Plateau Meteorology

Current Issue

28 April 2011, Volume 30 Issue 2   
  • Numerical Simulation and Structure CharacteristicAnalysis of a Plateau Vortex Process
  • 2011 Vol. 30 (2): 267-276. 
  • Abstract ( ) PDF (1434KB) ( )
  • Using the nonhydrostatic mesoscale numerical model MM5, a Plateau vortex process occurring during 29~31 July 2009 was simulated and diagnosticly analyzed. The resultsshow that the structure of vortex eye during the vortex development process which displayed by the TBB satellite data is similar totropical cyclone-like vortices. The MM5 model has enough ability to simulate the precipitation area, precipitation intensityas well asinner structure of vortex, and the positive potential vorticity area move toward east as the vortex move toward east.On the dynamic structure, the vorticity and divergence have little change in the vortex core during the vortex development process, the vertical velocity change ascending into sinking motions. The vertical profile of vorticity in the vortex eye is similar topotential vorticity, that is to say, the vortex core which has a positive vorticity on both sides is in an invertedΩ-type area.The vortex core has divergence sinking motion from lower to upper levels.On the thermal structure, the structure of vortex area is warm in south and cold in north, and the vortex eye is in the lower area on the vertical profile of potential equivalent temperature.
  • Reconstruction of MODIS Land Surface Temperature in NortheastQinghai-Xizang Plateau and Its Comparison with Air Temperature
  • 2011 Vol. 30 (2): 277-287. 
  • Abstract ( ) PDF (1430KB) ( )
  • Land surface temperature (LST) derived from remote sensing data is a good alternative because the traditional LST from meteorological station has a local problem. Yet remote sensing LST may suffer from noises from various sources, which greatly degrade the LST quality and hamper its efficient application. This paper presents a novel algorithm which can reconstruct the complete LST based on relationship of DEM and LST. TERRA MODIS-LSTsin northeast Qinghai-Xizang Plateau in 2008 are reconstructed using this method. Comparison of origin LST and reconstructed LST data with maximum air temperature (T) observations at 62 meteorological stations in the study region indicates that LST is significantly correlated with T,with correlation coefficient of 0.88 and 0.91, respectively, and average correlation coefficient is 0.898 at each station. By the average, LST has a 6.98 ℃bias over T. The land-atmosphere temperature difference is related with the sea level elevation, vegetation cover, season and noise. The heighter sea level elevation is, the larger land-atmosphere temperature difference is; the denser vegetation coverage is, the smaller earth-atmosphere temperature difference is; the higher temperature is, the larger temperature difference is. It is also found that there are still some residual noises in well-vegetated areas after reconstruction. Therefore, the further study is required to identify the sources of noises, for instance, using the quality control information and 1 day LST.
  • Satellite Retrieval Analysis on Microphysical Property of Thunderstormwith Light Precipitation over the Qinghai-Xizang Plateau
  • 2011 Vol. 30 (2): 288-298. 
  • Abstract ( ) PDF (1376KB) ( )
  • Taking three typical thunderstorms with light precipitation over the Qinghai-Xizang Plateau as examples, the microphysical propertiesof the three kind thunderstorms were analyzed, mainly based on the polar-orbit satellite retrievalmethodologies, and the properties and the cause of their formation were briefly investigated， combing the surface observation and reanalysis data from NECP. The clouds are the convective ones, whose basetemperatureis low and close to 0 ℃, 1.5~2.5 km above the surface, which causes the hydrateand the released latent heat in the clouds less than that the clouds of warm base do, this may be the one of the main reasons that few severeconvective disasters occurredover the Plateau. The glaciation temperatureof the clouds is rather high, and the glaciation level rather low, the cloud particles almost glaciateat the temperatureof -20~-25 ℃, it must has connectedwith the larger cloud effective radius (Re) at the cloud base. The main charge layer is between the level where Re reaches 15 μmand the glaciationlevel, its correspondingtemperatureranges from -10 to -25 ℃, and is the coexistentlayer of water and ice. The main body of thecloud develops above the temperaturebelow zero, their precipitation mainly is dominated by the cold cloud process, and the warm cloud is difficultto trigger in them. The growth process participated by ice phase is the main growth mode of cloud and rain particles.
  • Change Characteristic of Surface Wind in Dunhuang Gobi
  • 2011 Vol. 30 (2): 299-308. 
