간단화된 엘니뇨 모형에서의 동서 바람응력의 공간 분포에 대한 엘니뇨 특성 변화 연구

Abstract

The sensitivity of ENSO characteristics to spatial patterns of zonal wind stress in a linear coupled two-strip model is examined. The two-strip model based on recharge oscillator theory describes Kelvin wave and Rossby wave signals along the equatorial and off-equator strip, respectively. Two sets of sensitivity experiments were conducted using the model, the first one focused on how the zonal location of the zonal wind stress pattern modulates ENSO growth rate, and the second one focused on the relation between the meridional width of the pattern and ENSO period. In order to understand how the location modulates the ENSO stability, the first sensitivity experiment is conducted, and the results are analyzed using Bjerknes stability index (BJ index) which quantifies the growth rate of ENSO. The experiment demonstrates that the growth rate of ENSO and BJ index increase as the zonal wind stress moves to the east. The eastward shifted zonal advection and Ekman feedbacks due to shifted zonal wind are responsible for the increasing growth rate. The increasing sensitivity of the eastern thermocline depth anomaly to the zonal wind is another reason which enhances the thermocline feedback on eastern Pacific. The second experiment was designed to examine how the meridional width influences the ENSO cycle. The experiment demonstrates that the narrow (broad) pattern leads the short (long) ENSO period. This result was explored through the viewpoint of the recharge oscillator framework. By reducing the ocean wave equation to a two-box approximation in the model, it comes to be clear that the meridional width of the pattern can modulate the efficiency of discharging-recharging process of ocean heat content.