ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 42,Issue 6,2016 Table of Contents
2016, 42(6):649-663.
DOI: 10.7519/j.issn.1000-0526.2016.06.001
Abstract:
Based on WRF model and the Hybrid ensemble3Dvar data assimilation system, this study compares radar radial velocity (Vr) assimilation with TTREC (TyphoonTracking radar echoes by correlation) retrieved wind data assimilation and their impacts on the analyses and forecasts of tropical cyclone (TC) “Chanthu (2010)”. In addition to the cycling strategy of Vr assimilation and TTREC wind data assimilation, a combined radar data assimilation strategy is proposed, which assimilates TTREC winds at the first cycle and assimilates Vr data during the rest cycles. Concerning the respective advantages of two types of radar wind, the new cycling strategy aims at exploring the suitable radar data assimilation strategy for the forecasting of landfalling TCs. Comparing three different cycling strategies, the cycled assimilation of Vr data requires more analysis cycles, which leads to delayed starting time for the deterministic forecast. By contrast, the assimilation of TTREC data produces better analyses and intensity forecasts than the assimilation of Vr data during the earlier assimilation, due to the larger data coverage and more complete wind fields for TC circulation. However, as the TTREC winds contain retrieved errors, the increase of analysis cycles leads to degraded TC forecast. When the two types of radar wind data are jointly used, the combined radar data assimilation strategy provides favorable forecast results no matter how long the analysis cycles are.
Based on WRF model and the Hybrid ensemble3Dvar data assimilation system, this study compares radar radial velocity (Vr) assimilation with TTREC (TyphoonTracking radar echoes by correlation) retrieved wind data assimilation and their impacts on the analyses and forecasts of tropical cyclone (TC) “Chanthu (2010)”. In addition to the cycling strategy of Vr assimilation and TTREC wind data assimilation, a combined radar data assimilation strategy is proposed, which assimilates TTREC winds at the first cycle and assimilates Vr data during the rest cycles. Concerning the respective advantages of two types of radar wind, the new cycling strategy aims at exploring the suitable radar data assimilation strategy for the forecasting of landfalling TCs. Comparing three different cycling strategies, the cycled assimilation of Vr data requires more analysis cycles, which leads to delayed starting time for the deterministic forecast. By contrast, the assimilation of TTREC data produces better analyses and intensity forecasts than the assimilation of Vr data during the earlier assimilation, due to the larger data coverage and more complete wind fields for TC circulation. However, as the TTREC winds contain retrieved errors, the increase of analysis cycles leads to degraded TC forecast. When the two types of radar wind data are jointly used, the combined radar data assimilation strategy provides favorable forecast results no matter how long the analysis cycles are.
2016, 42(6):664-673.
DOI: 10.7519/j.issn.1000-0526.2016.06.002
Abstract:
Due to the lack of observational data over the tropical oceans, TC (tropical cyclone) initialization for numerical models is one of major difficulties in TC track forecasting. Since the National Meteorological Centre of China Meteorological Administration (NMC/CMA) put the global model T639 into operation in 2009, an effective TC initialization scheme has been used. When TC occurs at first cycle time, a bogus vortex is inserted into the background fields, which is called vortex formation. In the second, third, …, cycle time, the evolutive vortex generated with 6 h output of global model prediction at the previous time in the background fields is initialized by relocation (moving to observed position) and modification (adjusted to observed intensity) techniques. It is obvious that the vortex formation at the first cycle time is so important that it can affect the structure of TC and the forecast results of the subsequent cycle time. But the initial bogus vortex used in the first cycle time is not consistent with the dynamics and physics of the global model. Recently, a new vortex formation scheme based on T639 global analysisforecast cycle in NMC/CMA has been developed successfully. Compared with the operation scheme, the initial vortex of the new scheme is mostly formed by assimilating TC bogus data into the variational assimilation system. It is significant that the initial vortex structure is analyzed with constraint of variational method, not largely affected by the empirical and statistical manual factors. Meanwhile, the analyzed vortex is consistent with the dynamics and physics of the global model and also compatible with environmental flow in the boundary. To evaluate the impact of the new scheme on TC track predictions, more than 672 cases from 27 different TCs during 2011-2012 seasons are examined. The initial study result shows that, compared with operational scheme, the new scheme can generate reasonable and realistic vortex in the initial fields and produce TC track forecast more accurately. Statistical analysis shows a decrease in the average track error of 3%-15% during the 48-120 h time period.
