Abstract
Abstract. We have examined, for the first time, the spatial coherence of oceanic parameters, namely, the ocean surface wind and significant wave height (SWH), using near-instantaneous along-track sampling over vast oceanic tracks provided by Poseidon-2 Radar Altimeter onboard Jason-1. The spatial coherence length scales over the Arabian Sea and the Bay of Bengal regions, derived using Auto correlation analysis, display interesting characteristics in relation to onset and evolution of SW Monsoon over India. The estimated spatial coherence scales are found to be of the order of 100–500 km. Generally, SWH coherence lengths over Arabian Sea are observed to increase from June to July during good monsoon year (2012). This trend is not followed for the poor monsoon year (2002). Similar trend is observed for spatial coherence scales for wind speed. The temporal evolution of analyzed spatial coherence scales of winds and waves over Arabian Sea clearly brings out the distinction between a "good" (2012) and a "poor" (2002) monsoon year. The spatial coherence lengths of these parameters over the Bay of Bengal are found to be shorter and do not show any systematic relation to onset and evolution of SW monsoon. Anisotropy in coherence lengths is also analyzed by treating ascending and descending tracks separately. Generally, the descending tracks measurements show higher spatial coherence lengths than the ascending ones. Like the spatial coherence scales, the anisotropy of the coherence scales over the Arabian Sea also mimics the behaviour of the strength of SW Monsoon.
Highlights
Over the last more than two decades, precise dual frequency Radar Altimetry measurements from space have revolutionized many aspects of Oceanography
We have considered the Arabian Sea and Bay of Bengal tracks starting from equator to northernmost point where it approaches the Indian landmass
The results of the spatial coherence analysis of ocean state parameters namely significant wave height (SWH) and, Wind Speed are presented
Summary
Over the last more than two decades, precise dual frequency Radar Altimetry measurements from space have revolutionized many aspects of Oceanography. Sarkar et al (2002; 2006) dealt with auto correlation analysis of surface wind vectors and wave heights measured using the deep sea buoys located over the Bay of Bengal to estimate temporal de-correlation time scales. For the first time, the availability of high resolution along track measurements of oceanic winds and waves by space-borne Radar Altimeters for ‘spatial’ coherence studies. These along track measurements represent nearinstantaneous spatial transects of wind and wave fields over the ocean. We analyze these near-instantaneous along track Radar Altimeter measurements, of winds and waves over the Indian monsoon region, to estimate their spatial coherence scales using spatial auto-correlation analyses, and study their relation with monsoon activity
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