Stream and bed temperature variability in a coastal headwater catchment: influences of surface‐subsurface interactions and partial‐retention forest harvesting          下载免费PDF全文

S. M. Guenther  T. Gomi  R. D. Moore 《水文研究》2014,28(3):1238-1249

Stream temperature was recorded between 2002 and 2005 at four sites in a coastal headwater catchment in British Columbia, Canada. Shallow groundwater temperatures, along with bed temperature profiles at depths of 1 to 30 cm, were recorded at 10‐min intervals in two hydrologically distinct reaches beginning in 2003 or 2004, depending on the site. The lower reach had smaller discharge contributions via lateral inflow from the hillslopes and fewer areas with upwelling (UW) and/or neutral flow across the stream bed compared to the middle reach. Bed temperatures were greater than those of shallow groundwater during summer, with higher temperatures in areas of downwelling (DW) flow compared to areas of neutral and UW flow. A paired‐catchment analysis revealed that partial‐retention forest harvesting in autumn 2004 resulted in higher daily maximum stream and bed temperatures but smaller changes in daily minima. Changes in daily maximum stream temperature, averaged over July and August of the post‐harvest year, ranged from 1.6 to 3 °C at different locations within the cut block. Post‐harvest changes in bed temperature in the lower reach were smaller than the changes in stream temperature, greater at sites with DW flow, and decreased with depth at both UW and DW sites, dropping to about 1 °C at a depth of 30 cm. In the middle reach, changes in daily maximum bed temperature, averaged over July and August, were generally about 1 °C and did not vary significantly with depth. The pre‐harvest regression models for shallow groundwater were not suitable for applying the paired‐catchment analysis to estimate the effects of harvesting. However, shallow groundwater was warmer at the lower reach following harvesting, despite generally cooler weather compared to the pre‐harvest year. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Comparison of Estuarine Salinity Gradients and Associated Nekton Community Change in the Lower St. Johns River Estuary     

Cameron B. Guenther  Timothy C. MacDonald 《Estuaries and Coasts》2012,35(6):1443-1452

Salinity is an important determinant of estuarine faunal composition; previous studies, however, have indicated conflicting accounts of continuous vs. relatively rapid change in community structure at certain salinities from geographically distinct estuaries. This study uses a large fisheries monitoring database (n?>?5,000 samples) to explore evidence for estuarine salinity zonation by nekton in the lower St. Johns River estuary (LSJR). There was little evidence to support the presence of estuarine salinity zones except at the extremes of the salinity gradient (i.e., 0.1?C1.0 and 34?C39). The LSJR estuarine nekton community exhibits progressively slow ecological change throughout most of the salinity gradient with rapid change at the interfaces with fresh and marine waters??an ecoline bounded by ecotones. This study affirms the rapid change that occurs at the extremes of the salinity spectrum in certain estuaries and is relevant to efforts to manage surface water resources and estuarine ecosystems. Given the disparity in the results of the studies examining biological salinity zones in estuaries, it would be wise to have, at minimum, a regional understanding of how communities are structured along the gradient from freshwater to marine.  相似文献   

The case and fate of HD 75767 – neutron star or supernova?     

Klaus Fuhrmann  Eike Guenther  Brigitte König  Jan Bernkopf 《Monthly notices of the Royal Astronomical Society》2005,361(3):803-808

We report the discovery of the nearby  ( d = 24 pc)  HD 75767 as an eight billion year old quadruple system consisting of a distant M dwarf pair, HD 75767 C–D, in orbit around the known short-period   P = 10.25 d  single-lined binary HD 75767 A–B, the primary of which is a solar-like G star. On the reasonable assumption of synchronous orbital rotation as well as rotational and orbital coplanarity for the inner pair, we get   M _B= 0.96 M_⊙  for the unseen HD 75767 B, that is, the case of a massive white dwarf. Upon future evolution, mass transfer towards HD 75767 B will render the   M _A= 0.96 M_⊙  G-type primary, now a turnoff star, to become a helium white dwarf of   M _A∼ 0.33 M_⊙  . Depending on the mass accretion rate, accretion efficiency and composition of the massive white dwarf, this in turn may result in a collapse of HD 75767 B with the formation of a millisecond pulsar, i.e. the creation of a low-mass binary pulsar (LMBP), or, instead, a Type Ia supernova explosion and the complete disruption of HD 75767 B. Irrespective of which scenario applies, we point to the importance of the distant M dwarfs as the likely agents for the formation of the inner, short-period HD 75767 A–B pair, and hence a path that particularly avoids preceding phases of common envelope evolution.  相似文献   

