Widening of the tropics in global surface-air winds

An analysis of a dataset originally constructed to provide a boundary condition for oceanographic modeling reveals widening of the tropics. On the poleward side of the edges of the atmospheric Hadley cells, the surface air wind veers eastward while on the equatorial side it veers westward because of the Coriolis force, thereby making the latitude where the zonal mean zonal wind in the surface air is zero a robust indicator of the Hadley cell edges. We have detected a trend in the latitudes of those wind nulls over the world's oceans in the Cross-Calibrated Multi-Platform (CCMP) surface air wind dataset and found that the tropics have widened by [Formula: see text] from 1995 through 2024, mostly in the northern hemisphere and mostly in autumn and winter. The CCMP dataset is particularly well suited to detecting widening of the tropics because of the simple physics of the proxy and its dense, global, and continuous sampling. Climate models reproduce the widening well in the southern hemisphere but not as significantly in the north, with repercussions for future desertification, especially in North America.