The surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO

TitleThe surface diurnal warm layer in the Indian Ocean during CINDY/DYNAMO
Publication TypeJournal Article
Year of Publication2014
AuthorsMatthews A.J, Baranowski D.B, Heywood K.J, Flatau P.J, Schmidtko S.
JournalJournal of Climate
Volume27
Pagination9101-9122
Date Published2014/12
Type of ArticleArticle
ISBN Number0894-8755
Accession NumberWOS:000346055900007
Keywordsconvection; cycle; in-situ; intraseasonal oscillations; madden-julian oscillation; measuring mission; temperature; toga-coare; trmm; variability; western equatorial pacific
Abstract

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.

DOI10.1175/jcli-d-14-00222.1
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