|
|
Ancel A., Kooyman G.L., Ponganis P.J., Gendner J.P., Lignon J., Mestre X., Huin N., Thorson P.H., Robisson P. & Le Maho Y. (1992). Foraging behaviour of emperor penguins as a resource detector in winter and summer. Nature, 360, 336–338.
|
|
|
|
Lorius, C.; Jouzel, J.; Raynaud, D.; Hansen, J.; Treut, H.L. (1990). The ice-core record: climate sensitivity and future greenhouse warming. Nature, 347(6289), 139–145.
Abstract: The prediction of future greenhouse-gas-induced warming depends critically on the sensitivity of Earth's climate to increasing atmospheric concentrations of these gases. Data from cores drilled in polar ice sheets show a remarkable correlation between past glacial–interglacial temperature changes and the inferred atmospheric concentration of gases such as carbon dioxide and methane. These and other palaeoclimate data are used to assess the role of greenhouse gases in explaining past global climate change, and the validity of models predicting the effect of increasing concentrations of such gases in the atmosphere.
Programme: 159
|
|
|
|
Vimeux, F.; Masson, V.; Jouzel, J.; Stievenard, M.; Petit, J.R. (1999). Glacial-interglacial changes in ocean surface conditions in the Southern Hemisphere. Nature, 398(6726), 410–413.
Abstract: The stable-isotope signatures of oxygen and hydrogen in the water of preserved ice and snow are both widely used to infer local temperatures of past environments. A derived quantity based on these two signatures, the 'deuterium excess'1, provides additional palaeoclimatic information2, 3, 4, as this parameter depends on the meteorological and oceanic characteristics of the water's source-regions (in particular, their temperature2,3 and relative humidity4). Published studies mainly focus on records from the past 40,000 years. Here we present a deuterium-excess history obtained from ice cores from Vostok, East Antarctica, spanning the full glacial–interglacial cycle of the past 150,000 years. The deuterium-excess record shows a strong anticorrelation with the Earth's orbital obliquity (approx41,000-year periodicity), and values are markedly higher during the cold stage 5d (following the last interglacial) than during the other cold stages. We interpret the relationship with obliquity as resulting from changes in the latitudinal insolation gradient affecting ocean surface conditions and, thus, the delivery of moisture to the polar region. We argue that the high 5d values, relative to other cold stages, are driven by relatively less moisture delivered from high latitudes, and more from low latitudes. The deuterium-excess in Antarctic precipitation thus provides long-term, spatially integrated information on ocean surface conditions and ocean/atmosphere circulations in the Southern Hemisphere.
Programme: 159
|
|
|
|
Gros V, Poisson N, Martin D, Kanakidou M, Bonsang B,. (1998). Observations and modeling of the seasonal variation of surface ozone at Amsterdam Island: 1994–1996. J. Geophys. Res., 103(D21), 28103–28109.
Abstract: Since January 1994, continuous surface O3 measurements have been carried out at Amsterdam Island (37°S, 77°E) in the southern Indian Ocean using a UV absorption analyzer. Mean O3 concentrations and standard deviations are recorded every 5 min. This paper shows and discusses the O3 time series for a 3-year period (1994–1996). During this period, O3 shows a seasonal variation with maxima around 30 ppbv during winter (July – September) and minima around 13 ppbv during summer (December – February). O3 levels at Amsterdam Island are close to those observed at Cape Grim (Tasmania, 41°S, 145°E) for the period of 1991 to 1995. In order to improve the understanding of the mechanisms controlling the O3 seasonal variation at Amsterdam Island, our observations have been analyzed by using the global three-dimensional climatological Model of the Global Universal Tracer Transport in the Atmosphere (MOGUNTIA). The model reproduces well the observed O3 mixing ratios and their seasonal cycle. The seasonal variation of stratospheric origin O3 calculated by MOGUNTIA shows a maximum of 18 ppbv in September and a minimum of 13 ppbv in April. The oxidation of continentally emitted O3 precursors during their transport to Amsterdam Island contributes to the photochemical production of O3 by up to 12 ppbv during austral summer. From this amount, 3–7 ppbv are directly linked to nonmethane hydrocarbon oxidation chemistry under relatively high NOx conditions. In particular, biomass burning emissions contribute up to 5.5 ppbv to the observed O3 levels in September. Both photochemical production by biomass burning and stratospheric influx of O3 lead to a maximum in O3 mixing ratios during late winter to early spring in agreement with the observations. Minimum O3 mixing ratios observed during austral summer are related to photochemical O3 depletion.
Programme: 344
|
|
|
|
Mahowald, N.M.; Rasch, P.J.; Eaton, B.E.; Whittlestone, S.; Prinn, R.G. (). Transport of 222radon to the remote troposphere using the Model of Atmospheric Transport and Chemistry and assimilated winds from ECMWF and the National Center for Environmental Prediction/NCAR. J. Geophys. Res., 102.