Due to the lack of observational data over the tropical oceans, TC (tropical cyclone) initialization for numerical models is one of major difficulties in TC track forecasting. Since the National Meteorological Centre of China Meteorological Administration (NMC/CMA) put the global model T639 into operation in 2009, an effective TC initialization scheme has been used. When TC occurs at first cycle time, a bogus vortex is inserted into the background fields, which is called vortex formation. In the second, third, …, cycle time, the evolutive vortex generated with 6 h output of global model prediction at the previous time in the background fields is initialized by relocation (moving to observed position) and modification (adjusted to observed intensity) techniques. It is obvious that the vortex formation at the first cycle time is so important that it can affect the structure of TC and the forecast results of the subsequent cycle time. But the initial bogus vortex used in the first cycle time is not consistent with the dynamics and physics of the global model. Recently, a new vortex formation scheme based on T639 global analysisforecast cycle in NMC/CMA has been developed successfully. Compared with the operation scheme, the initial vortex of the new scheme is mostly formed by assimilating TC bogus data into the variational assimilation system. It is significant that the initial vortex structure is analyzed with constraint of variational method, not largely affected by the empirical and statistical manual factors. Meanwhile, the analyzed vortex is consistent with the dynamics and physics of the global model and also compatible with environmental flow in the boundary. To evaluate the impact of the new scheme on TC track predictions, more than 672 cases from 27 different TCs during 2011-2012 seasons are examined. The initial study result shows that, compared with operational scheme, the new scheme can generate reasonable and realistic vortex in the initial fields and produce TC track forecast more accurately. Statistical analysis shows a decrease in the average track error of 3%-15% during the 48-120 h time period.
2016, 42(6):674-685.
DOI: 10.7519/j.issn.1000-0526.2016.06.003
Abstract:
The advantages of the anomalous synoptic systems over the traditional total ones in locating regional heavy rain (RHR) have been revealed by recent work of the anomalybased synoptic chart. Fortyone daily heavy rain cases in eastern China from 1998 are grouped into seven patterns based on the anomalous synoptic systems. The seven patterns of anomalous synoptic systems associated with regional heavy rain include the shear in South China, vortex in South China, reversed trough in South China, shear and trough along the Yangtze River, vortex along the Yangtze River, vortex in North China and vortex in Northeast China. The RHR can be well located by the negative regions of anomalous geopotential height, wind anomalous convergence combined with high moisture anomaly, which is evident from both the vertical crosssections and the 850 hPa horizontal distributions. This overcomes the shortage of traditional synoptic chart in which total field systems and high moisture regions do not collocate with heavy rain areas. It is recommended that anomalybased synoptic chart should be applied in the practice of shortterm and mediumrange forecasts by using the products of the current stateoftheart operational numerical weather models.
The advantages of the anomalous synoptic systems over the traditional total ones in locating regional heavy rain (RHR) have been revealed by recent work of the anomalybased synoptic chart. Fortyone daily heavy rain cases in eastern China from 1998 are grouped into seven patterns based on the anomalous synoptic systems. The seven patterns of anomalous synoptic systems associated with regional heavy rain include the shear in South China, vortex in South China, reversed trough in South China, shear and trough along the Yangtze River, vortex along the Yangtze River, vortex in North China and vortex in Northeast China. The RHR can be well located by the negative regions of anomalous geopotential height, wind anomalous convergence combined with high moisture anomaly, which is evident from both the vertical crosssections and the 850 hPa horizontal distributions. This overcomes the shortage of traditional synoptic chart in which total field systems and high moisture regions do not collocate with heavy rain areas. It is recommended that anomalybased synoptic chart should be applied in the practice of shortterm and mediumrange forecasts by using the products of the current stateoftheart operational numerical weather models.
2016, 42(6):686-695.
