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Wind Speed Influences Sea Surface Temperature Anomalies in the Tropical North Atlantic

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Wind Speed Influences Sea Surface Temperature Anomalies in the Tropical North Atlantic

A CPO-funded study found that wind speed variability associated with the Atlantic Meridional Mode contributes to anomalies in sea surface temperatures in the eastern equatorial Atlantic and the Intertropical Convergence Zone region. An early version of the study’s paper was published in the Journal of Climate. 

Researchers analyzed sea surface temperature anomalies of the North Atlantic during 1982-2015 using satellite data, ocean and atmosphere reanalysis, and in situ measurements. Their analysis focused on anomalous sea surface cooling events in 2009 and 2015, as well an anomalous warming in 2010.

The paper states that the temperature anomalies in 2009, 2015, and 2010 may be related to pre-existing sea surface temperature irregularities along the equatorial region of the central tropical Atlantic. The paper also states it is important to study the observed anomalies in the tropical North Atlantic, considering that the strong cooling in 2009 led to severe flooding in Northeast Brazil and the anomalous warming in 2010 and 2015 resulted in normal rainfall.

Funded by the CPO’s Climate Observation Division, this research was led by researchers at the University of Colorado Boulder, the NOAA Atlantic Oceanographic and Meteorological Laboratory, and the Cooperative Institute for Marine and Atmospheric Studies.

Abstract:

This study examines the causes of observed sea surface temperature (SST) anomalies in the tropical North Atlantic between 1982 and 2015. The emphasis is on the boreal winter and spring seasons, when tropical Atlantic SSTs project strongly onto the Atlantic Meridional Mode (AMM). Results from a composite analysis of satellite and reanalysis data show important forcing of SST anomalies by wind-driven changes in mixed layer depth and shortwave radiation in the deep tropics (5°S–10°N), in addition to the well-known positive wind-evaporation-SST and shortwave radiation-SST feedbacks between 5°N–20°N. Anomalous surface winds also drive pronounced thermocline depth anomalies of opposite signs in the eastern equatorial Atlantic and intertropical convergence zone (ITCZ, 2°N–8°N). A major new finding is that there is strong event-to-event variability in the impact of thermocline depth on SST in the ITCZ region, in contrast to the more consistent relationship in the eastern equatorial Atlantic. Much stronger anomalies of meridional wind stress, thermocline depth, and vertical turbulent cooling are found in the ITCZ region during a negative AMM event in 2009 compared to a negative event in 2015 and a positive event in 2010, despite SST anomalies of similar magnitude in the early stages of each event. The larger anomalies in 2009 led to a much stronger and longer-lived event. Possible causes of the inconsistent relationship between thermocline depth and SST in the ITCZ region are discussed, including the preconditioning role of the winter cross-equatorial SST gradient.    

 
Access the paper: http://dx.doi.org/10.1175/JCLI-D-15-0867.1