Diagnosis of tropical cyclone activity through gravity wave energy density in the southwest Indian Ocean

Abstract

[1] Tropical cyclone (TC) activity is diagnosed through convective gravity waves (GWs) observed in the upper troposphere (UT)/lower stratosphere (LS) above Tromelin island (15.53°S, 54.31°E) in the tropical southwest Indian Ocean. Monthly and weekly GW total energy densities derived from daily GPS windsonde data are compared with Outgoing Longwave Radiation (OLR) and TC hours in the vicinity of Tromelin. A relationship between GW energy density and TC activity is observed in the LS, for the TC season 2001/2002. Moreover TCs (local convection) produce GWs with total energy density mostly higher (lower) than 12 J kg −1 . A 10-season climatology (1997/1998-2006/ 2007) confirms that large values of GW total energy density in the LS are associated with weak values of OLR during the TC passage. Monthly total, kinetic and potential GW energy densities within 2000 km radius of Tromelin can be estimated using linear relationships with TC hours for a threshold of above 6 TC days per month. A linear relationship also exists between weekly GW total energy density in the LS and the activity of intense TCs above a threshold of 2 TC days per week within 1000 km radius of Tromelin. GW energy density in the LS could be used as a possible index to investigate TC activity in the UT/LS. Citation: Ibrahim, C., F. Chane-Ming, C. Barthe, and Y. Kuleshov (2010), Diagnosis of tropical cyclone activity through gravity wave energy density in the southwest Indian Ocean, Geophys. Res. Lett., 37, L09807,

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

“…The opposite is observed in the UT. The contrast in energy intensification in the UT and the LS is consistent with climatological observations of GW activity during TC seasons (Ibrahim et al, 2010).…”

“…Vertical profiles of temperature and horizontal wind with 100 m resolution reached the mean altitude of 23 km. Radiosonde data quality and accuracy are described in Chane Ming et al ( , 2007 and Ibrahim (2010), which used similar vertical profiles to characterize GWs in the UT/LS. At Ivato airport (389 m altitude), 40 GPS radiosonde profiles were obtained twice a day at 00:00 and/or 09:00 and/or 12:00 UTC with a vertical resolution of 300 m and a mean maximum altitude of 23 km.…”

“…Recently, using radiosonde data, Chane also demonstrated a possible correlation between daily maximum surface wind speed and total energy density of inertia GWs produced by intense TCs Dina and Faxai in the UT/LS. Ibrahim et al (2010) extended this study analysing a climatology of Published by Copernicus Publications on behalf of the European Geosciences Union.…”

Statistical analysis of the mesospheric inversion layers over two symmetrical tropical sites: Réunion (20.8° S, 55.5° E) and Mauna Loa (19.5° N, 155.6° W)

“…This observation could be related to the increase in convective activity in the southwestern Indian Ocean (SWIO) basin during this period. It is well known that low-pressure and tropical cyclone systems are a source of low-frequency convective gravity waves in the SWIO basin (Chane-Ming et al, 2007Ibrahim et al, 2010). Based on a 10-season climatology investigation (1997/1998-2006/2007) obtained from GPS windsonde, Ibrahim et al (2010) showed a linear relationship between weekly gravity waves total energy density in the lower stratosphere and the activity of intense tropical cyclones in the SWIO basin.…”

“…It is well known that low-pressure and tropical cyclone systems are a source of low-frequency convective gravity waves in the SWIO basin (Chane-Ming et al, 2007Ibrahim et al, 2010). Based on a 10-season climatology investigation (1997/1998-2006/2007) obtained from GPS windsonde, Ibrahim et al (2010) showed a linear relationship between weekly gravity waves total energy density in the lower stratosphere and the activity of intense tropical cyclones in the SWIO basin. These gravity waves which were produced through the activity of intense tropical cyclones could also influence the dynamics of the middle atmosphere as well as the general circulation.…”