ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 38,Issue 8,2012 Table of Contents
2012, 38(8):897-902.
DOI: 10.7519/j.issn.1000-0526.2012.08.001
Abstract:
The surface temperature outcomes of determined forecasts of the European Centre for Medium range Weather Forecasts (ECMWF) during the period from January 2007 to December 2010 are examined with root mean square error (RMSE) and the error is corrected by utilizing the methods of unitary linear regression, multiple linear regression, unitary bias removed with unitary lead time forecast and bias removed mean with multi lead time forecasts, respectively. The results show that all of the four methods could considerably reduce the ECMWF forecast errors for multi lead time forecasts, generally about 1℃. The forecast skill of the unitary linear regression is higher than that of two consensus forecast methods considering multi lead time forecast outcomes for short range forecast. While two kinds of consensus forecasts have higher and more stable forecast skills for medium range forecast. The correction methods considering multi lead time forecast outcomes could reduce the forecast error more stably especially when the error is large.
The surface temperature outcomes of determined forecasts of the European Centre for Medium range Weather Forecasts (ECMWF) during the period from January 2007 to December 2010 are examined with root mean square error (RMSE) and the error is corrected by utilizing the methods of unitary linear regression, multiple linear regression, unitary bias removed with unitary lead time forecast and bias removed mean with multi lead time forecasts, respectively. The results show that all of the four methods could considerably reduce the ECMWF forecast errors for multi lead time forecasts, generally about 1℃. The forecast skill of the unitary linear regression is higher than that of two consensus forecast methods considering multi lead time forecast outcomes for short range forecast. While two kinds of consensus forecasts have higher and more stable forecast skills for medium range forecast. The correction methods considering multi lead time forecast outcomes could reduce the forecast error more stably especially when the error is large.
2012, 38(8):903-912.
DOI: 10.7519/j.issn.1000-0526.2012.08.002
Abstract:
Hourly precipitation data at 79 stations in Anhui Province during 1995 to 2009 were used to statistically compute the spatial and temporal distributions of short time heavy rainfall with different intensity. Then the environmental background characteristics of typical short time heavy rainfall were obtained so as to build three conceptual models of short time heavy rainfall and abstract large scale systems beneficial to its occurrence. By using the statistical analysis of physical parameters, conclusions can be drawn as follows. When short time heavy rainfall occurs, the atmospheric water vapor is abundant and there are wet thick layer and warm thick cloud layer, the latter ensures cloud particles from being evapored in the downdraft airflow of system. At the same time, moderate convective CAPE and higher KI index are beneficial for the appearance of high efficiency precipitation. On the other hand, there are two structural characters of radar reflectivity factor, i.e., the low quality core structure and high quality core structure. The important reasons for maintenance and development of heavy precipitation echo in some areas are attributed to small and mesoscale wind shear, convergence and cyclonic covergence zone. In addition, the boundary layer jet enhanced significantly half an hour before heavy rainfall is another important indicator of nowcasting of heavy rainfall.
Hourly precipitation data at 79 stations in Anhui Province during 1995 to 2009 were used to statistically compute the spatial and temporal distributions of short time heavy rainfall with different intensity. Then the environmental background characteristics of typical short time heavy rainfall were obtained so as to build three conceptual models of short time heavy rainfall and abstract large scale systems beneficial to its occurrence. By using the statistical analysis of physical parameters, conclusions can be drawn as follows. When short time heavy rainfall occurs, the atmospheric water vapor is abundant and there are wet thick layer and warm thick cloud layer, the latter ensures cloud particles from being evapored in the downdraft airflow of system. At the same time, moderate convective CAPE and higher KI index are beneficial for the appearance of high efficiency precipitation. On the other hand, there are two structural characters of radar reflectivity factor, i.e., the low quality core structure and high quality core structure. The important reasons for maintenance and development of heavy precipitation echo in some areas are attributed to small and mesoscale wind shear, convergence and cyclonic covergence zone. In addition, the boundary layer jet enhanced significantly half an hour before heavy rainfall is another important indicator of nowcasting of heavy rainfall.
2012, 38(8):913-920.
