ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 40,Issue 5,2014 Table of Contents
2014, 40(5):521-529.
DOI: 10.7519/j.issn.1000-0526.2014.05.001
Abstract:
The diagnosis relationship between isentropic potential vorticity conservation and baroclinic disturbance development has been used in forecasting cyclone development and understanding the dynamic fields of water vapor imagery. “Isentropic potential vorticity thinking” is based on isentropic thinking of isentropic analysis. This paper first reviews and discusses dynamic interpretation and operational application of isentropic physical fields according to the basic principles of atmospheric dynamics. The contents include isentropic surface distribution with height, vertical velocity in isentropic coordinates, moisture transport on isentropic surface, upper level fronts and jet stream characteristics on isentropic surface etc. Then, the physical fields and operational applicatoin on isentropic potential vorticity surface are discussed emphatically by comparing with physical fields on isentropic surface and quasi geostrophic vertical motion equation on baroclinic two layer model. The contents contain the definition of tropopause and its temperature, pressure and humidity distribution, fronts and jet stream characteristics on tropopause isentropic potential vorticity surface， vertical velocity on tropopause isentropic potential vorticity surface, cyclone development and potential vorticity in accordance with “isentropic potential vorticity thinking”, and how to improve numerical weather prediction model by using water vapor imagery etc.
The diagnosis relationship between isentropic potential vorticity conservation and baroclinic disturbance development has been used in forecasting cyclone development and understanding the dynamic fields of water vapor imagery. “Isentropic potential vorticity thinking” is based on isentropic thinking of isentropic analysis. This paper first reviews and discusses dynamic interpretation and operational application of isentropic physical fields according to the basic principles of atmospheric dynamics. The contents include isentropic surface distribution with height, vertical velocity in isentropic coordinates, moisture transport on isentropic surface, upper level fronts and jet stream characteristics on isentropic surface etc. Then, the physical fields and operational applicatoin on isentropic potential vorticity surface are discussed emphatically by comparing with physical fields on isentropic surface and quasi geostrophic vertical motion equation on baroclinic two layer model. The contents contain the definition of tropopause and its temperature, pressure and humidity distribution, fronts and jet stream characteristics on tropopause isentropic potential vorticity surface， vertical velocity on tropopause isentropic potential vorticity surface, cyclone development and potential vorticity in accordance with “isentropic potential vorticity thinking”, and how to improve numerical weather prediction model by using water vapor imagery etc.
2014, 40(5):530-540.
DOI: 10.7519/j.issn.1000-0526.2014.05.002
Abstract:
The characteristics of precipitation low frequency oscillation (LFO) over the southeast of Tibetan Plateau (TP) and especially the abnormal distribution and propagation of the 30-60 d filtered fields between positive and negative phases of precipitation LFO are investigated using daily NCEP/NCAR reanalysis and the observed daily rainfall data in 1998. The results are shown as follows: (1) There are several main periods of oscillation including the 10-20 d, 20-30 d and 30-60 d periods, and several significant rainfalls mainly occur in the positive phases of the 30-60 d oscillation, while significant negative rainfall anomaly in the negative phase. (2) During the positive (negative) phase, there is a low frequency cyclone (anticyclone) to the south side of the TP, and a low frequency anticyclone (cyclone) in the Sea of Japan. The southeast TP is influenced both by the southerly winds of the northeast side of the cyclone and the southerly winds of the southwest side of the anticyclone, and it is the low frequency moisture convergence (divergence) area. (3) During the positive phase, the southeast TP, Bay of Bengal (BOB) and South China Sea (SCS) are all low frequency heat source areas, but the 30-60 d filtered heat source/sink fields are opposite in the negative phase. (4) There exist westward propagating convergence (divergence) of moisture fluxes LFO and the 100 hPa divergence (convergence) LFO over the southeast TP which propagate from the West Pacific by the way of middle and lower reaches of Yangtze River, and they correspond well with the positive (negative) phase of precipitation LFO over the southeast TP when they propagate to the southeast TP.
