Passive microwave remote sensing of the historic February 2010 snowstorms in the Middle Atlantic region of the USA     

James L. Foster  Gail Skofronick‐Jackson  Huan Meng  James R. Wang  George Riggs  Paul J. Kocin  Benjamin T. Johnson  Judah Cohen  Dorothy K. Hall  Son V. Nghiem 《水文研究》2012,26(22):3459-3471

The snowfall in the Baltimore/Washington metropolitan area during the winter of 2009/2010 was unprecedented and caused serious snow‐related disruptions. In February 2010, snowfall totals approached 2 m, and because maximum temperatures were consistently below normal, snow remained on the ground the entire month. One of the biggest contributing factors to the unusually severe winter weather in 2009/2010, throughout much of the middle latitudes, was the Arctic Oscillation. Unusually high pressure at high latitudes and low pressure at middle latitudes forced a persistent exchange of mass from north to south. In this investigation, a concerted effort was made to link remotely sensed falling snow observations to remotely sensed snow cover and snowpack observations in the Baltimore/Washington area. Specifically, the Advanced Microwave Scanning Radiometer onboard the Aqua satellite was used to assess snow water equivalent, and the Advanced Microwave Sounding Unit‐B and Microwave Humidity Sounder were employed to detect falling snow. Advanced Microwave Scanning Radiometer passive microwave signatures in this study are related to both snow on the ground and surface ice layers. In regard to falling snow, signatures indicative of snowfall can be observed in high frequency brightness temperatures of Advanced Microwave Sounding Unit‐B and Microwave Humidity Sounder. Indeed, retrievals show an increase in snow water equivalent after the detection of falling snow. Yet, this work also shows that falling snow intensity and/or the presence of liquid water clouds impacts the ability to reliably detect snow water equivalent. Moreover, changes in the condition of the snowpack, especially in the surface features, negatively affect retrieval performance. Copyright © 2011. This article is a U.S. Government work and is in the public domain in the USA.  相似文献   

Coronal magnetic field of the Sun on 7 January 1969     

Dorothy E. Trotter  Gordon Newkirk Jr. 《Solar physics》1971,20(2):372-374

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Inter-relationships of MnO₂ precipitation, siderophore-Mn complex formation, siderophore degradation, and iron limitation in Mn-oxidizing bacterial cultures     

Dorothy L. Parker  Takami Morita  Rebecca Verity  James K. McCarthy 《Geochimica et cosmochimica acta》2007,71(23):5672-5683

To examine the pathways that form Mn^(III) and Mn^(IV) in the Mn^(II)-oxidizing bacterial strains Pseudomonas putida GB-1 and MnB1, and to test whether the siderophore pyoverdine (PVD) inhibits Mn^(IV)O₂ formation, cultures were subjected to various protocols at known concentrations of iron and PVD. Depending on growth conditions, P. putida produced one of two oxidized Mn species - either soluble PVD-Mn^(III) complex or insoluble Mn^(IV)O₂ minerals - but not both simultaneously. PVD-Mn^(III) was present, and MnO₂ precipitation was inhibited, both in iron-limited cultures that had synthesized 26-50 μM PVD and in iron-replete (non-PVD-producing) cultures that were supplemented with 10-550 μM purified PVD. PVD-Mn^(III) arose by predominantly ligand-mediated air oxidation of Mn^(II) in the presence of PVD, based on the following evidence: (a) yields and rates of this reaction were similar in sterile media and in cultures, and (b) GB-1 mutants deficient in enzymatic Mn oxidation produced PVD-Mn^(III) as efficiently as wild type. Only wild type, however, could degrade PVD-Mn^(III), a process linked to the production of both MnO₂ and an altered PVD with absorbance and fluorescence spectra markedly different from those of either PVD or PVD-Mn^(III). Two conditions, the presence of bioavailable iron and the absence of PVD at concentrations exceeding those of Mn, both had to be satisfied for MnO₂ to appear. These results suggest that P. putida cultures produce soluble Mn^(III) or MnO₂ by different and mutually inhibitory pathways: enzymatic catalysis yielding MnO₂ under iron sufficiency or PVD-promoted oxidation yielding PVD-Mn^(III) under iron limitation. Since PVD-producing Pseudomonas species are environmentally prevalent Mn oxidizers, these data predict influences of iron (via PVD-Mn^(III) versus MnO₂) on the global oxidation/reduction cycling of various pollutants, recalcitrant organic matter, and elements such as C, S, N, Cr, U, and Mn.  相似文献   

An experimental and theoretical determination of oxygen isotope fractionation in the system magnetite-H₂O from 300 to 800°C     

David R. Cole  Juske Horita  John W. Valley  Dorothy W. Coffey 《Geochimica et cosmochimica acta》2004,68(17):3569-3585

