Plateau Meteorology

Current Issue

28 June 2017, Volume 36 Issue 3   
  • Estimation of the Heat Transfer Coefficient over Inhomogeneous Underlying Surface on the Qinghai-Tibetan Plateau
  • GAO Shiyang;ZHANG Jie;LUO Qi
  • 2017 Vol. 36 (3): 596-609.  DOI:10.7522/j.issn.1000-0534.2016.00060
  • Abstract ( ) HTML PDF (1098KB) ( )
  • Combined with wind speed and temperature reanalysis data from ERA-Interim by ECMWF, the land surface observations data and a variety of satellite remote sensing data during 2000-2014, based on the profile-flux method, this paper aims to get the heat transfer coefficient (CH) that is applicable to Qinghai-Tibetan Plateau, by improving the accuracy of aerodynamic roughness and additional damping of heat transfer (kB-1).Enhanced Vegetation Index and vegetation height was added to the original profile formula to estimate roughness, which could reflect the effects of vegetation coverage and types on the change of roughness.The differences between ground and air temperature was used to revise the estimation method of kB-1 and get results closer to the actual value.Finally, based on the optimization of above parameters, the heat transfer coefficient over the Qinghai-Tibetan Plateau in neutral atmospheric stratification is calculated, and its time-space distribution characteristics are analyzed.Eddy correlation data from JICA experiment and gradient observation data from GAME-Tibet experiment in 2008 were used to test the estimates.The results show that the improved computational scheme can reflect the inhomogeneous features of topography and vegetation over Qinghai-Tibetan Plateau; Time-space distribution characteristics of roughness and other related parameters are closely related with vegetation height and density and thermal conditions of underlying surface; Heat transfer coefficient is higher in the south than in the north, it is higher in the east than in the west, and it in summer maximum and winter minimum; The values in different eco-geographical regions have significant difference, it is higher in regions with high vegetation and large differences between ground and air temperature.
  • Parameters Sensitivity Analysis on Simulation of Rainfall in Drought-Flood Year on Qinghai-Tibetan Plateau by WRF Model
  • WU Yao;LI Yueqing;JIANG Xingwen;DONG Yuanchang
  • 2017 Vol. 36 (3): 619-631.  DOI:10.7522/j.issn.1000-0534.2016.00057
  • Abstract ( ) HTML PDF (1132KB) ( )
  • For further evaluating and improving the skill of predicting extreme climate in Qinghai-Tibetan Plateau (QTP) using regional climate model (GCM).In this paper, the Weather Research Forecast (WRF) model was used to simulate summer rainfall on the southeastern QTP for the drought (1998) and flood (2006) years with various parameters, including boundary position, cumulus convection (CU) and planetary boundary layer (PBL) parameterization schemes, and horizontal resolution.Differences in rainfall simulated by various model parameters show that the simulated rainfall in the central and southeastern QTP is not sensitive to model boundary positions except south boundary position, but sensitive to PBL and CU parameterization schemes.Different CU parameterization schemes caused apparent differences in both spatial pattern and magnitude of simulated rainfall, while PBL parameterization schemes caused difference only in magnitude.The WRF exhibited higher skill in simulating rainfall in QTP and its adjacent areas with 15 km horizontal resolution.Overall, the simulated rainfall is strongly depended on the model horizontal resolution among the four model parameters.WRF shows better skill in simulating spatial pattern of rainfall compared to magnitude.It always produces a wet bias in central and southern QTP.Overall, the set of PBL and CU parameterization schemes shows the best skill in simulating rainfall for flood year, and also do the best for drought year.WRF has larger bias in simulating rainfall in slop of QTP compared to main body.It has an apparent dry bias in the Sichuan Basin.The dry bias is linked to the wet bias in southern Hunan, which excites an anomalous cyclone over northeastern Yunnan and Guizhou.Northeaster lies associated with the anomalous cyclone causes a reduction in water vapor entering the Sichuan Basin, resulted in an obvious relative dry bias there.The stronger than observed wester-lies to the south of QTP, associated with wet bias in south slop of QTP, causes higher than observed rainfall over the southwestern Yunnan.Thus, a better simulation of rainfall in the Sichuan Basin is depended on not only optimization of parameters of CU or PBL locally, but also improvement in climate outside.
