Colloquia for Spring 2013

Chemical, Biological, and Hygroscopic Properties of Aerosol Organics at Storm Peak

May 09, 2013

A. Gannet Hallar

Hosted by Christina McCluskey

Aerosols affect the EarthÂ’s radiation balance directly by scattering sunlight and indirectly through their role as cloud condensation nuclei (CCN). These effects are enhanced for hygroscopic aerosols, which absorb water as a function of relative humidity, grow in size, scatter more light, and serve as cloud condensation nuclei. Absorption of water vapor by aerosols to produce haze and cloud…

The stratospheric aerosol layer: uncertainties in our understanding and consequences for climate change and geoengineering

May 02, 2013

Thomas Peter

Hosted by Thomas Birner

Stratospheric aerosols are important climate forcers as they reflect a part of the incoming solar radiation, thereby cooling the earth surface and troposphere, and absorb a part of the outwelling terrestrial radiation, thereby heating the stratosphere. In addition they are important players in stratospheric ozone chemistry as they reduce the abundance of stratospheric nitrogen oxide radicals.…

Improvements and Remaining Challenges in the Parameterization of Microphysics and its Impact on Deep Convection

April 25, 2013

Hugh Morrison

Hosted by Russ Schumacher

With increasing use of high resolution (convection-permitting) models for numerical weather prediction and climate simulation, microphysics has moved to the forefront in terms of physical parameterizations. This is because without the use of traditional convection parameterizations in these models, microphysics is directly coupled to the convective dynamics. An overview of current approaches…

Impact of Chikira-Sugiyama Cumulus Scheme in Climate and Variability

April 18, 2013

Minoru Chikira

Hosted by Dave Randall

A cumulus scheme developed in Chikira and Sugiyama (2010) is an offshoot of the prognostic Arakawa-Schubert scheme. But it is characterized by state-dependent entrainment rate based on Gregory (2001) and a spectral representation of cloud types according to cloud base updraft velocity. The scheme naturally represents the effect of free-tropospheric humidity on deep convection through the…

Improving Communication of Weather Forecasts and Warnings to Aid Decisions

April 11, 2013

Rebecca E. Morss

Hosted by Russ Schumacher

Future weather is inherently uncertain, and weather forecasts are received and used every day by millions of people. This makes weather forecasting a common form of environmental risk communication that is familiar to much of the public. Weather forecasts and warnings are also used by public officials, members of the public, and others to help reduce negative impacts of hazardous weather events…

A University Perspective on Climate Modeling

April 04, 2013

Dave Randall

Hosted by Scott Denning

Climate modeling began about 50 years ago, as a purely academic endeavor. Although things have changed considerably, especially during the past 20 years, universities have a continuing major role in model development and applications, and in training young modelers-to-be. I will discuss the history, comment on where we are now, and offer some thoughts about where the field is going.

Precipitation Physics Revealed through Dual-polarization Radar Observations and Modeling

March 28, 2013

Matt Kumjian

Hosted by

Dual-polarization radar data provide great insight into the types and distribution of hydrometeors in storms. This information can be used to study a variety of precipitation processes. This talk will cover radar observations of warm-rain physics (collisional breakup, coalescence, evaporation, and size sorting), the lofting and freezing of raindrops in deep convective storms and the appearance…

Rossby Wake Breaking and Transport between the Tropics and Extratropics above the Subtropical Jet

March 14, 2013

Cameron Homeyer

Hosted by Thomas Birner

Rossby wavebreaking is an important mechanism for the two-way exchange of air between the tropical upper troposphere and lower stratosphere and the extratropical lower stratosphere. We present a 30-year climatology (1981-2010) of anticyclonically and cyclonically sheared wavebreaking events along the boundary of the tropics in the 350-500 K potential temperature range from ECMWF ERA-Interim…

Tropical cyclone genesis factors in paleoclimate simulations

March 07, 2013

Robert Korty

Hosted by Aaron Piña

Over the last twenty years, a pioneering group of geomorphologists has developed processes for extracting information about prehistoric, landfalling hurricanes back through the last several millennia by studying sedimentary over-wash deposits in geologic cores. They have found active periods interspersed among long intervals with little or no trace of significant activity, which raises…

Shock-Like Structures in the Hurricane Boundary Layer

February 22, 2013

Wayne Schubert

Hosted by Dick Johnson

This talk will present high horizontal resolution solutions of an axisymmetric, constant depth, slab boundary layer model designed to simulate the radial inflow and boundary layer pumping of a hurricane. For intense vortices the u(partial u/partial r) term in the radial equation of motion produces a shock-like structure in the radial wind, i.e., near the radius of maximum tangential wind the…

The challenge of tropospheric ozone in the western US

February 14, 2013

Dr. Dan Jaffe, Professor

Hosted by Sonia Kreidenweis

Ozone is a natural component of the stratosphere and a minor component in the lower atmosphere, but anthropogenic smog significantly enhances the concentrations in the troposphere. As a strong oxidizer, ozone will react with many substances including plant and animal tissues. Numerous health studies have demonstrated significant impacts on lung function from ozone exposure. As a result, over…

Understanding Arctic Mixed-Phase Clouds: Use of Doppler Velocity Spectra

February 07, 2013

Hans Verlinde

Hosted by Sue van den Heever

Observations reveal that long-lasting, mixed-phased stratiform clouds may be observed in all months of the year in the Arctic lower troposphere. These clouds have a large impact on radiative transfer through the atmosphere, and hence the surface energy budget. The ability of these clouds to persist for several days remains perplexing, because liquid-ice mixtures are inherently unstable and will…

Why is the ITCZ in the Northern Hemisphere? And why might it have shifted southward in the late 20th century?

January 31, 2013

Dargan Frierson

Hosted by Walter Hannah

The Northern Hemispheric maximum of the tropical rainfall is usually thought to be caused by properties of tropical landmasses, such as the size and shape of continents. However, a variety of recent studies have established that conditions even well outside the tropics also affect tropical circulation and rainfall. Using this new understanding, we demonstrate that the meridional overturning…

Faculty Intro Jamboree Part II

January 24, 2013

Profs. Collett, Kreidenweis, Maloney, Pierce, Rutledge, Schubert, van den Heever

Hosted by ATS

What: 5–10 min intros by individual faculty members Who: Profs. Collett, Kreidenweis, Maloney, Pierce, Rutledge, Schubert, van den Heever Why: provide overview of research areas & groups in the department Why2: gather for cookies & snacks afterwards