ATTILA: atmospheric tracer transport in a Lagrangian model   总被引：2，自引：0，他引：2  

CHRISTIAN REITHMEIER  ROBERT SAUSEN 《Tellus. Series B, Chemical and physical meteorology》2002,54(3):278-299

The model ATTILA has been developed to treat the global-scale transport of passive trace species in the atmosphere within the framework of a general circulation model (GCM). ATTILA runs online within the GCM ECHAM4 and advects the centroids of 80.000 to 190.000 constant mass air parcels. Each trace constituent is thereby represented by a mass mixing ratio in each parcel. ATTILA contains state-of-the-art parameterizations of convection, turbulent boundary layer mixing and inter-parcel transport, and provides an algorithm to map the tracer concentrations from the trajectories to the ECHAM model grid. The transport characteristics of ATTILA are evaluated against observations and the standard semi-Lagrangian transport scheme of ECHAM by two experiments. (1) We simulate the distribution of the short-lived tracer radon (²²²Rn) in order to examine fast vertical transport over continents, and long-range transport from the continents to remote areas. (2) We simulate the distribution of radiocarbon (¹⁴C) from nuclear weapon tests in order to examine upper tropospheric and stratospheric transport characteristics. Contrary to the semi-Lagrangian scheme, ATTILA shows a greatly reduced meridional transport in the upper troposphere and lower stratosphere, and a reduced downward flux from the stratosphere to the troposphere, especially in mid-latitudes. Since ATTILA is a numerically non-diffusive scheme, it is able to maintain steep gradients, which compare better to the observations than the rather smooth gradients produced by the semi-Lagrangian scheme.  相似文献   

Crystallization Pressure and Cooling History of the Giles Layered Igneous Complex, Central Australia   总被引：1，自引：0，他引：1  

BALLHAUS  CHRISTIAN; BERRY  RON F. 《Journal of Petrology》1991,32(1):1-28

The Giles Complex, central Australia, consists of a series oflarge layered gabbroic/ultramafic intrusions emplaced in acidicand intermediate granulites of the Middle Proterozoic Musgraveblock. Lithologies range from well-layered dunite, wehrlite,and pyroxenite in the lower primitive series, to massive olivinegabbro, gabbronorite, and anorthosite in the main units, andferrodiorites, vanadife-rous magnetite layers, and granophyresin the upper, most fractionated parts. Unlike many layered intrusions,the Giles Complex is tectonically dismembered to an extent thata reconstruction of the original morphology is difficult. The Complex is believed to be a type example for medium- tohigh-pressure differentiation. (1) Chilled margin samples (wherepreserved) are orthopyroxene-phyric, and liquidus olivine isreplaced by liquidus orthopyroxene at an mg-number of 0.77,suggesting a pressure-related expansion of the orthopyroxenestability field (Goode & Moore, 1975). (2) Tschermaks substitutioninto pyroxene and plagioclase-orthoclase solid solution areextensive, indicating unusually high crystallization temperaturerelated to high pressure; antiperthites in the Giles Complexare amongst the most calcic reported for terrestrial rocks.(3) The lower primitive cumulate units of the Complex are coroniticand feature a variety of subsolidus high-pressure reaction textures;olivine and cumulus chromite have reacted with calcic plagioclaseto orthopyroxene-clinopyroxene-spinel, olivine-spinel, and clinopyroxene-spinelsymplectites. The principal reaction mechanism for the symplectites was continuousmass transfer of alumina from plagioclase toward spinel, asthe Complex passed from the olivine-plagioclase stability fieldinto the pyroxene-spinel field during cooling. Geothermometersapplicable to the cumulates record a wide range of equilibrationtemperatures from late-magmatic to granulite-metamorphic conditions.FeMg₁ exchange gives closure temperatures around 600–700?C,whereas Al₂Mg₁Si₁ net-transfer equilibria have preserved highertemperatures around 750–900 ?C. Defocused beam bulk analysesof exsolved cumulus clinopyroxenes and intercumulus plagioclasesrecover magmatic compositions; i. e., two-pyroxene solvus CaMg_-1temperatures plot around 1120?50?C, whereas two-feldspar thermometersgive 1200?C. Pressures are calculated from thermochemical data with the heterogeneousequilibria 2 fo + an = en + di + sp, fo + an = di + Mg-Ts, andfo + an = en + Ca-Ts, after correcting spinel activities forselective retrograde FeMg_-1 exchange during cooling. These equilibria,combined with orthopyroxene-spinel Al₂Mg_-1Si_-1 temperaturesfor metamorphic assemblages and two-pyroxene temperatures forcumulus phases define a medium-pressure cooling path extendingfrom 1150 ?C (at 6?5 kb) to 750 ?C (at 6?2 kb). The resultssuggest an isobaric cooling path for the Giles Complex, withno evidence for a post-intrusive metamorphic overprint. Themagmas intruded at lower to middle crustal levels after thepervasive deformation in the Musgrave block, and probably afterthe peak metamorphic event.  相似文献   

