A global climatology of tropical easterly waves

Tropical easterly waves (TEWs) are westward-propagating off-equatorial waves that are typically convectively coupled. TEWs make significant contributions to the annual rainfall in many regions of the tropics, and often seed tropical cyclones. Climatologies of TEWs exist regionally and hemispherically, however, none exist at the global scale. The climatology in this study is the first attempt to study TEWs globally, applying a combination of the TRACK algorithm and objective criteria to all basins to identify TEW activity at both 850 and 700 hPa. In addition to areas of TEW activity in previously studied regions such as the North Atlantic and eastern North Pacific Ocean basins, this study has identified TEW activity in every other tropical ocean basin in both hemispheres. On average across the globe, the methods employed tracked 380 waves per year at 850 hPa and 638 waves per year at 700 hPa. There were no significant linear trends globally or hemispherically over the 41 years analyzed, but large interannual variability. Despite the variety of regions the TEWs occur in, the distribution of average speeds agrees with studies using other data and tracking methods, with averages between 7.5-8 m s-1 depending on the level and hemisphere. TEW activity shows a strong preference to the warm season, with approximately double the number of TEWs occurring in the warm season compared to the cold season, a pattern that is observed in both the northern and southern hemispheres. This database is publicly available to enable further work in understanding TEW behavior and predictability globally.

Automated summary

This study is the first attempt to investigate the climatology of tropical easterly waves (TEWs) globally. The results show that TEW activity exists in every tropical ocean basin and has a strong preference for the warm season. No significant linear trends were found globally or hemispherically, but large interannual variability was observed.