Abstract:The vertically pointing cloud radar (WACR) can measure not only the reflectivity of cloud particles but also Doppler spectra. Retrieval of vertical air motions in cloud is demonstrated using measurements by WACR at Shouxian site during a period of 1 November 2008. The distribution characteristics of reflectivity, Doppler mean velocity, and spectral width are initially discussed. Retrieval of vertical air motions is demonstrated by the liquid droplets trace method and the improved w0－Z relationship method which is based on the liquid droplets trace method. The results are comparatively analysed with Doppler spectra. The liquid droplets trace method performs great effect in the retrieval of vertical air motions in the weak turbulence. When the turbulence is strong, the error cannot be ignored. The improved method presents good performance in the area with strong turbulence.

Abstract:Based on the basic principle of dynamical analogue prediction, the authors have established the optimal dynamic multi-factor schemes to revise prediction errors. In this paper, the authors studied the correlations between the interactions of prophase key factors and the precipitation of rainy season in China and found the key atmospheric circulation predictor. According to the predictors which are abnormal in prophase, the authors compressed the dimensions of the factors to select the similar years through EOF analysis. Furthermore, a new dynamical analogue prediction scheme is constructed, which is based on the anomalous signals of prophase environment field. Analyses show that there is a good corresponding relationship between precipitation in North China and numbers of atmospheric circulation factors which are abnormal in prophase. The authors developed a comprehensive scheme to revise prediction errors of numerical model combined with the abnormal factors scheme and the optimal dynamic multi-factor scheme. Through the diagnostic analysis, the authors found that the comprehensive scheme has a good adaptability. Results of independent sample return during 2003－2009 show that the anomaly correlation coefficient (ACC) score has increased from 0.38 to 0.61. The similarity revised method has further improved the prediction capacity of numerical model and has a good application prospect for summer precipitation in North China.

Abstract:By using non-hydrostatic WRF (Weather Research Forecast) model, the landfall process of typhoon Fungwong are simulated in high resolution. The simulation is triple nesting with the highest resolution of 3 km and integrated 120 hours (5 days). The authors also carried out careful comparison between the simulation results and the real situation (the conventional and unconventional observational data). The results show that the WRF model successfully simulated the development and landfall process of typhoon Fungwong, the simulated path is quite consistent with the observed one. At the same time the model also successfully showed the evolution process and the feature of main radar echo in the whole simulation period, the simulation is successful. Further more, with the high-resolution simulated data the authors carried out diagnosis analysis of |Q| to the landing process of typhoon. It shows that the abnormal value area of |Q| always cover the rainfall area in the whole period, they have the similar spatial distributions and time evolution trends. And |Q| shows strong signals in the rainfall area and shows weak ones in the non-rainfall area. To sum up, |Q| has good indicative meanings to forecast of the strong precipitation.

Abstract:The relationship between the interannual variations of summer precipitation in eastern China and the SST anomalies in the East China Sea and its adjacent seas is analysed by using the methods of composite and correlation analyses and the daily data of summer (June－August) precipitation at 756 stations of China, GPCP2.1 and HadISST datasets from 1979 to 2008. The results show that when the SST of the East China Sea and its adjacent seas is in warm (cold) anomalies in summer, there are less (more) rainfall in the middle and lower reaches of the Yangtze River and the Yangtze River/Huaihe River valley (Jianghuai valley) and more (less) rainfall in the southern part of Northeast China. Moreover, a regional climate model (RegCM3) is used to examine the above-mentioned relationship. The simulation results indicate that the warm (cold) SST anomalies in the East China Sea and its adjacent seas can contribute to less (more) rainfall in the middle and lower reaches of the Yangtze River, the Yangtze River/Huaihe River valley (Jianghuai valley), and most of North China, and more (less) precipitation in South China, the southeast part of Northeast China, and the Korean Peninsula. Besides, the processes of atmospheric circulation variability over East Asia caused by the SST anomalies in these sea regions are explored based on the NCEP/NCAR reanalysis data and numerical simulation. The result shows that increase or decrease of SST in the above-mentioned seas has remarkable effect on zonal and meridional circulations over East Asia. When the SST of the East China Sea and its adjacent seas is above normal, a downward motion with a divergence at low levels and a convergence at upper levels can appear over the middle and lower reaches of the Yangtze Rive and the Yangtze River/Huaihe River valley (Jianghuai valley), and most of North China, which contributes to the decrease of summer rainfall in these areas, in addition to an upward motion with a strong convergence at low levels and a remarkable divergence at upper levels can be caused over the region to the east of these seas. And an upward motion with strong convergence at low levels and remarkable divergence at upper levels is caused in South China, the southern part of Northeast China, and the Korean Peninsula, thus, the summer precipitation increase obviously in these regions. When the SST of the East China Sea and its adjacent seas is below normal, the opposite phenomena appear in the above-mentioned areas. Consequently, it is suggested that the thermal state of the East China Sea and its adjacent seas may be one of the important factors affecting the summer precipitation in East China.

