Effect of SST Variation on ITCZ in APE Simulations

Rajendran, Kavirajan and Kitoh, Akio and Srinivasan, Jayaraman (2013) Effect of SST Variation on ITCZ in APE Simulations. In: JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN, 91A (SI). pp. 195-215.

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Abstract

The effect of meridional variation of sea surface temperature (SST) on tropical atmospheric circulation is analyzed using Aqua-planet Experiment (APE) simulations. The meridional SST gradient around the narrow SST peak in CONTROL simulation favours a strong and single equatorial Intertropical Convergence Zone (ITCZ, defined by the maximum of zonally averaged total precipitation) in all APE models. In contrast, flat equatorial SST peak (FLAT simulation) favours split/double ITCZs flanking the SST maximum, in the majority of the APE models. Although there is reasonable agreement for SST sensitivity of ITCZ among the APE models in CONTROL, there exists disparity among them in FLAT case. Similarly, while the total and convective precipitation responses are consistent among the models, the large-scale precipitation response shows considerable inter-model variations in FLAT case. The APE intercomparison indicates that the occurrence and positioning of the ITCZ are primarily related to boundary layer moisture convergence as a response to the meridional variation of SST. Furthermore, the meridional gradient of tropospheric temperature is found to be an important factor that can influence the positioning of ITCZ. FLAT SST distribution is found to be similar to the observed distribution over the Indian region during summer season. Models that yield double ITCZs in this case simulate an easterly jet over the equatorial region (similar to 15 degrees equatorward of the ITCZ). This is analogous to the Tropical Easterly Jet (TEJ), which is a unique feature observed over the Indian region during summer monsoon season, with its core at 12 degrees N, equatorward of the seasonal convergence zone centered along 25 degrees N. In these models, positive meridional temperature gradient and the associated easterly shear in the atmosphere strengthened by moisture convergence penetrate up to the upper troposphere, with which TEJ is in thermal wind balance.

Item Type:	Journal Article
Publication:	JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN
Publisher:	METEOROLOGICAL SOC JAPAN
Additional Information:	copyright for this article belongs to METEOROLOGICAL SOC JAPAN,
Keywords:	GCM; aqua planet; ITCZ; Indian summer monsoon
Department/Centre:	Division of Mechanical Sciences > Centre for Atmospheric & Oceanic Sciences
Date Deposited:	30 Dec 2013 12:20
Last Modified:	30 Dec 2013 12:20
URI:	http://eprints.iisc.ac.in/id/eprint/47988

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