Warm ocean anomaly, air sea fluxes, and the rapid intensification of tropical cyclone Nargis (2008)

Abstract

On 2 May 2008, category‐4 tropical cyclone Nargis devastated Myanmar. It was observed that just prior to its landfall, Nargis rapidly intensified from a weak category‐1 storm to an intense category‐4 storm within only 24 h. Using in situ ocean depth‐temperature measurements and satellite altimetry, it is found that Nargis' rapid intensification took place on a pre‐existing warm ocean anomaly in the Bay of Bengal. In the anomaly, the subsurface ocean is evidently warmer than climatology, as characterized by the depth of the 26°C isotherm of 73–101 m and the tropical cyclone heat potential of 77–105 kj cm−2. This pre‐existing deep, warm subsurface layer leads to reduction in the cyclone‐induced ocean cooling, as shown from the ocean mixed layer numerical experiments. As a result, there was a near 300% increase in the air‐sea enthalpy flux to support Nargis' rapid intensification.

Ocean Responses to Typhoon Namtheun Explored with Argo Floats and Multiplatform Satellites

“…Recent investigations indicate that warm core eddies favour the enhancement of typhoons, because the eddies have a large upper ocean heat content (UOHC) (Lin et al, 2009;Wu, Lee, & Lin, 2007). It has been found that the relatively warmer upper ocean, characterized by a large D26 (depth of the 26°C isotherm), leads to a reduction in cyclone-induced ocean cooling (Lin et al, 2009).…”

“…It has been found that the relatively warmer upper ocean, characterized by a large D26 (depth of the 26°C isotherm), leads to a reduction in cyclone-induced ocean cooling (Lin et al, 2009). For a slow-moving Category 5 typhoon (maximum sustained winds higher than 61 m s , respectively (Lin et al, 2009).…”

“…It has been found that the relatively warmer upper ocean, characterized by a large D26 (depth of the 26°C isotherm), leads to a reduction in cyclone-induced ocean cooling (Lin et al, 2009). For a slow-moving Category 5 typhoon (maximum sustained winds higher than 61 m s , respectively (Lin et al, 2009). Although the temporal heat flux varies from 0.6 × 10 3 W m −2 (Jacob et al, 2000;) to 2-3 × 10 3 W m −2 (Shay, Goni, & Black, 2000), the total enthalpy fluxes from the seawater to the air for typhoons are similar (0.7-1 × 10 8 J m −2 ); this is less than the pre-typhoon UOHC.…”

“…Vast energy interchanges within the atmosphere and ocean as a result of air-sea interactions have a great effect on both weather and ocean dynamics. The ocean's responses include sea surface cooling (Price, 1981), enhanced entrainment and vertical mixing (Han, Ma, & Chen, 2012;Jacob, Shay, Mariano, & Black, 2000;Lin, Chen, Pun, Liu, & Wu, 2009;Lin, Wu, Pun, & Ko, 2008), inertial oscillation (Black & Dickey, 2008;Morozov & Velarde, 2008;Price, 1981), and enhanced phytoplankton blooming (D'Asaro, 2003;Han et al, 2012;Subrahmanyam, Rao, Rao, Murty, & Sharp, 2002;Sun, Yang, Xian, Lu, & Fu, 2010;Wang & Zhao, 2008;Xian, Sun, Yang, & Fu, 2012;Yang, Fu, Sun, Liu, & Feng, 2010).…”

Development of tropical cyclone wind field for simulation of storm surge/sea surface height using numerical ocean model

“…The highest recorded storm surge (*12.5 m) was associated with the Backergunj cyclone that was originated in BoB in 1876 and struck near Meghna estuary in Bangladesh. In the historical cyclone records, seven of the top ten deadliest cyclones have formed in the BoB and the most recent example is cyclone Nargis (May 2008) in Myanmar (Webster 2008;Lin et al 2009;McPhaden et al 2009;Yanase et al 2010). TC Sidr (November 2007) which was a Category 4 storm in SaffirSimpson Tropical Cyclone Scale (SSTCS) brought about a devastating coastal flooding with *5.8 m of surge height and *1.7 billion (USD) of damage in Bangladesh.…”