Plateau Meteorology

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28 August 2013, Volume 32 Issue 4   
  • Comparison of Reanalysis Data and Observation about Summer/Winter Surface Air Temperature in Tibet
  • 2013 Vol. 32 (4): 909.  DOI:10.7522/j.issn.1000-0534.2012.00087
  • Abstract ( ) PDF (1570KB) ( )
  • Using in-situ observed summertime/wintertime air temperatures (OT) in Tibet, 2 m temperature reanalysis data of the NCEP/NCAR (NT1), the ERA-40 (ET1), the NCEP/DOE (NT2), the ERA-Interim(ET2) and the JRA-25 (JT) on a monthly basis, climate mean, variance, climate trend, interannual and interdecadal variability are explored. The results show that: (1) The values of the five reanalysis temperatures on Tibet are lower than that of observations, and the departure is greater in winter. After the terrain height revision, the differences decrease distinctly, especially ET1, ET2 and JT. (2) The variations of OT are greater in northern Tibet than that in southern and in winter than in summer in most areas. In eastern Tibet, ET1, ET2 and JT data ability to reproduce the interannual variation of air temperatures  is higher than NT1 data, in the midwestern Tibet, the four data are fairly; but NT2 data are poor. (3) While OT has the significant linear warming trend, and the trend is much greater in winter than in summer in most of Tibet, no trend is observed in reanalysis data. (4) Both NT1 and ET1 can not reflect the interdecadal variation of OT with features that is smaller value than average before 1980, keeping average during the period of early 1980 to late 1990, and shifting to a higher value than average in recent two decades. (5) ET2 and JT are close and can better to represent the observed climate mean, interannual variation and variability than NT2. (6) The order of similarity of distributions for correlation coefficient between observations and reanalysis temperature is JT>ET2>ET1>NT1>NT2 from small to big in winter and summer.
  • Verifications of Surface Air Temperature and Precipitation from CMIP5 Model in Northern Hemisphere and Qinghai-Xizang Plateau
  • 2013 Vol. 32 (4): 921.  DOI:10.7522/j.issn.1000-0534.2012.00088
  • Abstract ( ) PDF (871KB) ( )
  • Climate model is a powerful tool for climate change. For future climate change assessment and forecast，  climate model is the necessary technique to be assist. CMIP program has been performed to CMIP5 stage, and has been provided the longest and the most extensive database for climate change. This provides the unsubstantiated scientific basis for forecast the future climate change. Before detailed analysis of the simulation results, it is necessary to use the observational data to assess the simulation results, and the relatively good results are chose for analysis. This is benefit for simulation of the credibility and model development and improvement. In this paper, the observations data of Northern Hemisphere and Qinghai-Xizang Plateau were used by trend analysis, value comparison, wavelet analysis, and then simulation results by 8 models were compared. The results show that all models have well simulated at temperature changes in the Northern Hemisphere region. In general, the highest temperature is in July and August, the lowest temperature is in January, and there is no phase problem. All the modes have the consistent results in the interannual and interdecadal changes, but the maximum temperature difference can reach of 2\^8  ℃. About the average annual temperature from 1850 to 2005, the difference between maximum and minimum simulation results can up to 1.8  ℃. Besides one model, others can accurately simulate temperature break at least once. About the precipitation simulation in the Northern Hemisphere region, each model can simulate the seasonal changes in precipitation, but the trend show that four models simulate the increasing precipitation and whereas four modes simulate the reduced trend. About the temperature simulation in  Qinghai-Xizang Plateau, besides two models have passed the test of confident level of 95%, others have passed the test of confident level of 99%. Each model can simulate the precipitation center of the  Qinghai-Xizang Plateau, but precipitation values for each simulation model arequite different. After the comparative analysis, two models areselected for the follow-up study.