  • Cloud Occurrence Frequency and Structure over the Qinghai-Tibetan Plateau from CloudSat Observation
  • LIU Jianjun;CHEN Baode
  • 2017 Vol. 36 (3): 632-642.  DOI:10.7522/j.issn.1000-0534.2017.00028
  • Abstract ( ) HTML PDF (1298KB) ( )
  • By using 7-year (Data time series from May 2006 to May 2013) CloudSat observations, occurrence frequencies of 8 cloud types for different levels and seasons over the Qinghai-Tibetan Plateau are constructed to examine characteristics of their horizontal and vertical distributions and related physical causes, which could provide observational information for evaluating cloud simulated by numerical weather prediction models.It is found that the frequency of total cloud occurrence is about 35%.Among low, middle and high clouds, the highest frequency is low cloud near 21%, followed by middle clouds about 14%, and the lowest one is high cloud less than 1%.In terms of vertical structure, the maximum frequency of low clouds at a height of 5~6 km, 7~8 km for middle clouds and 11~12 km for high clouds.High frequency of total cloud occurrence is located in the Southeast and Northwest parts of the Qinghai-Tibetan Plateau which forms two centers of relatively plentiful clouds.The spatial distribution of low cloud frequency is consistent with that of total clouds, middle cloud frequency is high in the north and middle Plateau and low in the South Plateau which is obviously different with low cloud and on the other hand, high cloud frequently occurs in the South Plateau.For seasonal variation, in terms of high frequency of occurrence, during winter low cloud is over the west Plateau; During spring middle cloud over the middle north part and low clouds over the west and southeast; During summer high and low clouds over the south of the Plateau.There is very low occurrence frequency for all kinds of clouds during fall.It was indicated that the formation of low clouds is mainly due to orographic uplift, and middle clouds largely associated with the thermos-dynamical effects of the Plateau.
  • Distribution of Soil Moisture over the Qinghai-Tibetan Plateau and Its Effect on the Precipitation in June and July over the Mid-Lower Reaches of Yangtze River Basin
  • ZHUO Ga;DEJI Zhuoma;NIMA Ji
  • 2017 Vol. 36 (3): 657-666.  DOI:10.7522/j.issn.1000-0534.2016.00073
  • Abstract ( ) HTML PDF (744KB) ( )
  • Soil moisture has been widely recognized as one of the main drivers of the water and carbon cycle in the climate system.It plays an important role in the interactions between the atmosphere and the land surface with climate change through its influence on the surface albedo and vegetation.To understand the temporal and spatial distribution of soil moisture over the Qinghai-Tibetan Plateau and its influence on the precipitation in the mid-lower reaches of Yangtze River Basin, with monthly dataset of soil moisture derived from Climate Prediction Center (CPC) and monthly precipitation obtained from National Meteorological Information Center (NMIC) of Chinese Meteorological Administration (CMA) from 1961 to 2014, the distribution of soil moisture over the Qinghai-Tibetan Plateau has been investigated along with its effect on the precipitation in June and July over the mid-lower reaches of Yangtze River Basin.Result shows that seasonal distributions of soil moisture are consistent with the annual distribution and the soil moisture decrease from the southeast part to the northwest part of the Qinghai-Tibetan Plateau.The regional soil moisture presents that it is extremely dry in spring while the moisture is quite humid in autumn and summer over the plateau.Considering the most parts of the plateau, the annual and seasonal soil moistures exhibit slightly increasing trend during the past 50 years.The annual and the seasonal soil moisture basically indicate decreasing trend from 1960s to 1990s, and they increase gradually with small magnitude from twenty-first century to the present years.The precipitation in the mid-lower reaches of Yangtze River Basin is negatively related to the spring soil moisture over the plateau.The negative relation areas which exceed the significance level are mainly located in the northeast and southwest parts of the plateau in June.The negative areas are situated in the southern plateau while the positive areas are located in the northwest part of the Plateau in July.The spring soil moisture is contributed to the precipitation distribution in the mid-lower reaches of the Yangtze River Basin by means of its effect on the surface temperature, atmospheric circulation and thermal forcing over the Plateau.The spatio-temporal distribution of soil moisture and the correlation between spring soil moisture over the Qinghai-Tibetan Plateau and subsequent precipitation in the mid-lower reaches of Yangtze River Basin are investigated with soil moisture derived from CPC and precipitation from CMA.The impact of soil moisture on seasonal precipitation and its possible mechanism will be the subject of a future study.
