Plateau Meteorology

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28 February 2011, Volume 30 Issue 1   
  • Global, China-Mongolia Arid- and Semiarid\|Areas (CMASA) andthe Details of Precipitation Distribution in Part Regions of CMASA
  • 2011 Vol. 30 (1): 1-12. 
  • Abstract ( ) PDF (1494KB) ( )
  • In this paper, after the simply review and intercomparison of the global eight major arid-and semiarid-areas have been done, also and the CMASA size, area, name and the some details of the precipitation distribution over part regions of CMASA have been calculated and analysed. The some main conclusions are as follows: There are eight major semi-permanent arid- and semiarid-areas totally in the world. They are the North Africa-, MidwestAustralia-, Central Asia-, China-Mongolia and Midwest America arid- and semiarid\|areas and so on, are mainly located in Africa, Asia and Oceanica. The CMASA is linked together and should be treated as a whole, not in partly. If taking simply the multi-year mean rainfall less than 200 mm and 200~500 mm as the criterions of arid- and semiarid-areas, respectively, then the CMASA covers both the entire Mongolia and north China bording on Daxinganli-Luliangshan a line to the east and the latitude of 36°N to the south, has the totally area of 5×106 km2, with the main body, making up 69% of its total area, and the extremely arid on China side. And it is the homeland of nearly one hundred million populations in China-Mongolia. The CMASA is dry in the middle, something wet on its south- and north-sides. On the China side, the southmost part of Shaanxi is quite humid, with the mean rainfall as much as more than 900 mm, but in the inland hyper arid region, Toksun, the east end of South Xinjiang Basin, is with the rainfall less than 7 mm only; on the Mongolia side, its central and northern part is with the rainfall more than 400 mm; south part, nearly 100 mm; its southwest corner, just 30 mm. The CMASA is a unique mid-latitude, inland dry zone in the Earth. There are four dry centers in isolation in the extremely dry region of the east end of South Xinjiang basin. That is the common impact of the thermal dynamical inducing compensate descent of Qinghai-Xizang Plateau (QXP) topography on the large scale and Fohn effect on leeward side of East Tianshan and Arjinshan orography on the meso-scale. And also there is a obviousextending southward ‘V’ shappeddry valleyon the northeast side of the QXP, that is the impact of thermal compensatedescent of QXP orography as well.
  • Temporal and Spatial Change Features of Precipitation over CMASA（Ⅱ）：Synthetical Climate Subregions of the CMASA and Further Analysesof Periodic Change of Precipitation in Its Various Ones
  • 2011 Vol. 30 (1): 13-21. 
  • Abstract ( ) PDF (1236KB) ( )
  • As the continuation of the Part Ⅰ of the companion papers， the synthetical climate subregions of China\|Mongolia Arid\|and Semiarid\|Area(CMASA)and the further analyses of the periodcchange of the precipitation in its varions subregions were made．The main conclusions are as follows： (1)Based mainly on the abnormal modes of REOF analysis of the precipitation etc， the CMASA is divided into the Guanzhong and Hanzhong, on the east side of Gansu\|Ningxia section of the Yellow River, Gansu Corridor and Mongolia Gobi, North Xinjiang, South Xinjiang, Qaidam, South part of Qinghai Plateau， and Mid\| and North\|and Northwest\|partsof Mongolia， 9 subregions in all．(2) There exist the short period for quasi\|3 years for the precipitation in nearly each subregion； the middle period for quasi\|16 years and 8\|years， in some subregions．As usually， the 3 year period is the main one for most of subregions．Among the 9 subregions， some of them， like Guanzhong and Hanzhong， Mid\|, North\| and Northwest\|partsof Mongolia， have the quite clear and stably periodicity of precipitation； some， like on the east side of Gansu\|Ningxia section of the Yellow River， Gansu coridor and Mongolia Gobiand North Xinjiang， the less periodicity. Whilein South Xinjiang， Qaidam and South part of Qinghai Plateau， a poor periodicity． (3) We are also very much concerned about the point of ‘the climate pattern change in Northwest China(NWC)’． In our view， the recently obviousmoistening occurred in Middle Xinjiang only(not on thewholeNWC scale）； it is only the reflection of quasi\|20 year period for precipitation in Xinjiangonthe interdacadal (not on 100 years) scale．For the future(100 years) climate prediction of the arid area, particularly caution is needed．
  • Analysis on Cloud Vertical Structure over China andIts Neighborhood Based on CloudSat Data
  • 2011 Vol. 30 (1): 38-52. 
