stronger during 3-7 August because the high SST of Kuroshio was considered. In this paper, comprehensive and quantitative diagnostic analyses on main factors affecting typhoon intensity are performed. The results suggest that though the ocean thermal conditions are certainly favorable for the typhoon, the ambient field conditions, both the cold air advection and the ambient vertical wind shear, are unfavorable. The negative feedback which well matches the process is the main cause of the weakening.
Super Typhoon Muifa (1109) got enhanced and weakened twice during its 12 d lifetime. The intensity was predicted stronger during 3-7 August because the high SST of Kuroshio was considered. In this paper, comprehensive and quantitative diagnostic analyses on main factors affecting typhoon intensity are performed. The results suggest that though the ocean thermal conditions are certainly favorable for the typhoon, the ambient field conditions, both the cold air advection and the ambient vertical wind shear, are unfavorable. The negative feedback which well matches the process is the main cause of the weakening.
2013, 39(8):975-987.
DOI: 10.7519/j.issn.1000-0526.2013.08.004
Abstract:
Using the GRAPES_Meso model, the numerical simulation about the persistent flood rainstorm is carried out in Shaanxi and Sichuan Provinces from 16 to 18 September 2011. By comparing the three sets of sensitivity test results, it is revealed that the interaction between the airflow and the terrain contributes to the disaster rainstorm, and the detailed results are as follows: (1) by the common influence of typhoon and Mongolia high pressure during 16 to 18 September, an eastern water vapor channel is formed over the Yellow Sea and the Bohai Sea at 850 hPa, making a large quantity of moisture through the North China Plain transported to the West China region. The vapor is divided into two parts by Qinling Mountain: the north one and the south one. The north vapor is blocked and uplifted by Qinling Mountain and forms a water vapor convergence center. The south one enters the Hanzhong Plain and is influenced by the “bell mouth” terrain, which results in convergence and upward. (2) The parallel alternate ridges and valleys create positive and negative vertical wind band, forming a strong suction effect in the vertical direction, and moreover a plenty of water vapor convergence occurs in the same area, triggering the large scale severe precipitation. (3) The altitude and the sufface relief have great influence on rainfalls, and the greater the surface relief is when the altitude is the same, the easier rainstorm occurs.
Using the GRAPES_Meso model, the numerical simulation about the persistent flood rainstorm is carried out in Shaanxi and Sichuan Provinces from 16 to 18 September 2011. By comparing the three sets of sensitivity test results, it is revealed that the interaction between the airflow and the terrain contributes to the disaster rainstorm, and the detailed results are as follows: (1) by the common influence of typhoon and Mongolia high pressure during 16 to 18 September, an eastern water vapor channel is formed over the Yellow Sea and the Bohai Sea at 850 hPa, making a large quantity of moisture through the North China Plain transported to the West China region. The vapor is divided into two parts by Qinling Mountain: the north one and the south one. The north vapor is blocked and uplifted by Qinling Mountain and forms a water vapor convergence center. The south one enters the Hanzhong Plain and is influenced by the “bell mouth” terrain, which results in convergence and upward. (2) The parallel alternate ridges and valleys create positive and negative vertical wind band, forming a strong suction effect in the vertical direction, and moreover a plenty of water vapor convergence occurs in the same area, triggering the large scale severe precipitation. (3) The altitude and the sufface relief have great influence on rainfalls, and the greater the surface relief is when the altitude is the same, the easier rainstorm occurs.
2013, 39(8):988-994.
DOI: 10.7519/j.issn.1000-0526.2013.08.005
Abstract:
A high temperature weather process occurred in central and northern part of Ningxia from August 6 to 10 in 2011. Using conventional observation data, hourly ground observation data of mesoscale regional automatical weather stations and NCEP/NCAR 1°×1° reanalysis data, this paper analyzes the horizontal and vertical structure of the Tibetan high which has close relationship with the high temperature weather process. The results show that： Tibetan high is a thick warm negative vorticity system, whose inphase superpostion with the westerly long wave high pressure ridge strengthens the long wave high pressure ridge and warm high pressure over Tibetan plateau. The 586 dagpm line of the periphery of Tibetan high passes over Tibetan Plateau and maintains steadily near 85°-105°E, and the north boundary of Tibetan high extends to 40°-42°N. Most parts of Northwest China are under the control of Tibetan high over 584 dagpm and surface thermal low under 1000 hPa for a very long time. Polar front jet and upper level jet interact over Tibetan high, and the circulation converging in upper level and diverging in low level results in strong sinking motion over eastern Tibetan Plateau. It was cloudless in Ningxia where is located in that sinking motion region with low humidity, relatively high wind speed, strong warming and evaporating at ground and the surface sensible heat was much higher than latent heat. All these factors are benefitial for the occurrence of consistent high temperature weather. Finally, this paper proposes a conceptual model for summer high temperature weather in Ningxia.
