Abstract
During the CINDY/DYNAMO field campaign (fall/winter 2011), intensive measurements of the upper ocean, including an array of several surface moorings and ship observations for the area around 75°E–80°E, Equator-10°S, were conducted. In this study, large-scale upper ocean variations surrounding the intensive array during the field campaign are described based on the analysis of satellite-derived data. Surface currents, sea surface height (SSH), sea surface salinity (SSS), surface winds and sea surface temperature (SST) during the CINDY/DYNAMO field campaign derived from satellite observations are analyzed. During the intensive observation period, three active episodes of large-scale convection associated with the Madden-Julian Oscillation (MJO) propagated eastward across the tropical Indian Ocean. Surface westerly winds near the equator were particularly strong during the events in late November and late December, exceeding 10 m/s. These westerlies generated strong eastward jets (>1 m/s) on the equator. Significant remote ocean responses to the equatorial westerlies were observed in both Northern and Southern Hemispheres in the central and eastern Indian Oceans. The anomalous SSH associated with strong eastward jets propagated eastward as an equatorial Kelvin wave and generated intense downwelling near the eastern boundary. The anomalous positive SSH then partly propagated westward around 4°S as a reflected equatorial Rossby wave, and it significantly influenced the upper ocean structure in the Seychelles-Chagos thermocline ridge about two months after the last MJO event during the field campaign. For the first time, it is demonstrated that subseasonal SSS variations in the central Indian Ocean can be monitored by Aquarius measurements based on the comparison with in situ observations at three locations. Subseasonal SSS variability in the central Indian Ocean observed by RAMA buoys is explained by large-scale water exchanges between the Arabian Sea and Bay of Bengal through the zonal current variation near the equator.
Highlights
While the Madden-Julian Oscillation (MJO; [1]) has been intensively studied in the past few decades by observations, numerical modeling, and theories [2], most state-of-the-art coupled climate models are unable to simulate its salient features such as the coherent eastward propagation and the magnitude of intraseasonal convection [3,4]
Large-scale variations of the upper ocean surrounding the Cooperative Indian Ocean experiment on intraseasonal variability (CINDY)/Dynamics of the MJO (DYNAMO) arrays and locations of ship observations are described based on the satellite-derived data to provide a context for the future analysis of the data collected during the field campaign
The CINDY/DYNAMO international field program was designed to collect in situ observations for the purpose of advancing the understanding of MJO initiation processes and improving
Summary
While the Madden-Julian Oscillation (MJO; [1]) has been intensively studied in the past few decades by observations, numerical modeling, and theories [2], most state-of-the-art coupled climate models are unable to simulate its salient features such as the coherent eastward propagation and the magnitude of intraseasonal convection [3,4]. Large-scale variations of the upper ocean surrounding the CINDY/DYNAMO arrays and locations of ship observations are described based on the satellite-derived data to provide a context for the future analysis of the data collected during the field campaign. SST data on 0.25° × 0.25° grid from the blended product of satellite/in situ observations [20] are used to describe SST variability associated with the MJO events during CINDY/DYNAMO. We use the daily mean salinity, temperature, current and SST data from the buoy measurements These comparisons include near surface salinity data at three locations along 80.5°E (1.5°S, 4°S and 8°S) during fall 2011 when large subseasonal SSS variations associated with MJO events were observed
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