DOI: 10.7519/j.issn.1000-0526.2012.08.003
Abstract:
In this paper, an analysis is performed on the snow weather process taking place in Beijing on February 9 and 10, 2011. The NCEP final operational global analysis data as well as the observation data, both conventional and densely AWS data, are used in the analysis. It is shown in the analytical results that this snow process is a combined consequence of the eastward returning current and the surface inverted trough. The eastward returning current is characterized by its wedge structure of being shallow in northwest direction and deep in southeast direction, as well as being wet and cold. Although there is convergent ascending current and frontogenesis, the eastward returning current is not the primary dynamic mechanism of the snowfall. Instead, it plays the role as a cooling and wetting cushion. There are three primary dynamic mechanisms. First, a positive vorticity advection in front of 500 hPa short wave trough and a temperature advection at 850 hPa facilitate the development and eastward movement of surface inverted trough near Hetao. Second, the southwest current at east side of inverted trough ascends on the cooling cushion. Third, the overlay of convergent rising regions at the inverted trough and the front of east wind makes ascending motion strong. Finally, southwest warm and wet currents serve as the main water vapor source for the snow process.
In this paper, an analysis is performed on the snow weather process taking place in Beijing on February 9 and 10, 2011. The NCEP final operational global analysis data as well as the observation data, both conventional and densely AWS data, are used in the analysis. It is shown in the analytical results that this snow process is a combined consequence of the eastward returning current and the surface inverted trough. The eastward returning current is characterized by its wedge structure of being shallow in northwest direction and deep in southeast direction, as well as being wet and cold. Although there is convergent ascending current and frontogenesis, the eastward returning current is not the primary dynamic mechanism of the snowfall. Instead, it plays the role as a cooling and wetting cushion. There are three primary dynamic mechanisms. First, a positive vorticity advection in front of 500 hPa short wave trough and a temperature advection at 850 hPa facilitate the development and eastward movement of surface inverted trough near Hetao. Second, the southwest current at east side of inverted trough ascends on the cooling cushion. Third, the overlay of convergent rising regions at the inverted trough and the front of east wind makes ascending motion strong. Finally, southwest warm and wet currents serve as the main water vapor source for the snow process.
2012, 38(8):921-931.
DOI: 10.7519/j.issn.1000-0526.2012.08.004
Abstract:
Numerical simulation and diagnosis are applied to the heavy snow event happening during 6-7 January 2010 in North Xinjiang by using WRF model. The combination of the cold vortex near Balkhash Lake and the south moving trough from North Xinjiang, as well as the propagation and developing of the upper air jet was the key process connected with this serious blizzard. The synoptical conceptual model is set up for this heavy snow event. It is revealed through the diagnosis of temperature advection and frontogenesis function that, the mesoscale convergence in front of the topography led to the active contribution to the frontogenesis, and the vertical motion term in the frontogenesis function explained the most part of the active frontogenesis. The vertical movement due to the secondary circulation forced by the frontogenesis is the most importrant component through the frontogenesis secondary ciruculation diagnosis. Due to the topography effect the cold air was depositing before the mountain, and the front split into upper level part and lower part, and the change in the structure of front has obvious impact on the microphysical process of precipitation. The relative light precipitation happening in the daytime of 6 January 2010 is closely connected with the warm flow ascending along the topography and the stratus cloud in the upper level. After 20:00 BT 6 January, the warm advection was strengthened with distinct frontogenesis, the seeder feeder mechanism was formed by the split front structure, and the snowfall intensified clearly due to this more efficient microphysical process.
Numerical simulation and diagnosis are applied to the heavy snow event happening during 6-7 January 2010 in North Xinjiang by using WRF model. The combination of the cold vortex near Balkhash Lake and the south moving trough from North Xinjiang, as well as the propagation and developing of the upper air jet was the key process connected with this serious blizzard. The synoptical conceptual model is set up for this heavy snow event. It is revealed through the diagnosis of temperature advection and frontogenesis function that, the mesoscale convergence in front of the topography led to the active contribution to the frontogenesis, and the vertical motion term in the frontogenesis function explained the most part of the active frontogenesis. The vertical movement due to the secondary circulation forced by the frontogenesis is the most importrant component through the frontogenesis secondary ciruculation diagnosis. Due to the topography effect the cold air was depositing before the mountain, and the front split into upper level part and lower part, and the change in the structure of front has obvious impact on the microphysical process of precipitation. The relative light precipitation happening in the daytime of 6 January 2010 is closely connected with the warm flow ascending along the topography and the stratus cloud in the upper level. After 20:00 BT 6 January, the warm advection was strengthened with distinct frontogenesis, the seeder feeder mechanism was formed by the split front structure, and the snowfall intensified clearly due to this more efficient microphysical process.