DOI: 10.7519/j.issn.1000-0526.2016.06.004
Abstract:
By using regular meteorological observations data, regional automatic station observation data, Doppler radar data, 1°×1° NCEP 6 h interval reanalysis data and hourly FY2C satellite TBB data, the forming mechanism and mesoscale system activity feature of the heavy rainstorm seen in Shangqiu in 7-8 July 2012 are analyzed. The results show that the trough at 500 hPa and eastwest shear line in the low level are compatible with the lowlevel jet stream, forming the largescale circulation for the rainstorm. Mesoscale analysis shows that several convective cells develop into four rainfall centers, and the convective cells accompany the MαCS, which is merged and strengthened by some MγCS and MβCS. The MγCS and MβCS are triggered, generated and developed by the ground mesoscale convergent systems or convergence center. The movement and development of heavy precipitation echoes correspond better with ground moderate convergence systems. The rainstorm occurs after the formation of ground convergence system within 1-2 hours. The warming in some local areas caused by warm advection is the main cause for the formation of surface mesoscale convergence system. Rainfall intensity is proportional to the TBB gradient. When TBB/0.5°E≥34℃, and TBB≤-63℃, severe rainfall of 30 mm·h-1 would occur. When MCS (mesoscale convective system) gets matured, heavy precipitation occurs near the low TBB center of the mesoscale convective clouds and when TBB is lower than 31℃ in one hour, shorttime severe rainstorm of 50 mm intensity would appear in 1-2 hours. Therefore, the uneven local ground heat warming is the main cause of this moderate convergence system. Moreover, the development of ground moderate convergence systems trigger the evolution of mesoscale convective systems, leading to the generation of local heavy rainstorm. So according to the TBB intensity and the variation of mesoscale convective clouds, forecast of shorttime heavy rainfall can be made in advance of 1-2 hours.
By using regular meteorological observations data, regional automatic station observation data, Doppler radar data, 1°×1° NCEP 6 h interval reanalysis data and hourly FY2C satellite TBB data, the forming mechanism and mesoscale system activity feature of the heavy rainstorm seen in Shangqiu in 7-8 July 2012 are analyzed. The results show that the trough at 500 hPa and eastwest shear line in the low level are compatible with the lowlevel jet stream, forming the largescale circulation for the rainstorm. Mesoscale analysis shows that several convective cells develop into four rainfall centers, and the convective cells accompany the MαCS, which is merged and strengthened by some MγCS and MβCS. The MγCS and MβCS are triggered, generated and developed by the ground mesoscale convergent systems or convergence center. The movement and development of heavy precipitation echoes correspond better with ground moderate convergence systems. The rainstorm occurs after the formation of ground convergence system within 1-2 hours. The warming in some local areas caused by warm advection is the main cause for the formation of surface mesoscale convergence system. Rainfall intensity is proportional to the TBB gradient. When TBB/0.5°E≥34℃, and TBB≤-63℃, severe rainfall of 30 mm·h-1 would occur. When MCS (mesoscale convective system) gets matured, heavy precipitation occurs near the low TBB center of the mesoscale convective clouds and when TBB is lower than 31℃ in one hour, shorttime severe rainstorm of 50 mm intensity would appear in 1-2 hours. Therefore, the uneven local ground heat warming is the main cause of this moderate convergence system. Moreover, the development of ground moderate convergence systems trigger the evolution of mesoscale convective systems, leading to the generation of local heavy rainstorm. So according to the TBB intensity and the variation of mesoscale convective clouds, forecast of shorttime heavy rainfall can be made in advance of 1-2 hours.
2016, 42(6):696-708.
DOI: 10.7519/j.issn.1000-0526.2016.06.005
Abstract:
Using the data of conventional observation, mesoscale automatic station and new generation monostation radar, and networking and mosaic products, FY2C infrared images and 6 h NCEP reanalysis data, mesoanalysis was taken on the process of widespread hail in Taizhou of Zhejiang on 19 March 2014. The results show that: (1) According to the analysis of environmental field conditions and the corrected sounding data, the lower wet and upper dry structure in Taizhou was unstable. In the situation of increased ground temperature and convective available potential energy and relatively large vertical wind shear at 0-3 km and 0-6 km after noon, wetness was conductive to the formation of severe convective weather such as the gale and hail. (2) According to the movement and evolution of cold front that triggered the movement of synopticscale convective system, the whole process could be divided into four stages, and the thunderstorm, gale and widespread hail appeared in the third stage. (3) The mature stage could be divided into three stages of squall line formation, bow echo and outbreak of hailstorm cells due to the echo forms of the system, which revealed the significantly different element characteristics in the automatic station elements and radar products compared to other stages. (4) The abundant vapor in the nearsurface layer, lower lifting condensation level, southern oscillation of southern branch trough and northern transverse trough, systematic lifting on the left of upperlevel jet stream exit area, and triggering of cold front near surface, mesoscale convergence line and landform were the main causes for the enhanced outbreak of squall system in Taizhou, leading to hail weather with gale. (5) Forecasters make full use of timeliness advantages of automatic stations, carrying out the correction of mesoanalysis work can effectively improve the quality of nowcasting.