  • Constrct Analysis on Statistical Characteristic of MCSs over Qinghai-Xizang Plateau and East Asia in Warm Season
  • 2013 Vol. 32 (4): 929.  DOI:10.7522/j.issn.1000-0534.2012.00089
  • Abstract ( ) PDF (2326KB) ( )
  • Based on the hourly equivalent temperature of black body (TBB) data of GMS-5， FY-2C and FY-2E from 1996 to 2010， the mesoscale convective systems (MCSs) in warm season (from March to September) over the Qinghai-Xizang Plateau (QXP) and East Asia regions were investigated. The results show that:  (1) The QXP is one of the high-frequency area of MCSs in East Asia， where is higher average frequency in East Asia to the north of 25°N. The hinterland of the QXP is the high-frequency concentration area of MCSs， and its nearby (31°N， 88°E) is the highest frequency area. (2) There are obvious monthly variation characteristics of MCSs over the QXP， that the MCSs often occur in the northern and eastern areas of the QXP in spring and in the middle-eastern and southern areas in summer. The monthly variation in the QXP is similar with that of  East Asia， and the summer monsoon of  East Asia is the important factor. (3) The daily variation of MCSs over the QXP appears single peak distribution， but there are a few differences between spring and summer， that daily variation of MCSs over  the QXP is more obvious than eastern Asia in some respects. (4) The precipitation frequency of MCSs is 5.6% , the contribution rate  of precipitation is 10.1%，  the frequency of maximum MCSs precipitation is 12% and  the contribution rate  of  maximum MCSs precipitation is  27%. Comparing with the East Asian region, MCSs precipitation in the QXP is smaller. (5) The most of  MCSs over the QXP are eastward low-speed and short life cycle MβCS. The average life cycle of MCS is 4.6 h with 11.2×10-4 km2 of average area， whose average speed is 31.5 km·h-1 and 59.4% of them are eastward. Comparing with the MCSs in East Asian， the MCSs over the QXP show the different characteristics: Smaller scale and area， shorter life cycle， lower speed，  and average TBB and average lowest TBB are highter.
  • Multi-Scale Weather Analysis Theory and Application Ⅰ: Basic Principle and Essence of Weather System
  • 2013 Vol. 32 (4): 964-972.  DOI:10.7522/j.issn.1000-0534.2012.00092
  • Abstract ( ) PDF (773KB) ( )
  • Based on the atmospheric features of multi-scale motions and structure, multi-scale structure models of atmospheric micelle are proposed. It is considered that the atmosphere is made up of multi-scale micelles, that is, large-scale micelles are made of some small-scale sub-micelles, and sub-micelles are composed of some smaller micelles. Sub-micelle′s relative equation of motion is derived from Navier-Stokes equation. Equilibrium equation of sub-micelles is derived in the equilibrium background field. It is considered that the equation has the same form with basic electromagnetism equation and an analogy is made between light/heavy micelles and negative/positive ions. Occurrence and development of the weather system are studied according to the equations introduced. It is considered that the weather system is caused by abruption of sub-micelles from micelles and re-combination under the action of the environmental field. This process starts under the influence of the initial disturbance and the positive feedback makes the weather system continue to strengthen and achieve a state of equilibrium. The attraction between different types of sub-micelles is the cause that the weather systems become weakening and extinction. A weather system diagnostic equation is introduced by analysis of micelle rotation. The relationship between the occurrence of weather system and  distribution of the atmospheric environment field is diagnosed by using the equation. The result shows that the change of environmental wind speed，  large gradient of wind in the vicinity of jet,  positive vorticity of  environment field and the stronger  vertical wind speed are favorable for the occurrence of weather systems.
