Monitoring And Early Warning Of Downburst Based On The New Generation Of Weather Radar

Downburst means a local strong downdraft that has a outward wind and causes severe disasters. Downburst is one of low-level wind shear which seriously influence airplane landing safety. So the downburst attaches great importance to the domestic air community and meteorological community. On the basis of the characteristic that the downburst occurred before the parent thunderstorm(hereinafter referred to as the thunderstorm) reflectivity of nuclear decreased rapidly, and base on the radar data, defined the downburst occurrence and development of “equivalent potential energy per unit area” concept, and then combining the fact of thunderstorm middle convergence velocity filed during the period of downburst, obtained downburst outflow strength formula. Further use of radar measured data, simulation calculated strong center coefficient and middle convergence factor of the flow strength formula. Finally, based on the storm monomer recognition, designed the algorithm of downburst early warning, and used downburst produced by six thunderstorm monomer for analysis and testing. A conclusion can be obtained as follows:(1)The ground wind caused by downburst was above 22m/s, most of the maximum reflectivity of thunderstorms are more than 60 dbz, the maximum can reach 69 dbz, which has six times, before the downburst occurred thunderstorm appeared the middle convergence of the velocity field, the height of the convergence between 800 ~ 5600 m. At the same time before the downburst outbreak, thunderstorms strong center height are above the basic 7km, the maximum is more than 10 km, then, decreased rapidly. So that thunderstorms strong center height decreases rapidly and the middle convergence of the velocity field can be used as an early warning downburst factor.(2)Taking the rapid decrease of thunderstorms strong as the core, analyzed radar effective irradiation volume and the limitations of detection mode, and by defining the library hydrometeor equivalent potential energy, combining with the detection method of radar, through the vertical linear interpolation, designed accumulation per unit area equivalent potential, and calculated unit area equivalent potential energy to early warn downburst occurrence. From the energy point of view, according to the features of thunderstorm strong center declining rapidly and the velocity field middle convergence, combining equivalent potential energy per unit area, designed the downburst outflow strength formula. And using radar measured data, simulation calculated strong center coefficient and middle convergence factor of the flow strength formula.(3)Analysis found that the change trend of the index of potential energy per unit area is consistent with the change trend of thunderstorm monomer strong center height, before downburst occurrence, the index of potential energy per unit area reached its maximum value and then decreased rapidly, which clearly reflected the energy change of thunderstorm. Unit area equivalent potential energy difference of adjacent volume scan reflected the release quantity of thunderstorm energy, the difference of Unit area equivalent potential energy of 1~2 volume scan reached a maximum, which reflected downburst outbreak. So by setting release quantity of the equivalent potential energy per unit area early warn the downburst occurrence.(4)Six downburst warning results indicated that, the release of potential energy per unit area of the equivalent can warning of the occurrence of downbursts advance 6~ 12 minutes, and through the outflow strength formula to quantify the value of the ground wind caused by downburst, the error of early warning wind speed is determined by the distance from thunderstorm to radar, the closer the wind speed error is smaller, conversely, the greater the wind speed error. The calculation of outflow strength formula depends on the accurate identification of thunderstorms monomer, as the distance increases, the error of the thunderstorm parameter associated with outflow strength increases, at the same time the equivalent potential energy per unit area calculation, also deviates from the true value, directly affect the calculation of ground wind speed. Middle convergence is very important for the calculation of wind speed. Middle convergence appears a case of before the outbreak downburst, it takes the main part in downburst case, for such a case, the index and the outflow strength formula can be accurate early warning of strong winds on the ground.