  • Abstract ( ) PDF (1154KB) ( )
  • In order to understandthe variation characteristics of wind in Dunhuang gobi, using the micrometeorology data from the Dunhuang Experiment carried out during the period from 2002 to 2008, the characteristics of the probability distribution of wind direction and speed in the northwest arid region have been analyzed. The diurnal, annual and interannual change featuresof wind direction and speed have also been analyzed. The results indicate that: (1) In thisregion, the prevailing wind direction is east and west, the wind speed can be fitted well by Weibull distractionmode. (2) The wind direction and speed have obvious diural changes, the prevailing wind direction is east in daytime and south at night time, and the wind speed is higher in daytime than at night time. (3) Their annual variations are also apparent. The prevailing wind direction is north-east in summer and south in winter. Annual variation of wind speed is significant, in April the largest and the smallest in January. (4) The wind direction has no obvious interannual change, and they are almost the same in eachyear. Wind speed has a weak diminishing interannual trend.
  • Comparative Analysis on MCC of Two Different Precipitation Magnitudes
  • 2011 Vol. 30 (2): 328-338. 
  • Abstract ( ) PDF (1665KB) ( )
  • In order to enhance the forecast ability of the flooding rainstorm caused by MCC, the flooding rainstorm in the northeast of Sichuan Province on May 26, 2008 and the no flooding rainstorm in the west area of Chongqing on June 19, 2008 caused by MCC are analyzed through contrast by using the synoptic data such as satellite images, upper wind and others. The obtained conclusions are as follows: The primary cause is that the atmospheric stratification of MCC with large precipitation magnitude is convective instability, the mesoscale characteristic of the influence system on 200 hPa is obvious, the mesoscale subsistence movement in low level that emerged in the upstream of MCC to provide the triggering mechanism for the generation and development of MCC; the atmospheric stratification of MCC with small precipitation magnitude is convective stability; the TBB gradient of MCC with large precipitation magnitude is bigger than that of small precipitation magnitude; the high value MPV tongue from Tibetan Plateau extends to the area of the generation and development of MCC with large precipitation magnitude and coupling with the shear that influences MCC on 200 hPa, there is small MPV perturbation that extends to the southwest direction in MCC northwest for MCC with small precipitation magnitude. The helicity of MCC with large precipitation magnitude is bigger than that of small precipitation magnitude on 300~200 hPa.
  • Temporal and Spatial Distributions of Cloud Coverover Southwest China in Recent 46 Years
  • 2011 Vol. 30 (2): 339-348. 
  • Abstract ( ) PDF (1309KB) ( )
  • Through the wavelet analysis, linear trend analysis and SVD trend analysis methods and so on, the characteristics such as temporal and spatial distributions, variation tendency of cloud cover are analyzed, using the monthly mean cloud data at 85 observation stations in the Southwest China during the period from 1960 to 2005. The results show that the total cloud cover and the low cloud cover have obvious seasonal variations in southwest China. And in spring, autumn and winter, they are excessive in east and few in west. But the opposite is existent in summer. It can be also found that the total cloud cover and low cloud cover decrease in the past 46 years. And they have a quasi-eight-year changes in cycle. Additional, the annual mean total cloud cover and summer total cloud cover are yearly to decrease over the most of regions. The total cloud cover decrease in northwest of the West Sichuan Plateau, the south and east of Yunnan Province. At the same time, the low cloud cover decrease in Sichuan basin. The SVD analysis between temperature and total cloud cover shows that there is obvious negative correlation between temperature and total cloud in Southwest China, but the correlation between temperature and low cloud is not significant.
  • Validation of Multi-Model Ensemble to Air Temperature of Chinaand Projection of Air Temperature Changein China for the Next Three Decades
  • 2011 Vol. 30 (2): 363-370. 
  • Abstract ( ) PDF (707KB) ( )
  • Using the daily series of temperature observations at 701 meteorological stations of China in the period of 1961-1999, the simulated results of 20 global climate models (including BCCR_BCM2_0， CGCM3T47 etc.) at the same period are validated and analyzed； using three factor statistical methods the ensemble prediction results of multi-model are given, using the observation data in the period of 1991-1999, the ensemble results are tested and verified. The changes of annual mean temperature in the period of 2011-2040 under the emission scenarios of A2, A1B and B1 are analyzed, which are the predictive results of multi-model ensemble prediction. The analyzed results show that: (1) The global climate model can reproduce the regional spatial distribution of annual mean temperature in China, especially in the low latitude and eastern China. (2) At the factor of trend of annual mean temperature changing in reference period, there is obvious bias between the simulation and observation. (3) Testing the resemble result of multi-models in the period of 1991-1999, it can simulate the trend of temperature increasing， comparing with the observation, the result of different weighing ensemble predictions is better than the same weighing ensemble prediction. (4) In the period of 2011-2040, the increase of annual mean temperature in China which result from multi-model ensemble prediction is above 1 ℃， in the spatial distribution of annual mean temperature, under the emission scenarios of A2, A1B and B1, the increase in South China is the least, and its range is less than or equal 0.8 ℃; the northwest China region and south of Qinghai-Tibet Plateau are the biggest, and its range is more than 1 ℃.