Oxygen isotope fractionations have been determined between magnetite and water from 300 to 800°C and pressures between 10 and 215MPa. We selected three reaction pathways to investigate fractionation: (a) reaction of fine-grained magnetite with dilute aqueous NaCl solutions; (b) reduction of fine-grained hematite through reaction with dilute acetic acid; and (c) oxidation of fine iron power in either pure water or dilute NaCl solutions. Effective use of acetic acid was limited to temperatures up to about 400°C, whereas oxide-solution isotope exchange experiments were conducted at all temperatures. Equilibrium ¹⁸O/¹⁶O fractionation factors were calculated from the oxide-water experiments by means of the partial isotope exchange method, where generally four isotopically different waters were used at any given temperature. Each run product was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and on a limited basis, high-resolution transmission electron microscopy (HRTEM) and Mössbauer spectroscopy. Results from the microscopic examinations indicate the formation of well-crystallized octahedra and dodecahedra of magnetite where the extent of crystallization, grain size, and grain habit depend on the initial starting material, P, T, solution composition, and duration of the run.The greatest amount of oxygen isotope exchange (∼90% or greater) was observed in experiments where magnetite either recrystallized in the presence of 0.5 m NaCl from 500 to 800°C or formed from hematite reacted with 0.5 m acetic acid at 300, 350 and 400°C. Fractionation factors (10³ ln α_mt-H2O) determined from these partial exchange experiments exhibit a steep decrease (to more negative values) with decreasing temperature down to about 500°C, followed by shallower slope. A least-squares regression model of these partial exchange data, which accounts for analytical errors and errors generated by mass balance calculations, gives the following expression for fractionation that exhibits no minimum: 1000lnα_lmt-lw=−8.984(±0.3803)x+3.302(±0.377)x²—0.426(±0.092)x³ with an R² = 0.99 for 300 ≤ T≤ 800°C (x = 10⁶/T²). The Fe oxidation results also exhibit this type of temperature dependence but shifted to slightly more negative 10³ ln α values; there is the suggestion that a kinetic isotope effect may contribute to these fractionations. A theoretical assessment of oxygen isotope fractionation using β-factors derived from heat capacity and Mössbauer temperature (second-order Doppler) shift measurements combined with known β-factors for pure water yield fractionations that are somewhat more negative compared to those determined experimentally. This deviation may be due to the combined solute effects of dissolved magnetite plus NaCl (aq), as well as an underestimation of β_mt at low temperatures. The new magnetite-water experimental fractionations agree reasonably well with results reported from other experimental studies for temperatures ≥ 500°C, but differ significantly with estimates based on quasi-theoretical and empirical approaches. Calcite-magnetite and quartz-magnetite fractionation factors estimated from the combination of magnetite β’s calculated in this study with those for calcite and quartz reported by Clayton and Kieffer (1991) agree very closely with experimentally determined mineral-pair fractionations.  相似文献   

Metal and Bi/Pb microdistribution studies of an L3 chondrite: their implications for a meteorite parent body     

Dorothy S. Woolum  D.S. Burnett 《Geochimica et cosmochimica acta》1981,45(9):1619-1632

We find strong localizations (relative to bulk) of Bi and to a lesser extent Pb. in some of the kamacite grains in Khohar. Other kamacite grains show no such enrichments. There are distinctive and correlated differences in the Ni contents of the two kamacite populations, with the Bi/Pb-rich kamacite grains having consistently lower Ni levels (sometimes unusually low. ~ 2% Ni) than the Bi/Pb-poor kamacite, which typically have ~ 6–7% Ni. The Bi/Pb-rich kamacite grains are also distinguished on the basis of their etching behavior, exhibiting a highly reactive attack, which has not been observed previously and which we believe may be due to the fact that the Bi/Pb-rich kamacite is finely polycrystalline.We conclude that the trace element microdistributions were not established in the nebula. Nor is it likely that the enrichments occurred with slow cooling in the presence of a vapor phase during the kamacite-taenite phase transition. Rather, the Bi/Pb-rich kamacite most likely reflect the occurrence of a brief reheating episode (or episodes), which may have been shock-induced and which was followed by rapid cooling. We find fine-grained metal-sulfide intergrowths which testify to such a reheating event, and one likely candidate for the site of this event is a hot ejecta blanket at the parent body surface. Iron oxides are found in our Khohar sections. We believe that they are not due to terrestrial alteration, that they are magnetite and that the magnetite probably originated in the same dynamic event in which the Bi/Pb distributions were established. The present data do not allow us to confidently determine whether the event occurred prior to, during, or after the compaction of this meteorite, although the simplest interpretation of the data would indicate the first alternative. Bulk Bi data for Khohar has been used for inferring accretion temperatures and this now appears inappropriate.  相似文献   

Bismuth and ²⁰⁸Pb microdistributions in enstatite chondrites     

Dorothy S. Woolum  D.S. Burnett  L.S. August 《Geochimica et cosmochimica acta》1979,43(11):1819-1828

