Stratospheric Gravity Waves Can Be a Proxy for Tropical Cyclones' Intensification
Tropical cyclones (TCs) are among the most destructive natural weather phenomena and can cause extensive damage to coastal countries and regions. Close monitoring and accurate forecasts of the tracks and intensity of TCs are needed to reduce human and financial losses.
As a TC intensifies, gravity waves (GWs) are emitted into the stratosphere to partially rebalance the sudden energy changes. If a correlation between TC intensification and GWs is verified, observing stratospheric GWs with satellite instruments could provide a possible predictor of TC intensification.
Structure of a tropical cyclone and the stratospheric gravity waves excited by it. (Figure downloaded from https://www.internetgeography.net/ and re-edited by Dr WU Xue.)
Recently, scientists from the Institute of Atmospheric Physics at the Chinese Academy of Sciences, Jülich Supercomputing Centre, University of Bath, Yonsei University, and NorthWest Research Associates, US, used mesoscale model simulations to study the correlation between TC intensification and GWs and found that stratospheric GW activity increases prior to peaks in TC intensity.
This recent study is a follow-on study to their earlier collaborative study. In that study, from long-term satellite observations, they found a statistically robust correlation –more intensive stratospheric GWs are observed during the intensification of TCs than during weakening. So, they conducted numerical simulations to verify the statistical correlation revealed by long-term satellite observations and examine the possibility of using GW activity as a proxy for TCs intensity change.
"Our current study confirms that intensive stratospheric GW activity generated by a TC can be a proxy for the intensification of the TC itself." Said Dr. WU Xue, the lead author of the team's recent study published in Geophysical Research Letters. Analyses show a clear distinction of GW occurrence frequencies with respect to TC intensity change: stratospheric GW activity is more frequent and intensive when the TC intensifies rather than when it weakens. This phenomenon is particularly prominent for the strongest GW events.
Based on this study, it is possible to monitor and even warn about the intensification of TCs by observing stratospheric brightness temperature perturbations using satellite instruments of microwave and infrared channels. This approach is advantageous when clouds obscure the direct view from above by visible and infrared instruments into the inner state of the TC.
Wu, X.*, Hoffmann, L., Wright, C. J., Hindley N. P., Kalisch S., Alexander M. J., Wang Y. N.: Stratospheric gravity waves as a proxy for hurricane intensification: a case study of weather research and forecast simulation for Hurricane Joaquin, Geophys. Res. Lett., https://doi.org/10.1029/2021GL097010.