The characteristics of precipitation low frequency oscillation (LFO) over the southeast of Tibetan Plateau (TP) and especially the abnormal distribution and propagation of the 30-60 d filtered fields between positive and negative phases of precipitation LFO are investigated using daily NCEP/NCAR reanalysis and the observed daily rainfall data in 1998. The results are shown as follows: (1) There are several main periods of oscillation including the 10-20 d, 20-30 d and 30-60 d periods, and several significant rainfalls mainly occur in the positive phases of the 30-60 d oscillation, while significant negative rainfall anomaly in the negative phase. (2) During the positive (negative) phase, there is a low frequency cyclone (anticyclone) to the south side of the TP, and a low frequency anticyclone (cyclone) in the Sea of Japan. The southeast TP is influenced both by the southerly winds of the northeast side of the cyclone and the southerly winds of the southwest side of the anticyclone, and it is the low frequency moisture convergence (divergence) area. (3) During the positive phase, the southeast TP, Bay of Bengal (BOB) and South China Sea (SCS) are all low frequency heat source areas, but the 30-60 d filtered heat source/sink fields are opposite in the negative phase. (4) There exist westward propagating convergence (divergence) of moisture fluxes LFO and the 100 hPa divergence (convergence) LFO over the southeast TP which propagate from the West Pacific by the way of middle and lower reaches of Yangtze River, and they correspond well with the positive (negative) phase of precipitation LFO over the southeast TP when they propagate to the southeast TP.
2014, 40(5):541-548.
DOI: 10.7519/j.issn.1000-0526.2014.05.003
Abstract:
Precipitations in North China were 45% more than normal during July 2012, accompanied with serious flood disasters. Utilizing precipitation data in China and other data, the characteristics of the anomalies and the possible causes ware analyzed. The results show that it might be attributed to the influence of multiple factors. On the 500 hPa level, the large scale circulation exhibits “two ridges and one trough” pattern over mid high latitude of Eurasian Continent. The northward shift of the western Pacific subtropical high is also detected. Under this circumstance, the cold and the warm air converge strongly over North China, causing the serious precipitation anomalies. Further study shows that the SST of the equatorial western Pacific Warm Pool remains abnormally warmer in July 2012, generating strong convective activities and driving the subtropical high to north. As a result, the subtropical high shifts northward. On the other hand, affected by the positive SSTA in the North Pacific, an anomalous anticyclone circulation prevails over the northeast of East Asia and North Pacific region, causing the subtropical high stretching towards north.
Precipitations in North China were 45% more than normal during July 2012, accompanied with serious flood disasters. Utilizing precipitation data in China and other data, the characteristics of the anomalies and the possible causes ware analyzed. The results show that it might be attributed to the influence of multiple factors. On the 500 hPa level, the large scale circulation exhibits “two ridges and one trough” pattern over mid high latitude of Eurasian Continent. The northward shift of the western Pacific subtropical high is also detected. Under this circumstance, the cold and the warm air converge strongly over North China, causing the serious precipitation anomalies. Further study shows that the SST of the equatorial western Pacific Warm Pool remains abnormally warmer in July 2012, generating strong convective activities and driving the subtropical high to north. As a result, the subtropical high shifts northward. On the other hand, affected by the positive SSTA in the North Pacific, an anomalous anticyclone circulation prevails over the northeast of East Asia and North Pacific region, causing the subtropical high stretching towards north.
2014, 40(5):549-554.
DOI: 10.7519/j.issn.1000-0526.2014.05.004
Abstract:
Based on the monthly observational data of sunshine hours, using Rotated Empirical Orthogonal Function (REOF), linear trend analysis, Mann Kendall mutation test and Morlet wavelet analysis, the climate characteristics and trend of sunshine hours over the Yangtze Huaihe Basin in summer half year (May to October) were statistically analyzed. Results show that sunshine hours over this area in summer half year were 1000 to 1200 h overall, increasing from the south to the north of spatial distribution characteristics. However, regional differences existed for the factors of topography. The standard deviation and average sunshine hours do not present the same distribution. The sunshine hours in Yangtze Huaihe Basin are divided into four areas furthermore, north area respectively Ⅰ, northeast area Ⅱ, southwest area Ⅲ, southeast area Ⅳ, sunshine hours of each area declined significantly, but remarkable differences exist in linear trend, mutation, time and variation period.
Based on the monthly observational data of sunshine hours, using Rotated Empirical Orthogonal Function (REOF), linear trend analysis, Mann Kendall mutation test and Morlet wavelet analysis, the climate characteristics and trend of sunshine hours over the Yangtze Huaihe Basin in summer half year (May to October) were statistically analyzed. Results show that sunshine hours over this area in summer half year were 1000 to 1200 h overall, increasing from the south to the north of spatial distribution characteristics. However, regional differences existed for the factors of topography. The standard deviation and average sunshine hours do not present the same distribution. The sunshine hours in Yangtze Huaihe Basin are divided into four areas furthermore, north area respectively Ⅰ, northeast area Ⅱ, southwest area Ⅲ, southeast area Ⅳ, sunshine hours of each area declined significantly, but remarkable differences exist in linear trend, mutation, time and variation period.
