Coupled Ocean-Atmosphere Summer Intraseasonal Oscillation over the Bay of Bengal

Rahaman, Hasibur and Raj, G N Bharath and Ravichandran, M (2019) Coupled Ocean-Atmosphere Summer Intraseasonal Oscillation over the Bay of Bengal. In: PURE AND APPLIED GEOPHYSICS, 176 (12). pp. 5415-5429.

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Abstract

This study shows the active role of subsurface ocean temperature in the evolution of coupled intra-seasonal oscillation (ISO) in the Bay of Bengal (BoB) using multi-satellite observations and ocean analysis product. Satellite-derived humidity profiles obtained from the atmospheric infrared sounder (AIRS) show that intense rains over the BoB are associated with the moistening (drying) in the lower and mid-troposphere during the active (break) phase of summer intraseasonal oscillation (ISO). Anomalous moistening in the mid-troposphere up to 500 hPa ahead of the maximum precipitation band over north BoB gives a precursor signal for the northward movement of the rain band. During the active (break) phase, the upper-tropospheric positive (negative) temperature anomaly ahead of the maximum rain band also sets a precondition by heating the mid- to upper troposphere. Daily subsurface temperature from Global Ocean Data Assimilation System (GODAS) analysis show that during the active phase, tropospheric moistening (drying) coincides with the subsurface warm (cold) temperature up to 200-m depth. The upper ocean warms uniformly by \~ 1 degrees C during the active phase as compared to the break phase in the entire BoB. The presence of a thin warm layer below the maximum rain band creates an environment conducive to sustaining the active phase on the ISO time scale. A positive sea surface temperature (SST) anomaly along with upper ocean warming ahead of a rain band in the north BoB in association with lower and mid-tropospheric moistening sets a precondition for the northward movement of the rain band. The anomalous warming (cooling) in the thermocline is associated with deeper (shallower) thermocline depth 23 degrees isotherms (D23)] and coincides with the mixed-layer warming

Item Type:	Journal Article
Publication:	PURE AND APPLIED GEOPHYSICS
Publisher:	SPRINGER BASEL AG
Additional Information:	Copyright of this article belongs to SPRINGER BASEL AG
Keywords:	Indian summer monsoon; intraseasonal oscillation; active and break phase of summer monsoon; northward propagation
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	01 Jan 2020 06:01
Last Modified:	01 Jan 2020 06:01
URI:	http://eprints.iisc.ac.in/id/eprint/64096

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