Space-based infrared interferometry to study exoplanetary atmospheres     

D. Defrère  A. Léger  O. Absil  C. Beichman  B. Biller  W. C. Danchi  K. Ergenzinger  C. Eiroa  S. Ertel  M. Fridlund  A. García Muñoz  M. Gillon  A. Glasse  M. Godolt  J. L. Grenfell  S. Kraus  L. Labadie  S. Lacour  R. Liseau  G. Martin  B. Mennesson  G. Micela  S. Minardi  S. P. Quanz  H. Rauer  S. Rinehart  N. C. Santos  F. Selsis  J. Surdej  F. Tian  E. Villaver  P. J. Wheatley  M. Wyatt 《Experimental Astronomy》2018,46(3):543-560

The quest for other habitable worlds and the search for life among them are major goals of modern astronomy. One way to make progress towards these goals is to obtain high-quality spectra of a large number of exoplanets over a broad range of wavelengths. While concepts currently investigated in the United States are focused on visible/NIR wavelengths, where the planets are probed in reflected light, a compelling alternative to characterize planetary atmospheres is the mid-infrared waveband (5–20 μm). Indeed, mid-infrared observations provide key information on the presence of an atmosphere, the surface conditions (e.g., temperature, pressure, habitability), and the atmospheric composition in important species such as H₂O, CO₂, O₃, CH₄, and N₂O. This information is essential to investigate the potential habitability of exoplanets and to make progress towards the search for life in the Universe. Obtaining high-quality mid-infrared spectra of exoplanets from the ground is however extremely challenging due to the overwhelming brightness and turbulence of the Earth’s atmosphere. In this paper, we present a concept of space-based mid-infrared interferometer that can tackle this observing challenge and discuss the main technological developments required to launch such a sophisticated instrument.  相似文献   

Non‐Matrix‐Matched Calibration for the Multi‐Element Analysis of Geological and Environmental Samples Using 200 nm Femtosecond LA‐ICP‐MS: A Comparison with Nanosecond Lasers     

Klaus Peter Jochum  Brigitte Stoll  Ulrike Weis  Dorrit E. Jacob  Regina Mertz‐Kraus  Meinrat O. Andreae 《Geostandards and Geoanalytical Research》2014,38(3):265-292

LA‐ICP‐MS is one of the most promising techniques for in situ analysis of geological and environmental samples. However, there are some limitations with respect to measurement accuracy, in particular for volatile and siderophile/chalcophile elements, when using non‐matrix‐matched calibration. We therefore investigated matrix‐related effects with a new 200 nm femtosecond (fs) laser ablation system (NWRFemto200) using reference materials with different matrices and spot sizes from 10 to 55 μm. We also performed similar experiments with two nanosecond (ns) lasers, a 193 nm excimer (ESI NWR 193) and a 213 nm Nd:YAG (NWR UP‐213) laser. The ion intensity of the 200 nm fs laser ablation was much lower than that of the 213 nm Nd:YAG laser, because the ablation rate was a factor of about 30 lower. Our experiments did not show significant matrix dependency with the 200 nm fs laser. Therefore, a non‐matrix‐matched calibration for the multi‐element analysis of quite different matrices could be performed. This is demonstrated with analytical results from twenty‐two international synthetic silicate glass, geological glass, mineral, phosphate and carbonate reference materials. Calibration was performed with the certified NIST SRM 610 glass, exclusively. Within overall analytical uncertainties, the 200 nm fs LA‐ICP‐MS data agreed with available reference values.  相似文献   

Identifying eastern Baltic cod nursery grounds using hydrodynamic modelling: knowledge for the design of Marine Protected Areas   总被引：1，自引：0，他引：1  

Hinrichsen  Hans-Harald; Kraus  Gerd; Bottcher  Uwe; Koster  Fritz 《ICES Journal of Marine Science》2009,66(1):101-108

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West Antarctica's sensitivity to natural and human‐forced climate change over the Holocene     

P. A. Mayewski  K. A. Maasch  D. Dixon  S. B. Sneed  R. Oglesby  E. Korotkikh  M. Potocki  B. Grigholm  K. Kreutz  A. V. Kurbatov  N. Spaulding  J. C. Stager  K. C. Taylor  E. J. Steig  J. White  N. A. N. Bertler  I. Goodwin  J. C. Simões  R. Jaña  S. Kraus  J. Fastook 《第四纪科学杂志》2013,28(1):40-48

