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Li H.,Chinese Academy of Meteorological Sciences | Li H.,Nanjing University of Information Science and Technology | Li H.,Institute of Heavy Rain | Xu X.,Chinese Academy of Meteorological Sciences
Advances in Atmospheric Sciences | Year: 2017

Various types of radars with different horizontal and vertical detection ranges are deployed in China, particularly over complex terrain where radar blind zones are common. In this study, a new variational method is developed to correct three-dimensional radar reflectivity data based on hourly ground precipitation observations. The aim of this method is to improve the quality of observations of various types of radar and effectively assimilate operational Doppler radar observations. A mudslide-inducing local rainstorm is simulated by the WRF model with assimilation of radar reflectivity and radial velocity data using LAPS (Local Analysis and Prediction System). Experiments with different radar data assimilated by LAPS are performed. It is found that when radar reflectivity data are corrected using this variational method and assimilated by LAPS, the atmospheric conditions and cloud physics processes are reasonably described. The temporal evolution of radar reflectivity corrected by the variational method corresponds well to observed rainfall. It can better describe the cloud water distribution over the rainfall area and improve the cloud water analysis results over the central rainfall region. The LAPS cloud analysis system can update cloud microphysical variables and represent the hydrometeors associated with strong convective activities over the rainfall area well. Model performance is improved and the simulation of the dynamical processes and moisture transport is more consistent with observation. © 2017, Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

Zhou Y.,Nanjing University of Information Science and Technology | Zhou Y.,Institute of Heavy Rain | Niu S.,Nanjing University of Information Science and Technology | Lu J.,Nanjing University of Information Science and Technology
Advances in Atmospheric Sciences | Year: 2013

Both direct and indirect effects of freezing drizzle on ice accretion were analyzed for ten freezing drizzle events during a comprehensive ice thickness, fog, and precipitation observation campaign carried out during the winter of 2008 and 2009 at Enshi Radar Station (30°17′N, 109°16′E), Hubei Province, China. The growth rate of ice thickness was 0.85 mm h-1 during the freezing drizzle period, while the rate was only 0.4 mm h-1 without sleet and freezing drizzle. The rain intensity, liquid water content (LWC), and diameter of freezing drizzle stayed at low values. The development of microphysical properties of fog was suppressed in the freezing drizzle period. A threshold diameter (Dc) was proposed to estimate the influence of freezing drizzle on different size ranges of fog droplets. Fog droplets with a diameter less than Dc would be affected slightly by freezing drizzle, while larger fog droplets would be affected significantly. Dc had a correlation with the average rain intensity, with a correlation coefficient of 0.78. The relationships among the microphysical properties of fog droplets were all positive when the effect of freezing drizzle was weak, while they became poor positive correlations, or even negative correlations during freezing drizzle period. The direct contribution of freezing drizzle to ice thickness was about 14.5%. Considering both the direct and indirect effects, we suggest that freezing drizzle could act as a "catalyst" causing serious icing conditions. © 2013 Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag Berlin Heidelberg.

Yang H.,Nanjing University of Information Science and Technology | Yang H.,Institute of Heavy Rain | Jiang Z.,Nanjing University of Information Science and Technology | Li L.,Laboratoire Of Meteorologie Dynamique
Climate Dynamics | Year: 2016

A dynamical downscaling is performed to improve the regional climate simulation in China. It consists of using a variable resolution model LMDZ4 nested into three global climate models (GCMs): BCC-csm1-1-m, FGOALS-g2 and IPSL-CM5A-MR, respectively. The regional climate from different simulations is assessed in terms of surface air temperature and rainfalls through a comparison to observations (both station data and gridded data). The comparison includes climatic trends during the last 40 years, statistical distribution of sub-regional climate, and the seasonal cycle. For surface air temperature, a significant part of the improvement provided by LMDZ4 is related to the effect of surface elevation which is more realistic in high-resolution simulations; the rest is related to changes in regional or local atmospheric general circulation. All GCMs and the downscaling model LMDZ4 are, more or less, able to describe the spatial distribution of surface air temperature and precipitation in China. LMDZ4 does show its superiority, compared to GCMs, in depicting a good regional terrain including the Tibetan Plateau, the Sichuan Basin and the Qilian Mountains. © 2016 Springer-Verlag Berlin Heidelberg

