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Matthews, AJ, Baranowski DB, Heywood KJ, Flatau PJ, Schmidtko S.  2014.  The surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO. Journal of Climate. 27:9101-9122.   10.1175/jcli-d-14-00222.1   AbstractWebsite

A surface diurnal warm layer is diagnosed from Seaglider observations and develops on half of the days in the Cooperative Indian Ocean Experiment on Intraseasonal Variability/Dynamics of the Madden-Julian Oscillation (CINDY/DYNAMO) Indian Ocean experiment. The diurnal warm layer occurs on days of high solar radiation flux (>80 W m(-2)) and low wind speed (<6 ms(-1)) and preferentially in the inactive stage of the Madden-Julian oscillation. Its diurnal harmonic has an exponential vertical structure with a depth scale of 4-5m (dependent on chlorophyll concentration), consistent with forcing by absorption of solar radiation. The effective sea surface temperature (SST) anomaly due to the diurnal warm layer often reaches 0.8 degrees C in the afternoon, with a daily mean of 0.2 degrees C, rectifying the diurnal cycle onto longer time scales. This SST anomaly drives an anomalous flux of 4Wm(-2) that cools the ocean. Alternatively, in a climate model where this process is unresolved, this represents an erroneous flux that warms the ocean. A simple model predicts a diurnal warm layer to occur on 30%-50% of days across the tropical warm pool. On the remaining days, with low solar radiation and high wind speeds, a residual diurnal cycle is observed by the Seaglider, with a diurnal harmonic of temperature that decreases linearly with depth. As wind speed increases, this already weak temperature gradient decreases further, tending toward isothermal conditions.