Radar Analysis And Simulation Study Of A Severe Convection At East Side Of Taihang Mountaills

A strong convective hail storm which happened at east side of Taihang Mountains on26May2011is investigated using Doppler radar data, Micaps data, conventional observations and WRF mesoscale numerical model. The mesoscale weather characteristics before hailstorm, radar echo characteristics of hail cloud and impacts of Taihang Mountains on severe convection are discussed in this paper.The analysis of observational data shows that severe convective storm is likely to happen under the condition of strong convective instability, moderate or above vertical wind shear and the height of0℃level at about4km. The development of hailstorm is very fast, less than5hours from beginning to end. The speed of hailstorm is about37km/h. In the mature stage, radar echo intensity can be above65dBz. V-gap and three-body scatter spike echo can be found during hail falling. With the statistical analysis of16hail storms happened at Xingtai and Baoding from2006to2011, the hail storms with the echo top height of45dBz maintaining4km above0℃level account for about93percent, which can be the criterion for recognizing hail storm in advance. In addition, suitability verification of criterion indicates that echo top height of50dBz keeping above-20℃level can also recognize hail storm effectively. The low level of radial velocity diagram shows strong cyclonic convergence before hail falling, corresponding divergent airflow at the high level of radial velocity. Both the convergence and divergence weaken after hail falling. The VIL of hail cloud is more than three times as much as that of thunder cloud. Furthermore, VIL jumps before hail falling, which can be reference for hail warning.The simulated results indicate that the east warm moist air flow is blocked by Taihang Mountains and joins the southwest warm moist air flow from southeast side of shear line, leading to high value of water vapor at east side of Taihang Mountains. The upward heat flux at the east slope of Taihang Mountains is apparently higher than that of the North China Plain. It results pseudo-equivalent potential temperature gradient at850hPa level between mountain slope and plain reaching0.2K/km and vertical gradient of pseudo-equivalent potential temperature between850hPa level and600hPa level reaching4K/km in the afternoon. The resulting upslope wind can lead to strong ascending velocity above1m/s, offering dynamic conditions for convection development at east slop of Taihang Mountains. Dry and cold westerly flow passes over the warm moist air layer of east side of Taihang Mountains, resulting strong static instability. The occurrence of strong convection at east side of Taihang Mountains is caused by a combination of strong instability, high values of water vapor and upslope wind. With the local small scale orographic uplift and gravity wave generated by Luliang Mountains, there is a weak convection cell develops at Taiyuan Basin. The weak convection cell develops when it moves to west slope of Taihang Mountains because of uplift by blocking. When the west convection cell passes the Taihang Mountains, combining with the strong convection at east side of Taihang Mountains, the combined convection develops intensely.