  • Abstract ( ) PDF (1678KB) ( )
  • Using the 2B-GEOPROF-LIDAR data of CloudSat from July 2006 to February 2009, the cloud vertical structure (CVS) over China and its neighborhood (0°～60°N, 70°～140°E) were analyzed. Also analysis of cloud vertical structure over 8 regions of China and its neighborhood were performed, respectively. The results show that the multilayer clouds account for 39% of all clouds over the whole region and are predominately two\|layer(77%). Multilayer clouds over tropics occur more frequently than over midlatitude, and there are more multilayer clouds in summer than in winter over the Indian Ocean monsoon zone. The average cloud\|top and cloud base heights are 8.2 and 5.4 km above mean sea level (MSL), and the average separation distance between consecutive layers is 4.4 km. Furthermore, the average separation distance between two\|layer is greater than that between three\|layer. The average top height of all clouds over tropics is higher than that over midlatitude, and the zone with maximal cloud\|top height of highest cloud layers corresponds to the location of the intertropical convergence zone, shifting from the equator in winter to high latitudes in summer. The mean thickness of cloud layers in the subtropics has remarkable seasonal variations, and there are more cirrus (thin, high) clouds in winter over the whole region. Analysis of the cloud vertical structure over the 8 regions show that the zone of Indian Ocean monsoon, South China Sea and the West Pacific Ocean have the same characteristic of CVS, but differences of CVS among other regions are obvious.
  • Does Non-Occurrence of Meiyu Take Place in Yangtze\|HuaiheBasins during Summer of 2009?
  • 2011 Vol. 30 (1): 53-64. 
  • Abstract ( ) PDF (1656KB) ( )
  • Meiyu precipitation in Yangtze\|Huaihe basins is abnormal in summer of 2009. During usual Meiyu period (i.e. from mid June to early July), Meiyu precipitation is too less than climatology to come up to the standard of occurrenceof Meiyu. And some people view it as empty Meiyu or untypicalMeiyu. But during the period from late July to the beginning of August, Meiyu belt retreats to Yangtze\|Huaihe basins again. The so\|called ‘secondary Meiyu’or ‘late Meiyu’has so abundant precipitation that standard of occurrenceof Meiyu is satisfied. Why does Meiyu in 2009 exhibit characteristics of former weak and later severe precipitation? To answer the question, largescale circulation background and mechanism of abnormal Meiyu from the angle of interseasonal oscillation are discussed. The results indicate that: (1) Anomalous Asian summer monsoon provides largescale condition for the occurrenceof Meiyu during the end of June to the beginning of July and from late July to the beginning of August, respectively. The former Meiyu which takes place during the period of distinctively weak Asian summer monsoon has short duration and low rainfall; while the latter occurred after the remarkable strengthening of Asian summer monsoon and meanwhile the time period usually with little rainfall, has long duration and severe precipitation. (2) Anomalously strong Northeast Cold Vortex with long duration blocks the northward advance of west Pacific subtropical high, which brings about late beginning of the first Meiyu period. And weak influences of moisturetransport by summer monsoon attributes much to the lack of precipitation during the first Meiyu period. During the second Meiyu period, due to the southward retreat of the west Pacific subtropical high under the influence of strengthening of Northeast Cold Vortex, anomalous moisture transport from the west Pacific converges with those from North China in Yangtze\|Huaihe basins, which exerts important effects on anomalously sustainable precipitation. (3) 15~30\|day atmospheric oscillation may be the possible mechanism of abnormal Meiyu in 2009. Different from the usually important influences of northward propagation of 30~60\|day low frequency oscillation (LFO) on Meiyu, the obviously northward propagation of 15~30\|day LFO of east Asian summer monsoon joins the southward propagation of 15~30\|day LFO from the North China in the Yangtze\|Huaihe basins, which plays the important roles on the occurrenceof the two Meiyu periods. In addition, the persistent and severe precipitation during the secondary Meiyu relates to the anomalously strengthening of 15~30\|day LFO.
  • Numerical Experimentation of Local Underlying Surface EffectBased on WRF Model in Three Gorges Area
  • 2011 Vol. 30 (1): 83-93. 
