Improving our fundamental understanding of the role of aerosol−cloud interactions in the climate system

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol−cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty

The influence of hemispheric asymmetry and realistic basic states on tropical stationary waves in a shallow water model

Thesis (Ph. D.)--University of Washington, 2005.A shallow water model is used to study the stationary waves in the tropical upper troposphere. Realistic zonal-mean winds are generated by imposing a zonally-symmetric topography distribution underneath a thin fluid layer and relaxing the fluid towards its global-mean depth. Basic states with zero mean meridional flow are also constructed by balancing the height field with the equilibrium zonal-mean zonal winds. Both hemispherically-symmetric (equinoctial) and hemispherically-asymmetric (solstitial) basic states are considered. Stationary waves are generated by adding a mass source-sink distribution along or near the equator.Westerly zonal-mean flow in the subtropics amplifies the stationary wave response to tropical eddy forcing and shifts the eddy height and vorticity maxima to the east, bringing the simulated eddies into better agreement with the observed seasonally varying eddy circulations in the tropical upper troposphere. Moving the wave forcing off the equator amplifies the response in the forced hemisphere, but the response in the opposite hemisphere decreases only slightly because the eddy divergent winds act over a wide latitudinal range. The zonal-mean circulation in the solstitial basic state enhances the eddy response in the winter hemisphere and limits the response in the summer hemisphere. Hemispheric asymmetry in either the eddy forcing or the basic state also leads to cross-equatorial eddy momentum fluxes. Linear experiments exhibit stronger subtropical anomalies, weaker variations along the equator, and less hemispheric symmetry than nonlinear integrations.When the eddy forcing is located in the summer hemisphere of the solstitial basic state, the mean meridional winds enhance the propagation of wave activity across the equator, leading to stronger cross-equatorial eddy momentum fluxes and an eddy response with similar amplitudes in both hemispheres. Hence, the anti-correlation between the mean meridional flow and eddy momentum fluxes over the equator and the striking hemispheric symmetry of the tropical stationary waves over the course of the seasonal cycle can both be attributed to the tendency for the maximum eddy and zonal-mean diabatic forcing to occur in the same latitude band. The influence of the mean meridional flow on eddy momentum fluxes at low latitudes is also demonstrated in a simple linear barotropic model

Demeter – A Land Use and Land Cover Change Disaggregation Model

Demeter is an open source Python package that was built to disaggregate projections of future land allocations generated by an integrated assessment model (IAM). Projected land allocation from IAMs is traditionally transferred to Earth System Models (ESMs) in a variety of gridded formats and spatial resolutions as inputs for simulating biophysical and biogeochemical fluxes. Existing tools for performing this translation generally require a number of manual steps which introduces error and is inefficient. Demeter makes this process seamless and repeatable by providing gridded and land cover change (LULCC) products derived directly from an IAM—in this case, the Global Change Assessment Model (GCAM)—in a variety of formats and resolutions commonly used by ESMs. Demeter is publicly available via GitHub and has an extensible output module allowing for future ESM needs to be easily accommodated. Funding statement: This research was supported by the U.S. Department of Energy, Office of Science, as part of research in Multi-Sector Dynamics, Earth and Environmental System Modeling Program. It builds on previous work supported by the National Aeronautics and Space Administration Carbon Monitoring System and ACCESS programs under projects NNH12AU35I and NNH13AW58I, and by the Laboratory Directed Research and Development Program at Pacific Northwest National Laboratory (PNNL), a multi-program national laboratory operated by Battelle for the U.S. Department of Energy under Contract DE-AC05- 76RL01830

Improving our fundamental understanding of the role of aerosol-cloud interactions in the climate system

The effect of an increase in atmospheric aerosol concentrations on the distribution and radiative properties of Earth’s clouds is the most uncertain component of the overall global radiative forcing from preindustrial time. General circulation models (GCMs) are the tool for predicting future climate, but the treatment of aerosols, clouds, and aerosol−cloud radiative effects carries large uncertainties that directly affect GCM predictions, such as climate sensitivity. Predictions are hampered by the large range of scales of interaction between various components that need to be captured. Observation systems (remote sensing, in situ) are increasingly being used to constrain predictions, but significant challenges exist, to some extent because of the large range of scales and the fact that the various measuring systems tend to address different scales. Fine-scale models represent clouds, aerosols, and aerosol−cloud interactions with high fidelity but do not include interactions with the larger scale and are therefore limited from a climatic point of view. We suggest strategies for improving estimates of aerosol−cloud relationships in climate models, for new remote sensing and in situ measurements, and for quantifying and reducing model uncertainty