Relationships between Gulf of California moisture surges and mesoscale convection derived from multi-year GOES imagery archives and North American Regional Reanalysis data

This presentation describes the influence of organized convective activity in modulating the intensity of moisture surges over the Gulf of California (GoC) using a multiyear set of surge events. Understanding the role that both the synoptic-scale and mesoscale convective systems (MCS's) play in modifying moisture surges is crucial to improve both short-term and intra-seasonal forecasting in the region. This study systematically diagnoses the effect of convective activity over the eastern Pacific and the southern GoC on the development of Gulf of California moisture surges.

A surge classification technique is first developed to identify surge events based on their triggering mechanisms and their convective activity signature along the GoC. The forcing of the surges is then identified from independent data sets. Tropical Easterly Waves (TEW) events emanating from the Gulf of Mexico and Caribbean Sea are identified using North American Regional Reanalysis (NARR) 700 hPa meridional wind component variations over the eastern Pacific; significant tropical cyclones (TCs) in the eastern Pacific are tracked using National Hurricane Center data; and the occurrence of organized convection in the form of MCSs have been identified by using cloud top temperature thresholds from 10 km International Satellite Cloud Climatology Project (ISCCP) products. Surges are stratified according to their synoptic forcing type – either by TEWs or TCs, and also by their relationship with organized convective activity occurring at different stages of the surge's lifetime. In particular, we argue that the presence of MCSs in the southern GoC immediately before surge onset can modulate the intensity of the moisture surge regardless of the type of tropical synoptic-scale disturbance associated with the surge. Mean surge environments will be composited by surge type using the NARR products. Differences in the convective cloudiness are then computed to compare the strength and evolution with and without pre-surge MCSs over the southern GoC.