  • Possible Linkage between Winter Surface Sensible Heat Flux Anomalies over the Mid-High Latitudes of the Eurasian Continent and Summer Precipitation in the Eastern Part of Northwest China
  • PANG Xueqi;LI Dongliang;YAO Huiru
  • 2017 Vol. 36 (3): 675-684.  DOI:10.7522/j.issn.1000-0534.2016.00054
  • Abstract ( ) HTML PDF (830KB) ( )
  • On the basis of daily precipitation observations at 156 stations from 1979 to 2012 in eastern part of Northwest China and the monthly means of surface sensible heat flux of NCEP/DOE reanalysis data, physical mechanism and possible linkage between winter surface sensible heat flux anomalies over mid-high latitudes of the Eurasian Continent (61°N-67°N, 53°E-68°E) and summer precipitation over eastern part of Northwest China are analyzed in this study. The results show that when the sensible heat flux over mid-high latitudes of the Eurasian Continent transported from atmosphere to land surface is larger in winter, the sensible heat flux transportation from land surface to atmosphere will be larger in spring and summer as a consequence, the Ural blocking high and Mongolian low are strengthened, the northwest Pacific subtropical high is strengthened and migrating more west than normal, the subtropical westerly jet is anomalously northward and the South Asian high is far eastward, resulting in the ascending flow over eastern part of Northwest China strengthened. In addition, the transportation of the warm and moist air flows in low-level are strengthened in eastern part of Northwest China, as well as the water vapor convergence. All these contribute to the precipitation increasing over Eastern Part of Northwest China because of its location at the bottom of the Mongolian low and to the northwest of the subtropical high, in contrast, when the sensible heat flux transported from atmosphere to the surface is smaller in winter, the sensible heat flux transportation from land surface to atmosphere will also be smaller in spring and summer leading to the opposite atmospheric circulation anomalies in the summer, which will make the summer precipitation over the eastern part of Northwest China decreasing.
  • Mechanism of Long Lifespan Sichuan Basin Vortex's Activity Influence the Precipitation in Sichuan-Chongqing Region on Summer
  • LI Chao;LI Yueqing;JIANG Xingwen
  • 2017 Vol. 36 (3): 685-696.  DOI:10.7522/j.issn.1000-0534.2016.00064
  • Abstract ( ) HTML PDF (1894KB) ( )
  • Based on the ERA-interim reanalysis data and the daily meteorological precipitation data of 824 China stations during 1983 and 2012, we analysed the inter-annual variation of Sichuan Basin Vortex (SBV) whose lifespan is equal to or more than 24 hours (defined as long lifespan) and the corresponding cause, as well as its influence on seasonal precipitation on summer. The main conclusions are as follows:(1) The birthplace of long lifespan SBV was located in southwest and northeast of Sichuan Basin, SBV could be classified into two types (Southwest Type and Northeast Type) based on the birthplace. (2) The frequency of Southwest Type was much higher than Northwest Type, and Southwest Type contributed much more to seasonal precipitation as a result, however Northeast Type caused much more daily precipitation and influenced broader region in mostly case. Because Southwest Type was stable and less dynamic, its influenced region was limited within its birthplace. However, Northeast type was active, its influenced area was surrounded subtropical high. There was obvious difference on precipitation range between Southwest Type and Northeast Type. (3) As to seasonal scale, the key atmosphere circulation factors which influenced the frequency of the two types were various from each other. When the intensity of long wave trough in middle attitude got stronger, the subtropical high extended westward more, besides the South Branch Trough of the plateau got stronger, it was advantageous to produce more Southwest Type SBV. On the contrary, when the intensity of South Asia high got weaker, Siberia high ridge was stably maintained, as well as the edge of subtropical high was just located near the east of Yun Gui Plateau, it was advantageous to produce more Northeast Type SBV.