The location and intensity of the austral westerlies strongly influence southern hemisphere precipitation and heat transport with consequences for human society and ecosystems. With future warming, global climate models project increased aridity in southern mid‐latitudes related to continued poleward contraction of the austral westerlies. We utilize Antarctic ice cores to investigate past and to set the stage for the prediction of future behaviour of the westerlies. We show that Holocene West Antarctic ice core reconstructions of atmospheric circulation sensitively record naturally forced progressive as well as abrupt changes. We also show that recent poleward migration of the westerlies coincident with increased emission of greenhouse gases and the Antarctic ozone hole has led to unprecedented penetration, compared with >100,000 years ago, of air masses bringing warmth, extra‐Antarctic source dust and anthropogenic pollutants into West Antarctica. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

VSOP observations of the BL Lac object 2007+777     

C. Jin  T.P. Krichbaum  A. Witzel  R. Nan  B. Peng  A. Kraus  A. Lobanov  S. Qian  J.A. Zensus 《Astrophysics and Space Science》2001,277(1-2):97-100

A numerical model of magnetic turbulence allows us to compute the diffusion coefficients for different degrees of anisotropy, and in particular for the cases corresponding to the solar wind. We consider here the problem of the propagation of the energetic particles accelerated by corotating interaction regions (CIRs) and observed by Ulysses at high heliographic latitudes. The excursion in latitude of a magnetic field line located at large heliospheric distance is evaluated with a Monte Carlo simulation. In the calculations, the random `force' terms are proportional to the square root of the diffusion coefficient in each direction. By tracing a large number of field lines, we can devise how the particles would be seen by Ulysses. Good agreement with the actual observations is found. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

Actinic Radiation and Photolysis Processes in the Lower Troposphere: Effect of Clouds and Aerosols     

W. Junkermann  C. Brühl  D. Perner  E. Eckstein  T. Trautmann  B. Früh  R. Dlugi  T. Gori  A. Ruggaber  J. Reuder  M. Zelger  A. Hofzumahaus  A. Kraus  F. Rohrer  D. Brüning  G. Moortgat  A. Horowitz  J. Tadić 《Journal of Atmospheric Chemistry》2002,42(1):413-441

Within the German Tropospheric Research Program (TFS) a series of projects were performed focussing on aspects of radiation transfer and the effects of UV-radiation on air chemistry. The individual projects covered laboratory investigations, instrument development for photolysis processes as well as field studies of actinic radiation and comparison to model calculations. One and three-dimensional models were tested against field campaign data. The results confirm the improvement of measurement technology achieved through deployment of new techniques like spectroradiometry that offer a wider range of investigations than was previously attainable using chemical actinometry or fixed wavelength filter radiometry. Reasonable agreement was also found between measurements and models for a few selected and well defined cloudy conditions. On the other hand, using simple stratiform geometry models yielded significant deviations between measurement and model in both directions particularly in the case of high zenith angles and with high aerosol load. Further tools both for experimental investigations and for model calculations were developed within the framework of the Troposphere Research Program (TFS) and deficiencies were identified demanding further investigations when broken clouds and more complex cloud layers prevail.  相似文献   

Enhanced cold front propagation due to turbulent mixing     

A. Becker  K. Keuler  C. M. Ewenz  H. Kraus  E. Schaller 《Meteorology and Atmospheric Physics》1997,62(3-4):201-214

Summary The influence of turbulent friction on the propagation of cold fronts is investigated by numerical simulations using a two-dimensional mesoscale model. We compare the frictional effect with the effects of large-scale shear forcing and energy conversion at the earth's surface and discuss the synergic effect of all three mentioned processes. There is no pure superposition of these effects indicating that nonlinear interaction plays a role. In addition it is possible to show that—depending on the along-front jet—friction does not necessarily slow down the front but can also accelerate it. The direction of the along-front jet within the planetary boundary layer (PBL) is crucial for that question.With 12 Figures  相似文献   

Structural geology of the Mesozoic Miers Bluff Formation and crosscutting Paleogene dikes (Livingston Island, South Shetland Islands, Antarctica) – Insights into the geodynamic history of the northern Antarctic Peninsula     

S. Kraus  H. Miller  D. Dimov  E. Hegner  M. McWilliams  Z. Pecskay 《Journal of South American Earth Sciences》2008,26(4):498-512

