Si. An et Is. Kang, Sensitivity of the equatorial air-sea coupled system to the zonal phase difference between SST and wind stress, ADV ATMOS S, 18(2), 2001, pp. 155-165
An eigen analysis of the equatorial air-sea coupled model is carried out to
understand the mechanism of the slowly varying mode for various zonal phas
e differences between SST and wind stress. The frequency and growth rate of
the slow mode highly depend on the zonal phase difference between SST and
wind stress anomalies and the wave scale. For ultra-long waves longer than
20,000 km, the system propagates westward regardless of the position of win
d stress. However, for the long waves observed in the Pacific, the slow mod
e tends to propagate eastward when the SST and wind stress anomalies are cl
ose to each other (within a quadrature phase relationship). On the other ha
nd, when the wind stress is located far away from SST, the slow mode tends
to propagate westward. The coupled system produces the unstable modes when
the westerly (easterly) wind stress is located in the west of warm (cold) S
ST. It is noted that for the Pacific basin scale, the eastward propagating
unstable waves can be produced when the wind stress is located to the west
of SST with a few thousand kilometer distance. Also examined in the present
study is the relative role of the thermocline displacement and zonal advec
tion effects in determining the propagation and instability of the coupled
system.