2012, 38(8):932-942.
DOI: 10.7519/j.issn.1000-0526.2012.08.005
Abstract:
On the basis of the data obtained by conventional observations, ground densified automatic weather stations (AWS), and NCEP 1°×1° reanalysis data, the synoptic causation of the sandstorm happening over Henan Province on March 27, 2006 was analyzed. The results show that the sandstorm occurred during the passage of a cold front. The upper air affecting synoptic system was a short wave trough which carried cold air, moved southeastward, developed and eventually substituted the former East Asia major trough. The deficient anterior precipitation resulted in the dryness of the surface. The Yellow River Flood Plain in North and East Henan Province provided abundant sand and dust to the occurrence of sandstorm. During the passage of cold front, the powerful temperature advection intensified wind power and vertical motion. The frontogenesis strengthened weather phenomena resulting from cold front. The cold front not only was the triggering system of static instability energy, but also had symmetrical instability inside which played an important role in the further enhancement of vertical motion and sending dust and sand to high levels. Mesoscale filtering of ground densified observations indicated that the formation and development of mesoscale low not only strengthened turbulent mixing, but also intensified the release of instability energy. The sandstorm was eventually formed by the effects of powerful wind, strong turbulent mixing and intensified upward air flow.
On the basis of the data obtained by conventional observations, ground densified automatic weather stations (AWS), and NCEP 1°×1° reanalysis data, the synoptic causation of the sandstorm happening over Henan Province on March 27, 2006 was analyzed. The results show that the sandstorm occurred during the passage of a cold front. The upper air affecting synoptic system was a short wave trough which carried cold air, moved southeastward, developed and eventually substituted the former East Asia major trough. The deficient anterior precipitation resulted in the dryness of the surface. The Yellow River Flood Plain in North and East Henan Province provided abundant sand and dust to the occurrence of sandstorm. During the passage of cold front, the powerful temperature advection intensified wind power and vertical motion. The frontogenesis strengthened weather phenomena resulting from cold front. The cold front not only was the triggering system of static instability energy, but also had symmetrical instability inside which played an important role in the further enhancement of vertical motion and sending dust and sand to high levels. Mesoscale filtering of ground densified observations indicated that the formation and development of mesoscale low not only strengthened turbulent mixing, but also intensified the release of instability energy. The sandstorm was eventually formed by the effects of powerful wind, strong turbulent mixing and intensified upward air flow.
2012, 38(8):943-949.
DOI: 10.7519/j.issn.1000-0526.2012.08.006
Abstract:
The visibility change was analyzed with the observations from ground stations and the aerosol optical depth (AOD) data from Moderate resolution Imaging Spectroradiometer (MODIS) in the Yangtze River Delta region in recent 30 years. It shows that the annual mean visibility was 19.5±1.8 km during 1980-2009 with a maximum value of 21.9 km in 1984 and a minimum value of 16.1 km in 2007. The visibility has a downward trend in recent 30 years at a rate of -0.20±0.013 km/a and tends to become stable in the last few years. The visibility changes with the seasons in this region which is the highest in summer, followed by autumn and spring and the lowest in winter; the visibility in the coastal areas is higher than that in inland, and it is lower along the rivers; the decreasing rate along the rivers and the coast areas is higher, especially in the southeastern Zhejiang. The EOF method was used to analyze the visibility of the Yangtze River Delta region. The result shows that the eigenvectors of the first mode are all positive, indicating the decreasing trend of the visibility in the whole region. The analysis on the regional and long term visibility change made by the MODIS AOD data coincides with that by the ground station observations.
The visibility change was analyzed with the observations from ground stations and the aerosol optical depth (AOD) data from Moderate resolution Imaging Spectroradiometer (MODIS) in the Yangtze River Delta region in recent 30 years. It shows that the annual mean visibility was 19.5±1.8 km during 1980-2009 with a maximum value of 21.9 km in 1984 and a minimum value of 16.1 km in 2007. The visibility has a downward trend in recent 30 years at a rate of -0.20±0.013 km/a and tends to become stable in the last few years. The visibility changes with the seasons in this region which is the highest in summer, followed by autumn and spring and the lowest in winter; the visibility in the coastal areas is higher than that in inland, and it is lower along the rivers; the decreasing rate along the rivers and the coast areas is higher, especially in the southeastern Zhejiang. The EOF method was used to analyze the visibility of the Yangtze River Delta region. The result shows that the eigenvectors of the first mode are all positive, indicating the decreasing trend of the visibility in the whole region. The analysis on the regional and long term visibility change made by the MODIS AOD data coincides with that by the ground station observations.
