Abstract
The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely been observed. Here, we present upper-ocean turbulence data that provide evidence for a strongly elevated vertical diffusive heat flux across the base of the mixed layer in the presence of a NIW, thereby cooling the mixed layer at a rate of 244 W m−2 over the 20 h of continuous measurements. We investigate the seasonal cycle of strong NIW events and find that despite their local intermittent nature, they occur preferentially during boreal summer, presumably associated with the passage of atmospheric African Easterly Waves. We illustrate the impact of these rare but intense NIW induced mixing events on the mixed layer heat balance, highlight their contribution to the seasonal evolution of sea surface temperature, and discuss their potential impact on biological productivity in the tropical North Atlantic.
Highlights
The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely been observed
The ePIRATA product contains daily averages of several terms in the heat balance, including net surface longwave radiation, shortwave radiation absorbed in the mixed layer (ML), air–sea turbulent heat fluxes, horizontal advection, and ML heat storage rate
The largest terms from the ePIRATA heat balance are shortwave radiation absorbed in the ML, net outgoing longwave radiation and the latent heat flux
Summary
The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely been observed. Deviations from the mean seasonal cycle of SST result in variations of the position and strength of the rainfall belt impacting, e.g., the onset of the West African Monsoon[3,4] or droughts over Northeast Brazil[5,6]. The prediction of such rainfall variability or other tropical climate extremes such as tropical cyclones is essential for countries surrounding the tropical. Models have severe difficulties simulating realistic biological productivity and biogeochemical cycles, including chlorophyll a distribution[12], which are potentially related to biases in SST and ITCZ representation[13,14]
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