  • Spatial-Temporal Variation of Extreme Precipitation Events from June to July over Yangtze-Huaihe River Basin and the Circulation Anomalies
  • YANG Wei;XU Min;ZHOU Shunwu;LUO Liansheng
  • 2017 Vol. 36 (3): 718-735.  DOI:10.7522/j.issn.1000-0534.2016.00047
  • Abstract ( ) HTML PDF (1691KB) ( )
  • Based on the recent 53 years (1961-2013) daily observational precipitation and NCEP/NCAR reanalysis data, extreme precipitation thresholds from June to July over Yangtze-Huaihe River Basin are defined by using percentile method. Extreme precipitation events are classified into three patterns according to EOF analysis, which are patterns along Huaihe River, along Yangtze River and south of Yangtze River. The typical cases of each pattern are selected and the atmospheric circulation situations are diagnosed subsequently. The results show that:When three patterns of extreme precipitation events happen, southwest low-level jets exist from western south China to middle and lower reaches of Yangtze River at 850 hPa without exception. Jet intensity of pattern along Huaihe River expresses the strongest with the jet axis locating northernmost, pattern along Yangtze River is the second, while pattern south of Yangtze River is the weakest and southernmost. Ridge line and western ridge point of West Pacific Subtropical High at 500 hPa mainly change the location of jet axis to affect the extreme precipitation region. At 200 hPa, upper westerly jet is stronger with a narrow jet band, the right side of upper jet entrance coincides with north side of lower jet reasonably. It is pointed that under the corporate effect of lower and upper jets, vertical velocity above the extreme precipitation region represents abnormally stronger with anomalous larger specific humidity, the location of Meiyu front is attributed to the region of extreme precipitation. Water vapors for all three patterns mainly come from the Bay of Bengal to South China Sea.
  • Improvements of Ground Clutter Identification Algorithm for Doppler Weather Radar
  • WEN Hao;LIU Liping;ZHANG Yang
  • 2017 Vol. 36 (3): 736-749.  DOI:10.7522/j.issn.1000-0534.2016.00063
  • Abstract ( ) HTML PDF (2055KB) ( )
  • Ground clutter is an unpredictable event which often contaminates the radar products. In order to get high-quality radar base data and post-secondary radar exported products, ground clutter must be suppressed effectively. In this paper, according to the missed alarm rate of ground clutter and the false alarm rate of meteorological echo in the old ground clutter identification algorithm, which have been assessed in ROSE (Radar Operational Software Engineering) system, we propose an improved method. The radial velocity and spectral width are simply processed before the ground clutter is identified, so that the radial velocity quality in dual PRF mode is improved, and the missed alarm rate of ground clutter is reduced. In addition, echo intensity and radial velocity processing thresholds are added to the new algorithm; The threshold of numbers changes in slope within the gate-to-gate echo intensity is adjusted, and the vertical gradient parameter of reflectivity is increased. Four hundred and thirty-two ground clutter echo and meteorological echo data have been used to analyze and compare the identification effect of the new and old algorithm. The results show that the average radial velocity of ground clutter in dual PRF mode is close to zero after processing, and the accuracy of ground clutter identification is improved by 6. 84%. The added thresholds and the improvements of the characteristic parameters also could decrease the false alarm rate of meteorological echo about 1% to 2%. However, the new ground clutter identification algorithm fails to solve the false recognition problem completely. Meteorological echo, which have no radial velocity data (especially 230 km outside) and have great change in horizontal and vertical echo intensity, is very difficult to distinguish from ground clutter. This also needs to continue to do more work in the future. In particular, we could increase the new probe measurement, such as using dual polarization radar.