A high temperature weather process occurred in central and northern part of Ningxia from August 6 to 10 in 2011. Using conventional observation data, hourly ground observation data of mesoscale regional automatical weather stations and NCEP/NCAR 1°×1° reanalysis data, this paper analyzes the horizontal and vertical structure of the Tibetan high which has close relationship with the high temperature weather process. The results show that： Tibetan high is a thick warm negative vorticity system, whose inphase superpostion with the westerly long wave high pressure ridge strengthens the long wave high pressure ridge and warm high pressure over Tibetan plateau. The 586 dagpm line of the periphery of Tibetan high passes over Tibetan Plateau and maintains steadily near 85°-105°E, and the north boundary of Tibetan high extends to 40°-42°N. Most parts of Northwest China are under the control of Tibetan high over 584 dagpm and surface thermal low under 1000 hPa for a very long time. Polar front jet and upper level jet interact over Tibetan high, and the circulation converging in upper level and diverging in low level results in strong sinking motion over eastern Tibetan Plateau. It was cloudless in Ningxia where is located in that sinking motion region with low humidity, relatively high wind speed, strong warming and evaporating at ground and the surface sensible heat was much higher than latent heat. All these factors are benefitial for the occurrence of consistent high temperature weather. Finally, this paper proposes a conceptual model for summer high temperature weather in Ningxia.
2013, 39(8):995-1003.
DOI: 10.7519/j.issn.1000-0526.2013.08.006
Abstract:
Based on JTWC tropical cyclone data, NCEP reanalysis data and Hadly Center SST data, the abnormal year’s climatic features and background for accumulated cyclone energy (ACE) over the Northwest Pacific are analyzed. The results show that ACE has significant interannual and interdecadal variations. In the abnormal years of ACE, due to the notable difference of the longitude that the eastern flow from monsoon trough reaches, the passageway and intensity difference of cross equatorical flows, and the location difference of subtropical high, the frequency, intensity and the persistence of typhoons are different. The abnormality of ACE is closely connected with tropical Pacific SSTA in May-August. When SST anomaly at equatorial central and eastern Pacific is positive and that of Southwest Pacific is negative, as a result of favorable cross equatorical southern flow provided by downflow branches of abnormal Walker and Hadley Circulations, the year’s ACE tends to be positively abnormal. Otherwise, ACE tends to be negatively abnormal.
Based on JTWC tropical cyclone data, NCEP reanalysis data and Hadly Center SST data, the abnormal year’s climatic features and background for accumulated cyclone energy (ACE) over the Northwest Pacific are analyzed. The results show that ACE has significant interannual and interdecadal variations. In the abnormal years of ACE, due to the notable difference of the longitude that the eastern flow from monsoon trough reaches, the passageway and intensity difference of cross equatorical flows, and the location difference of subtropical high, the frequency, intensity and the persistence of typhoons are different. The abnormality of ACE is closely connected with tropical Pacific SSTA in May-August. When SST anomaly at equatorial central and eastern Pacific is positive and that of Southwest Pacific is negative, as a result of favorable cross equatorical southern flow provided by downflow branches of abnormal Walker and Hadley Circulations, the year’s ACE tends to be positively abnormal. Otherwise, ACE tends to be negatively abnormal.
2013, 39(8):1004-1013.