  • Spatial-Temporal Variations of Temperature and Precipitationin Northern China in Recent 50 Years
  • 2011 Vol. 30 (2): 385-390. 
  • Abstract ( ) PDF (743KB) ( )
  • The spatial-temporal variations of temperature and precipitation in Northwestern China during the period of 1959-2008 were studied, using the observed surface air temperature and precipitation data at 180 stations from 1959 to 2008 and the climate trend coefficient and climate tendency ratio. The results show that: (1) The temperature of the region has markedly ascended in the last 50 years, the warming rate of 0.32 ℃·(10 a)-1 is significantly higher than rest of China and global average rate of warming at the same period. The warming rate of 0.37 ℃·(10 a)-1 in winter is significantly higher than other seasons. (2) In details, the mean temperature ascended in the early of 1960s, but dropped in late of 1960s, whereas it ascended in 1980s again and ascended sharply in 1990s. (3) The variability of precipitation is regionally different. There is significantly increasing trend of precipitation in western and middlle of northwestern China, however declining trend in eastern of northwestern China. (4) The monthly trend of precipitation is different to seasonal precipitation and annual precipitation regionally, however in spring, summer and fall the trends of precipitation are accordant to trend of annual precipitation.
  • Analysis and Application of Irrotational Wind Component in theDrastically Increasing and Decreasing Processes of ‘Saomai’ Typhoon
  • 2011 Vol. 30 (2): 406-415. 
  • Abstract ( ) PDF (1458KB) ( )
  • Using the Regional Spectrum Model(RSM) reanalysis data from Janpan Meteorology Agency with a horizontal resolution of 20 km and a time interval of 6 h, the convergence and divergence characteristics of the lower and upper levels of the super typhoon ‘Saomai’(0608) in the drastically increasing and decreasing processes were analyzed. The results show that the irrotational wind component is obtained from the limited regional harmonic-cosine series expansion wind partition method is more than the wind horizontal divergence to significantly reflect the variation characteristic of wind field in the processes of increasing and decreasing of ‘Saomai’. When ‘Saomai’ significantly increases over some distance offshore, there is a change of irrotational wind component from divergence to convergence on 850 hPa; when ‘Saomai’ decreases, the irrotational wind divergence intensification almost does not change in the upper level, and the thickness of convergence level reduces in the middle and lower level, but the convergence of irrotational wind component abruptly strengthens in the lower level, the strongest wind convergence region shifts from the outside cloud wall areas to the inner part of the eye of typhoon ‘Saomai’, which makes the convergence of lower level exceeds the divergence of upper levels, and causes the typhoon center filled up. So the irrotational wind component has some indicative functions in the wind change of increasing and decreasing processes of typhoon, especially when the horizontal resolution is relative high, from the scalar quantity-horizontal wind divergence, it can not analyze clearly the dynamic structure of wind convergence in the lower level and divergence in the upper level, but the irrotiontal wind component is more intuitional and clear to reflect this structure.
  • Numerical Simulation of Tropiall Depression Structure in ShanghaiTorrential and Its Intensifying Analysis
  • 2011 Vol. 30 (2): 416-427. 
  • Abstract ( ) PDF (2104KB) ( )
  • Using the nonhydrostatic mesoscale model MM5 of NCAR/PSU, the structure of No.9 tropical depression(TD) caused torrential rainstorm in Shanghai on 5 August 2001 is diagnostically analyzed. The result shows that the mesoscale vortex in middle level is one of main characteristics of TD. The cyclonic circulation, maximum low disturbance center and maximum positive vorticity center of TD in the period of torrential rainstorm in Shanghai mainly locate in the middle level (850~400 hPa) of troposphere. The cyclonic circulation at surface layer or low center is no obvious, tropopause is anticyclonic circulation, which is different with typical typhoon structure. The sensitivity test shows that the feedback action on latent heat release to mesoscale convective complex development is significant, while the dircet effect on TD could ignored. Vorticity equation analysis indicates that the divergence term makes a greater contribution to TD intensification. The main reason of TD intensification is that it has moved into the large scale convergence fields, which is favourable for its development, the convergence movement change into the positive vorticity tendency to cause TD intensification under the function of geostrophic deviating force.