2014, 40(5):555-561.
DOI: 10.7519/j.issn.1000-0526.2014.05.005
Abstract:
Based on the verification and evaluation of the quality of CFSR (Climate Forecast System Reanalysis) cloud amount reanalysis data by satellite remote sensing data MODIS, we analyze the average distribution of global total and low, middle, high cloud amount from 1979 to 2009 as well as the cloud amount variation along the latitude. Also, by using empirical mode decomposition (EMD) method, we analyze the change trend of each cloud amount in the recent 30 years. The results show that: (1) the global average total cloud amount in recent 30 years is about 59%, the global total and low, middle, high cloud amounts have obvious zonal distribution characteristics, and there are 3 peak value zones and 3 low value zones for the total cloud amount. (2) The difference of land sea distribution for low cloud amount is obvious and the amount of low cloud over the land is significantly lower than that over the ocean. Except for the two polar regions, the amount of low cloud in the Southern Hemisphere is more than that of the corresponding latitudes in the Northern Hemisphere; the locations of maximum and minimum of high cloud amount are between the mid low latitudes (30°) of Southern, and Northern Hemispheres respectively. In addition, the low value center mainly distributes in the eastern ocean. (3) The variation of total cloud amount is in an increasing trend, and it is specificly displayed as skyrocketed after a slightly decrease with the time. Its jump point year is around 1993, after which total cloud amount increases significantly. Low and high cloud amounts show a decreasing trend, in contrast, middle cloud amount is decreasing. Low cloud amount increases the most by nearly 2% while the change of high cloud amount is smaller.
Based on the verification and evaluation of the quality of CFSR (Climate Forecast System Reanalysis) cloud amount reanalysis data by satellite remote sensing data MODIS, we analyze the average distribution of global total and low, middle, high cloud amount from 1979 to 2009 as well as the cloud amount variation along the latitude. Also, by using empirical mode decomposition (EMD) method, we analyze the change trend of each cloud amount in the recent 30 years. The results show that: (1) the global average total cloud amount in recent 30 years is about 59%, the global total and low, middle, high cloud amounts have obvious zonal distribution characteristics, and there are 3 peak value zones and 3 low value zones for the total cloud amount. (2) The difference of land sea distribution for low cloud amount is obvious and the amount of low cloud over the land is significantly lower than that over the ocean. Except for the two polar regions, the amount of low cloud in the Southern Hemisphere is more than that of the corresponding latitudes in the Northern Hemisphere; the locations of maximum and minimum of high cloud amount are between the mid low latitudes (30°) of Southern, and Northern Hemispheres respectively. In addition, the low value center mainly distributes in the eastern ocean. (3) The variation of total cloud amount is in an increasing trend, and it is specificly displayed as skyrocketed after a slightly decrease with the time. Its jump point year is around 1993, after which total cloud amount increases significantly. Low and high cloud amounts show a decreasing trend, in contrast, middle cloud amount is decreasing. Low cloud amount increases the most by nearly 2% while the change of high cloud amount is smaller.
2014, 40(5):562-569.
DOI: 10.7519/j.issn.1000-0526.2014.05.006
Abstract:
For understanding the influence of dry intrusion on the precipitation of northeast cold vortex, a typical cold vortex over northeastern China on July 2011 was simulated by WRF model. The results show that: Dry intrusion has affected the cold vortex precipitation in two aspects. On the one hand, the dense air from upper level lifts the warm moist air ahead of dry intrusion, and as a consequence, it promotes the cold vortex precipitation; On the other hand, the forward moving of the descending cold air makes its front interface more steep and the atmospheric stratification instable, which helps to promote the vertical development of rain clouds. The cold voltex precipitation mainly concentrates below the central section of the rain clouds.
For understanding the influence of dry intrusion on the precipitation of northeast cold vortex, a typical cold vortex over northeastern China on July 2011 was simulated by WRF model. The results show that: Dry intrusion has affected the cold vortex precipitation in two aspects. On the one hand, the dense air from upper level lifts the warm moist air ahead of dry intrusion, and as a consequence, it promotes the cold vortex precipitation; On the other hand, the forward moving of the descending cold air makes its front interface more steep and the atmospheric stratification instable, which helps to promote the vertical development of rain clouds. The cold voltex precipitation mainly concentrates below the central section of the rain clouds.
2014, 40(5):570-579.