Xu G.,Institute of Heavy Rain | Ware R.S.,Radiometrics | Zhang W.,Institute of Heavy Rain | Feng G.,Institute of Heavy Rain | And 2 more authors.
Atmospheric Research | Year: 2014

Microwave radiometers (MWRs) can be useful for the detection of mesoscale phenomena because they provide thermodynamic profiles in a minute time scale. These profiles are mainly used in non-precipitation conditions due to degraded accuracy of the MWR measurements in precipitation. Recently, Radiometrics Corporation used proprietary neural network methods to retrieve temperature, humidity and liquid profiles from off-zenith (15° elevation) radiometer observations to provide higher accuracy during precipitation. In this paper, using the MWR-retrieved temperature and humidity profiles with collocated radiosondes from June 2010 to September 2013 in Wuhan, the impact of precipitation on the MWR measurement accuracy as well as the effect of off-zenith neural network methods on it is investigated. In precipitation, the correlation coefficients of the MWR temperature and vapor density profiles against radiosondes are smaller than those in non-precipitation, and the bias and RMS against radiosondes also increase, especially around 2km heights. For the MWR relative humidity profile, the correlation coefficient in precipitation is obvious smaller than that in non-precipitation below 4.5km, and the bias and RMS against radiosondes are clearly larger above 5.5km. Moreover, the differences between the precipitation and non-precipitation cases mostly are statistically significant. Compared with the results of the zenith observation, the off-zenith observation makes a positive effect on reducing the impact of precipitation on the accuracy of MWR temperature and vapor density retrievals. On the whole, the MWR temperature bias and RMS against radiosondes in precipitation are reduced from 3.6 and 4.2K to 1.3 and 3.1K, respectively, and the MWR vapor density bias is also reduced from 1.10g/m3 to 0.18g/m3 with the RMS decreasing from 2.90g/m3 to 1.91g/m3. The temperature correlation coefficient between the MWR and radiosonde in precipitation is clearly improved above 3km heights, and the temperature bias and RMS are significantly reduced at most heights. For the MWR vapor density retrievals in precipitation, the correlation coefficient, bias and RMS against radiosondes are clearly improved above 2km heights. Additionally, the off-zenith observations during non-precipitation cases are also better compared to zenith observations. Therefore, off-zenith observations generally are better than zenith observations. This could be due to the fact that the off-zenith observations are more representative of the conditions in which radiosonde observations are also taken. © 2014 Elsevier B.V.

Numerical simulations with version 3.2 of the Weather Research and Forecasting (WRF) Model are performed to study a localized extremely heavy rainfall event during midsummer in central China. The event occurred in a complex topographical area on 3 July 2008. The extremely heavy rainfall was produced by a quasi-stationary back-building mesoscale convective system (MCS), which was initiated and developed in the exit region of a low-level jet (LLJ). The main mesoscale dynamical process responsible for the MCS formation was the low-level convergence directly generated by the LLJ. The gravity waves excited by the unbalanced dynamics due to the LLJ's abrupt intensification might be another dynamical factor for the MCS initiation. The LLJ was of obvious diurnal variation, which was nearly in an opposite phase with the variations of the planetary boundary layer (PBL) height and of the surface heat and moisture fluxes. The diurnal variation of the LLJ was mainly dominated by the solar-radiation-driven evolution of the PBL height and the surface heat fluxes below the LLJ. The dynamical uplifts forced by the Wufeng mountainous area and the Wushan Mountain were favorable for the formation and development of MCS. The topographic Froude number was less than one at night due to the increase of atmospheric stability in the lower level. The LLJ was blocked mainly by the Dabashan Mountain, and partly by the Wufeng mountainous area and the Wushan Mountain, leading to the MCS in the exit region of the LLJ to remain quasi-stationary and produce the localized extremely heavy rainfall. © 2012 Elsevier B.V.

