Abstract
Abstract. Conventional and wavelet methods are combined to characterize gravity-waves (GWs) produced by two intense tropical cyclones (TCs) in the upper troposphere and lower stratosphere (UT/LS) from GPS winsonde data. Analyses reveal large contribution of GWs induced by TCs to wave energy densities in the UT/LS. An increase in total energy density of about 30% of the climatological energy density in austral summer was estimated in the LS above Tromelin during TC Dina. Four distinct periods in GW activity in relation with TC Faxai stages is observed in the UT. Globally, GWs have periods of 6 h–2.5 days, vertical wavelenghts of 1–3 km and horizontal wavelengths <1000 km in the UT during the evolution of TCs. Horizontal wavelengths are longer in the LS and about 2200 km during TCs. Convective activity over the basin and GW energy density were modulated by mixed equatorial waves of 3–4 days, 6–8 days and 10–13 days confirmed by Hövmöller diagram, Fourier and wavelet analyses of OLR data. Moreover, location of GW sources is below the tropopause height when TCs are intense otherwise varies at lower tropospheric heights depending on the strength of convection. Finally, the maximum surface wind speeds of TCs Dina and Faxai can be linearly estimated with total energy densities.
Highlights
Gravity-waves (GWs) produced by tropical cyclone-induced convection impact on the dynamics as well as the distribution of chemical constituents of the Earth’s middle atmo-sphere (Sato, 1993; Pfister et al, 1993; Danielsen, 1993; Dhaka et al, 2003; Cairo et al, 2008). Chane Ming et al (2002) showed that such GWs can be characterized using high resolution daily radiosonde data in the upper troposphere and lower stratosphere (UT/LS) within a radius of about 2000 km above the radiosonde station
Analysis of radiosondes clearly indicates that Tromelin is under the direct influence of tropical cyclones (TCs) Dina on 22 and 23 January
The sounding profiles used in Dina case were launched twice daily and daily at the SWIO islands of Mahe and Tromelin, respectively
Summary
Gravity-waves (GWs) produced by tropical cyclone-induced convection impact on the dynamics as well as the distribution of chemical constituents of the Earth’s middle atmo-sphere (Sato, 1993; Pfister et al, 1993; Danielsen, 1993; Dhaka et al, 2003; Cairo et al, 2008). Chane Ming et al (2002) showed that such GWs can be characterized using high resolution daily radiosonde data in the UT/LS within a radius of about 2000 km above the radiosonde station. Gravity-waves (GWs) produced by tropical cyclone-induced convection impact on the dynamics as well as the distribution of chemical constituents of the Earth’s middle atmo-. Observations of GWs appear to be common in landfalling tropical cyclones (TCs) in atmospheric boundary layer when cool surface temperatures promote stable conditions over land (Knupp et al, 2006). When propagating up to the upper atmosphere, GWs excited by TCs (Shen, 1982; Sun et al, 2007) bring forth the observable traveling ionospheric disturbances (TIDs) in the form of ionization in the F-region (Hung, 1977a, b). Using a reverse ray tracing technique, Hung and Kuo (1978a) and Hung and Smith (1978b) identified tropical cyclones as possible sources of GWs at the ionospheric heights
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