The Antarctic Peninsula has been part of a magmatic arc since at least Jurassic times. The South Shetland Islands archipelago forms part of this arc, but it was separated from the Peninsula following the Pliocene opening of the Bransfield Strait. Dikes are widespread throughout the archipelago and are particularly accessible on the Hurd Peninsula of Livingston Island. The host rocks for the dikes are represented by the Miers Bluff Formation, which forms the overturned limb of a large-scale fold oriented 63/23 NW. The orientation of minor structures indicates a fold axis oriented NNE–SSW (24/0). Structural analysis of the dikes and their host rocks shows that the tectonic regime was similar to other parts of the archipelago and that only minor changes of the stress field occurred during dike emplacement.Based on crosscutting field relationships and geochemical data, six early Paleocene to late Eocene intrusive events can be distinguished on Hurd Peninsula. In contrast to calc-alkaline dikes from other parts of the South Shetland Islands, the majority of the Hurd Peninsula dikes are of tholeiitic affinity. Nd and Pb isotope data indicate a significant crustal component, particularly during initial magmatic activity.Plagioclase ⁴⁰Ar/³⁹Ar and whole rock K–Ar ages show that dike emplacement peaked during the Lutetian (48.3 ± 1.5, 47.4 ± 2.1, 44.5 ± 1.8 and 43.3 ± 1.7 Ma) on Hurd Peninsula and also further northeast on King George Island. Dike intrusion continued on Livingston Island at least until the Priabonian (37.2 ± 0.9 Ma). The type of magma sources (mantle, slab, crust and sediment) did not change, though their relative magmatic contributions varied with time.During Cretaceous and Early Paleogene times, the Antarctic Peninsula including the South Shetland Islands was situated southwest of Patagonia; final separation from South America occurred not before the Eocene. Thus, the geological evolution of Livingston Island is related as much to the development of Patagonia as of Antarctica, and needs to be considered within the history of southernmost South America.  相似文献   

Surface-layer fog considered using a modified Monin-Obukhov theory     

Helmut Kraus 《Boundary-Layer Meteorology》1993,66(3):219-235

The Prandtl-layer concept, assuming constant turbulent fluxes in the lowest meters or decameters of the atmosphere under horizontal homogeneous and steady-state conditions, is widely used; and it is also one of the fundamentals of Monin-Obukhov similarity theory. Thus, surface-layer condensation processes-essentially formation of shallow fog layers-implying convergence and divergence of turbulent fluxes of water vapour, liquid water content and sensible heat, cannot be treated within this concept. This paper tries to overcome this restriction by a modified Monin-Obukhov theory, which deals with constant fluxes of total water content and moist static energy (instead of water vapour and sensible heat). It shows that surface-layer fog situations (under steady-state and horizontally homogeneous conditions and neglecting radiational effects) can be treated by this modified theory, which yields turbulent vertical fluxes of sensible heat, water vapour and liquid water content and their divergences.The paper also derives a simple formula for the divergence of the turbulent flux of water vapour (E/z) under saturation conditions, which elucidates convergence ofE very close to the ground and divergence ofE higher up independent of whether the stratification is stable or unstable, i.e., whether there is fog over cold or warm ground. Model computations with the modified Monin-Obukhov theory are in full accordance with this formula. Thus a steam-fog case can be given as a demonstration of vertical profiles of turbulent fluxes of sensible heat, water vapour and liquid water content and their divergences.  相似文献   

Literature review of sand transport by wind on a dry sand surface   总被引：1，自引：0，他引：1  

Kiyoshi Horikawa  Shintaro Hotta  Nicholas C. Kraus 《Coastal Engineering》1986,9(6)

A critical and comprehensive literature survey of sand transport by wind on a dry sand surface is made from the perspective of engineering use. Principal findings are: (1) Most predictive expressions for the sand transport rate show a cubic dependence on the shear velocity, or obey a similar power law. (2) Some difference is found in the value of the multiplicative empirical coefficient in the various formulas, and much of the scatter may be ascribed to relative trap efficiency. (3) Verification of predictive formulas has mainly rested on laboratory measurements, and reliable but limited field verification has not been made until recently. (4) The laboratory and field data indicate that both the Bagnold and the Kawamura formulas are applicable to a well-sorted sand and can be used for estimation of wind-blown sand transport on dry natural beaches. Modifications have been made for a widely distributed sand and for fluctuating wind velocity.  相似文献