DOI: 10.7519/j.issn.1000-0526.2013.08.007
Abstract:
The bright band at 0℃ level is a phenomenon of sudden enhancement of the radar reflectivity due to the melting of snowflakes or ice crystals near the 0℃ isotherm. It is an important factor for the quality of radar data, often causing the over estimation of precipitation. The altitude of Tibetan Plateau is high and the 0℃ level there is low, and the precipitation scopes under the layer are very limited, so the impact of bright band on the precipitation estimate of radar over the Tibetan Plateau is quite remarkable. Therefore, identifying and correcting the bright band automatically is of great significance to improve the precision of radar based quantitative precipitation estimation (QPE) over Tibetan Plateau. Considering the serious blockage of radar beam over Tibetan Plateau, this paper identifies the 0℃ level bright band by calculating the vertical profile of reflectivity and corrects the bright band areas, using the hybrid scan reflectivity before and after the correction to estimate QPE respectively and analyzing the effect of bright band correction on QPE errors. The results show that the height of the bright band from radar is usually several hundred meters under the 0℃ level. Before the bright band correction, the vertical profile of reflectivity curves obviously near the 0℃ layer, causing very clear over estimation of precipitation, but after the bright band correction, the obvious curve of the vertical profile of reflectivity disappears near the 0℃ level so that the radar based QPE is more consistent to the gauge observations and the QPE errors are reduced significantly.
The bright band at 0℃ level is a phenomenon of sudden enhancement of the radar reflectivity due to the melting of snowflakes or ice crystals near the 0℃ isotherm. It is an important factor for the quality of radar data, often causing the over estimation of precipitation. The altitude of Tibetan Plateau is high and the 0℃ level there is low, and the precipitation scopes under the layer are very limited, so the impact of bright band on the precipitation estimate of radar over the Tibetan Plateau is quite remarkable. Therefore, identifying and correcting the bright band automatically is of great significance to improve the precision of radar based quantitative precipitation estimation (QPE) over Tibetan Plateau. Considering the serious blockage of radar beam over Tibetan Plateau, this paper identifies the 0℃ level bright band by calculating the vertical profile of reflectivity and corrects the bright band areas, using the hybrid scan reflectivity before and after the correction to estimate QPE respectively and analyzing the effect of bright band correction on QPE errors. The results show that the height of the bright band from radar is usually several hundred meters under the 0℃ level. Before the bright band correction, the vertical profile of reflectivity curves obviously near the 0℃ layer, causing very clear over estimation of precipitation, but after the bright band correction, the obvious curve of the vertical profile of reflectivity disappears near the 0℃ level so that the radar based QPE is more consistent to the gauge observations and the QPE errors are reduced significantly.
2013, 39(8):1014-1022.
DOI: 10.7519/j.issn.1000-0526.2013.08.008
Abstract:
One snowstorm process in January 19-20, 2011 was analyzed by using Doppler radar data from Jiujiang and Nanchang, observation data and NCEP reanalysis data (0.5°×0.5°). The results showed that the ascending of strong and ample warm wet southwest airflow ahead of south trough and along the low level return cold airflow over the Yangtze River Basin is the dynamic mechanism responsible for this heavy snow. The secondary circulation is produced by the coupling of low and upper level jets. The positive vorticity advection over 700 hPa and the low level warm advection denote the strong upward motion. The stable θse isoline dense section at 700 hPa indicates that the frontal zone is maintained. The low level warm advection, the increase of wind velocity in the middle and lower level and the decrease of jet stream center are good indices for the enhancement of snow echoes. The low level warm advection structure develops into cold advection structure, indicating the snow echoes get weakened. The abnormal high radar reflectivity is not caused by large water droplets and solid precipitation particles such as hails. Ice crystals melt as they fall through warm layer above 0℃ coalescing, aggregating and growing by themselves, which leads to abnormal high radar reflectivity similar to large water droplets, without convective weather such as thunders. The strong upward motion in the middle and lower troposphere and the feedback mechanism of latent heat create partial high radar reflectivity, so producing the snow storm.
One snowstorm process in January 19-20, 2011 was analyzed by using Doppler radar data from Jiujiang and Nanchang, observation data and NCEP reanalysis data (0.5°×0.5°). The results showed that the ascending of strong and ample warm wet southwest airflow ahead of south trough and along the low level return cold airflow over the Yangtze River Basin is the dynamic mechanism responsible for this heavy snow. The secondary circulation is produced by the coupling of low and upper level jets. The positive vorticity advection over 700 hPa and the low level warm advection denote the strong upward motion. The stable θse isoline dense section at 700 hPa indicates that the frontal zone is maintained. The low level warm advection, the increase of wind velocity in the middle and lower level and the decrease of jet stream center are good indices for the enhancement of snow echoes. The low level warm advection structure develops into cold advection structure, indicating the snow echoes get weakened. The abnormal high radar reflectivity is not caused by large water droplets and solid precipitation particles such as hails. Ice crystals melt as they fall through warm layer above 0℃ coalescing, aggregating and growing by themselves, which leads to abnormal high radar reflectivity similar to large water droplets, without convective weather such as thunders. The strong upward motion in the middle and lower troposphere and the feedback mechanism of latent heat create partial high radar reflectivity, so producing the snow storm.
