In situ observations of gravity waves over tropical cyclone Hinnamnor (2022) suggest that TC gravity wave amplitudes are underestimated in ERA5 reanalysis

Tropical cyclones (TCs) are known to regularly excite near-concentric outwardly radiating gravity waves in the lower stratosphere, with horizontal wavelengths of a few hundred kilometers. These disturbances can potentially drive in situ cirrus production, but their amplitudes have been poorly known: satellite observations produce substantially lower amplitudes than those in models or reanalysis, and there have been few aircraft overflights to provide in situ measurements. We present here data from a new TC overflight of supertyphoon Hinnamnor by the NASA WB-57 in 2022 during ACCLIP (the Asian Summer Monsoon Chemical and CLimate Impact Project). Hinnamnor produced a clear and large gravity wave temperature signal in the lower stratosphere, at 9.6 K peak-to-peak, nearly an order of magnitude larger than typical satellite studies and three times as large as in contemporaneous ERA5 reanalysis. The measured value would fall in the 97th percentile in ERA5, based on a sample of 114 summertime TCs in the Western Pacific basin, which produce near-ubiquitous but weaker concentric gravity waves. A metanalysis and comparison of ERA5 to observed winds suggests that both satellite retrievals and reanalysis underestimate TC gravity wave amplitudes because of resolution constraints. Satellite retrievals dampen short-vertical wavelength perturbations, while reanalyses fail to capture the rapid intensification of tropical cyclones that is associated with strong gravity wave production. These results imply that high-resolution measurements are needed to quantify the influence of TC-induced gravity waves on the stratospheric water budget.