  • Relationship between Spring Mongolian Cyclones, the North Atlantic Sea Surface Temperature in Winter and the Snow Depth in Eurasia
  • HUANG Xin;BUHE Chaolu;LIN Dawei;Lü Guanru
  • 2017 Vol. 36 (3): 750-762.  DOI:10.7522/j.issn.1000-0534.2016.00050
  • Abstract ( ) HTML PDF (1398KB) ( )
  • Based on the four times daily NCEP/NCAR reanalysis dataset, NOAA sea surface temperature reconstruction dataset and JRA-55 reconstruction snow depth dataset, the 850 hPa relative vorticity cyclone tracking method was employed to identify the genesis regions in Mongolian cyclones for the years 1948-2013 in spring. The inter-annual and inter-decadal variations of the frequencies of Mongolian cyclones were investigated. According to the geopotential height anomaly distribution of the years with high and low frequencies of Mongolian cyclones, the main circulation pattern which had significant impact on Mongolian cyclones was revealed. Meanwhile, the impact of snow depth and sea surface temperature on the Mongolian cyclones was analyzed. The main conclusions are as follows:(1) The frequency of the Mongolian cyclones has shown an decreasing trend in the beginning-1980s and ending-1990s, an increasing trend since the beginning of the 21st century. (2) The circulation pattern to the northwest of Lake Baikal had a significant impact on the frequency of the Mongolian cyclones. The increased sea surface temperature in winter over the south of Greenland would induce a circulation pattern which could reduce the snow depth over the northern part of Ural Mountains. Then the decreased snow depth would lead to the positive height anomaly to the northwest of Lake Baikal. As a result, the frequency of the Mongolian cyclones would decrease. (3) The winter snow depth over the northern part of Ural Mountains in winter could be a predictor for the frequency of the Mongolian cyclones. There is a positive correlation between the frequency of Mongolian cyclones and the winter snow depth over the northern part of Ural Mountains.
  • Numerical Study on the Feedback between Latent Heating and Convection in a Qinghai-Tibetan Plateau Vortex
  • XU Weijie;ZHANG Yaocun
  • 2017 Vol. 36 (3): 763-775.  DOI:10.7522/j.issn.1000-0534.2016.00061
  • Abstract ( ) HTML PDF (2022KB) ( )
  • The influence of latent heating and its feedback effect on a Qinghai-Tibetan Plateau vortex occurring on 29 July 2009 was examined by using the WRF model in this study. Two experiments were conducted. In the control experiment, all physical processes were retained. In the sensitivity experiment, latent heat released by large-scale and cumulus convective precipitation was removed, while other physical processes were kept. By comparing model results and reanalysis data, it is found that the model can simulate the vortex moving path, intensity and the vortex-induced precipitation well in the control experiment. Without taking the latent heating into account, the simulated vortex moves quite slowly and disappear in the middle of the plateau, with little precipitation. The comparison of these two numerical simulations demonstrates that there is a positive feedback mechanism between the latent heating and the convection. The latent heating leads to intensive convective activity, and the convection extends to the upper level, thus much latent heat releases to the atmosphere. The potential vortices diagnostic analysis shows that, in low level, positive potential vorticity (PV) tendency caused by the vertical gradient of latent heating is beneficial to the strengthening and migrating of the plateau vortex. The PV tendency generated by vertical flux divergence term is contrary to that caused by vertical gradient of latent heating. In the development period of plateau vortex, because of the positive feedback mechanism between the latent heating and the convection, the positive PV tendency generated by the vertical gradient of latent heating increases rapidly, and the latent heating plays a leading role in the PV change at low levels. When the vortex develops into mature period, the contribution of latent heating decreases and divergence terms play important roles.
