The TEPPS cruise had two scientific missions:

The Intertropical Convergence Zone

The Intertropical Convergence Zone (ITCZ) in the tropical eastern Pacific is a persistent band of clouds and storms which have a strong influence on global circulations and climate. Satellite-borne microwave sensors indicate that this area is one of the rainiest on earth while the satellite-borne infrared sensors indicate much less precipitation. The purpose of the PACS 1997 Process Study cruise is to document the 3-D structure of the clouds and precipitation in the tropical eastern Pacific from the surface. The timing and location of the cruise are designed to permit the ship's instruments to sample storms when and where there is the greatest difference between the satellite precipitation estimates.

It is important to resolve this discrepancy between the satellite precipitation estimates since satellite-borne sensors are the main method of routinely measuring precipitation over the oceans (i.e., most of the globe). The amount and distribution of precipitation are critical inputs to global climate models used for climate and weather prediction. The difference between the satellite-borne microwave versus the infrared precipitation estimates has a large effect on the resulting forecasts.

The scientific objectives of ITCZ study were to use a powerful Doppler radar in combination with other instruments to document horizontal and vertical structure of clouds and precipitation in the eastern Pacific Intertropical Convergence Zone and to understand the physical reasons behind the difference in precipitation estimates based on infrared and microwave satellite data. An additional goal was to estimate precipitation with radar.

Stratus and stratocumulus clouds over the subtropical ocean

During the second part of the TEPPS cruise the ship's instruments were used to study the stratus and stratocumulus clouds to the west of Mexico. These clouds form in a shallow layer at the top of the planetary boundary layer. This layer of clouds covers a large region and together with similar clouds over other oceanic regions have a large impact on the earth's climate as they reflect the sun's radiation and absorb infrared radiation from the ocean below. One of the major uncertainties in the physics of these shallow clouds is in how much water falls out of the cloud layer in the form of drizzle. This cruise uses the same Doppler radar used in the ITCZ study to detect the drizzle drops forming and falling out of the stratus cloud layer.