EISCAT observations of unusual flows in the morning sector associated with weak substorm activity     

N. J. Fox  M. Lockwood  S. W. H. Cowley  M. P. Freeman  E. Friis-Christensen  D. K. Milling  M. Pinnock  G. D. Reeves 《Annales Geophysicae》1994,12(6):541-553

A discussion is given of plasma flows in the dawn and nightside high-latitude ionospheric regions during substorms occurring on a contracted auroral oval, as observed using the EISCAT CP-4-A experiment. Supporting data from the PACE radar, Greenland magnetometer chain, SAMNET magnetometers and geostationary satellites are compared to the EISCAT observations. On 4 October 1989 a weak substorm with initial expansion phase onset signatures at 0030 UT, resulted in the convection reversal boundary observed by EISCAT (at \sim0415 MLT) contracting rapidly poleward, causing a band of elevated ionospheric ion temperatures and a localised plasma density depletion. This polar cap contraction event is shown to be associated with various substorm signatures; Pi2 pulsations at mid-latitudes, magnetic bays in the midnight sector and particle injections at geosynchronous orbit. A similar event was observed on the following day around 0230 UT (\sim0515 MLT) with the unusual and significant difference that two convection reversals were observed, both contracting poleward. We show that this feature is not an ionospheric signature of two active reconnection neutral lines as predicted by the near-Earth neutral model before the plasmoid is “pinched off”, and present two alternative explanations in terms of (1) viscous and lobe circulation cells and (2) polar cap contraction during northward IMF. The voltage associated with the anti-sunward flow between the reversals reaches a maximum of 13 kV during the substorm expansion phase. This suggests it to be associated with the polar cap contraction and caused by the reconnection of open flux in the geomagnetic tail which has mimicked “viscous-like” momentum transfer across the magnetopause.  相似文献   

Kinetics of removal of iron colloids from estuaries     

Lewis E. Fox  Steven C. Wofsy 《Geochimica et cosmochimica acta》1983,47(2):211-216

Laboratory experiments indicate that colloidal Fe is aggregated in estuarine waters by a second-order kinetic mechanism. The corresponding rate coefficient is proportional to the square of the salinity. A simple theoretical formulation is presented to describe the distribution of Fe in an estuary, based on observed second-order kinetics. The distribution depends on a single parameter whose value may be determined from measurements of the physical characteristics of the estuary. The theoretical expression accurately predicts observed distributions of Fe in a variety of estuaries, suggesting general applicability.  相似文献   

The annual cycle of zooplankton in a Long Island estuary     

Jefferson T. Turner 《Estuaries and Coasts》1982,5(4):261-274

Zooplankton and chlorophyll-a samples and associated hydrographic data were collected at approximately weekly intervals in the Peconic Bay estuary for most of the period between May 1978 and June 1979. Surface zooplankton samples were obtained by simultaneously-towed 73 μm- and 202 μm-mesh nets, and subsurface samples were collected with 505 μm-mesh nets. Zooplankton numbers and displacement volumes fluctuated widely throughout the year, with highest values in early spring and summer. Juvenile or adult copepods accounted for means of 90.0% and 85.0% of the animals recorded for the 202 μm- and 73 μm-net samples, respectively. The combination of Acartia tonsa and A. hudsonica adults+copepodids accounted for a mean of 81.4% of the zooplankton recorded for the 202 μm-net samples, and the combination of copepod nauplii, Acartia spp. adults+copepodids, Oithona colcarva and Parvocalanus crassirostris accounted for a mean of 82.7% of the animals recorded for the 73 μm-net samples. Copepod nauplii were the most abundant zooplankters collected in the 73 μm-net samples, and they were generally collected in higher numbers than the total number of animals in the 202 μm-net samples. During the colder months, late copepodids and adults of larger copepod species comprised greater proportions of the total zooplankton than during the warmer months when nauplii and copepodids of smaller copepod species were predominant. The ctenophore Mnemiopsis leidyi and the medusa Cyanea capillata also had periods of abundance during warmer months. Differences between numbers of larger zooplankters collected over different depth intervals or in successive replicate tows over the same depth intervals, reveal the likely effects of both vertical and horizontal patchiness. Comparisons of zooplankton numbers from the present investigation, which were obtained with relatively fine-mesh nets, with values from previous studies in adjacent waters which used coarser-mesh nets, suggest that many previous investigations have seriously underestimated the numbers of smaller zooplankters, particularly copepod nauplii.  相似文献   

