|
Rousseau, D.-D.; Duzer, D.; Etienne, J.-L.; Cambon, G.; Jolly, D.; Ferrier, J.; Schevin, P. (2004). Pollen record of rapidly changing air trajectories to the North Pole. J. Geophys. Res., 109.
Abstract: Tracing modern atmospheric dynamics is important for constraining models used in past climate reconstruction. However, these models must be verified by modern observations. We present the rapid changeover of two different air trajectories to the North Pole determined by studying the long distance transport of pollen. Samples were collected on a manned floating capsule drifting southward on the sea ice from the North Pole in 2002. It was observed that an air mass at 3000 m altitude transported birch and pine pollen released in Western Europe during week 22 (May 27). Two weeks later, during week 24 (June 10), alder, birch and willow pollen from eastern Siberia reached the drifting station with an air mass at 1000 m altitude. These particular patterns support independent investigations of air trajectories in the Arctic, especially the transport of anthropogenic pollutants such as sulfate and nitrate.
Keywords: 0305 Atmospheric Composition and Structure: Aerosols and particles; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 1620 Global Change: Climate dynamics; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions
Programme: 349
|
|
|
Legrand, M.; Preunkert, S.; Jourdain, B.; Aumont, B. (2004). Year-round records of gas and particulate formic and acetic acids in the boundary layer at Dumont d'Urville, coastal Antarctica. J. Geophys. Res., 109.
Abstract: Multiple year-round levels of acetate and formate in gas and aerosol phases were investigated at Dumont d'Urville (DDU, a coastal Antarctic site) by using mist chamber and aerosol filter sampling. Formate and acetate aerosol levels range from <0.5 ppt in winter to 3 ppt in summer. With corresponding gas phase levels of more than a hundred of pptv, formic and acetic acids are mainly (99%) present in the gas phase, representing the 2 major acidic gases before inorganic species (HCl, HNO3 and SO2) there. Mixing ratios of formic acid are minimal from May to August (70 pptv) and increase regularly toward November–February months when levels reach ?200 pptv. Mixing ratios of acetic acid exhibit a more well-marked seasonal cycle with values remaining close to 70 pptv from April to October and strongly increase during November–February months (mean value of 400 pptv). These seasonal changes suggest that the 2 carboxylic acids mainly originate from biogenic emissions of the Antarctic ocean whose variations follow the annual cycle of sea ice extent and solar radiation via photochemical production of alkenes from dissolved organic carbon released by phytoplankton. In summer, acetic acid levels show daily variations with maxima at noon and minima at night whereas formic acid levels peaks later in the afternoon. These dial variations in summer suggest that carboxylic acids are rapidly produced during the day and lost at night due to dry deposition on wet surface. It is suggested that the reactions of peroxy acetyl radical produced from propene with HO2 and CH3O2 in these poor NOx environments represent in summer the dominant chemical mechanisms producing acetic acid whereas ozone-alkene reactions remain of minor importance at that season. Neither ozone-alkene reactions nor aqueous phase HCHO oxidation can explain the summer levels of formic acid. In winter the long range transport of alkenes emitted at more temperate oceanic regions and reactions with ozone could account for the observed level of formic acid and possibly of acetic acid.
Keywords: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0330 Atmospheric Composition and Structure: Geochemical cycles; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry
Programme: 414
|
|
|
Savarino, J.; Bekki, S.; Cole-Dai, J.; Thiemens, M.H. (2003). Evidence from sulfate mass independent oxygen isotopic compositions of dramatic changes in atmospheric oxidation following massive volcanic eruptions. J. Geophys. Res., 108.
Abstract: Oxygen isotopic ratio measurements (?17O and ?18O) of background and volcanic sulfate preserved in South Pole snow and ice were used to investigate the impact on the oxidation state of the atmosphere by explosive volcanic eruptions. By comparing different paleovolcanic events, we observe a difference in the SO2 oxidation pathway between moderate (tens of teragrams (Tg) of SO2) and massive (hundreds of Tg) eruptions. Both isotopic data and numerical simulations suggest the shutdown of stratospheric OH chemistry and the opening of unaccounted oxidation channels for SO2, such as the reaction with O(3P) atoms when hundreds of Tg of SO2 are injected into the stratosphere. It is very likely that oxidation rates and pathways and concentrations of most traces gases are also dramatically affected, with potentially important implications for climate forcing.
Keywords: 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0370 Atmospheric Composition and Structure: Volcanic effects; 1040 Geochemistry: Isotopic composition/chemistry; 1863 Hydrology: Snow and ice
Programme: 457
|
|
|
Park, Y.-H. (2004). Determination of the surface geostrophic velocity field from satellite altimetry. J. Geophys. Res., 109.