2013, 39(8):1023-1030.
DOI: 10.7519/j.issn.1000-0526.2013.08.009
Abstract:
The situation and mesoscale wind field of the blizzard that occurred from 10 to 12 November 2009 in Shijiazhuang are analyzed in detail by using the conventional observation, radar and 4D VAR inversion wind field data. This snowstorm can be divided into two phases according to the influence system: backflow and west trough snowfall. The backflow snowfall is the main period when the snowfall in the western mountains is obviously heavier than in the eastern plains. In comparison, the west trough snowfall is more uniform in the whole region. It can be seen from the radar reflectivity factor and radial velocity on 10 November that the echoes have convective characteristics, continuously moving towards Shijiazhuang from the western mountain, generating the “train effect” and causing the intensive snow in the urban and western areas. From 11 to 12, the intensity of snowfall is abated along with echoes weakening. On the basis of the 4D VAR inversion wind field, the following results are obtained: (1) The retrieval wind field can accurately demonstrate the time and height of east wind, and the whole influence process of west trough, which is a good reference for forecasters to extrapolate the intensity of snowfall qualitatively. (2) There is a narrow east wind band in low level retrieval horizontal wind field, and the echoes move from west to east along the east wind band. The urban area of Shijiazhang is influenced for a long time due to its location near the north northeast “backflow wall” where the echoes are slowed down and piled up. Meanwhile, the echoes are strengthened or maintained around Shijiazhuang since there exist wind direction and wind speed convergences. (3) In the vertical profile of retrieval wind field, there is an “anticyclone” over the low level east wind during the backflow snowfall period, and the strong echoes are located in the “anticyclone” zone.
The situation and mesoscale wind field of the blizzard that occurred from 10 to 12 November 2009 in Shijiazhuang are analyzed in detail by using the conventional observation, radar and 4D VAR inversion wind field data. This snowstorm can be divided into two phases according to the influence system: backflow and west trough snowfall. The backflow snowfall is the main period when the snowfall in the western mountains is obviously heavier than in the eastern plains. In comparison, the west trough snowfall is more uniform in the whole region. It can be seen from the radar reflectivity factor and radial velocity on 10 November that the echoes have convective characteristics, continuously moving towards Shijiazhuang from the western mountain, generating the “train effect” and causing the intensive snow in the urban and western areas. From 11 to 12, the intensity of snowfall is abated along with echoes weakening. On the basis of the 4D VAR inversion wind field, the following results are obtained: (1) The retrieval wind field can accurately demonstrate the time and height of east wind, and the whole influence process of west trough, which is a good reference for forecasters to extrapolate the intensity of snowfall qualitatively. (2) There is a narrow east wind band in low level retrieval horizontal wind field, and the echoes move from west to east along the east wind band. The urban area of Shijiazhang is influenced for a long time due to its location near the north northeast “backflow wall” where the echoes are slowed down and piled up. Meanwhile, the echoes are strengthened or maintained around Shijiazhuang since there exist wind direction and wind speed convergences. (3) In the vertical profile of retrieval wind field, there is an “anticyclone” over the low level east wind during the backflow snowfall period, and the strong echoes are located in the “anticyclone” zone.
2013, 39(8):1031-1041.
