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1.
1. Introduction The strong convective weather is developed under the favorable large-scale circulations, which demon- strated the large-scale weather system's controlling ef- fect on strong convections. Once the convection is formed, it will produce the feedback effect on the large-scale environmental conditions by transporting momentum, heat and moisture upward, and influence or change the environmental wind, humidity, tem- perature, atmospheric stratification fields and so on, thus forming t…  相似文献   

2.
1. Introduction China is located in the East Asian monsoon re- gion. Every year's weather and climate in this region is deeply affected by the monsoon activities. Es- pecially, during flooding season (May to September), the summer monsoon controls large-scale precipitation patterns, the movement of seasonal rain belt and oc- currence of drought/flood disasters. The Asian mon- soon can be divided into two systems (Tao and Chen, 1987). As a major component and its unique location, the South …  相似文献   

3.
The summer monsoon onset over the northern South China Sea (SCS) in May 16-20, 1998 was characterized by the abrupt onset of mesoscale convective activities and rapid increase of precipitation. The possible mechanism for formation of the mesoscale convective systems (MCSs) and related rain belts were revealed through discussing their forming physical conditions under the large-scale background: (1) The high pseudo-equivalent potential temperature and the convective instability in the lower troposphere, the low-level southwesterly confluence and the high-level divergence over South China and the northern SCS provided the favorable large-scale thermodynamic and dynamic conditions for development of MCSs. The southwesterly flow from the Bay of Bengal (BOB) interacted with that to the western flank of the subtropical high, which constituted the major moisture channels, thus bringing about deep wet layers and strong moisture convergence;(2) triggered by several cold troughs from high and mid latitudes, the convectively unstable energy was released and the convective activities over the northern SCS broke out abruptly;(3)analysis of retrieved precipitation based on the dual-Doppler radar during South China Sea Monsoon Experiment (SCSMEX) indicated that active convection influenced by the monsoon trough and corresponding wind shear line organized and formed continually some mesoscale convective rainbelts. During May 15-19,about 12 precipitation processes with 6-12-hour life span or more were observed;and (4) under the favorable synoptic conditions, establishment of the monsoon trough and shear line in the low levels, as well as production and development of mesoscale low vortex were all necessary conditions for the formation and maintenance of MCSs.  相似文献   

4.
Summary  A mesoscale convective system (MCS) case that developed over the Yellow Sea (12–13 July 1993) is studied by using a 23-level, 30 km-mesh Penn State/NCAR mesoscale model MM5. This MCS was generated in northern China, south of the Changma front, in a convectively unstable environment, under the influence of a short-wave trough accompanied by a marked cold vortex aloft. The model with all model physics (refereed to as CNTL) captured the major features of this MCS. A mesoscale low-level jet (mLLJ), with a horizontal scale of a few hundred km, developed within the MCS. Available wind data support the realism of this mLLJ. This mLLJ not only transports convectively unstable air directly toward the MCS but is also responsible for a strong low-level convergence in the MCS. At 200 hPa, an anticyclonic northwesterly flow with a relatively high wind speed core on the east of MCS was simulated. This relatively high-speed flow can be regarded as a mesoscale upper level jet (mULJ), acted as an upper outflow over the MCS. Low-level convergence on the left-front of the mLLJ and upper divergence in the right-rear of the mULJ creates a strong upward motion (≅ 40 cm s−1) in the MCS. Heavy precipitation up to 45 mm between 1800–2100 UTC was observed after this MCS landed on the southern Korean Peninsula. The CNTL run captured this heavy rainfall event. A maximum rainfall of 50 mm 3 h−1 was simulated. In another experiment, with surface sensible and moisture fluxes withheld (NOSF), the 3-h simulated rainfall was decreased to 30 mm. Less latent heat released in the NOSF led to a weaker MCS and mLLJ. The concurrent surface fluxes sustained a high low-level moisture field over the Yellow Sea, which helped the development of the MCS and enhanced its precipitation in this case. Received January 8, 1999  相似文献   