Abstract: Presently available marine geoid models are not accurate enough to extract the mean surface circulation directly from satellite altimetry. A novel method for estimating the mean velocity field of major ocean current systems is derived from the free surface boundary condition. With a given quasi-geostrophic balance for the horizontal surface flow, a scaling analysis of this boundary condition indicates that although the vertical velocity w is mostly balanced by the local change of the free surface, ???/?t, useful information on the mean current ($\overline{u}$, $\overline{v}$) is contained in a small ageostrophic departure (???/?t ? w). Our method consists in the development of a simple algebraic equation with two unknowns ($\overline{u}$, $\overline{v}$) and an adjustable parameter $\widetilde{\alpha}$ associated with ???/?t, assuming that the latter is proportional to (???/?t ? w). Most interestingly, ???/?t and all other coefficients of the equation can be determined from altimetry. The altimeter data used is combined TOPEX/Poseidon-ERS gridded data, and the solution is obtained by least squares, minimizing the contribution from the time-variable part of the parameter $\widetilde{\alpha}$ and prescribing the zonal direction of the mean current. The method, which is found to be particularly useful for quasi-zonal high-energy current systems, has been validated against direct observations in the Gulf Stream and Southern Ocean. Comparisons with direct observations and Monte Carlo experiments suggest an overall solution error of about 10 cm s?1. Once calibrated against regional velocity statistics, this method will be able to determine from altimetry the mean or instantaneous surface velocity field down to the frontal scale, with a realism that has been inaccessible because of the geoid constraint.
Keywords: 4512 Oceanography: Physical: Currents; 4528 Oceanography: Physical: Fronts and jets; 4556 Oceanography: Physical: Sea level variations
Programme: 335
|
|
|
Debayle, E.; Sambridge, M. (2004). Inversion of massive surface wave data sets: Model construction and resolution assessment. J. Geophys. Res., 109, B02316.
Abstract: A new scheme is proposed for the inversion of surface waves using a continuous formulation of the inverse problem and the least squares criterion. Like some earlier schemes a Gaussian a priori covariance function controls the horizontal degree of smoothing in the inverted model, which minimizes some artifacts observed with spherical harmonic parameterizations. Unlike earlier schemes the new approach incorporates some sophisticated geometrical algorithms which dramatically increase computational efficiency and render possible the inversion of several tens of thousands of seismograms in few hours on a typical workstation. The new algorithm is also highly suited to parallelization which makes practical the inversion of data sets with more than 50,000 ray paths. The constraint on structural and anisotropic parameters is assessed using a new geometric approach based on Voronoi diagrams, polygonal cells covering the Earth's surface. The size of the Voronoi cells is used to give an indication of the length scale of the structures that can be resolved, while their shape provides information on the variation of azimuthal resolution. The efficiency of the scheme is illustrated with realistic uneven ray path configurations. A preliminary global tomographic model has been built for SV wave heterogeneities and azimuthal variations through the inversion of 24,124 fundamental and higher-mode Rayleigh waveforms. Our results suggest that the use of relatively short paths (<10,000 km) in a global inversion should minimize multipathing, or focusing/defocusing effects and provide lateral resolution of a few hundred kilometers across the globe.
Keywords: 7218 Seismology: Lithosphere and upper mantle; 7255 Seismology: Surface waves and free oscillations; 7260 Seismology: Theory and modeling; 8180 Tectonophysics: Tomography
Programme: 133;906
|
|
|
Yagova, N.V.; Pilipenko, V.A.; Lanzerotti, L.J.; Engebretson, M.J.; Rodger, A.S.; Lepidi, S.; Papitashvili, V.O. (2004). Two-dimensional structure of long-period pulsations at polar latitudes in Antarctica. J. Geophys. Res., 109.
Abstract: Two-dimensional (2-D) statistical distributions of spectral power and coherence of polar geomagnetic variations with quasi-periods about 10 min are analyzed using data from magnetometer arrays in Antarctica. Examination of the 2-D patterns of spectral power and coherence shows the occurrence of significant variations in geomagnetic power levels but with low spatial coherence near the cusp projection and in the auroral region. At the same time, low-amplitude pulsations, which we coin Pi cap
3 pulsations, are very coherent throughout the polar cap. The region occupied by coherent Pi cap
3 pulsations is shifted toward local MLT night from the geomagnetic pole and is decoupled from the regions of auroral and cusp ULF activity. The spectral power varies with time at polar latitudes in a manner different from that at auroral latitudes. Diurnal variations of power at different stations at the same geomagnetic latitude exhibit different behavior depending on the station's position relative to geomagnetic and geographic poles. This asymmetry is shown to be partly attributed to the variations of the ionospheric conductance. The primary source of polar pulsations is probably related to intermittent magnetosheath turbulence and tail lobe oscillations, though a particular propagation mechanism has not as yet been identified.
Keywords: 2776 Magnetospheric Physics: Polar cap phenomena; 2752 Magnetospheric Physics: MHD waves and instabilities; 2744 Magnetospheric Physics: Magnetotail; 2724 Magnetospheric Physics: Magnetopause, cusp, and boundary layers
Programme: 905
|
|
|
Ferrari, C.P.; Dommergue, A.; Boutron, C.F.; Jitaru, P.; Adams, F.C. (2004). Profiles of Mercury in the snow pack at Station Nord, Greenland shortly after polar sunrise. Geophysical research letters, 31.