  • Numerical Simulation and Diagnostic Analysis of a HeavyFog Process in Shanghai-Nanjing Expressway
  • 2011 Vol. 30 (2): 428-436. 
  • Abstract ( ) PDF (1683KB) ( )
  • Using the WRF2.2, a new generation of mesoscale numerical forecasting model, and NCEP reanalysis datawith 1°×1° grid, a heavy fog process appeared in the southern part of Jiangsu Province which cover the Shanghai-Nanjing Expressway on 26 October 2007 was simulated. The effect of the simulations was verified by the comparison between the simulated and observed data from the Auto-meteorological Monitoring System (AMW) ( one time per minute) on the Expressway.It is found that the simulation in this fog weather process is successful. The results are as follows: (1) One of the main reasons accounted for the heavy fog event occurs a rainfall process before the fog formation. The rain bring abundant water vapor and make the maximum value of relative humidity reachs over 90% in the region. At same time, it shows that the fog region is a weak convergence zone of air stream. (2) The vorticity field with the minor and negative value is advantageous to the sinking of the air and it ensures the moist air not to spill over. (3) The cold advection and ground radiation cooling are the important factors of the engendering, developing and maintaining of thisfog weather process. The ground radiation coolingis a dominant factor in the thermal conditions and the effect of cold advectionis far less than the ground radiation cooling.
  • Numerical Simulation of Aerosol Impact on Cloud Physics of Hailstorm
  • 2011 Vol. 30 (2): 445-460. 
  • Abstract ( ) PDF (1607KB) ( )
  • The impact of aerosol on cloud microphysics and precipitation of spring hailstorm in semi-arid area is numerically simulated. Using the Regional Atmospheric Modeling System (RAMS) of Colorado State University. The results show that: (1) Aerosols have a great impact on vertical distribution of cloud liquid water content. The hydrometeor spatial distribution is affected by aerosol concentration. (2)The hail is mainly formed by supercooled rain water freezing in clean cloud; supercooled rain water freezing and graupel colliding with cold cloud water are important in hail formation of polluted cloud, and in serious polluted cloud the graupel colliding with cold cloud water plays a leading role of hail formation. (3) The increase of aerosol concentration leads to the decrease of accumulative precipitation. (4) Ice phase precipitation from polluted cloud (C2) is the highest. The contribution of ice-phase precipitation to the total precipitation has the same trend with the aerosol concentration. (5) Hail has the major contribution to the total ice-phase precipitation in the clean and polluted clouds (C1 and C2), but hail and graupel both have great contribution to total ice-phase precipitation in the serious polluted cloud(C3). (6) The vertical velocity is maximum in the polluted cloud(C2), which means the increasing aerosol concentration strengthens of the hailstorm, but when the aerosol concentration is too high (C3), the updraft will decrease.
  • Comparisons of Microphysical Property of Cloud Retrievedfrom FY-3A/VIRR and TERRA/MODIS
  • 2011 Vol. 30 (2): 461-470. 
  • Abstract ( ) PDF (1143KB) ( )
  • In order to better learn and utilize the satellite source of FY-3A, the parametersof microphysical properties of cloud were retrieved with the multiple spectrum data from FY-3A VIRR and TERRA/MODIS, based on the selected different kinds of clouds including deep cumulus, clouds at upper, middle and low levels on 18 April and 21 May 2009. The reliability and stability of FY-3A satellite data were analyzed by comparison of the retrieved items from two satellite sources, which included the retrieved effective radius (Re), temperature on the cloud top, the visualized composite RGB image using 0.6 μm reflectance (red), 3.7 μm reflectance (green) and 10.8 μm brightness temperature (blue). The comparative results show that: (1) the rich color arrangement and change of composite BGB image using FY-3A data were similar with that using MODIS data, can be used to qualitatively analyze the cloud properties. (2) the reflectance of visible channel of FY-3A tends to 5% less than that of MODIS, the cloud top average temperature of FY-3A tends to be lower 1～5 ℃ than that of MODIS, and the scope of detectable temperature of FY-3A tends to be narrower than that of MODIS, but the extent of lower tendency is stable in the cases of April and May, which should be considered, although the retrieved values can be used, in the quantitative analysis. (3) rather larger differences have between the retrieved Re with the date from FY3A and MODIS in the following 4 aspects, the first is the narrow scopes of Re at the same height of cloud top, which suggest that the size of particles can not be fully detected or obtained, the second is the obvious tendency to be bigger in the small Re, sometimes arriving 8 μm (5 μm from MODIS and 13μm from the FY-3A), the third is fluctuation in the large Re, and the forth is the difference of the case in May becoming larger than that of April. All results from the comparisons suggest that the accuracy, sensitivity, calibration technique and stabilization of VIRR sensor need further improve.