5.
Summary Mesoscale Convective Systems (MCSs) data registers from June to December during 1990–94 were obtained from the Spanish National Meteorological Institute (INM). Fifteen Mesoscale Convective Complexes (MCCs) were identified through this database. Most of the MCCs developed during the last week of September. The dominant synoptic patterns related to the mesoscale systems were cold fronts at the surface with warm and moist low-level cores, and cut-off low or deep trough throughout the middle and upper levels. These synoptic patterns were found in all the fifteen cases studied.The hourly centroid location of each MCC was used to trace their tracks, which followed a general direction towards the E or NE in almost all cases. These trajectories are clearly related to the synoptic patterns found. Finally, two MCCs chosen as representative of their evolution are described and the related physical processes are discussed.With 14 Figures  相似文献   

6.
The real time operational severe convective weather forecast experiment carried out during May to July in 1990 over the Changjiang Delta is briefly described. The heavy rainfall and severe conveetive weather forecast worksheets for the Changjiang Delta have been proposed and used in the daily forecasting. Results show that the ability of 0-12h convective weather prediction has been improved significantly after the development of the forecast methods and the establishment of a mesoscale forecast base at Shanghai Meteorological Center during 1986 to 1990.Three cases of convective weather systems (meso-alpha, meso-beta, meso-gamma) during the experiment period are described and discussed.  相似文献   

7.
Numerical simulation of meso-β-scale convective cloud systems associated with a PRE-STORM MCC case has been carried out using a 2-D version of the CSU Regional Atmospheric Modeling System (RAMS) nonhydrostatic model with parameterized microphysics. It is found that the predicted meso-γ-scale convective phenomena are basically unsteady under the situation of strong shear at low-levels, white the meso-β-scale convective system is maintained up to 3 hours or more. The meso-β-scale cloud system exhibits characteristics of a multi-celled convective storm in which the meso-γ-scale convective cells have lifetime of about 30 min. Pressure perturbation depicts a meso-low after a half hour in the low levels. As the cloud system evolves, the meso-low inten-sifies and extends to the upshear side and covers the entire domain in the mid-lower levels with the peak values of 5-8 hPa. Temperature perturbation depicts a warm region in the middle levels through the entire simulation period. The meso-γ-scale warm cores with peak values of 4-8oC are associated with strong convective cells. The cloud top evapo-ration causes a stronger cold layer around the cloud top levels.Simulation of microphysics exhibits that graupel is primarily concentrated in the strong convective cells forming the main source of convective rainfall after one hour of simulation time. Aggregates are mainly located in the stratiform region and decaying convective cells which produce the stratiform rainfall. Riming of the ice crystals is the predominant precipitation formation mechanism in the convection region, whereas aggregation of ice crystals is the predominant one in the stratiform region, which is consistent with observations. Sensitivity experiments of ice-phase microphysical processes show that the microphysical structures of the convective cloud system can be simulated better with the diagnosed aggregation collection efficiencies.  相似文献   

8.
Initiation Mechanism of Meso-β Scale Convective Systems   总被引：16，自引：0，他引：16  
With the aid of the Penn State-NCAR MM5 model, the initiation mechanism of meso-β scaleconvective systems (MCS) is investigated on the basis of simulation of the temporal and spatialthermodynamic structure of the MCS that occurred in Wuhan, Hubei, China and its surrounding area on 21July 1998. Using the PV inversion method, comparisons among the upper-, middle-, and low-leveltropospheric potential vorticity (PV) perturbations, as well as their effects on the initiation of MCS, indicatethat the low-level tropospheric PV perturbations play an important role in the triggering of MCS. Furtheranalysis reveals that the interaction between the southwest low-level jet and the gravity-inertia wave indeedinitiates MCS in the conditionally unstable ambient atmosphere.  相似文献   

9.
The multi-scale weather systems associated with a mei-yu front and the corresponding heavy precipitation during a particular heavy rainfall event that occurred on 4 5 July 2003 in east China were successfully simulated through rainfall assimilation using the PSU/NCAR non-hydrostatic, mesoscale, numerical model （MM5） and its four-dimensional, variational, data assimilation （4DVAR） system. For this case, the improvement of the process via the 4DVAR rainfall assimilation into the simulation of mesoscale precipitation systems is investigated. With the rainfall assimilation, the convection is triggered at the right location and time, and the evolution and spatial distribution of the mesoscale convective systems （MCSs） are also more correctly simulated. Through the interactions between MCSs and the weather systems at different scales, including the low-level jet and mei-yu front, the simulation of the entire mei-yu weather system is significantly improved, both during the data assimilation window and the subsequent 12-h period. The results suggest that the rainfall assimilation first provides positive impact at the convective scale and the influences are then propagated upscale to the meso- and sub-synoptic scales.
Through a set of sensitive experiments designed to evaluate the impact of different initial variables on the simulation of mei-yu heavy rainfall, it was found that the moisture field and meridional wind had the strongest effect during the convection initialization stage, however, after the convection was fully triggered, all of the variables at the initial condition seemed to have comparable importance.  相似文献   

