Signature of Tropical Cyclone Intensification: An Assessment of Frozen Water Content in Numerical Simulations

The relationship between the structure and amount of frozen water particles and tropical cyclone (TC) intensity change is examined using numerical simulations based on an idealized 3-D full physics model with different initial TC structures. Previous observational studies have demonstrated a large-scale enhancement of ice water content (IWC) for intensifying TCs, with the largest increases occurring near the eyewall. The increased IWC near the eyewall is consistent with theoretical studies that have emphasized the importance of latent heat release in this region to TC intensification. However, the cause and consequences of increased IWC outside the eyewall remain unclear due, in part, to the lack of observations with sufficient coverage to characterize the spatial structure of IWC. To investigate this issue, we use an idealized WRF model with high temporal and spatial resolutions to examine the mechanisms responsible for greater IWC in intensifying TCs. In the WRF simulations, we find that strengthening storms have ~20% more frozen water content than weakening storms, especially in the mid-troposphere near the eyewall region. The signature of TC intensification found in the WRF simulations is shown to be consistent with IWC observations from CloudSat, both in amplitude and spatial extent. Such consistency encourages the use of numerically based simulations to further investigate the mechanism for such precursors of TC intensity change. Moreover, the major source of the extensive increases in IWC, either from the local production associated with convections or advection by TC outflow, can be examined.