Atmospheric pressure response to mesoscale sea surface temperature variations in the Kuroshio Extension region: In situ evidence

Several research cruises were conducted across the Kuroshio Extension front to examine the low-level atmospheric responses to mesoscale variations in sea surface temperature (SST). Surface meteorological observations, including sea level pressure (SLP) and SST, were collected at two moored buoys that were located on either side of the Kuroshio Extension, and from a research vessel, as it moved between the two buoys during the various cruises. Spatial perturbations in SLP along the ship transects, calculated by subtracting moored-buoy SLP from that of the moving ship, tend to be positive (negative) where SST is lower (higher) on spatial scales of about 100 km, and the magnitude of these SLP perturbations near the SST front can exceed 1.0 hPa. Radiosonde data also show that the atmospheric boundary layer thins (thickens) over lower (higher) SST. Although the contribution of across-track component in the wind cannot be calculated, the along-track component of divergence suggests low-level convergence over higher SST. The thermally induced pressure gradient is important in the momentum budget, suggesting that sea breeze-like local circulations formed over the SST fronts. Indeed, the pressure adjustment mechanism can sometimes dominate even on a scale of 100 km, although it is not always observed. The time scale in which the boundary layer thickness adjusted to SST is estimated to be 1 day or less.