Abstract: The Model of Atmospheric Transport and Chemistry (MATCH) is used to simulate the transport of 222Rn using both European Centre for Medium-Range Weather Forecasts (ECMWF) winds and National Center for Environmental Prediction/National Center for Atmospheric Research (hereafter referred to as NCEP) reanalysis winds. These winds have the advantage of being based on observed winds but have the disadvantage that the subgrid-scale transport processes are not routinely archived. MATCH derives subgrid-scale mixing rates for the boundary layer using a nonlocal scheme and for moist convective mixing using one of two parameterizations (Tiedtke [1989] or Pan and Wu [1997]). This paper describes the ability of the model to recreate mixing rates of 222Rn using the forecast center winds. Radon 222 is a species with a continental crust source and a simple sink involving radioactive decay with an e-folding timescale of 5.5 days. This atmospheric constituent is therefore a good tracer for testing the vertical transport in the chemical transport model, as well as the horizontal transport from continental regions to remote oceanic regions. The various simulations of 222Rn are compared with observations as well as with each other, allowing an estimate of the uncertainty in transport due to uncertainties in the winds and subgrid-scale processes. The calculated vertical profiles over the western United States are somewhat similar to observed, and the upper tropospheric concentrations compare reasonably well in their spatial distribution with data collected during Tropospheric Ozone II (TROPOZ II), although the model values tend to be higher than observed values, especially in the upper troposphere. The model successfully simulates specific observed pollution events at Cape Grim. It has more difficulty at sites farther from continental source regions, although the model captures the seasonal structure of the pollution events at these sites (Macquarie Island, Amsterdam Island, Kerguelen Island, and Crozet Island). Inclusion of a moist convective mixing scheme in MATCH increases 222Rn concentrations in the upper troposphere by 50% compared to not having moist convective mixing, while surface concentrations do not appear to be very sensitive to moist convection. In addition, differences between the upper tropospheric concentrations of radon predicted using the ECMWF and NCEP winds can be 30% for large areas of the globe, due to either differences in the forecast center winds themselves or the moist convective mixing schemes used in conjunction with them. This has implications for model simulations of radiatively and chemically important trace species in the atmosphere.
Programme: 146
|
|
|
|
Jacob, Daniel J., Prather, Michael J., Rasch, hilip J., Shia, Run-Lie, Balkanski, Yves J., eagley, Stephen R., Bergmann, Daniel J., lackshear, W. T., Brown, Margaret, Chiba, Masaru, hipperfield, Martyn P., de Grandpré, J., Dignon, ane E., Feichter, Johann, Genthon, Christophe, rose, W. L., Kasibhatla, Prasad S., Köhler, Ines, ritz, Mark A., Law, Kathy, Penner, Joyce E., amonet, Michel, Reeves, Claire E., Rotman, Douglas ., Stockwell, Deianeira Z., Van Velthoven, Peter F. J., Verver, Gé, Wild, Oliver, Yang, Hu, Zimmermann, Peter. (1997). Evaluation and intercomparison of global atmospheric transport models using ²²²Rn short-lived tracers. J. Geophys. Res., 102, 5953–5970.
|
|
|
|
Pettré Paul, Payan Christophe, Parish Thomas R, . (1993). Interaction of Katabatic Flow With Local Thermal Effects in a Coastal Region of Adelie Land, East Antarctica
. J. Geophys. Res., 98(D6), 10429–10440.
Abstract: Katabatic flows largely dominate the climate of the Adelie Land coastal region. A detailed climatological data analysis of Dumont d'Urville has been conducted. Results of this study support the idea that katabatic flow can be locally enhanced by the diurnal cycle of solar insolation and the temperature contrast between the continent and the ocean. The interaction between katabatic wind and local thermal effects is expressed in terms of scale analysis. Except for surface stress, all terms in the momentum equation for a katabatic flow in a coastal region of Antarctica can reach the same order of magnitude. The local circulation then is the result of a relatively tenuous force balance which can be disrupted even by a weak perturbation of any term. To estimate the effect of the temperature contrast between the ocean and the continent on the katabatic flow, two numerical experiments have been conducted. The simulations consider an ocean free of sea ice representative of the summer months, and another winter case with the ocean covered by thick sea ice. These simulations show that with the ocean free of sea ice, the katabatic flows extend only a limited distance over the open ocean during the day due to the local thermal effects. With the ocean covered by sea ice, the katabatic winds are not constrained and extend a considerable distance offshore.
Programme: 211
|
|
|
|
G. Picard, H. Löwe, F. Domine, L. Arnaud, F. Larue, V. Favier, E. Le Meur, E. Lefebvre, J. Savarino, A. Royer. (2022). The Microwave Snow Grain Size: A New Concept to Predict Satellite Observations Over Snow-Covered Regions (Vol. 3). Bachelor's thesis, , .
