Recommendations for Improving Chapter 3 of the Plan

  • The implementation strategy and the deliverables of Chapter 3 of the plan should be reexamined.

  • It is important that a more comprehensive and inclusive review of the work on this topic be conducted. The specific contributions of GAPP in this area should be articulated in the plan in the context of other ongoing work.

CHAPTER 4: “WARM SEASON PRECIPITATION”

Comments

The study of warm season precipitation builds on the lessons learned from GCIP and aims to extend that work to problems related to the understanding and prediction of precipitation in the complex terrain west of the Mississippi River Basin during the warm season. This research element is intended to contribute to both observational climatic data and theoretical understanding of the dynamics of the North American continental warm season precipitation regimes (the so-called North American Monsoon System [NAMS]), which has been initiated by the CLIVAR program. The North American Monsoon Experiment is one of the first GEWEX-CLIVAR coordinated research efforts and is considered a major milestone in bridging two important aspects of climate research. It is also an international collaboration involving both Latin American and U.S. scientists.

The study of the NAMS should provide opportunities to build and expand upon GAPP research strengths with regard to the roles of land-atmosphere interactions, including the dynamical feedbacks associated with snow cover and vegetation heterogeneity, and the role of topography in the organization of convective activity, which modulates the spatial characteristics of precipitation from diurnal-to-interannual time scales. This research focus also provides an opportunity to expand the range of temporal scales in the study of land-memory mechanisms (NOAA-NASA 2004, Chapter 2) and to integrate the study of the hydrometeorology of orographic systems (NOAA-NASA 2004, Chapter 3) into a comprehensive investigation of the predictability of warm season precipitation in the West and Southwest regions of the continental United States.

The background section on objectives (NOAA-NASA 2004, p. 24) identifies and briefly discusses the goals for this research element, which include

  1. improved simulation of convective precipitation in climate models;

  2. improvements in sustained observations, derived products, and information dissemination; and

  3. improvement in operational climate prediction of warm season precipitation.

These objectives are stated without establishing clear linkages to the previous science background section, and they do not appear to be directly related to these goals. The first objective relates solely to the development of improved convective parameterization schemes, but the basis for this is not transparent. Although it refers to GAPP-funded research that has illustrated the sensitivity of model simulations of precipitation to the choice



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