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Delman, AS, McClean JL, Sprintall J, Talley LD, Bryan FO.  2018.  Process-specific contributions to anomalous Java mixed layer cooling during positive IOD events. Journal of Geophysical Research-Oceans. 123:4153-4176.   10.1029/2017jc013749   AbstractWebsite

Negative sea surface temperature (SST) anomalies associated with positive Indian Ocean Dipole (pIOD) events first appear in the seasonal upwelling zone along the southern coast of Java during May-July. The evolution of anomalous SSTs in this coastal region is analyzed by computing a temperature budget using output from a strongly eddy-active ocean general circulation model. The seasonal cooling south of Java in May-July is driven by a reduction in incoming shortwave radiation and by vertical mixing, consistent with earlier studies in the region; however, the model budget also shows an advective contribution that drives anomalous cooling at the onset of pIOD events. To identify which process(es) are responsible for the anomalous advective cooling during pIOD events, a novel process index regression method is used to estimate the contributions of wind stress, equatorial Kelvin waves, mesoscale eddies, and Lombok Strait flow to anomalous cooling south of Java. Using this method, wind stress forcing along the west coast of Sumatra is found to make the most substantial contribution to anomalous cooling south of Java, with lesser contributions from equatorially sourced Kelvin waves and local wind stress. Mesoscale eddies redistribute heat from the Lombok Strait outflow, and have an anomalous warming effect on the eastern side of the upwelling region. The process-specific temperature budget south of Java highlights the importance of wind stress forcing west of Sumatra relative to equatorial and local forcing, and explains most of the mixed layer temperature anomaly evolution associated with advection during pIOD events. Plain Language Summary Climate variations from year to year in much of the Indian Ocean region are controlled by a phenomenon called the Indian Ocean Dipole, which is similar to El Nino but centered on the Indian Ocean basin. The positive phase of the Indian Ocean Dipole, or pIOD, typically brings drought conditions to Indonesia and unusually heavy rainfall to east Africa. These pIOD events are caused in part by unusually strong cooling in sea surface temperatures south of the Indonesian island of Java, but the series of events that causes this strong cooling has not been well understood previously. This paper uses the results obtained from a high-resolution ocean model, together with a new method for analyzing these results, to study exactly how much sea surface cooling (or warming) is caused by specific processes in the Java region. The study finds that changes in wind patterns adjacent to the Indonesian island of Sumatra can explain nearly all of the unusual cooling that develops south of Java in years when these pIOD events happen. The analysis method introduced in this paper may be adapted to study how processes in the ocean or atmosphere cause changes in the Earth's climate system.

Ogle, SE, Tamsitt V, Josey SA, Gille ST, Cerovecki I, Talley LD, Weller RA.  2018.  Episodic Southern Ocean heat loss and its mixed layer impacts revealed by the farthest south multiyear surface flux mooring. Geophysical Research Letters. 45:5002-5010.   10.1029/2017gl076909   AbstractWebsite

The Ocean Observatories Initiative air-sea flux mooring deployed at 54.08 degrees S, 89.67 degrees W, in the southeast Pacific sector of the Southern Ocean, is the farthest south long-term open ocean flux mooring ever deployed. Mooring observations (February 2015 to August 2017) provide the first in situ quantification of annual net air-sea heat exchange from one of the prime Subantarctic Mode Water formation regions. Episodic turbulent heat loss events (reaching a daily mean net flux of -294W/m(2)) generally occur when northeastward winds bring relatively cold, dry air to the mooring location, leading to large air-sea temperature and humidity differences. Wintertime heat loss events promote deep mixed layer formation that lead to Subantarctic Mode Water formation. However, these processes have strong interannual variability; a higher frequency of 2 sigma and 3 sigma turbulent heat loss events in winter 2015 led to deep mixed layers (>300m), which were nonexistent in winter 2016.

Holte, J, Talley LD, Gilson J, Roemmich D.  2017.  An Argo mixed layer climatology and database. Geophysical Research Letters. 44:5618-5626.   10.1002/2017gl073426   AbstractWebsite

A global climatology and database of mixed layer properties are computed from nearly 1,250,000 Argo profiles. The climatology is calculated with both a hybrid algorithm for detecting the mixed layer depth (MLD) and a standard threshold method. The climatology provides accurate information about the depth, properties, extent, and seasonal patterns of global mixed layers. The individual profile results in the database can be used to construct time series of mixed layer properties in specific regions of interest. The climatology and database are available online at . The MLDs calculated by the hybrid algorithm are shallower and generally more accurate than those of the threshold method, particularly in regions of deep winter mixed layers; the new climatology differs the most from existing mixed layer climatologies in these regions. Examples are presented from the Labrador and Irminger Seas, the Southern Ocean, and the North Atlantic Ocean near the Gulf Stream. In these regions the threshold method tends to overestimate winter MLDs by approximately 10% compared to the algorithm.