DOI: 10.7519/j.issn.1000-0526.2013.08.010
Abstract:
Based on the rotated empirical orthogonal function (REOF) method, the precipitation patterns during the “Dragon Boat Water” from 1961 to 2009 are analyzed. What’s more, the spatial and temporal characteristics are discussed by adopting linear tendency estimation, experimental mode decomposition (EMD), Morlet wavelet analysis and Mann Kendall test. The results show that there are three kinds preferred precipitation patterns in Southeast Coast, the North region and Southwest Coast, respectively, and all of them show 6-8 year periodic oscillations. Southeast Coast has decreasing trend in precipitation, while the North region and Southwest Coast share an increasing trend in the past 49 years. However, the precipitation “dragon boat water” has occurred more frequently in the North region since mid 1990s, and the rainfalls in Southeast and Southwest Coast have shown positive anomalies in recent several years. Two abrupt jumps occurred in mid 1970s and early 1990s in Southeast Coast and the North region, respectively, but there was no obvious change in Southwest Coast. Finally, the different atmospheric circulation features are compared from the aspects of Northwest Pacific subtropical high, blocking high, monsoon trough, low layer shear, vertical velocity speed and the total water vapor transport.
Based on the rotated empirical orthogonal function (REOF) method, the precipitation patterns during the “Dragon Boat Water” from 1961 to 2009 are analyzed. What’s more, the spatial and temporal characteristics are discussed by adopting linear tendency estimation, experimental mode decomposition (EMD), Morlet wavelet analysis and Mann Kendall test. The results show that there are three kinds preferred precipitation patterns in Southeast Coast, the North region and Southwest Coast, respectively, and all of them show 6-8 year periodic oscillations. Southeast Coast has decreasing trend in precipitation, while the North region and Southwest Coast share an increasing trend in the past 49 years. However, the precipitation “dragon boat water” has occurred more frequently in the North region since mid 1990s, and the rainfalls in Southeast and Southwest Coast have shown positive anomalies in recent several years. Two abrupt jumps occurred in mid 1970s and early 1990s in Southeast Coast and the North region, respectively, but there was no obvious change in Southwest Coast. Finally, the different atmospheric circulation features are compared from the aspects of Northwest Pacific subtropical high, blocking high, monsoon trough, low layer shear, vertical velocity speed and the total water vapor transport.
2013, 39(8):1042-1049.
DOI: 10.7519/j.issn.1000-0526.2013.08.011
Abstract:
Based on the visibility data of 99 weather stations in Hebei Province during l980 to 2010, the change characteristics of low visibility events were analyzed, providing references for the environmental protection and comprehensive management in Hebei Province. The results show that the low visibility days appear fewer in northern Hebei， but more in southern Hebei, especially in the eastern part of Taihang Mountains, where the top 6 cities with the most low visibility days are located. In 1980s, the low visibility events are relatively fewer, but have a rapid growth in 1990s, then along with the attention to environmental protection, the low visibility days have been dropping since 2000. Comparatively, the low visibility days in December and in January are more, occupying 37.9% of a whole year, but are fewer in May and June, accounting for about 5%. The weather stations that show an increasing trend of low visibility days are mainly located in the eastern part of Taihang Mountains and southeastern part of Zhangjiakou where the industry is developed and the transportation is convenient. The weather stations showing a decreasing trend of low visibility days are mainly located in the plateau of north of Hebei Province and Hengshui Region， as well as the coastal areas of Qinhuangdao and Cangzhou. The relative humidity and visibility have a remarkably negative correlation. The events of visibility under 2 km are seen mainly in the days with the relative humidity above 80% while the events of visibility above 5 km are mainly appear when the relative humidity is under 60%.
Based on the visibility data of 99 weather stations in Hebei Province during l980 to 2010, the change characteristics of low visibility events were analyzed, providing references for the environmental protection and comprehensive management in Hebei Province. The results show that the low visibility days appear fewer in northern Hebei， but more in southern Hebei, especially in the eastern part of Taihang Mountains, where the top 6 cities with the most low visibility days are located. In 1980s, the low visibility events are relatively fewer, but have a rapid growth in 1990s, then along with the attention to environmental protection, the low visibility days have been dropping since 2000. Comparatively, the low visibility days in December and in January are more, occupying 37.9% of a whole year, but are fewer in May and June, accounting for about 5%. The weather stations that show an increasing trend of low visibility days are mainly located in the eastern part of Taihang Mountains and southeastern part of Zhangjiakou where the industry is developed and the transportation is convenient. The weather stations showing a decreasing trend of low visibility days are mainly located in the plateau of north of Hebei Province and Hengshui Region， as well as the coastal areas of Qinhuangdao and Cangzhou. The relative humidity and visibility have a remarkably negative correlation. The events of visibility under 2 km are seen mainly in the days with the relative humidity above 80% while the events of visibility above 5 km are mainly appear when the relative humidity is under 60%.
