ALBERT

Description: Prior work indicates that the frequency of summertime mid-latitude cyclones tracking across the Great Lakes Storm Track (GLST, bounded by: 70° W, 90° W, 40° N, and 50° N) are strongly anticorrelated with ozone (O3) pollution episodes over the Northeastern United States (US). We apply the MAP Climatology of Mid-latitude Storminess (MCMS) algorithm to 6-hourly sea level pressure fields from over 2500 yr of simulations with the GFDL CM3 global coupled chemistry-climate model. These simulations include (1) 875 yr with constant 1860 emissions and forcings (Pre-industrial Control), (2) five ensemble members for 1860–2005 emissions and forcings (Historical), and (3) future (2006–2100) scenarios following the Representative Concentration Pathways (RCP 4.5 and RCP 8.5) and a sensitivity simulation to isolate the role of climate warming from changes in O3 precursor emissions (RCP 4.5*). The GFDL CM3 Historical simulations capture the mean and variability of summertime cyclones traversing the GLST within the range determined from four reanalysis datasets. Over the 21st century (2006–2100), the frequency of summertime mid-latitude cyclones in the GLST decreases under the RCP 8.5 scenario and in the RCP 4.5 ensemble mean. These trends are significant when assessed relative to the variability in the Pre-industrial Control simulation. In addition, the RCP 4.5* scenario enables us to determine the relationship between summertime GLST cyclones and high-O3 events (〉 95th percentile) in the absence of emission changes. The summertime GLST cyclone frequency explains less than 10% of the variability in high-O3 events over the Northeastern US in the model, implying that other factors play an equally important role in determining high-O3 events.

Description: In the course of the climate change and increased focus on CO2-neutral energy sources, the use of wood-driven small heating systems (SHS) becomes more important. But, their contribution to air pollution, especially particulate matter, is about as high as the emissions from car engines. The specific formation of harmful substances in wood fires and possible countermeasures by continuously operating sensor and control systems are covered. Impedance spectra of interdigital electrode (IDE) structures are taken before and after mounting in wood-driven SHS to get information about the particles in the exhaust stream. It appears that the capacitive parts of the impedance spectra at a fixed frequency are appropriate for a fast signal evaluation. The good correlation with established offline measuring methods is discussed and the capability of thermal regeneration is demonstrated. The offline measurements of this work shall give the experimental basis for the development of online measurements in order to control the particle emissions of wood-driven SHS.

Description: In the often discussed Aral Sea basin (Central Asia), water availability depends essentially on the high mountains located in its eastern part, especially from the Pamir Alay Range where the Vakhsh and Pyandj Rivers, the main tributaries of the Amu Darya River, flow. In this region, the cryosphere, glaciers, and snow cover significantly impact the water cycle and the flow regime, which could be deeply modified by climate change. The present study, part of a project funded by the EU FP6, analyzes the hydrological situation in six benchmark basins covering areas between 1800 and 8400 km2, essentially located in Tajikistan, with a variety of topographical situations, precipitation amounts, and glacierized areas. Four types of parameter are discussed: temperature, glaciers, snow cover, and river flows. Two time periods are considered: (i) a long time series ending in the 1990s with the collapse of the Soviet Union and based on field observations and data collection; (ii) a May 2000 to May 2002 interval, using scarce monitored data and satellite information to follow snow cover dynamics. The results confirm the global homogeneous trend of temperature increase in the mountain range and its impacts on the surface water regimes. Concerning the snow cover, significant differences are noted regarding the location, the elevation, the orientation and the morphology of the respective basins. Finally the expected changes in the flow river regime are regulated by the combination of the snow cover dynamics and the increasing trend of the air temperature. It confirms the high sensitivity of this region to the warming as identified by the 4rd IPCC Assessment Report.

Description: There is evidence of ice melt, sea level rise to +5–9 m, and extreme storms in the prior interglacial period that was less than 1 °C warmer than today. Human-made climate forcing is stronger and more rapid than paleo forcings, but much can be learned by combining insights from paleoclimate, climate modeling, and on-going observations. We argue that ice sheets in contact with the ocean are vulnerable to non-linear disintegration in response to ocean warming, and we posit that ice sheet mass loss can be approximated by a doubling time up to sea level rise of at least several meters. Doubling times of 10, 20 or 40 years yield sea level rise of several meters in 50, 100 or 200 years. Paleoclimate data reveal that subsurface ocean warming causes ice shelf melt and ice sheet discharge. Our climate model exposes amplifying feedbacks in the Southern Ocean that slow Antarctic bottom water formation and increase ocean temperature near ice shelf grounding lines, while cooling the surface ocean and increasing sea ice cover and water column stability. Ocean surface cooling, in the North Atlantic as well as the Southern Ocean, increases tropospheric horizontal temperature gradients, eddy kinetic energy and baroclinicity, which drive more powerful storms. We focus attention on the Southern Ocean's role in affecting atmospheric CO2 amount, which in turn is a tight control knob on global climate. The millennial (500–2000 year) time scale of deep ocean ventilation affects the time scale for natural CO2 change, thus the time scale for paleo global climate, ice sheet and sea level changes. This millennial carbon cycle time scale should not be misinterpreted as the ice sheet time scale for response to a rapid human-made climate forcing. Recent ice sheet melt rates have a doubling time near the lower end of the 10–40 year range. We conclude that 2 °C global warming above the preindustrial level, which would spur more ice shelf melt, is highly dangerous. Earth's energy imbalance, which must be eliminated to stabilize climate, provides a crucial metric.