  • Multi-Scale Wather Analysis Theory and Application Ⅱ： Front and Cyclone Formation Mechanisms
  • 2013 Vol. 32 (4): 973-982.  DOI:10.7522/j.issn.1000-0534.2012.00093
  • Abstract ( ) PDF (938KB) ( )
  • Using the multi-scale weather analysis theory, the front and cyclone formation mechanisms have been studied. It is found that the warm and cold air mass formations are due to the different kinds of sub-micelles moving in the different directions in effect of the environmental force, and their interface is the front. The kinetic energy gradient force  force in the vicinity jet stream can promote the separation of sub-micelles from a micelle, so there is a good correlation between the front and the jet. There is the stable structure that the warm and humid air under dry and cold air in the vicinity of low-level jet, because the energy gradient force above the jet and gravity are in the opposite directions, which led that the force micelles bear equals zero in the region, so a stable structure forms. But when the micelles move to the jet exit, this balance exists no longer, the warm and humid sub-micelles move upward, and the cold and dry sub-micelles move downward, the violent weather forms. Centrifugal force formed by the earth rotation makes the light micelles produce the northward and upward movement components, which leads to the northward slope of the polar front. Cyclone is also generated by separation of the sub-micelles. When the light micelles left the micelle, they will rotate in the effect of the environment absolute vorticity field. The rotation direction is in the same direction with the initial vorticity, and geostrophic vorticity direct upward in the Northern Hemisphere, so it rotates counterclockwise and clockwise in the Southern Hemisphere. In the process of cyclone formation, light sub-micelles move along spiral path under the action of the pressure gradient force and the absolute vorticity force field, it is the reason.that common cyclone system presents with a spiral cloud and rain belt. Water vapor is the basic energy source of the cyclone in the process of the formation and strengthening. because of differences in occurrence location, there is difference in water vapor transport method between the extratropical cyclones and typhoons, extratropical cyclone mainly rely on low-level warm conveyor belt for transporting of water vapor,  as typhoon occurs in tropical oceans,  the moisture and abundant supply of water vapor exists at all levels. Cyclonic movement constrained mainly by three forces: The environmental pressure gradient force, the absolute vorticity force and the environmental vorticity force. The action of these three forces leads to the typhoon moving along the edge of the subtropical high, and sometimes manifesting as snake-like path and looping track.
  • New Evolution Features of Autumn Rainfall in West China and Its Responses to Atmospheric Circulation
  • 2013 Vol. 32 (4): 1019-1031.  DOI:10.7522/j.issn.1000-0534.2013.00018
  • Abstract ( ) PDF (1744KB) ( )
  • The autumn rainfall in West China （21°N-39°N， 95°E-114°E） is one of the main climatic characteristics in the autumn, and the prolonged and continuous rainfall is detrimental to crop production. The  daily precipitation data at 166 station in West China during 1961-2010 was used to define IAR ( Index of autumn rainfall), which takes the both precipitation and rainy days into consideration. The interdecadal variation and the temporal and spatial distribution characteristics of IAR was analysed with EOF & wavelet method, and the atmospheric circulations was also studied. The results show that: There are maximum IAR centers in both the northern and southern area, with an obvious interdecadal variation in its intensity and range during the last 50 years. The northern part of it gets northward and stronger, and the range increases. The main anomalous type of IAR indicates a ‘northeast-north and west-southwest reversal pattern’ and a ‘consisitent pattern on the whole’. When the axis of the climatological subtropical westerly jet gets stronger and migrates westward, the subtropical high migrates westward and northward, and Indian-Myanmar trough gets deeper in the autumn, both the ascending flows and northward vapor transportation strengthens, which contributes to the pattern of more rainfall in the north and less in the southwest part.