  • Improvement of Soil Moisture Simulation over Chinese Main Land by LDAS-IAP/CAS-1.0
  • LAI Xin;WEN Jun;FAN Guangzhou;SONG Haiqing;ZHANG Yongli;ZHU Lihua;WANG Bingyun
  • 2017 Vol. 36 (3): 776-787.  DOI:10.7522/j.issn.1000-0534.2016.00126
  • Abstract ( ) HTML PDF (1319KB) ( )
  • In order to validate the ability of The Land Data Assimilation System, and provide references for development and application of the system. The Land Data Assimilation System of Institute of Atmospheric Physics, Chinese Academy of Sciences(LDAS-IAP/CAS-1. 0) driven by the china meteorological forcing dataset(CMFD)was used to obtain soil moisture (SM) data from 2003 to 2010 over China. Without considering the assimilation of bright temperature of satellite remote sensing, the community land model version 3. 0 (CLM3. 0) driven by the same forcing data was used to simulate SM from 2003 to 2010 over China. The two simulated SM, observations, climate forecast system reanalysis (CFSR) of national centers for environmental prediction (NCEP) and global soil moisture data record based on active and passive micro wave sensors(SM-MW) were compared with each other. The results showed that the spatial distribution of simulated SM without considering the assimilation of bright temperature of satellite remote sensing and simulated SM considering the assimilation demonstrated obvious difference. Compared with observations, assimilated SM showed some improvement to simulated SM in Qinghai, Gansu, Ningxia and Shaanxi. The simulated and assimilated SM have more detail depiction in southern regions of 35°N compared to the other two products. After assimilation of bright temperature of satellite remote sensing, on the basis of the four seasons and annual SM from 2003 to 2010, the spatial distributions were characterized by a gradually increasing pattern from the northwest to southeast. From the spatial distributions, the most humid regions were located in the Northeast China Plain, the Jianghuai region, and the Qinghai-Tibetan Plateau, whereas dry regions were located in Xinjiang and Inner Mongolia. From the variation trend, the annual SM mainly increased in Inner Mongolia, the Tibetan Plateau and southern Xinjiang, and decreased mainly in other regions.
  • Comparison and Application of Two Kinds Vertical Wind Profile Data Part Ⅰ:Consistency Analysis
  • DONG Xinning;FANG Dexian;ZHOU Guobing;WU Zheng;ZHANG Yong;HUANG Anning
  • 2017 Vol. 36 (3): 788-800.  DOI:10.7522/j.issn.1000-0534.2016.00043
  • Abstract ( ) HTML PDF (989KB) ( )
  • Based on the wind vertical profile data observed by Doppler radar (SA) and wind profile radar (TWP8-L) over Chongqing, China during 2013, the characteristics and evolution of wind profiles under four different weather conditions (i.e., clear sky, light rainfall, moderate rainfall and heavy rainfall) have been studied. The main results show that:(1) Under the weather condition of clear sky or light rainfall, the moisture condition is so weak that the wind vertical profiles observed by Doppler radar are mostly identified as "ND" (No Data) and wind speeds (directions) observed by wind profile radar are weak (ill-organized). Meanwhile, the observed vertical wind shears are weak and ill-organized as well, unfavorable for the development and maintenance of convection systems; (2) As for moderate rainfall, precipitation property is dispersed with weak hourly accumulated precipitation amount. The wind directions in lower levels are ill-organized, while consistent southwesterlies prevail over the middle-upper levels with unified directions of vertical wind shears. All the above conditions are favorable for the development and persistence of convection systems; (3) As for heavy rainfall, the wind vertical profiles observed by Doppler radar present good consistency with those observed by those by the wind profile radar. During the period preceding the heavy rainfall events, the easterlies at the lower level gradually change to westerlies at the higher level. Such change favors to trigger convection activity. During the precipitation period, the vertical wind shears with consistent directions and the low-level jets prevailing at the lower-middle levels favor the maintenance of convection systems. At the end of precipitation events, the decreased wind speeds and northerlies at the lower-middle levels lead to disperse of the convection systems.
  • Optimal Identification Method of Squall Line and Thunderstorm Winds Analysis
  • LI Zhe;LI Guocui;LIU Liping;YANG Ji
  • 2017 Vol. 36 (3): 801-810.  DOI:10.7522/j.issn.1000-0534.2016.00040
  • Abstract ( ) HTML PDF (941KB) ( )
  • Squall line is an important system to produce thunderstorm wind, which has great strength and wide influence. Based on automatic identification of linear mesoscale convective system, optimal identification method of squall line is put forward. The main parameters are reflectivity factor, long axis length, area and linear degree. The radar echo is identified by using four groups single parameters, reflectivity factor is increased by 5 dBZ. It is the best result of optimal identification which has high linear degree and strongest echo. The performance of the method is evaluated and the corresponding wind is analyzed based on 140 body scan and 126 squall lines, the results show:The optimal identification method can identify strong and weak squall line at the same time, really response squall line at different stages of development, and the effect is improved more obviously than single parameter method. The hit rate of optimal identification method is improved 26. 3%, 10%, 40% and 89% than the method of four groups single parameters identification. Strong thunderstorm winds occur in strong echo band of squall line, bow echo edge and the gap between different storms, the area of squall line recognition and disaster winds is quite similar, and it can be used as a gale warning area. The wind direction of squall line is mostly along the moving direction of the storm.
