Diurnal and Longitudinal Variations in Tropical Easterly Wave Structures

While tropical easterly waves (TEWs) can, at their simplest, be characterized by a westward-propagating low-level cyclonic circulation, structural variability exists between waves across the world’s tropical oceanic basins. By grouping points along objectively-defined TEW tracks into 15° wide longitude bands, we are able to illustrate differences in wave structure across the tropics, and also examine the diurnal cycle in each latitude band. Currently, there has not been a large, systematic comparison of easterly wave structures across the tropics. There are also few comparisons of how TEW structure and precipitation varies diurnally across different regions. Better understanding of TEW structure across the tropics may improve identification and forecasting of TEWs and associated precipitation. For all longitude bands, rain rate composites show the highest rainfall in the hours nearest local sunrise. However, the magnitude and spatial distribution of greatest rain rates varies across longitude bands. While clear diurnal variations are evident in the composite precipitation structure surrounding TEWs, initial analysis using a small subset of years shows less diurnal variation in vertical cross sections of zonal wind. However, clear differences in vertical structure exist when comparing between longitude bands, even within the same ocean basin. For example, in the eastern North Atlantic, zonal cross sections of zonal wind through TEW centers maximize easterly wind between 850 and 600 hPa, while in the western North Atlantic, these maxima are below 850 hPa. Similar changes in height and vertical depth of the cyclonic circulation can be seen in meridional cross sections of zonal wind. The different wind and precipitation structures seen for TEWs across different longitudes imply that TEWs in different regions rely on different dynamic and thermodynamic processes, something that has been previously suggested, but not fully explored across the tropics. We plan to extend our analysis with meridional wind, specific humidity, and vertical velocity, to better understand the processes occurring in TEWs across the tropics.