2013, 39(8):1050-1056.
DOI: 10.7519/j.issn.1000-0526.2013.08.012
Abstract:
The Flood Situation Reports released by Beijing Municipal Flood and Drought Control Headquarters Office from 2007 to 2011, daily rainfall data from 20 climate stations and hourly rainfall data from more than 200 automatic weather stations in Beijing are used to make statistical analyses of correlation between heavy rainfall intensity and road waterlogging in Beijing in the past five years, in order to find out the rainfall features, critical indicator of hourly rainfall intensity and road waterlogging caused by rainfall in two hours in Beijing urban area. After applied in road waterlogging 10 times during the flood season (June to August) in 2011, this critical indicator of road waterlogging is proved to have good reference values for road waterlogging forecasting service in the future.
The Flood Situation Reports released by Beijing Municipal Flood and Drought Control Headquarters Office from 2007 to 2011, daily rainfall data from 20 climate stations and hourly rainfall data from more than 200 automatic weather stations in Beijing are used to make statistical analyses of correlation between heavy rainfall intensity and road waterlogging in Beijing in the past five years, in order to find out the rainfall features, critical indicator of hourly rainfall intensity and road waterlogging caused by rainfall in two hours in Beijing urban area. After applied in road waterlogging 10 times during the flood season (June to August) in 2011, this critical indicator of road waterlogging is proved to have good reference values for road waterlogging forecasting service in the future.
2013, 39(8):1057-1068.
DOI: 10.7519/j.issn.1000-0526.2013.08.013
Abstract:
A convective precipitation is simulated by using a 3 D convective cloud salt seeding model. The model considers the microphysical processes between salt particles, liquid and ice particles. The simulation results indicate that seeding at a single time with seeding particle size of 20 μm can produce a good seeding effect, which can achieve 20% precipitation enhancement. Increasing the number of seeding time causes precipitation reduction. Graupel melting into rain is the main mechanism of raindrop increasing, and graupel collecting raindrop is the main mechanism of graupel increasing. The two processes get enhanced after seeding. Seeding brings changes to mixing ratios of cloud water, ice crystal, graupel and rain. The sizes of rain and graupel gain in seeded cloud.
A convective precipitation is simulated by using a 3 D convective cloud salt seeding model. The model considers the microphysical processes between salt particles, liquid and ice particles. The simulation results indicate that seeding at a single time with seeding particle size of 20 μm can produce a good seeding effect, which can achieve 20% precipitation enhancement. Increasing the number of seeding time causes precipitation reduction. Graupel melting into rain is the main mechanism of raindrop increasing, and graupel collecting raindrop is the main mechanism of graupel increasing. The two processes get enhanced after seeding. Seeding brings changes to mixing ratios of cloud water, ice crystal, graupel and rain. The sizes of rain and graupel gain in seeded cloud.
2013, 39(8):1069-1075.
DOI: 10.7519/j.issn.1000-0526.2013.08.014
Abstract:
Since national automatic weather stations were run in dual sets, the algorithm to make multiple sets of data generated by the double automatic stations into one set of data has become an important issue that must be resolved before the double stations are put into operation. This article presents the master and slave law based on the space consistency from the standpoint of the data of “hot spare”, and also presents two data processing algorithms based on revised synthesis method according to spatial consistency difference from basic statistical principles and the angle to ensure that the data are continuous. We evaluate the integrity and differences of the results by the two algorithms using the hourly temperature data from Xiuning Station. Many assessment methods are used including missing rate, the mean of difference values, the standard deviation of difference values, the consistency rate of difference, ultra slip and coarse slip etc. The results show that both of the two algorithms can guarantee the integrity of the data well, and the results of these algorithms are closer to the “true value” and also can reflect the true situation of the atmosphere. Comparatively, however, the result based on the difference between the revised synthesis is better. Finally, the double station observation data collected from Kuche, Anqing and other three stations are used to assess the spatial consistency method which involves the algorithm. It is indicated that this method is effective in general. Especially, it has a better discriminant ability in humidity, pressure and temperature, but is less effective in distinguishing wind speed, which may be affected by local topography or the impact of selected reference stations.
