Phytoplankton reference communities for Chesapeake Bay and its tidal tributaries     

Claire Buchanan  Richard V. Lacouture  Harold G. Marshall  Marcia Olson  Jacqueline M. Johnson 《Estuaries and Coasts》2005,28(1):138-159

Phytoplankton reference communities for Chesapeake Bay were quantified from least-impaired water quality conditions using commonly measured parameters and indicators derived from measured parameters. A binning approach was developed to classify water quality. Least-impaired conditions had relatively high water column transparency and low concentrations of dissolved inorganic nitrogen and orthophosphate. Reference communities in all seasons and salinity zones are characterized by consistently low values of chlorophylla and pheophytin coupled with relative stable proportions of the phytoplankton taxonomic groups and low biomasses of key bloom-forming species. Chlorophyll cell content was lower and less variable and average cell size and seasonal picophytoplankton biomass tended to be greater in the mesohaline and polyhaline reference communities as compared to the impaired communities. Biomass concentrations of the nano-micro phytoplankton size fractions (2–200 μm) in 12 of the 16 season-specific and salinity-specific reference communities were the same or higher than those in impaired habitat conditions, suggesting that nutrient reductions will not decrease the quantity of edible phytoplankton food available to large consumers. High (bloom) and low (bust) biomass events within the impaired phytoplankton communities showed strikingly different chlorophyll cell content and turnover rates. Freshwater flow had little effect on phytoplankton responses to water quality condition in most of the estuary. Improved water column transparency, or clarity, through the reduction of suspended sediments will be particularly important in attaining the reference communities. Significant nitrogen load reductions are also required.  相似文献   

Real-time measurement of volcanic SO2 emissions: validation of a new UV correlation spectrometer (FLYSPEC)     

Keith A. Horton  Glyn Williams-Jones  Harold Garbeil  Tamar Elias  A. Jeff Sutton  Peter Mouginis-Mark  John N. Porter  Steven Clegg 《Bulletin of Volcanology》2006,68(4):323-327

A miniaturized, lightweight and low-cost UV correlation spectrometer, the FLYSPEC, has been developed as an alternative for the COSPEC, which has long been the mainstay for monitoring volcanic sulfur dioxide fluxes. Field experiments have been conducted with the FLYSPEC at diverse volcanic systems, including Masaya (Nicaragua), Poás (Costa Rica), Stromboli, Etna and Vulcano (Italy), Villarica (Chile) and Kilauea (USA). We present here those validation measurements that were made simultaneously with COSPEC at Kilauea between March 2002 and February 2003. These experiments, with source emission rates that ranged from 95 to 1,560 t d⁻¹, showed statistically identical results from both instruments. SO₂ path-concentrations ranged from 0 to >1,000 ppm-m with average correlation coefficients greater than r ²=0.946. The small size and low cost create the opportunity for FLYSPEC to be used in novel deployment modes that have the potential to revolutionize the manner in which volcanic and industrial monitoring is performed.  相似文献   

Lifetime of Intranetwork Magnetic Elements     

Zhang  Jun  Lin  Ganghua  Wang  Jingxiu  Wang  Haimin  Zirin  Harold 《Solar physics》1998,178(2):245-250

Using a 10-hour time sequence of very deep magnetograms of Big Bear Solar Observatory, we have studied the lifetime of Intranetwork Magnetic Elements for the first time. The analysis reveals the following results:(1) The lifetime of intranetwork elements ranges from 0.2 hr to 7.5 hr with the mean of 2.1 hr. There appears to be a quasi-linear dependence of the lifetime on the total flux of elements. (2) Most intranetwork elements appear as a cluster of mixed polarities from an emergence center somewhere within the network boundary and are destroyed by three mechanisms: merging with intranetwork or network elements of the same polarity, cancellation of opposite polarity elements, or separation and disappearance at the position where they appear. (3) We estimate that the total energy released from the recycling of IN elements isinebreak1.6 × 10²⁸ ergs s^-1, which seems to be comparable to the energy required to heat the corona.  相似文献   

Estimation of the dielectric constant of H2O from experimental solubilities of quartz,and calculation of the thermodynamic properties of aqueous species to 900°C at 2 kb     

William F. McKenzie  Harold C. Helgeson 《Geochimica et cosmochimica acta》1984,48(11):2167-2177

Experimental quartz solubilities in H₂O (Anderson and Burnham, 1965, 1967) were used together with equations of state for quartz and aqueous species (Helgesonet al., 1978; Walther and Helgeson, 1977) to calculate the dielectric constant of H₂O () at pressures and temperatures greater than those for which experimental measurements (Heger, 1969; Lukashovet al., 1975) are available ($\text{0.001 ? P ? 5}\text{kb}$ and $\text{0 ? T ? 600°C}$). Estimates of computed in this way for 2 kb (which are the most reliable) range from 9.6 at 600°C to 5.6 at 800°C. These values are 0.5 and 0.8 units greater, respectively, than corresponding values estimated by Quist and Marshall (1965), but they differ by <0.3 units from extrapolated values computed from Pitzer's (1983) adaptation of the Kirkwood (1939) equation. The estimates of generated from quartz solubilities at 2 kb were fit with a power function of temperature, which was then used together with equations and data given by Helgeson and Kirkham (1974a,b, 1976) Helgesonet al. (1981), and Helgeson (1982b, 1984) to calculate Born functions, Debye Hückel parameters, and the thermodynamic properties of Na⁺, K⁺, Mg⁺⁺, Ca⁺⁺, and other aqueous species of geologic interest at temperatures to 900°C.  相似文献   

Digital topography of volcanoes from radar interferometry: an example from Mt Vesuvius,Italy     

Peter J. Mouginis-Mark  Harold Garbeil 《Bulletin of Volcanology》1993,55(8):566-570

