Doppler Radar Data Research Articles

Explosion mechanisms at Arenal volcano, Costa Rica: An interpretation from integration of seismic and Doppler radar data

We execute an integrated analysis of broadband seismic and Doppler radar data to gain insights into the subsurface mechanisms that drive repetitive, mildly explosive activity of Arenal volcano (Costa Rica). We find large variability of both seismic and radar waveforms, and nonsystematic relationships between the two. Seismic recordings display long‐lasting tremor sequences and numerous explosion quakes. Radar measurements show that tephra emissions are poorly correlated, in both time and energy, to the seismic activity. Tephra emissions were found in association with explosion quakes but also during episodes of tremor and seismic quiescence. Moreover, the exit velocity, mass loading, and kinetic energy of the emissions show no clear relationship with the coeval seismic amplitude and frequency content. We propose a conceptual source model whereby degasing is controlled by opening and closing of fractures that crosscut a rigid cap atop the conduit. When the fracture's strength is overcome by the gas pressure building up below, it suddenly opens and high‐velocity gas escapes, producing high‐frequency elastic waves typical of explosion quakes. Gas release also occurs in relation to periodic opening and closure of the fractures to produce repetitive pressure pulses, this being the source of tremor. In both cases, varying quantities of fragmented material may be carried by the gas, which can be detected by the radar if their concentration is high enough. Moreover, the highly variable, constantly changing state of lava cap (e.g., thickness, fracture network and gas permeability) results in nonrepeatable source conditions and explains the complex relationship between tephra emissions and associated seismic signals.

Retrieval of three-dimensional wind fields from Doppler radar data using an efficient two-step approach

Abstract. In this work, we describe an efficient approach for wind retrieval from dual Doppler radar data. The approach produces a gridded field that not only satisfies the observations, but also satisfies the anelastic mass continuity equation. The method is based on the so-called three-dimensional variational approach to the retrieval of wind fields from radar data. The novelty consists in separating the task into steps that reduce the amount of data processed by the global minimization algorithm, while keeping the most relevant information from the radar observations. The method is flexible enough to incorporate observations from several radars, accommodate complex sampling geometries, and readily include dropsonde or sounding observations in the analysis. We demonstrate the usefulness of our method by analyzing a real case with data collected during the TPARC/TCS-08 field campaign.

Precipitation Forecasting Using Doppler Radar Data, a Cloud Model with Adjoint, and the Weather Research and Forecasting Model: Real Case Studies during SoWMEX in Taiwan

Abstract The quantitative precipitation forecast (QPF) capability of the Variational Doppler Radar Analysis System (VDRAS) is investigated in the Taiwan area, where the complex topography and surrounding oceans pose great challenges to accurate rainfall prediction. Two real cases observed during intensive operation periods (IOPs) 4 and 8 of the 2008 Southwest Monsoon Experiment (SoWMEX) are selected for this study. Experiments are first carried out to explore the sensitivity of the retrieved fields and model forecasts with respect to different background fields. All results after assimilation of the Doppler radar data indicate that the principal kinematic and thermodynamic features recovered by the VDRAS four-dimensional variational data assimilation (4DVAR) technique are rather reasonable. Starting from a background field generated by blending ground-based in situ measurements (radiosonde and surface mesonet station) and reanalysis data over the oceans, VDRAS is capable of capturing the evolution of the major precipitation systems after 2 h of simulation. The model QPF capability is generally comparable to or better than that obtained using only in situ observations or reanalysis data to prepare the background fields. In a second set of experiments, it is proposed to merge the VDRAS analysis field with the Weather Research and Forecasting Model (WRF), and let the latter continue with the following model integration. The results indicate that through this combination, the performance of the model QPF can be further improved. The accuracy of the predicted 2-h accumulated rainfall turns out to be significantly higher than that generated by using VDRAS or WRF alone. This can be attributed to the assimilation of meso- and convective-scale information, embedded in the radar data, into VDRAS, and to better treatment of the topographic effects by the WRF simulation. The results illustrated in this study demonstrate a feasible extension for the application of VDRAS in other regions with similar geographic conditions and observational limitations.

