Next-Generation Satellite Observations of Wave Propagation in Rapidly-Intensifying Tropical Cyclones

The dynamics that govern the intensification of tropical cyclones (TC) are dominated by rapidly evolving moist convective processes in the inner-core region. Remotely sensed satellite observations are typically available but in the past have lacked the necessary resolution to sufficiently examine TC intensification processes. However, as a result of the recent launch of next-generation high-resolution satellites (JMA's Himawari-8 and NOAA/NASA’s GOES-16), the spatial and temporal frequency of remotely-sensed observations of TCs have increased significantly. In particular, rapidly refreshing “mesoscale” domains have the capability of providing imagery with 2-km resolution for high-impact events, such as tropical cyclones, as frequently as once every 30 seconds.

This study utilizes brightness temperatures observed by the Advanced Himawari Imager (on Himawari-8) and the Advanced Baseline Imager (on GOES-16) to examine the structure of Typhoon Soudelor (2015), Hurricane Harvey (2017), and Hurricane Irma (2017) throughout their respective rapid intensification (RI) events. Two-dimensional wavenumber decompositions are performed on brightness temperature fields that correspond to channels sensitive to upper-, mid-, and lower-level water vapor, IR longwave radiation, and cirrus cloud detection to study wave features associated with the inner-core region. A scale-separation is also performed to assess the degree to which the intensification processes are dominated by phenomenon of various wavelengths. Higher-order wavenumbers reveal asymmetric features that propagate outwards from the storms on short time scales (~1–2 h). In addition, storm-centered difference fields between consecutive satellite images reveal the propagation speed and directions of these features. It is found that these propagating waves, likely upper-tropospheric gravity waves, are present in many quadrants of the storm, at various distances from the TC center, and propagate in various directions. A more in-depth analysis of these waves and their contribution to intensification is ongoing.