The Annual Cycle of Air-Sea Fluxes in the Northwest Tropical Atlantic

Abstract

In this article we analyze 11 years of near-surface meteorology using observations from an open-ocean surface mooring located in the Northwestern Tropical Atlantic (51°W, 15°N). Air-sea fluxes of heat, freshwater, and momentum are derived from these observations using the Coupled Ocean–Atmosphere Response Experiment (COARE) bulk parameterization. Using this dataset, we compute a climatology of the annual cycle of near-surface meteorological conditions and air-sea fluxes. These in situ data are then compared with three reanalyses: the National Centers for Environmental Prediction-Department of Energy [NCEP-DOE (hereafter referred to as NCEP-2)], the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim and the Modern-Era Retrospective analysis for Research and Applications, version 2 (MERRA-2) reanalyses. Products from the Clouds and the Earth’s Radiant Energy System (CERES) and the Tropical Rainfall Measuring Mission (TRMM) are also used for comparison. We identify the agreements and characterize the discrepancies in the annual cycles of meteorological variables and the different components of air-sea heat fluxes (latent, sensible, shortwave, and longwave radiation). Recomputing the reanalyses fluxes by applying the COARE algorithm to the reanalyses meteorological variables results in better agreement with the in situ fluxes than using the reanalyses fluxes directly. However, the radiative fluxes (longwave and shortwave) from some of the reanalyses show significant discrepancies when compared with the in situ measurements. Longwave radiation from MERRA-2 is biased high (too much oceanic heat loss), and NCEP-2 longwave does not correlate to in situ observations and other reanalyses. Shortwave radiation from NCEP-2 is biased low in winter and does not track the observed variability in summer. The discrepancies in radiative fluxes versus in situ fluxes are explored, and the potential regional implications are discussed using maps of satellite and reanalyses products, including radiation and cloud cover.

Strong cloud–circulation coupling explains weak trade cumulus feedback

“…The ERA5 fluxes, however, overestimate the surface buoyancy flux compared with the sonde-derived flux by 25%, which is mostly because of the overestimation of the sensible heat flux by 64% relative to the observations (9.8 W m −2 and 6.0 W m −2 for ERA5 and dropsondes, respectively). A strong overestimation of the sensible heat flux compared with buoy measurements in the region is also present in the predecessor ERA-Interim reanalysis 55 . Overall, the good correspondence of our sonde-derived surface buoyancy flux with the independent data lends credibility to our estimation procedure.…”

EUREC<sup>4</sup>A

“…As highlighted by Bodenschatz et al (2010), the range of scales, from micro-to megameters, that clouds encompass has long been one of their fascinating aspects. Measurements made during EUREC 4 A quantified, for the first time, the main processes that influence trade wind clouds across this full range of scales.…”