Abstract
Abstract. The characteristics of horizontal divergence induced by typhoon-generated gravity waves (HDTGWs) and the influence of HDTGW on typhoon evolution are investigated based on the simulation results of Typhoon Saomai (2006) using the Weather Research and Forecasting (WRF) model. The power spectral density of HDTGW shows dominant powers at horizontal wavelengths of 20–30 km and at periods of less than 1 h. This is associated with gravity waves generated by vigorous convective clouds in an inner core region of the typhoon. However, the domain-averaged HDTGW in the upper troposphere and lower stratosphere had a spectral peak at 24 h, which is well correlated with the minimum sea-level pressure of the typhoon, especially during a rapidly developing period. The 24 h period of the averaged HDTGW stems from the inertia–gravity waves generated by the convective clouds in the spiral rainbands, and showed no clear association with the thermal tides or the diurnal variation of precipitation.
Highlights
A typhoon consists of strong convective clouds having various spatiotemporal scales, which can generate inertia– gravity waves (IGWs) that reach to the stratosphere
We examine the characteristics of the horizontal divergence of typhoon-generated gravity waves (HDTGWs) in the upper troposphere and lower stratosphere (UTLS), and their contribution to typhoon evolution based on the Weather Research and Forecasting (WRF) model-simulated results of Typhoon Saomai (2006) that was reported by Kim and Chun (2010; KC10 hereafter)
No spectral analysis of the horizontal divergence induced by typhoon-generated gravity waves (HDTGWs) was performed in KC11, this result is somewhat unexpected because the dominant spectral peak of the TGWs shown in the vertical velocity of KC10 was less than 1 h
Summary
A typhoon consists of strong convective clouds having various spatiotemporal scales, which can generate inertia– gravity waves (IGWs) that reach to the stratosphere. Several observational (e.g., Dhaka et al, 2003; Chun et al, 2007) and numerical modeling (e.g., Kim et al, 2005; Kuester et al, 2008; Kim and Chun, 2010, 2011) studies have investigated the characteristics of vertically propagating gravity waves generated by the convective clouds associated with typhoons. Among these, Rappin et al (2011) showed that a typhoon can be intensified by reducing resistance of the upper-level outflow associated with the secondary circulation of typhoon convection based on the Carnot theory of the maximum potential intensity (Emanuel, 1986). They suggested that typhoon outflow weakens the environmental inertial stability, even under the upper-level jet, which minimizes the energy expended in developing and expanding the outflow, and allows for more energy to be utilized for typhoon intensification
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