Mobile Sampling of the North American Monsoon

A vehicle-mounted mobile observing system has been used to document seasonal and spatial patterns across the North American monsoon system and surroundings during summer of 2017. Long-distance transects between Texas and southern California were made during pre-monsoon (June 12-17) and active monsoon (July 23-August 1) periods. During the active monsoon transects, several areas of convective precipitation were intercepted. Additional transects were conducted between the California coast (at San Diego) and the Imperial Valley. The most pronounced local features and seasonal changes were noted in humidity variables. Mixing ratios within the monsoon domain increased roughly by a factor of three between June and July. In contrast, areas east of 102 W had lower mixing ratios in July than in June. Mesoscale peaks of mixing ratio around irrigation districts of southern California and Arizona were about double the value of surrounding deserts in both months. Details of thermal and moisture structure were noted in relation to thunderstorm and stratiform rain areas, mainly in Arizona and New Mexico.