Simulating the outer layers of Procyon A: a comparison with the Sun     

F. J. Robinson  P. Demarque  D. B. Guenther  Y.-C. Kim  K. L. Chan 《Monthly notices of the Royal Astronomical Society》2005,362(3):1031-1037

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Measurement of biogenic sulfur emissions from soils and vegetation: Application of dynamic enclosure methods with Natusch filter and GC/FPD analysis   总被引：3，自引：0，他引：3  

B. Lamb  H. Westberg  G. Allwine  L. Bamesberger  A. Guenther 《Journal of Atmospheric Chemistry》1987,5(4):469-491

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A photometric study of the nova‐like variable TT Arietis with the MOST satellite     

N. Vogt  A.‐N. Chen  A.F.J. Moffat  J.M. Matthews  R. Kuschnig  D.B. Guenther  J.F. Rowe  S.M. Rucinski  D. Sasselov  W.W. Weiss 《Astronomische Nachrichten》2013,334(10):1101-1106

Variability on all time scales between seconds and decades is typical for cataclysmic variables (CVs). One of the brightest and best studied CVs is TT Ari, a nova‐like variable which belongs to the VY Scl subclass, characterized by occasional low states in their light curves. It is also known as a permanent superhumper at high state, revealing “positive” (P_S > P₀) as well as “negative” (P_S < P₀) superhumps, where PS is the period of the superhump and P₀ the orbital period. TT Ari was observed by the Canadian space telescope MOST for about 230 hours nearly continuously in 2007, with a time resolution of 48 seconds. Here we analyze these data, obtaining a dominant “negative” superhump signal with a period P_S = 0.1331 days and a mean amplitude of 0.09 mag. Strong flickering with amplitudes up to 0.2 mag and peak‐to‐peak time scales of 15–20 minutes is superimposed on the periodic variations. We found no indications for significant quasi‐periodic oscillations with periods around 15 minutes, reported by other authors. We discuss the known superhump behaviour of TTAri during the last five decades and conclude that our period value is at the upper limit of all hitherto determined “negative” superhump periods of TTAri, before and after the MOST run. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

Transiting exoplanets from the CoRoT space mission Resolving the nature of transit candidates for the LRa03 and SRa03 fields     

C. Cavarroc  C. Moutou  D. Gandolfi  B. Tingley  M. Ollivier  S. Aigrain  R. Alonso  J.-M. Almenara  M. Auvergne  A. Baglin  P. Barge  A. S. Bonomo  P. Bordé  F. Bouchy  J. Cabrera  S. Carpano  L. Carone  W. D. Cochran  S. Csizmadia  H. J. Deeg  M. Deleuil  R. F. Díaz  R. Dvorak  M. Endl  A. Erikson  M. Fridlund  M. Gillon  E. W. Guenther  T. Guillot  A. Hatzes  G. Hébrard  L. Jorda  A. Léger  H. Lammer  T.-O. Lev  C. Lovis  P. J. MacQueen  T. Mazeh  A. Ofir  H. Parviainen  T. Pasternacki  M. P?tzold  D. Queloz  H. Rauer  D. Rouan  B. Samuel  A. Santerne  J. Schneider  J. Weingrill  G. Wuchterl 《Astrophysics and Space Science》2012,337(2):511-529

CoRoT is a space telescope which aims at studying internal structure of stars and detecting extrasolar planets. We present here a list of transits detected in the light curves of stars observed by CoRoT in two fields in the anti-center direction: the LRa03 one observed during 148 days from 3 October 2009 to 1 March 2010 followed by the SRa03 one from the 5 March 2010 to the 29 March 2010 during 25 days. 5329 light curves for the LRa03 field and 4169 for the SRa03 field were analyzed by the detection team of CoRoT. Then some of the selected exoplanetary candidates have been followed up from the ground. In the LRa03 field, 19 exoplanet candidates have been found, 8?remain unsolved. No secured planet has been found yet. In the SRa03 field, there were 11 exoplanetary candidates among which 6 cases remain unsolved and 3 planets have been found: CoRoT-18b, CoRoT-19b, CoRoT-20b.  相似文献   

Impacts of Weather Conditions Modified by Urban Expansion on Surface Ozone： Comparison between the Pearl River Delta and Yangtze River Delta Regions   总被引：11，自引：0，他引：11  

