Development of an integrated vertical slantwise convective parameterization scheme and its numerical experiments

KeyWord:Snowstorm, Typhoon, Conditional symmetric instability (CSI), The integrated-vertical-slantwise convective parameterization scheme, Numerical simulation

Abstract:

      An integrated vertical-slantwise convective parameterization scheme, based on the vertical Kuo-Anthes and slantwise Nordeng convection parameterization schemes, is presented and introduced into the MM5 model. By employing MM5 model with the proposed scheme, some numerical simulations are conducted with the snowstorm event occurred over the southern China on 28-29 January 2008 as well as Typhoon Haitang (2005) process as the examples. The results indicate that the atmosphere was mainly convective stable in the vertical direction in the simulation on the snowstorm event, but with a conditional symmetric instablity occurred in the lower troposphere; and that when the area of conditional symmetric instability (CSI) developed toward the upper levels, the strong rising motion as the trigger mechanism released large amount of energy of CSI, producing more convective precipitation with the total precipitation much more closer to that of the observed. In the simulation, the developing and strengthening of CSI were corresponding to changes in the intensity of snowfall, the convergence, and the strong ascending motion of air, revealing CSI to be one of the important mechanisms responsible for the initiation and growth of the snowstorm. The results from a 72 h explicit simulation on Typhoon Haitang indicate that the CSI occurred mainly at the lower levels in the typhoon, with well defined spiral structure; and that CSI tended to have a larger impact on the intensity of typhoon than on the track. The minimum pressures at the typhoon center for 72 hour runs with the integrated vertical slantwise convective parameterization scheme used were 3 hPa on average with the maximum of 8 hPa, lower than those of the runs with only vertical cumulus parameterization scheme involved. The simulation results are encouraging as introducing the influence of CSI into the model can better improve the warm core structure at the middle and upper levels of the model typhoon, with the strong and persistent upward motion of air to cause much more convective precipitation and the latent heat released through convection in turn to make the typhoon develop further.