| January 24 |
No colloquium - AMS Meeting |
| January 31 |
Clouds: Their Effect on Aerosol and Vice-versa |
Jeff Snider, University of Wyoming |
Removal of the atmospheric aerosol by hydrometeors (i.e., droplets, rain and snow) is the main process by which the atmosphere is cleansed of particulate matter. Aerosol particles and hydrometeors interact by impaction, by diffusive processes, and when particles function as condensation or ice nuclei. These removal processes influence the aerosol, obviously, and can also indirectly impact the microphysical and macrophysical structure of clouds.
This work uses airborne measurements of cloud kinematics, obtained from a dual-beam Doppler cloud radar, airborne measurements of aerosol, and a Lagrangian parcel model to study the removal of aerosol via their interaction with clouds.
Two cloud types are considered. First, we analyze data from a summertime marine stratocumulus system and document the scavenging of particles large enough to have served as cloud droplet nuclei in this liquid-only cloud system. Second, we analyze observations from a winter mountain cloud using vertical and horizontal wind velocities derived from the radar. In this case the scavenging process is passive, i.e. the particles attached to hydrometeors by Brownian diffusion. Combining the kinematics with a Lagrangian parcel model leads to interesting results regarding particle removal via Brownian diffusion as well as insight into the spatial distribution of cloud water in mixed-phase mountain cloud systems. |
| February 7 |
Rethinking Convective Quasi-Equilibrium |
David Neelin, UCLA |
Convective quasi-equilibrium (QE) has for several decades stood as a key postulate for parameterization of the impacts of moist convection at small scales upon the large-scale flow.
Observational results aimed at helping to constrain convection schemes suggest some important features, like a coherent free tropospheric temperature, work as a leading approximation, while other aspects are in need of revision. The properties of precipitation as a function of water vapor and temperature conform to those of critical phenomena associated with a continuous phase transition. This is used to infer empirically the temperature-moisture dependence of the critical point at which precipitation increases rapidly. While the system's attraction to the critical point is predicted by QE, several fundamental properties of the transition, including high precipitation variance in the critical region, need to be added to the theory. Long-range correlations imply that this variance does not reduce quickly under spatial averaging; scaling associated with this spatial averaging has potential implications for superparameterization. Long tails of the distribution of water vapor create relatively frequent excursions above criticality with associated strong precipitation events. |
| February 14 |
Lidar observed inter-annual variability in the middle atmospheric temperature |
Tao Li, NASA NPL |
As a key instrument of the Network for the Detection of Atmospheric Composition Change (NDACC), the Jet Propulsion Laboratory Rayleigh-Raman lidar located at Mauna Loa Observatory (MLO), Hawaii (19.5°N, 155.6°W) has been measuring the vertical temperature profiles from 15 to 85 km routinely since 1993. A linear regression analysis including the components of the Quasi-Biennial Oscillation (QBO), El Niño-Southern Oscillation (ENSO), and the 11-year solar cycle, was applied to the deseasonalized monthly mean temperature from January 1994 to June 2007. A significant QBO signal (1-3 K) in the stratosphere and mesosphere, and a strong winter signature of ENSO (-1.5 K/MEI) in the stratosphere were revealed. A response to the solar cycle was observed, characterized by two statistically significant maxima of ~1 K/100 f10.7 unit in the upper stratosphere (annual mean). Finally, a statistically significant signature of ENSO in the middle mesosphere was observed for the first time, consistent with the findings of recent model simulations, and further confirmed by the calculation of temperature gravity wave variances.
As an introduction to the long-term study that leads to the above result, I will briefly describe the purpose of NDACC and the associated lidar measurements as well as the nature of the proxies used for the linear regression analysis. |
| February 21 |
No colloquium |
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| February 28 |
An overview of the policy landscape for dealing with climate change |
Michele Betsill, CSU |
As the scientific evidence of global climate change becomes more conclusive, societies have increased their efforts to come up with policies to mitigate greenhouse gas emissions. These policies are being developed at all levels of human organization, from the global to the local level and involve governments, the private sector and civil society. This talk will provide a tour through this landscape providing illustrations of different types of climate change policies, ranging from the Kyoto Protocol to the development of carbon markets. Along the way, I will discuss some of the political debates that shape the ways societies choose to address the climate issue. |
| March 6 |
A stool with Three Legs: Sources of Uncertainty in the Climate of the 21st Century |
A. Scott Denning |
Reliable projections of future climate are hard to make. Atmospheric composition is changing rapidly, with concentrations of greenhouse gases higher than they have been in many millions of years. Enhanced downward longwave radiation will certainly warm the Earth's surface unless negative feedbacks counteract it. The degree of warming to expect and the associated changes in other aspects of the climate system, however, is very difficult to predict. There are three leading sources of uncertainty in projections of future climate, all of similar magnitude.
