The east Pacific ITCZ appears as a band of persistent cloudiness between roughly 10°S and 10°N, depending on the season. The annual cycle in solar insolation tends to dominate the annual variability in the east Pacific convection, with a dominant amplitude in the northern hemisphere. The tropical ITCZs constitute the upward branch of the Hadley circulation, which transports heat, moisture and momentum out of the tropics, to the midlatitudes, making them a primary driver of global climate. The wind stress curl in the east Pacific ITCZ also forces upwelling in the ocean at this location, and establishes the transition between the westward moving north equatorial current (NEC) and the eastward moving north equatorial counter current (NECC). The upwelling is strongest in boreal fall when the zonal wind stress curl has a distinct maximum and the trades have a distinct minimum around 10°N. This region is additionally distinguished as the most prolific producer of tropical cyclones per unit area in the world, with on average nine of these cyclones reaching hurricane strength each year.
The atmosphere in the east Pacific ITCZ is comprised largely of convectively coupled westward propagating synoptic waves. Our primary objective is to investigate the role of synoptic variability in deter- mining the location and seasonality of the east Pacific ITCZ, and any coupled or one- way interactions with the underlying SST. We will investigate the seasonal and interannual modulation of these waves in the atmospheric boundary layer, sea surface temperature, and upper ocean stability and mixing processes. As the SST has significant seasonal and interannual variability in this region, we will also investigate potential feedbacks between the SST and synoptic waves on these same time scales. Our overall intent is to investigate the consequences for air-sea coupling given the generally accepted view that the ITCZ is comprised of convectively coupled synoptic-scale disturbances.