7 Diagnostic Analysis of Thermal and Dynamical Characteristics of a Heavy Dust Storm in Hexi Corridor
2012, 38(8):950-959.
DOI: 10.7519/j.issn.1000-0526.2012.08.007
Abstract:
By using the (1°×1°) reanalysis data of NCEP and the data of upper air sounding and surface observations, the thermal and dynamical features of a heavy dust storm occurring on 24 April 2010 in the Hexi Corridor are analyzed. The calculated results show that before the dust storm occurs, the sensible heat flux reaching the maximum value increased the atmospheric instability. The gale and dust storm are in accordance with the great value area of the momentum flux, and the momentum flux plays an important role in the transporting upwards dust. Nearby the strong frontal zone, the geostrophic balance is destructed, the dust storm mainly appears in the area of great allobaric gradient and the allobaric wind is the principal constituent of the surface gale. This heavy dust storm is a process of strong frontogenesis and the latter causes the frontal secondary circulation strengthening. The greater the negative (absolute) value of horizontal helicity is, the greater the surface wind speed will be. The gale and dust storm mainly appear between the right front of the horizontal helicity negative value center and zero contour. The upper level jet traversing geopotential height surface along isentropic surface slides down to 2000 gpm and forms the westerly low level jet. The low level jet plays a crucial role in the producing process of the dust storm.
By using the (1°×1°) reanalysis data of NCEP and the data of upper air sounding and surface observations, the thermal and dynamical features of a heavy dust storm occurring on 24 April 2010 in the Hexi Corridor are analyzed. The calculated results show that before the dust storm occurs, the sensible heat flux reaching the maximum value increased the atmospheric instability. The gale and dust storm are in accordance with the great value area of the momentum flux, and the momentum flux plays an important role in the transporting upwards dust. Nearby the strong frontal zone, the geostrophic balance is destructed, the dust storm mainly appears in the area of great allobaric gradient and the allobaric wind is the principal constituent of the surface gale. This heavy dust storm is a process of strong frontogenesis and the latter causes the frontal secondary circulation strengthening. The greater the negative (absolute) value of horizontal helicity is, the greater the surface wind speed will be. The gale and dust storm mainly appear between the right front of the horizontal helicity negative value center and zero contour. The upper level jet traversing geopotential height surface along isentropic surface slides down to 2000 gpm and forms the westerly low level jet. The low level jet plays a crucial role in the producing process of the dust storm.
2012, 38(8):960-970.
DOI: 10.7519/j.issn.1000-0526.2012.08.008
Abstract:
A heavy rainstorm on 17 August 2007 in Shandong Province was studied on the mesoscale characters by the data of conventional and AWS observations, satellite, Doppler radar, lightning location instrument and WRF simulation. And the sensitivity experiment of numerical model was carried out to investigate the influence of topography. The results are as follows. The heavy rainstorm was caused by the K H instability, wind shear and vortex. Meanwhile, terrain played an important role in the location and intensity of rainstorm, which brought more rainfall and made heavy rain located in the further south area. The numerical simulation comparison test was worked between the two similar rain processes. The result shows that there are more obviously consistences in many ways, including rainfall area, central intensity and distributions except the intensity of heavy rainfall. The terrain has a stronger effect to the heavy rainfall. The wind shear caused by terrain made stronger vapor convergence and vertical velocity. What’s more, the terrain also affected the distribution of cloud vapor and rain vapor. As a result, the favorable circulation and terrain are the important factors to produce the heavy rainstorm.
A heavy rainstorm on 17 August 2007 in Shandong Province was studied on the mesoscale characters by the data of conventional and AWS observations, satellite, Doppler radar, lightning location instrument and WRF simulation. And the sensitivity experiment of numerical model was carried out to investigate the influence of topography. The results are as follows. The heavy rainstorm was caused by the K H instability, wind shear and vortex. Meanwhile, terrain played an important role in the location and intensity of rainstorm, which brought more rainfall and made heavy rain located in the further south area. The numerical simulation comparison test was worked between the two similar rain processes. The result shows that there are more obviously consistences in many ways, including rainfall area, central intensity and distributions except the intensity of heavy rainfall. The terrain has a stronger effect to the heavy rainfall. The wind shear caused by terrain made stronger vapor convergence and vertical velocity. What’s more, the terrain also affected the distribution of cloud vapor and rain vapor. As a result, the favorable circulation and terrain are the important factors to produce the heavy rainstorm.
