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
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.
(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.