Using the data of conventional observation, mesoscale automatic station and new generation monostation radar, and networking and mosaic products, FY2C infrared images and 6 h NCEP reanalysis data, mesoanalysis was taken on the process of widespread hail in Taizhou of Zhejiang on 19 March 2014. The results show that: (1) According to the analysis of environmental field conditions and the corrected sounding data, the lower wet and upper dry structure in Taizhou was unstable. In the situation of increased ground temperature and convective available potential energy and relatively large vertical wind shear at 0-3 km and 0-6 km after noon, wetness was conductive to the formation of severe convective weather such as the gale and hail. (2) According to the movement and evolution of cold front that triggered the movement of synopticscale convective system, the whole process could be divided into four stages, and the thunderstorm, gale and widespread hail appeared in the third stage. (3) The mature stage could be divided into three stages of squall line formation, bow echo and outbreak of hailstorm cells due to the echo forms of the system, which revealed the significantly different element characteristics in the automatic station elements and radar products compared to other stages. (4) The abundant vapor in the nearsurface layer, lower lifting condensation level, southern oscillation of southern branch trough and northern transverse trough, systematic lifting on the left of upperlevel jet stream exit area, and triggering of cold front near surface, mesoscale convergence line and landform were the main causes for the enhanced outbreak of squall system in Taizhou, leading to hail weather with gale. (5) Forecasters make full use of timeliness advantages of automatic stations, carrying out the correction of mesoanalysis work can effectively improve the quality of nowcasting.
2016, 42(6):709-715.
DOI: 10.7519/j.issn.1000-0526.2016.06.006
Abstract:
Based on NOAA OLR, NCEP/NCAR height and wind monthly reanalysis data and CMA tropical cyclone data during 1951-2013, the causes of more tropical cyclones (TCs) that affected Guangxi in 2013 are analyzed. The results show that the West Pacific subtropical high (WPSH) was exceptionally stronger than in other years and its west ridge point abnormally stretched westward and northward from June to September 2013, which is favorable for more TCs to affect Guangxi. At the same time, the condensation latent heat released by rainfall on the south side of WPSH may be in favor of the northward extension of WSPH. Besides, the Somali crossequatorial flow was stronger than normal, and joined in a southeast air flow on the southwest side of north Pacific anticyclone over South China Sea and Philippines, forming a monsoon trough, which is very conducive to the generation of more TCs in 2013. The results also show that there were much more activities and eastward (westward) propagation of lowfrequency convections over India Ocean and west Pacific Ocean, lower SST in the eastern equatorial Pacific, stronger Hadley and Walker circulations and a westward deviation of the ascending branch of Walker circulation, and all of these factors could lead to the occurrence of more TCs in 2013.
Based on NOAA OLR, NCEP/NCAR height and wind monthly reanalysis data and CMA tropical cyclone data during 1951-2013, the causes of more tropical cyclones (TCs) that affected Guangxi in 2013 are analyzed. The results show that the West Pacific subtropical high (WPSH) was exceptionally stronger than in other years and its west ridge point abnormally stretched westward and northward from June to September 2013, which is favorable for more TCs to affect Guangxi. At the same time, the condensation latent heat released by rainfall on the south side of WPSH may be in favor of the northward extension of WSPH. Besides, the Somali crossequatorial flow was stronger than normal, and joined in a southeast air flow on the southwest side of north Pacific anticyclone over South China Sea and Philippines, forming a monsoon trough, which is very conducive to the generation of more TCs in 2013. The results also show that there were much more activities and eastward (westward) propagation of lowfrequency convections over India Ocean and west Pacific Ocean, lower SST in the eastern equatorial Pacific, stronger Hadley and Walker circulations and a westward deviation of the ascending branch of Walker circulation, and all of these factors could lead to the occurrence of more TCs in 2013.
2016, 42(6):716-723.
DOI: 10.7519/j.issn.1000-0526.2016.06.007
Abstract:
The diagnosis analysis for the development mechanism of a cyclone over ChangjiangHuaihe and rainstorm that occurred from 25 to 27 May 2013 was studied utilizing the NCEP/NCAR reanalysis data. The results indicate that positive vorticity advection in upper level, warm air advection in lower level, the divergence located in the right side of the entry of upper jet and convergence located in the left side of the exit of low jet are the most important physical factors for the developing of the cyclone. The development of cyclone is consistent with the mpv1 and mpv2 of moist potential vorticity. Formation and development mechanisms of the cyclone correspond to development of vorticity column troposphere, and the download of positive vorticity advection in upper level intensifies the vortex in lower troposphere. The downward extension of moist potential vorticity could have increased the positive vorticity in the lower level and induced cyclonic circulation. The rainstorm triggered by the cyclone is located in the left front of moving track of the cyclone. Coupling structure of intensity convergence and positive vorticity center enhances the convergence of water vapor and energy, which creates the conditions for the maintenance of rainstorm.