Condensation nuclei counts on the slopes of Little Whiteface Mountain in New York State     

Jefferson Tester 《Pure and Applied Geophysics》1964,57(1):181-188

Summary Concentrations of condensation nuclei were measured on the slopes of the Little Whiteface Mt. between 1200 and 3670 feet altitude in July 1963. On the average the concentration decreases exponentially with altitude and shows a strong dependence on wind direction. In addition, the influence of local contamination from a car park and a large domestic heating furnace on nuclei counts was studied and it was found that even downwind at a distance of about 1000 feet (or 350 m) the contamination by these sources is negligible.

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Zusammenfassung Im Juli 1963 wurde die Konzentration von Kondensationskernen entlang des Little Whiteface Mt. zwischen 1200 und 3670 Fuss ü. d. M. gemessen. Im Mittel nimmt die Konzentration mit der Höhe exponentiell ab und zeigt eine starke Abhängigkeit von der Windrichtung. Zusätzlich wurde der Einfluss der lokalen Verunreinigung durch einen Autopark und eine Heizanlage eines grösseren Restaurants auf die Kernzahl studiert. Man fand, dass in einer Entfernung von ungefähr 350 m, selbst in der vorherrschenden Windrichtung, die Verunreiningung durch diese Quellen vernachlässigbar ist.

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Pioneers of Photogrammetry Commemorated In Antarctic Place-Names     

A. J. Fox  & A. Roberts 《The Photogrammetric Record》1996,15(88):601-605

Unique place-names are essential for scientific fieldwork in Antarctica. This shorter contribution describes how duplication of place-names in British Antarctic Territory has been avoided by the systematic naming of geographically related features according to groups of associated ideas. One such theme, commemorating pioneers in the development of photogrammetry, recognizes the important contribution of photogrammetry to Antarctic mapping and research.  相似文献   

Unlocking the time capsule of historic aerial photography to measure changes in antarctic peninsula glaciers     

Adrian J.  Fox  Andreas  Cziferszky 《The Photogrammetric Record》2008,23(121):51-68

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Macrophyte Abundance in Waquoit Bay: Effects of Land-Derived Nitrogen Loads on Seasonal and Multi-Year Biomass Patterns     

Sophia E. Fox  Erica Stieve  Ivan Valiela  Jennifer Hauxwell  James McClelland 《Estuaries and Coasts》2008,31(3):532-541

Anthropogenic inputs of nutrients to coastal waters have rapidly restructured coastal ecosystems. To examine the response of macrophyte communities to land-derived nitrogen loading, we measured macrophyte biomass monthly for 6 years in three estuaries subject to different nitrogen loads owing to different land uses on the watersheds. The set of estuaries sampled had nitrogen loads over the broad range of 12 to 601 kg N ha⁻¹ year⁻¹. Macrophyte biomass increased as nitrogen loads increased, but the response of individual taxa varied. Specifically, biomass of Cladophora vagabunda and Gracilaria tikvahiae increased significantly as nitrogen loads increased. The biomass of other macroalgal taxa tended to decrease with increasing load, and the relative proportion of these taxa to total macrophyte biomass also decreased. The seagrass, Zostera marina, disappeared from the higher loaded estuaries but remained abundant in the estuary with the lowest load. Seasonal changes in macroalgal standing stock were also affected by nitrogen load, with larger fluctuations in biomass across the year and higher minimum biomass of macroalgae in the higher loaded estuaries. There were no significant changes in macrophyte biomass over the 6 years of this study, but there was a slight trend of increasing macroalgal biomass in the latter years. Macroalgal biomass was not related to irradiance or temperature, but Z. marina biomass was highest during the summer months when light and temperatures peak. Irradiance might, however, be a secondary limiting factor controlling macroalgal biomass in the higher loaded estuaries by restricting the depth of the macroalgal canopy. The relationship between the bloom-forming macroalgal species, C. vagabunda and G. tikvahiae, and nitrogen loads suggested a strong connection between development on watersheds and macroalgal blooms and loss of seagrasses. The influence of watershed land uses largely overwhelmed seasonal and inter-annual differences in standing stock of macrophytes in these temperate estuaries.  相似文献   