Abstract:Due to the topographic effect of the Tibetan Plateau and its vicinity, some small but strong high and low pressure systems often occur on the isobaric levels of the lower atmosphere by extrapolation, and the real systems cannot be reflected clearly. Therefore, it is still a difficult problem to analyze and diagnose the vortexes near the surface of the Tibetan Plateau with current isobaric analysis methods. In recent years, there has been significant progress in the numerical models, but the problem of weather analyses near the surface of Tibetan Plateau is not yet solved well. One of the reasons is that the pattern of geopotential height contour on the terrain following σ coordinate commonly used in models is similar to the topography and cannot represent the synoptic systems. In the article, a new variable, which is referred to equivalent isobaric geopotential (øe) and satisfies quasi-geostrophic relation, is introduced based on the averaged harmoic-cosine vecter decomposition in a limited region. It can be used in the same way as the geopotential used on p coordinate. As an example, a eastward moving Tibetan Plateau vortex is analyzed. The results show some small but low and high systems always exist over the Tibetan Plateau due to extrapolation in the sea level pressure field, but at σ=0.995 level, the process of the eastward moving Tibetan Plateau vortex coupling with the southeast vortex at lower levels can be depicted well by the distribution of øe, and these artificial systems in the Tibetan Plateau disappear. Therefore, the weather system near the surface of Tibetan Plateau can be analyzed well with the analysis method of equivalent isobaric geopotential height. On the other side, the distribution of øe can link the synoptic pattern over the Tibetan Plateau with that in its lower reaches, which is favorable to reveal how the systems over the plateau impact the weather in the lower reaches.

Abstract:The monsoon has great impacts on the regional and global climate to which many scientists dedicate themselves for better understanding it theoretically and numerically. Based on Thermal Adaptation Theory, the authors evaluate the performances on the global diabatic heating of the newest spectral atmospheric general circulation model (SAMIL, hereafter), developed at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP), and further make some analyses and explanations on the simulations of the components of the East Asian Summer Monsoon (EASM). The results show that SAMIL has good performances on the quadruplet heating pattern (LOSECOD) in the boreal subtropics compared to the NCEP/DOE AMIP-II Reanalysis (Reanalysis-2), except for biases in strength. The sensible heating simulated by SAMIL is universally stronger over the continent, and the condensation heating is stronger on the two sides of the Indian peninsula and over the western Pacific (especially at 10°N and 10°S), whereas it is weaker near the equator and over the regions of the Indo-China Peninsula and the South China Sea. The authors further point out that the South Asia high can be well simulated and main features of the subtropical high over the western Pacific can be generally captured. But the subtropical high has stronger strength and more westward location, which are mainly caused by the stronger latent heating over the western Pacific (near 30°N). It also can exhibit the two centers of the westerly jet which is some 10 m/s smaller than that from Reanalysis-2 resulting from the weaker latent heat, sensible heat, and shortwave radiation. It further points out that the cloud parameterization and cumulus convective parameterization cause the biases in the sensible heating and latent heating. From this point, modifying and updating the physical parameterizations in SAMIL will be the priority in the near future.

