Effect of the Trans‐Volcanic Axis on meridional propagation of summer precipitation in western Mexico

Abstract

AbstractThe Trans‐Volcanic Axis (TVA)—comprising ridges and terrain elevations above 1,900 m—strongly affects meridional propagation of summer precipitation in western Mexico. This barrier modifies atmospheric moisture content and changes the annual precipitation cycle configuration, which distinguishes it from the precipitation cycle on both sides of the TVA. Using upper‐air observations and rainfall records, this study demonstrates that the TVA is the region where the North American monsoon (NAM) and the mid‐summer drought (MSD) influence intersections regarding precipitation. This region affects both northward extent of double precipitation maxima with the MSD and the southward extent of the NAM single precipitation peak. This study proposes that the forcing mechanism that controls the annual precipitation cycle in the TVA region relies on latent heat loss via ground cooling by reducing air temperature below dewpoint temperature in the 700–500 hPa layer, consistent with local terrain elevations. The orographic effect increases specific humidity in the atmospheric column—sufficiently large to enhance local precipitation accumulation—resulting in a mid‐summer drought intensity decline but not enough to yield a single peak in precipitation. Consequently, the TVA becomes an uncategorized region that does not display the NAM nor the characteristic features of the MSD.