Boundary Layer Turbulence and Orographic Precipitation Growth in Cold Clouds: Evidence from Profiling Airborne Radar Data

Abstract Airborne vertically pointing Doppler radar data collected in 10 winter storms over the Medicine Bow Range in Wyoming are used to examine the importance of boundary layer (BL) turbulence for orographic precipitation growth. In all 10 cases, the cloud-base temperature was below 0°C and the bulk Froude number was more than 1.0, implying little or no blocking of the flow by the mountain barrier. Seven of the 10 storms sampled were postfrontal, with weak static stability and relatively shallow cloud tops. Doppler vertical velocity transects depict an approximately 1-km-deep turbulent layer draped over the terrain, sometimes clearly distinct from the stratified flow in the free troposphere aloft, where vertical motion is largely controlled by gravity wave dynamics. Spectral analysis of near-surface Doppler vertical velocity data in terrain-following coordinates reveals an inertial subrange with decreasing power with height toward the BL top. The composite of radar data profiles from the 10 flights is analyzed in frequency-by-altitude diagrams, with altitude expressed above ground level. These diagrams indicate a wide range of vertical velocities in the BL, and rapid snow growth within the BL as air rises through the cloud base, especially when BL turbulence is more intense. This snow growth is concentrated on the windward side of mountains, above the terrain–cloud base intersection. The dominant snow growth mechanism in the BL (i.e., by accretion or vapor deposition) cannot be established because of restrictions in aircraft flight level over complex terrain. Snow aggregation may have contributed to the observed rapid increase in reflectivity in the BL along the windward slope.

Thermodynamics of tropical cyclogenesis in the northwest Pacific

[1] This paper presents analyses of five tropical disturbances of various types, derived from observations made over the northwest Pacific in August and September of 2008. Various dynamic and thermodynamic products were derived from dropsonde and airborne Doppler radar data, with the goal of increasing our understanding of tropical cyclogenesis. From these analyses we draw the following tentative conclusions: The formation of a strong midlevel circulation, with its associated cold core at low levels and warm core aloft, greatly aids the spin-up of a tropical cyclone by changing the vertical mass flux profile of deep convection from top heavy to bottom heavy. This has two effects: (1) the enhancement at low levels of the convergence of mass and hence vorticity, thus aiding the spin-up of a warm-core vortex and (2) the suppression of the lateral export of moist entropy by deep convective inflows and outflows from the core of the developing system. This allows the relative humidity to build up, resulting in more intense convection and further development. Our results also suggest that strong horizontal strain rate at middle levels, as measured by a form of the Okubo-Weiss parameter, is detrimental to tropical cyclogenesis. Not only can such flow tear apart the midlevel vortex, it can also import air with low moist entropy. In our small sample, the Okubo-Weiss parameter was the best indicator of the potential for development. Vertical shear appeared to play a less important role in the systems we investigated.

Kinematics of the Secondary Eyewall Observed in Hurricane Rita (2005)

Abstract Airborne Doppler radar data collected from the concentric eyewalls of Hurricane Rita (2005) provide detailed three-dimensional kinematic observations of the secondary eyewall feature. The secondary eyewall radar echo shows a ring of heavy precipitation containing embedded convective cells, which have no consistent orientation or radial location. The axisymmetric mean structure has a tangential wind maximum within the reflectivity maximum at 2-km altitude and an elevated distribution of its strongest winds on the radially outer edge. The corresponding vertical vorticity field contains a low-level maximum on the inside edge, which is part of a tube of increased vorticity that rises through the center of the reflectivity tower and into the midlevels. The secondary circulation consists of boundary layer inflow that radially overshoots the secondary eyewall. A portion of this inflowing air experiences convergence and supergradient forces that cause the air to rise and flow radially outward back into the center of the reflectivity tower. This mean updraft stretches and tilts the vorticity field to increase vorticity on the radially inner side of the tangential wind maximum. Radially outside this region, perturbation motions decrease the vorticity at a comparable rate. Thus, both mean and perturbation motions actively strengthen the wind maximum of the secondary eyewall. These features combine to give the secondary eyewall a structure different from the primary eyewall as it builds to become the new replacement eyewall.