2012, 38(8):971-976.
DOI: 10.7519/j.issn.1000-0526.2012.08.009
Abstract:
Based on the T639 model data (1°× 1°) of 72 h height field from 2009 to 2010 and the objective analysis data of ECMWF from September 2007 to February 2008 as well as the classification of synoptic system in Xinjiang， the forecast products were validated by synoptic verification method in terms of start time, intensity of system center, position of trough line, and the moving velocity of synoptic system． The results indicate that the forecast of synoptic system in Xinjiang is accurate based on T639 model, especially for 48 h forecasts. Forecast ability is different because of the difference of influence system and prediction time. The deeper the upper level trough, the better. The start time of synoptic system had an earlier prediction to West Siberian trough and Ural trough, and just the opposite for northern transversal trough and central Asia low pressure system. The position of trough line had a faster moving prediction to West Siberian trough and central Asia low pressure system, and just the opposite for northern transversal trough and Ural trough.
Based on the T639 model data (1°× 1°) of 72 h height field from 2009 to 2010 and the objective analysis data of ECMWF from September 2007 to February 2008 as well as the classification of synoptic system in Xinjiang， the forecast products were validated by synoptic verification method in terms of start time, intensity of system center, position of trough line, and the moving velocity of synoptic system． The results indicate that the forecast of synoptic system in Xinjiang is accurate based on T639 model, especially for 48 h forecasts. Forecast ability is different because of the difference of influence system and prediction time. The deeper the upper level trough, the better. The start time of synoptic system had an earlier prediction to West Siberian trough and Ural trough, and just the opposite for northern transversal trough and central Asia low pressure system. The position of trough line had a faster moving prediction to West Siberian trough and central Asia low pressure system, and just the opposite for northern transversal trough and Ural trough.
2012, 38(8):977-984.
DOI: 10.7519/j.issn.1000-0526.2012.08.010
Abstract:
Based on the 1953-2010 meteorological records at the Nanyue Mountain Observatory, the climatic variations of winds are examined by using the trend analysis, the vector decomposition, the wavelet analysis, and the Mann Kendall test statistics. The results can be shown that: (1) the prevailing winds over the Nanyue Mountain exhibit significant seasonal variations, with the prevailing wind being southwesterly in spring and summer and being northerly in autumn and winter; (2) annual mean wind speed experienced statistically significant decreasing at an averaged rate of -0.25 m·s-1/decade, with the maximum trend occurring in summer and minimum trend in winter. In addition, vector decomposition analysis indicates that both meridional and zonal wind speeds show decreasing trends, with the meridional declining faster than the zonal declining. For the meridional slowdown, the north wind decrease is faster than the south wind. Statistically significant declining trends in the west and south wind components can only be detected in summer, while significant slowdown in the north wind can be found in all seasons except in summer. Analysis also indicates that winds over the Nanyue Mountain exhibit significant interannual and interdacedal variations. Oscillations with 16 year periods can be detected both in annual mean and winter wind speeds, but they are remarkably changed after the 1990s. It is suggested that the interdecadal variation of wind speed may be closely associated with the variations of large scale East Asian monsoon systems.
Based on the 1953-2010 meteorological records at the Nanyue Mountain Observatory, the climatic variations of winds are examined by using the trend analysis, the vector decomposition, the wavelet analysis, and the Mann Kendall test statistics. The results can be shown that: (1) the prevailing winds over the Nanyue Mountain exhibit significant seasonal variations, with the prevailing wind being southwesterly in spring and summer and being northerly in autumn and winter; (2) annual mean wind speed experienced statistically significant decreasing at an averaged rate of -0.25 m·s-1/decade, with the maximum trend occurring in summer and minimum trend in winter. In addition, vector decomposition analysis indicates that both meridional and zonal wind speeds show decreasing trends, with the meridional declining faster than the zonal declining. For the meridional slowdown, the north wind decrease is faster than the south wind. Statistically significant declining trends in the west and south wind components can only be detected in summer, while significant slowdown in the north wind can be found in all seasons except in summer. Analysis also indicates that winds over the Nanyue Mountain exhibit significant interannual and interdacedal variations. Oscillations with 16 year periods can be detected both in annual mean and winter wind speeds, but they are remarkably changed after the 1990s. It is suggested that the interdecadal variation of wind speed may be closely associated with the variations of large scale East Asian monsoon systems.
