Abstract
This study examines potential impacts of the lower stratosphere on the development and the inner-core structure of intense tropical cyclones (TCs). By initializing the Hurricane Weather Research and Forecasting (HWRF) model with different monthly averaged sounding profiles in the Northwestern Pacific and the North Atlantic basins, it is shown that the lower stratosphere layer (LSL) can impose a noticeable influence on the TC structure and development via formation of an extra warm core near the tropopause along with a thin layer of inflow in the LSL at the high-intensity limit. Specifically, a lower tropopause level allows for higher TC intensity and a more distinct double warm core structure. Likewise, a weaker LSL stratification also corresponds to a warmer upper-level core and higher intensity. Of further significance is that the double warm core formation is more sensitive to tropopause variations in the Northwestern Pacific basin than those in the North Atlantic basin, given the same sea surface temperature. The results suggest that variations in tropopause level and LSL stratification could be an important factor that is responsible for the long-term variability of TC intensity.
Highlights
Tropical cyclones (TCs) are dynamical systems that are intrinsically governed by moist processes.A key feature that distinguishes TC dynamics from those of other strongly rotational systems is the presence of a warm core, which is defined as a positive temperature anomaly at the storm center with respect to the far-field environment
The efficiency of such energy conversion is proportional to the difference in sea surface temperature and outflow temperature, which dictates the maximum potential intensity (MPI) limit that a TC can attain in a given environmental condition
The underlying motivation for investigating such stratosphere–TC interaction stems from recent real-time forecasts of TCs in the WPAC basin by the NOAA National Center for Environmental Prediction (NCEP) center, which consistently captured the development of a double warm-core structure in almost all intense TCs in the WPAC basin
Summary
A key feature that distinguishes TC dynamics from those of other strongly rotational systems is the presence of a warm core, which is defined as a positive temperature anomaly at the storm center with respect to the far-field environment. This warm core structure directly follows from the decrease of the tangential wind with height that determines the horizontal temperature gradient through the thermal wind relationship.
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