10.
With the high-speed development of high-powered computer techniques, it is possible that a high-resolution and multi-scale unified numerical model is applied to the operational weather prediction. Some techniques about mesoscale non-hydrostatic numerical weather prediction are addressed, and the impact of the vertical coordinate system is one of them. Based on WRF (Weather Research and Forecasting) model, the influence of vertical coordinates on the non-hydrostatic mesoscale high-resolution model is compared. The results show that the error of various coordinates in lower levels is almost same when we use the geometry height (z) and the pressure (p) to set up a terrain-following coordinate; but the error of the height terrain-following coordinate in higher levels is smaller than that of the pressure terrain-following coordinate. The higher the resolution is, the bigger the error will be. The results of the high-resolution simulation exhibited that the trend of the difference in the two coordinates existed. In addition, the correlative coefficient and standard error are also analysed by the comparison between the forecast fields and the corresponding analysis fields.  相似文献   

11.
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12.
Sun et al., (1983) have given some favourable environmental conditions and have shown that there are four common features in convective rainstorms. In this paper, an important process of evolution of cloud systems was revealed when heavy rainfall occurred based on the diagnostic analysis of heavy rainfall cases. When the different cloud systems merge into a large one, the mesoscale heavy rainfall occurs and enhances. In other words, the process of evolution of cloud systems emphasized in this paper is the process of interaction between two cloud systems when the heavy rainfall occurs. The favourable environmental condition is also investigated.  相似文献   

13.
This paper describes the procedure and methodology to formulate the convective weather potential （CWP） algorithm. The data used in the development of the algorithm are the radar echoes at 0.5° elevation from Guangzhou Doppler Radar Station, surface observations from automatic weather stations （AWS） and outputs of numeric weather prediction （NWP） models. The procedure to develop the CWP algorithm consists of two steps： （1） identification of thunderstorm cells in accordance with specified statistical criteria; and （2） development of the algorithm based on multiple linear regression. The thunderstorm cells were automatically identified by radar echoes with intensity greater than or equal to 50 dB（Z） and of an area over 64 square kilometers. These cells are generally related to severe convective weather occurrences such as thunderstorm wind gusts, hail and tornados. In the development of the CWP algorithm, both echo- and environment-based predictors are used. The predictand is the probability of a thunderstorm cell to generate severe convective weather events. The predictor-predictand relationship is established through a stepwise multiple linear regression approach. Verification with an independent dataset shows that the CWP algorithm is skillful in detecting thunderstorm-related severe convective weather occurrences in the Pearl River Delta （PRD） region of South China. An example of a nowcasting case for a thunderstorm process is illustrated.  相似文献   

14.
An ICSED (Improved Cluster Shade Edge-Detection) algorithm and a series of post-processing technique are discussed for automatic delineation of mesoscale structure of the ocean on digital IR images. The popular derivative-based edge operators are shown to be too sensitive to edge fine-structure and to weak gradients. The new edge-detection algorithm is ICSED (Improved Cluster Shade Edge-detection) method and it is found to be an excel lent edge detector that exhibits the characteristic of fine-structure rejection while retaining edge sharpness. This char acteristic is highly desirable for analyzing oceanographic satellite images. A sorting technique for separating clouds or land well from ocean at both day and night is described in order to obtain high quality mesoscale features on the IR image This procedure is evaluated on an AVHRR (Advanced Very High Resolution Radiometer) image with Kuroshio. Results and analyses show that the mesoscale features can be well identified by using ICSED algorithm.  相似文献   

