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  • Author or Editor: David Karoly x
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Melissa S. Bukovsky and David J. Karoly

Abstract

This note examines the sensitivity of simulated U.S. warm-season precipitation in the Weather Research and Forecasting model (WRF), used as a nested regional climate model, to variations in model setup. Numerous options have been tested and a few of the more interesting and unexpected sensitivities are documented here. Specifically, the impacts of changes in convective and land surface parameterizations, nest feedbacks, sea surface temperature, and WRF version on mean precipitation are evaluated in 4-month-long simulations. Running the model over an entire season has brought to light some issues that are not otherwise apparent in shorter, weather forecast–type simulations, emphasizing the need for careful scrutiny of output from any model simulation. After substantial testing, a reasonable model setup was found that produced a definite improvement in the climatological characteristics of precipitation over that from the National Centers for Environmental Prediction–National Center for Atmospheric Research global reanalysis, the dataset used for WRF initial and boundary conditions in this analysis.

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Diandong Ren, David J. Karoly, and Lance M. Leslie

Abstract

The temperate glaciers in the greater Himalayas (GH) and the neighboring region contribute to the freshwater supply for almost one-half of the people on earth. Under global warming conditions, the GH glaciers may melt more rapidly than high-latitude glaciers, owing to the coincidence of the accumulation and ablation seasons in summer. Based on a first-order energy balance approach for glacier thermodynamics, the possible imposed additional melting rate was estimated from three climate simulations using the Geophysical Fluid Dynamics Laboratory Global Coupled Climate Model version 2.1 (GFDL-CM2.1), the Model for Interdisciplinary Research on Climate 3.2, high-resolution version (MIROC3.2-hires), and the Met Office’s Third Hadley Centre Coupled Ocean–Atmosphere General Circulation Model (HadCM3). The simulations were carried out under the Special Report on Emissions Scenarios (SRES) A1B scenario. For the 30-yr period of 2001–30, all three CGCMs indicate that the glacial regions most sensitive to regional warming are the Tianshan–Altai Mountains to the north and Hengduan Mountains to the south. A map of potential melting was produced and was used to calculate the glacier-melting speed, yielding an additional spatially averaged glacier depth reduction of approximately 2 m for the 2001–30 period for those areas located below 4000 m. Averaged over the entire GH region, the melting rate is accelerating at about 5 mm yr−2. The general circulation over the GH region was found to have clear multidecadal variability, with the 30-yr period of 2001–30 likely to be wetter than the previous 30-yr period of 1971–2000. Considering the possible trend in precipitation from snow to rain, the actual melting rates of the GH glaciers may even be larger than those obtained in this research.

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