Working Group 1 of the Intergovernmental Panel on Climate Change highlighted uncertainties associated with the strength of climate feedbacks to enhanced greenhouse forcing, especially those related to clouds. Many cloud processes are unresolved in global climate models, and involve very strong interactions among radiation, vertical motion, energy transport, and the hydrologic cycle that have the potential to modulate climate change. These effects will amplify or damp greenhouse forcing, but climate science is currently unable to confidently predict which or how much.
A second and very substantial source of uncertainty in projections of future climate is the future emissions of additional greenhouse gases by human societies. Economists and social scientists have developed a large suite of scenarios or "story lines" regarding future changes in population, economic development, international trade, and technology that lead to very different visions of future emissions. Used in climate models, the range of these emission scenarios produces a range of future climates that is even larger than the range associated with uncertainties in climate feedbacks due to clouds, aerosols, and other aspects of the physical climate system.
Even given a certain scenario of greenhouse gas emissions and physical climate sensitivity, the response of the Earth's biogeochemical cycles to changes in emissions is highly uncertain. The range of projections of future levels of greenhouse forcing for a given emission scenario is also very large, due to uncertain behavior of the carbon cycle both on land and in the oceans in response to changing climate. Previous calculations have almost certainly overestimated future land sinks of CO2 because of a subtle but one-sided error in the treatment of ice core data. The range of future greenhouse forcing due to these uncertainties is comparable to that associated with uncertain social science, and produces climate uncertainty comparable to that arising from uncertain physics |
| March 13 |
Gravity currents in a deep anelastic atmosphere |
George Bryan, NCAR MMM |
The region of relatively cold air that develops near the ground below deep moist convection is usually referred to as a "cold pool." Cold pools play a fundamental role in the organization and propagation of mesoscale convective systems (MCSs). Using special observations collected during BAMEX, analysis has revealed that cold pools are often 4 km deep in intense, midlatitude MCSs. Such large cold pool depths have raised concerns about the applicability of certain theoretical formulas that are used to study cold pools, such as Benjamin's famous formula for the propagation speed of cold pools. These formulas are derived from studies of gravity currents -- i.e., the flows that develop as cold air spreads along a flat surface -- and the formulas were developed using the incompressible equations, which are valid only for shallow flows (< 1 km). To gain new insight, an analytic study was undertaken using the anelastic equations, which are appropriate for deep (~10 km) flows. Two key results emerged from this study. First, the maximum propagation speed of atmospheric cold pools is about 25% less than is indicated by Benjamin's formula. Second, it is impossible to have a steady cold pool greater than 4 km deep in the Earth's troposphere (under the assumptions used in this study). These results will be explained in this talk, partly by drawing an analogy to flow over an airfoil. |
| March 20 |
No colloquium - Spring Break |
| March 24 |
The Impacts of the Cold pool and Gust Front on Convective Storms |
Sue van den Heever, CSU ATS |
The cold pool and associated gust front produced by convective storms are frequently involved in subsequent convective development, whether by strengthening the original convective storm producing the cold pool, or by generating new convection. This development may occur through a number of different processes including the forced lifting of environmental air up and over the progressing gust front, as well as due to boundary collisions between gust fronts of neighboring storms. In addition to enhancing convection, the presence of cold pools may also be destructive to the development of subsequent convective storms through their influence on the thermodynamics, humidity and static stability of the boundary layer.