2012, 38(8):985-996.
DOI: 10.7519/j.issn.1000-0526.2012.08.011
Abstract:
By using the surface observation data at 12 stations in the coast of West Guangdong from 2000 to 2010 and the sea fog observation data on Donghai Island in Zhanjiang during March 2010, the climatic and microphysical characteristics of coastal fog are statistically analyzed. Results show that the fog day number has a variation tendency in West Guangdong, i.e. western (17.8 d·a-1)>eastern (7.7 d·a-1)> central (3.5 d·a-1). The annual change is significantly different and has a gradually rising trend during 2000—2010 except the 2008. There are more fog days in winter and spring, and less in summer and autumn. Generally most fog events in a certain day occur between 02:00 and 08:00 BT, and have an average probability of 50.8%. The duration of sea fog process is mostly between 1 and 3 days. The comprehensive weather conditions of fog generation mainly are that wind speed is ≤7 m·s-1 and wind directions are NNE-ESE and calm wind, and the appropriate air temperature is between 15.0 and 25.0℃, and the 3 h pressure change is in an interval of -3.5-2.5 hPa, and depression of the dew point continuously approaches to 0.0-2.0℃. The synoptic situations favorable for the fog formation and development on the Leizhou Peninsula can be roughly divided into five classes: high pressure system, low trough system, cold front, stationary front, saddle type pressure field or isobaric field. The droplet size distribution is quite different during fog process. The average droplet size distribution is generally consistent with exponential distribution, and the type of the average droplet size distribution is similar to the “single peak” structure. Drops significantly bias the small end of the spectrum, and the droplet spectrum diameters mainly appear in 2-10 μm.
By using the surface observation data at 12 stations in the coast of West Guangdong from 2000 to 2010 and the sea fog observation data on Donghai Island in Zhanjiang during March 2010, the climatic and microphysical characteristics of coastal fog are statistically analyzed. Results show that the fog day number has a variation tendency in West Guangdong, i.e. western (17.8 d·a-1)>eastern (7.7 d·a-1)> central (3.5 d·a-1). The annual change is significantly different and has a gradually rising trend during 2000—2010 except the 2008. There are more fog days in winter and spring, and less in summer and autumn. Generally most fog events in a certain day occur between 02:00 and 08:00 BT, and have an average probability of 50.8%. The duration of sea fog process is mostly between 1 and 3 days. The comprehensive weather conditions of fog generation mainly are that wind speed is ≤7 m·s-1 and wind directions are NNE-ESE and calm wind, and the appropriate air temperature is between 15.0 and 25.0℃, and the 3 h pressure change is in an interval of -3.5-2.5 hPa, and depression of the dew point continuously approaches to 0.0-2.0℃. The synoptic situations favorable for the fog formation and development on the Leizhou Peninsula can be roughly divided into five classes: high pressure system, low trough system, cold front, stationary front, saddle type pressure field or isobaric field. The droplet size distribution is quite different during fog process. The average droplet size distribution is generally consistent with exponential distribution, and the type of the average droplet size distribution is similar to the “single peak” structure. Drops significantly bias the small end of the spectrum, and the droplet spectrum diameters mainly appear in 2-10 μm.
2012, 38(8):997-1003.
DOI: 10.7519/j.issn.1000-0526.2012.08.012
Abstract:
On the basis of the successful experience of artificial precipitation experiment summarized at Zhexi Reservoir during many years, the climatic characteristics, the situation of flood control, the electrical power requirement and the safe production requests over the Zishui Basin are analyzed, and the suitable time period of artificial precipitation operation at Zhexi Reservoir are defined. According to the analysis of 37 synoptic cases and precipitation characteristics of the typical precipitation day in the recent five years, the main cause for precipitation is attributed to the westerly system, easterly system and orographical clouds. Moreover, the optimized layout and operation mode of artificial precipitation operation at Zhexi Reservoir are proposed. After discussing a typical example of torrential rain leading to flood in the reservoir area, we found that the artificial precipitation operation at Zhexi Reservoir needs avoiding the high risk areas of the heavy rainfall caused natural disasters. The effect and benefit of artificial precipitation operations at Zhexi Reservoir are significantly increased throught practical application, and this method is available for reference to artificial precipitation experiments at other large reservoirs.