The diagnosis analysis for the development mechanism of a cyclone over ChangjiangHuaihe and rainstorm that occurred from 25 to 27 May 2013 was studied utilizing the NCEP/NCAR reanalysis data. The results indicate that positive vorticity advection in upper level, warm air advection in lower level, the divergence located in the right side of the entry of upper jet and convergence located in the left side of the exit of low jet are the most important physical factors for the developing of the cyclone. The development of cyclone is consistent with the mpv1 and mpv2 of moist potential vorticity. Formation and development mechanisms of the cyclone correspond to development of vorticity column troposphere, and the download of positive vorticity advection in upper level intensifies the vortex in lower troposphere. The downward extension of moist potential vorticity could have increased the positive vorticity in the lower level and induced cyclonic circulation. The rainstorm triggered by the cyclone is located in the left front of moving track of the cyclone. Coupling structure of intensity convergence and positive vorticity center enhances the convergence of water vapor and energy, which creates the conditions for the maintenance of rainstorm.
2016, 42(6):724-731.
DOI: 10.7519/j.issn.1000-0526.2016.06.008
Abstract:
By analyzing the NCEP 1°×1° 6 h reanalysis data and conventional and nonconventional observation data from May to September during 2007-2013, the warmsector rainstorms over the middlelower reaches of the Yangtze River are studied. The warmsector rainstorms in this area can be divided into three types based on the weather situation, which are coldfront, warm shearline and the edge of subtropical high. The statistical results show that the warmsector rainstorms occur generally in the warm sector being 100-300 km away from the shear line at 850 hPa (cold front on the ground). The significant characteristics obtained from the research are: (1) the coldfronttype precipitation often occurs in May and June, with weak intensity and uniform distribution. The warm shearlinetype rainfall usually occurs in the south part of this area with high frequency and strong intensity, mainly in June and July. The precipitation on the edge of subtropical high occurs least but with the strongest intensity and often in July and August. The orographic action of the Dabie Mountain and Wannan Mountain provide favorable conditions for local heavy rains. (2) Shorttime heavy rainfalls make great contribution to the rainstorm. (3) The warmsector rainstorms under the background of cold front generally happen in the prefrontal trough, and the rainfall area is closely related to the coupling of upper and lowlevel jets. In the second type, the rainstorms have high correlations with the structure of mesoscale jet and topographic forcing under the background of warm shear line in the lower level and stationary front on the ground. And the heavy rainfall happens on the edge of the subtropical high has close relations with accumulation of water vapor and the development of convective instability condition. Thus, three kinds of conceptual model have been built based on the above.
By analyzing the NCEP 1°×1° 6 h reanalysis data and conventional and nonconventional observation data from May to September during 2007-2013, the warmsector rainstorms over the middlelower reaches of the Yangtze River are studied. The warmsector rainstorms in this area can be divided into three types based on the weather situation, which are coldfront, warm shearline and the edge of subtropical high. The statistical results show that the warmsector rainstorms occur generally in the warm sector being 100-300 km away from the shear line at 850 hPa (cold front on the ground). The significant characteristics obtained from the research are: (1) the coldfronttype precipitation often occurs in May and June, with weak intensity and uniform distribution. The warm shearlinetype rainfall usually occurs in the south part of this area with high frequency and strong intensity, mainly in June and July. The precipitation on the edge of subtropical high occurs least but with the strongest intensity and often in July and August. The orographic action of the Dabie Mountain and Wannan Mountain provide favorable conditions for local heavy rains. (2) Shorttime heavy rainfalls make great contribution to the rainstorm. (3) The warmsector rainstorms under the background of cold front generally happen in the prefrontal trough, and the rainfall area is closely related to the coupling of upper and lowlevel jets. In the second type, the rainstorms have high correlations with the structure of mesoscale jet and topographic forcing under the background of warm shear line in the lower level and stationary front on the ground. And the heavy rainfall happens on the edge of the subtropical high has close relations with accumulation of water vapor and the development of convective instability condition. Thus, three kinds of conceptual model have been built based on the above.
