Atmospheric Response To The Spring Kuroshio Front Over The East China Sea And Its Mechanism

By using QuickSCAT, AVHRR, TRMM high resolution satellite data and CFSR reanalysis data, the pressure adjustment mechanism in the atmospheric response to the spring Kuroshio front (KF) in the East China Sea is investigated along with its interannual variability. Results show that the spring KF lies to the northwest of the Kuroshio warm tongue with a southwest-northeast orientation, which is parallel to the isobars of large-scale background SLP. The local SLP gradient between the warm water in the southeast of the KF (SE-KF) and the cold water in the northwest of the KF (NW-KF) will superimpose with the large-scale SLP background gradient, resulting in the resultant northwest-to-southeast SLP gradient reaching its maximum near the KF, and the 10-m vector wind speed thus being the strongest there. Due to the friction factor, such a vector wind will be NNE wind. The difference in component of NNE wind along (across) the KF will produce cyclonic shear vorticity (convergence in wind speed) over the SE-KF, thereby forming ascending motion and enhanced precipitation. In contrast, over the NW-KF, there is anticyclonic shear vorticity (divergence in wind speed) along (across) the KF and descending motion and weak rainfall. A secondary circulation across the KF is thereby induced.On interannual timescale, stronger (weaker) spring KF corresponds to greater (weaker) local SLP gradient between the NW- and SE-KF. The greater (weaker) local SLP gradient, superimposed with large-scale SLP background gradient, will produce stronger (weaker) NNE wind, thus making cyclonic shear vorticity, convergence in wind speed, ascending motion and precipitation all being stronger (weaker) over the SE-KF, and making anticyclonic shear vorticity, divergence in wind speed, and descending motion all being stronger (weaker) over the NW-KF, thus finally leading to stronger (weaker) secondary circulation across the KF. This indicates that the pressure adjustment mechanism still exists on interannual timescale.The vertical mixing mechanism can be explained by momentum and energy. Because of the strong air sea heat flux and air sea temperature and humidity difference at the warm zone of the SSTF, enhanced air sea instability, which enables the high momentum transfer from aloft, and increases sea surface wind eddy kinetic energy, making the scalar wind maximum at warm side of SSTF, meanwhile boundary layer height and buoyancy flux reach the maximum, accompanied by a strong in vapor transmission upward, which can provide favourable condition for the convective precipitation.The Kuroshio warm tongue has obvious interdecadal variation which is different from SSTF. On interdecadal timescale, stronger (weaker) Kuroshio corresponds to stronger (weaker) instability, which accompanied by stronger (weaker) air sea heat flux, water vapor transmission and buoyancy flux. The stronger (weaker) momentum transfer and EKE10m leading to the stronger (weaker) scalar wind speed. Stronger (weaker) Kuroshio warm tongue corresponds with the stronger (weaker) convective precipitation which indicates that the vertical mixing mechanism still exists on interdecadal timescale.