>WATER CYCLES ACROSS SCALES >RESEARCH

The IHOP_2002 field experiment was conducted over the Southern Great Plains of the United States from 13 May to 30 June 2002. It's goal was to improve the characterization of the four-dimensional distribution of water vapor and to improve the understanding and prediction of convection. There are four coordinated and overlapping research components, namely to: 1) investigate improvement in warm season QPF skill resulting from improved characterization of the water vapor field, 2) improve understanding and prediction of processes that determine where and when deep convection initiates, 3) improve understanding of the relationship between atmospheric water vapor and surface and boundary layer processes as they relate to QPF, and 4) determine the optimal mix of water vapor measurement strategies to better predict warm season rainfall. IHOP_2002 is thus closely aligned to our water-cycle objectives. The following questions are scientific questions and studies that advanced the goals of this initiative.

• How well do current and near-future (i.e., AQUA and CloudSat) satellite measurements observe 3-D distributions of water vapor over the continental U.S.?
  
• How well do reanalysis products capture observed diurnal variations in the vertical distribution of water vapor?
  
• Are there thermodynamic or dynamic signals in the IHOP_2002 measurements of the discrete continental propagation of convective systems noted by Carbone et al. (2001)?
  
• How well do large-scale models and CRMs replicate the commonly observed nocturnal convection that occurs where the most unstable conditions exist above the nocturnal inversions?
  
• What are the most common triggering mechanisms for convection over this region, and why is convection initiated too easily and too early in many large-scale models?
  
• Do high-resolution 4-D water vapor measurements improve 0-12 hr convective storm forecasts, and what are the implications of these improved precipitation forecasts for runoff models?
  
• How does the vertical distribution of water vapor evolve during moisture-return periods associated with the low-level jet?

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Some of the USWRP-supported activities are directly relevant to our water-cycle initiative, especially quantitative precipitation forecasting and the predictability and prediction of heavy warm-season rainfall. Indeed the main objective of a USWRP proposal to investigate the mechanisms associated with the predictability of major rainfall events over the U.S. continent is fully complementary, involving radar analysis, cloud-resolving numerical models, regional prediction models and (in the 1-12 hr time frame) "expert systems", as distinct from deterministic models. The USWRP proposals "Predictability and Prediction of Heavy Warm Season Rainfall" (Carbone et al.) and "'Improved Direct and Indirect Measurement of Atmospheric Water Vapor and Their Impact on Warm Season Precipitation Forecasts" (Weckwerth et al.) are particularly relevant.

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The Clouds in Climate Program (CCP) has been heavily engaged in understanding multiscale tropical convection through using CRMs evaluated against field observations, for example, in association with GATE (Grabowski et al. 1998) and TOGA COARE (Wu et al. 1998). This approach can be used in the context of IHOP_2002. CCP has also worked on convective parameterization (e.g., Liu and Moncrieff 2001), and conducted basic research on tropical intraseasonal oscillations (Grabowski and Moncrieff 2001). The CRM that is now mainly used stems from Smolarkiewicz and Margolin (1997), and will be the mainstay of our convection simulations over the U.S. continent2, after a land-surface model is added. Because of the compatible scales, the LSM (or simplified versions of it) could be used for this purpose. This program has had a major influence on the development of the World Climate Research Programme (WCRP) Global Energy and Water-cycle Experiment (GEWEX) Cloud System Study (GCSS) whose approach is to use CRMs and large-eddy simulation (LES) to examine cloud systems and their parameterization (GCSS 2000, Moncrieff et al. (1997).

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The Thunderstorm Operational Research Program (THOR) is a multi-agency (NWS, FAA, NASA, and Air Force) multi-year project starting in 2002. The two primary objectives are 1) to mitigate aviation delays through better convective storm forecasts and 2) to provide better severe storm and flash flood forecasts. Using leveraged funding from USWRP, FAA and NWS, we plan to investigate the following questions that have direct connections to the goals of this initiative.

• What is the origin and predictability of the various types of convergence lines that control the evolution of convective storms?
  
  
• Can the boundary layer model (VDRAS) produce 0-2 hr forecasts of boundary layer winds that improve convective storm forecasts?
  
  
• Can numerical models accurately forecast convective storms?
  
  
• Can real-time detection of gravity waves improve thunderstorm evolution forecasts?
  
  
• What is the optimum way to combine numerical model prediction and observations in an expert system to produce a 1-12 hour forecast of convection?

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