This paper will report on the goals and some recent accomplishments of the NCAR initiative on the water cycle across scales. The goal of this initiative is to understand how water vapor, precipitation, and land-surface hydrology interact across scales to define the hydrological cycle, and to use this information to improve both large and small scale weather prediction, climate models, and surface-hydrologic forecasting. A number of NCAR scientists have been involved with various aspects of the water cycle in the past; this initiative is an attempt to coordinate these efforts across the institution and to more closely align our efforts with ongoing work on the water cycle in the community. The particular aspects of the water cycle that we have chosen to emphasize were determined based on an assessment of the research needs and in consideration of NCARs relative strengths in observations, modeling and analysis. In order to have a manageable size of the research effort, we also decided to focus the first phase of this initiative on continental North America during the warm season. Four main thrusts have been developed:

1. Diagnostic Analysis of Precipitation on a Continental Scale, The goal of this research is to examine the diurnal cycle of precipitation from observations and document the intensity, frequency, and amount of precipitation. The observed diurnal cycle will be compared to the climate and weather model prediction of the diurnal cycle, and areas needing improvement identified.

2. Cloud System Simulation, Research will focus on understanding relationships between precipitation and the multi-scale organization of convection in regard to the atmospheric component of the water cycle. Cloud-resolving models having large domains will be used extensively. Results from the numerical simulations will be used to evaluate and improve convective parameterization and cloud-microphysical parameterization. Studies will include key aspects such as the diurnal cycle of precipitation and the role of organized cloud systems. Verification data will be obtained from the IHOP_2002 field experiment analysis and other relevant sources.

3. Water vapor and Warm Season Convection, and

The main thrust of this effort is the IHOP field program on water vapor and convective initiation and the analysis of the resulting data. Scientist goals are to better understand the variability of water vapor in the atmosphere and its role in convective initiation and the water cycle.

4. Land-Atmosphere Interaction. The objectives here are aimed at improving our knowledge of land-surface processes and land-atmosphere interaction, and our ability to predict such processes. We will focus our efforts on an analysis of the surface sensor array data from the IHOP field program.

These areas of emphasis are also consistent with the recent Hornberger report regarding climate research related to the water cycle and also weather research efforts under the U.S. Weather Research Program. This paper will describe the research goals and priorities under each of these areas and also some of the recent results.