The role of convective available potential energy for tropical cyclone intensification

The research project will focus on the investigation of the relevance of convective available potential energy (CAPE) for tropical cyclone intensification. Numerical model simulations will be conducted and analysed to find out whether, and if so how much, CAPE exists during the intensification phase, its distribution, and the particular role it may play for the evolution dynamics. According to the WISHE theory for tropical cyclogenesis (WISHE = Wind Induced Surface Heat Exchange), the existence of CAPE is not required in the intensification process. However, this theory only leads to a conclusive result if the net latent heating in the outer region of a tropical cyclone vanishes due to a very low relative humidity. Such an assumption is not necessary when CAPE can be stored in the inflow boundary layer. The axisymmetric cloud-resolving model HURMOD and the 3-dimensional cloud model CM1 will be applied in the study. intensification rate. A CM1 simulation of tropical cyclogenesis indeed reveal the existence of CAPE during intensification (see Figure 1). The research is based on the hypothesis that CAPE contributes to an increase of the This hypothesis can be verified by a simple convective parameterization scheme, in which CAPE is reduced with a prescribed time scale. When intensification also takes place with an arbitrarily small relaxation time scale, it indicates that WISHE is relevant. A conceptual model will be developed to make the effect of CAPE on intensification more comprehensible. This project is being funded by the German Research Foundation (DFG) under an individual grant.

Participating researchers: Marguerite Lee and Thomas Frisius

 

 

Figure 1: CAPE (coloured shadings, J/kg) and wind speed at height 2.25 km (isolines, m/s) of a CM1 tropical cyclogenesis simulation at the time of maximum intensification