  • Abstract ( ) PDF (1484KB) ( )
  • Based on WRF model, the local effect of the Yangtze River and local topography were studied betweenprecipitation and non\|precipitation events in the Three Gorges area. The results showed that in the process of precipitation event, the underlying surface water bodies provided the local water vapor for precipitation, and the near\|surface valley wind that was forced dynamically by the local bell mouth and canyon terrain increased. The southerly airstream affected by the bell topography carried moisture northward, and the valley easterly wind compelled by ‘narrow pipe’ effect of the canyon terrain increased in the downstream section of the Three Gorges area, which enhanced westerly water vapor transportation that converged on the northward moisture affected by northerly wind in the end of the bell mouth terrain. Meanwhile, the changed underlying surface provided latent heat energy for rainfall. The airflow with water vapor was uplifted compulsorily by local terrain and converged with the dry and cold air caused by the unstable stratification from the height, the latent heat energy released instability to lead to precipitation increasing in theregion. On the other hand, in the process of non-precipitation event, the Yangtze River cancool/warmatthe day/night accordingly, and had cold/warm lake effect. The latent heat concentrated in the end of bellmouth with the water underlying surface imbedding and the terrain action. There was no terrain blocking effect on flow, and the southerly flow and the easterly flow enhanced.The variations of circulation characteristicsuggested that both of the water underlying surface and the local terrain were ineligiblyimportant for the weather in the Three Gorges areain different events.
  • Study on Perturbing Method in Regional BGM Ensemble Prediction System
  • 2011 Vol. 30 (1): 94-102. 
  • Abstract ( ) PDF (1038KB) ( )
  • Based on the establishing an ensemble prediction system with BGM method of the regional numerical prediction model AREM, three different perturbations, namely Initial Random Perturbation, Perturbation Restriction, which bothbelonging to Static State Perturbation (SSP) and Dynamic State Perturbation (DSP) are designed and carried out with a evere precipitation process happening during July 20~21, 2008,in order to research the impacts of the perturbations on precipitation. The results show that both SSP and DSP play a positive role in prediction of mesoscale precipitation, such as lowering the missed rate of precipitation prediction. SSP mainly benefits 24 h prediction, while DSP could improve both 24 h and 48 h predictions. Dynamic State Perturbation could be better than two static state perturbations in correct rate of regional precipitation prediction, however, a little bit higher in failed rate at the same time. Dynamic State Perturbation enlarges on some extent disperse of the EPS, good for EPS. Therefore, Dynamic State Perturbation in regional BGM ensemble prediction system is worth researching more and deeply.
  • Helicity Analysis and Numerical Simulation of the ‘4.29’Strong Duststorm in Northwest China
  • 2011 Vol. 30 (1): 115-124. 
  • Abstract ( ) PDF (1391KB) ( )
  • The strongest regional duststorm in Northwest China happened in 28～30 April 2009. Firstly, the synoptic analysis is done by using the observational data. Then the numerical model‘GRAPES_SDM’ is used to simulate the duststrom. Also the helicity theory is used to research the dynamical structure of the process. The results show that the 500 hPa trough and the frontal zone， the surface cold front and heat depression is the principle system creating the strong duststorm. There are two regions with |θ| bigger value at the north of Xinjiang and the Tibetan Plateau， that is propitious for the happening of the severe convection weather. The model GRAPES_SDM successfully simulates the dynamical structure of the strong duststorm， it could be used to predict and research duststorms in Northwest China. The axis of negative center of total helicity lies in front of 500 hPa trough, which has obviously indication for the trough developing. At the dense equivalent area near the zero line of the total helicity， the duststorm appeared. The x helicity was the main part of the total helicity， which could not only forecast the happening of the severe convection weather， but also provide favorable conditionsfor the formation or development of the zhelicity. The position and trend of its negative centre have the coherence with 500 hPa trough. The sand weather appears in front of the trough and after the ridge where positive x helicity and negative y helicty exist together. The temporal variable character of the z helicity and the ω structure can reflect the evolutive process of the sanddust storm. There is a positive helicity and a negative helicity centre in the duststorm region. The time when sand weather occurscorresponds to the emergence and development of the rotational risingmotionat the low\|middle level， when the rotationalsinkingmotionattain the most at the high level.
  • Diagnostic Analysis on Severe Cold Surge, Rain and Ice\|Snowin South China in January 2008
  • 2011 Vol. 30 (1): 150-157. 