2016, 42(6):732-742.
DOI: 10.7519/j.issn.1000-0526.2016.06.009
Abstract:
This paper introduced geographical position of 5 100 m high meteorological towers in Urumqi. A series of quality control methods were advanced to deal with observation data, such as logical extreme check, static check, time consistency check and similarity check. Besides, a series of data interpolation methods were advanced to interpolation controlled data, such as four point moving average interpolation, elements of vertical distribution fitting and linear regression. Especially in the treatment process, using manual intervention can make the test results more reliable. The quality control method was applied to data from the 5100 m high meteorology towers from 1 April 2012 to 30 April 2014 in Urumqi. The results showed that the method can differentiate the missing, error and dubious. The data of 5 towers are reliable with normal data accounting for 97.17% of the total data, which is the best quality of Hongguangshan tower (normal data accounting for 99.01% of the total data). Abnormal data only account for a small proportion (accounting for 2.83% of the total data), including missing data and error data. Missing data accounts for 6.23% of the abnormal data, which mainly occurred in Midong Tower and Yannanlijiao; error data accounts for 93.77% of the abnormal data. Among error data, false data accounts for 89.99% of the error data (mainly wind speed and wind direction); static data accounts for 5.47% of the error data (mainly air temperature and relative humidity); extreme error data accounts for 0.41% of the error data (mainly air temperature in Shuitashan Tower); consistency error data accounts for 4.13% of error data (mainly relative humidity in Yannanlijiao Tower). The effect of temperature and relative humidity interpolation are better by using the four points moving average interpolation method, elements of vertical distribution fitting method and linear regression method between different meteorological towers.
This paper introduced geographical position of 5 100 m high meteorological towers in Urumqi. A series of quality control methods were advanced to deal with observation data, such as logical extreme check, static check, time consistency check and similarity check. Besides, a series of data interpolation methods were advanced to interpolation controlled data, such as four point moving average interpolation, elements of vertical distribution fitting and linear regression. Especially in the treatment process, using manual intervention can make the test results more reliable. The quality control method was applied to data from the 5100 m high meteorology towers from 1 April 2012 to 30 April 2014 in Urumqi. The results showed that the method can differentiate the missing, error and dubious. The data of 5 towers are reliable with normal data accounting for 97.17% of the total data, which is the best quality of Hongguangshan tower (normal data accounting for 99.01% of the total data). Abnormal data only account for a small proportion (accounting for 2.83% of the total data), including missing data and error data. Missing data accounts for 6.23% of the abnormal data, which mainly occurred in Midong Tower and Yannanlijiao; error data accounts for 93.77% of the abnormal data. Among error data, false data accounts for 89.99% of the error data (mainly wind speed and wind direction); static data accounts for 5.47% of the error data (mainly air temperature and relative humidity); extreme error data accounts for 0.41% of the error data (mainly air temperature in Shuitashan Tower); consistency error data accounts for 4.13% of error data (mainly relative humidity in Yannanlijiao Tower). The effect of temperature and relative humidity interpolation are better by using the four points moving average interpolation method, elements of vertical distribution fitting method and linear regression method between different meteorological towers.
2016, 42(6):743-755.
DOI: 10.7519/j.issn.1000-0526.2016.06.010
Abstract:
In this study, the differences of temperature and humidity profiles over China obtained from L band sounding system, COSMIC occulation observation system and ERAInterim reanalysis data during the period 2011-2013 are compared. Time series comparisons show a good positive linear correlation among these three data sets. In addition to a few levels above 10 hPa, L band, COSMIC occultation and ERAInterim reanalysis temperature data accord well with each other, with the temperature bias ranging within ±0.4℃, and the standard deviation between 1℃ and 2℃. L band temperature is higher due to the great influence by solar radiation in the middle to upper troposphere, with the maximum bias of 0.64℃ when compared with COSMIC occultation. As for relative humidity, things are strikingly different. L band relative humidity data exhibit a varying degree of dry bias between the lower troposphere and the upper troposphere. Moreover, there are obvious diurnal, seasonal and climate regional differences, and the differences become even more evident during daytime, spring/summer period, and over south moisture climate areas. Generally, the dry bias is more obvious in the region near the top of troposphere; L band relative humidity turns to wet bias at above 200 hPa atmospheric pressure layer. L band and COSMIC occultation sounding relative humidity, ERAInterim relative humidity have positive correlations obviously below the top of troposphere. Nevertheless, there is a negative correlation above the tropopause.