  • Development Mechanism of Multi-scale Perturbation Based on Different Perturbation Methods in convection-allowing ensemble prediction
  • ZHUANG Xiaoran;MIN Jinzhong;WU Tianjie;DENG Xu;CAI Yuanchen
  • 2017 Vol. 36 (3): 811-825.  DOI:10.7522/j.issn.1000-0534.2016.00049
  • Abstract ( ) HTML PDF (1401KB) ( )
  • A storm-scale ensemble was conducted by WRF model during Beijing "7·21" extreme precipitation event. Three initial perturbation methods is tested. The first one is produced by ETKF update and forecast cycle which contained analysis uncertainty. The second method (DOWN) is downscaled from NCEP global forecast perturbation, and the third one is produced by blending ETKF and DOWN using barnes filter with wavelength of 180 km (80~280 km). Results show that each perturbation energy can grow with time, in which ETKF has more medium and small scale energy due to flow-dependent analysis uncertainty and DOWN has more large scale energy in early time. BLEND has the most perturbation energy during most forecast time. Energy from each perturbation all grow to medium scale (64~128 km) and the fastest growing composition are focused on small scale at early forecast hours, while the medium scale component grow slowly. These results motivate further studies on how to choose properly wavelength to construct a blending initial perturbation. When coming to the error of precipitation, spurious perturbation may lead to small spurious precipitation in early hours. Forecast perturbations for different methods all have better performance in sampling error during front precipitation than warm area precipitation. All in all, ETKF has advantage in small scale and lead time error sample and DOWN is better at large scale in the later forecast time, BLEND has both advantages of ETKF and DOWN during the whole forecast time. The threat score also show that BLEND has the best overall performance.
  • Near-Surface Wind Simulation over Acrid Lakeshore Area and Sensitivity Studies using the WRF-LES
  • SUN Xuejin;LI Yan;ZHANG Yanhong;NING Hui;TANG Jing;WEN Yuanhong;MIAO Qingjian
  • 2017 Vol. 36 (3): 835-844.  DOI:10.7522/j.issn.1000-0534.2016.00058
  • Abstract ( ) HTML PDF (864KB) ( )
  • Because of the relative larger mesh-grids, meso-scale atmospheric models cannot fully capture the spatial and temporal variability of near-surface wind fields over complex terrain, whereas the large turbulence-eddy resolving LES is a more promising model to account for this challenge. This paper performs a real-case near-surface wind simulation test over acrid lakeshore area close to Bosteng Lake in Xinjiang province utilizing the WRF-LES model with six nested domains. The simulation period is 28 hours and the model results were verified and analyzed against in-situ observations for one day. To assess the sensitivity of model results to local land-surface characteristics, three sensitivity tests were conducted by varying parameters such as the terrain resolution, soil-moist and surface roughness. For one sensitivity test, two digital elevation datasets were used, one is ASTER GDEM with 1 sec resolution and the other is MODIS with 30 sec resolution. For the other two sensitivity tests, disturbance factor with values 0. 4 through 2. 8 was used respectively to change the properties of land-surface. The test results demonstrate that the WRF-LES is more capable to regenerate the near-surface wind than meso-scale simulations in small-scale region with complex terrain owing to its explicit resolving of large atmospheric turbulence eddies. Thus the time series of wind speeds and wind directions more resemble the real atmosphere than those of meso-scale simulations. And the spectra of wind speeds is also more preferable. The sensitivity tests showed that the resolution of terrain data can affect the simulation results significantly so it should be treated with care. By increasing soil-moist the allocation of daytime land-surface heat fluxes is altered, thus the strength of large eddies is increased and so do the near-surface wind speeds, whereas the impact of surface roughness on model results is more complex. For one hand, increasing Z0 will enhance the transportation of momentum from upper air to near-surface flow, for another hand, larger value of Z0 is a negative factor when the wind speeds at 10 m height to be diagnosed by the land-surface model based on the Monin-Obukhov similarity theory and the atmospheric stability condition should be considered when analyze the impact of Z0 on near-surface wind speeds.
