Plateau Meteorology

Current Issue

28 December 2016, Volume 35 Issue 6   
  • Spatial Distribution Characteristics of MODIS Land Surface Albedo Inversions over the Qinghai-Xizang Plateau
  • CHEN Aijun;LIANG Xuewei;BIAN Lingen;LIU Yujie
  • 2016 Vol. 35 (6): 1409-1418.  DOI:10.7522/j.issn.1000-0534.2015.00111
  • Abstract ( ) HTML PDF (12355KB) ( )
  • In order to promote the application of MODIS (MODerate Imaging Spectra-radiometer) land surface albedo (LSA) and the improvement of its retrieval algorithm, the spatial distribution of MODIS retrievals over the Qinghai-Xizang Plateau (QXP) for different kind of retrieval quality with the MODIS LSA retrieval quality product MCD43B2 from 2003 to 2013 were statistically analyzed, as well as the digital elevation model (DEM) and the MODIS land surface cover classification product MOD12Q1. The results are as following:(1) The MODIS LSA full inversions (FI) are mainly located on the central and west regions, and the north regions of the QXP. The probability of FI over these regions is above 80% in spring. In summer, not only the area with high probability of FI shrinks to the north-west of the QXP, but also the probability decreases. The area with high probability of FI in autumn is the largest, while the smallest in winter. (2) Main areas with high probability of MODIS LSA magnitude inversions (MI) are distributed over the north-west and the south-east of the QXP in winter, while over Changdu Prefecture, Nagqu Prefecture, Nyingchi Prefecture, Shannan Prefecture and Lhasa City in the other three seasons. (3) The probability of no inversions (NI) for MODIS LSA is the highest over the Chinese character "into"-shaped area, which is formed in the central and east of Shannan Prefecture, Nyingchi Prefecture and its adjacent area of Changdu Prefecture. Moreover, the probability over this area is high over the four seasons and the highest is close to 100%. (4) The general trend for the probability of FI is decreasing as the increase of the elevation, while it is opposite for that of MI. The probability of NI is relatively stable and no more than 10% in each elevation range. (5) Among three main kinds of land cover type over the QXP, the probabilities of FI over the open shrubs and the naked (sparse vegetated) are around 70% and higher than that over the grassland. Accordingly, the probability of MI over the grassland is the highest and 30% or so. The probability of NI for these three kinds of land cover type is about same and no less than 10%. All above reveal that the spatial distribution of MODIS LSA retrieval quality over the QXP indicates obviously regional characteristics and it has a certain relationship with local altitude and surface cover type.
  • Relations betweenIntensity of the Qinghai-Xizang Plateau Monsoon and Movement of the Northern Hemisphere Westerlies
  • FANG Yun;FAN Guangzhou;LAI Xin;HUA Wei;ZHANG Yongli
  • 2016 Vol. 35 (6): 1419-1429.  DOI:10.7522/j.issn.1000-0534.2015.00106
  • Abstract ( ) HTML PDF (5761KB) ( )
  • Based on the NCEP/NCAR daily and monthly mean reanalysis data of wind field and temperature field from 1951 to 2012, relations between the intensity of the Qinghai-Xizang Plateau (QXP) monsoon and the movement of the northern hemisphere westerlies and the causes of the location change of the westerlies were studied. The results show that the movement of the northern hemisphere westerlies is related to the intensity of the Qinghai-Xizang Plateau monsoon. The times of northward jump and southward retreat of the westerlies are the 30th pentad (1 pentad earlier), and the 59th pentad, respectively, in a year with strong monsoon, and the 33rd pentad (2 pentads later), and 63rd pentad (4 pentads later), respectively, in a year with weak monsoon. This phenomenon is also global. During the northward jump of the westerlies, the South Asian High enhances and moves northwards, the west trough of Lake Baikal enhances, and the trough within the longitude range of the QXP deepens, causing earlier northward jump time of the westerlies in a year with strong QXP monsoon, compared with a normal year. The cases are reversed in a year with weak monsoon. During the southward retreat of the westerlies, the location of the subtropical high is relatively southerly, the East Asian trough deepens. This is favorable for the south retreat of the westerlies in a year with strong QXP monsoon, compared with a normal year. The cases are reversed in a year with weak monsoon.
  • The Numerical Prediction Uncertainties of the Tibetan Plateau Impacting the Forecasts of Its Downsteam Region
  • ZHANG Yu;CHEN Dehui;ZHONG Jiqin
  • 2016 Vol. 35 (6): 1430-1440.  DOI:10.7522/j.issn.1000-0534.2015.00110
  • Abstract ( ) HTML PDF (3537KB) ( )
  • The influence of the initial uncertainties on the NWP forecasts over the Tibetan Plateau (TP) and adjacent regions was studied based on the GFS forecasts/WRF model and OSSE experiments. The result shows that:(1) The large uncertainties of Tibetan Plateau (TP), because of the scarcely observations and complex terrain, can affect the NWP forecasts over the TP region and decrease the forecast skill of the downstream region of TP. After comparing the forecast errors over the TP and the downstream regions, it is found that the errors over the TP region are larger than the errors over the TP adjacent/Pacific Ocean and Rocky Mountain regions on the first 24 hours' integration:the error amplification rate over the TP adjacent region are larger than other regions evidently. (2) The forecast error rise faster over the downstream of TP region than the downstream of the Rocky Mountain (US). The WRF model forecasts results, with/without the large terrain (TP/Rocky Mountain), indicate that the forecast errors over the downstream region of the TP/Rocky Mountain are larger if the model domain contains the large terrain areas:this error divergence significantly after 2-days integration. (3) The observation data over TP region have effect on the forecasts of the downstream areas:additional "synthetic" observation data can decrease the initial uncertainties over the TP region and then improve the forecast skills over the downstream of TP region. Therefore, this study suggests that in order to reduce the initial uncertainties influence over the TP region, the additional observations even the "synthetic" observations over the TP region could assimilated to the NWP model.
