On the Mechanisms Driving Latent Heat Flux Variations in the Northwest
Tropical Atlantic
Abstract
The Northwest Tropical Atlantic (NWTA) is a region with complex surface
ocean circulation. The most prominent feature is the North Brazil
Current (NBC) and its retroflection at 8ºN that leads to the formation
of numerous mesoscale eddies known as NBC rings. The NWTA also receives
the outflow of the Amazon River, generating freshwater plumes that can
extend up to 100,000 km2. These two processes affect the spatial
variability of the region’s surface latent heat flux (LHF). First, the
presence of surface freshwater modifies the vertical stratification of
the ocean limiting the amount of heat that can be released to the
atmosphere. Second, they create a highly heterogeneous mesoscale
sea-surface temperature (SST) field that directly influences
near-surface atmospheric circulation. These effects are illustrated byd from the ElUcidating the RolE of Cloud-Circulation Coupling
in ClimAte - Ocean Atmosphere (EUREC4A-OA) and Atlantic
Tradewind Ocean-Atmosphere Interaction Campaign (ATOMIC) experiments,
satellite and reanalysis data. We decompose the LHF budget into several
terms controlled by different atmospheric and oceanic processes to
identify the mechanisms leading to LHF changes. We find LHF variations
of up to 160 W m2, of which 100 W m2 are associated with
wind speed changes and 40 W m2 with SST variations. Surface
currents or stratification-change associated heat release remain as
second-order contributions with LHF variations of less than 10 W
m2 each. Although this study is limited by the paucity of
collocated observations, it highlights the importance of considering
these three components to properly characterize LHF variability at
different spatial scales.