DOI: 10.7519/j.issn.1000-0526.2014.05.007
Abstract:
By using conventional meteorological observation data, satellite data, NCEP FNL reanalysis data, the severe rainstorm process which happened on 14 June, 2011 in northern Jiangxi was analyzed in this paper. The results show that: (1) The severe rainstorm over Meiyu front happens in extremely favorable weather situations and frontogenesis and terrain result in the vigorous development of meso β scale system. (2) With stable circulations, cold air flow behind the 500 hPa trough stands facing the warm and wet flow in south, continuously, causing to the rainstorm maintain over the northern part of Jiangxi. The favourable ambient field for this event is formed by strong thermal instability, strong vertical wind sheer, plentiful water supply in low level and strong convergent lifting.(3) Co operation between multi scale systems makes extremely strong southwest jet and the strong ascending motion, strong divergence in higher levels, strong convergence in lower levels are coupled with the development of meso scale system. All of these factors trigger the rainstorm happen on the Meiyu front. The positive vorticity develops upward along the front area of θse, which enhances convective ascending motion and releases lots of instable energy. (4) Main precipitation core located in northeast Jiangxi is due to the joining of air flows in different levels and the interaction between convergence at boundary layer and trumpet shaped terrain.
By using conventional meteorological observation data, satellite data, NCEP FNL reanalysis data, the severe rainstorm process which happened on 14 June, 2011 in northern Jiangxi was analyzed in this paper. The results show that: (1) The severe rainstorm over Meiyu front happens in extremely favorable weather situations and frontogenesis and terrain result in the vigorous development of meso β scale system. (2) With stable circulations, cold air flow behind the 500 hPa trough stands facing the warm and wet flow in south, continuously, causing to the rainstorm maintain over the northern part of Jiangxi. The favourable ambient field for this event is formed by strong thermal instability, strong vertical wind sheer, plentiful water supply in low level and strong convergent lifting.(3) Co operation between multi scale systems makes extremely strong southwest jet and the strong ascending motion, strong divergence in higher levels, strong convergence in lower levels are coupled with the development of meso scale system. All of these factors trigger the rainstorm happen on the Meiyu front. The positive vorticity develops upward along the front area of θse, which enhances convective ascending motion and releases lots of instable energy. (4) Main precipitation core located in northeast Jiangxi is due to the joining of air flows in different levels and the interaction between convergence at boundary layer and trumpet shaped terrain.
2014, 40(5):580-588.
DOI: 10.7519/j.issn.1000-0526.2014.05.008
Abstract:
Using frequency or area matching method, an experiment is performed to correct precipitation forecast bias from AREM model over China during June-August, 2012 (rainy season). The method is first introduced including its meteorological principle and mathematical means, and its performance is evaluated. Then in depth analysis is done to understand its advantages and limitations, and future research directions are suggested. Three conclusions are drawn from this study. (1) The method can effectively eliminate biases in precipitation amount and areal coverage. The corrected precipitation amount and area coverage are much closer to the observations. (2) The method works better when bias is higher. (3) This method, in principle, has no ability to correct precipitation position errors, but through precipitation area alternation, large area of erroneous or spurious light rain from model forecasts can be effectively removed, resulting in significantly improved TS and ETS scores for light precipitation. Therefore, this calibration method can greatly increase the accuracy of a “rain or no rain” dichotomous forecast in numerical weather prediction. In addition, five possible approaches are proposed to remedy the inability of this method in correcting precipitation position error. This method can also be used at single station. Hydrological application of this method is apparent since an accurate input of precipitation amount and areal coverage is critical to a hydrological forecast model over a watershed. Besides for precipitation, this method can also be applied to correct forecast bias for other variables like fog.
Using frequency or area matching method, an experiment is performed to correct precipitation forecast bias from AREM model over China during June-August, 2012 (rainy season). The method is first introduced including its meteorological principle and mathematical means, and its performance is evaluated. Then in depth analysis is done to understand its advantages and limitations, and future research directions are suggested. Three conclusions are drawn from this study. (1) The method can effectively eliminate biases in precipitation amount and areal coverage. The corrected precipitation amount and area coverage are much closer to the observations. (2) The method works better when bias is higher. (3) This method, in principle, has no ability to correct precipitation position errors, but through precipitation area alternation, large area of erroneous or spurious light rain from model forecasts can be effectively removed, resulting in significantly improved TS and ETS scores for light precipitation. Therefore, this calibration method can greatly increase the accuracy of a “rain or no rain” dichotomous forecast in numerical weather prediction. In addition, five possible approaches are proposed to remedy the inability of this method in correcting precipitation position error. This method can also be used at single station. Hydrological application of this method is apparent since an accurate input of precipitation amount and areal coverage is critical to a hydrological forecast model over a watershed. Besides for precipitation, this method can also be applied to correct forecast bias for other variables like fog.