  • Circulation Features of Sustained Departure Qinghai-Xizang Plateau Vortex at Upper Tropospheric Level
  • YU Shuhua;GAO Wenliang
  • 2016 Vol. 35 (6): 1441-1455.  DOI:10.7522/j.issn.1000-0534.2016.00026
  • Abstract ( ) HTML PDF (52969KB) ( )
  • By using NCEP/NCAR reanalysis data, historic weather graphs and Qinghai-Xizang Plateau vortex and shear line yearbooks, on basis of circulation features analysis on middle tropospheric level, according to the former sorted types of sustained departure Plateau Vortex with strong influence (SISDPV), the various physical fields on upper tropospheric level of different types of SISDPV are studied by composite and comparison methods in formation phase, departure phase, sustained strong phase and weak and varnishing phase from 1998 to 2012. The results show that the same circulation features on upper tropospheric level of various types of SISDPV are as follows:The South Asian High ridge line is within 25°N28°N latitude and extend easterly out of the 100°E longitude. There is west wind jet core region with speed more than 32 m·s-1 around or at north side of the SISDPV on 200 hPa and there is strong leaning west direction wind flow with speed more than 20 m·s-1 too. There are divergence regions on 200 hPa, just over the 500 hPa weather systems, which influence the SISDPV activities. This reflects that the divergence on upper level, frontal zone on upper level benefit to stronger convergence of SISDPV and pass down the high potential vorticity, which will strengthen the SISDPV vorticity field. The study also gained the main differences of circulation features and the physical images of various types of SISDPV on upper tropospheric level.
  • Influence of the Southern Branch Trough on Plateau of Southwestern China Daily Precipitation in Wintertime
  • LIN Zhiqiang
  • 2016 Vol. 35 (6): 1456-1463.  DOI:10.7522/j.issn.1000-0534.2015.00091
  • Abstract ( ) HTML PDF (6116KB) ( )
  • Mainland China (MC) precipitation is mainly affected by the monsoon, therefore MC precipitation is few in wintertime (from November to next April). Southern Branch Trough (SBT) is one of the main weather system affected precipitation in MC in wintertime. An objective method was used to identify the SBT activity dataset from NCEP/NCAR reanalysis dataset from 1981 to 2013. Using the SBT dataset and daily precipitation percentage anomaly data of MC, the influence of SBT to MC precipitation was shown. The most significant influence on the precipitation area of SBT is the Qinghai-Xizang Plateau (QXP) and the Yunnan (YN) region, a significant increase in daily precipitation SBT activity days than the ones with no SBT activity. In Northeast China and Xinjiang regions, SBT shows opponent influence with QXP and YN. SBT position of QXP and YN's Top50 strong precipitation days showed that, when SBT's impact region lays in QXP, SBT more located near 80°E, and SBT less activities in the west of 75°E and east of 85°E; when SBT mainly produce heavy rainfall in YN, SBT mainly located in east of 90°E. SBT located at different positions, it emerged different precipitation distribution. SBT located in west of 80°E, precipitation areas are mainly located in western Xizang. SBT Located between 80°E and 90°E, precipitation areas are mainly located in central Tibet, central south Qinghai and northwest YN. SBT located in east of 90°E, precipitation areas are mainly located in the central QXP and eastern YN.
  • Analysis and Application of the Two Type Vorticity Vectors on a Heavy Rainfall in Sichuan Basin
  • SONG Wenwen;LI Guoping
  • 2016 Vol. 35 (6): 1464-1475.  DOI:10.7522/j.issn.1000-0534.2015.00115
  • Abstract ( ) HTML PDF (4903KB) ( )
  • By using the WRF model, NCEP 1°×1° reanalysis datasets and conventional observational data, numerical simulation and diagnostic analysis is performed for a heavy rainfall in Sichuan basin occurring during June 29th-July 2nd, 2013. The results showed the heavy rainfall was caused by the interaction of plateau vortex and southwest vortex, and the blocking effect formed by the west pacific subtropical high westward extension and stabilize in Sichuan Basin led to stagnate of plateau vortex and southwest vortex. WFR model can better simulate the affecting system, precipitation area and strength of the precipitation. θe analysis showed the heavy rainfall area was in the high temperature and high humidity area, and the lower level of the heavy rainfall area was convective instability area. Equivalent potential temperature was dense in the middle and upper level, and the isothermal surface of the equivalent potential temperature was steep. As the rainfall went on, the convective instability energy released, and the equivalent potential temperature declined. By using the convective vorticity vector (CVV) and moist vorticity vector (MVV), diagnostic analysis result of the heavy rainfall showed the vertical integration of the CVV and MVV vertical component and the trend of the positive cincture of the horizontal distribution was consistent with the precipitation area, and the maximum center could better correspond to the precipitation center. The distribution and development of the maximum area of the CVV and MVV vertical component was consistent with the movement and development of the precipitation area, the coincident positive distribution from low level to top level of the precipitation area was indicative to the heavy rainfall development. The CVV and MVV vertical component can well indicate the development and evolution of the heavy rainfall system in Sichuan Basin.
