- Greenhouse-gas induced warming trends are projected to be particularly amplified in the Arctic. The reasons are complex, but are most usually attributed to changes in sea ice cover and associated feedbacks to the atmosphere. A component of this problem that has been previously overlooked is the role of long-range transport of pollution aerosol from mid-latitudes. "Arctic Haze" , a recognized phenomenon since the 1800's, may be contributing to winter surface warming by increasing low-cloud thermal emission. This thermal "indirect effect" will be described, along with its potential to increase Arctic surface temperatures. But care must be taken when ascribing meaning to this or any other argued climate forcing from aerosol pollution. Cloud and precipitation feedbacks are an intrinsic part of the aerosol-climate system, and they make separating cause and effect an ambiguous exercise at best. Using chemical tracers as proxies for component physical processes may point to some form of solution.



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In this presentation I will discuss results from on-going research work that aims to unravel the complexity of atmospheric organic aerosol through applying new instrumental and data analysis techniques for field measurements with the AMS. A factor analysis technique for a quantitative classification of organic aerosols into distinct and physically meaningful classes will be presented. The basis of the technique and its application to the analysis of ambient particles at multiple urban, rural, and remote locations in the northern hemisphere will be discussed. I will also present results from a resent deployment of a high mass resolution time-of-flight aerosol mass spectrometer (HR-TOFAMS), which has a maximum mass resolution of approximately 5000, at the peak of the Whistler Mountain in Canada. The separation of ion fragments with the same integer mass but very small mass differences (of the order of 0.01 amu) by the HR-TOFAMS allows a better understanding of the chemical composition of organic aerosol and provides unique insights into the sources and process of this substance.

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- Overview of activities at the annual DOE ARM Program Science Team Meeting, held in Albuquerque, New Mexico from Mar. 27 - 31, 2006.

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- Radiation transport in the three-dimensional (3D) vegetation canopy is critical to remote sensing of vegetation and modeling of land surface energy budget in climate models. The theory of radiative transfer in stochastic media provides the most logical linkage between radiation transport and 3D canopy structure through a closed system of simple equations. The potential of stochastic radiative transfer in the field of satellite remote sensing or climate modeling has not been fully realized because of the lack of canopy pair correlation function models. The pair correlation function is defined as the probability of finding simultaneously phytoelements at two spatial points. Using the theory of stochastic geometry, we derive analytical pair correlation functions for vegetation canopies with hierarchical clumping structure. It is shown that the spatial correlation between phytoelements is primarily responsible for the effects of the 3D canopy structure on canopy optical properties. The pair correlation function, therefore, is the most natural and physically meaningful measure of the canopy structure over a wide range of scales. By extending the pair correlation function to a mixed vegetation canopy, we are also able to investigate the effects of species mixture on the radiation regime. The model performance is evaluated by in situ measurements. The simulated canopy reflectances compare well with the PARABOLA measurements in the BOREAS Southern Study Areas.

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- Large uncertainties in aerosol properties and simple assumptions in aerosol models have made accurate prediction of aerosol radiative forcing and climate impact difficult. A common assumption in most models is that that black carbon (BC) aerosol consists of spherical particles. In reality, BC particles consist of smaller particles that aggregate into clusters having highly irregular and complex morphology. These properties have consequences regarding the atmospheric lifetime and optical properties of BC. Despite the complexity, the overall structure of BC aggregates can be described by fractals. Using fractal modeling, we can better understand the fate of BC and its optical properties.

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- An alternative method to measuring aerosol absorption will be presented: measurement of the thermal dissipation of the spectrally absorbed energy through interferometry. The use of this coherent optical detection technique is particularly well suited to measuring the refractive index change that accompanies this energy transfer process. This technique was even demonstrated towards measuring aerosol absorption in the mid-1980s. Attractive features of this technique for measuring aerosol absorption include its insensitivity to aerosol scattering, its ability to conduct the measurement in situ, its inherent high sensitivity, and near real-time response.

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- NASA released ROSES (Research Opportunities in Space and Earth Sciences) 2006, which is a tentative schedule for all NASA proposal calls for 2006. We will discuss the different opportunities that will be coming up and their tentative timeframes so that people are aware of them.

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