Convective precipitation associated with tropical depression (TD) is one primary type of post-flooding season rainfall in South China (SC). Observations of the Tropical Rainfall Measuring Mission (TRMM) satellite have shown specific diurnal features of convective rainfall in South China, which is somewhat different from that in other seasons or regions of China. Convective precipitation is usually organized into a rainfall band along the southeastern coast of South China in the early morning hours. The rainfall band develops and intensifies quickly in the morning, then moves inland in the afternoon and, finally, diminishes at night. The daily convective rainfall along the coast is much more than that in the inland region, and heavy rainfall is often found along the coast. A long-duration heavy rainfall event associated with tropical depression "Fitow" during the period from 28 August to 6 September 2001, is selected in this study to explore the diurnal feature of convective rainfall and its formation mechanism. Modeling results of the 10-day heavy rainfall event are compared with both rain-gauge observation and satellite-retrieved rainfall. Total precipitation and its spatial distribution, as well as diurnal variations are reasonably simulated and agree well with observations. Further analysis reveals that the development and movement of convective precipitation is mainly related to the land and sea breezes. The anomalous height-latitudinal circulation in the morning-to-noon hours is completely reversed in the afternoon-to-late-evening hours, with the convective rainfall swinging back and forth, following its updraft branch. Sensitivity experiments show that the afternoon convective rainfall in the inland region of SC is caused by the diurnal variation of solar radiation forcing. The mountain range along the coast and the complex topography in the inland region of SC plays a critical role in the enhancement of diurnal convective rainfall everywhere. The formation of a heavy rainfall band along the southeastern coast of SC and the diurnal variation of the rainfall pattern are mainly the results of the land-sea thermal contrast. © 2013 by the authors.

Zhang R.,Chinese Academy of Meteorological Sciences | Ni Y.,Chinese Academy of Meteorological Sciences | Liu L.,Chinese Academy of Meteorological Sciences | Luo Y.,Chinese Academy of Meteorological Sciences | Wang Y.,Institute of Heavy Rain
Journal of the Meteorological Society of Japan | Year: 2011

The South China Heavy Rainfall Experiments (SCHeREX) was staged during 2008 and 2009 in the southern part of China by the Chinese Academy of Meteorological Sciences under the support of the Chinese Ministry of Science and Technology and China Meteorological Administration. SCHeREX aims at obtaining abundant observational datasets at the meso-β scale, better understanding of the structure and evolution of heavy precipitation systems in south China, exploring establishment of an operational platform for heavy rainfall monitoring and prediction, and improving the ability of heavy rainfall monitoring and prediction. Four zones were selected in SCHeREX, namely, the southern China, the middle reaches of the Yangtze River valley, the Huai River valley, and the lower reaches of the Yangtze River valley. The observation phases were May 1-June 10 in the southern China zone and June 10-July 20 in the other three zones. The efforts have led to the establishment of the meso-β scale observing networks with enhanced capacity to observe precipitation systems at the meso- β scale level. The collected data have been utilized in meso-β scale reanalysis not only to reveal the fine structures of the precipitation systems but also to provide better initial conditions for meso-β scale numerical models to make short-term forecasts. Assimilation of the dropsonde data has improved the analysis of the locations and intensities of typhoons Goni and Morakot. With the real-time field data being part of the forecast system, the experiments have allowed more efficient interactions between the observing system and the forecast system and thus improve the performance of meso-β scale heavy rainfall forecasts. © 2011, Meteorological Society of Japan.