  • Impact of the Madden-Julian Oscillation on Autumn Rainfall in West China
  • ZHAO Jiayu;MA Zhenfeng;FAN Guangzhou
  • 2016 Vol. 35 (6): 1487-1497.  DOI:10.7522/j.issn.1000-0534.2015.00089
  • Abstract ( ) HTML PDF (26078KB) ( )
  • The Madden-Julian Oscillation (MJO) plays a regulatory role on rainfall in China, studying the impact of MJO on autumn rainfall in West China has important significance for improving intraseasonal prediction ability of autumn rainfall in West China. Anomaly composite analyses have been conducted to investigate the impact of MJO on autumn rainfall in West China and the circulation background fields corresponding characteristics by using the real-time multivariate MJO index from Australian Meteorological Bureau and the daily rainfall of gauge stations in China and the daily NCEP reanalysis data from September to October during 1979-2012. The results show that autumn rainfall patterns change from enhanced to suppressed in West China when the main MJO convective body propagating from west to east. When the main MJO convective body is situated over the central and western Indian Ocean (at phase 1~2), autumn rainfall in West China is above normal level. When the main MJO convective body is situated over the eastern Indian Ocean and central and western Pacific Ocean (at phase 3~8), autumn rainfall in West China is below normal level. The maximum positive and negative rainfall anomalies are found when the main MJO convective body is situated over the central and eastern Indian Ocean and western Pacific Ocean, exactly at phase 2 and phase 7. At the same time, analyzing the corresponding anomalies in the upper air circulation field and the middle-lower flow field, water vapor transportation and vertical motion at various MJO phases. At phase1 and phase 2, we find that the circulation feature is two trough-one ridge pattern or west low-east high pattern over China, the activity of cold air in West China is frequent at this point, and water vapor from Bay of Bengal, South China Sea and Western Pacific Ocean transports to West China is strong, which will helps dry-cold air meets with warm-wet air in West China, the water vapor convergence and upward motion are significant, such environment is in favor of rainfall enhancement. In contrast, at phase 7, we find that China is under the control of the westerly long wave high pressure ridge, and water vapor from the three ocean areas transports to West China is weak, the water vapor divergence and downward motion are strong, such environment is in favor of rainfall suppression.
  • Sensitivity Study of Middle-low Level Temperature Increase for Mesovortex Formation in a Heavy Rainfall Case
  • CHEN Guichuan;WU Zheng;CHEN Yun;LI Qiang;ZHU Yan
  • 2016 Vol. 35 (6): 1498-1511.  DOI:10.7522/j.issn.1000-0534.2016.00070
  • Abstract ( ) HTML PDF (35651KB) ( )
  • An extreme precipitation event characterized by hourly rainfall of 180.9 mm·h-1 occurred near Panlong, Chongqing from 22:00 to 23:00 on July 21 2012, which was fairly rare among rainstorms caused by the southwest vortex. An analysis of Radar data reveals that during the process, a mesovortex that almost rivals a mesocyclone was observed to had been forming and evolving. To investigate the impact of low-level warming exerted on the formation of mesovortex, basing on WRF model, a set of numerical simulations that combined complex cloud analysis and ARPS-3DVAR method that incorporated radar assimilation, together with the sensitivity experiment of center temperature increment assimilation (CTIA) on low-level atmosphere, had been carried out to explore the relationship between mesovortex and aforementioned extreme precipitation. The results indicate that after the assimilation of reflectivity and radial velocity of radar, the GFS forecast performs well on the simulation of the qusi-linear convective system (QLCSs), the area and the center of heavy rainfall and the meso-β-scale cyclonic circulation in the eastern part of Southwest vortex near Panlong with a meso-γ-scale vortex embedded in. The intensity of meso-γ-scale vortex was increased due to CTIA done at both level of 850 hPa and 700 hPa. With 2 Celsius degree's incensement of CTIA at 700 hPa, the mesovortex which was comparable to a mesocyclone was successfully simulated. Meanwhile, the mechanism of the forming of mesovortex could be explained as follows:the abnormal warmness and humidity at low level lead to the abnormal intensification of convective instability, which further triggered the booming development of updraft. As vapor flux converges drastically, a large amount of vapor condenses, rapidly releasing latent heat. The geopotential height near the warming center dropped rapidly as warm and humid air column stretches due to the intensification of updraft. The horizontal gradient of geopotential height thus increase as well as the wind speed surges simultaneously. The mesovortex evolves into a typical mesocyclone swiftly. These indicate that in the background of weak vertical wind shear, the abnormal warmness and humidity at lower level provides significant prerequisite for the formation of intense updraft and the mesovortex which is comparable to mesocyclone.
  • Relationships between North Indian Summer Monsoon and Midsummer Rainfall in Hetao and Its Vicinity Regions of China
  • LI Dongliang;ZHANG Qian;YAO Huiru;LI Xiao
  • 2016 Vol. 35 (6): 1512-1523.  DOI:10.7522/j.issn.1000-0534.2016.00075
  • Abstract ( ) HTML PDF (5715KB) ( )
  • Based on monthly rainfall series of seven homogeneous zones in India and 160 observational stations in China during 1951 to 2006, as well as monthly mean reanalysis data from NCEP/NCAR and NOAA, the relationships between rainfall in each subregions over India and China are investigated. The results show that rainfall in July and August over the northwest and north mountains of India and Hetao and its vicinity areas (Hetao for short) of China exhibit a significant positive correlation, thus defining the midsummer rainfall of the northwest and North Mountains of India as North Indian summer monsoon (NISM). To further reveal the relevant mechanism of the NISM on the rainfall of Hetao, we discuss the relation from two aspects of teleconnection and water vapor transport. It is indicated that when the NISM is strong, Hetao is controlled by the southerly stream in front of abnormal depression, which is located to the southeast of Lake Baikal and tilts westward with the increase of altitude. In addition, the enhancement of NISM also induces the reinforcement of water vapor transporting to Hetao, which is favorable for more rainfall there than normal, and vice versa. Strong/weak NISM is often companied by a La Niña/El Niño event. Eastern equatorial Pacific anomalous SST plays an important role on Hetao rainfall through NISM, while NISM is still significantly correlated with the rainfall of Hetao after excluding the effect of eastern equatorial Pacific SST anomalies.