  • Analyses on Reflectivity and Airflow Structure for DifferentTypes of Supercell Storm in Jinan Region
  • 2011 Vol. 30 (2): 489-497. 
  • Abstract ( ) PDF (1313KB) ( )
  • Using Jinan Doppler radar data from 2003 to 2008, the storm structures of 54 supercells occurred in Jinan region, Shandong Province, including the maximum reflectivity (DBZM), maximum reflectivity height (HT), cell\|based vertically integrated liquid (C-VIL) and top of storm cell(TOP), the base,top and maximum shear of mesocyclones, etc, were analyzed. At the same time, the typical airflow structures were analyzed. The results show that the values of DBZM, C-VIL, HT and TOP for isolated type supercell were significantly higher than that of mosaic type supercell, the difference values between the two classifications were 4 dBz, 14.8 kg·m-2, 1 km and 1.3 km, respectively. Comparing the parameter of isolated type and mosaic type supercells with mesocyclones lasting for 5 volume coverage pattern continuously, their difference values were 5 dBz, 20 kg·m-2, 1.7 km and 2.2 km, respectively. The mesocyclone formed in the mid\|levels of updraft. The mesocyclone base descended and its depth increased in the mature stage. The mesocyclone base ascended, its top descended, and its depth decreased in the decaying stage. The base and top of mesocyclone for mosaic type were significantly lower than the isolated type. The probability of occurring hail of isolated type had significantly higher, but probability of occurring gale is lower than the mosaic type. The mesocyclone parameter differences between the isolated and mosaic type supercells determined differences in the reflectivity structure and weather phenomenon. The longer the duration of mesocyclones is, the thicker the depth of mesocyclones is, it is the more favorable for the storm to maintain a long time and leading to extreme disaster. There are obvious different for the airflow structures of two types, the isolated type is main that the airflow in middle level go around the right\|rear part of storm to produce the gale, the mosaic type is main that the airflow in rear part of storm is direct downdraft which overly with downdraft mesocyclone circulation to produce the surface gale.
  • An Improvement of Polarimetric Radar Rainfall Estimates
  • 2011 Vol. 30 (2): 498-507. 
  • Abstract ( ) PDF (988KB) ( )
  • The quantitative estimation of rain rates using the meteorological radar has been one of main themes in radar meteorology and radar hydrology. The conventional single-polarized Doppler radar uses the measurement of radar reflectivity, radial velocity, and storm structure to infer some aspects of hydrometeor types and amounts. The relationships between rain rate R and the radar reflectivity factor Z (Z-R relations) have been widely used to estimate rainfall amounts. However, the classic rain estimation method has many sources of error. The sensitivity of Z-R relations to variations in raindrop size distribution (DSD) is the major source of error. Raindrop size distribution is determined by microphysical processes such as coalescence and breakup, condensation, evaporation, and melting of snowflakes, etc. DSD also changes in time and space, in correspondence with changes in microphysical process in a given precipitation system. Under the Watershed Airborne Telemetry Experimental Research (WATER) a lot of raindrop size distribution data were collected from May to July, 2008. The experiment area (38.85°N, 100.41°E) was carried out in the northeast of Qinghai-Xizhang Plateau, and the altitude is 1 515 m. The relationship between the terminal velocity of rain drop and rain drop diameter was obtained: v(D)=4.67D0.53. Four types of estimators for X-band polarimetric radar are examined: A classical estimator R(Z), and three types of polarimetric radar estimator R(KDP) R (Z, ZDR) and R (KDP, Z, ZDR), where R is the rain rate, Z is the reflectivity factor , KDP is the specific differential phase, and ZDR is the differential reflectivity. According to the simulated results, the normalized errors of R(Z), R(KDP), R (Z, ZDR) and R (KDP, Z, ZDR), for stratiform rain and convective rain are 32.0%, 18.2%, 15.0%, 12.3 % and 28.0%, 16.8%, 14.2%, 11.3%, respectively. The percentage root-mean-squared error of R(Z), R(KDP), R (Z, ZDR) and R (KDP, Z, ZDR), for stratiform rain and convective rain are 33.2%, 19.1%, 15.1%, 13.3 % and 30.8%, 16.9%, 14.0%, 10.3%, respectively. The simulated results show that the classical estimator R(Z) is the most sensitive to variations in DSD and the estimator R (KDP, Z, ZDR) is the least sensitive.
