Characteristics of Convection-triggering Drylines in the Drainage Area of Huanghe and Huaihe Rivers

Abstract

Based on the surface and sounding datasets, ERA5 reanalysis data from European Centre for Medium-Range Weather Forecasts (ECMWF) and the satellite images, the characteristics of convection-triggering drylines in the drainage area of Huanghe and Huaihe Rivers of China from April to September during 2010-2019 are analyzed. The result shows that the drylines mainly appear at Dezhou of Shandong, and surroundings in the north of Henan. Most of them are distributed in the quasi northwest-southeast and northeast-southwest direction, with the length of 100-200 km and the width of 50-100 km, and they generally occur at 1400 BT or 1700 BT during the daytime. The drylines mostly occur under the 500 hPa cold vortex located in Northeast China and North China, with convergence lines (or shear lines) on 700 hPa and 850 hPa weather chart, and within the low pressure behind the coastal high on the surface chart. The statistics of the surface elements shows that the temperature on the dry side is 1.9 ℃ higher than that on the wet side, while the dew point temperature on the wet side is 6.8 ℃ higher than that on dry side. The gradient of temperature, dew point temperature and specific humidity on both sides of drylines are -2.7 ℃·(100 km)-1, 10.1 ℃·(100 km)-1 and 5.9 g·kg-1·(100 km)-1, respectively. According to the statistics of sounding environment parameters, precipitable water in the wet side is higher than that on the dry side. The specific humidity on the wet side is higher than that on the dry side at 925 hPa, 850 hPa and 700 hPa. The mean convective available potential energy on the wet side is much larger than that on the dry side. The temperature differences are very small on both sides of the drylines at 850 hPa and 500 hPa, 700 hPa and 500 hPa. The significant difference on both sides of the dry side in convective available potential energy is mainly caused by the difference in water condition of the lower layers in the drainage area of Huanghe and Huaihe Rivers of China. The hydrostatic instability (conditional instability) on both sides of the drylines is similar. Also, the vertical wind shear of 0-6 km is a little bit stronger on wet side than that on the dry side.

Keywords

• convection-triggering
• dryline
• statistical analysis