  • Evaluation of CMIP5 Climate Models on Simulating the Amount and Frequency of Convective and Stratiform Precipitation in East Asia
  • SUN Yue;WU Tongwen;JIN Xia;Laurent Li
  • 2016 Vol. 35 (6): 1524-1539.  DOI:10.7522/j.issn.1000-0534.2015.00107
  • Abstract ( ) HTML PDF (25232KB) ( )
  • Based on the hourly merged precipitation data and Tropical Rainfall Measuring Mission (TRMM) 3A25 monthly averaged precipitation data, the simulation performances about the total precipitation amount, amount and frequency of precipitation (both convective and stratiform) in East Asia in 19 coupled ocean-atmosphere climate models of CMIP5 have been assessed. Results indicate that:(1) All models can simulate the basic pattern of precipitation in East Asia, high-and medium-resolution models can simulate the main precipitation centers:southern slope of the Himalayas, Southern China and the adjacent ocean areas. But low-resolution models can hardly do so. Total precipitation amount in autumn and winter is better simulated than in other seasons. The spatial correlation coefficients of the total precipitation between the simulation and observation exceed 0.7 for autumn and winter, but only 0.50 and 0.61 for spring and summer. (2) According to TRMM, main convective precipitation centers lie over the Philippines, Bay of Bengal and southern of the Himalayas, while stratiform precipitation centers lie on the southern of the Himalayas, downstream of the Yangtze River, East China Sea and Bay of Bengal. As for simulations, high-and medium-resolution models are better than low-resolution models. By comparing the multi-model average with the TRMM data, convective precipitation amount is better simulated, but there are too little stratiform precipitations in the tropics. (3) As for the frequency of total precipitation in East Asia, results from 13 models exceed 60%. For the frequency of different precipitation intensities, the frequency located between 0.001~1 mm·h-1 is the highest in most of the models, while the frequency of intensity which is greater than 1.0 mm·h-1 is quite small. (4) For the stratiform precipitation frequency, high-and medium-resolution models are closer to the multi-model average, but for the convective precipitation, high-and medium-resolution models are not significantly better than low-resolution models. Therefore, the performance of high-and medium-resolution models is generally better than low-resolution models. Improving resolution of models is then necessary to improve their performance in simulating precipitation in East Asia.
  • Discussion on Area Forecast of Two Persistence Heavy Rain Processes
  • KANG Lan;HAO Liping;PU Jiguang;NIU Junli
  • 2016 Vol. 35 (6): 1540-1550.  DOI:10.7522/j.issn.1000-0534.2015.00101
  • Abstract ( ) HTML PDF (20375KB) ( )
  • Using the data of routine weather, automatic weather stations, FY-2E satellite and forecast products of numerical model commonly used in business, two processes were compared that one occurred on June 18 to 20, 2013 and the other from 29 June to 1 July 2013. Rainfall forecast of numerical model for two processes are all concentrated in the western basin, but the drop zone of live have bigger difference. Heavy rain area of "6·18" process located in western basin which is consistent with the prediction. But the one of "6·29" located in the central of the basin as the center which has obvious deviation when compared with prediction. The discussion of this paper focused on the relationship between the circulation background, environmental conditions, satellite image features, evolution of the surface observation data and the heavy rain area. The results show that we can judge the movement speed of influence system and correct the situation forecast and heavy rain fall area correction model in the short-term forecast by analyzing the form and ridge line of subtropical high in the real sounding data and the interaction between the subtropical high and the mid-low latitude system, and satellite image features before the start of process. The analysis found that high energy, high humidity and unstable potential stratification are the favorable environmental conditions for the formation and development of MCS. The relatively high energy and relatively high water vapor conditions are the regions where MCS is most likely to be generated and developed. Tracking the evolution of high temperature, high humidity, unstable zones and Determining the location of the uplifting triggering conditions are key issues in the short-term prediction of strong precipitation. Based on the analysis on environmental field conditions, comprehensive analysis relatively high space-time density of satellite images and observation data and tracking the location of the lifting effect in warm air and its evolution trend, which can be judged the birth, elimination, development and moving path of clouds in 1 to 3 hours, help to determine the heavy rain area in 1 to 3 hours from the point of near short-time forecast, and correct short-range forecast. In the actual business, on the basis of the model forecast, comprehensive analysis of a various observation data correction model forecast is an effective way to improve the accuracy of the heavy rains forecast.
  • Analysis on Mesoscale Characteristics of a Rainstorm Process in Southeastern Gansu
  • WANG Baojian;KONG Xiangwei;FU Zhao;HUANG Yuxia
  • 2016 Vol. 35 (6): 1551-1564.  DOI:10.7522/j.issn.1000-0534.2015.00114
  • Abstract ( ) HTML PDF (23191KB) ( )
  • A rare torrential rainfall process which show the long lasting, strong concentrating and obvious mesoscale characteristics attacked southeastern Gansu province on 19-20 June 2013. This rainfall process consisted of 76.8% warm-area precipitation and low-level shear line precipitation. The causes of torrential rainfall and characteristics of mesoscale system are studied in detail by using conventional and unconventional observation data, NCEP reanalysis data, satellite data and Tianshui radar data. During the period of warm-area precipitation, it shows that the related circulation patternare similar to the typical circulation patternin this area. However, thelow-level wind shear shifts westward and the rainfall area isaffected by the warm air. High temperature and high humidity in the low level reduce the LCL and LFC height and weaken the lifting condition, corresponding withthecold trough in the middle level and then forming theunstable stratification. Besides, the low-level temperature inversion in the early stage isalso conducive to the accumulation of unstable energy. On the other hand, the low-level vertical wind shear, jet stream, and the effect of terrain elevation arelikely to play an important role in triggering and maintaining the convection there. The Strong convectioncorrespondsto the low-level jet stream. The convective cells mainly generateoverthe Huixian-Chengxian basin. The mesoscale convective system showthe characteristics of warm cloud precipitation, low-mass center, high efficiency, backward propagation and train effects. During the period of low-level shear line precipitation, the Wudu vortex located overthe northeast Qinghai-Xizang Plateau developsand strengthensdue to the warm advection, positive vorticity advection in the middle level, and low-level cold air intrusion. Besides, the thickness of wet layer increasesin the troposphere, and the thermal instability condition diminishessignificantly. As a result, the low-level shear line, vortex, and the ground convergence line formthe synoptic-scale upward movement, causing a wide range of stability precipitation. For both the warm-area precipitation and low-level shear line precipitation, there showthree obvious water vapor transportation channel in the lower troposphere:around the east of the Qinghai-Xizang Plateau from the bay of Bengal, through Central China from the South China Sea, and through East China from the east coast. Warm and moist air areconstantly transported to the torrential rainfall area from the tropical and subtropical and result thewater vapor convergence.