  • Characteristic of M-component in Artificially-InitiatedTriggered Lightning
  • 2011 Vol. 30 (2): 508-517. 
  • Abstract ( ) PDF (891KB) ( )
  • Using the channel base current, vertical lightning field of different distances and optical data of high camera obtained from artificially-initiated triggered lightning experiment of Shandong in the period of 2005-2008. A statistical analyses of the characteristics of current waveforms for 33 M-components in 10 return strokes have been done. The results show that a typical M-component in triggered lightning is characterized by a more or less symmetrical current waveform. The geometric mean values of peak current of M-component, 10%~90% risetime on wavefront, the half-peak width, duration are 743 A, 241 μs, 318 μsand 1.1 ms, respectively. The logarithmic standard deviations of theseparameters are 0.55, 0.46, 0.36 and 0.24, respectively. The waveform of return stroke in triggered lightning is wilder than M-component and the peak current of later is lower than the former. There is a relatively well correlation between half-peak width, duration and rise time. There is a correlation between the risetime and half-peak width (correlation coefficient is 0.84), and between the risetime and duration (correlation coefficient is 0.73). The correlation coefficient of duration and half-peak width is 0.7. The correlation between half-peak width, risetime, duration and peak current is negative, the correlation coefficient are -0.47, -0.45 and -0.37, respectively.
  • Study on the CO2 Flux Characteristic in the TanggualaApline Meadow Ecosystem of the Qinghai-Xizang Plateau
  • 2011 Vol. 30 (2): 525-531. 
  • Abstract ( ) PDF (902KB) ( )
  • Diurnal and seasonal variations of CO2 flux was measured with a open-path eddy covariance system for Tanggula apline meadow ecosystem in 2007 in order to assess carbon for apline meadow ecosystems in the Qinghai-Xizang Plateau. The results showed that the CO2 flux was distinct in the processes of daily and seasonal changes. During the freezing season, from September to June, CO2 flux showed small fluctuation with the largest net CO2 flux of 0.29 g m-2 h-1 in May. The diurnal CO2 flux was close to zero during most time of the day, but it showed a small net CO2 flux from 11:00 to 20:00. The thawing season, from July to August, the system exhibited net CO2 peak value from 11:00 to 20:00, but the net CO2 emission is from 20:00 to 11:00. Maximum CO2 peak value appeared from 12:00 to 14:00. The CO2 flux also had obviously seasonal variation. Remarkable peak value occurred in March, and relatively big release happed in May and September. The maximum daily net CO2 flux appeared in July and August, and CO2 flux was close to zero during winter. CO2 flux showed a linearily increase relations with 5 cm depth soil temperature and soil moisture content during spring and autumn, and a linearily regression relation appeared during summer.
  • Characteristic Analysis on Surface Wind Fieldat Xinjin Airport in Sichuan
  • 2011 Vol. 30 (2): 545-551. 
  • Abstract ( ) PDF (989KB) ( )
  • Based on the observational surface wind dataat Xinjin airport in Sichuan Province from January 2005 to February 2010, the diurnal change of seasonal mean, seasonal and annual variation features of surface wind at Xinjin airport are statistically analyzed. The relation between surface instantaneous wind and airport runway is studied and the forecast of surface instantaneous wind withwind velocity≥5 m·s-1are explored. The results indicate that the airport aremainly affected by north wind, west wind and southeast wind; the wind velocities of north and southeast winds are the largest; the strongwind mainly appeared in spring. Furthermore, the north wind is common in every season. However, the frequency of north wind appeared common in autumn and winter is far more than that in spring and summer. The wind velocity gradually increases in the morning and reaches the maximum value on the afternoon, and then it begin to gradually decrease at nighttime. Comparing with the daytime, its change is smaller than that at night. Annual mean wind velocity is small with small interannual change, static wind and small wind have high frequency. The surface instantaneous windwith wind velocity≥5 m·s-1and lasting for a long timeis the forecasting emphasisof the weather system.

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