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Eric R. Snodgrass, Larry Di Girolamo, and Robert M. Rauber

Abstract

Precipitation characteristics of trade wind clouds over the Atlantic Ocean near Barbuda are derived from radar and aircraft data and are compared with satellite-observed cloud fields collected during the Rain in Cumulus over the Ocean (RICO) field campaign. S-band reflectivity measurements Z were converted to rainfall rates R using a Z–R relationship derived from aircraft measurements. Daily rainfall rates varied from 0 to 22 mm day−1. The area-averaged rainfall rate for the 62-day period was 2.37 mm day−1. If corrected for evaporation below cloud base, this value is reduced to 2.23 mm day−1, which translates to a latent heat flux to the atmosphere of 63 W m−2. When compared with the wintertime ocean-surface latent heat flux from this region, the average return of water to the ocean through precipitation processes within the trade wind layer during RICO was 31%–39%. A weak diurnal cycle was observed in the area-averaged rainfall rate. The magnitude of the rainfall and the frequency of its occurrence had a maximum in the predawn hours and a minimum in the midmorning to early afternoon on 64% of the days. Radar data were collocated with data from the Multiangle Imaging Spectroradiometer (MISR) to develop relationships between cloud-top height, cloud fraction, 866-nm bidirectional reflectance factor (BRF), and radar-derived precipitation. The collocation took place at the overpass time of ∼1045 local time. These relationships revealed that between 5.5% and 10.5% of the cloudy area had rainfall rates that were > 0.1 mm h−1, and between 1.5% and 3.5% of the cloudy area had rainfall rates that were >1 mm h−1. Cloud-top heights between ∼3 and 4 km and BRFs between 0.4 and 1.0 contributed ∼50% of the total rainfall. For cloudy pixels having detectable rain, average rainfall rates increased from ∼1 to 4 mm h−1 as cloud-top heights increased from ∼1 to 4 km. Rainfall rates were closely tied to the type of mesoscale organization, with much of the rainfall originating from shallow (<5 km) cumulus clusters shaped as arcs associated with cold-pool outflows.

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Robert M. Rauber, Bjorn Stevens, Jennifer Davison, Sabine Goke, Olga L. Mayol-Bracero, David Rogers, Paquita Zuidema, Harry T. Ochs III, Charles Knight, Jorgen Jensen, Sarah Bereznicki, Simona Bordoni, Humberto Caro-Gautier, Marilé Colón-Robles, Maylissa Deliz, Shaunna Donaher, Virendra Ghate, Ela Grzeszczak, Colleen Henry, Anne Marie Hertel, Ieng Jo, Michael Kruk, Jason Lowenstein, Judith Malley, Brian Medeiros, Yarilis Méndez-Lopez, Subhashree Mishra, Flavia Morales-García, Louise A. Nuijens, Dennis O'Donnell, Diana L. Ortiz-Montalvo, Kristen Rasmussen, Erin Riepe, Sarah Scalia, Efthymios Serpetzoglou, Haiwei Shen, Michael Siedsma, Jennifer Small, Eric Snodgrass, Panu Trivej, and Jonathan Zawislak

The Rain in Cumulus over the Ocean (RICO) field campaign carried out a wide array of educational activities, including a major first in a field project—a complete mission, including research flights, planned and executed entirely by students. This article describes the educational opportunities provided to the 24 graduate and 9 undergraduate students who participated in RICO.

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