Ocean Surface Current Effects on the Tropical Atmospheric Circulation in DYNAMO Hindcasts with the Navy Earth System Model

Ocean surface currents modify the wind shear at the surface, and thus directly impact air-sea fluxes. In the Navy Earth System Model (NESM), which is under development as part of the National Earth System Prediction Capability program, the Navy Global Environmental Model (NAVGEM) and the Hybrid Coordinate Ocean Model (HYCOM) both account for this surface current effect in their implementation of a modified version of the COARE 3.0 air-sea flux scheme. Recent improvements in the NESM representation of the MJO in hindcasts of the DYNAMO campaign period in fall 2011 make possible a look at the impacts of the surface current/flux connection in extended range NESM MJO hindcasts. The presentation will show results of small-ensemble sensitivity tests, including the diagnosed direct impact of currents on air-sea fluxes, as well as resultant effects on the atmospheric circulation. Impacts on surface latent heat fluxes in some areas exceed 10 W m-2. Preliminary results suggest that the most significant impact on MJO development for this period derives from enhancement of an equatorial jet in the Indian Ocean during the westerly wind burst that occurred in association with the second MJO event. Impacts of ocean surface currents on the broader tropical circulation in the hindcasts will also be examined.