  • Analyses on a Heavy Rainstorm and Structure of Low Vortex in Gansu Province on July 2010
  • 2013 Vol. 32 (4): 1032-1041.  DOI:10.7522/j.issn.1000-0534.2012.00098
  • Abstract ( ) PDF (1193KB) ( )
  • Using the water vapor budget method and numerical experiment, the low vortex system that resulted in a heavy rainstorm in Eastern of Gansu Province in July 2010 was analyzed. The result  show that:  (1) At development stage of the low vortex,  the vertical advection of potential pseudo-equivalent temperature and specific humidity have absolute advantage in the apparent heat source and apparent moist sink, it indicates  that  the vertical advection has positive correlation with the development of low vortex and heavy rainstorm. (2) The center of ascending motion is corresponding to the apparent heat source and apparent moist sink, and they have the same change trends, it indicates that  the atmospheric heating is closely related to ascending motion during process of precipitation，and the atmospheric heat source come from the condensation latent heat releasing. (3) The development of low vertex is accompanied with low-level southwest jet,  strong center of positive vorticity， low-level convergence, high-level divergence, strong ascending motion and low-level moisture flux convergence. (4) There are convectived instability at the low-level which has no significantly change with time, and conditional symmetric instability at the mid to mid-high level has significantly strengthen. Potential instability and conditional symmetrical instability result in the producing and maintain of the vertical ascending movement in big value area  of potential pseudo-equivalent temperature.
  • A Low-Level Gravity Wave Triggering Mechanism For Rainstorm of Warm Zone in South China
  • 2013 Vol. 32 (4): 1050-1061.  DOI:10.7522/j.issn.1000-0534.2012.00100
  • Abstract ( ) PDF (1641KB) ( )
  • A warm zone rainstorm before front in South China was analysed and high-resolutionnumerical simulation was done using the high resolution observational data and regionalmodel. The results show that the distribution of hourly rainfall at frontal and warm zones  is a wave train, and 850 hPa divergence at frontal and warm zones  appear acute oscillation at 1~2 h before the rain beginning, and the oscillation is later about 1 h at warm sector than that of frontal zone. Hourly  divergence increments on 850 hPa  for grids along the line linking frontal and warm zones  distribute distinctly as a wave train too. Wavelet analysis approve that there are two waves with same period and different half phase at frontal and warm zones, and the waves belong to gravity wave. Further analysis indicate that about 3 h before warm zone rainstorm beginning, there is a very superficial low-level stable layer locate at 950~850 hPa approximately between frontal and warm  zones, and the stable layer's presence satisfy the propagating situation of gravity wave, and when a low-level gravity wave is excitated by front convection, it would propagated from frontal to warm zones  along the stable layer, then excitated low-level ascending motion at warm zone. Updraft touches off the release of middle and low level unstable energyand then generated a warm zone rainstorm.
  • Analysis on Formation Reason of Sudden Torrential Rainstorm in Yunnan Province
  • 2013 Vol. 32 (4): 1062-1073.  DOI:10.7522/j.issn.1000-0534.2012.00085
  • Abstract ( ) PDF (1829KB) ( )
  • The satellite cloud image, radar, automatic rainfall station observing cryptographic data and NCEP/NCAR 1°×1° reanalysis data are used to analyze the forming reason of four extraordinary heavy rainstorm events happened in Yunnan Province. The result indicated that, the sudden rainstorm process main is the convergence of low vortex shear line on mid-lower layers  and  southwest airflow to cause the accumulation of vapor, energy, warming and humidifying on lower layer, and 500 hPa dry and cold air intrusion on the layer that form convective instability area, which made sudden torrential rainstrom. When the vapor is rich on lower layer and the local atmosphere is potentially unstable or has proper toggle conditions, heavy torrential rainstrom event happen easily in the area under the control of northwest current.  The satellite cloud image revealed that the convective clouds' merging and strengthening to mesoscale convective cloud lead to the torrential rainstrom event.  In the moving  and development processes of radar echo, the merging effect always happened with the moving of echoes. The echo forward move slowly but the its backward develope frequently, so little monomers generate and merge fast, which make the whole block echo steady. And the stronger convergence of wind direction and wind speed appeared at the stage of severe precipitation.
