Common Gravity Wave Patterns from Multi-Hurricane Analysis

Hurricanes are important sources of convectively generated gravity waves (GWs) that play a critical role in modifying the thermodynamics in the upper troposphere-lower stratosphere (UTLS) region. There are several widely used theories that describe the GW convective generation, but their validation using model simulations or satellite measurements is not sufficient due to the lack of high resolution measurements and the difficulties in isolating the convection force.  The GNSS - radio occultation (RO) measurements therefore stand out since they are capable of determining the hurricane thermal structures and identify the small-vertical-scale GWs, because of their high-vertical-resolution (<0.1km) and high accuracy (<0.5K) temperature retrievals.

This study seeks to characterize the GWs generated by hurricanes by investigating three intense hurricanes of similar intensity, to determine their common GW features that can be extended and compared to GWs induced by other hurricanes. We approach this goal by analyzing the GW properties using multiple RO temperature retrievals along each hurricane’s track by illustrating the consistency of the tropopause height and convection strength within the analyzed periods. We then evaluate the correspondence between the RO-determined GW properties and the hurricane environment revealed by the ERA5 model-level data. This comparison clearly demonstrates that the RO profiles could vertically penetrate the hurricane structure close to the eye with a small horizontal drift, allowing us to identify the link between the wave characteristics and their sources of generation. Our results show a good agreement with the conceptual GW theories, from which we identify three distinct GW wavelength bands that correspond to different generation mechanisms with strong consistency among the hurricanes studied. The Least Squares Wavelet Analysis (LSWA) also uniquely demonstrates the wind filtering effects that modify the GW wavelength via the dispersion relation. Our study suggests a common GW pattern exhibited by multiplication of the selected profiles from each studied hurricanes that might be applicable to other hurricanes of similar intensity.