Description: Prior work indicates that the frequency of summertime mid-latitude cyclones tracking across the Great Lakes Storm Track (GLST, bounded by: 70° W, 90° W, 40° N, and 50° N) are strongly anticorrelated with ozone (O3) pollution episodes over the Northeastern United States (US). We apply the MAP Climatology of Mid-latitude Storminess (MCMS) algorithm to 6-hourly sea level pressure fields from over 2500 yr of simulations with the GFDL CM3 global coupled chemistry-climate model. These simulations include (1) 875 yr with constant 1860 emissions and forcings (Pre-industrial Control), (2) five ensemble members for 1860–2005 emissions and forcings (Historical), and (3) future (2006–2100) scenarios following the Representative Concentration Pathways (RCP 8.5 (one member; extreme warming); RCP 4.5 (three members; moderate warming); RCP 4.5* (one member; a variation on RCP 4.5 in which only well-mixed greenhouse gases evolve along the RCP 4.5 trajectory)). The GFDL CM3 Historical simulations capture the mean and variability of summertime cyclones traversing the GLST within the range determined from four reanalysis datasets. Over the 21st century (2006–2100), the frequency of summertime mid-latitude cyclones in the GLST decreases under the RCP 8.5 scenario (m = −0.06 a−1, p 〈 0.01) and in the RCP 4.5 ensemble mean (m = −0.03 a−1, p 〈 0.01). These trends are significant when assessed relative to the variability in the Pre-industrial Control simulation (p 〉 0.06 for 100-yr sampling intervals; −0.01 a−1 〈 m 〈 0.02 a−1). In addition, the RCP 4.5* scenario enables us to determine the relationship between summertime GLST cyclones and high-O3 events (〉95th percentile) in the absence of emission changes. The summertime GLST cyclone frequency explains less than 10% of the variability in high-O3 events over the Northeastern US in the model. Our findings imply that careful study is required prior to applying the strong relationship noted in earlier work to changes in storm counts.

Description: A two-dimensional isotropic Composite Right/Left-Handed (CRLH) waveguide structure is proposed which is designed for operation in X-band. The balanced structure possesses left-handed behaviour over a large bandwidth from 7.5 GHz up to its transition frequency at 10 GHz. Above this region, the unit cell behaves in a right-handed manner up to 13.5 GHz. Operating the structure within these bands yields a frequency dependent index of refraction ranging from −2.5 ≤ n ≤ 0.8. Isotropic characteristics are obtained between 8.5 GHz ≤ f ≤ 12 GHz resulting in −1.5 ≤ n ≤ 0.8. The planar CRLH structure is designed based on transmission line theory, implemented in microstrip technology and optimized using full-wave simulation software. An equivalent circuit model is determined describing the electromagnetic behaviour of the structure whose element values are obtained by even and odd mode analysis. The design of the unit cell requires an appropriate de-embedding process in order to enable an analysis in terms of dispersion characteristics and Bloch impedance, which are performed both.

Description: Flow tube reactors are employed to study gas-phase atmospheric chemistry and secondary organic aerosol formation. A new laminar flow tube reactor, the Caltech PhotoOxidation flow Tube (CPOT), has been designed with the aim of achieving a well-characterized fluid dynamic and residence time environment. We present here the design and fluid dynamical characterization of the CPOT, based on the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet of the CPOT, which was based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate rapid development of the characteristic laminar flow parabolic profile. A CFD laminar flow model is developed to simulate the residence time distribution (RTD) of vapor molecules and particles in the CPOT. To assess the extent to which the actual performance adheres to the theoretical CFD model, RTD experiments were conducted with O3 and sub-micrometer ammonium sulfate particles. The measured RTD profiles do not strictly adhere to theory, owing to slightly non-isothermal conditions in the reactor, which lead to secondary flows. Introducing an enhanced eddy-like diffusivity for the vapor molecules and particles in the laminar flow model significantly improves the model-experiment agreement. These characterization experiments, in addition to the idealized computational behavior, provide a basis on which to evaluate the performance of the CPOT as a chemical reactor.