2014, 40(5):589-597.
DOI: 10.7519/j.issn.1000-0526.2014.05.009
Abstract:
How to extract the echo intensity used for quantitative precipitation estimation (QPE) from the 3 D mosaic data of China New Generation Weather Radar (CINRAD) is the key to improve the radar rainfall estimation. With the purpose of analyzing hybrid echo intensity quality extracted from the 3 D mosaic data and the influence on the precipitation estimation, by using the radar data of Zhejiang Province and nationwide rainfall station data, this paper studies the relationship between the echo intensity and the suface precipitation amount and analyzes several factors that affect the accuracy of precipitation estimation. According to the ratio distribution, which is got by the whole weather process accumulation of precipitation estimation from the radar echo intensity and the collected rainfall from the automatic rainfall stations in Zhejiang Province and the surrounding areas, several abnormal regions are found including the region where regional echo intensity is relatively high, the region where regional echo intensity is underestimated, the region where regional echo intensity varies with topography, the region where regional echo intensity is estimated to be relatively reasonable and the region where regional echo intensity is gradually overestimated with increasing latitude. The analysis results show that the 0℃ bright band, the residual ground echo, the abnormal radar echo intensity vertical profile, the quality of the rainfall station data, etc. are causes for the abnormal relationship between echo intensity and ground precipitation amount. Finally, by using parts of the rainfall station data, the precipitation estimation from the radar is corrected and the results show that the rainfall station correction can alleviate the degree of the regional overestimation or underestimation to some extent.
How to extract the echo intensity used for quantitative precipitation estimation (QPE) from the 3 D mosaic data of China New Generation Weather Radar (CINRAD) is the key to improve the radar rainfall estimation. With the purpose of analyzing hybrid echo intensity quality extracted from the 3 D mosaic data and the influence on the precipitation estimation, by using the radar data of Zhejiang Province and nationwide rainfall station data, this paper studies the relationship between the echo intensity and the suface precipitation amount and analyzes several factors that affect the accuracy of precipitation estimation. According to the ratio distribution, which is got by the whole weather process accumulation of precipitation estimation from the radar echo intensity and the collected rainfall from the automatic rainfall stations in Zhejiang Province and the surrounding areas, several abnormal regions are found including the region where regional echo intensity is relatively high, the region where regional echo intensity is underestimated, the region where regional echo intensity varies with topography, the region where regional echo intensity is estimated to be relatively reasonable and the region where regional echo intensity is gradually overestimated with increasing latitude. The analysis results show that the 0℃ bright band, the residual ground echo, the abnormal radar echo intensity vertical profile, the quality of the rainfall station data, etc. are causes for the abnormal relationship between echo intensity and ground precipitation amount. Finally, by using parts of the rainfall station data, the precipitation estimation from the radar is corrected and the results show that the rainfall station correction can alleviate the degree of the regional overestimation or underestimation to some extent.
2014, 40(5):598-604.
DOI: 10.7519/j.issn.1000-0526.2014.05.010
Abstract:
During the winter 2012, Beijing suffered 3 high influence weather events: lasting cold weather in December, continuous fog and haze in January 2013 and freezing rain on 31 January 2013. The three events brought many adverse effects to Beijing, and have become the focus of the whole society. Using conventional observation data and the atmospheric component data， the causes for the three extreme events are studied, and the intrinsic relations among them are analyzed. The results show that: (1) Frequent cold air activities and intensity are the main cause for the continuous low temperature event, which leads to continuous fog, haze and freezing rain. (2) From the atmospheric stability analysis, we find that the horizontal stability of cold and warm advection is corresponding to the level of pollutant concentration; and, vertically, the low temperature in boundary layer and dry warm advection to the top of the boundary layer play an important role for the accumulation of haze. (3) Low temperature in low level and warm air in the sky contribute to a freezing rain stratification. Therefore, one extreme weather event that may lead to other extreme weather events should be concerned about.
During the winter 2012, Beijing suffered 3 high influence weather events: lasting cold weather in December, continuous fog and haze in January 2013 and freezing rain on 31 January 2013. The three events brought many adverse effects to Beijing, and have become the focus of the whole society. Using conventional observation data and the atmospheric component data， the causes for the three extreme events are studied, and the intrinsic relations among them are analyzed. The results show that: (1) Frequent cold air activities and intensity are the main cause for the continuous low temperature event, which leads to continuous fog, haze and freezing rain. (2) From the atmospheric stability analysis, we find that the horizontal stability of cold and warm advection is corresponding to the level of pollutant concentration; and, vertically, the low temperature in boundary layer and dry warm advection to the top of the boundary layer play an important role for the accumulation of haze. (3) Low temperature in low level and warm air in the sky contribute to a freezing rain stratification. Therefore, one extreme weather event that may lead to other extreme weather events should be concerned about.
