Publications (6)4.6 Total impact
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Article: Climate sensitivity of tropical and subtropical marine low cloud amount to ENSO and global warming due to doubled CO2
08/2007; -
Article: Simulation of Aerosol Distributions and Radiative Forcing
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ABSTRACT: this paper, we use a model which is consistent with the field observations to derive JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 107, NO. D19, 8028, doi:10.1029/2000JD000032, 2002 Copyright 2002 by the American Geophysical Union04/2003; -
Article: Atmospheric absorption during the Atmospheric Radiation Measurement (ARM) Enhanced Shortwave Experiment (ARESE)
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ABSTRACT: The objectives of the Atmospheric Radiation Measurement (ARM) program Enhanced Shortwave Experiment (ARESE) are to directly measure clear and cloudy sky shortwave atmospheric absorption, and to quantify any absorption found in excess of model predictions. We undertake detailed model comparisons to near infrared and total solar flux timeseries observed by surface and airborne radiometric instruments during the ARESE campaign. Model clear sky absorption biases generally fall within the range of uncertainty generated by sample size, and assumptions of aerosol properties and surface albedo. Direct measurements by stacked aircraft on the overcast day of October 30, 1995 confirm the detection of enhanced cloud shortwave absorption during ARESE. The detection is substantiated by, and consistent with, three independent measures of cloudy sky absorption estimated in previous studies: cloud forcing ratio, insolation forcing ratio, and albedo/transmission slope. A significant portion of the enhanced absorption occurs at visible wavelengths. Collocated measurements of liquid water path (LWP) suggest the magnitude of the enhanced absorption increases with LWP.02/1998; -
Article: Climate sensitivity of the NCAR Community Climate Model (CCM2) to horizontal resolution
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ABSTRACT: The dependence on horizontal resolution of the climate simulated by the National Center for Atmospheric Research Community Climate Model (CCM2) is explored. Simulations employing R15, T21, T31, T42, T63, and T106 horizontal spectral truncations are compared. Parameters associated with the diagnostic cloud scheme are modified for each resolution to provide similar global average cloud radiative forcing at each resolution. Overall, as with earlier studies, there are large differences between the low resolution R15 and T21 simulations and the medium resolution T42 simulation. Many climate statistics show a monotonic signal with increasing resolution, with the largest variation occurring from low to medium resolution. Although the monotonic signal is often from the low resolution simulations toward atmospheric analyses, in some cases it continues beyond the analyses at the highest resolution. Where convergence occurs, it is not always to the atmospheric analyses, and the highest resolution simulations are not the best by all measures. Although many climate statistics converge, the processes that maintain the climate do not, especially when considered on a regional basis. The implication is that the finer scales are required to capture the nonlinear processes that force the medium scales. Overall, it appears that, at a minimum, T42 resolution is required, but higher resolution would be better. Applications at T42 should take into consideration how model errors indicated by these resolution signals might affect any findings.Climate Dynamics 08/1995; 11(7):377-397. · 4.60 Impact Factor -
Article: The Community Climate System Model version 3 (CCSM3)
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ABSTRACT: The Community Climate System Model version 3 (CCSM3) has recently been developed and released to the climate community. CCSM3 is a coupled climate model with components representing the atmosphere, ocean, sea ice, and land surface connected by a flux coupler. CCSM3 is designed to produce realistic simulations over a wide range of spatial resolutions, enabling inexpensive simulations lasting several millennia or detailed studies of continental-scale dynamics, variability, and climate change. This paper will show results from the configuration used for climate-change simulations with a T85 grid for the atmosphere and land and a grid with approximately 1° resolution for the ocean and sea ice. The new system incorporates several significant improvements in the physical parameterizations. The enhancements in the model physics are designed to reduce or eliminate several systematic biases in the mean climate produced by previous editions of CCSM. These include new treatments of cloud processes, aerosol radiative forcing, land–atmosphere fluxes, ocean mixed layer processes, and sea ice dynamics. There are significant improvements in the sea ice thickness, polar radiation budgets, tropical sea surface temperatures, and cloud radiative effects. CCSM3 can produce stable climate simulations of millennial duration without ad hoc adjustments to the fluxes exchanged among the component models. Nonetheless, there are still systematic biases in the ocean–atmosphere fluxes in coastal regions west of continents, the spectrum of ENSO variability, the spatial distribution of precipitation in the tropical oceans, and continental precipitation and surface air temperatures. Work is under way to extend CCSM to a more accurate and comprehensive model of the earth's climate system. Author Posting. © American Meteorological Society 2006. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Climate 19 (2006): 2122–2143, doi:10.1175/JCLI3761.1. We would like to acknowledge the substantial contributions to and support for the CCSM project from the National Science Foundation (NSF), the Department of Energy (DOE), the National Oceanic and Atmospheric Administration, and the National Aeronautics and Space Administration. -
Article: Simulation of aerosol distributions and radiative forcing for INDOEX: Regional climate impacts
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ABSTRACT: 1] The direct radiative forcing by aerosols over the Indian Ocean region is simulated for the Indian Ocean Experiment (INDOEX) Intensive Field Phase during Spring 1999. The forcing is calculated for the top-of-atmosphere (TOA), surface, and atmosphere by differencing shortwave fluxes computed with and without aerosols. The calculation includes the effects of sea-salt, sulfate, carbonaceous, and soil-dust aerosols. The aerosol distributions are obtained from a global aerosol simulation including assimilation of satellite retrievals of aerosol optical thickness (AOT). The time-dependent, three-dimensional aerosol distributions are derived with a chemical transport model driven with meteorological analyses for this period. The surface albedos are obtained from a land-surface model forced with an identical meteorological analysis and satellite-derived rainfall and insolation. These calculations are consistent with in situ observations of the surface insolation over the central Indian Ocean and with satellite measurements of the reflected shortwave radiation. The calculations show that the surface insolation under clear skies is reduced by as much as 40 W/m 2 over the Indian subcontinent by natural and anthropogenic aerosols. This reduction in insolation is accompanied by an increase in shortwave flux absorbed in the atmosphere by 25 W/m 2 . The inclusion of clouds in the calculations changes the direct effect by less than 2 W/m 2 over the Indian subcontinent, although the reduction is much larger over China. The magnitude of the difference between all-sky and clear-sky forcing is quite sensitive to the three-dimensional spatial relationship between the aerosol and cloud fields, and other estimates of the difference for the INDOEX Intensive Field Phase are as large as 5 W/m 2 .J. Geophys. Res. 0345(8028).