  • Diagnostic Analysis on a Meiyu Front Rainstorm Process in Mid- and Low-Reaches of Yangtze River
  • 2013 Vol. 32 (4): 1074-1083.  DOI:10.7522/j.issn.1000-0534.2012.00101
  • Abstract ( ) PDF (1639KB) ( )
  • A Meiyu front rainstorm process is analyzed using NCEP 1°×1° reanalysis data, the temperature of black body and the high resolution output from WRF model. The results show that the large scale background is  related to this rainstorm process including the interaction between westly trough and subtropical high, the existence of wind shear in mid-low troposphere and the eastward movement and development of low vortex. TBB data shows that the mesoscale convective cloud clusters continually emerge and develop eastwardly near the wind shear. In the corresponding rainstorm area, there exists multiple β  mesoscale centers of moisture flux convergence in the left of lower level south-west jet and a series of divergent centers in the right of upper level west jet entrance, indicating that there is strong moisture convergence and upward motion in these areas. The high temperature and humidity in lower troposphere and colder air incursion in mid-upper levels make the atmosphere profile in steady state. The distribution of moisture potential vorticity and its center are good indicators for the location and intensity of rainstorm. The potential voticity (PV) advection near the rainstorm areas induce PV turbulence to move continuingly from upstream to downstream regions. The vertical column of PV in mid-low troposphere in warm sector can promote the development of cyclonic flow and upward motion.
  • Observation and Simulation Analyses on Dynamical Structure Features in a Severe Squall Line Process on 3 June 2009
  • 2013 Vol. 32 (4): 1084-1094.  DOI:10.7522/j.issn.1000-0534.2012.00102
  • Abstract ( ) PDF (1937KB) ( )
  • Using the various observation data with numerical simulation results, the evolution characteristics and development mechanism of mesoscale dynamical structure in a rare strong squall line process occurred in Huang-Huai area on June 3-4, 2009 are studied. The results show that, companing with shortwave disturbance at the rear of northeast cold vortex, the cold advection are overlapped the warm ridge in lower troposphere under stable environment, which constructs a favorable atmospheric unstable stratification for the occurring of squall line; the development of squall line is closely related to surface mesoscale convergence line, with the relation of interdependence and mutual promotion; the movement of squall line corresponds to the propagation of horizontal vortex tube in lower troposphere. In the propagation process, the inclination in horizontal vortex tube makes transformation of horizontal vorticity to vertical one, which promotes the development of squall line; the dynamic structure of squall line has remarkable difference at each stage of its development. At maturity stage, squall line has clear systematic structure, which is gradually loose with the squall line decreases and dissipates. Factors are no longer closely cooperating with each other, whose specific convective organization would cease to exist. Furthermore, the surface pressure field presents significant mesoscale disturbance characteristics in the development process of squall line. The combination of mesoscale thunderstorm high emerging at the rear of squall line with the divergence center in wind field is one of the main reasons causing the strong surface wind.
  • System Characteristic of Atmospheric Circulation from Drought to First Effective Rainfall during Springtime in Inner Mongolia
  • 2013 Vol. 32 (4): 1095-1105.  DOI:10.7522/j.issn.1000-0534.2012.00103
  • Abstract ( ) PDF (1616KB) ( )
  • Using the daily precipitation data at 104 stations in Inner Mongolia, the first effective precipitation event in spring of the past 50 years (1960-2009) have been investigated, The features of the spring precipitation events which happened after a long-term drought and the decadal variations were summarized. The atmospheric circulation patterns for the effective precipitation events were analyzed based on the NCEP/NCAR reanalysis data. The results indicate that the effective precipitation occurs just once or twice from 1960s to 1980s, which happens three times on average from 1990s to 2000s, and significantly increased after the 1998. For the precipitation events in the period of 1960-1990, there is a pattern of one-ridge and one-trough in the high latitude region on 500 hPa geopotential height field over the Eurasian continent. In this pattern, the Ural Mountains is high-pressure ridge, while a stationary trough appears over Siberia, the westerly jet is between 50°-60°N. Under this condition, the most area of Inner Mongolia is controlled by a strong western wind. This westerly jet trough over the mid-low latitude range plays a crucial role in an effective precipitation in springtime. The location of 500 hPa eastern Asian trough during 1990-2007 is more northward than that of normal, while the westerly jet over the Eurasian continent from 50°-60°N approache northward to 70°-80°N. In addition, there is a vortex  over the region of the Lake Baikal, the Mongolian Plateau and northeastern region of China. In the region of the mid-low latitude, the short wave trough and ridge act frequently to result in effective precipitation in Inner Mongolia. The circulation characteristic emergenced  in 2008 and 2009  is same as in 1960s-1980s. 500 hPa circulations are classified into three types: A type is Mongolian cold trough (vortex), B type is Baikal vortex and C type is Northeastern China vortex, which are the main atmospheric circulation components of leading to effective precipitation in spring of Inner Mongolia.
