Stratospheric gravity waves excited by Hurricane Joaquin in 2015: 3-D characteristics and the correlation with hurricane intensification
Abstract. Despite progress, accurately forecasting tropical cyclone (TC) intensity, especially rapid intensification, remains a significant challenge. The correlations between the stratospheric gravity waves (GWs) excited by TCs and TC intensity have been recognized. However, partly due to the limitations of conventional analysis methods and observational filters of current satellite instruments, the characteristics of stratospheric GWs that indicate TC intensification remain unclear. This study examined the specific characteristics of GWs and their linkage to hurricane intensification by high-resolution, realistic model simulations and 3-D wave analysis method. First, the stratospheric GWs excited by Hurricane Joaquin in 2015 were simulated using the Advanced Weather Research and Forecasting (WRF) model. Then, the GW characteristics were analyzed using the novel 3-D Stockwell transform method. The GWs excited by Hurricane Joaquin are in the mid-frequency range and propagate outward from the hurricane center counterclockwise while moving upward in a spiral. A high-level time-lagged correlation exists between the intensities of the hurricane and stratospheric GWs during hurricane intensification, making it possible to detect an increase in hurricane intensity by observing an increase in stratospheric GW intensities. Compared to the weakening period, the stratospheric GWs excited during hurricane intensification exhibit relatively higher frequencies, shorter horizontal wavelengths, and longer vertical wavelengths, with this contrast particularly evident near the center of the hurricane. This study provides further knowledge for potentially monitoring hurricane intensification by observing stratospheric GWs using satellite instruments in the infrared and microwave bands when it is difficult to use other measurement techniques.
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