PTCE Overview and Objectives

The Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment (TOGA COARE) was an experiment program aimed at investigating the scientific phenomena associated with the ocean, atmosphere and the interaction between the two in the warm pool region of the western Pacific ocean. The program was international in scope and several U.S. agencies participated, including NASA. The field experiment phase of the program took place from November 1992 to February 1993.

The siting of the Intensive Flux Array (IFA) for TOGA COARE was dictated by the location of the tropical warm pool region (monthly mean sea surface temperature greater than 28¡C). This region coincided with an area of low OLR (monthly mean OLR less than 200 w/m square). During the austral summer, this region was situated around New Guinea and the Solomon Islands. The basic structure of the experiment began with a moored ship array containing Doppler radars. The moored array was augmented with a number of research vessels sampling ocean and atmosphere state variables and interface fluxes. In addition, measurements were carried out on a number of moored buoys.

The aircraft deployed for the experiment included turboprops (2 P-3's, an Electra, C-130, and Cessna) bearing airborne Doppler radars, microphysics, radiation, and flux instrumentation. Upper troposphere measurements were supplied by the NASA DC-8 and lower stratosphere measurements by the NASA ER-2. Both NASA aircraft were equipped with remote sensing and radiation instruments. The DC-8 was equipped with microphysics instruments. Satellite observations were also an integral part of the experiment.

The NASA component of TOGA COARE, while contributing directly to overall COARE objectives, emphasized scientific objectives associated with the Tropical Rainfall Measuring Mission (TRMM), an understanding of convection in general, and NASA's cloud and radiation program. The highest priority was given to the observations related to TRMM science, i.e., tropical ocean precipitation climatology (rainfall at the surface), vertical structure of precipitation, convection processes, physical processes associated with precipitation, water budget estimates, and all aspects of the water cycle over the COARE domain. Cloud and radiation objectives were closely associated with the International Satellite Cloud Climatology Project (ISCCP) and First ISCCP Regional Experiment (FIRE) project objectives, in particular the Pilot Tropical Cirrus Experiment (PTCE).

PTCE

The TOGA COARE experiment offered a unique opportunity for FIRE. Although there were fundamentally important reasons to study tropical cirrus, the complex logistics of tropical experiments, particularly those in oceanic areas, made them so expensive to mount that it was beyond the capability of the FIRE program. However, by taking advantage of COARE that was carried out in a prime region of interest, FIRE conducted an pilot tropical cirrus experiment at relatively low cost and, at the same time, addressed elements of the scientific goals of COARE and TRMM.

SCIENTIFIC OBJECTIVES

The scientific objectives of PTCE were to:

1. Describe the radiative properties of tropical cirrus. This included fluxes at cloud top, cloud base, and the surface (ocean or land), as well as flux divergence and the associated heating rates in the cirrus.
2. Quantify the morphology of tropical cirrus. Of interest here were both spatial and temporal structure and the variability of that structure.
3. Describe the microphysical properties of tropical cirrus. Associated with obtaining information about crystal size and habit would be the related impacts on radiative heating and remotely sensed radiative fields.
4. Study the physical process linkages between deep convection and tropical cirrus. This was a complex relationship but certainly includes surface radiative forcing, moisture transport, latent heat release, and flow fields.