The 1998 Ice Storm: Local flow fields and linkages to precipitation

A major freezing rain storm causing catastrophic losses occurred in early January 1998 over eastern Canada and the northeastern United States. The various types of precipitation and associated flow and precipitation features of this storm are discussed with a particular emphasis on the effects due to precipitation phase changes in the Montréal area. Hourly surface observations, Doppler radar data and model reanalysis information are used to describe the hydrometeor phase and production. There were two periods of significant ice accumulation at the ground. They were characterized by more organized precipitation compared to other times but there were also distinct differences between the two periods in terms of wind fields. This hydrometeor development was linked in part to the flow fields in the St. Lawrence River Valley and its topographic features. The results from a time dependent microphysical model suggest that there was considerable horizontal temperature advection that balanced the warming/cooling of the atmosphere due to precipitation phase changes aloft and at the surface. Overall, local-scale factors significantly affected the nature of this major event.

Analysis and simulation of mesoscale convective systems accompanying heavy rainfall: The goyang case

We investigated a torrential rainfall case with a daily rainfall amount of 379 mm and a maximum hourly rain rate of 77.5 mm that took place on 12 July 2006 at Goyang in the middlewestern part of the Korean Peninsula. The heavy rainfall was responsible for flash flooding and was highly localized. High-resolution Doppler radar data from 5 radar sites located over central Korea were analyzed. Numerical simulations using the Weather Research and Forecasting (WRF) model were also performed to complement the high-resolution observations and to further investigate the thermodynamic structure and development of the convective system. The grid nudging method using the Global Final (FNL) Analyses data was applied to the coarse model domain (30 km) in order to provide a more realistic and desirable initial and boundary conditions for the nested model domains (10 km, 3.3 km). The mesoscale convective system (MCS) which caused flash flooding was initiated by the strong low level jet (LLJ) at the frontal region of high equivalent potential temperature (θe) near the west coast over the Yellow Sea. The ascending of the warm and moist air was induced dynamically by the LLJ. The convective cells were triggered by small thermal perturbations and abruptly developed by the warm θe inflow. Within the MCS, several convective cells responsible for the rainfall peak at Goyang simultaneously developed with neighboring cells and interacted with each other. Moist absolutely unstable layers (MAULs) were seen at the lower troposphere with the very moist environment adding the instability for the development of the MCS.

Characteristics of Sonoran Desert Microbursts

Abstract During the 2008 North American monsoon season, 140 microburst events were identified in Phoenix, Arizona, and the surrounding Sonoran Desert. The Sonoran microbursts were studied and examined for their frequency and characteristics, as observed from data collected from three Doppler radars and electrical power infrastructure damage reports. Sonoran microburst events were wet microbursts and occurred most frequently in the evening hours (1900–2100 local time). Stronger maximum differential velocities (20–25 m s−1) were observed more frequently in Sonoran microbursts than in many previously documented microbursts. Alignment of Doppler radar data to reports of wind-related damage to electrical power infrastructure in Phoenix allowed a comparison of microburst wind damage versus gust-front wind damage. For these damage reports, microburst winds caused more significant damage than gust-front winds.

The vorticity budget of developing typhoon Nuri (2008)

Abstract. The formation of west Pacific tropical cyclone Nuri (2008) was observed over four days from easterly wave to typhoon stage by aircraft using scanning Doppler radar and dropsonde data. This disturbance developed rapidly in a significantly sheared environment. In spite of the shear, overlapping closed circulations existed in the frame of reference of the storm in the planetary boundary layer and at 5 km elevation, providing a deep region protected from environmental influences. The rapid spinup of Nuri can be attributed to the strong increase with height at low levels of the vertical mass flux during and after the tropical depression stage, and the correspondingly strong vorticity convergence in the planetary boundary layer. As Nuri developed, convective regions of boundary layer vortex stretching became fewer but more intense, culminating in a single nascent eyewall at the tropical storm stage. A non-developing tropical wave case was also analyzed. This system started with much weaker circulations in the boundary layer and aloft, leaving it unprotected against environmental intrusion. This may explain its failure to develop.

Radiometer and Profiler Analysis of the Effects of a Bore and a Solitary Wave on the Stability of the Nocturnal Boundary Layer

