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Interannual variability in the Biannual Rossby waves in the tropical Indian Ocean and its relation to Indian Ocean Dipole and El Nino forcing

Gnanaseelan, C and Vaid, BH (2010) Interannual variability in the Biannual Rossby waves in the tropical Indian Ocean and its relation to Indian Ocean Dipole and El Nino forcing. Ocean Dynamics, 60 (1). pp. 27-40.

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The interannual variability of the tropical Indian Ocean is studied using Simple Ocean Data Assimilation (SODA) sea surface height anomalies (SSHA) and Hadley Centre Ice Sea Surface Temperature anomalies. Biannual Rossby waves (BRW) were observed along the 1.5° S and 10.5° S latitudes during the Indian Ocean Dipole (IOD) years. The SODA SSHA and its BRW components were comparable with those of Topex/Poseidon. The phase speed of BRW along 1.5° S is -28 cm/s, which is comparable with the theoretical speed of first mode baroclinic (equatorially trapped) Rossby waves. This is the first study to show that no such propagation is seen along 1.5° S during El Nino years in the absence of IOD. Thus the westward propagating downwelling BRW in the equatorial Indian Ocean is hypothesized as a potential predictor for IOD. These waves transport heat from the eastern equatorial Indian Ocean to west, long before the dipole formation. Along 10.5° S, the BRW formation mechanisms during the El Nino and IOD years were found to be different. The eastern boundary variations along 10.5° S, being localized, do not influence the ocean interior considerably. Major portion of the interannual variability of the thermocline, is caused by the Ekman pumping integrated along the characteristic lines of Rossby waves. The study provides evidence of internal dynamics in the IOD formation. The positive trend in the downwelling BRW (both in SODA and Topex/Poseidon) is of great concern, as it contributes to the Indian Ocean warming.

Item Type: Article
Additional Information: Copyright of this article belongs to Springer.
Uncontrolled Keywords: Baroclinic; Boundary variations; Characteristic lines; Down-welling; Eastern equatorial Indian ocean; Ekman pumping; EL Nino; Equatorial Indian Ocean; Formation mechanism; Indian ocean; Indian Ocean dipole; Indian ocean dipoles; Interannual variability; Internal dynamics; Phase speed; Rossby wave; Sea surface temperature anomalies; Sea-surface height anomalies; Simple ocean data assimilations; TOPEX/poseidon; Tropical Indian ocean, Atmospheric temperature; Climate change, Ocean currents, annual variation; baroclinic wave; data assimilation; downwelling; Ekman pumping; El Nino; Hadley cell; heat transfer; Rossby wave; sea surface height; sea surface temperature; thermocline; TOPEX-Poseidon, Indian Ocean; Indian Ocean (Tropical)
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 31 Oct 2014 10:16
Last Modified: 31 Oct 2014 10:16

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