Observations from two new spaceborne microwave instruments in 1999 clearly reveal the atmospheric manifestation of tropical instability waves north of the Pacific equatorial cold tongue. A unique zonal-temporal band-pass filter enables the isolation of the propagating signals and the determination of their phase differences. The phase differences between the propagation of wind and sea surface temperature (SST) signals observed from space and the vertical wind profiles measured from a research ship are consistent with the hypothesis that the coupling between wind and SST is caused by buoyancy instability and mixing, which reduces the wind shear in the atmospheric boundary layer. The coupling causes higher evaporative cooling over the warm phase and infers a negative thermal feedback. ¿ 2000 American Geophysical Union