The International H2O Project (IHOP_2002) is one of the largest North American meteorological field experiments in history. From 13 May to 25 June 2002, over 250 researchers and technical staff from the United States, Germany, France, and Canada converged on the Southern Great Plains to measure water vapor and other atmospheric variables. The principal objective of IHOP_2002 is to obtain an improved characterization of the time-varying three-dimensional water vapor field and evaluate its utility in improving the understanding and prediction of convective processes. The motivation for this objective is the combination of extremely low forecast skill for warm-season rainfall and the relatively large loss of life and property from flash floods and other warm-season weather hazards. Many prior studies on convective storm forecasting have shown that water vapor is a key atmospheric variable that is insufficiently measured. Toward this goal, IHOP_2002 brought together many of the existing operational and new state-of-the-art research water vapor sensors and numerical models.

The IHOP_2002 experiment comprised numerous unique aspects. These included several instruments fielded for the first time (e.g., reference radiosonde); numerous upgraded instruments (e.g., Wyoming Cloud Radar); the first ever horizontal-pointing water vapor differential absorption lidar (DIAL; i.e., Leandre II on the Naval Research Laboratory P-3), which required the first onboard aircraft avoidance radar; several unique combinations of sensors (e.g., multiple profiling instruments at one field site and the German water vapor DIAL and NOAA/Environmental Technology Laboratory Doppler lidar on board the German Falcon aircraft); and many logistical challenges. This article presents a summary of the motivation, goals, and experimental design of the project, illustrates some preliminary data collected, and includes discussion on some potential operational and research implications of the experiment.

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Atmospheric Technology Division, National Center for Atmospheric Research * Boulder, Colorado

Forecast Systems Laboratory, NOAA Research, Boulder, Colorado

Joint Office for Science Support, University Corporation for Atmospheric Research, Boulder, Colorado

Mesoscale and Microscale Meteorology Division, National Center for Atmospheric Research* Boulder, Colorado

Mesoscale Atmospheric Processes Branch, NASA GSFC, Greenbelt, Maryland

Institute Pierre-Simon Laplace/Service d'Aéronomie, Centre National de la Recherche Scientifique, Université Pierre et Marie Curie, Paris, France

Department of Atmospheric Science, University of Wyoming, Laramie, Wyoming

Atmospheric Technology Division, National Center for Atmospheric Research* Boulder, Colorado

Cooperative Institute for Meteorological Satellite Studies, Space Science and Engineering Center, University of Wisconsin—Madison, Madison, Wisconsin

*The National Center for Atmospheric Research is sponsored by the National Science Foundation.