Initiatives in Brief

In this series, the UCAR Quarterly profiles one or more of the NCAR strategic initiatives each issue.

The Water Cycle across Scales

NCAR steering committee: Mitchell Moncrieff, David Parsons, Kevin Trenberth, Tom Warner, James Wilson

Goals: Understand how water vapor, precipitation, and land-surface hydrology interact across scales to define the hydrological cycle; use this information to improve both large- and small-scale weather prediction and climate models.

Roy Rasmussen. (Photo by Carlye Calvin.)

Recent progress:

• Developing and deploying reference radiosondes and soil moisture/temperature sensors at the the International H2O Project (IHOP)
• Producing IHOP-related model simulations and studies of convective triggering
• Documenting deficiencies in the model treatment of the diurnal cycle of clouds, precipitation, and surface-atmosphere exchanges over the continental United States
• Isolating deficiencies in the operational measurement of water vapor in the upper troposphere
• Improving understanding of how the dependence of surface-atmosphere exchanges on vegetation and soil moisture varies with climatic regime
• Developing accurate estimates of the discharge of fresh water from continents
• Simulating U.S. convective cloud formation at high resolution, using cloud-resolving models, for the purpose of improving the parameterization of clouds in weather and climate models

University collaborators:

Jeffrey Basara (University of Oklahoma)
Richard Cuenca (Oregon State University)
George Diak (University of Wisconsin–Madison)
Frederic Fabry and Ishtar Zawadski (McGill University)
Istvan Geresdi (University of Pecs)
Robert Grossman and Peter Blanken (University of Colorado)
Peter Hobbs and Clifford Mass (University of Washington)
Yuri Knyazikhin and Ranga Myeni (Boston University)
Andy Majda (Courant Institute for Mathematical Sciences)
Dev Niyogi (North Carolina State University)
David Stauffer and Kenneth Davis (Pennsylvania State University)
Roger Wakimoto (University of California, Los Angeles)
Volker Wulfmeyer (University of Hohenheim)
Guang Zhang (Scripps Institution of Oceanography)

In the literature:

Dai, A., and K. E. Trenberth, 2002: Estimates of freshwater discharge from continents: Latitudinal and seasonal variations. Journal of Hydrometeorology 3, 660–687.

Several papers in “Symposium on Observing and Understanding the Variability of Water in Weather and Climate,” 83rd Annual Meeting, American Meteorological Society, Long Beach, California, February 2003. (CD-ROM: VARIH2O)

Trenberth, K. E., A. Dai, R. M. Rasmussen and D. B. Parsons, 2003: The changing character of precipitation. Bulletin of the American Meteorological Society 84, 1205–1217.

LeMone, M.A., R. Grossman, F. Chen, K. Ikeda, and D. Yates, 2003: Choosing the averaging interval for comparison of observed and modeled fluxes along aircraft transects over heterogeneous terrain. Journal of Hydrometeorology 4, 179–195.

Coming up: The initiative’s focus through fiscal year 2005 will be warm-season convection over the continental United States. Specific ­projects will address how to answer such diverse questions as:

• Will global warming lead to increased frequency and intensity of droughts and floods?
• Will severe thunderstorms develop on a particular afternoon over the Midwest, leading to tornadoes and diversion of air traffic?

Contact: Roy Rasmussen, rasmus@ucar.edu, 303-497-8430

Initiatives in Brief: The Water Cycle across Scales

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