Intensification of Aila (May 2009) due to a warm core eddy in the north Bay of Bengal
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A very severe cyclonic storm “Aila” hit West Bengal on 26 May 2009. The storm intensified when it encountered with a warm core (SST = 31°C) anti-cyclonic eddy (ACE4) in the north Bay of Bengal. The storm intensity increased by 43% due to this eddy, which is comparable with that (34%) obtained from a best fit line (derived from several numerical experiments over north-west Pacific Ocean). The shallow mixed layer of the large-scale ocean and deep mixed layer inside the eddy appear to be crucial parameters besides translation speed of the storm (Uh), ambient relative humidity and thermal stratification below mixed layer, in the storm intensification. From the eddy size and Uh, the eddy feedback factor is found to be about 0.4 (i.e. 40%), which is close to the above. Since there exists an inverse relationship between Uh and UOHC (upper ocean heat content), slow (fast) moving storms require high (low) UOHC. The warm ACE4 with a high UOHC of 149 kj/cm2 (300% higher than the climatological value) and deep warm layer (D26 = 126 m) opposes the cooling induced by the storm and helps for the intensification of the storm through the supply of large enthalpy (latent + sensible) flux.
KeywordsAila Bay of Bengal Upper ocean heat content Warm eddy Mixed layer
The authors would like to thank Dr. S. R. Shetye, Director, N.I.O. and Dr. V. S. N. Murty, Scientist-in-Charge, NIO, Regional centre, Visakhapatnam (CSIR, New Delhi), for their support and encouragement. Mrs. Maneesha is thankful to CSIR (Council for Scientific and Industrial Research), New Delhi, for providing the Senior Research Fellowship (SRF). Thanks to all the project teams for making the data sets (SSHA,TMI SST, Argo data, RAMA buoys data, monthly mean vertical temperature profiles) available on the websites. The authors are thankful to the anonymous reviewers for their valuable suggestions, which helped to improve the original version of the manuscript. This is NIO contribution number 4969.
- Ali MM, Sharma R, Cheney R (1998) An atlas of the north Indian Ocean eddies from TOPEX altimeter derived sea surface heights. Spec Publ ISRO-SAC, SP, 69–98, Indian Space Res Org, Bangalore, IndiaGoogle Scholar
- Ali MM, Jagadish PSV, Jain S (2007) Effect of eddies on Bay of Bengal cyclone intensity. EOS Trans AGU 88(8). doi: 10.1029/2007EO08001
- Behringer DW, Xue Y (2004) Evaluation of the global ocean data assimilation system at NCEP: the Pacific Ocean. Eighth symposium on integrated observing and assimilation systems for atmosphere, oceans, and land surface, AMS 84th annual meeting, Washington State Convention and Trade Center, Seattle, Washington, 11–15Google Scholar
- Goni GJ, Trinanes JA (2003) Ocean thermal structure monitoring could aid in the intensity forecast of tropical cyclone. EOS Trans AGU 84(51). doi: 10.1029/2003EO510001
- Kotal SD, Roy Bhowmik RSK, Kundu PK (2008) Application of statistical-dynamical scheme for real time forecasting of the Bay of Bengal very severe cyclonic storm “Sidr” of November 2007. Geofizika 25(2):139–158Google Scholar
- Lin I-I, Chen CH, Pun IF, Liu WT, Wu CC (2009b) Warm ocean anomaly, Air-sea fluxes and the rapid intensification of tropical cyclone Nargis, 2008. Geophys Res Letts 36:LO3817. doi: 10.1029/2008GL035815
- Murthy VSN, Guptha GVM, Sarma VV, Rao BP, Jyothi D, Shastri PNM, Supraveena Y (2000) Effect of vertical stability, circulation on the depth of chlorophyll maximum in the Bay of Bengal during May–June, 1996. Deep Sea Res 47(5):103–117Google Scholar
- Sadhuram Y, Ramana Murty TV, Somayajulu YK (2006) Estimation of cyclone heat potential in the Bay of Bengal and it’s role in the genesis and intensification of the storms in Bay of Bengal. Ind J Mar Sci 35(2):132–138Google Scholar
- Sadhuram Y, Maneesha K, Ramana Murthy TV (2010) Importance of upper Ocean heat content in the intensification and translation speed of cyclones over the Bay of Bengal. Curr Sci 99(9):1191–1194Google Scholar
- Subrahmanyam B, Murty VSN, Sharp RJ, Obrien JJ (2005) Air-sea coupling during the tropical cyclones in the Indian Ocean: a case study using satellite observations. Pure Appl Geophys 162:1643–1672Google Scholar
- Sujatha P, Mohanthy UC (2008) A comparative study on performance of MM5 and WRF models in simulation of tropical cyclones over Indian seas. Curr Sci 95(7):923–936Google Scholar