王雪梅  陈飞  吴志勇  张美根 《大气科学进展》2009,26(5):962-972

In this paper, the online weather research and forecasting and chemistry (WRF-Chem) model is used to explore the impacts of urban expansion on regional weather conditions and its implication on surface ozone concentrations over the Pearl River Delta(PRD) and Yangtze River Delta(YRD) regions. Two scenarios of urban maps are used in the WRF-Chem to represent the early 1990s (pre-urbanization) and the current urban distribution in the PRD and the YRD. Month-long simulation results using the above land-use scenarios for March 2001 show that urbanization increases both the day- and night-time 2-m temperatures by about 0.6^oC and 1.4^oC, respectively. Daytime reduction in the wind speed by about 3.0 m s^-1 is larger than that for the nighttime (0.5 to 2 m s^-1). The daytime increase in the PBL height (> 200 m) is also larger than the nighttime (50--100 m). The meteorological conditions modified by urbanization lead to detectable ozone-concentration changes in the PRD and the YRD. Urbanization increases the nighttime surface-ozone concentrations by about 4.7%--8.5% and by about 2.9%--4.2% for the daytime. In addition to modifying individual meteorological variables, urbanization also enhances the convergence zones, especially in the PRD. More importantly, urbanization has different effects on the surface ozone for the PRD and the YRD, presumably due to their urbanization characteristics and geographical locations. Even though the PRD has a smaller increase in the surface temperature than the YRD, it has (a) weaker surface wind speed, (b) smaller increase in PBL heights, and (c) stronger convergence zones. The latter three factors outweighed the temperature increase and resulted in a larger ozone enhancement in the PRD than the YRD.  相似文献   

Relaxed Eddy Accumulation Simulations of Aerosol Number Fluxes and Potential Proxy Scalars   总被引：1，自引：1，他引：0  

Andreas Held  Edward Patton  Luciana Rizzo  Jim Smith  Andrew Turnipseed  Alex Guenther 《Boundary-Layer Meteorology》2008,129(3):451-468

Direct eddy-covariance measurements of aerosol number fluxes obtained during the 2007 CHATS field experiment in Dixon, California, USA are compared with relaxed eddy accumulation simulations using temperature and water vapour concentration as proxy scalars. After a brief discussion of the limited time response of the aerosol measurement, the applicability of temperature and water vapour concentration as proxy scalars for aerosol number concentration is investigated by evaluating scalar and spectral correlation coefficients as simple measures of scalar similarity. In addition, the proportionality factor b, which compensates for the use of a constant sampling flow in relaxed eddy accumulation, is derived from the time series of aerosol number, temperature and water vapour, and its variability is analyzed. The reduction of the b factor due to application of a deadband, i.e. the rejection of data when the vertical wind speed is close to zero, is evaluated for all three studied scalars, and compared with published functional relationships. In this study, using temperature or water vapour as proxy scalars for aerosol number shows no advantage over the use of a constant b factor. Thus, it is suggested to apply a deadband H _REA  = w′/σ _w  = 0.6 to 0.8 (where w′ is the vertical velocity fluctuation and σ _w is its standard deviation), to use a theoretical b factor based on a parameterization that includes a stability dependence, and to calculate the deadband effect according to a derived relation for aerosol relaxed eddy accumulation.  相似文献   

Relevance of ion-induced nucleation of sulfuric acid and water in the lower troposphere over the boreal forest at northern latitudes     

M. Boy  J. Kazil  E.R. Lovejoy  A. Guenther  M. Kulmala 《Atmospheric Research》2008,90(2-4):151-ICNAA07

The relevance of ion-induced nucleation of sulfuric acid and water (IINSW) in the troposphere over the boreal forest at northern latitudes is investigated by combining two existing and previously published models (MALTE — model to predict new aerosol formation in the lower troposphere; PARNUC — a parameterized steady-state model of neutral and ion-induced nucleation of sulfuric acid and water for atmospheric conditions). Simulations were performed for 4 days with observed new particle formation at ground level by using input data from the SMEAR II station in Hyytiälä, Finland. The selected days were chosen to cover a wide range of values of the parameters most relevant for IINSW. The results showed that ion-induced nucleation of sulfuric acid and water can contribute up to 15% to the total amount of newly formed particles in the size range of 3–10 nm inside the mixed layer at the Hyytiälä site. The importance of IINSW seemed to increase in the free troposphere above the boundary layer, however, lack of measurements in the vertical structure of the input parameters suggest that the model results are burdened with high uncertainties.  相似文献