  • Abstract ( ) PDF (1113KB) ( )
  • Using the atmosphere data of T213L31 model, four forms of synoptic precipitation with perpendicular motion, i.e. condensation\|function precipitation, moisture\|flux divergence precipitation, convective unstability precipitation and stratificative unstability precipitation are designed and diagnostic calculated for analyzing the severe cold surge, rain and ice\|snow in South China during January 2008. The large\|scale, stable ascending motion of the condensation\|function precipitation and the synoptic\|scale wave of the moisture\|flux divergence precipitation can both reflect synoptic systems, as well as their real precipitation, in the atmospheric westerly belt, and response of the long wave adjustment and reset processes, accompanying so called ‘coming trough and going ridge’ with large\|scale moisture phase change in the air saturation field, and both could organize the mesoscale stratificative unstability precipitation motions. Because the La Nia event is the background for the unusual general circulation over the Eurasian continent during January 2008, the winter meridional circulation and East Asian monsoon should be improved, against that of the ocean\|atmosphere interplay, the up/down stream effect in waves of the westerly belt and the teleconnection in the atmosphere, meanwhile, the subtropical high may be stronger and northward then normal in the West Pacific, therefore the severe cold surges, coming from the Siberian High and the Mongolia High, invade southwardly to China and meet with worm and wet jet\|flows northwardly in the lower troposphere, which come from west side of the subtropical ridge and maintain long time, so that, the anomalous weather of rain, freezing rain and ice\|snow take place in South China. It shows that, in view of the diagnostic calculations of synoptic precipitation motions for the activities of such surface cold front, upper trough and low eddy, etc., the condensation\|function precipitation and the moisture\|flux divergence precipitation were two main weather forms in 4 times of rain and/or snow in the winter 2008, while the convective unstability precipitation and the stratificative unstability precipitation just occurred at the first time of heavy rain and snow in South China, that accompanied by a long wave adjustment and a severe cold surge.
  • Meteorological Conditions in Ice Freezing Day of Chinaand Its Discriminate Model
  • 2011 Vol. 30 (1): 158-163. 
  • Abstract ( ) PDF (767KB) ( )
  • Characteristics of the ice freezing weather, especially the glaze and rime in China are first analyzed, using the daily observation data of temperature, relative humidity, wind speed at 700 stations and weather phenomena at 603 stations in China from 1954 to 2008. Then the favorable meteorological conditionsfor the formation of the ice freezing are obtained and the discriminatemodel of the ice freezing days is developed. It is found that the low temperature, high relative humidity and small wind speed are the important meteorological conditions for the formation of the ice freezing. Among the three meteorological variables, the daily mean temperature appears the decreasing trend from the north to the south, while the relative humidity and wind speed present little difference in China. The discriminate model of the ice freezing days, which is established basing the daily mean temperature and the weather phenomena, can distinguish well whether the ice freezing occur or not on the certain day. The accuracy rate of the discriminate model reaches up to 60% in northwestern Yunnan, Guizhou, northern Guangxi, southern Hunan, southern Jiangxi, and so on, where the ice freezing frequently occurs. And the simulated average false days are only 1 to 5 days. Totally, thediscriminatemodel has a relatively high practicability for the ice freezing monitoring and early warning by routine observations and prediction.
  • Research for Length Change of Four Seasonsover China in Recent 47 Years
  • 2011 Vol. 30 (1): 182-190. 
  • Abstract ( ) PDF (1119KB) ( )
  • Using the daily temperature data at 599 stations in 1961-2007, the length change trends of four seasons during the past 47 years was analyzed. The results show that throughout the change region of length of seasons are: The spring becomes shorter（-0.8 d·(10a)-1）, the summer, longer（3.2 d·(10a)-1）, the autumn, shorter（-0.5 d·(10a)-1）, and the winter, shorter（-1.6 d·(10a)-1）. This trend is different in spatial distribution, namely more obvious in the North of China than in the South, and more obvious in the eastern part of China than in the western part. Summer change is the most obvious, but autumn change has little comparatively. This trend is highly obvious in the North, East China, Central China and South China. In the Southwest of China the summer becomes longer and the winter shorten starts in the 21st century. The Plateau region has a trend that the spring becomes longer and the winter becomes shorter from 1980s. The average annual temperature increases during the past 47 years, the change of the average annual temperature occurs preceding the season length, the average annual temperature has a rather influence on the length change of season.
  • Climatic Characteristic and Cause Analysis of WinterTemperature Anomaly in Shanxi Province
  • 2011 Vol. 30 (1): 200-207. 
  • Abstract ( ) PDF (1098KB) ( )
  • The temporal and spatial characteristics of winter (from December to February) temperature anomaly in Shanxi Province is analyzed by EOF, synthetic and correlation analysis, using the temperature data at 42 stations in Shanxi Province, NCEP sea level pressure, 500 hPa height and the SST of global from 1961 to 2006. And its cause is analyzed from atmospheric circulation and SST. The results show that the decadal variation of temperature in winter is obvious, there is cold period from 1960s to mid 1880s, and a warm period after 1987, especially, the late 1990s to 2004, is the warmest period for the past 46 years. There is a sharp rising trend of winter temperature in Shanxi Province, and climate trend rate is 0.52℃·(10a)-1, while slight regional differences. The regional difference of warming trend is no obvious. The atmospheric circulation in cold and warm winters is significant. The key regions are the Siberia in sea level pressure field, and 500 hPa height in west Loop to east Iran. The impact factors of preceding\|autumn are the 500 hPa height in western Pacific, near the Gulf of Mexico, the Canary islands and India of subtropical; the impact factors of preceding\|summer are 500 hPa height in west of Tony Lake Loop, Caspian Sea Mediterranean, and the North Atlantic of subtropical. SST of southeast coast of China and south of Japan, and SST at the same period are closely related to the temperature anomaly in winter of Shanxi Province. When the SSTs above areas are warmer (colder), the temperature warmer (colder) in winter. There is a good correlation between the SST of the North Atlantic and Indian Ocean in the early autumn and the winter temperature. When the SST is warmer (colder), the temperature is warmer (colder) in winter.
