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The Earth's climate is regulated by the energy absorbed from the Sun and the loss of energy to space through both the reflection of the solar radiation itself and the [...]

Accurately accounting for radiative energy balance between the incoming solar and the outgoing infrared radiative fluxes is very important in modeling the Earth's climate. Water vapor absorption plays a critical role in the radiative heating rate profile in the midtroposphere by strongly absorbing both infrared and solar radiation in several absorption bands throughout the electromagnetic spectrum. One of the most important of these absorption bands is in the far-infrared portion of the spectrum, where the far-infrared is defined here to be wavelengths longer than 15 microns. A large fraction (~40%) of the outgoing infrared flux is emitted by water vapor in the far-infrared. Errors in the radiative transfer models associated with the far-infrared and other strong water vapor absorption bands will therefore affect the calculation of the planet's total outgoing radiative flux and its vertical distribution of the radiant energy; these errors may result in inaccurate modeling of the general circulation of the planet. A set of field experiments, called the Radiative Heating in Underexplored Bands Campaigns (RHUBC), has been conducted as part of the Atmospheric Radiation Measurement (ARM) program. The RHUBC campaigns deployed spectrally resolved far-infrared spectrometers alongside other ARM observations in extremely dry environments to provide a robust and complete dataset that allows radiative transfer models to be evaluated in the far-infrared and other spectral regions where water vapor absorbs strongly. RHUBC I was conducted in February-March 2007 in Barrow, Alaska, and RHUBC II was conducted in August-October 2009 in the Atacama Desert region of Chile at an altitude of 5.3 kin. The motivation for and initial results from these experiments are described, as well as the implications for global climate models. DOI: 10.1175/2010BAMS2904.1

Despite considerable technological advances, aviation impacts on global climate are significant and may constitute a future constraint on the continued growth of air travel. The most important but least understood component in aviation climate impact assessments are contrails, which form as line-shaped ice clouds (linear contrails) and transform into irregularly shaped ice clouds (contrail cirrus) in favorable meteorological conditions. No reliable best estimate of the contribution of contrail cirrus to climate change exists, but statistical evidence from cirrus trend analyses suggests a potentially large contribution. This article reviews the scientific knowledge and key problems regarding the modeling of the life cycle of contrail cirrus (including linear contrails), their global climate impact, and the validation of model simulations with suitable observational datasets. The prerequisites for global modeling of contrail cirrus, such as the representation of ice supersaturation and the processes governing contrail cirrus evolution as well as improvements in the cloud schemes regarding cirrus, are discussed. Recommendations are given for avenues of research to ensure that future decisions aimed at mitigating the climate impact of contrails and contrail cirrus are based on increasingly sound scientific knowledge. DOI: 10.1175/2009BAMS2656.1

Information about climate and how it responds to increased greenhouse gas concentrations depends heavily on insight gained from numerical simulations by coupled climate models. The confidence placed in quantitative estimates of the rate and magnitude of future climate change is therefore strongly related to the quality of these models. In this study, we test the realism of several generations of coupled climate models, including those used for the 1995, 2001, and 2007 reports of the Intergovernmental Panel on Climate Change (IPCC). By validating against observations of present climate, we show that the coupled models have been steadily improving over time and that the best models are converging toward a level of accuracy that is similar to observation-based analyses of the atmosphere.

Regional climate models are important research tools available to scientists around the world, including in economically developing nations (EDNs). The Earth Systems Physics (ESP) group of the Abdus Salam International Centre for Theoretical Physics (ICTP) maintains and distributes a state-of-the-science regional climate model called the ICTP Regional Climate Model version 3 (RegCM3), which is currently being used by a large research community for a diverse range of climate-related studies. The RegCM3 is the central, but not only, tool of the ICTP-maintained Regional Climate Research Network (RegCNET) aimed at creating south-south and north-south scientific interactions on the topic of climate and associated impacts research and modeling. In this paper, RegCNET, RegCM3, and illustrative results from RegCM3 benchmark simulations applied over south Asia, Africa, and South America are presented. It is shown that RegCM3 performs reasonably well over these regions and is therefore useful for climate studies in EDNs.

A new approach, called transferability intercomparisons, is described for advancing both understanding and modeling of the global water cycle and energy budget. Under this approach, individual regional climate models perform simulations with all modeling parameters and parameterizations held constant over a specific period on several prescribed domains represent ing different climatic regions. The transferability framework goes beyond previous regional climate model intercomparisons to provide a global method for testing and improving model parameterizations by constraining the simulations within analyzed boundaries for several domains. Transferability intercomparisons expose the limits of our current regional modeling capacity by examining model accuracy on a wide range of climate conditions and realizations. Intercomparison of these individual model experiments provides a means for evaluating strengths and weaknesses of models outside their 'home domains' (domain of development and testing). Reference sites that are conducting coordinated measurements under the continental-scale experiments under the Global Energy and Water Cycle Experiment (GEWEX) Hydrometeorology Panel provide data for evaluation of model abilities to simulate specific features of the water and energy cycles. A systematic intercomparison across models and domains more clearly exposes collective biases in the modeling process. By isolating particular regions and processes, regional model transferability intercomparisons can more effectively explore the spatial and temporal heterogeneity of predictability. A general improvement of model ability to simulate diverse climates will provide more confidence that models used for future climate scenarios might be able to simulate conditions on a particular domain that are beyond the range of previously observed climates.

The swirls of ocean circulation known as mesoscale eddies are essentially 'the weather of the ocean,' says Brown University's Baylor Fox-Kemper, who notes that these eddies, which range from tens [...]