Abstract:Shandong Artificially Triggering Lightning Experiment (SHATLE) has been conducted continuously since the summer of 2005. During the six years from 2005 to 2010, twenty-two negative lightning flashes containing eighty-eight return strokes were successfully triggered. Channel base currents, close electromagnetic fields, and high-speed camera images were obtained simultaneously for some of the strokes. Based on directly measured currents for thirty-six return strokes, the geometric mean of return stroke peak current was about 12.1 kA with a maximum of 41.6 kA and a minimum of 4.4 kA, the half peak width of current varied from 1 to 68 μs, and the geometric mean values of 10%－90% risetime, charge transfer, and action integral were about 1.9 μs, 0.86 C, and 2.6×103A2?s, respectively. The surface electric field at 30 m away from the discharge channel caused by a return stroke with peak current of 16.5 kA reached 111.9 kV/m. The geometric mean of magnetic field at 60 m away from the discharge channel was about 52 μT. The peak current and charge transfer of some large M components were comparable with those of return stroke. The speed of upward positive leaders in the initial stage of triggered flashes was about 0.96×10.5 m/s.

Abstract:The knowledge on measurement-based spatial－temporal distributions of summertime cloud water contents is greatly important for numerical weather prediction, climate projection, and weather modification experiment. By using the data provided by CloudSat, the study examines the vertical, geographic, and monthly variations of cloud water content over China during the summers of 2006－2008. Results show the significant influences of the Tibetan Plateau topography and East Asian summer monsoon on formation, vertical and geographic distributions of monthly average cloud water content. In the regions of central China (27°N－35°N), monthly average liquid cloud water contents in the middle and upper layers of the tropospheric atmosphere are remarkably larger than those in southern and northern China regions. There are two peaks in the vertical profiles of monthly average liquid cloud water contents, which may result from combined effect of large-scale atmospheric parameter, the Tibetan Plateau topography and East Asian summer monsoon. The high values of monthly average ice water contents are mostly concentrated in the layer of 6－18 km above sea level, namely the upper tropospheric atmosphere. The revealed features of monthly average cloud water content can provide baseline information for the further researches on weather and climate models improvement, weather modification, and cloud-radiation-climate interaction.

Abstract:2－4 weeks extended range forecast (ERF) has become an important research area for operational developments of both weather forecast and climate prediction in the last decades. In order to provide scientific clues to establish ERF, by taking Meiyu over the Yangtze－Huaihe basin as an example, based on intraseasonal oscillation (ISO) signals of rainfall, key influential systems and strong signals of tropical MJO extracted by Ensemble Empirical Mode Decomposition (EEMD) and multi-variable EOF, optimal subset regression (OSR) statistical method, empirical wave propagation (EWP) dynamical method, and global ocean－atmosphere coupled model output are respectively employed to explore ERF of rainfall variation over the Meiyu region. Experimental results suggest that (1) the ISO may be an important system contacting weather processes and weather anomaly, which can be potential signals of the extended range forecast for pentad rainfall over the Meiyu region.(2) LFO (Low Frequency Oscillation) predictors extracted from rainfall in the Meiyu region during earlier period by EEMD can be used to forecast pentad rainfall amount in the Meiyu region about 30 days in advance by the OSR statistical method. (3) For the EWP method in dynamical sense, it can well forecast the eastward propagation of the tropical ITCZ 40 days in advance. At the same time, the EWP method has potential ability of forecasting wind anomaly over the Meiyu region. (4) The global ocean－atmosphere coupled model output is a worthwhile reference for the ERF of atmospheric circulation and MJO index 20 days in advance.

Abstract:By using the satellite Temperature of Brightness Blackbody (TBB) data, NCEP 1°×1° reanalysis data, and nonhydrostatic mesoscale numerical model MM5, control experiment and six sensitivity experiments which are adiabatic, no surface sensible heating, double surface sensible heating, no evaporation effect, no latent heat of condensation, and no water vapor, are performed for two cases of plateau vortex occurring during 28－29 July 2005 and 29－31 July 2009, and the happening, development, and structure change of the plateau vortex during 28－29 July 2005 are mainly discussed. The results show that the vortex center and the vortex structure at 500 hPa simulated in the control experiment are the same as actuality. The adiabatic conditions affect the formation, development and structure change of the vortex most remarkably. The latent heat of condensation and the water vapor do not play decisive roles in formation of the vortex, but play key roles in vortex maintenance and structure characteristics evolvement. Surface latent heat has some effect on the development of the vortex, and no surface latent heat slightly decreases the strength of the vortex. The effect of surface sensible heat on the vortex is different for different cases, and depends on the developing stage of the vortex, and also that the developing stage is daytime or night.