A glacial chronology for northern East Greenland   总被引：3，自引：1，他引：3  

CHRISTIAN HJORT 《Boreas: An International Journal of Quaternary Research》1981,10(3):259-274

In East Greenland between 75 and 76N three different glacial episodes can be identified: (1) An early period with more or less total ice cover and in which the ice reached out onto the continental shelf - the Kap Mackenzie stadial; (2) a period with glaciation of intermediate extent, when nunataks and a few ice-free lowland areas existed - the Muschelbjerg stadial; and (3) a final period with glacial advance, when the glaciers were mainly restricted to fjords and larger valleys - the Nanok stadial. Each of these stadials was followed by a period with general deglaciation, from which marine shell-bearing sediments have been found; the Hochstetter Forland interstadial, the Peters Bugt interstadial and the Flandrian interglacial, respectively. The marine limit sank with each of these ice-free periods; probably an isostatic effect of the decreasing amplitude of the glacial advances. The deglaciation after the Nanok stadial began about 9500 B.P. It is not known for certain when this glacial advance started, but 13,000 B.P. or earlier is suggested. According to ¹⁴C datings the Peters Bugt interstadial dates from at least 45,000 B.P. and the Hochstetter Forland interstadial from at least 49,000 B.P. However, amino acid analyses indicate a distinct age difference between these two interstadial, and Th/U datings give age estimates of 70,000–115,000 B.P. for the Hochstetter Forland interstadial, which therefore seems to be of Early Weichselian age although a pre-Weichselian age cannot be excluded. The same applies to the preceding Kap Mackenzie stadial. The correspondence between the present glacial chronology and similar tripartite ones on Bafffin Island, Ellesmere Island and Svalbard seems reasonably good  相似文献   

Aspects of the Weichselian chronology in central East Greenland     

SVEND FUNDER  CHRISTIAN HJORT 《Boreas: An International Journal of Quaternary Research》1973,2(2):69-84

From central East Greenland, C₁₄ ages between 19,500 > 40,000 years B.P. have been obtained for six samples of marine bivalve shells. The ages seem to be consistent with geological observations and form the basis for a tentative chronology for the Weichselian ice age in the region. It appears that the maximum glaciation during Weichselian times was attained more than 40,000 years ago, and that since then ice-free areas have existed. This assumption agrees with evidence of botanical refugia in the region, and the restricted glacier activity especially during the Upper Pleniglacial (ca. 30,000–15,000 years B.P.) is explained by a reduced supply of moisture. A comparison with evidence from other parts of Greenland indicates that different glacial histories can be expected for different sectors of the Greenland Inland Ice.  相似文献   

Radiocarbon dated common mussels Mytilus edulis from eastern Svalbard and the Holocene marine climatic optimum     

CHRISTIAN HJORT  JAN MANGERUD  LENA ADRIELSSON  STEIN BONDEVIK  JON Y. LANDVIK  OTTO SALVIGSEN 《Polar research》1995,14(2):239-243