  • The Prediction and Forewarning System as well as Weather Characteristics Anlyses of Hail in the East of Gansu
  • LU Yaqi;CAO Yanchao;ZHANG Feng;JIAO Meiling;LI Xiangke
  • 2016 Vol. 35 (6): 1565-1576.  DOI:10.7522/j.issn.1000-0534.2015.00116
  • Abstract ( ) HTML PDF (9318KB) ( )
  • In order to establish the index of hail forecast in Eastern Gansu to provides the reference for hail forecasting and warning to improve the accuracy of forecast, we analyzed the 53 collected hail cases from the aspects of circulation background, physical characteristics and radar products by means of mathematical statistics and cumulative frequency method, using the annual general observation data, regional station data and automatic station data, as well as the disaster information from 2008 to 2013 thus establishing Eastern Gansu hail weather conceptual model, physical quantity prediction index and radar early warning indicators. And the they were tested with some cases in 2014 alone. The result showed that:(1) The difference in temperature of 700 hPa and 500 hPa in hail weather is over 16℃ and the index K is over 19℃. SI is smaller than 2℃ and LI is smaller than 2℃. θse500-θse700 is smaller than 3℃. The vertical wind shear under 6 kilometers is bigger than 1.0×10-3 s-1. The layer height of -20℃ and 0℃ are respectively 7.6 kilometers and 4.6 kilometers. (2) The echo intensity is over 42 dBZ 12 to 18 minutes before hailing and the Echo top is over 9 kilometers. Vertically accumulated liquid water content is over 31 kg·m-2 and the height of strong center and the 45 dBZ echo are both 2 kilometers above the 0℃ layer. (3) physical indicators, such as, the difference of the temperature between 700 hPa and 500 hPa、K index、SI index、LI index、θse500-θse700、the heights of 0℃ and -20℃、0~6 km vertical wind shear, offer effective reference for the potential predictability of hail in the coming 0~12 hours in this area; (4) forecasting indicators of the radar products, such as, echo intensity, echo top heights、vertical liquid amount of water、height of the 45 dBZ、H45dBZ-H0、relevant height of the strongest echo, can provide qualitative and quantitative criteria for the forecasting and warning of the coming 12~30 min for the hail; (5) It shows that conceptual model, forecast and early warning index obtained by analysis on circulation background, physical condition, radar product of hail in Longdong Area have better forecast and early warning effect.
  • Impact of Meteorological Conditions and Pollutant Emissions on Winter Air Quality in Lanzhou
  • HE Jianjun;YU Ye;LIU Na;ZHAO Suping;CHEN Jinbei;YU Lijuan
  • 2016 Vol. 35 (6): 1577-1583.  DOI:10.7522/j.issn.1000-0534.2015.00087
  • Abstract ( ) HTML PDF (556KB) ( )
  • To quantify the impact of meteorological conditions and pollutant emissions on air quality in Lanzhou, this paper developed an artificial neural network (ANN) model to forecast winter daily average pollutant concentrations in Lanzhou based on six years meteorology and pollutant concentration data, and the model was used to investigate the influence of meteorological conditions and pollutant emissions on daily and interannual variations of pollutant concentrations via sensitivity test. The high resolution meteorological data in Lanzhou was acquired from the Weather Research and Forecasting (WRF) model. The results showed that ANN model had a good performance to NO2, followed by SO2 and PM10. The statistical performance indicated that the input data selected in this study may be more suitable for NO2. The relative low statics for SO2 and PM10 were caused by the complex emissions for SO2 (elevated point sources) and PM10(local dust). With good performance, the NO2 was selected to analysis the influence of meteorological conditions and pollutant emissions. The change of meteorological conditions is the main factor causing the daily variation of NO2 concentration, while pollutant emissions change is mainly responsible for the interannual variation of NO2 concentration. Utilizing factor separation method, the contribution of meteorological conditions, pollutant emissions and interactions to NO2 concentration daily variation are 57.9%, 24.5% and 17.6%, respectively, and 13.7%, 73.3% and 13% for NO2 concentration interannual variation. The simple assumption of emission information has an adverse impact on the results, and the improvement of emission information will be needed in the further research.
  • Influence of Urban Heat Island on Pollution Diffusion in Suzhou
  • ZHU Yan;LIU Hongnian;SHEN Jian;JI Yan
  • 2016 Vol. 35 (6): 1584-1594.  DOI:10.7522/j.issn.1000-0534.2015.00084
  • Abstract ( ) HTML PDF (11302KB) ( )
  • Urban heat island is the most typical manifestation of the impact of urbanization on the urban climate. The main reason for this phenomenon is that the economic and social development of human beings has changed the nature of the underlying surface. The urban heat island (UHI) would affect the urban pollution diffusion because of the changes of urban thermal environment and urban wind field caused by UHI circulation. The effects of urban environment on the pollution diffusion mainly include both thermal and dynamic processes. In this paper, urban air quality mode of Nanjing University (NJUCAQPS) was used to study the influence of urban heat island on the pollution diffusion in Suzhou by two group sensitive tests which separate out the urban thermal and dynamic effects. The results show that the urban heat island increase the atmosphere instability and arise the urban heat island circulation, which convergence to the urban area and increase the vertical velocity in the urban. The net effect of urban heat island is increase the diffusion capability of pollution. The urban heat island would decrease the pollution concentration near the surface, for example, with a reduction of 5×10-9 kg·m-3 of PM10 and PM2.5 in urban area, and with a decreasing tendency of urban aerosol species and AQI at different level. On the contrary, the urban heat island would increase the visibility near surface with the extreme value of 0.5 km. Above 180 meters height, PM10 and PM2.5 and the main aerosol species are increased by the effect of urban heat island. At 400 m altitude, the increase of PM10 and PM2.5 can reach the values of 11 and 9×10-9 kg·m-3 respectively. Dynamic effects of urban architectures significantly decrease the wind velocity atmospheric diffusion capacity in urban area, while the heat island effects (thermal effects) are opposite to the dynamic effects of architectures, but effects of heat island on pollution diffusion are less than the effects of dynamic effects of urban.