Variability of Winter-Spring Bloom <Emphasis Type="Italic">Phaeocystis pouchetii</Emphasis> Abundance in Massachusetts Bay     

David G. Borkman  P. Scott Libby  Michael J. Mickelson  Jefferson T. Turner  Mingshun Jiang 《Estuaries and Coasts》2016,39(4):1084-1099

Abundance of the prymnesiophyte Phaeocystis pouchetii was quantified via light microscopy at 2-week to monthly intervals in Massachusetts Bay (southern Gulf of Maine, NW Atlantic) during 1992–2012. Variability in the abundance and seasonal cycle of Phaeocystis are described and synoptic hydrographic, nutrient, and meteorological data were analyzed to identify factors that may influence Phaeocystis abundance. The maximum Phaeocystis abundance was 14?×?10⁶ cells L^?1 (10 Apr 2008). It was frequently (5 of 8 years) absent prior to year 2000, but not thereafter. Seasonally, it first appeared in February to early March, reached peak abundance in mid-April, and persisted until May or early June for a duration of 0–112 days (mean 34 days). A long-term alternation between Phaeocystis and centric diatom abundance was apparent, suggesting winter-spring selection of either Phaeocystis or centric diatoms. Phytoplankton community analysis suggested that blooms affected the rest of the phytoplankton community. Phaeocystis blooms were manifest as a substantial increase in particulate nutrients above normal levels. Phaeocystis blooms were preceded in February by a slightly elevated concentration of NO₃ (9.3 vs. 6.5 μM when absent) and PO₄ (0.99 vs. 0.79 μM when absent). Blooms were also preceded by elevated ratios of NO₃/PO₄, NO₃/Si, and PO₄/Si, and warmer, saltier waters reflecting reduced river discharge. The correlation with salinity and river discharge suggests that Phaeocystis bloom variability is partially determined by annually varying circulation processes that determine the degree of low nutrient, low salinity coastal water intrusion into Massachusetts Bay.  相似文献   

Using cosmo-skymed images to detect wet snow cover on the Kraków Ice Field,King George Island,Antarctica     

Kátia Kellem da Rosa  Cláudio Wilson Mendes Jr.  Jorge Arigony-Neto  Jefferson Cardia Simões 《国际地球制图》2016,31(9):1032-1043

This work analysed the spatio-temporal variation of snow cover on the Kraków Ice Field, located in the King George Island, Antarctica. High spatial resolution images of COSMO-SkyMed were used in this study. These X-band images are vertically and horizontally co-polarized and their intensity data were converted to amplitude (dB). The COSMO-SkyMed images were classified by a minimum distance algorithm and post-classified based on knowledge of adjacency relationships of snow zones. Hypsometric, slope, aspect and solar radiation maps to support the interpretation of backscatter patterns in the COSMO-SkyMed images. Three radar zones were classified in these images: percolation, slush and wet snow radar zone. Positive surface air temperatures and rainfall events, registered from a meteorological station, lead to increase in wet snow and slush zones. The COSMO-SkyMed images and minimum distance algorithm were adequate to discriminate the snow cover and to assess the supraglacial melting pattern during the ablation season in the study area.  相似文献   

Precipitation in the EURO-CORDEX 0.11^{\circ } and 0.44^{\circ } simulations: high resolution,high benefits?     

A. F. Prein  A. Gobiet  H. Truhetz  K. Keuler  K. Goergen  C. Teichmann  C. Fox Maule  E. van Meijgaard  M. Déqué  G. Nikulin  R. Vautard  A. Colette  E. Kjellström  D. Jacob 《Climate Dynamics》2016,46(1-2):383-412

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