The common mussel Mytilus edulis is an indicator of milder marine conditions in the Arctic, with stronger Atlantic Water influx, during the Holocene and earlier interglacials. Twelve Holocene radiocarbon dates of mytilus from eastern Svalbard fall between ca 8800 and 5000 BP and roughly delimit the marine climatic optimum period there. The beginning of this period in the east coincides with the immigration of boreal extralimital molluscs to western Svalbard, indicating the culmination of Holocene Atlantic influence.  相似文献   

Distinguishing fluvio‐deltaic facies by bulk geochemistry and heavy minerals: an example from the Miocene of Denmark     

METTE OLIVARIUS  ERIK S. RASMUSSEN  VOLKERT SIERSMA  CHRISTIAN KNUDSEN  GUNVER K. PEDERSEN 《Sedimentology》2011,58(5):1155-1179

  相似文献   

Morphogenetic impact of microbial mats on surface structures of Kimmeridgian micritic limestones (Cerin, France)     

P. BERNIER  C. GAILLARD  J. C. GALL†  G. BARALE‡  J. P. BOURSEAU  E. BUFFETAUT§  S. WENZ¶ 《Sedimentology》1991,38(1):127-136

For several years, palaeoecological research has been conducted on micritic limestones of late Kimmeridgian age in the southern Jura Mountains. The sedimentary environment is that of a lagoon with an irregular bottom, which was repeatedly exposed. Between two stages of lime deposition, a microbial mat grew over the muddy surface, giving cohesion to the sediment, restraining erosion and preserving fossil remains and reptile tracks. Various structures at the microbial mat surface can be observed: crescentic wavy, radial wavy, torn, petee and mixed structures. They imply the presence of desiccation periods and a slight bottom slope leading to a downward sliding of the microbial mat. Such features may also be generalized to explain superficial microbial structures of other shallow carbonate-mud environments.  相似文献   

Weather influence on passive microwave brightness temperatures     

STIG M. LøVAS  IRENE RUBINSTEIN  CHRISTIAN ULSTAD 《Polar research》1994,13(1):67-81

  相似文献   

The Quaternary of the Kattegat area, Scandinavia: a review   总被引：1，自引：0，他引：1  

HOLGER LYKKE-ANDERSEN  KAREN LUISE KNUDSEN  CHRISTIAN CHRISTIANSEN 《Boreas: An International Journal of Quaternary Research》1993,22(4):269-281

The Quaternary sedimentary history and its relations to the pre-Quaternary in the Kattegat region are reviewed. The Quaternary in the area is restricted to relatively young sediments, including scattered findings of Saalian deposits and more continuous occurrences from the Eemian, the Weichselian and the Holocene. Glacial and interglacial palaeoenvironmental reconstructions, including Holocene changes in oceanographic circulation, are reviewed, and the recent sedimentary processes and the present hydrographic regime are outlined. Furthermore, Quaternary and present tectonic activity in connection with some of the pre-Quaternary fault zones is discussed.  相似文献   

Dynamics of the last glaciation in eastern Svalbard as inferred from glacier-movement indicators     

OTTO SALVIGSEN  LENA ADRIELSSON  CHRISTIAN HJORT  MICHAEL KELLY  JON Y. LANDVIK  LARS RONNERT 《Polar research》1995,14(2):141-152

Glacial striae and other ice movement indicators such as roche moutonées, glacial erratics, till fabric and glaciotectonic deformation have been used to reconstruct the Late Weichselian ice movements in the region of eastern Svalbard and the northern Barents Sea. The ice movement pattern may be divided into three main phases: (1) a maximum phase when ice flowed out of a centre east or southeast of Kong Karls Land. At this time the southern part of Spitsbergen was overrun by glacial ice from the Barents Sea; (2) the phase of deglaciation of the Barents Sea Ice Sheet, when an ice cap was centred between Kong Karls Land and Nordaustlandet. At the same time ice flowed southwards along Storfjorden; and (3) the last phase of the Late Weichselian glaciation in eastern Svalbard is represented by local ice caps on Spitsbergen, Nordaustlandet, Barentsoya and Edgeøya.
The reconstructed ice flow pattern during maximum glaciation is compatible with a centre of uplift in the northern Barents Sea as shown by isobase reconstructions and suggested by isostatic modelling.  相似文献