Numerical Study of Near‐Surface Jet in the Atmospheric Surface Layer Over an Oceanic Temperature Front

Abstract

The interaction between atmospheres and oceans plays an important role in the global climate. In a field experiment of atmospheric flows over the Gulf Stream, when the wind blew from the cold water to the warm water, we observed a near‐surface jet over the warm water. We then conducted direct numerical simulations and large‐eddy simulations of atmospheric turbulence in the vicinity of the front and captured the near‐surface jet in simulations for the first time. Analyses of the data obtained from the high‐resolution three‐dimensional simulations revealed the dominant generation mechanisms of the near‐surface jet, which are the strong vertical mixing by the enhanced streamwise rolls and the mean downward motion. Around the near‐surface jet, the magnitude of the negatively valued Richardson number significantly increases, indicating the dominance of buoyancy effects in the flow dynamics there. The development of the near‐surface jet suggests that the Monin‐Obukhov similarity theory (MOST) needs to be modified in representing marine atmospheric boundary layers over sea surface temperature fronts.