Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa
Dual-Polarization Radar Observations of Deep Convection over Lake Victoria Basin in East Africa
复制标题
东非维多利亚湖盆地深层对流的双偏振雷达观测
作者：
P. Waniha;R. Roberts;James W. Wilson;A. Kijazi;Benedicto Katole
东非的维多利亚湖支撑着成千上万渔民的生计，据估计，每年有3000-5000人死于该湖。据推测，这些死亡人数中的大多数是由于雨季期间湖上强烈雷暴产生的局部强风和旱季期间湖上更大规模的强风。强烈的风产生了一个粗糙的湖的状态（大浪高），导致渔船倾覆。在这一地区，天气雷达从未成为监测和预报高影响天气的主要工具。坦桑尼亚气象局在坦桑尼亚姆万扎维多利亚湖海岸设有一个S波段偏振雷达。该雷达收集高时间和空间分辨率数据，目前正用于探测和监测湖上深对流的形成，并提高对风暴动态和强度的科学认识。姆万扎雷达很好地观测到了湖上的夜间雷暴和对流的形成，这些雷暴和对流是由湖风和陆风以及阵风锋强烈强迫的。出乎意料的是，在湖面上空探测到了距离≥100公里的晴空回波，这使得观测低空风、阵风锋和湖面附近的其他辐合线成为可能。广泛的晴空和低层辐合线的频繁观测为临近预报强风、对流启动和随后的雷暴发展提供了机会，并将这些信息纳入拟议为维多利亚湖盆地（LVB）建立的区域预警系统。两个天气事件，说明明显不同的夜间对流启动湖上演变成强烈的早晨雷暴。由于姆万扎的雷达观测，这些恶劣天气事件的演变是可能的;单靠卫星图像不足以预测风暴的形成、发展、移动和衰减。
Lake Victoria in East Africa supports the livelihood of thousands of fishermen and it is estimated that 3000–5000 human deaths occur per year over the lake. It is hypothesized that most of these fatalities are due to localized, severe winds produced by intense thunderstorms over the lake during the rainy season and larger scale, intense winds over the lake during the dry season. The intense winds produce a rough state of the lake (big wave heights) that cause fishing boats to capsize. In this region, weather radars have never been a primary tool for monitoring and nowcasting high impact weather. The Tanzania Meteorological Agency operates an S-band polarimetric radar in Mwanza, Tanzania, along the south shore of Lake Victoria. This radar collects high temporal and spatial resolution data that is now being used to detect and monitor the formation of deep convection over the lake and improve scientific understanding of storm dynamics and intensification. Nocturnal thunderstorms and convection initiation over the lake are well observed by the Mwanza radar and are strongly forced by lake and land breezes and gust fronts. Unexpected is the detection of clear air echo to ranges ≥100 km over the lake that makes it possible to observe low-level winds, gust fronts, and other convergence lines near the surface of the lake. The frequent observation of extensive clear air and low-level convergence lines opens up the opportunity to nowcast strong winds, convection initiation, and subsequent thunderstorm development and incorporate this information into a regional early warning system proposed for Lake Victoria Basin (LVB). Two weather events are presented illustrating distinctly different nocturnal convection initiation over the lake that evolve into intense morning thunderstorms. The evolution of these severe weather events was possible because of the Mwanza radar observations; satellite imagery alone was insufficient to provide prediction of storm initiation, growth, movement, and decay.