Research Interests:

Deep cumulonimbus clouds form the upward branch of large scale thermal circulations in the tropics. These circulations, which include the global Hadley-Walker circulation and regional monsoon flows, are of crucial importance not only to the tropics, but to mid-latitude weather and climate as well. However, the mechanisms which control the strength and location of these circulations are imperfectly understood. Some of the biggest uncertainties are related to how cumulus convection is controlled, and to the structure and vertical transfer characteristics of this convection. The way in which water vapor is vertically redistributed is an issue of particular concern.

Traveling tropical disturbances such as the Madden-Julian oscillation, Kelvin waves, mixed Rossby-gravity waves, easterly waves, and tropical storms are also very sensitive to cumulus convection.

My current interests are in unraveling how deep atmospheric convection interacts with tropical circulations and how these circulations work as a result. The TCS-08, PREDICT, and OTREC projects (see below) are providing insight into this process in the context of developing and intensifying tropical storms. In addition, we are using simple analytical models, numerical models, including cumulus ensemble models, and a simplified large-scale equatorial beta plane model, to test ideas about how convection works in large scale tropical circulations. Ultimately, knowledge gained from modeling, theory, and field observations should lead to better representations of convection in numerical models, and hence better weather and climate predictions. To this end we are also studying how convection works in NCEP's Global Forecast System (GFS) model.


OTREC (Organization of Tropical East Pacific Convection) is an NSF-sponsored project with Zeljka Fuchs and David Raymond as lead investigators, and with US collaborators from Harvard University, Colombia University, University of Wisconsin, Colorado State University, University of Washington, and NOAA. In addition, OTREC has international collaborators from the University of Costa Rica, the Faculty of Mines and SIATA in Medellin, the National University of Colombia in Bogota, the National Autonomous University of Mexico, and ECMWF. The field phase of OTREC occurred in August and September of 2019 using the NSF/NCAR Gulfstream-V aircraft with a base in Liberia, Guanacaste Province, Costa Rica. Missions were flown in the East Pacific ITCZ, in the Choco jet region off the Pacific coast of Colombia, and in the SW Caribbean. The G-V deployed dropsondes and made measurements with NCAR's Hiaper Cloud Radar. In addition to the primary mission to study tropical convection, the G-V flew a collaborative mission with a NOAA P-3 documenting the development of tropical cyclone Ivo. Radiosonde soundings were made in Santa Cruz and Limon, Costa Rica as well as in Nuqui and various other sites in Colombia. GPS precipitable water measurements were made in both Colombia and Costa Rica and oxygen isotope measurements were made in rainwater in both countries as well.


PREDICT (Pre-Depression Investigation of Cloud-systems in the Tropics) was based in St. Croix, US Virgin Islands, in August and September of 2010. The purpose of this project was to study the processes responsible for the formation of tropical cyclones in the western Atlantic and Caribbean. The primary tool used was the NSF/NCAR G-V aircraft, a long-range, high-altitude business jet converted for research use. The G-V deployed dropsondes and made other measurements in several developing and non-developing systems. PREDICT was held in conjunction with cooperative projects from NASA and NOAA.


In August and September of 2008 we participated in TPARC/TCS-08, a project to study the formation and structure change of western Pacific typhoons. Three aircraft were based in Guam; the NRL P-3 aircraft with the ELDORA Doppler radar, Doppler lidar, and dropsondes, as well as two Air Force C-130 "hurricane hunters" deploying dropsondes. Other aircraft in this project were the Taiwanese Dotstar jet, based in Taiwan, and the German DLR Falcon, based in Japan. We flew numerous missions on the NRL P-3 in conjunction with the C-130 aircraft and a few with Dotstar and the Falcon. Excellent data were obtained on the formation and structure change of a number of typhoons and on the extratropical transition of typhoon Sinlaku.


EPIC was a program consisting of enhanced monitoring, modeling, and intensive process studies designed to help us understand the coupled ocean-atmosphere system of the east Pacific. EPIC was a part of the U. S. CLIVAR Program with connections to other national programs in Mexico, Central America, and South America. EPIC2001 was a process study proposed under the umbrella of EPIC for a 6 week period in September-October 2001 with the purpose of studying the east Pacific intertropical convergence zone, the associated cross-equatorial inflow, and the east Pacific warm pool. It also contained an exploratory study of the ocean and atmosphere in the east Pacific stratus region south of the equator. Read my personal view of EPIC's accomplishments.

Weak Temperature Gradient Cumulus Ensemble Model

The source code for the latest version of our weak temperature gradient cumulus ensemble model is available here. It is in the form of a gzipped tar file. The model is coded in the C language, and it needs a version of MPI such as LAM/MPI to run, as well as the Candis system.

Papers and Preprints

Links to publications may be found here.