  • Review on the Impacts of the Southern Annular Mode on Climate over China
  • MA Hao;LI Zhengquan;ZHANG Li
  • 2016 Vol. 35 (6): 1595-1608.  DOI:10.7522/j.issn.1000-0534.2015.00098
  • Abstract ( ) HTML PDF (2873KB) ( )
  • Southern Annular Mode (SAM) is the leading mode of interannual variability of Southern hemispheric atmospheric circulation. Advances in the study of impacts of SAM on climate over China during the past decades are summarized based on the logic sequence. Chinese scientists have noticed Southern Hemisphere-Northern Hemisphere interaction in the early researches, and indicated that Southern hemispheric circulation could influence China's climate through modulating East Asian summer monsoon. In recent years, studies on the teleconnective impacts of SAM have gone deep. A large number of works investigated impacts of SAM on Chinese climate from two viewpoints, i. e. the Pacific pathway and the Indian Ocean pathway. Change of SAM is able to adjust meridional atmospheric circulation over Pacific and trigger meridional teleconnective wave train, and lead to climate anomalies over the western Pacific Warm Pool and anomalous western Pacific subtropical High, which finally induce variation of China's climate. In such way, the Pacific pathway is established. Moreover, SAM anomaly can also propagate to tropical Indian Ocean and the South China Sea with the help of oceanic tunnel, and affect Chinese climate through regional ocean-atmosphere interaction. Therefore, the Indian Ocean pathway also exists. The Pacific and Indian Ocean pathway can interact with each other. Besides, SAM is able to significantly influence regional climate over China. After summing up previous results, some valuable scientific issues and potential research topics in future studies are proposed in order to push the research of SAM teleconnection to move forward.
  • Prediction of Extreme Winter Cold Days
  • SHAN Jikun;LIANG Xiaoyun;SUN Linhai;GONG Zhensong;LIU Yunyun
  • 2016 Vol. 35 (6): 1609-1614.  DOI:10.7522/j.issn.1000-0534.2015.00112
  • Abstract ( ) HTML PDF (6136KB) ( )
  • Extreme events become more and more frequent under the global warming. It is very important to provide an extreme events prediction. Based on daily minimum temperature data for more than 700 observation stations over China and 1983-2010 winter hindcasts of the first generation atmospheric-ocean coupled model in Beijing Climate Center, a new prediction of extreme winter cold days (EWCD) over China is developed by using the stepwise regression statistical downscaling model (SRSDM). Results show that the correlation coefficient of EWCD between predictions using SRSDM and observations for 1983-2010 years exceed the 95% significant level in most of China. Moreover, inter-annual variability of EWCD predicted by SRSDM is well agreed with observations during 1983-2010. The realtime prediction of EWCD in 2011/2012 using the SRSDM was carried out. It is very well that the prediction is successfully and the prediction of EWCD by SRSDM in 2011/2012 is basically in accordance with the observation. Above all proved the method to predict EWCD over China by SRSDM can be employed in operational application.
  • Temporal Variation of Temperature in the Gulang River Basin from 1959 to 2014
  • WANG Tingting;FENG Qi;GUO Xiaoyan;WANG Yamin;LI Zongxing
  • 2016 Vol. 35 (6): 1615-1624.  DOI:10.7522/j.issn.1000-0534.2016.00105
  • Abstract ( ) HTML PDF (7470KB) ( )
  • The variation characteristics of temperature in the Gulang River Basin in the period of 19592014 were examined using the monthly temperature dataset with the Correction analysis, Wavelet Analysis and Mann-Kendall Analysis. The result show that temperature increased significantly over the past 56 years at annual and seasonal scales. Specifically, the annual mean temperature of the Gulang River Basin in creased with an average warming rate of about 0.42℃·(10a)-1 in the upper reaches and about 0.48℃·(10a)-1 in the lower reaches. Warming rate in the lower reaches were generally much higher than in the upper reaches. The significant increase of annual mean temperature could mostly be attributed to the remarkable warming trend in summer, autumn and winter. The annual mean temperature had a prominent cycle of 11 years, it made the local climate changed from cold to warm about six times during 1959-2014. The abrupt changes of annual and seasonal mean temperatures in the upper reaches have happened early compared with the lower reaches, indicating the high altitude regions were more sensitive to climate change. This research is not only helpful in improving understanding of temperature response to global warming in the basin but also provides a basis for basin management.
