Observational investigation of relationships between moisture surges and mesoscale‐ to large‐scale convection during the North American monsoon

Abstract

ABSTRACTThis article consists of a comprehensive climatological study of moisture surges (MSs) in the North American monsoon (NAM) core region using a multiyear (1990–2006) set of surges, surface and upper air data, satellite‐estimated mesoscale convective systems (MCSs), and North American Regional Reanalysis (NARR) products. Composites of surges are created with respect to MCSs occurrence in the NAM core region. MSs are further stratified based on co‐occurrence with tropical easterly waves and tropical storms/tropical cyclones. These results provide new insights into the nature of the Gulf of California (GoC) moisture flux variability and describe the influence of these multi‐scale processes on the occurrence and intensity of surges and the GoC diurnal circulations – especially the Gulf of California low‐level jet (GCLLJ). Results show that over the GoC Coastal Plain, MCSs modulate the diurnal cycle of the GoC low‐level circulation during ‘major surge’, ‘minor surge’, and ‘non‐surge’ environments. We found that MCS activity enhances the offshore flow along the eastern GoC coast, which then enhances the GCLLJ. On the other hand, immediately before major surges onset, the occurrence of MCSs over the southern GoC produces more intense surges. It is also shown that this relationship holds regardless of the intensity and type of tropical synoptic‐scale disturbance forcing the surge.