Analysis of radar echo characteristics of rare force 10 gale with a strong squall line event in Jiangxi

Using the products from Doppler weather radars at Yichun, Nanchang, Jingdezhen and other places, as well as conventional observations and observational data from regional automatic weather stations, we have conducted an analysis of the cause and radar echo characteristics of the rare regional force 10 gale during a strong squall line event in Jiangxi on 4 March 2018. Results are as follows. (1) The squall lines in this event occur in the warm zone in front of a trough, and strong southwest warm and wet airflow in the low-level, dry and cold air in the middle level, and the maintenance of strong vertical wind shear between middle and low-level provide the favorable environmental conditions for the stability and continuance of squall lines. (2) The downward transport of momentum by the inflow jet on the rear side of the squall lines and the evaporation of the dry air wrapping up storm result in the strong descending airflow, then lead to the cold pool moving rapidly and cause surface gale. (3) The radar echo of regional force 10 thunderstorm gale is characterized by bow-shaped echo being 200-450 km in scale, 55-60 dBz in centre intensity and 100-120 km·h^-1 in moving speed. Its low-level radial velocity is much large and appears aliasing. The radial convergence at front side of high wind core is strong. The maximum radial velocity shear value at the lower level is large, and strong echo centre, high radial velocity core and radial convergence zone all have a forward tilting feature. (4) High velocity cores above 31 m·s^-1 and radial velocity shears above 30 m·s^-1·(10 km)^-1 in the radial velocities of low elevation angles, bow-shaped echoes with moving speed more than 100 km·h^-1 in the reflectivity factor chart, and the descending of high velocity cores of 20 m·s^-1 in the VWP production can be used as the reference indicators for early warning of the force 10 gale.