Large-Scale Circulations in the East Pacific and West Africa Regions and Their Interaction with Convective Structures
Abstract
The interaction of large-scale atmospheric circulations with convective systems in two tropical regions (i.e., the East Pacific and West Africa) is studied using field campaign, reanalysis, and satellite datasets. In the East Pacific, organized cloud systems that propagate eastward or westward at synoptic time scales can alter the shallow meridional circulation (SMC) and deep meridional circulation (DMC) seen in the Intertropical Convergence Zone (ITCZ). During boreal winter, I identified convective disturbances that propagate eastward at 10 m/s within the central and East Pacific north of the ITCZ and exhibit high cloudiness associated with upper-level divergence. These eastward propagating disturbances do not impact the SMC, but the DMC in the northern part of the ITCZ strengthens. During boreal spring, convectively-coupled Kelvin waves initiate in the West Pacific and propagate along the ITCZ axis into the East Pacific at 15 m/s. The shallow convection ahead of the Kelvin wave enhances the SMC and the deep convection within the Kelvin wave enhances the DMC. During boreal summer and fall, easterly waves appear to strongly modulate the SMC and DMC in the East Pacific ITCZ. The easterly wave trough enhances the DMC, and the subsequent convectively-suppressed easterly wave ridge enhances the SMC over the southern part of the ITCZ. Additionally, the vertical velocity associated with the SMC and DMC in the East Pacific is assessed using the Organization of Tropical East Pacific Convection (OTREC) field campaign dataset. The OTREC 2019 field campaign observations were crucial to identify deficiencies in reanalysis and satellite products. Reanalyses underestimate the DMC observed in the northern part of the ITCZ and satellite products underestimate the SMC observed in southern part of the ITCZ. Finally, the diurnal variation of the SMC and DMC over West Africa during the pre-monsoon and monsoon seasons is also studied. A daytime sea breeze and two nocturnal low-level jets (NLLJs) are shown to have varying impacts on the meridional overturning circulation and convective organization over West Africa. The daytime sea breeze initiates strong northward-propagating convection from the coast, especially during the pre-monsoon season, a coastal NLLJ enhances northward moisture transport during the monsoon season, and an inland NLLJ promotes the dry SMC over the Sahara during both seasons.
Citation
Huaman Chuquihuaccha, Lidia (2021). Large-Scale Circulations in the East Pacific and West Africa Regions and Their Interaction with Convective Structures. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196071.