A multi-scale analysis of moisture supply associated with precipitation on Isla del Coco, Costa Rica
Wrapped by the Pacific waters and the mist of shipwrecks and pirates stories, one of the rainiest Eastern Pacific islands protects a biodiversity treasure: Isla del Coco. This study presents the analysis of moisture sources linked with contributions to precipitation in the area. The diurnal cycle of precipitation on the island was reviewed from GPS station data previously evaluated using available meteorological data from field campaigns held on the island in 2011 and 2012. Near-surface salinity patterns were also analyzed along with sea surface temperature, evaporation, Ongoing Longwave Radiation (OLR) as well as latent and sensible heat fluxes. Moisture contributions to precipitation on the island are supplied by evaporative sources, and moisture recycling is important. Regional precipitation is a continuous supply of moisture for the atmosphere whereas transport from evaporative sources is seasonally constrained. The analysis of the diurnal cycle of moisture supply suggests that contributions from available moisture linked with precipitation recycling show a slightly delayed response to deep convection in the region. The diurnal cycle of contributions to precipitation from evaporative moisture sources, based on the modeling component of the work, is consistent with the diurnal cycle of precipitation. The trajectory analysis remarks the role of the low level winds, the Intertropical Convergence Zone (ITCZ) position and the stability conditions to modulate the supply of moisture. The moisture contributions from the sources present a different sensitivity to El Niño-Southern Oscillation (ENSO). Contributions from precipitation recycling showed a large variability linked to ENSO as increasing contributions were determined to be related with El Niño during boreal summer and autumn months. The variability of the contributions from a North-east evaporative source is modulated by the response of the Caribbean Low Level Jet (CLLJ; Amador, 1998; Amador, 2008) to ENSO. The South-western evaporative source showed sensitivity to El Niño, as transport was found to decrease (increase) from November to March (May to July), meanwhile the response to La Niña was small. Good agreement amongst the ENSO response of the fields and the known dynamics of the region was found.