11 Case Analysis of Marine Effect Snowstorm in Northwestern Laizhou Bay and Northern Shandong Peninsula
2014, 40(5):605-611.
DOI: 10.7519/j.issn.1000-0526.2014.05.011
Abstract:
Based on the conventional observational data, NCEP reanalysis data and automatic weather station data, the marine effect snowstorm which happened in the west of Laizhou Bay on 8 December 2011 was analyzed diagnostically. The findings show that snowfall occurs in appropriate ambient field, favorable air sea temperature difference and more intensive cold advection. However, differences exist in wind field configuration, air sea temperature difference range, water vapor distribution dynamic conditions and thermal conditions. During this snowfall process, northwest winds blow above 900 hPa whice under the level, it maintains sustained northeasterly which is the main reason for this marine effect snowstorm process. This wind field is different from the northern peninsula where northwest winds blow in both upper and low airs. By analyzing the physical field, the marine effect snowfall belongs to shallow convective snowfall. There is upward motion, moisture convergence center, unstable stratification and large air sea temperature difference under 900 hPa in the west of Laizhou Bay, and the shear line of near surface triggers the release of unstable energy in the process. The heavy snowfall area is the warm tongue of equivalent potential temperature at 1000 hPa. The position of warm tongue here is different from that in the north of Shandong Peninsula. The former is in Laizhou Bay, while the latter is in the northern coast of the peninsula. From the cloud images, the cold airflow clouds on the sea show a streamwise cloud line, and the cloud is individual cells. When nearing the land, the clouds get thickened, cloud line deflects and the intensity of snowfall increases.
Based on the conventional observational data, NCEP reanalysis data and automatic weather station data, the marine effect snowstorm which happened in the west of Laizhou Bay on 8 December 2011 was analyzed diagnostically. The findings show that snowfall occurs in appropriate ambient field, favorable air sea temperature difference and more intensive cold advection. However, differences exist in wind field configuration, air sea temperature difference range, water vapor distribution dynamic conditions and thermal conditions. During this snowfall process, northwest winds blow above 900 hPa whice under the level, it maintains sustained northeasterly which is the main reason for this marine effect snowstorm process. This wind field is different from the northern peninsula where northwest winds blow in both upper and low airs. By analyzing the physical field, the marine effect snowfall belongs to shallow convective snowfall. There is upward motion, moisture convergence center, unstable stratification and large air sea temperature difference under 900 hPa in the west of Laizhou Bay, and the shear line of near surface triggers the release of unstable energy in the process. The heavy snowfall area is the warm tongue of equivalent potential temperature at 1000 hPa. The position of warm tongue here is different from that in the north of Shandong Peninsula. The former is in Laizhou Bay, while the latter is in the northern coast of the peninsula. From the cloud images, the cold airflow clouds on the sea show a streamwise cloud line, and the cloud is individual cells. When nearing the land, the clouds get thickened, cloud line deflects and the intensity of snowfall increases.
12 Droplet Spectrum Characteristics and Depth Forecast Method of Two Snowstorms in Northwest of Hubei
2014, 40(5):612-618.
DOI: 10.7519/j.issn.1000-0526.2014.05.012
Abstract:
The droplet spectrum variation characteristics and snow depth forecast of the two snowstorms in 14-15 December 2010 and 20-22 January 2012 are studied by using Thies Clima laser precipitation monitor (TCLPM) and artificial observation data from Danjiangkou Station. The results show that: (1) the TCLPM can automatically identify the precipitation phase state. Combined with surface artificial dense observations, the temperature higher than 0.7℃ is for precipitation phase state, less than 0.7℃ is for sleet, below -0.5℃ is for pure snow. At the same time, when the surface temperature is below 0.5℃, snow begins to accumulate. The surface wind speeds in the two processes are relatively slow, conducive to snow accumulation on the ground; (2) the TCLPM can monitor the variation of droplet spectrum characteristics of heavy snowfall weather, the echo intensity (Z), average diameter (Dm), water content (W), snowfall particle number concentration (N) which increases with the enhancement of snowfall intensity. During the two snowstorm events, there are different levels of positive correlations among Dm, Z, N, W and VSD, better correlation between W and VSD, respectively reaching 0.844 and 0.926; (3) Selecting the first order fitting snow particles in water content W and surface snow rate, the snow rate forecast equation is derived compare surface snow rate forecast (VSDF) in the pure snow stage and the surface snow depth forecasts (SDF) to VSD, SD retrieved with the observation data by TCLPM it is found that they are very close, indicating this method can be used to estimate VSD and SD on the surface snow rate and snow depth, which can reflect the main time period with quick increase of surface snow.
