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Modeling and Analysis of the Earth's Hydrologic Cycle

P.I.: Donald R. Johnson
Space Science and Engineering Center
University of Wisconsin – Madison

Summary

A key aim of this project is to advance the understanding of global water vapor and inert trace constituent transport in relation to climate change through analysis of simulations produced by the global University of Wisconsin (UW) hybrid isentropic coordinate models. Research has established that simulations in isentropic coordinates are remarkably more accurate in the transport of water vapor, and inert and chemical constituents compared against corresponding sigma coordinate models.

1. Introduction

The primary objectives of this research are to; 1) advance the modeling of climate change by developing a hybrid isentropic model for global and regional climate simulations, 2) advance the understanding of physical processes involving water substances and the transport of trace constituents, and 3) examine the limits of global and regional climate predictability. Model development has proceeded through a hierarchy of models from a preliminary channel model to the full fledge global climate model in use today [the University of Wisconsin-Madison isentropic-eta (UW Φ-η ) coordinate model]. Studies of a wide variety of Eulerian and semi-Lagrangian numerics and different algorithms for parameterization of boundary layer processes and dry and moist convection have been carried out.

2. Significance of Research

This research addresses fundamental issues underlying the understanding and modeling of hydrologic processes. Hydrologic processes, including surface evaporation, long-range transport of water substances, release of latent heating involving evaporation/condensation and attenuation of the radiative flux of energy by water vapor and clouds, are central in the regulation of global and regional climate.

A premise of this work is that accurate simulation of the long-range transport of mass, momentum, energy, water vapor and other trace constituents is crucial for modeling the climate state. Substantial evidence exists illustrating the inherent difficulties in simulating the long-range transport of water vapor and other trace constituents utilizing conventional sigma coordinate climate models. This limitation stems primarily from problems associated with vertical advection of water vapor and other trace constituents in sigma models. The water vapor structure and its transport are primarily two dimensional in isentropic coordinates except in regions of moist convection. The problems associated with vertical advection remain negligible in isentropic coordinates relative to sigma coordinate models over much of the global domain.

3 The UW Model

The UW q - h model is a global grid point model employing piecewise parabolic method (PPM) transport numerics and two-level forward time differencing. The model incorporates the full suite of physical parameterizations obtained from the National Center for Atmospheric Research (NCAR) community climate model version 3 (CCM3). Over the past year a prognostic cloud prediction scheme developed by NASA Goddard scientists has been implemented in the UW model. This addition provides the capability to more accurately simulate and assess the impact of clouds and water vapor on atmospheric circulation.

4. Accomplishments

During the past year the P.I. has had frequent interaction with scientists from DOE, NASA and NOAA concerning climate modeling and the importance of hydrologic processes. He also serves as NOAA's National Centers for Environmental Prediction Special Project Scientist.

Results from a 14 -year climate simulation with the UW q - h model at 2.8125 ° latitude-longitude resolution have been conditionally accepted for publication in the Journal of Climate . Daily 5-day forecasts at 0.7° latitude-longitude resolution (approximately 4,000,000 model grid points) have been ongoing for the last 23 months.

The NASA Langley 3D chemical module has been incorporated in the UW model to provide a global chemical modeling system involving 55 chemicals in the troposphere and stratosphere. Results from this joint project have been published in the Journal of Geophysical Research.

5. Computational Approach

The UW model can currently use multiple processors on one node of the IBM/SP using either OpenMP parallelism or MPI message passing. An effort is under way to convert the code to use both MPI message passing and OpenMP to maximize the use of multiple nodes. This capability, which is 70-80% complete, will greatly enhance our research efforts by providing much faster throughput for climate simulations. The use of multiple nodes will allow substantial increases in both horizontal and vertical resolution for climate simulation and NWP. The increased computational capability also allows the use of more realistic (although more computationally intense) physical parameterizations. The use of the SciDAC terascale computing facility will provide the capability to conduct longer and more complex climate simulations in a reasonable time and greatly assist the determination of the impact of different physical parameterizations and different spatial resolutions.

6. Future Plans

During the coming year, the conversion of the UW model to use both MPI message passing and OpenMP parallelism will be completed. The completion of this effort will greatly facilitate the achievement of the scientific goals of our research effort.

Numerous seasonal and multi-year simulations will be analyzed to further our investigations of regional climate in relation to energy balance and atmospheric hydrologic processes. This effort will also continue to investigate the relative abilities of isentropic and sigma coordinate models to transport water vapor and explicitly predict cloud substances, and to diagnose the impact of the explicitly simulated clouds on cloud radiative forcing. The impact of increased horizontal and vertical resolution will also be ascertained.

The increased processing capability will allow implementation of more highly developed physical parameterizations into the UW model including more realistic prognostic simulation of clouds. The robust simulation capabilities of the UW model have led to the desire to couple the UW model to a sophisticated ocean model in order to provide a stand-alone system for climate simulation. The terascale computing capability provided by SciDAC is critical to this effort.

The above efforts seek to take advantage of the increased numerical accuracies of long-range transport utilizing hybrid isentropic coordinates to improve the simulation of moist reversible processes involving water vapor and cloud water and ice and related hydrological processes. This increased accuracy is essential to increasing the accuracies of other important processes that interact strongly with other hydrologic, chemical and biospheric processes, all of which are critical to accurately simulating the climate state regionally and globally.

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