Mesoscale Analysis And Data Assimilation Technology Based On LAPS At Shanghai

Mesoscale convective storm is a type of abrupt sever weather, and forecasters need a technology platform of processing and assimilating lots of different spatiotemporal resolution data rapidly. As a local analysis and prediction system assimilating multi-source observational data, LAPS has been used in many countries and regions successfully. This paper selects Yangtse River Delta as researched area. Based on the LAPS researches by Shanghai Meteorological Bureau, data assimilation examine and Shanghai urban effect influence on local convective weather analysis are done, and LAPS application research in Mesoscale analysis for Shanghai local convective weather is discussed in particular. The followings are the main conclusions and results:(1) The3-D wind field is improved significantly through combining surface and sounding data into LAPS system based on numerous schemes of data combination, and includes more information of meso-micro scale weather. Doppler radar velocity assimilation is effective and several radars assimilation have better effect than single ones by LAPS. It’s showed that LAPS wind analysis field is better close to radar reflectivity field by several Doppler radars mosaic than1°×1°NCEP reanalysis wind field.(2) Urban heat island, land and sea breeze/land and lake breeze, and water vapor transport are all influenced obviously in summer by unique characteristics of Shanghai which is a seaside city beside Taihu Lake, then have a further effect in occurrence and development of mesoscale convective storm. On one hand, continuous weak convergence of lake breeze and sea breeze, which are westerly and easterly respectively, provides a trigger mechanism for the storm, on the other abundant vapor that brought from Taihu Lake and the East China Sea makes up the lack of moisture supply resulting from Shanghai urban dry island effect. Meanwhile, it affords convective storm favorable thermal conditions that urban heat island is significant (Heat island intensity is about2℃under the weak wind field background and high energy region (CAPE>3500J/kg) maintains.(3) Through analysis of meso-micro scale features of sever convection weather processes in Shanghai on August2010and July2011, cooperation of middle and low level shear, convergence and significant streamline provide the dynamic uplift mechanism and trigger the instability energy, and new convective cells are usually aroused in outflow gust front of old ones.(4) The main characteristics of different stages in mesoscale convective weather development are summarized. The formation stages:positive vorticity, convergence and vertical wind shear high value area appear at the middle layer and below, surface instability energy increases rapidly, and the maximum updraft and non-divergence level develop to high layer. The mature stage:convergence area develops to high layer, at about200hPa, and vertical wind shear at middle layer and downdraft make updraft slantwise and prevent it from weakening by downdraft dragging force. The decaying stage: the positive vorticity area and convergence area diminishes rapidly, vertical wind shear weakens, bottom of the convective cell is control by downdraft, and vertical circulation structure is destroyed finally.(5) It is a fairly good reference to judgment of convective cell type, strength and life cycle that3-D wind field of LAPS cooperate with surface thermodynamic parameters field, such as CAPE, K index, and the radar reflectivity field. A mesoscale weather analysis support program by LAPS for Shanghai is proposed from three aspects of dynamics, thermodynamics and moisture condition with the help of all discusses above.