Abstract: Mercury (Hg) species have been measured in the snow pack at Station Nord, Greenland both in the snow and in the air of snow from February 25 to March 15, 2002, during twilight and low solar irradiation periods. More than 99% of Hg is in the snow itself (?94–97% as Hg2+ and ?5% as MeHg+) while less than 1% is in the interstitial air of snow as Hg°. Gaseous Elemental Mercury (Hg°) concentrations, decreased exponentially with depth from ?1.5 ng/m3 outside to ?0.1 ng/m3 at 120 cm depth in the snow air. Hg° incorporation flux to the snow pack has been evaluated to ?5.8–7.0 pg/m2/h which is weak, indicating that this process does not change significantly the Hg content in the snow. We believe that this decrease in the air of snow is the result of fast oxidation processes of Hg° rather than adsorption of Hg° onto snow surfaces.
Keywords: 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0330 Atmospheric Composition and Structure: Geochemical cycles
Programme: 399
|
|
|
Genthon, C.; Cosme, E. (2003). Intermittent signature of ENSO in west-Antarctic precipitation. Geophysical research letters, 30.
Abstract: Precipitation data from the new ERA40 reanalyses and from a 200-year simulation confirm a robust main mode of precipitation variability in west Antarctica. An intermittently strong ENSO signature is found in this mode. However, high correlation with ENSO indices appears infrequent. Thus, the high correlation found in ERA40, and previously in other chronologically realistic data, in the late 1980s and the 1990s may not be expected to last. Unlike previously suggested by others, the sign of the correlation between ENSO indices and west Antarctic precipitation, when significant, does not appear to change in time: Precipitation variability at the ENSO pace in the Bellingshausen-Weddell (Ross-Amunsden) region is consistently in phase (phase opposition, respectively) with the Southern Oscillation Index. This is consistent with a tropospheric wave train connecting the tropical Pacific and west Antarctic regions, which modulates in phase opposition the advection of air and moisture in the 2 regions.
Keywords: 3349 Meteorology and Atmospheric Dynamics: Polar meteorology; 3354 Meteorology and Atmospheric Dynamics: Precipitation; 1620 Global Change: Climate dynamics; 1655 Global Change: Water cycles; 9310 Information Related to Geographic Region: Antarctica
Programme: 411
|
|
|
Savarino, J.; Romero, A.; Cole-Dai, J.; Bekki, S.; Thiemens, M.H. (2003). UV induced mass-independent sulfur isotope fractionation in stratospheric volcanic sulfate. Geophysical research letters, 30.
Abstract: Sulfuric acid aerosols produced in the stratosphere following massive volcanic eruptions possess a mass-independent sulfur isotopic signature, acquired when volcanic SO2 experiences UV photooxidation. The volcanic data are consistent with laboratory SO2 photooxidation experiments using UV light at 248 nm (maximum absorption of ozone), whereas sulfur isotopic anomalies previously observed in Archean samples are consistent with photodissociation at 190–220 nm. A mechanism of SO2 photooxidation, occurring in the early stage of a stratospheric volcanic plume, in the range of 220–320 nm (weak band absorption of SO2), is also proposed. Since mass-independent sulfur isotope anomalies in stratospheric volcanic sulfate appear to depend on the exposure of SO2 to UV radiation, their measurements might therefore offer the possibility to determine the degree of UV penetration in the ozone-absorption window for the present and past atmospheres. They can also be used to determine the stratospheric or tropospheric nature of volcanic eruptions preserved in glaciological records, offering the possibility to reassess the climatic impact of past volcanic eruptions.
Keywords: 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0370 Atmospheric Composition and Structure: Volcanic effects; 1040 Geochemistry: Isotopic composition/chemistry; 1827 Hydrology: Glaciology
Programme: 457
|
|
|
Caillon, N.; Jouzel, J.; Severinghaus, J.P.; Chappellaz, J.; Blunier, T. (2003). A novel method to study the phase relationship between Antarctic and Greenland climate. Geophysical research letters, 30.
Abstract: A classical method for understanding the coupling between northern and southern hemispheres during millennial-scale climate events is based on the correlation between Greenland and Antarctic ice core records of atmospheric composition. Here we present a new approach based on the use of a single Antarctic ice core in which measurements of methane concentration and inert gas isotopes place constraints on the timing of a rapid climate change in the North and of its Antarctic counterpart. We applied it to the Marine Isotope Stage (MIS) 5d/c transition early in the last glaciation ?108 ky BP. Our results indicate that the Antarctic temperature increase occurred 2 ky before the methane increase, which is used as a time marker of the warming in the Northern Hemisphere. This result is in agreement with the “bipolar seesaw” mechanism used to explain the phase relationships documented between 23 and 90 ky BP [
Blunier and Brook, 2001].
Keywords: 3344 Meteorology and Atmospheric Dynamics: Paleoclimatology; 4267 Oceanography: General: Paleoceanography; 1827 Hydrology: Glaciology; 4870 Oceanography: Biological and Chemical: Stable isotopes; 1620 Global Change: Climate dynamics
Programme: 902
|
|