The droplet spectrum variation characteristics and snow depth forecast of the two snowstorms in 14-15 December 2010 and 20-22 January 2012 are studied by using Thies Clima laser precipitation monitor (TCLPM) and artificial observation data from Danjiangkou Station. The results show that: (1) the TCLPM can automatically identify the precipitation phase state. Combined with surface artificial dense observations, the temperature higher than 0.7℃ is for precipitation phase state, less than 0.7℃ is for sleet, below -0.5℃ is for pure snow. At the same time, when the surface temperature is below 0.5℃, snow begins to accumulate. The surface wind speeds in the two processes are relatively slow, conducive to snow accumulation on the ground; (2) the TCLPM can monitor the variation of droplet spectrum characteristics of heavy snowfall weather, the echo intensity (Z), average diameter (Dm), water content (W), snowfall particle number concentration (N) which increases with the enhancement of snowfall intensity. During the two snowstorm events, there are different levels of positive correlations among Dm, Z, N, W and VSD, better correlation between W and VSD, respectively reaching 0.844 and 0.926; (3) Selecting the first order fitting snow particles in water content W and surface snow rate, the snow rate forecast equation is derived compare surface snow rate forecast (VSDF) in the pure snow stage and the surface snow depth forecasts (SDF) to VSD, SD retrieved with the observation data by TCLPM it is found that they are very close, indicating this method can be used to estimate VSD and SD on the surface snow rate and snow depth, which can reflect the main time period with quick increase of surface snow.
2014, 40(5):619-627.
DOI: 10.7519/j.issn.1000-0526.2014.05.013
Abstract:
Using 2008-2013 NOAA/AVHRR 1B satellite data and weather observation data, preliminary research of haze indentification is carried out by digitizing image color processing technology, frequency distribution figure of apparent reflectance and technology of apparent reflectance threshold of visible light channel. And the distinguish indices were applied in haze monitoring of Beijing and surrounding area. The results show that haze is easily distinguished by the color composition of red, green and blue channels with NOAA/AVHRR bands 1, 2, 1 or bands 4, 2, 1 pattern and the colors of remote sensing images are mainly grey, purple and blue. Generally, it is difficult to distinguish haze from mist only by remote sensing images, but with the help of prior knowledge, surrounding environment information and image color, haze can be identified. Apparent reflectance of the first channel of NOAA/AVHRR 1B can be used as spectral index of haze identification. The apparent reflectance values for haze identification in winter, spring, summer, autumn are 0.15-0.32, 0.15-0.30, 0.14-0.30, 0.14-0.32, respectively. And the verification analysis shows that accuracy of haze identification using these spectral indices is 82％. The color indices and reflectance indices are effectively applied in haze monitoring over Beijing and surrounding area from January to March 2013.
Using 2008-2013 NOAA/AVHRR 1B satellite data and weather observation data, preliminary research of haze indentification is carried out by digitizing image color processing technology, frequency distribution figure of apparent reflectance and technology of apparent reflectance threshold of visible light channel. And the distinguish indices were applied in haze monitoring of Beijing and surrounding area. The results show that haze is easily distinguished by the color composition of red, green and blue channels with NOAA/AVHRR bands 1, 2, 1 or bands 4, 2, 1 pattern and the colors of remote sensing images are mainly grey, purple and blue. Generally, it is difficult to distinguish haze from mist only by remote sensing images, but with the help of prior knowledge, surrounding environment information and image color, haze can be identified. Apparent reflectance of the first channel of NOAA/AVHRR 1B can be used as spectral index of haze identification. The apparent reflectance values for haze identification in winter, spring, summer, autumn are 0.15-0.32, 0.15-0.30, 0.14-0.30, 0.14-0.32, respectively. And the verification analysis shows that accuracy of haze identification using these spectral indices is 82％. The color indices and reflectance indices are effectively applied in haze monitoring over Beijing and surrounding area from January to March 2013.
2014, 40(5):628-636.
