In-situ Observed Atmospheric and Oceanic Variations over Seychelle-Chagos Thermocline Ridge during CINDY/DYNAMO

To investigate the detailed nature and mechanism of the intraseasonal variations, especially Madden-Julian Oscillation (MJO), over the Indian Ocean, the project Cooperative Indian Ocean experiment on intraseasonal variability in the Year 2011 / the Dynamics of the Madden-Julian Oscillation (CINDY/DYNAMO) was carried out in the boreal autumn and winter of 2011/2012. As a component of CINDY/DYNAMO, we deploy the research vessel "Mirai" was stationed at 8S, 80E for two months in October and November in 2011 at (8S, 80E). The stationary observation at the southeastern corner of the CINDY/DYNAMO sounding array reveals the atmospheric and oceanic variation over the Seychelle-Chagos Thermocline Ridge (SCTR).

The principal component of the observation was a 3-hourly cycle of observations. One cycle consists of one radiosonde launch, one conductivity - temperature - depth - oxygen (CTDO) profiling to 500m depth (to 1000m once in a day), two oceanic microstructure profilings to 300m depth, and one upwind cruise for the atmospheric turbulent flux measurement. A lowered acoustic Doppler current profiler (LADCP) was also attached to the CTDO unit to obtain a high vertical resolution measurement of the ocean currents. The continuous observations by scanning C-band Doppler radar, 95-GHz vertically-pointing radar, and multi-spectral lidars captured a vast range of the cloud systems in detail. Sea surface temperaturewas measured by aninfrared radiometer for skin, a floating thermistor for surface centimeters, andthe ship's water intake for 5m depth. A number of CFH water vapor sondes were launched occasionallyon sunnydays.

The two-month period from September 30th started with intermittent rainy days. From the middle of October, extremely dry conditions (40 mm or less in precipitable water) prevailed. The precipitable water, CAPE and radar echo area gradually recovered in November. In the ocean, a gradual deepening of the mixed layerand thermocline was observed in October, while in November there was a strong barrier layer. A diurnal warm layer was also observed in much of the observation period.