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News & Events

About February 2011

This page contains all entries posted to Physics Announcements in February 2011. They are listed from oldest to newest.

December 2010 is the previous archive.

March 2011 is the next archive.

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February 2011 Archives

February 2, 2011

Seminar: Wednesday, February 2, 2011 at 3:30pm

Clouds, Aerosols, and 3D Radiative Processes
Dr. Tamás Várnai

Some of the largest uncertainties in understanding human impacts on climate arise from difficulties in quantifying the effects of atmospheric aerosols on solar radiation and clouds. A better understanding of these effects will require accurate calculations of solar heating and accurate measurements of aerosol and cloud properties. The three-dimensional (3D) nature of radiative processes can create challenges such as accommodating computational demands and specifying necessary inputs—and as a result, both climate simulations and satellite data interpretation methods use one-dimensional (1D) radiation models that treat each atmospheric column separately, without considering their interactions.

The presentation will first discuss solar heating calculations for a multiyear dataset of clouds observed at three Department of Energy sites. These calculations indicate that horizontal radiative interactions cause 1D radiation models to underestimate average solar heating by a few W/m2. The talk will next present CALIOP and MODIS satellite data in examining atmospheric particles and 3D radiative processes near clouds. The results indicate that clouds are surrounded by a wide transition zone of increased particle size, enhanced light scattering, and significant 3D radiative interactions. The talk will also outline some possibilities for considering 3D radiative interactions in dynamical simulations and satellite remote sensing.

Location: Physics Bldg., Room 401

February 9, 2011

Seminar: Wednesday, February 9, 2011 at 3:30pm

Remote Sensing of Global Cloud Properties from MODIS
Dr. Zhibo Zhang

Clouds cover about 2/3 of Earth’s surface. They play a crucial role in regulating Earth’s energy budget. Clouds reflect part of the sunlight back to space (i.e., albedo effect), which reduces the solar energy available to Earth’s surface. At the same time, clouds also act like greenhouse gases—they block the emission of heat to space and inhibit the ability of the planet to release its absorbed solar energy (i.e., greenhouse effect). The net radiative effect of clouds on the climate depends on the global distribution of clouds and their optical and microphysical properties. Satellite-based, long-term, global cloud observation is the key to understanding the role of clouds in the current climate system and how clouds will change with global warming.

In this talk, I will provide an overview of the remote sensing of global cloud properties using a NASA satellite sensor—MODIS (Moderate Resolution Imaging Spectroradiometer). In the first part, I will explain the fundamental physics behind the retrieval of two key cloud parameters, cloud optical thickness and cloud particle effective radius, from MODIS cloud reflection measurements. In the second part of this talk, I will present our recent studies on several key issues in MODIS cloud retrieval algorithm. Topics will include: i) an assessment of the uncertainties in MODIS ice cloud products due to the complex and variable nature of ice crystals; ii) an investigation of the influence of cloud vertical structure on cloud particle effective radius retrieval; and iii) a study on the 3-D radiative transfer effect on MODIS cloud particle effective radius retrieval.

Location: Physics Bldg., Room 401

February 14, 2011

PhD Proposal Defense - Tao Peng

Tao successfully defended his PhD Proposal on February 14, 2011.

Simulation of Multi-photon Qubit for Quantum Computing

Quantum computer has drawn a lot of attention over decades due to its huge potential and the recent progress is encouraging. One of the critical issues of quantum computing is the requirement of entangled states with a large number of particles. Although the study of entangled states greatly advanced our understanding about the physics of multi-particle superposition, we are still facing difficulties producing entangled states with more than three particles. Comparing with entangled states, it is not that difficult to achieve a superposition among a large number of multi-photon amplitudes for chaotic-thermal light.

A set of experiments have been successfully done to simulate Bell-state with two independent thermal radiations. Moreover, I propose a serial of further works to simulate entangled three-photon, generate N-digit qubits as well as multi-photon interferometry of chaotic-thermal light. This can be used for computation purpose, such as factorize a large number.

February 23, 2011

Seminar: Wednesday, February 23, 2011 at 3:30pm

Solar Forced Thermal Tides in the Atmosphere
Dr. Jian Du-Caines
University of Cambridge, UK

While gravitationally forced lunar tides generate significant amplitude periodic oscillations in the global oceans the corollary is not true for the atmosphere. In fact the lunar tides in the atmosphere are quite small in comparison to the thermally forced solar tides. These atmospheric tides are forced by the periodic absorption of solar radiation in the infra-red by water vapor in the troposphere and the ultraviolet by ozone in the stratosphere. Conserving energy and propagating vertically through the atmosphere these waves can reach significant amplitudes of 30-50 m/s in the horizontal wind field and 10-20K in the temperature field of the mesosphere before breaking or dissipating. This provides a mechanism for the redistribution of energy throughout the atmosphere.

In this talk I will provide a brief overview of the solar forced atmospheric tides, results from current modelling efforts and discuss recent observations from space and ground-based instruments. One of the potential generation mechanisms for the atmospheric tides – non-linear interactions between waves and the transport effect of atmospheric waves in the mesosphere are also briefly discussed.

Location: Physics Bldg., Room 401