Ding F.,CAS Institute of Geology and Geophysics | Wan W.,CAS Institute of Geology and Geophysics | Xu G.,Institute of Heavy Rain | Yu T.,National Center for Space Weather | And 2 more authors.
Journal of Geophysical Research: Space Physics | Year: 2011

The 15-month climatology of medium-scale traveling ionospheric disturbances (MSTIDs) during a solar minimum period has been constructed from observations of a dense GPS receiver array in Central China. In total, 793 MSTID events are identified, with peaks in occurrence at 1500 LT and 0100 LT. The occurrence of MSTIDs decreases following an increase in geomagnetic activity, with 46% of the MSTIDS occurring in the daytime. Daytime MSTIDs are characterized by a major occurrence maximum around the winter solstice and by an equatorward propagation direction. The period, phase velocity, azimuth, and amplitude of daytime MSTIDs are 20-60 min, 100-400 m/s, 130-270, and 0.8-1.5%, respectively. The remaining 54% of the MSTIDs occurred at night, and were characterized by a peak in occurrence at the summer solstice and by a southwestward propagation direction. The period, phase velocity, azimuth, and amplitude of nighttime MSTIDs are 20-70 min, 50-230 m/s, 170-300, and 2-7%, respectively. The propagation directions and the seasonal behaviors support the view that daytime MSTIDs are an ionospheric manifestation of atmospheric gravity waves from the lower atmosphere, while a possible excitation mechanism of nighttime MSTIDs is the electrodynamics process caused by plasma instability in the F layer. Copyright 2011 by the American Geophysical Union.

Wan Y.,Institute of Heavy Rain
WIT Transactions on Information and Communication Technologies | Year: 2014

Traditional serial processing method cannot cope with large-scale weather radarnet real-time operation. To overcome this, a high-frequency real-time national weather radar data processing parallel computing system is designed using shared-memory architecture multicore processor high-performance computer. In accordance with the characteristics of single weather radar processing and multiradar mosaic, a two-level parallel method of process level and fine-grained thread level shared memory programming is proposed. Then a reasonable spawned thread fineness member is given, and the program efficiency of access file is improved by the method of sharing memory files. A parallel processing and analyzing experiment is made using data from 14 radars of Wuhan Regional Meteorological Center and the radars of six divisions in the Yangtze River Valley. Result shows that such a two-level parallel method can meet the need of national weather radar-net real-time operation. © 2014 WIT Press.

Zhao Y.,Institute of Heavy Rain | Zhao Y.,Chinese Academy of Meteorological Sciences
Meteorology and Atmospheric Physics | Year: 2015

On 24–25 July 2010, a Plateau Vortex system forming to the north of Tibetan Plateau dramatically changed its moving direction to westward after several days of eastward movement. Observational analysis showed that, during its westward movement, a low-level southeasterly or easterly wind developed over the Sichuan basin. The large-scale forcing became favorable for the convection development. The low-level warm advection was more favorable for convection development than the differential vorticity advection. The daytime scattered convections were organized into a mesoscale convective system (MCS) after sunset, which produced extremely heavy rainfall in the eastern slope of the Western Sichuan Plateau. The observational evidences and numerical simulations have indicated that the topographically induced dynamical lifting over the lower topography and the convergence caused by the topographical blocking provided strong support for the convection initiation. The cold outflows caused by surface evaporative cooling of rain steered the MCS to move away from its original place, while the convergence between the cold outflows and the environmental southeasterly flow apparently helped the maintenance of the MCS. The intensification of the low-level flow, which was associated with the diurnal variation of radiative forcing, contributed to the organization and intensification of the MCS. The results of sensitivity experiments further confirmed the impact of topography in the convection initiation, and the influences of cold outflows caused by surface evaporative cooling of rain on the movement and maintenance of the MCS. The effects of the diurnal variation of radiative forcing on the organization of the MCS are also well represented in the model results. © 2014, Springer-Verlag Wien.

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