The Structure of the Warm Core in Numerically Simulated Tropical Cyclones

We examine the thermodynamic structure of the eye (i.e., the warm core) of numerically simulated tropical cyclones. While the largest temperature perturbations in tropical cyclones are generally believed to occur in the upper troposphere (>10 km), recent work (Stern and Nolan 2011) has shown that mid-level (4-8 km) maxima are found in idealized simulations, and that the “typical” structure and variability of the warm core in real storms remains uncertain. Here, we further explore this issue with idealized simulations, and with real-data simulations of multiple storms. Comparisons to dropsonde observations are presented for simulations of Hurricane Earl (2010).

In some simulations, there is a remarkable steadiness to the height of the maximum perturbation temperature throughout periods of rapid intensification, and so the height of the warm core need not be directly related to intensity. Dual maxima in perturbation temperature are often found in both idealized and real-data simulations, with the upper maximum typically between 12-14km.

We present potential temperature budgets and trajectory analyses in order to gain further insight into the thermodynamic structure of the eye. It is also shown that the vertical velocity field in the eye is not characterized by a steady, horizontally, homogeneous, weak subsidence, but rather is dominated by high-frequency gravity waves, whose amplitudes (up to several m/s) are much greater than the time-mean vertical velocity (~1-5 cm/s descent). The vertical structure of the mean descent is not steady, and varies substantially from day to day.