ALBERT

Description: The Pacific Walker circulation variability is associated with El Niño-Southern Oscillation and Interdecadal Pacific Oscillation and affects the global climate. The Walker circulation has strengthened since the comprehensive satellite observations began. This trend apparently contradicts with climate model simulations driven by historical radiative forcing, which show its weakening. Regarding this model-observation inconsistency, recent studies argue the influence of biases in the South Pacific and Southern Ocean. In the present study, we examine the remote influence of extratropical SST variability on the Pacific Walker circulation by extratropical ocean pacemaker experiments with a climate model. Restoring SST variability toward observations poleward of 15º latitudes in the Pacific (with a linearly tapering buffer zone between 10º and 15º) greatly constrains the Walker circulation variability in the interannual to multidecadal time scales. This extratropical pacemaker effect remains, albeit weaker, if the restoring region is limited to poleward of 25º latitudes. These results suggest the importance of subtropical and midlatitude SST variability in attributing, predicting, and projecting the Walker circulation changes.

Description: The magnetosphere-ionosphere coupled convection is affected by the magnetic field configuration which is derived from the null-separator structure. In the present talk, we will investigate the interaction in detail from the numerical results of the global MHD simulation. The main findings of this research are as follows; The null-separator structure in the vacuum field forms a torus and two cylinders [Lau and Finn, 1990]. In the solar wind environment, as the two cylinders bend toward the magnetic equatorial plane on the night side, the anti-parallel magnetic field lines appear in the equatorial plane. However, these anti-parallel field lines can not merge because there is no null point in the equatorial plane of the tail magnetosphere. Therefore, the closed field lines must occupy the region between the two cylinders. This is the formation of the plasma sheet. The cylinder accompanies the open slot from the tail magnetosphere to the solar wind in the magnetotail. Plasmas and electromagnetic energy of the solar wind can intrude the tail magnetosphere through the slot. Furthermore, the plasmas entering through the slot create a plasma bulge in the magnetotail. In the northern hemisphere of the negative IMFBy condition, the Poynting flux passing the dayside magnetopause in the morning / afternoon side of the separator line enters the inner magnetosphere / escapes from the magnetosphere through the magnetotail. This behavior is associated with the magnetic field configuration of the null-separator structure. Lau, Y.-T. and Finn, J. M. (1990), Astrophysical Journal, 350, 672-691.