Abstract This study uses data from a microwave profiling radiometer (MPR), along with 915-MHz wind profiler, Doppler radar, and surface data to quantify the kinematic and thermodynamic effects of two wave features, an undular bore and a soliton, on the nocturnal boundary layer (NBL) at high temporal resolution. Both wave features passed directly over the MPR and the wind profiler, allowing for detailed analyses. The effects of the wave features on the convective environment are examined, and convective initiation (CI) associated with the wave features is discussed. The undular bore was illustrated well in Doppler velocity data, and profiler measurements indicated that it produced four wavelengths of upward and downward motion. MPR-derived time–height sections of potential temperature and mixing ratio showed an increase in the depth of the stable boundary layer, along with a decrease in stability, partially associated with mixing of the NBL. The soliton produced a temporary decrease in the depth of the NBL, and also produced destabilization. Trajectory analyses were performed assuming the wave features were two-dimensional, allowing a time-to-space conversion of profiler data. Trajectory analyses, in addition to propagation speed, confirm that the wave features were indeed a bore and a soliton, and that there was vertical divergence in the NBL, likely associated with the decrease in static stability. MPR data were also used to produce time series of convective parameters, including CAPE, convective inhibition (CIN), and the level of free convection (LFC). The CIN was initially too large for free convection despite sufficient CAPE, but MPR data showed that the CIN decreased by more than 50% upon passage of the bore, and again with the soliton. The waves also decreased the LFC due to cooling above the NBL and slight warming near the surface in the bore. Both the reduction in CIN and the lowering of the LFC made convection more likely. Convective initiation occurred behind both wave features, and the vertical motion provided by the waves may have also aided in this CI.

Regularization method of assimilating Doppler radar data and its influence on precipitation forecast

A new regularization method is proposed to directly assimilate Doppler radar data into mesoscale numerical weather forecast based on the traditional 3DVAR. For seeking the minimum module solution of the Yo=H(X) with bias δ, the regularization method is adopted and leads to a new cost function. A group of experiments were designed to study the case of a locally strong rainstorm occurred in Beijing area on August 14, 2008. The L-curve principle is used to determine the optimal regularization parameter and the result is α=0.1. Numerical results demonstrate that both regularization method and 3DVAR scheme can efficiently assimilate the Doppler radar data, and that the improved initial condition can alleviate the spin-up phenomenon and improve the nowcasting precipitation forecast. However, when an optimal regularization parameter is choser, better improvement, more accurate precipitation forecast and higher TS score are expected.

Effect of Doppler Radial Velocity Data Assimilation on the Simulation of a Typhoon Approaching Taiwan: A Case Study of Typhoon Aere (2004)

Compared to conventional data, radar observations have an advantage of high spatial and temporal resolutions, and Doppler radars are capable of capturing detailed characteristics of flow fields, including typhoon circulation. In this study, the possible improvement of short-term typhoon predictions near Taiwan, particularly with regard to related rainfall forecasts over the mountainous island, using Doppler radial wind observations is explored. The case of Typhoon Aere (2004) was chosen for study, and a series of experiments were carried out using the Penn State University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model Version 5 (MM5) with its three-dimensional variational (3D-VAR) data assimilation system. The results show that once the Doppler radial velocities were assimilated into the model, the typhoon's circulation intensified within one hour. However, when Typhoon Aere approached from the east and only the western half of its core area could be observed by the radar, the assimilation caused the typhoon to deflect southward due to the incomplete and uneven data coverage. In another experiment in which Doppler radar data assimilation did not start until Typhoon Aere moved closer, such that its entire core region could be observed. A similar track deflection was avoided. Overall, the assimilation of Doppler radial velocity data reduced the intensity error (in wind speed) by about 25%. Furthermore, the improvements in location, intensity, and circulation structure of Typhoon Aere lead to better rainfall prediction over the island of Taiwan.

Review of Research of Forcing Data for Regional Scale Hydrological Model

Hydrometeological forcing data with high spatio-temperal resolution,such as wind,temperature,pressure,humidity,radiation,precipitation,is needed for driving regional-scale and watershed-scale hydrological,ecological,land models or data simulations system.In this paper,the importance of regional-scal and watershed-scale forcing data is clarified;methods of producing forcing data,such as interpolation based on observation data,reanalysis data,dynamical downscaling method,statistical downscaling method and multi-source information fusion method,are described in detail;some cases about precipitation,radiation,temperature and other variables are given;some case studies on producing forcing data for land data assimilation systems are introduced,such as Global Land Data Assimilation System(GLDAS),European Land Data Assimilation System to predict Floods and Droughts(ELDAS),North American Land Data Assimilation System(NLDAS),Chinese Land Data Assimilation System(CLDAS) and Land Information System(LIS).Finally,existing problems of producing high spatio-temperal forcing data for regional-scale and watershed-scale hydrological,ecological,land models or data simulations system are pointed out in detail,and four proposals are put forward: ①it is difficult to satisfy all forcing variables by one simple method;②it is urgent to provide proper land surface initial condition for dynamical downscaling model;③it is a major method to combine with Doppler radar data,drop size meter and rain gauge observations to improve the accuracy of rainfall;④it is a trend to input remote sensing images into dynamical downscaling model by data assimilation method to generate high spatio-temperal forcing data.Some ideas on preparing forcing data for land surface model of Western China are proposed.