A new airborne radar technique can generate digital topographic data for volcanoes at a scale of 10 m spatial and 1–5 m vertical, with a swath width of 6.4 km. Called TOPSAR, the intrument is an interferometric radar flown on the NASA DC-8 aircraft. TOPSAR data permit the quantification of volcano slopes, volumes, and heights, and as such will be valuable for the analysis of lava flows, domes, and lahar channels. This instrument will be flown over several volcanoes in the near future, providing volcanologists with valuable data sets for the analysis of high-resolution topography. We briefly illustrate the potential use of TOPSAR data through examples from Mt Somma and Vesuvius, Italy.  相似文献   

Strong transverse fields in δ-spots     

Harold Zirin  Haimin Wang 《Solar physics》1993,144(1):37-43

Spectroscopic measurements of the strength and direction of transverse magnetic fields in six -spots are presented. The field direction is determined by the relative strength of the - and -components at different polarizer orientations, and is, with one exception, parallel to the neutral line and as strong as the umbral field. Field strengths determined by line splitting are as high as 3980 G.  相似文献   

The roots of coronal structure in the Sun's surface     

Leon Golub  Harold Zirin  Haimin Wang 《Solar physics》1994,153(1-2):179-198

We have compared the structures seen on X-ray images obtained by a flight of the NIXT sounding rocket payload on July 11, 1991 with near-simultaneous photospheric and chromospheric structures and magnetic fields observed at Big Bear. The X-ray images reflect emission of both Mgx and Fexvi, formed at 1 × 10⁶ K and 3 × 10⁶ K, respectively. The brightest H sources correspond to a dying sub-flare and other active region components, all of which reveal coronal enhancements situated spatially well above the H emission. The largest set of X-ray arches connected plages of opposite polarity in a large bipolar active region. The arches appear to lie in a small range of angle in the meridian plane connecting their footpoints. Sunspots are dark on the surface and in the corona. For the first time we see an emerging flux region in X-rays and find the emission extends twice as high as the H arches. Many features which we believe to correspond to X-ray bright points (XBPs) were observed. Whether by resolution or spectral band, the number detected greatly exceeds that from previous work. All of the brighter XBPs correspond to bipolar H features, while unipolar H bright points are the base of more diffuse comet-like coronal arches, generally vertical. These diverge from individual features by less than 30°, and give a good measure of what the canopies must do. The H data shows that all the H features were present the entire day, so they are not clearly disappearing or reappearing. We find a new class of XBPs which we call satellite points, elements of opposite polarity linked to nearby umbrae by invisible field lines. The satellite points change rapidly in X-ray brightness during the flight. An M1.9 flare occurred four hours after the flight; examination of the pre-flare structures reveals nothing unusual.  相似文献   

ASSESSING DISASTER MAGNITUDE: A SOCIAL SCIENCE APPROACH     

Harold D. Foster 《The Professional geographer》1976,28(3):241-247

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Hubble Space Telescope observations of Comet 9P/Tempel 1 during the Deep Impact encounter     

Paul D. Feldman  Stephan R. McCandliss  Harold A. Weaver  Michael J.S. Belton 《Icarus》2007,187(1):113-122

We report on the Hubble Space Telescope program to observe periodic Comet 9P/Tempel 1 in conjunction with NASA's Deep Impact Mission. Our objectives were to study the generation and evolution of the coma resulting from the impact and to obtain wide-band images of the visual outburst generated by the impact. Two observing campaigns utilizing a total of 17 HST orbits were carried out: the first occurred on 2005 June 13-14 and fortuitously recorded the appearance of a new, short-lived fan in the sunward direction on June 14. The principal campaign began two days before impact and was followed by contiguous orbits through impact plus several hours and then snapshots one, seven, and twelve days later. All of the observations were made using the Advanced Camera for Surveys (ACS). For imaging, the ACS High Resolution Channel (HRC) provides a spatial resolution of 36 km (16 km pixel⁻¹) at the comet at the time of impact. Baseline images of the comet, made prior to impact, photometrically resolved the comet's nucleus. The derived diameter, 6.1 km, is in excellent agreement with the 6.0±0.2 km diameter derived from the spacecraft imagers. Following the impact, the HRC images illustrate the temporal and spatial evolution of the ejecta cloud and allow for a determination of its expansion velocity distribution. One day after impact the ejecta cloud had passed out of the field-of-view of the HRC.  相似文献   

The Meteoritical Bulletin,No. 92, 2007 September     

Harold C. Connolly  Caroline Smith  Gretchen Benedix  Luigi Folco  Kevin Righter  Jutta Zipfel  Akira Yamaguchi  Hasnaa Chennaoui Aoudjehane 《Meteoritics & planetary science》2007,42(9):1647-1694

Abstract— In this edition of The Meteoritical Bulletin, 1394 recognized meteorites are reported, 27 from specific locations within Africa, 133 from Northwest Africa, 1227 from Antarctica (from ANSMET, PNRA, and PRIC expeditions), and 7 from Asia. The Meteoritical Bulletin announces the approval of four new names series by the Nomenclature Committee of the Meteoritical Society, two from Africa and one from Asia, including Al Haggounia, from Al Haggounia, Morocco, which is projected to be on the order of 3 metric tons of material related to enstatite chondrites and aubrites. Approved are two falls from Africa, Bassikounou (Mauritania) and Gashua (Nigeria). Approved from areas other than Antarctica are one lunar, two Martian, 32 other achondrites, three mesosiderites, two pallasites, one CM, two CK, one CR2, two CV3, one CR2, and four R chondrites. The Nomenclature Committee of the Meteoritical Society announces 48 newly approved relict meteorites from two new name series, Österplana and Gullhögen (both from Sweden).  相似文献