In this study, the differences of temperature and humidity profiles over China obtained from L band sounding system, COSMIC occulation observation system and ERAInterim reanalysis data during the period 2011-2013 are compared. Time series comparisons show a good positive linear correlation among these three data sets. In addition to a few levels above 10 hPa, L band, COSMIC occultation and ERAInterim reanalysis temperature data accord well with each other, with the temperature bias ranging within ±0.4℃, and the standard deviation between 1℃ and 2℃. L band temperature is higher due to the great influence by solar radiation in the middle to upper troposphere, with the maximum bias of 0.64℃ when compared with COSMIC occultation. As for relative humidity, things are strikingly different. L band relative humidity data exhibit a varying degree of dry bias between the lower troposphere and the upper troposphere. Moreover, there are obvious diurnal, seasonal and climate regional differences, and the differences become even more evident during daytime, spring/summer period, and over south moisture climate areas. Generally, the dry bias is more obvious in the region near the top of troposphere; L band relative humidity turns to wet bias at above 200 hPa atmospheric pressure layer. L band and COSMIC occultation sounding relative humidity, ERAInterim relative humidity have positive correlations obviously below the top of troposphere. Nevertheless, there is a negative correlation above the tropopause.
2016, 42(6):756-763.
DOI: 10.7519/j.issn.1000-0526.2016.06.011
Abstract:
Using daily lowest temperature observation data of five meteorological stations in the east of Hexi Corridor during 1961-2010, the number of strong cooling ［the lowest temperature drop rate is ≥ 8 (10)℃ and the minimum temperature is ≤ 4℃ in 24(48 h) in recent 50 years］ was calculated. Climatic characteristics of spatiotemperal distribution and intensity of strong cooling were systematically analyzed with statistical methods. Then the ECMWF 500 hPa numerical forecast grid data (2.5°×2.5°) from 1991 to 2010 was used to analyze the strong cooling circulation features in this region. Finally, relations between strong cooling times and atmospheric circulation characteristics were studied. The results show that strong cooling times distribute differently in eastern Hexi Corridor and it is more obviously in highelevation mountains and northern desert edge than in oasis plain area due to the block of terrain, vegetation and mountains. Strong cool weather has obvious regional characteristics, and the times reduces with the increase of strong cooling station number. The decadal and annual times of strong cooling show a decreasing trend, and time series of strong cooling times has 4-6 year quasiperiodic variation, but no mutations. Such weather occurs mainly from January to May and from September to December, but most in April. Times of strong cooling with different intensities varies greatly reducing rapidly with the increase of cooling intensity. Intensity of 24 h strong cooling has a weak reducing tendency, while that of 48 h strong cooling shows a slightly increasing trend. Typical circulation of strong cooling weather in eastern Hexi Corridor is divided into two categories, including northwest airflow type and northern airflow type, and the number of northwest airflow type is more than that of northern airflow type. A significantly positive correlation exists between monthly strong cooling times and circulation characteristics including highaltitude cold air strength and cold air moving path, which means that a close relationship exists between strong cooling times and the highlevel cold air strength and cold air moving path. Intensity and moving path of highlevel cold air are strong signals for the forecasting of strong cooling weather.
Using daily lowest temperature observation data of five meteorological stations in the east of Hexi Corridor during 1961-2010, the number of strong cooling ［the lowest temperature drop rate is ≥ 8 (10)℃ and the minimum temperature is ≤ 4℃ in 24(48 h) in recent 50 years］ was calculated. Climatic characteristics of spatiotemperal distribution and intensity of strong cooling were systematically analyzed with statistical methods. Then the ECMWF 500 hPa numerical forecast grid data (2.5°×2.5°) from 1991 to 2010 was used to analyze the strong cooling circulation features in this region. Finally, relations between strong cooling times and atmospheric circulation characteristics were studied. The results show that strong cooling times distribute differently in eastern Hexi Corridor and it is more obviously in highelevation mountains and northern desert edge than in oasis plain area due to the block of terrain, vegetation and mountains. Strong cool weather has obvious regional characteristics, and the times reduces with the increase of strong cooling station number. The decadal and annual times of strong cooling show a decreasing trend, and time series of strong cooling times has 4-6 year quasiperiodic variation, but no mutations. Such weather occurs mainly from January to May and from September to December, but most in April. Times of strong cooling with different intensities varies greatly reducing rapidly with the increase of cooling intensity. Intensity of 24 h strong cooling has a weak reducing tendency, while that of 48 h strong cooling shows a slightly increasing trend. Typical circulation of strong cooling weather in eastern Hexi Corridor is divided into two categories, including northwest airflow type and northern airflow type, and the number of northwest airflow type is more than that of northern airflow type. A significantly positive correlation exists between monthly strong cooling times and circulation characteristics including highaltitude cold air strength and cold air moving path, which means that a close relationship exists between strong cooling times and the highlevel cold air strength and cold air moving path. Intensity and moving path of highlevel cold air are strong signals for the forecasting of strong cooling weather.
