Abstract.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 bandpass 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.
[1] The high-resolution wind vectors observed by the space-based scatterometer QuikSCAT, from 1999QuikSCAT, from to 2002 show that the double intertropical convergence zones (ITCZ) exist in the Atlantic and the eastern Pacific oceans for most of the annual cycle, and are far more extensive than previously recognized. For most of the time, the southern ITCZ is weaker than the northern one. The stronger ITCZ occurs when the northerly trade winds meet the southerly trade winds over warm water, resulting in deep convection. The weaker ITCZ over cooler water is caused by the deceleration of the surface winds as they approach the cold upwelling water near the equator. Decreases in vertical mixing and increases in vertical wind shear in the atmospheric boundary layer are suggested to be the causes of the deceleration of the trade winds as they move from warmer to colder water.
[1] Probability distribution and power density of wind speed over global oceans are computed from eight years of QuikSCAT measurements. They describe the variation and higher moments of wind speed that are critical in relating the non-linear effects of wind on electric power generation capability, shipping hazard, and air-sea exchanges in heat, water, and greenhouse gases. The power density distribution confirms our general knowledge of atmospheric circulation related to mid-latitude storm tracks, trade winds, and monsoons. It also reveals regions of high wind power associated with flow distortion by land, wind channeled by land topography, and buoyancy effect on turbulent stress driven by ocean fronts.
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