Since national automatic weather stations were run in dual sets, the algorithm to make multiple sets of data generated by the double automatic stations into one set of data has become an important issue that must be resolved before the double stations are put into operation. This article presents the master and slave law based on the space consistency from the standpoint of the data of “hot spare”, and also presents two data processing algorithms based on revised synthesis method according to spatial consistency difference from basic statistical principles and the angle to ensure that the data are continuous. We evaluate the integrity and differences of the results by the two algorithms using the hourly temperature data from Xiuning Station. Many assessment methods are used including missing rate, the mean of difference values, the standard deviation of difference values, the consistency rate of difference, ultra slip and coarse slip etc. The results show that both of the two algorithms can guarantee the integrity of the data well, and the results of these algorithms are closer to the “true value” and also can reflect the true situation of the atmosphere. Comparatively, however, the result based on the difference between the revised synthesis is better. Finally, the double station observation data collected from Kuche, Anqing and other three stations are used to assess the spatial consistency method which involves the algorithm. It is indicated that this method is effective in general. Especially, it has a better discriminant ability in humidity, pressure and temperature, but is less effective in distinguishing wind speed, which may be affected by local topography or the impact of selected reference stations.
2013, 39(8):1076-1082.
DOI: 10.7519/j.issn.1000-0526.2013.08.015
Abstract:
In order to improve the ability to apply the products of T639, a synoptic verification on its medium range forecasting in Spring 2013 is made in comparison with the NWP of ECMWF and Japan models. The results show that all the three models have good performances on the aspect of predicting the large scale circulation evolution and adjustment in Asian. As a whole, the ECMWF model is better in forecasting most weather systems compared with the T639 and Japan models. Taking the sandstorm process during 8-9 March 2013 as a case, it is found that the ECMWF model is more effective than the other two models in medium range forecasting of the surface high pressure system that causes the sand and dust weather process this time.
In order to improve the ability to apply the products of T639, a synoptic verification on its medium range forecasting in Spring 2013 is made in comparison with the NWP of ECMWF and Japan models. The results show that all the three models have good performances on the aspect of predicting the large scale circulation evolution and adjustment in Asian. As a whole, the ECMWF model is better in forecasting most weather systems compared with the T639 and Japan models. Taking the sandstorm process during 8-9 March 2013 as a case, it is found that the ECMWF model is more effective than the other two models in medium range forecasting of the surface high pressure system that causes the sand and dust weather process this time.
2013, 39(8):1083-1088.
DOI: 10.7519/j.issn.1000-0526.2013.08.016
Abstract:
The following are the main characteristics of the general circulation of atmosphere in May 2013. There is one polar vortex center in the Northern Hemisphere, and the strength is 2-4 dagpm lower than normal years. The circulation presents a four wave pattern in high latitudes, of which there is a cut off low votex in Novosibirsk, bringing cold air mass to Northern Xinjiang. The south branch trough is more active than normal years. Monsoon starts earlier than normal years over South China Sea, and the subtropical high moves towards west and north gradually. The monthly mean temperature is 16.9℃, which is 0.7℃ warmer than normal years. The national average precipitation is 85.5 mm, which is 23% more than the normal and recorded as the 2nd largest amount for the corresponding period since 1961. The main weather characteristics in this month is as follows: heavy rainfalls occur in Southern China frequently, high winds and hails hit more than 20 provinces and cities, and one sand dust event is seen in the Northern China.
The following are the main characteristics of the general circulation of atmosphere in May 2013. There is one polar vortex center in the Northern Hemisphere, and the strength is 2-4 dagpm lower than normal years. The circulation presents a four wave pattern in high latitudes, of which there is a cut off low votex in Novosibirsk, bringing cold air mass to Northern Xinjiang. The south branch trough is more active than normal years. Monsoon starts earlier than normal years over South China Sea, and the subtropical high moves towards west and north gradually. The monthly mean temperature is 16.9℃, which is 0.7℃ warmer than normal years. The national average precipitation is 85.5 mm, which is 23% more than the normal and recorded as the 2nd largest amount for the corresponding period since 1961. The main weather characteristics in this month is as follows: heavy rainfalls occur in Southern China frequently, high winds and hails hit more than 20 provinces and cities, and one sand dust event is seen in the Northern China.
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ISSN:1000-0526 CN:11-2282/P