Quantifying the global impact of tropical cyclone‐associated gravity waves using HIRDLS, MLS, SABER and IBTrACS data

Abstract

Tropical convective systems are major sources of atmospheric gravity waves (GWs). These waves are a key driver of global atmospheric circulation, especially in the middle and upper atmosphere. Tropical cyclones (TCs) such as hurricanes and typhoons are particularly dramatic examples of such systems, and are therefore potentially significant individual sources of GWs. To investigate this effect, GW observations from three satellite limb sounders in the vicinity of TCs are produced and analysed. By statistically combining 15 years of GW observations from 1,379 individual TCs represented in the International Best Track Archive for Climate Stewardship, it is shown that TCs are associated with a 15% increase of GW amplitudes over background and a 25% increase in measured momentum fluxes, primarily during the period immediately before the TC. It is further shown that this additional contribution is small relative to other GW‐generating processes, and thus that individual TCs do not have a large quantitative effect on the dynamics of the middle and upper atmosphere as a whole. Thus, it is concluded that accurate modelling of TC‐generated short vertical wavelength GWs need not be a development priority for the next generation of weather and climate models. The results also demonstrate that stronger GW activity is associated with TCs that will later develop into hurricane‐intensity storms than is observed for those that will not, and thus that better space‐based monitoring of stratospheric GW activity could be a useful tool to help improve the forecasting of strong hurricane events in the presence of obscuring tropospheric cloud.