  • Analysis on a Meso\|γ Scale of Local Short-Time Heavy Rainstorm
  • 2011 Vol. 30 (1): 217-225. 
  • Abstract ( ) PDF (1608KB) ( )
  • A local short\|time heavy rainstorm, which takes place in the north\|west of Shijiazhuang on 14 August 2008, is analyzed by means of Doppler radar, ground automatic station data and 4DVAR wind retrieval method. The obtained conclusions are as follows: (1) In general, the radar reflectivity exceed 60 dBz and convergence zone exist in radial velocity PPI when short\|time heavy rainstorm occur. (2) It is possible that the short\|time heavy rainstorm is forecasted more than 18 min in advance based on the radar products such as ET and VIL. (3) 4DVAR method can clearly reveal the low\|levelwind field structure of rainstorm: A cyclonic vortex is first generated in the region of heavy rain, and then the southwest airflow in front of the vortex arouses severe convection echo which maintain stability because of the convergence always existing, and lead the local heavy rainstorm. Whereby, the meso\|γ scale or small scale systems can be revealed by 4DVAR wind field retrieval, which can play an important role in forecasting the drop zone of heavy rainstorm, tracking the generation and evolution of meso\|γ scale vortex, and understanding the mechanism of the local short\|time rainstorm clearly.
  • Diagnostic Analysis of the Effect of ThermalInhomogeneous Field on the Hail
  • 2011 Vol. 30 (1): 226-234. 
  • Abstract ( ) PDF (1351KB) ( )
  • Using the new data which are combined by the data from Automatic Weather Stations(AWS) in Tianjin and the data above 850 hPa in Beijing, a hail case in Tianjing before dawn of 27 August 2008 is diagnostically analyzed. The hail is observed in two areas, in which is Jixian mountain, other is Hangu area that is near to the sea. Through the research on the thermal and dynamic parameters, the results show that: (1) Using the new sounding data, the calculated convective parameters can reflect the distribution of the characteristics of the severe mesoscale convective weather, especially, the high value area of CAPE and low value area of LI is well correspording to occurrence area of severe convective weather. Besides, it shows that the thermal and dynamic characteristics in the boundary layer are significant to the short\|time nowcasting of the local severe convective weather. (2)The thermal parameters of CAPE (LI) in Hangu area are increasing (decreasing) with time and it is opposite to the phenomena in Jixian area. This phenomena show that there is more significant difference in the reasons of causing the hail between those two locations. The former is dominated by thermal effect while the latter is not. In Hangu area, the reason is that the inhomogeneous distribution of thermal effect causes secondary circulation and upward motion, so that water vapor condense and release the heat. Due to the uplift effect of Jixian mountain, the upward system of the eastward movement is strengthened to cause the hail.
  • Analysis on Hail Suppression Effect by Catalyse to Two Hailclouds
  • 2011 Vol. 30 (1): 252-257. 
  • Abstract ( ) PDF (843KB) ( )
  • In order to study scientificity of artificial hail suppression and evaluate objective effect of hail suppression and reduce disaster of hail, using the comparative method in the physical validity checking theory, the evolution of 711\|type radar echo of two hail clouds before and after hail suppressions on July 24, 2007 have been analyzed. The results show that, after the one times hail suppression, the maximum echo intensity of A hailcloud is decreased 10 dBz and the 45 dBz echo top height is lowered 0.8 km and its width is increased and echo intensity is weakened and echo is expanded and split and stopped moving and combined behind clouds the reverse merger on PPI. After the four times hail suppression, the echo top height of B hailcloud is lowered 1.3～0.4 km (average 0.85 km) and the 45 dBz echo top height is lowered 0.9～0.4 km (average 0.65 km) and echo is split two parts and expanded after the previous two operations and echo area continues to increase and split after the last two operations. Therefore, the artificial hail suppression to two hail clouds is effective.

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