2016, 42(6):764-769.
DOI: 10.7519/j.issn.1000-0526.2016.06.012
Abstract:
The test procedure and result analysis of the comparative observation experiment on some laser ceilometers at Beijing Meteorological Observatory and Changsha Meteorological Service from June to October 2014 are introduced. Fifteen instruments from four manufacturers were tested in the experiment that lasted for more than three months. The experiment used the observation results of HYCL51 and CYY2B Laser Ceilometers as the standard cloud heights. The artificial observations played a subsidiary role in testing the accuracy of these instruments when cloud heights are detected. The results show that observation omission and misjudgment tend to happen to all these laser ceilometers. Fog and haze impact the performance of the instruments significantly. Comparatively, HYCL31 has a higher accuracy rate, which can meet the needs of meteorological service.
The test procedure and result analysis of the comparative observation experiment on some laser ceilometers at Beijing Meteorological Observatory and Changsha Meteorological Service from June to October 2014 are introduced. Fifteen instruments from four manufacturers were tested in the experiment that lasted for more than three months. The experiment used the observation results of HYCL51 and CYY2B Laser Ceilometers as the standard cloud heights. The artificial observations played a subsidiary role in testing the accuracy of these instruments when cloud heights are detected. The results show that observation omission and misjudgment tend to happen to all these laser ceilometers. Fog and haze impact the performance of the instruments significantly. Comparatively, HYCL31 has a higher accuracy rate, which can meet the needs of meteorological service.
2016, 42(6):770-776.
DOI: 10.7519/j.issn.1000-0526.2016.06.013
Abstract:
The atmospheric general circulation of March 2016 is characterized by the following：The polar vortex was in a dipole pattern with its main body located over the Western Hemisphere. A weak ridge spanned from Lake Balkhash to East China, and the degree of meridionality was lower than normal. The ridge of the Western Pacific Subtropical High was located more southward than normal, and there was a subtropical high belt spaning from Western Pacific all the way to African continent. The Bay of Bengal trough was weaker than normal while the Tibetan plateau trough was stronger. The monthly mean precipitation over China was 29.3 mm, close to its normal value (29.5 mm). The monthly mean temperature was 6.1℃, 2 ℃ higher than normal, ranked the third in record. One cold air process and two rainfall processes occurred in March. Guangdong Province declared the beginning of flood season on 21 March, 16 days earlier than normal. Two foghaze processes occurred in the central and eastern part of China, and three sanddust processes in northern China. Drought emerged in the provinces of Shanxi， Shaanxi and Henan. Thunderstorm, gust, hail and shorttime severe precipitation hit the vast areas of the southwest, the central and southern part of the south to Yangtze River, and the central and eastern part of South China.
The atmospheric general circulation of March 2016 is characterized by the following：The polar vortex was in a dipole pattern with its main body located over the Western Hemisphere. A weak ridge spanned from Lake Balkhash to East China, and the degree of meridionality was lower than normal. The ridge of the Western Pacific Subtropical High was located more southward than normal, and there was a subtropical high belt spaning from Western Pacific all the way to African continent. The Bay of Bengal trough was weaker than normal while the Tibetan plateau trough was stronger. The monthly mean precipitation over China was 29.3 mm, close to its normal value (29.5 mm). The monthly mean temperature was 6.1℃, 2 ℃ higher than normal, ranked the third in record. One cold air process and two rainfall processes occurred in March. Guangdong Province declared the beginning of flood season on 21 March, 16 days earlier than normal. Two foghaze processes occurred in the central and eastern part of China, and three sanddust processes in northern China. Drought emerged in the provinces of Shanxi， Shaanxi and Henan. Thunderstorm, gust, hail and shorttime severe precipitation hit the vast areas of the southwest, the central and southern part of the south to Yangtze River, and the central and eastern part of South China.
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ISSN:1000-0526 CN:11-2282/P