Abstract:Using the WRF/ARW model to simulate a proceeding of cold vortex over Northeast China during 8－12 July 2007. The analysis of synoptic weather indicates that the cold air mass above the north of Lake Baikal moves to the cold vortex over Northeast China and enforces it. What is more, a part of the cold air transfers to the middle and lower troposphere from the tropopause, which causes the process of dry intrusion. Besides, in the east of cold vortex, there is the convergence of water vapor transport, which indicates the water vapor is plentiful there, and the intersection of the cold dry air and the warm wet air benefits the formulation of rainfall. The results of wind structure of mesoscale convective system (MCS) prove that the southeast and northeast parts of cold vortex, where there exists the maximum of cyclonic curvature, are the areas prone to MCS, which leads to the heavy rainfall. Finally, the vertical component of convective vorticity (CVV) is used to diagnose the location of MCS rainfall, and the corresponding of CVV and rainfall shows that CVV could indicate the area of rainfall.

Abstract:Effects of cloud condensation nuclei (CCN) concentration on explicit-deep convection simulations of precipitation associated with a squall line that developed in Guangdong Province, China are investigated using the Weather Research and Forecasting model. Four groups of simulations are conducted, each with a different bulk microphysical scheme (Morrison, Thompson09, Thompson07, and WDM6) and consisting of three members with low, median, and high CCN concentration, respectively. Changes caused by the CCN concentration variation in the surface rainfall rates within the regions of deep convection, stratiform cloud, and shallow convection, as well as in their areas, are compared among the four groups of simulations. Then the microphysical processes and strength of dynamical circulation in the simulations are examined. It is found that: (1) The CCN－precipitation impacts among the four groups of simulations exhibit both similarities and differences, due to the direct or indirect relationships between the microphysical processes and CCN concentration, the complicated linkage among various microphysical processes, and the nonlinear coupling between microphysical and dynamical processes.(2) The simulated CCN－precipitation impacts are the most significant with the Thompson09 or Thompson07 scheme and the least notable with the WDM6 scheme.(3) In these experiments, precipitation is delayed and weakened during the early stage of the simulations and rainfall amount is also decreased during the late stage, while the CCN－precipitation impacts are more complicated during the mature stage of the simulated squall line.

Abstract:This study evaluates the performance of the Global Forecast System (GFS) of the U.S. National Centers for Environmental Prediction (NCEP) against the Climate Modeling Best Estimate (CMBE) observational dataset made by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program at the southern Great Plains (SGP) site for the years of 2001－2008. The investigation focuses on the vertical distributions of air temperature (T), relative humidity (RH), and cloud fraction. The major findings are as follows: (1) NCEP GFS was able to largely capture the seasonal variations of T and RH. However, on seasonal average, the model overestimated T at the heights of 1.5－12 km, while underestimated T at 13－16 km in spring and winter and at 0－1.5 km in autumn and winter, by less than 1℃. Both the predicted and observed RH had double peaks located near the surface and around 12 km, respectively. However, the model overestimated RH in the upper and middle troposphere (4－12 km). Increase of model resolution from T170L42 to T254L64 significantly improved the prediction of RH at 14－18 km. (2) NCEP GFS generally underestimated cloud fraction at heights below 10 km and slightly overestimated cloud fraction at 11－13 km. Moreover, the prediction missed the daytime nonprecipitating low-level clouds and underestimated precipitating cloud amounts below 8 km, indicating that activities of shallow convection and deep convection in the model were not active enough. (3) Using the observed RH and the predicted cloud water/ice mixing ratio (qc) to calculate cloud fraction with the diagnostic method in the NCEP GFS model, the result shows that cloud fraction from this calculation is more significantly underestimated compared to the NCEP GFS predicted cloud fraction, suggesting that the underestimation of cloud cover at heights below 11 km by the NCEP GFS is probably contributed by an underestimate of qc at these altitudes. (4) Improvements in the prediction of T, RH, and cloud fraction were insignificant during 2001－2008. The inaccurate prediction of cloud fraction and qc is probably related to uncertainties of parameterizations of deep and shallow convection, as well as cloud microphysics, in the NCEP GFS model.