On the basis of the successful experience of artificial precipitation experiment summarized at Zhexi Reservoir during many years, the climatic characteristics, the situation of flood control, the electrical power requirement and the safe production requests over the Zishui Basin are analyzed, and the suitable time period of artificial precipitation operation at Zhexi Reservoir are defined. According to the analysis of 37 synoptic cases and precipitation characteristics of the typical precipitation day in the recent five years, the main cause for precipitation is attributed to the westerly system, easterly system and orographical clouds. Moreover, the optimized layout and operation mode of artificial precipitation operation at Zhexi Reservoir are proposed. After discussing a typical example of torrential rain leading to flood in the reservoir area, we found that the artificial precipitation operation at Zhexi Reservoir needs avoiding the high risk areas of the heavy rainfall caused natural disasters. The effect and benefit of artificial precipitation operations at Zhexi Reservoir are significantly increased throught practical application, and this method is available for reference to artificial precipitation experiments at other large reservoirs.
2012, 38(8):1004-1011.
DOI: 10.7519/j.issn.1000-0526.2012.08.013
Abstract:
The study primarily depends upon the climate data to analyze the climatic characteristics related to lightning activity, and the data collected by the lightning location finder is also required to denote the cloud to ground lightning density of each grid cell. According to its degree of exposure to lightning and the characteristics of lightning protection and avoidance, the potential lightning striking areas are classified as the building, the outdoor area under the building canopy and the open field area. The expected lightning stroke times (frequency) on each class of lightning striking area have been worked out properly with the parameters of CG flash density, equivalent intercepting area to lightning, lightning protecting capability and position factor in these areas. Eventually the risk assessment has been carried with the formula of risk = frequency×population. The assessment reveals that with dense population and aggregated belongings, the central urban district is the highest risk zoning of lightning, as well as its high flash density, while the risk of the suburbs and rural areas are not high. The conclusion is demonstrated by the distribution of lightning disaster event occurring in Beijing from 2004 to 2008, and the result of the risk assessment is correspondent to the actual trend and situation.
The study primarily depends upon the climate data to analyze the climatic characteristics related to lightning activity, and the data collected by the lightning location finder is also required to denote the cloud to ground lightning density of each grid cell. According to its degree of exposure to lightning and the characteristics of lightning protection and avoidance, the potential lightning striking areas are classified as the building, the outdoor area under the building canopy and the open field area. The expected lightning stroke times (frequency) on each class of lightning striking area have been worked out properly with the parameters of CG flash density, equivalent intercepting area to lightning, lightning protecting capability and position factor in these areas. Eventually the risk assessment has been carried with the formula of risk = frequency×population. The assessment reveals that with dense population and aggregated belongings, the central urban district is the highest risk zoning of lightning, as well as its high flash density, while the risk of the suburbs and rural areas are not high. The conclusion is demonstrated by the distribution of lightning disaster event occurring in Beijing from 2004 to 2008, and the result of the risk assessment is correspondent to the actual trend and situation.
2012, 38(8):1012-1016.
DOI: 10.7519/j.issn.1000-0526.2012.08.014
Abstract:
Using the data of 3 consecutive rainfall days and no rain days during mid September to early October in near 50 years (1961-2009) from 12 representative stations in major apple cultivating counties of Shaanxi, the index of continuous rainfall days (ICRD) has been designed and calculated, and is divided into the strongest, stronger, medium, weak and weaker five levels, on the basis of which, conducting the independent sample trial by using typical K order autoregressive AR (K) forecasting model. The basic result of this research is that the ICRD could objectively reflect the intensity of continuous rainfall days in apple maturity period. In addition, the typical K order autoregressive forecasting model has about 83% forecasts being accurate or basically accurate, indicating that the effect of this forecasting model is still good and of practical value.
Using the data of 3 consecutive rainfall days and no rain days during mid September to early October in near 50 years (1961-2009) from 12 representative stations in major apple cultivating counties of Shaanxi, the index of continuous rainfall days (ICRD) has been designed and calculated, and is divided into the strongest, stronger, medium, weak and weaker five levels, on the basis of which, conducting the independent sample trial by using typical K order autoregressive AR (K) forecasting model. The basic result of this research is that the ICRD could objectively reflect the intensity of continuous rainfall days in apple maturity period. In addition, the typical K order autoregressive forecasting model has about 83% forecasts being accurate or basically accurate, indicating that the effect of this forecasting model is still good and of practical value.