  • Implement of ENVISAT-ASAR Observed Data in the Wind Fields Investigation of the Offshore Area in Jiangsu Province
  • CHEN Yan;XU Xiazhen;HUANG Jingfeng;GUO Qiaoying
  • 2017 Vol. 36 (3): 852-864.  DOI:10.7522/j.issn.1000-0534.2016.00052
  • Abstract ( ) HTML PDF (1130KB) ( )
  • When the study the characteristics of offshore wind farms, less direct observations at sea is an important constraint. Satellite observation is high resolution and all-weather observation; It is an important method to overcome the lack of in-situ observations of wind fields over sea surface. This paper focus on the offshore area of Jiangsu Province and take advantage of the ASAR (Advanced Synthetic Aperture Radar) observations in ocean wind field's investigations. The ocean winds retrieval form 11 ASAR observed data in year 2008 are firstly evaluated with observations from 21 meteorological stations in coastal/offshore area, then the ocean winds retrieval form ASAR data are assimilated into the WRF (Weather Research and Forecasting model) for the numerical simulations. The results show that:The ocean winds retrieval form ASAR observed data agree well with the meteorological station observations. The wind speeds retrieval form ASAR data are slightly greater than station observations with an absolute error of 0. 5 m·s-1, a relative error of 15. 3% and a root mean square error (RMSE) of 1. 8 m·s-1; 83. 6% of the wind speeds retrieval form ASAR data are of a bias of ±2 m·s-1. The wind speeds retrieval form ASAR data overestimate while meteorological station observed wind speed less than 6. 0 m·s-1. The inversed wind directions have a north shift with a mean bias of -10. 6° and a RMSE of 39. 3°; 83. 6% of the wind directions retrieval form ASAR data are of a bias of ±22.5°. The ASAR observations are proved to be a good data source for sea surface wind field analysis. With the ocean winds retrieval form ASAR observed data assimilated, the RMSE of WRF model simulations in wind speed decreases from 1. 4 m·s-1 to 0. 9 m·s-1 in the January case, and from 2. 9 m·s-1 to 1. 6 m·s-1 to the July case, the simulated errors at 80% observation stations are less than 2. 0 m·s-1. The simulated RMSE in wind direction decreases from 73. 1° to 57. 3° in the January case, and from 67. 1° to 50. 6° in the July case, the simulated errors at 40% observation stations are less than ±22.5°. The wind speed of the site which is far away from the land is effect by the sea, while compare with the wind speed of land site. ASAR observed data carry more authentic wind information. The model performance improves better over the remote sea surface with the ASAR observations assimilated.
  • Impact of the ENSO Cycle on the Stratospheric Ozone Distribution over East Asia
  • WANG Mingsheng;GUO Shichang
  • 2017 Vol. 36 (3): 865-874.  DOI:10.7522/j.issn.1000-0534.2016.00068
  • Abstract ( ) HTML PDF (747KB) ( )
  • The Oceanic Niño Index (ONI) of the NOAA and ozone reanalysis data of ECMWF were used in this paper, the lag correlation method was used to analysis the influence of the ENSO circulation on the distribution of the stratospheric ozone over the East Asia. According to the composite analysis of the ozone anomaly percentage of El Niño and La Niña, the effect of the ENSO to the ozone force was investigated and the change can be explained by the residual circulation. The results show:(1) The effect of the ENSO to the stratospheric ozone was distinct over East Asia, which was more evident at 30 hPa, and 70 hPa than others, and that the correlation coefficient reached the maximum when lag equals 8 months. (2) After the El Niño occurred 8 months, at stratospheric 30 hPa, the ozone had a decrease over the mid-latitude region and an increase over the high latitude. At 70 hPa, the ozone had an increase over the mid-latitude, but a decrease over both high and low latitudes. However, the situation was contrary after La Niña. (3) The similar change has been obtained from the SVD analysis for the SST of Niño3.4 and the ozone 8 month later. (4) The difference of the effect of the El Niño and La Niña to the ozone was significant, and the difference of the ozone content could reach 25% when the El Niño and La Niña had occurred 8 months later. (5) ENSO can modulat the residual circulation, then it can influence the ozone distribution.

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