  • Analysis on Heavy Rainstorm in Hubei Province on 18 June 2011
  • 2013 Vol. 32 (4): 1106-1114.  DOI:10.7522/j.issn.1000-0534.2012.00104
  • Abstract ( ) PDF (1231KB) ( )
  • Using the conventional observation and surface station data, NCEP 1°×1 ° reanalysis data，  FY-2E satellite cloud image, Wuhan and Jingzhou Doppler radar data,  the heavy rainstorm in Hubei Povince on 17-18 June 2011 was analyzed for the Dynamic diagnosis and mesoscale weather analyses. The obtained results are as follows: (1) The heavy rainstorm is produced in the large scale background and the special region. This heavy rainstorm is triggered by severe intersection of cold dry air from the north and warm moist air in the south of Jianghan plain and the eastern part of Hubei Province. (2) Mesoscale convective clouds have three types: A single cloud, combined cloud and the rapid development cloud. The greater the cloud scale, the longer the life history. The new cloud development around the α mesoscale convective cloud is the most rapidly, and rainfall is the largest. (3) Mesoscale echo group, which rotation is cyclonic, and mesoscale complex which is produced by a strong north wind and low-level south wind jet streams in cooperation with the scale of this rainstorm complex process, are the main forms of the radar echo. (4) Terrain for the intensity of rainstorm and the zones play the important roles. The middle reach of the Yangtze River region due to specific topographic effects formed three airflow. Mesoscale convergence system which is composed by the airflow plays an important role in the formation and development of mesoscale convective clouds.The strengthening and development of the F-cloud  is closely related to the terrain.
  • Study on Water Vapor Characteristic of Typical Heavy Snowstorm Case in Northern Xinjiang
  • 2013 Vol. 32 (4): 1115-1125.  DOI:10.7522/j.issn.1000-0534.2012.00105
  • Abstract ( ) PDF (1479KB) ( )
  • Using the daily precipitation at 51 weather stations in the Northern Xinjiang from November to March during 2000—2012 and daily water vapor of NCEP/NCAR 6 h 1°×1° reanalysis data, the water vapor characteristics of 11 typical heavy snowstorm cases were studied. The result shows that the 11 cases are classified into 3 types: West of Northern Xinjiang and along Tianshan edge, north and east of Northern Xinjiang, west of Northern Xinjiang and west Tianshan. There are two main water vapor sources: Near the Mediterranean Sea, the Red Sea or near the Persian Gulf. There are two water vapor transport routes which are west, southwest and northwest, respectively. Water vapor from southwest route is more, that from northwest route is less. The top of water vapor is close to 300 hPa. The strongest water vapor transport level is between 650～750 hPa. Before the every occurrence of 11 heavy snowstorm processes, there are water vapor convergence between 600～1 000 hPa in Northern Xinjiang.There are positive correlations between the snowstorm intensity and water vapor convergence between 600～1 000 hPa, as well as the convergence strength, rang and duration time in Northern Xinjiang. Hence, some lowest values of the strongest water vapor transport, water vapor convergence and the upper and lower level jet streams are resented also and gave useful references for accurate heavy snowstorm forecasting.