Orographic signature on multiscale statistics of extreme rainfall: A storm‐scale study

Rainfall intensity and spatiotemporal patterns often show a strong dependence on the underlying terrain. The main objective of this work is to study the statistical signature imprinted by orography on the spatial structure of rainfall and its temporal evolution at multiple scales, with the aim of developing a consistent theoretical basis for conditional downscaling of precipitation given the topographic information of the underlying terrain. The results of an extensive analysis of the high‐resolution stage II Doppler radar data of the Rapidan storm, June 1995, over the Appalachian Mountains is reported in this study. The orographic signature on the elementary statistical structure of the precipitation fields is studied via a variable‐intensity thresholding scheme. This signature is further explored at multiple scales via analysis of the dependence of precipitation fields on the underlying terrain both in Fourier and wavelet domains. The generalized normal distribution is found to be a suitable probability model to explain the variability of the rainfall wavelet coefficients and its dependence on the underlying elevations. These results provide a new perspective for more accurate statistical downscaling of orographic precipitation over complex terrain with emphasis on preservation of extremes.

The genesis of Typhoon Nuri as observed during the Tropical Cyclone Structure 2008 (TCS-08) field experiment – Part 1: The role of the easterly wave critical layer

Abstract. An observational and real-time model forecast study of the genesis of Typhoon Nuri during the Tropical Cyclone Structure 2008 (TCS-08) field campaign in the western North Pacific sector is presented. Analysis and observational data show that the surrounding base state is an easterly trade wind flow and the precursor disturbance to Typhoon Nuri is an easterly wave that originates in the ITCZ in the Central Pacific. This disturbance can be tracked more than 10 days prior to tropical storm formation. An overview of the field data is presented here using a newly proposed dynamical framework for tropical cyclone formation within the critical layer of an easterly wave. Despite propagating through a hostile environment ripe with strong vertical wind shear and relatively dry air, the easterly wave critical layer protects the proto-vortex and allows it to gestate until it reaches a more favorable environment. Within this protective "Kelvin cat's eye flow" located within the wave's critical layer existed a sweet spot, defined as the intersection between the wave trough and critical latitude, which is the preferred location for tropical cyclogenesis. Global Forecast System Final Analyses and IR satellite imagery, which shows convective bands wrapping around the sweet spot as genesis nears, confirm that this sweet spot is the location where Typhoon Nuri's dominant low-level circulation emerges. United States Air Force C130 and Naval Research Laboratory P3 research flights on 16 and 17 August collected flight-level, dropwindsonde, and Doppler radar data that allowed an evaluation of the dynamic and thermodynamic processes within the cat's eye circulation. The dropwindsonde analyses identifies the precursor easterly wave disturbance on 16 August and identifies an area of weak low-level cyclonic circulation on 17 August. Real-time forecasts were produced using operational global prediction model data to support scientific missions during TCS-08. These forecasts were found to be useful in flight planning discussions and predicted Typhoon Nuri's eventual genesis latitude within 1.5 degrees 72 h in advance.

Assimilation of the dual‐polarization Doppler radar data for a convective storm with a warm‐rain radar forward operator