Abstract: Satellite observations of snow-covered regions in the microwave range have the potential to retrieve essential climate variables such as snow height. This requires a precise understanding of how microwave scattering is linked to snow microstructural properties (density, grain size, grain shape and arrangement). This link has so far relied on empirical adjustments of the theories, precluding the development of robust retrieval algorithms. Here we solve this problem by introducing a new microstructural parameter able to consistently predict scattering. This “microwave grain size” is demonstrated to be proportional to the measurable optical grain size and to a new factor describing the chord length dispersion in the microstructure, a geometrical property known as polydispersity. By assuming that the polydispersity depends on the snow grain type only, we retrieve its value for rounded and faceted grains by optimization of microwave satellite observations in 18 Antarctic sites, and for depth hoar in 86 Canadian sites using ground-based observations. The value for the convex grains (0.6) compares favorably to the polydispersity calculated from 3D micro-computed tomography images for alpine grains, while values for depth hoar show wider variations (1.2–1.9) and are larger in Canada than in the Alps. Nevertheless, using one value for each grain type, the microwave observations in Antarctica and in Canada can be simulated from in-situ measurements with good accuracy with a fully physical model. These findings improve snow scattering modeling, enabling future more accurate uses of satellite observations in snow hydrological and meteorological applications.
Keywords: microstructure microwave modeling porous media remote sensing snow
Programme: 1110,1177
|
|
|
|
Sara Labrousse, Alexander D. Fraser, Michael Sumner, Takeshi Tamura, David Pinaud, Barbara Wienecke, Roger Kirkwood, Yan Ropert‐Coudert, Ryan Reisinger, Ian Jonsen, Rick Porter‐Smith, Christophe Barbraud, Charles-André Bost, Rubao Ji, Stéphanie Jenouvrier. (2019). Dynamic Fine-Scale Sea Icescape Shapes Adult Emperor Penguin Foraging Habitat in East Antarctica (Vol. 46). Bachelor's thesis, , .
Abstract: The emperor penguin, an iconic species threatened by projected sea ice loss in Antarctica, has long been considered to forage at the fast ice edge, presumably relying on large/yearly persistent polynyas as their main foraging habitat during the breeding season. Using newly developed fine-scale sea icescape data and historical penguin tracking data, this study for the first time suggests the importance of less recognized small openings, including cracks, flaw leads and ephemeral short-term polynyas, as foraging habitats for emperor penguins. The tracking data retrieved from 47 emperor penguins in two different colonies in East Antarctica suggest that those penguins spent 23% of their time in ephemeral polynyas and did not use the large/yearly persistent, well-studied polynyas, even if they occur much more regularly with predictable locations. These findings challenge our previous understanding of emperor penguin breeding habitats, highlighting the need for incorporating fine-scale seascape features when assessing the population persistence in a rapidly changing polar environment.
Keywords: emperor penguin fast ice foraging ecology iceberg polynya sea ice
Programme: 109,394,1091
|
|
|
|
O. I. Berngardt, J. M. Ruohoniemi, J.-P. St‐Maurice, A. Marchaudon, M. J. Kosch, A. S. Yukimatu, N. Nishitani, S. G. Shepherd, M. F. Marcucci, H. Hu, T. Nagatsuma, M. Lester. (2019). Global Diagnostics of Ionospheric Absorption During X-Ray Solar Flares Based on 8- to 20-MHz Noise Measured by Over-the-Horizon Radars (Vol. 17). Bachelor's thesis, , .
Abstract: An analysis of noise attenuation during 80 solar flares between 2013 and 2017 was carried out at frequencies 8–20 MHz using 34 Super Dual Auroral Radar Network radars and the EKB ISTP SB RAS radar. The attenuation was determined on the basis of noise measurements performed by the radars during the intervals between transmitting periods. The location of the primary contributing ground sources of noise was found by consideration of the propagation paths of radar backscatter from the ground. The elevation angle for the ground echoes was determined through a new empirical model. It was used to determine the paths of the noise and the location of its source. The method was particularly well suited for daytime situations, which had to be limited for the most part to only two crossings through the D region. Knowing the radio path was used to determine an equivalent vertical propagation attenuation factor. The change in the noise during solar flares was correlated with solar radiation lines measured by GOES/XRS, GOES/EUVS, SDO/AIA, SDO/EVE, SOHO/SEM, and PROBA2/LYRA instruments. Radiation in the 1 to 8 Å and near 100 Å are shown to be primarily responsible for the increase in the radionoise absorption, and by inference, for an increase in the D and E region density. The data are also shown to be consistent with a radar frequency dependence having a power law with an exponent of −1.6. This study shows that a new data set can be made available to study D and E regions.
Keywords: \special t4ht@.D layer; \special t4ht@.E layer; decameter radars; ionosphere; radionoise absorption; X-ray solar flares
Programme: 312
|
|
