华北一次强降水过程的分阶段对比分析

利用GPS可降水量、多普勒天气雷达和地面加密自动站等高时空分辨率资料,对2011年6月23-24日发生在京津冀的强降水天气过程的不同阶段进行了对比分析.结果表明:(1)第一阶段降水为时间短、强度大的积状云对流降水；GPS可降水量的峰值与强降水对应,在降水之前6h左右会有GPS可降水量峰值出现；在空间分布上,高值中心的演变表现为东移南压趋势.(2)第二阶段降水表现为持续时间较长的系统性降水；雷达回波以大面积层状云降水回波为主；此阶段的GPS可降水量长时间维持在高值阶段,空间分布上GPS可降水量等值线“南高北低”并逐渐南压,西部GPS可降水量明显偏高.(3)在液态水与气态水对比上,雷达VIL随时间的变化不连续,而GPS可降水量表现为连续性演变,二者的峰值或高值对应较好,二者均可反映降水出现时间和降水性质,其中雷达VIL大值与降水出现时段吻合得好,而GPS可降水量的大小和演变趋势可以提前预示降水的出现时间和降水性质,对降水天气预报有指示意义.

Comparative analysis of different stages of a heavy rainfall in north China

Based on precipitable water vapor received from ground-based GPS, Doppler radar, ground automatically stations observation, two stages of a heavy rainfall in Hebei province is comparatively studied. The results show that: (1) the first stage of convective precipitation is in the evening of 23 June, whose precipitation intensity is stronger but lasting time is shorter; the main affecting system is high-altitude cold vortex, the southeast quadrant of which is the corresponding precipitation area. The main radar echo classification is convective, moving from northwest to southeast, and the echo intensity is more than 50 dBz; the value of VIL and ET is higher than the indicators of convective weather in Hebei province; heavy rainfall is corresponding with the peak of GPS PWV, while the other peak is usually occurred 6 h before precipitation. It experienced a rapid rise before the rainfall, and a fall phases after the rainfall; it shows a clear clockwise rotation in the GPS spatial distribution, and the center of a large value is corresponding with the heavy precipitation area. (2) The second stage on 24 June is mostly stratiform precipitation, whose lasting time is longer; the major affecting system is low-altitude shear line and easterly winds. The stratiform rain echoes move along the steering flow of 700 hPa, and the height of east wind is from the ground to 2 km. In this stage, the value of GPS precipitable water maintained at high-value level, especially in the west of Hebei province; the contours of GPS precipitable water vapor move from north to south in the spatial distribution, which is related with easterly winds and the Taihang Mountain terrain. (3) In contrast to the liquid and gaseous water, the emergence of peak of VIL and GPS PWV is generally the same, both of which can reflect the time and nature of precipitation; the time of VIL and precipitation is just fit, and the evolution trend of GPS PWV can indicate the starting, continuing and ending time in the precipitation, which can provide a reference for forecasting.