  • Applied Analyses on Palmer, SPEI and CI Indices of Drought Process in Yangtze-Huaihe River Basins during Winter of 2010/Spring of 2011
  • 2013 Vol. 32 (4): 1126-1139.  DOI:10.7522/j.issn.1000-0534.2012.00106
  • Abstract ( ) PDF (1700KB) ( )
  • The precipitation of Yangtze-Huaihe River basins from the autumn of 2010 to spring of 2011 was less than normal which  happened the continuous drought. During the summer, the precipitation in the south of Yangtze-Huaihe River basins increased, but still less in the north, that caused to turn to flood sharply in the southeast; and still drought in the northwest. The daily data at 70 observational stations in the Yangtze-Huaihe River basins in 1961-2011 were used to calculate the Palmer(PDSI), SPEI and CI indices, and the drought informations during 2010-2011 was analyzed based on the data of the monthly and seasonally climate impact assessment, ten-day/monthly agricultural meteorological report etc. comparing the three indices with precipitation and the drought informations. The results show that the three kinds of drought indices can describe the drought process in the Yangtze-Huaihe River basins, but the performance of winter drought weren′t well. They have their own advantages and disadvantages. The PDSI index can describe well the drought area, development and persistent, but lagged in response to precipitation, and the drought in the early winter is not reflected; SPEI in monthly scale is sensitive to drought event, but it is too dependent on precipitation change, and the drought area is often biased in winter; Seasonally SPEI do well in the gradual development of drought, but lagged in the beginning of drought. CI index can detect the occurrence of drought in time, but the development of drought is too fast. The drought intensity, especially in the winter, is too heavy. And the drought persistence is not good enough.
  • Variation of FY-3A/MERSI Data after Atmospheric Correction Based on FLAASH Model
  • 2013 Vol. 32 (4): 1140-1147.  DOI:10.7522/j.issn.1000-0534.2012.00107
  • Abstract ( ) PDF (855KB) ( )
  • Atmospheric correction is necessary to retrieve the real surface reflectance of the surface objects by removing the atmospheric effects induced by aerosol, solar radiation et al. In this paper, the FY-3A/MERSI data with a resolution of 1 km was selected and atmospheric correction was conducted based on the FLAASH model in Henan Province, China. Comparing with the data before the atmospheric correction, variations of the FY-3A/MERSI data are mainly as follows: (1) The reflectance of short-wave infrared band only increased by 4.1% and reflectance of the sixth band decreased by 1.5% while reflectance of the seventh band increased by 9.6%. (2) The reflectance of all visible bands decreased by -82.7% averagely. The reflectance of the red, green  and blue bands averagely decreased by 21%, 63% and 137%, respectively. After the atmospheric correction, reflectance variation amplitude increased and different objects could be distinguished more clearly by visible bands. (3) The reflectance of near-infrared band all increased with an average of 46.2%, except for the 19th band decreasing by 54%. Reflectance from band 15th to band 18th and 20th increased by 28%, 4%, 41%, 252% and 6%, respectively. (4) After the atmospheric correction, vegetation was highlighted with the value of NDVI increasing by 35%, Nevertheless the value of NDWI varied little, decreasing only by 8.7%.
