Surface Wind Minimum Along The SST Fronts And The Pressure Adjustment Mechanism

By using QuickSCAT and AVHRR high resolution satellite data and CFSR reanalysis data,the atmospheric response to the SST fronts (SSTFs) in the Gulf Stream (GS), the East China Sea Kuroshio (ESK), the Brazil-Malvinas Confluence (BMC) and the Agulhas Return Current (ARC) is investigated. The minimum surface wind is found to be universal along the above SSTFs. And conditions of this phenomenon, formation mechanism and influence factors are discussed in this paper.The results showed that the minimum surface wind which along the above SSTFs occurs in JJA for the GS, June for ESK, year-round both for the BMC and ARC. The condition for generating the minimum surface wind is that the warmer (colder) side of the SSTFs correspond to the high (low) large-scale sea level pressure (SLP). This can be explained as follows according to the SLP adjustment mechanism (SAM):under the above conditions, the warmer (colder) side of the SSTFs will produce lower (higher) SLP, and such a local SLPG will counteract with the large-scale SLPG, thus leading to the minimum resultant SLPG as well as the minimum surface wind along the fronts. Furthermore, the surface wind will turn to the lower SLP side due to the friction. The difference between components of surface wind along (across) the fronts will produce cyclonic shear vorticity (convergence in wind speed) over the warmer side of the fronts, thereby forming ascending motion and enhanced precipitation there. The atmospheric response is opposite to that over the colder side of the fronts. In addition, the response characteristics of the above exists on daily timescale.The intensity of SSTFs and large-scale SLPG have effects on the minimum surface wind along the above SSTFs on the interannual time scale. For the years of stronger SSTFs and the years of weaker large-scale SLPG both induce weaker surface wind above the SSTFs. And v. v.Not only the minimum surface wind along the above SSTFs is universal, but also the significant levels in this phenomenon also express regional and seasonal differences. Overall, the most significant of this phenomenon occurs on ESK and least on BMC. On month scale, the most significant minimum surface wind alone the above SSTFs occurs on June for BMC, and the least significant phenomenon appears on October for GS.