  • Estimation of Roughness Length of Beijing Area based on Satellite Data and GIS Technique
  • LIU Yonghong;FANG Xiaoyi;LUAN Qingzu
  • 2016 Vol. 35 (6): 1625-1638.  DOI:10.7522/j.issn.1000-0534.2015.00068
  • Abstract ( ) HTML PDF (10290KB) ( )
  • A method is established in this paper for estimating aerodynamic roughness length Z0 for vegetation region and urban area on regional scale. Based on satellite data and GIS techniques and morphological model, three key parameters, vegetation types, canopy leaf area index (LAI) and plant height, are taken as inputs to estimate the Z0 for vegetation region. And buildings density and height are involved to calculate the Z0 for urban area. With the proposed model, the Z0 of vegetation region with resolution 1 km are estimated firstly. Here the vegetation canopy LAIs are derived from Moderate-Resolution Imaging Spectro radiometer (MODIS) satellite data in 2012. The height of forest is estimated with Geoscience Laser Altimeter System (GLAS) satellite data in 2005. And the height of crop is phonological constant. Then the Z0 with resolution 100 m within urban region is estimated with 1:2000 basic geographical data. To validate the results the existing similar researches are involved into comparing and analysis. The results show that in 2012 the Z0 is 0~1.3 m in vegetation region, and the generalized roughness length Z0/Zh is 0.01~0.13, which varies distinctly according to the seasons. Generally, the Z0 is 0.6~1.3 m in mountainous forests, and Z0/Zh 0.06~0.10, which is higher in winter than in summer. While for the farmland in plain region, the Z0 is 0~0.4 m, and Z0/Zh 0.01~0.13, higher in summer than in winter. For Z0 in urban area, generally 0.1~8.0 m, there exists obvious spatial variation which demonstrate the strong heterogeneity of the surface. The regions with Z0 higher than 1.0 m include area inside the forth-ring, and the large residential community, economic development zone outside the forth-ring, and country center in suburbs. Inside the second-ring region, there is a zone with low values, lower than 0.5 m. The estimated Z0 value around the atmospheric tower, a typical urban scientific experiment plot with 325 m high in Beijing urban area, is 4.0~9.0 m, which is consistent with the results based on metrological methods. Our results have demonstrated the proposed method is reasonable and credible in the study area, which also indicates that remote sensing and GIS technology is a valid approach to estimate aerodynamic parameters of complicated underlying surface at regional scale.
  • Analysis of Cloud Microphysical Characteristics on a Precipitation Stratocumulus
  • DANG Juan;LIU Weiguo;TAO Yue
  • 2016 Vol. 35 (6): 1639-1649.  DOI:10.7522/j.issn.1000-0534.2015.00104
  • Abstract ( ) HTML PDF (6220KB) ( )
  • The precipitation process is closely related to cloud microphysical characteristics in addition to cloud macroscopically dynamic and thermodynamic conditions. The mixed phase stratiform cloud system is main target of rainfall enhancement over Northwest of China. To understand the precipitation mechanism and develop scientifically operation of precipitation enhancement, it is necessary to study microphysical structure characteristics of the kind of cloud system in depth. Using the cloud physical data measured by airplane in a stratocumulus precipitation process in southeast of Gansu province on 29 June 2004, the microphysical structural characteristics of stratocumulus cloud system were researched. The synoptic background, precipitation and cloud system evolution during flight measurement were presented, and the cloud microphysical characteristics including number concentration, scale size, 2D image and size distribution of cloud particles at different height levels and horizontal level near stratocumulus top were analyzed. The observation indicates the cloud system is consisted of upper pure cold altocumulus and lower stratocumulus. The study shows that vertical and horizontal distribution characteristics of microphysical structure of the stratocumulus are very uneven. The variation of cloud particles characteristic parameter in lower layer of stratocumulus is larger than of stratocumulus upper layer. The water content and big cloud particle concentration increase with altitude. The difference of particle characteristics in similar altitude suggests that the situation of both formation and growth is variant in different horizontal cloud area at same altitude. The liquid water content is high in stratocumulus, and the maximum is 0.34 g·cm-3 in warm cloud region. There are thermal inversion layers near cloud bottom. The inversion layer near cloud bottom has strong intensity and impact on cloud microphysical structure, including more cloud drop and higher liquid water content near both top and bottom of inversion layer, but it has less obvious influence on larger water drop. The warm rain process is general in stratocumulus, and it is most active in the middle of stratocumulus. The ice phase particles near stratocumulus top enhanced the warm rain process and contribute to rainfall.
  • Cloud Radar Doppler Spectra Calibration and Air Vertical Velocity Retrieval Experiment
  • ZHENG Jiafeng;LIU Liping;LIU Yanxia;CUI Zhehu
  • 2016 Vol. 35 (6): 1650-1661.  DOI:10.7522/j.issn.1000-0534.2015.00064
  • Abstract ( ) HTML PDF (5268KB) ( )
  • Fine detection of cloud and precipitation is still a great interest topic in atmospheric research. In recent years, millimeter-wavelength cloud radars have become the major instrument for cloud and light-precipitation observation. Because of their short wavelengths, cloud radars have excellent sensitivity to small cloud droplets and ice crystals, can be configured to have high temporal and spatial resolutions, and can operate with antennas that have narrow beamwidths and limited sidelobes. In a vertically pointing mode, cloud radar can record the Doppler spectral data which can be benefited for the microphysical and dynamic study of cloud and precipitation system. As an important prerequisite, cloud radar Doppler spectra calibration is crucial for accurately calculating radar measurements, in result, this article present a calibration method for a new 35 GHz cloud radar, produced by Chinese Academy of Meteorological Sciences and plan to participate the 3td Tibetan Plateau Atmospheric Science Experiment from 2014. The accuracy of three radar noise-level compute method are assessed by using simulated data and spectra processing technologies are researched in this research. Another interesting work in this paper is the air vertical velocity retrieval by cloud radar Doppler spectra. At last, retrieval result and reliability of convective and stratiform cloud collected at Guangdong Yanjiang in June 2014 are verified and analyzed. Mainly conclusions are as follows:(1) base on gaussian characteristic of signal and white noise of cloud radar, combined with statistical fluctuation extents, the method can simulate the cloud spectra closed to real, and they can be used as an effective source data for spectra quantitative study. (2) The segment method is the most accurate and stable method, the max-speed method can be affected by noise fluctuations, the objective method is overrated as Doppler velocity and spectral width become large, as long as can cause an apparent error. (3) Inspection results by using the spectral line intensity threshold show that, all traced spectral line intensity in convective cloud are less than this threshold, 100% gates in cloud can be inverted and results are reliable. Apart from a few gates, most of traced spectral line intensity in stratiform cloud are less than this threshold too, 96% gates in cloud can be inverted reliably.
