Observation and a numerical study of gravity waves during tropical cyclone Ivan (2008)

Abstract

Abstract. Gravity waves (GWs) with horizontal wavelengths of 32-2000 km are investigated during tropical cyclone (TC) Ivan (2008) in the southwest Indian Ocean in the upper troposphere (UT) and the lower stratosphere (LS) using observational data sets, radiosonde and GPS radio occultation data, ECMWF analyses and simulations of the French numerical model Meso-NH with vertical resolution < 150 m near the surface and 500 m in the UT/LS. Observations reveal dominant low-frequency GWs with short vertical wavelengths of 0.7-3 km, horizontal wavelengths of 80-400 km and periods of 4.6-13 h in the UT/LS. Continuous wavelet transform and image-processing tools highlight a wide spectrum of GWs with horizontal wavelengths of 40-1800 km, short vertical wavelengths of 0.6-3.3 km and periods of 20 min-2 days from modelling analyses. Both ECMWF and Meso-NH analyses are consistent with radiosonde and GPS radio occultation data, showing evidence of a dominant TCrelated quasi-inertia GW propagating eastward east of TC Ivan with horizontal and vertical wavelengths of 400-800 km and 2-3 km respectively in the LS, more intense during TC intensification. In addition, the Meso-NH model produces a realistic, detailed description of TC dynamics, some highfrequency GWs near the TC eye, variability of the tropospheric and stratospheric background wind and TC rainband characteristics at different stages of TC Ivan. A wave number 1 vortex Rossby wave is suggested as a source of dominant inertia GW with horizontal wavelengths of 400-800 km, while shorter scale modes (100-200 km) located at northeast and southeast of the TC could be attributed to strong localized convection in spiral bands resulting from wave number 2 vortex Rossby waves. Meso-NH simulations also reveal GWrelated clouds east of TC Ivan.

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

“…The spectral range of stratospheric GWs observed or modelled in association with TCs is extremely broad and spans multiple orders of magnitude both in terms of vertical wavelengths (from as short as 0.7 km (e.g, Chane Ming et al . ) to as long as 10 km or more [e.g. Wu and Zhang, ; Hecht et al .…”

Satellite Observations of Stratospheric Gravity Waves Associated With the Intensification of Tropical Cyclones

“…TC‐induced gravity waves (GWs) have been widely studied with model simulations, satellite, and ground‐based observations, as well as reanalysis data (Chen et al, ; Chane Ming et al, , ; Kuester et al, ; Kim et al, ; Miller et al, ; Nolan & Zhang, ; Wu et al, ; Yue et al, ). Typical characteristics, namely, the vertical and horizontal wavelength, period, and propagation direction have been assessed.…”

Gravity Wave Activities Associated With Convective Phenomena at a Tropical Location Near Land‐Sea Boundary

“…The spectral analysis of the fluctuations of temperature, zonal, and meridional wind during Aila revealed that the vertical wavelengths in the range 2.5–3.2 km, corresponding to wave number of 2 to 3 cycles/km, of GW dominate in LS. Several previous studies have revealed that vertical wavelengths in the range of 0.7–3 km are dominant during tropical cyclones Hudah, Ivan, Dina, and Faxai in the LS (Chane Ming et al, ; Chane‐Ming et al, ; Chane‐Ming et al, ). Also, a previous study of GW in LS over Bay of Bengal during TCs using Welch method agrees to the present findings (Rakshit et al, ).…”