2012, 38(8):1017-1022.
DOI: 10.7519/j.issn.1000-0526.2012.08.015
Abstract:
In order to improve the ability to use the products of T639, a synoptic verification on its medium range forecasts in spring 2012 is made in comparison with the NWP products of ECMWF and Japan models. The results show that the three models have good performances on the aspect of predicting the large scale circulation evolution and adjustment in Asian middle and high latitude areas. 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 the period of April 22-23, 2012 as a case, it is found that the Japan model is more effective than the other two models in medium range forecasts of strong surface wind, causing the sand and dust weather process.
In order to improve the ability to use the products of T639, a synoptic verification on its medium range forecasts in spring 2012 is made in comparison with the NWP products of ECMWF and Japan models. The results show that the three models have good performances on the aspect of predicting the large scale circulation evolution and adjustment in Asian middle and high latitude areas. 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 the period of April 22-23, 2012 as a case, it is found that the Japan model is more effective than the other two models in medium range forecasts of strong surface wind, causing the sand and dust weather process.
2012, 38(8):1023-1028.
DOI: 10.7519/j.issn.1000-0526.2012.08.016
Abstract:
The following are the main characteristics of the general circulation of atmosphere in May 2012:there is only one polar vortex center in the Northern Hemisphere with stronger strength than normal years. More troughs occur in middle high latitudes in the Asian area, and lead to several cold air currents to influence China. The subtropical high is slightly stronger than normal years. The East Asia major trough is clearly stronger than usual at the same time period. The south branch trough at 90°E is slightly stronger than normal years. The monthly mean temperature averaged over China is 16.8℃， which is 1.0℃ higher than the same period of normal years. The mean precipitation (66.1 mm) is 2.63% more than normal(64.4 mm). There are 5 precipitation processes in May 2012. Extreme precipitation events occur in Provinces Gansu and Hunan, and drought is mitigated in Yunnan. High temperature occurs in Sichuan, Yunnan, Guizhou and Guangxi. Strong wind and hail disasters hit many regions in China in May.
The following are the main characteristics of the general circulation of atmosphere in May 2012:there is only one polar vortex center in the Northern Hemisphere with stronger strength than normal years. More troughs occur in middle high latitudes in the Asian area, and lead to several cold air currents to influence China. The subtropical high is slightly stronger than normal years. The East Asia major trough is clearly stronger than usual at the same time period. The south branch trough at 90°E is slightly stronger than normal years. The monthly mean temperature averaged over China is 16.8℃， which is 1.0℃ higher than the same period of normal years. The mean precipitation (66.1 mm) is 2.63% more than normal(64.4 mm). There are 5 precipitation processes in May 2012. Extreme precipitation events occur in Provinces Gansu and Hunan, and drought is mitigated in Yunnan. High temperature occurs in Sichuan, Yunnan, Guizhou and Guangxi. Strong wind and hail disasters hit many regions in China in May.
2012, 38(8):1029-1032.
DOI: 10.7519/j.issn.1000-0526.2012.08.017
Abstract:
Transmitter limit improvement factor is one of the most important technological indexes for delivery test of CINRAD and it comprises transmitter input and output limit improvement factors. Based on the testing methods offered by Plessey Siemens Company, a spectrum analyzer is used to measure the signal power spectrum density distribution, and then the signal to noise ratio (S/R) is obtained. However, during the delivery test and patrol examination, the interfering spikes at different frequency are often found on the graph of signal power spectrum density distribution and they may affect measurement indexes of transmitter limit improvement factor and transmitter phase stability and so on. This paper analyzes test signal circuit and examines causes for interfering spikes and repairing methods and hence provides useful field maintenance experience for radar technologists.
Transmitter limit improvement factor is one of the most important technological indexes for delivery test of CINRAD and it comprises transmitter input and output limit improvement factors. Based on the testing methods offered by Plessey Siemens Company, a spectrum analyzer is used to measure the signal power spectrum density distribution, and then the signal to noise ratio (S/R) is obtained. However, during the delivery test and patrol examination, the interfering spikes at different frequency are often found on the graph of signal power spectrum density distribution and they may affect measurement indexes of transmitter limit improvement factor and transmitter phase stability and so on. This paper analyzes test signal circuit and examines causes for interfering spikes and repairing methods and hence provides useful field maintenance experience for radar technologists.
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ISSN:1000-0526 CN:11-2282/P