  • Analysis on Cloud Structure of a Severe Convective Storm Using Radar and Satellite Data
  • 2013 Vol. 32 (4): 1148-1156.  DOI:10.7522/j.issn.1000-0534.2012.00108
  • Abstract ( ) PDF (1309KB) ( )
  • Using FY-2D satellite data, SWAN radar product, CINRAD/SA radar data, combined with LAPS, automatic weather station and sounding data, the cloud structure of a severe convective storm in Suizhou, Hubei Province on 26 July 2011  was analyzed. The results show that the developing centre of convective storm corresponds with the region of large reflectivity factor, low  and high TBB gradients. The merging effect is beneficial to the development and maintenance of storm. The radar data from single station is applicable to the shape identification and analysis of dynamic field. There are two bow echo stages in this process, both existed obviousRIN, weak low-echo region, speed fuzzy and storm body tilt characteristics at the development stage of the first bow echo, while only heavy precipitation took place at the second bow echo stage. Comparing with the second bow echo, the occurrence of hail benefited from more, faster accumulation of convective available potential energy  and greater vertical integration liquid water content. From the T-Re vertical distribution of FY-2D, it is observed that at the early stage of hailstorm, stronger updrafts are revealed by the delayed growth of Re to greater heights and lower T, because there is less time for the cloud and raindrops to grow by coalescence. The strong updrafts also delayed the development of a mixed phase cloud and its eventual glaciation to colder temperatures.
  • Fluid Dynamics Analysis on Solar Radiation Error of Radiosonde Temperature Measurement
  • 2013 Vol. 32 (4): 1157-1164.  DOI:10.7522/j.issn.1000-0534.2012.00109
  • Abstract ( ) PDF (877KB) ( )
  • Temperature measurement errors of thermistors induced by solar radiation pose an important bottleneck against the improvement of the precision of numerical weather forecast as well as the climate change research. To tackle this problem, a numerical analysis method was proposed. Thermal numerical in different pressures of the range from 0  to 32 km altitudes obtained by sounding temperature sensor was simulation analyzed by employing the computational fluid dynamics (CFD). In this model, the thermal environment of the thermistors has been taken into consideration. The boundary conditions of external convection and solar radiation are thermally coupled in the model, in which the reflectivity of the surface coating and the body dimension of the thermistors play critical roles. The simulated results show that the relationship between the altitude and the error caused by solar radiation heating is not a simple linear, but for a parabolic relation, with the slop increasing as the altitude increases. Correction values of the radiosonde temperature measurement result vary with respect to the altitude. According to the modeling results based on the state-of-the-art thermistors, the improvement of surface reflectivitiy and the shrinkage of the dimensions of the thermistors offer an effective way to minimize solar radiation error under high barometric pressure. Nevertheless, under low barometric pressure the solar radiation has considerable impacts on the accuracy of temperature measurement, where numerical method presented in this paper may find its applications.
  • System Bias Calibration of Differential Reflectivity for Dual Linear Polarization Radar
  • 2013 Vol. 32 (4): 1174-1185.  DOI:10.7522/j.issn.1000-0534.2012.00084
  • Abstract ( ) PDF (1271KB) ( )
  • Differential reflectivity ZDR can have noticeable deviation which does not change with the space accumulation because of the influence of radar itself. So radar calibration is essential and critical to high quality data and products. At the present, the radar data observed at vertical incidence is commonly used to calibrate system bias of ZDR. This method, however, cannot be implemented with some radar because the antenna has elevation limit determined by the structural configuration of the antenna's pedestal. In this case, the light rain and dry aggregated snow are used as natural reflectors for ZDR calibration due to these two atmospheric scatters with low variability of intrinsic ZDR at high elevation angle and the intrinsic ZDR is close to zero. Based on the observation in field experiment by a C-band polarimetric Doppler radar on Wheel which was built in the State Key Laboratory of Severe Weather, Chinese Academy of Meteorological Sciences. In this paper, taking the calibration result of vertical scan data as a reference, the difference of calibration of ZDR by light rain and dry aggregated snow at the highest elevation of volume scan mode is analyzed. The results of analysis indicate that both light rain and dry aggregated snow can calibrate ZDR very well, but dry aggregated snow exhibits much lower variability of ZDR than light rain (even at high elevation) and, therefore, can be considered as the optimal weather target for calibration of ZDR. It becomes the best alternate method for system bias calibration of ZDR by vertical scan data.

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