Upscale and downscale energy transfer over the tropical Pacific revealed by scatterometer winds

16 pages, 12 figures, 1 tableThe direction of the energy cascade in the mesoscales of atmospheric turbulence is investigated using near-surface winds over the tropical Pacific measured by satellite scatterometers SeaWinds (QuikSCAT) and ASCAT (MetOp-A). The tropical Pacific was subdivided into nine regions, classified as rainy or dry. Longitudinal third-order along-track structure functions DLLLa and skewness SLa were calculated as a function of separation r for each region and month during the period November 2008 to October 2009. We find that the results support both downscale and upscale interpretations, depending on region and month. The results indicate that normally energy cascades downscale, but cascades upscale over the cold tongue in the cold season and over the west Pacific in summer months. An explanation is offered based on the heating or cooling of the air by the underlying sea surface temperature. It is also found that the signature of intermittent small-scale (