DOI: 10.7519/j.issn.1000-0526.2014.05.014
Abstract:
Using Puyang CINRDA/SB Doppler radar detection data, conventional data, intensive operational data, this paper analyzed a tornado process that occurred in Puyang on 16 July 2009. The diagnostic results show that the tornado occurs in the northwest of subtropical high edge, the left front of low level jet and near the warm shear line. Before the tornado there are powerful convective instability energy in atmospheric environment, and large wind vertical shear and abundant water vapor in lower levels. In the Doppler radar reflectivity factor chart, the north of mobile bow echo is strongly developed into hooked echo, and the tornado is detected near the weak echo area. Radial velocity diagram shows there is a meso γ scale cyclonic vortex field with convergence. The strengthened vortex leads to the central tornado vortex, producing the tornado weather. In addition, the strong echo, low echo top high, lower strong vertical wind shear are all the characteristics of Doppler radar products.
Using Puyang CINRDA/SB Doppler radar detection data, conventional data, intensive operational data, this paper analyzed a tornado process that occurred in Puyang on 16 July 2009. The diagnostic results show that the tornado occurs in the northwest of subtropical high edge, the left front of low level jet and near the warm shear line. Before the tornado there are powerful convective instability energy in atmospheric environment, and large wind vertical shear and abundant water vapor in lower levels. In the Doppler radar reflectivity factor chart, the north of mobile bow echo is strongly developed into hooked echo, and the tornado is detected near the weak echo area. Radial velocity diagram shows there is a meso γ scale cyclonic vortex field with convergence. The strengthened vortex leads to the central tornado vortex, producing the tornado weather. In addition, the strong echo, low echo top high, lower strong vertical wind shear are all the characteristics of Doppler radar products.
2014, 40(5):637-641.
DOI: 10.7519/j.issn.1000-0526.2014.05.015
Abstract:
In order to improve the ability to use the products of T639, a synoptic verification on its medium range forecasts from December 2013 to February 2014 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 middle and high latitude areas. For temperatures at 850 hPa, ECMWF’s prediction error is the least among the three models, followed by Japan and T639 models in order. Compared with the temperature prediction for the last autumn, the results from the three models are not so good. For the sea level pressure, ECMWF model still shows the best performance among the models. As a whole, the ECMWF model is much better in forecasting most weather systems and meteorological elements than the T639 and Japan models.
In order to improve the ability to use the products of T639, a synoptic verification on its medium range forecasts from December 2013 to February 2014 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 middle and high latitude areas. For temperatures at 850 hPa, ECMWF’s prediction error is the least among the three models, followed by Japan and T639 models in order. Compared with the temperature prediction for the last autumn, the results from the three models are not so good. For the sea level pressure, ECMWF model still shows the best performance among the models. As a whole, the ECMWF model is much better in forecasting most weather systems and meteorological elements than the T639 and Japan models.
2014, 40(5):642-648.
DOI: 10.7519/j.issn.1000-0526.2014.05.016
Abstract:
The main characteristics of the general atmospheric circulation in February 2014 are as follows: There were two polar vortex centres in the Northern Hemisphere and both of them are stronger than normal. The atmospheric circulation represents a four wave pattern over the middle high latitudes. The northwestern Pacific subtropical high is weaker than normal and the south branch trough is more to the west than normal. The monthly mean temperature is -2.3℃, 0.6℃ lower than normal. The monthly mean precipitation amount is 17.5 mm, which is similar to the normal value. During this month, there is one nationwide cold wave process. Obvious rain and snow weathers are seen in the north of China, relieving the drought situation in the winter wheat area. The snow and rain processes are more in the south of China with a large range impacted, which makes many places suffer from cryogenic rain/snow weather and cold damages. Besides, three fog and haze processes appear in the middle and eastern part of China.
The main characteristics of the general atmospheric circulation in February 2014 are as follows: There were two polar vortex centres in the Northern Hemisphere and both of them are stronger than normal. The atmospheric circulation represents a four wave pattern over the middle high latitudes. The northwestern Pacific subtropical high is weaker than normal and the south branch trough is more to the west than normal. The monthly mean temperature is -2.3℃, 0.6℃ lower than normal. The monthly mean precipitation amount is 17.5 mm, which is similar to the normal value. During this month, there is one nationwide cold wave process. Obvious rain and snow weathers are seen in the north of China, relieving the drought situation in the winter wheat area. The snow and rain processes are more in the south of China with a large range impacted, which makes many places suffer from cryogenic rain/snow weather and cold damages. Besides, three fog and haze processes appear in the middle and eastern part of China.
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ISSN:1000-0526 CN:11-2282/P