  • Preliminary Analysisof the VHF Lightning Radiation Pulse Power and Charge Structure in a Thunderstorm
  • LIU Yanxiu;ZHANG Guangshu;WANG Yanhui;LI Yajun;WU Bin;ZHANG Rong;YU hai
  • 2016 Vol. 35 (6): 1662-1670.  DOI:10.7522/j.issn.1000-0534.2016.00051
  • Abstract ( ) HTML PDF (4499KB) ( )
  • A balloon-borne Lightning Radiation Source Simulation Device (LRSSD for short, its center frequency is 270 MHz) has been developed. It was used to calibrate the pulse power received by lightning VHF radiation receiver in Pingliang, Gansu Province. The LRSSD connects two receiving systems. One is the calibration system standard that uses the logarithmic antenna and the Spectrum analyzer to receive the 267~273 MHz of the simulated lightning signal, thus measuring the VHF radiation lightning pulse power. The other is the dipole antenna that connects preamplifier, logarithmic amplifier, and the data receiving system, thus measuring the output voltage. A relationship between the measured voltage value and the standard received radiation pulse power was established by using the nonlinear least squares method and changing the distance between the input and output within the working scope of amplifier. Then the calculation formula of the pulse radiation power value of the lightning was obtained. 29 cases space-time distribution of lightning radiation pulse power were obtained. Statistical results indicate the positive intracloud flash, the average radiation pulse power is about 4.8 W and 1.6 W in the upper positive and lower negative charge region, respectively. The radiation power in the upper positively charge area is higher than that in the lower negatively charge area. The negative intracloud flash, the average radiation pulse power is about 3.2 W and 2.6 W in the lower positive and upper negative charge region, respectively. The radiation power in the lower positively charged area is higher than that in the upper negatively charged area. The negative ground flash, the average radiation pulse power is about 3.0 W and 4.7 W in the negative and positive charge region, respectively. The results indicate that the source points in the negative charge area are less than that in the positive charge area. Most average radiation pulse power in positive charge area is greater than in the negative charge area. For some individual lightning flashes, the situation is reversed.
  • Development and Preliminary Application of Environmental Meteorology Numerical Model System in Central China
  • BAI Yongqing;QI Haixia;LIU Lin;CUI Chunguang;LIN Chunze;TAN Chenghao
  • 2016 Vol. 35 (6): 1671-1682.  DOI:10.7522/j.issn.1000-0534.2015.00086
  • Abstract ( ) HTML PDF (2732KB) ( )
  • In order to support central China environment meteorological prediction services, and protect environment reducing air pollution, the environmental meteorology numerical model system was developed basing on the regional chemical dynamical model (WRF/Chem). It could provide the numerical forecasting product of air quality for regional environment. The system was preliminary applied in numerical prediction of air pollution in Wuhan at present, and was compared with CUACE forecast products. In addition, an air pollution optimal control plan was discussed through this test. The results show that:The numerical simulation results of model system could validate the temporal variation and spatial distribution of the air pollutants concentration inWuhan.The population correlation coefficients and the forecasting effectiveness of PM10, PM2.5, SO2, NO2, CO concentrations were credible, and the mean absolute percentage error (MAPE) was controlled in 20%~40%. The O3 concentration correlation coefficient was satisfactory, but the forecast results appeared positive deviation in winter. Compared with CUACE forecast products of every 3 hours concentrations of six air pollutants in Wuhan from September 2014 to January 2015, WRF/Chem products was better. It means that WRF/Chem was more referential value for the air quality forecast in Wuhan. Furthermore, an optimal adjustment test for air pollution control was tentative discussed by changing hourly emissions of pollution source. It suggests that without reduction of daily total emission, the air pollutants concentration can be reduced to some extent by changing the diurnal variations of the emissions according to the characteristics of atmospheric boundary layer height at different times of the day. In the later, we will collect longer observation data in more cities, and evaluate the accuracy and stability of WRF/Chem system.
  • An Interpolation Method for Weather Radar Data Based on Fourier Spectrum Analysis
  • JIAO Pengcheng;WANG Zhenhui;CHU Zhigang;HAN Jing;ZHANG Shuai;ZHU Yiqing
  • 2016 Vol. 35 (6): 1683-1693.  DOI:10.7522/j.issn.1000-0534.2015.00108
  • Abstract ( ) HTML PDF (12197KB) ( )
  • Interpolation is essential in radar data coordinate transformation and radar network process due to the polar coordinate storage of radar data. In order to improve the effect and observation ability of radar network, an interpolation method based on Fourier spectrum analysis ("Fourier interpolation method" for short) has been developed for weather radar echo imagery data. The principle of this method is based on fitting discrete radar-sampling points with Fourier spectrum analysis and then re-sampling for the purpose of interpolation. The algorithm is introduced by steps and cases like typhoon and heavy rain radar images detected by Fuzhou radar and Nanjing SA radar have been studied by comparing Fourier interpolation with bilinear interpolation method in processing radar echo image at low angle. Bilinear interpolation method could narrow the strong echo area because of its "average" process, but Fourier interpolation method can avoid this problem in a certain extent with spectral analysis and sampling properties. Fourier interpolation method can highlight the structural characteristics of strong echo area when processing cumuliform cloud echo derived from convective precipitation in a proper distance, and in the far distance it can interpolate the strong echo centers that low resolution radar cannot detect. Due to the fitting equation, in the strong echo area, the results of Fourier interpolation have a better consistency with true value (fitting degree R2 is more than 0.98; slope is 0.98; intercept is only 0.31 dBZ, closed to 0 dBZ), but the consistency between the bilinear interpolation and the true value is worse (fitting degree R2 is 0.94, the slope is only 0.79, intercept is more than 8.04 dBZ). Fourier interpolation method performs better than the commonly-used bilinear interpolation method in highlighting the structure characteristics of strong echoes in severe convective area and is conducive to showing some severe convective centers which cannot be detected because of the lower spatial resolution at long distance. Due to the large amount of calculation, further research is needed to shorten the calculation time.

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