Ocean Interactions
Ocean and Atmosphere connecting Scientists, Teachers & Students

RICO, 2004-2005

Rain in Cumulus over the Ocean Experiment

The Rain in Cumulus over the Ocean (RICO) experiment focuses on the study of maritime cumulus clouds, which are some of the most prevalent cloud types on the planet. These "trade wind" cumuli typically extend to no greater than 4 km altitude and are characterized as warm rain clouds. They are ubiquitous over much of the tropical oceans, and characterizing their properties is important to understanding the global energy balance and climate. To understand these clouds and how rain develops within them, we need to study a wide range of scales (from micro-meters to tens of kilometers). The broad objective of RICO is to measure and understand the properties of trade wind cumulus at all scales, with particular emphasis on determining the importance of the development of rain. One fundamental problem – recognized for over a half century – is explaining how precipitation rapidly occurs in these important tropical clouds. Also, scientists are trying to understand why the coverage of the clouds is so sparse. We will attempt to use statistics to describe some of the attributes of the clouds (cloud height, how much water is within the cloud, etc) to describe the behavior of trade wind clouds, and this information will be used in weather models for better prediction capability. As with all clouds, there is an exchange of radiant energy and moisture between the surface and the cloud, and measurements under and within the cloud will help us understand these exchanges better.

Satellite photo of clouds over Antigua (center) and Barbuda (top)

RICO will focus on the following interrelated scientific issues:

The initiation of precipitation in trade wind cumulus: A goal of RICO is to obtain the critical observations that, when analyzed and compared to numerical model output, will provide the key information about how precipitation forms in the cloud.

Research on the microphysics of rain formation: Cloud microphysics are the smallest scale processes within the cloud….how cloud droplets form from moist air, how cloud droplets grow within the cloud, and how raindrops form from the cloud droplets.

Research on the organization of trade wind clouds: The mechanisms by which these clouds organize (see the satellite photos) in the trade wind area are poorly understood. An objective of RICO is to understand the cloud and near-surface processes that lead to the development and organization of convective structures in the trades.

Research on the water budget of trade wind cumulus: Although shallow cumulus cover vast expanses of the world’s oceans, very little is known about how much they precipitate and how precipitation affects their statistical properties. One objective of RICO will be to estimate the water budget of trade wind cumulus using modern radar and satellite remote sensing, calibrated with in situ data.

Research on the large-scale trade wind cloud environment: An objective of RICO will be to make predictions of precipitation amounts by using data on the large-scale environment (for example, air temperature, relative humidity, wind speed, etc), clouds (how thick are the clouds, how much water is within the cloud, etc), and other information. These data will be used to test hypotheses regarding cloudiness, cloud base height and exchange of mass and energy with the surface,

RICO will also involve a number of additional studies. These include research on 1) the age of clouds, 2) the chemistry and origin of aerosols, 3) radar remote-sensing, 4) developing a satellite cloud climatology, and 5) studies of the effects of clouds on radiation.

RICO funding comes from the NSF Physical Meteorology program.
For more information, see www.joss.ucar.edu/rico.