Abstract:The spatial and temporal characteristics of spring (March－May) rainfall in China and its relations with the previous winter (December－January) and spring sea surface temperature (SST) over the tropical Pacific Ocean and spring snow over Eurasia are investigated using the observed rainfall dataset for the period 1979－2004. The leading EOF mode of normalized spring rainfall shows the most robust variability in the vast regions from the Yangtze River valley to North China (YRNC), representing the variation of spring rainfall in the middle-latitude eastern China. The anomaliesof spring rainfall in eastern China show a meridional dipole mode across the Yangtze River valley. The interannual variability of springtime rainfall is notable and becomes more robust after the late 1980s. The anomalies of springtime rainfall over YRNC are significantly correlated with the SST in the tropical Pacific Ocean during the previous winter and spring. Positive spring rainfall anomalies in YRNC correspond to warmer tropical East Pacific Ocean and colder tropical West Pacific Ocean, and vice versa. Although more rainfall over YRNC is associated with increased snow water equivalent (SWE) in the Chukchi Peninsula and the Tibetan Plateau and reduced SWE in the area from south of Lake Baikal to Northeast China, and this correlation becomes insignificant after subtracting El Niño－South Oscillation (ENSO) effect. Thus, the link between Eurasian snow and springtime rainfall over YRNC is probably a component of the relationship between ENSO and rainfall.

Abstract:Calculating the number of frozen days in January in southwestern China when satisfying the conditions with daily minimum temperature in the context of -10℃ and 1 ℃, relative humidity greater than 80%, and sunshine duration less than or equal to 2 hours at the same time, by using daily meteorological elements data for the period of 1961－2009 from 96 stations in southwestern China. Using NCEP/NCAR reanalysis grid data, the circulation features in the icing and no-icing years were analyzed. The results show that, in icing years in southwestern China, the 500-hPa height anomaly field are “north-higher and south-lower” in Eurasia, “west-higher and east-lower” in the high latitudes, and “west-lower and east-higher” in the low latitudes, indicating that the high pressure around the Ural Mountains, depression around the Caspian Sea, and the subtropical high are all strong, in favour of cold and warm air confluence in southwestern China, which is the basic condition of icing there; the best related areas of the Middle East jet stream and the icing in southwestern China are the boundary of Sichuan－Yunnan－Guizhou provinces, most of Guizhou Province, the boundary between northern Yunnan Province and southeastern Tibet, the southwest of Shaanxi Province, and about Erlang Mountain, which are the most areas of strong icing on average. Further studies indicate that 500-hPa trough activity around Central Asia is the bond between the Middle East jet stream and the icing in southwestern China. If the sea surface temperature near Bermuda in the north Atlantic is colder in the prior December, the Middle East jet stream will be much stronger in January.

Abstract:The Characteristics of regional droughts in fall in South China and related general circulation anomalous patterns are statistically analyzed with the observed precipitation data and the NCEP/NCAR reanalysis data from 1968 to 2009. The seasonal droughts in fall in South China occurred mainly in the region-wide event. There exist two dominant patterns of sea surface temperature anomalies (SSTA) related to the fall droughts in South China. The first SSTA pattern shows positive anomalies in the tropical western Pacific and the Maritime Continent in a horseshoe-shape and negative anomalies in the western tropical Indian Ocean, the area from the South China Sea northeastward to the subtropical northwestern Pacific and the central and eastern tropical Pacific with a cooling center in the east. The second SSTA pattern exhibits a feature of negative anomalies in the tropical and subtropical western Pacific, the South China Sea, and the tropical Indian Ocean, and positive anomalies in the tropical central and eastern Pacific and the subtropical northeastern and southeastern Pacific. Corresponding to the first SSTA pattern, the fall droughts in South China result from the enhanced ascending motion over the Maritime Continent and its surrounding area, which is forced by the warmer underlying sea surface temperature. However, corresponding to the second SSTA pattern, the droughts in South China mainly result from the prominent anomalous ascending motion over Northeast Asia which might be forced by the adjustment of the large-scale synoptic activities in the mid-latitudes. The anomalous ascending motion over the subtropical northwestern Pacific to the east of Taiwan and the Philippines exerts also influence on the fall drought events in South China. Two categories of fall droughts in South China are induced by the anomalous descending motions over South China, which are forced by the anomalous general circulation. Furthermore, the two categories of droughts in South China are related to the decrease of tropical cyclones in fall over the central and northern South China Sea and the increase of tropical cyclones over the subtropical northwestern Pacific east of Taiwan and the Philippines, which reduces the frequency of tropical cyclone landfall on South China and thus results in the fall drought events.