15.
Summary ?On August the 11th, 1999 Central Europe saw a spectacular astronomical event, a total solar eclipse. We present a model study concerning the meteorological effects of this eclipse in central Europe using the state-of-the-art limited area forecast model Deutschland-Modell DM from the German Weather Service DWD. Under typical summer radiation conditions very strong anomalies in the surface energy flux and temperature in screen height are simulated. The main temperature signal in the lower troposphere is delayed by about one hour with respect to the surface. Furthermore it is connected with a well defined dynamical signal which is reminiscent to a large scale land – sea circulation. The event could be used as a test case for mesoscale atmospheric models. Received February 19, 1999/Revised May 18, 1999  相似文献   

16.
An adjoint sensitivity analysis of one mesoscale low on the mei-yu Front is presented in this paper. The sensitivity gradient of simulation error dry energy with respect to initial analysis is calculated. And after verifying the ability of a tangent linear and adjoint model to describe small perturbations in the nonlinear model, the sensitivity gradient analysis is implemented in detail. The sensitivity gradient with respect to different physical fields are not uniform in intensity, simulation error is most sensitive to the vapor mixed ratio. The localization and consistency are obvious characters of horizontal distribution of the sensitivity gradient, which is useful for the practical implementation of adaptive observation. The sensitivity region tilts to the northwest with height increasing; the singular vector calculation proves that this tilting characterizes a quick-growing structure, which denotes that using the leading singular vectors to decide the adaptive observation region is proper. When connected with simulation of a mesoscale low on the mei-yu Front, the sensitivity gradient has the following physical characters： the obvious sensitive region is mesoscale, concentrated in the middle-upper troposphere, and locates around the key system; and the sensitivity gradient of different physical fields correlates dynamically.  相似文献   

17.
On 20 July 2021, northern Henan Province in China experienced catastrophic flooding as a result of an extremely intense rainstorm, with a record-breaking hourly rainfall of 201.9 mm during 0800–0900 UTC and daily accumulated rainfall in Zhengzhou City exceeding 600 mm(“Zhengzhou 7.20 rainstorm” for short). The multi-scale dynamical and thermodynamical mechanisms for this rainstorm are investigated based on station-observed and ERA-5 reanalysis datasets.The backward trajectory tracking shows that...  相似文献   

18.
A double-plume convective parameterization scheme is revised to improve the precipitation simulation of a global model(Global-to-Regional Integrated Forecast System; GRIST). The improvement is achieved by considering the effects of large-scale dynamic processes on the trigger of deep convection. The closure, based on dynamic CAPE, is improved accordingly to allow other processes to consume CAPE under the more restricted convective trigger condition. The revised convective parameterization is eva...  相似文献   

19.
A case study of the convectively driven monsoon boundary layer has been carried out using the aerological observations at four stations in the region of monsoon trough during Monsoon Trough Boundary Layer Experiment (MONTBLEX) 1988. The Convective Boundary Layer (CBL) in the region of monsoon trough did not show double mixing line structure. A single mixing line representing the CBL with different stabilities with respect to the convective activities was observed.  相似文献   

20.
Radar data, which have incomparably high temporal and spatial resolution, and lightning data, which are great indicators of severe convection, have been used to improve the initial field and increase the accuracies of nowcasting and short-term forecasting. Physical initialization combined with the three-dimensional variational data assimilation method(PI3 DVar_rh) is used in this study to assimilate two kinds of observation data simultaneously, in which radar data are dominant and lightning data are introduced as constraint conditions. In this way, the advantages of dual observations are adopted. To verify the effect of assimilating radar and lightning data using the PI3 DVar_rh method, a severe convective activity that occurred on 5 June 2009 is utilized, and five assimilation experiments are designed based on the Weather Research and Forecasting(WRF) model. The assimilation of radar and lightning data results in moister conditions below cloud top, where severe convection occurs; thus, wet forecasts are generated in this study.The results show that the control experiment has poor prediction accuracy. Radar data assimilation using the PI3 DVar_rh method improves the location prediction of reflectivity and precipitation, especially in the last 3-h prediction, although the reflectivity and precipitation are notably overestimated. The introduction of lightning data effectively thins the radar data, reduces the overestimates in radar data assimilation, and results in better spatial pattern and intensity predictions. The predicted graupel mixing ratio is closer to the distribution of the observed lightning,which can provide more accurate lightning warning information.  相似文献   

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