Gravity Waves in the Middle Atmosphere
Gravity (buoyancy) waves play an important role in transferring momentum from source regions in the lower atmosphere to the middle and upper atmosphere. Body forces produced by breaking waves lead to residual circulations that profoundly affect the state of the atmosphere. This talk will summarize results from recent campaigns to measure wave generation and propagation and the associated momentum fluxes.
High-Speed Spectral Imagery of Lightning Flashes: What Have We Learned; What Can We Learn?
Observations of lightning at framing rates exceeding 15,000 frames per second are revealing recoil streamer details and break down processes that were previously only speculation in intracloud components of lightning. Spectral observations of flashes at these high framing rates, in the near future, may yield clues to identifying intracloud and cloud-to-ground flashes from satellites.
Evaluation of Cloud Reflectance Models Using Dual-Angle Satellite Measurements
Cloud microphysical properties such as effective particle size, Re, and optical depth, OD, are routinely retrieved from visible, infrared, and near-infrared radiances measured by satellite imagers. The retrievals rely on radiative transfer model calculations that assume a particular scattering phase function for either ice crystals or water droplets in the clouds. The former depends on the particle shapes and the latter is typically assumed to be easily determined from Mie scattering theory. Typical ice crystal models assume some distribution and/or mixture of smooth crystals of various shapes. Optical depths retrieved with those models typically underestimate the cloud optical depth. Theoretical calculations suggest that crystals with roughened facets can produce more accurate optical depths. Time series of water cloud Re and OD retrievals from geostationary satellite imagery reveal some systematic anomalies in certain angles of the backscattering hemisphere. Typically, large jumps in the values occur at those angles and then disappear within an hour or so because of changing viewing and illumination angles. These shortcomings in the ice and water cloud reflectance models are examined using dual-angle measurements from a pair of geostationary satellites. Roughened ice crystal models are tested to determine if they provide more accurate representations of the reflectance fields and yield more accurate optical depth retrievals. The sensitivity of the reflectance field to the width of the droplet size distributions is examined to determine its impact on the observed water cloud anomalies. Empirical corrections are also considered. When possible, the retrievals are compared with surface radiometer measurements of optical depth and liquid water path. The results should be valuable for improving the retrievals of these important cloud radiative properties.
Volatile Organic Compound Emissions from Dairy Farming and their effect on San Joaquin Valley Air Quality
The San Joaquin Valley Air Pollution Control District of California issued a report identifying dairies as a main source of Volatile Organic Compounds (VOCs). A dairy study funded by the California Air Resources Board commenced shortly after the report was issued. Our University of California Irvine group teamed with California State University Fresno to determine the major sources of VOCs from various dairy operations and from a variety of dairy types. This study identified ethanol and methanol as two gases produced in major quantities throughout the dairies in the San Joaquin valley as by-products of yeast fermentation of silage. Three different types of sampling protocols were employed in order to determine the degree of enhancement of the target oxygenates in the valley air shed. Their sources, emission profiles, and emission rates were determined from whole air samples collected at various locations at the six dairies studied. An assessment of the impact of dairy emissions in the valley was achieved by using data obtained on low altitude NASA DC-8 flights through the valley, and from ground level samples collected though out the valley in a grid like design. Our data suggest that a significant amount of O3 production in the valley may come from methanol, ethanol, and acetaldehyde (a photochemical by-product ethanol oxidation). Our findings indicate that improvement to valley air quality may be obtained by focusing on instituting new silage containment practices and regulations.
Interactions of Chemistry and Meteorology: Transforming Air Pollution into Climate Change
PThe common goal of understanding and protecting Earth's environment has brought together chemists and meteorologists, despite the once widely held view that these are natural adversaries. Historically, dynamics, physics, chemistry, and biology were explored as isolated aspects of air quality and climate, but nature has proved to be much more interesting than that. Emissions and atmospheric photochemistry create air pollutants, but meteorology drives day to day variability in air quality. Air pollution, no matter how severe, has no substantive impact on global atmospheric composition or climate unless it is transported away from the sources, usually through frontal passage and advection, isentropic lifting or, especially lofting in deep convective clouds and thunderstorms. At higher altitudes, greater actinic flux accelerates photochemistry, stronger winds speed dispersal, and lower temperatures slow losses while amplifying radiative heating of greenhouse forcing substance such as ozone and carbonaceous aerosols. Examples include the transport of reactive nitrogen compounds from one part of North America to another, or on to the remote North Atlantic and Europe. Although measurement of NOy and NHx gases and particles still presents an analytical challenge, these trace species have major impacts on ecosystems and biogeochemical cycles. In East Asia chemistry and meteorology conspire to intensify long-range, even intercontinental transport of mineral dust and air pollutants. Recent discovery of a nonlocal dynamical driver to the Urban Heat Island effect shows that the adverse impact of urbanization can cascade to exacerbate heat stress, photochemical smog, and haze well downwind. A balanced consideration of meteorology and chemistry not only helps to identify and understand environmental problems, it can also provide powerful, policy relevant science that has led to success stories such as a regional approach to emissions controls and cleaner air over the eastern US.
Lessons Learned in Regional Climate Assessments
While climate change is a global problem, its impacts occur at the local and regional scale. Regional integrated climate assessments are critical for informing sound climate policy. In this presentation, we draw on experiences from recent studies and regional assessments to illustrate how consistent analysis based on the latest climate science can be generated for diverse sectors ranging from water supply to human health. In these studies, simulations from a range of the latest global climate models were combined with advanced dynamical and statistical downscaling techniques to produce fine-scale climate projections for IPCC SRES higher and lower emission scenarios. There are advantages and disadvantages to each downscaling technique; however, often the most pressing concern for an assessment is cost and efficiency. These high- resolution climate projections are then used in studies of regional climate impacts. The climate assessment we led for the city of Chicago and the ongoing assessment for the Midwest are used as key examples. The general methodology described here is generally applicable across many other parts of the world, serving as a pattern for future regional assessments to directly inform adaptation and mitigation policy at the local to regional scale.
Past and Contemporary Climate Change: Evidence From Earth's Ice Cover
Ice cores from Greenland and Antarctica as well as from glaciers and ice caps at high elevations in lower latitudes have provided unique insights on Earth's climate history and variability. Cores from high accumulation regions provide histories with temporal detail sufficient to resolve timing issues such as the arrival of sulfate aerosols over Greenland from the Icelandic Laki eruption (was it 1783 or 1784?). Multi-millennial climatic and environmental histories from the tropics to the poles provide a critical long term context for assessing contemporary climate variability. Abrupt climate change is not a recent phenomenon. Current widespread retreat and/or melting of glaciers suggest large and rapid changes in the climatic regimes that sustain them. Glaciers in the Andes, Himalayas, on Kilimanjaro, in the Antarctic Peninsula and now in parts of West Antarctica are responding rapidly and dramatically. A spatially extensive snow accumulation network at South Pole Station reveals a slightly positive trend over the last 12 years that if regionally representative, would suggest some amelioration of global sea level rise over the last decade. Implications for disruptions in local to regional water supplies and impacts on sea level now have the attention of governments and their policymakers.