In this talk, the constructive or destructive role of the cold pool and gust front in convective storm development will be explored using numerical simulations of several different convective regimes. Simulations of tropical convection over Florida demonstrate the role of the gust front in temporarily counteracting the influences of aerosol on the production of precipitation. The re-development and strengthening of convective storms downwind of an urban region demonstrates the ability of the cold pool and the gust front to further modify convection enhanced by the presence of an urban air mass. The longevity of a left-moving supercell storm illustrates how the characteristics of the cold pool influence the lifetime of the storm. Simulations of tropical oceanic convection demonstrate that the production of new shallow convection appears to be associated with variations in humidity and static stability associated with the cold pool development. Finally, the results of idealized simulations of the storm development following gust front collisions, is presented. Although each of these scenarios show convective storms forced by very different initial conditions, several generalizations can be made about the role of the cold pool and gust front in the subsequent convective development. |
| March 27 |
Terrain-induced Rotor Experiment: New Insights into Lee Waves and Atmospheric Rotors |
Vanda Grubisic, Dessert Research Institute |
Atmospheric rotors are three-dimensional anisotropic atmospheric vortices that form parallel to and downwind of a mountain crest under conditions conducive to generation of large-amplitude lee waves. Intermittency, high-levels of turbulence, and complex small-scale internal structure are defining characteristics of rotors, which pose a known hazard to aviation. The central objective of the Terrain-induced Rotor Experiment (T-REX, March-April 2006, Sierra Nevada, CA) was to provide a comprehensive set of in situ and remotely-sensed meteorological observations from the ground to the upper tropospheric-lower stratospheric altitudes for the documentation of spatiotemporal characteristics of a tightly coupled system, consisting of an atmospheric rotor, terrain-induced internal gravity waves, and a complex-terrain boundary layer. Along with a concise overview of the entire project, presented will be new insights into the structure of atmospheric rotors and their relation to atmospheric lee waves that have emerged from our T-REX observational analyses to date and the related real-data and idealized numerical modeling studies of lee waves and, more generally, flow over complex terrain. |
| April 1 |
Submesoscales and Mixed Layer Eddies |
Baylor Fox Kemp, CU |
Oceanographers have traditionally viewed turbulence in two
categories--fine scale and mesoscale--the fine scale turbulence being
three-dimensional and effective at mixing across density classes while
mesoscale turbulence is quasi-two-dimensional and nearly adiabatic.
Recent work has shown that the scales in between, the submesoscales,
have interesting dynamics distinct from either smaller or larger
scales and a direct impact on climate. I will present some dynamical
results of the submesoscale, as well as a parameterization developed
to capture the most important effects of submesoscale eddies on
climate. |
| April 3 |
Multiscale observations and modeling of land-atmosphere interactions |
David Gochis, NCAR RAL |
The complexity of land-atmosphere coupling occurring across a wide range of temporal and spatial scales makes it difficult to isolate cause and effect relationships in hydrometeorological and hydroclimatic events. In turn, such complexity and non-linearity inhibits the definition of generalized or simply parameterized functional relationships for describing land atmosphere interactions across scales. In this seminar, recent work related to developing and deploying advanced multiscale land surface processes in both weather and climate models will be presented. This work aims to explicitly and implicitly improve characterization of landscape complexity and its impact on hydormeteorological and hydroclimatic processes such as convective initiation, the diurnal cycle of rainfall, precipitation-runoff responses and soil moisture-vegetation interactions. First, results from a recent suite of climate simulations using the coupled CAM/CLM modeling system and a new sub-grid fine-mesh parameterization are presented. Results from these simulations show significant impact from sub-grid precipitation disaggregation on land atmosphere coupling as well as trans-seasonal runoff responses in transient snow/complex terrain regions of N. America. The dependence of regional hydroclimatology on precipitation character from this and other studies is then expanded upon using findings from several years of observational studies from the North American Monsoon region of western Mexico. Lastly, the impact of analyzed and forecasted precipitation character on detailed runoff processes (hillslope redistribution, groundwater coupling, streamflow and reservoir levels) using a newly enhanced land surface parameterization are presented. The seminar concludes with a preview of findings from a planned flash flood forecast demonstration project to be conducted over the Colorado Front Range region during the spring and summer of 2008. |