In this paper, a data assimilation scheme is built to utilize the dual‐polarization Doppler radar observations collected by the C band Advanced Radar for Meteorological and Operational Research and is tested with a case study for a mesoscale convective system (MCS) over northern Alabama in the afternoon of 15 March 2008. Three variables, horizontal reflectivity, differential reflectivity, and radial velocity are assimilated into the advanced research version of the Weather Research and Forecasting model. A warm rain radar operator is constructed to assimilate the horizontal reflectivity and differential reflectivity data with the three‐dimensional variational data assimilation (3DVAR) system. The main goals of this paper are to, first, demonstrate the improvements in short‐term forecasts of the moist convection when fields unique to the dual‐polarization radar are assimilated into a regional model and, second, to understand how these fields may best be integrated in a data assimilation system like 3DVAR to improve short‐term storm forecast. The results show that the horizontal reflectivity, differential reflectivity, and radial velocity data can be successfully assimilated using our data assimilation scheme. The assimilation of the horizontal reflectivity and radial velocity data has a significant positive impact on the reflectivity distribution of the MCS. An additional improvement (10%–20%) in the initial condition is found when the differential reflectivity data are further assimilated. Moreover, the improved initial condition leads to apparent improvement in short‐term forecast of the MCS. The best forecast is produced when both horizontal and differential reflectivity and radial velocity data are assimilated. This improvement can be attributed to the improved estimate of liquid water content by using the radar operator with combined information of both horizontal reflectivity and differential reflectivity. This study demonstrates the benefit of utilizing the observations from single dual‐polarization radar. With the forthcoming upgrade of the current U. S. “NEXRAD” radar system (set to begin in ∼2010), a dual‐polarization radar network will be available. Assimilating observations from the dual‐polarization Doppler radar network could be a potential technique to further improve the short‐term numerical forecasts of convective storms.

An Undular Bore and Gravity Waves Illustrated by Dramatic Time-Lapse Photography

Abstract On 6 May 2007, an intense atmospheric undular bore moved over eastern Iowa. A “Webcam” in Tama, Iowa, captured dramatic images of the effects of the bore and associated gravity waves on cloud features, because its viewing angle was almost normal to the propagation direction of the waves. The time lapse of these images has become a well-known illustration of atmospheric gravity waves. The environment was favorable for bore formation, with a wave-reflecting unstable layer above a low-level stable layer. Surface pressure and wind data are correlated for the waves in the bore, and horizontal wind oscillations are also shown by Doppler radar data. Quantitative analysis of the time-lapse photography shows that the sky brightens in wave troughs because of subsidence and darkens in wave ridges because of ascent.

A Velocity Dealiasing Technique Using Rapidly Updated Analysis from a Four-Dimensional Variational Doppler Radar Data Assimilation System

Abstract A Doppler velocity dealiasing algorithm is developed within the storm-scale four-dimensional radar data assimilation system known as the Variational Doppler Radar Analysis System (VDRAS). The innovative aspect of the algorithm is that it dealiases Doppler velocity at each grid point independently by using three-dimensional wind fields obtained either from an objective analysis using conventional observations and mesoscale model output or from a rapidly updated analysis of VDRAS that assimilates radar data. This algorithm consists of three steps: preserving horizontal shear, global dealiasing using reference wind from the objective analysis or the VDRAS analysis, and local dealiasing. It is automated and intended to be used operationally for radar data assimilation using numerical weather prediction models. The algorithm was tested with 384 volumes of radar data observed from the Next Generation Weather Radar (NEXRAD) for a severe thunderstorm that occurred during 15 June 2002. It showed that the algorithm was effective in dealiasing large areas of aliased velocities when the wind from the objective analysis was used as the reference and that more accurate dealiasing was achieved by using the continuously cycled VDRAS analysis.

Analysis on the Doppler Radar Data of a Heavy Rainfall Process in the Central Hexi Corridor

This paper analyzed a heavy rainfall process.Occurred in the central Hexi Corridor from 30 June to 2 July 2005 using the CINRAD/CC Doppler radar data,hourly rainfall data derived by the automatic meteorological stations,and DEM and conventional meteorological observation data in Zhangye.The results show that the heavy rainfall was caused by a plot of mixing cumulostratus with the typical echo characteristics of rainfall;the cumuliform cloud was mainly generated from the development of convection bubble under the effect of terrain in the Qilian Mountains,and the rainfall occurred mainly in the northern slope of the Qilian Mountains and the southwest piedmont of the Longshou Mountains;the velocity field was reflected by the low-level cold advection and the high-level warm advection,which resulted in the continuous development of rainfall and the stabilization of echo;the area of low-level negative speed zone was enlarged but that of positive one was reduced,the flow field was superposed by the large-scale convergence and the warm advection,which provided the dynamic and thermal conditions for the successional water vapor transport and rainfall;VWP could be used to identify the vertical wind shear,stratospheric height and echo,and then to infer the intensity,occurrence and termination of rainfall;the special pocket-shaped terrain was the main mechanism causing the heavy rainfall.