A number of studies have examined differences in the structure of convection and associated precipitation characteristics between the tropical east and west Pacific. However, few studies have attempted to quantify possible differences within the east Pacific domain itself. Satellite data indicates large differences in the spatial distribution and magnitude of seasonal rainfall across the eastern Pacific depending on the algorithm utilized and satellite sensors available, suggesting important differences in precipitation vertical structure across the region.

Previous ship-based radar studies (Yuter et al. 2000; Serra and Houze 2002; Petersen et al. 2003) have shown that convective activity is strongly modulated by the passage of Easterly waves in both the Pan American Climate Studies Tropical Eastern Pacific Process Study (TEPPS) and the East Pacific Investigation of Climate Processes in the Coupled Ocean-Atmosphere System (EPIC) domains. TEPPS (EPIC) was conducted at 7.8º N, 125º W (10º N, 95º W) in August (September) 1997 (2001). Broadly speaking, the EPIC and TEPPS regions are both located within the east Pacific ITCZ; however, the EPIC region is located only ~ 400 km from the Americas while the TEPPS domain is more representative of an open ocean location.

In this study, radar and upper air sounding data are used to compare precipitation structure and environmental characteristics between the TEPPS and EPIC regions. Meridional wind and pressure data are used to partition the radar and sounding data into different phases of easterly waves so that comparisons of vertical and horizontal structure and thermodynamic characteristics can be quantified. Comparisons of the diurnal cycle are also analyzed.

Results indicate that the EPIC and TEPPS domains display large differences in environmental properties and precipitation feature characteristics, despite the fact that both field campaigns were conducted during periods of similar SST’s. Moreover, previous studies have shown that convective activity in EPIC and TEPPS was heavily modulated by the passage of Easterly Waves. However, the radar and upper air sounding data indicate that the environment is more conducive to intense, deep convection and that this deep convection occurs much more frequently in EPIC compared to TEPPS. The proximity of the EPIC domain to land and the location of TEPPS relative to the descending branch of the Walker circulation are likely causes for the observed differences.