| April 10 |
Atmospheric Chemistry In and Near a Megacity: The 2006 Mexico City MILAGRO Field Campaigns |
Sasha Madronich, NCAR |
The atmosphere near North America’s largest megacity, Mexico City, was studied intensively in March 2006 under project MILAGRO and its components MCMA-2006, MIRAGE-Mex, MAX-Mex, and INTEX-B/1. Instruments to measure chemical composition of gases and particles, optical and microphysical properties, spectral radiation, and meteorological variables were deployed at numerous surface locations in and near the city, and onboard 6 airplanes to provide regional coverage. A major objective was to gain better understanding of the chemical evolution of pollutants during the transition from the urban to the regional scale. Analyses of the results are still in early stages, but already suggest that photochemical formation of oxidants (e.g. ozone) and secondary aerosols (esp. organics) continues vigorously in the urban outflow for several days. This is due at least in part to the fact that urban reactivity is inhibited by high emissions of nitrogen oxides and by aerosol-induced reductions in photolytic ultraviolet radiation, so that a substantial fraction of yet-to-be reacted pollutants is exported to the regional atmosphere. Such results suggest that, contrary to an old adage, the solution to pollution is not dilution, and the effects of urbanization may be felt quite far downwind of their sources. |
| April 17 |
What's it like to go into Space? |
Piers Sellers, NASA JSC
CMMAP Lecture Series |
Piers Sellers is an astronaut who flew on two Shuttle missions to the International Space Station; STS-112 in 2002, and STS-121 in 2006. On each mission he carried out three spacewalks.
Piers will show you what its like to go into space with the help of video, some great pictures and some cheap props. Anyone who is interested in Space, complex engineering and the future of space exploration is encouraged to attend.
Before becoming an astronaut, Piers worked as a scientist on climate problems at the NASA Goddard Spaceflight Center. He collaborated closely with the climate research group here at CSU. |
| April 24 |
Representing Organic Aerosols: From new particle formation to absorptive partitioning |
Kelley Barsanti, NCAR ASP |
As we strive to predict the impacts of particulate matter (PM) reduction strategies on air
quality, and the feedbacks between aerosols and a changing climate, we struggle on a more
fundamental level with understanding the formation of organic aerosols (OA) in the real
atmosphere. It is known that particles are emitted directly to the atmosphere; and formed
in the atmosphere via nucleation and absorptive partitioning of oxidized volatile organic
compounds. However, there is incomplete knowledge of the suite of compounds that
contribute to OA, and the pathways by which organic PM (OPM) is formed. To some extent,
it is this incomplete understanding that has precluded our ability to accurately represent
atmospheric OPM levels with regional and global climate models. Additionally, there are
challenges associated with incorporating our growing understanding of OA into existing
model frameworks. Presented here are some of the advancements in our understanding of
the pathways that lead to particle formation in the atmosphere and some thermodynamic
considerations of those pathways, as well as a more general modeling framework in which
such advancements can be considered. Ideally, with advancements in our fundamental
understanding of OA, we will be able to predict atmospheric OPM levels more accurately
and therefore, make better predictions regarding the interactions between aerosols, air
quality, and future climate.
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| April 29 |
A Study of the Madden-Julian Oscillation Using a Global Cloud-Resolving Model |
Hiroaki Miura, JAMSTEC/CSU |
A global cloud-resolving model has been developed at the Frontier Research Center for Global Change in Japan. We have used the model to simulate a Madden-Julian Oscillation (MJO) event that occurred in December 2006 and January 2007. The slow eastward movement of the convectively active region of the MJO event was reproduced at least marginally. The eastward shift of the convective center, from the Indian Ocean to the Pacific Ocean, was probably related to the n=1 Rossby wave, which brought abundant moisture from the east, as discussed by Masunaga et al. (2006). Tropical depression-type disturbances might account for the strong eastward propagating signals inside the envelope of active convection. Sensitivity runs suggest that the zonal sea surface temperature (SST) gradient and the effects of New Guinea had some influence on the MJO, but the time change in the SST did not modulate the eastward movement speed very much. |
| May 1 |
Riehl Award Ceremony |
| May 8 |
No Colloquium - Finals Week |
Please contact Dave Randall [randall (at) atmos.colostate.edu] or Scott Denning [denning (at) atmos.colostate.edu] for more information.
