Trajectory Analyses on the Warm Core Development and Pressure Falls of a Developing Typhoon as Simulated by a Cloud-Resolving Model

Abstract

The central pressure fall in a typhoon is associated with the development of the warm core and mass divergence in the eye. Trajectory analyses were utilized to investigate the origins of air moving into the warm core and the paths of air parcels leaving the eye. First, developing Typhoon Wipha (2007) was simulated using a high-resolution (2 km) cloud-resolving model to represent the central pressure fall and axisymmetric structures such as the warm core in the upper levels of the eye, the eyewall, and the secondary circulation. Then, using the model output data, backward trajectories were calculated from the eye; the results show that the air parcels comprising the warm core originated from the lower troposphere and the lower stratosphere. Those originating from the lower troposphere, whose equivalent potential temperature (θ_e) is increased by the latent heat flux from the sea, ascend through the eyewall and move inward in the upper troposphere. Those originating in the lower stratosphere, which have high potential temperature (θ), descend from the lower stratosphere to the upper troposphere. Hence, the warm core comprises high-θ_e air from the lower troposphere and high-θ air from the lower stratosphere. Next, forward trajectories were calculated to examine the paths of air parcels leaving the eye; the results show that air parcels leave the eye through the eyewall throughout the troposphere, particularly at heights below 2 km and between 9 km and 12 km, which ultimately results in a central pressure fall.