Polished sections of 5 enstatite chondrites have been irradiated with 30 MeV ⁴He ions to produce the alpha-radioactive nuclei ²¹¹At and ²¹⁰Po from ²⁰⁹Bi and ²⁰⁸Pb, respectively. The distribution of alpha activity can be mapped, using cellulose nitrate as an alpha track detector, to give the corresponding Bi or Pb distributions in the meteorite. No strong localization of Bi or ²⁰⁸Pb was found; relatively uniform track distributions were observed. In particular, metal or sulfide grains are not enriched in Bi or Pb (relative to bulk), which is in agreement with the predictions of nebular condensation calculations. While the track distributions appear uniform, the results of detailed, track-by-track mappings of the Bi detectors indicate that the Bi is not totally randomly distributed; the statistical fluctuations in the observed track density are different for the cases where the Bi is totally randomly distributed and where the Bi is localized in point sources. Assuming that the Bi in a given sample is localized in identical point sources which are uniformly distributed throughout the sample, the observed relative population densities of clusters (‘stars’) of small numbers of tracks (2–5) corresponds to Bi being localized, with ~90% in grains with about 10^?16g-Bi (~3 × 10⁵Biatoms), and with ~10% in 4 × 10^?14 g-Bi sources. If these are elemental Bi, as predicted theoretically, they are ~ 10² Å and 10³ Å in size, respectively.  相似文献   

Sedimentary studies in the Shenandoah Valley of Virginia     

Dorothy Carroll 《International Journal of Earth Sciences》1955,43(2):383-384

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Medieval Warming, Little Ice Age, and European impact on the environment during the last millennium in the lower Hudson Valley, New York, USA   总被引：1，自引：0，他引：1  

Dee Cabaniss Pederson  Dorothy M. Peteet  Dorothy Kurdyla  Tom Guilderson 《Quaternary Research》2005,63(3):363-249

Establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts. We present a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency from a tidal marsh in the Hudson River Estuary. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from 800–1300 A.D., paralleling paleorecords southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. The presence of the Little Ice Age ensues with increases in Picea and Tsuga, coupled with increasing organic percentages due to cooler, moister conditions. European impact is manifested by a decline in arboreal pollen due to land clearance, increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), and an increase in inorganic particles to the watershed.  相似文献   

Sakmarian geography     

Dorothy Hill 《International Journal of Earth Sciences》1959,47(2):590-629

The known palaeontological and stratigraphical evidence is used as a basis for the construction of maps of the continents showing the extent of their inundation by the sea in Sakmarian time in the Upper Palaeozoic. In the northern hemisphere apart from India the evidence is sufficiently reliable to give reasonable maps, and the great extent of the inundations suggests that the climate would be considerably modified from that of today; no undoubted Sakmarian glacials occur there. In Southern continents and India, the Gondwana biogeographical province has made correlation with the northern continents controversial, but reasons are given for assuming that Gondwana glacial deposits were at least in part Sakmarian; the resultant maps show that the Gondwana land surfaces were but little reduced in area, and that the main glacials (except for India) lie within a belt between 40 S and 20 S. Present lack of knowledge of Sakmarian conditions in Antarctica makes reconstructions of climatic belts too hazardous for possible use in enunciating or checking hypotheses of continental drift and polar wandering.  相似文献   

Mineralogical and Geochemical Constraints on the Sediment Sources of Late Stone Age Pottery from the Birimi Site,Northern Ghana     

J. Victor Owen  Joanna L. Casey  John D. Greenough  Dorothy Godfrey‐Smith 《Geoarchaeology》2013,28(4):394-411

The mineralogy and bulk chemical compositions of 15 Kintampo (Late Stone Age) potsherds from the Birimi site on the Gambaga Escarpment and eight samples of local sediment were determined with the intent of characterizing these wares and identifying the material used in their manufacture. Sediment from clay pits still used by potters north of the escarpment contains iron‐rich laterite clasts (100 × XFeO_t = 100 × FeO_t/[FeO_t + Al₂O₃ + SiO₂] ≥10). Sedimentary clasts in stream sediments are relatively siliceous and iron‐poor (100 × XFeO_t < 10). Bulk geochemical data together with the compositions of lithic clasts (laterite, siltstone/sandstone) link the pottery to sediment sources, including escarpment sediments not presently used by Ghanaian potters. Fresh granite clasts found in some of the sherds were not found in the analyzed sediment samples, although some of their distinctive mineralogical constituents (e.g., variably barian alkali feldspar) are present. The analytical data suggest that pots found at Birimi were made locally by mixing escarpment sediment with clay and stream sediment brought in from below the escarpment. This contrasts with present‐day practice, whereby the pots themselves are imported. The place where Birimi pottery was made and the outcrop source of aluminous sediment (mudstone with an “escarpment” trace element signature) used in these wares, however, remain unidentified. © 2013 Wiley Periodicals, Inc.  相似文献