The effect of rainfall on the wind in the surface layer     

D. R. Caldwell  W. P. Elliott 《Boundary-Layer Meteorology》1972,3(2):146-151

Raindrops falling into a wind-shear zone do not adjust their horizontal speeds immediately to the new wind. Thus, stresses develop which accelerate the air. The effect of raindrops falling into a layer with a logarithmic wind profile is investigated numerically. We find the adjustment of the wind to this situation to be quite small and only barely detectable, even in heavy rain conditions. The effect on the stress distribution is greater. Stress variations of 10–20 % and greater in the lowest 10 m are possible under certain conditions.  相似文献   

The long-term effects of crude oil on microbial processes in subarctic marine sediments     

Robert P. Griffiths  Bruce A. Caldwell  William A. Broich  Richard Y. Morita 《Estuarine, Coastal and Shelf Science》1982,15(2):183-198

Subarctic marine sediments were exposed to fresh and ‘weathered’ crude oil from Cook Inlet, Alaska. The crude oil was thoroughly mixed with the sediment at various concentrations and some of the oil-sediment mixtures were placed on top of unamended sediments. Both sediments with added oil and those overlain by oiled sediments were investigated. These sediments were placed either in trays or aquaria. The trays were incubated in situ near the site from which the sediments were originally collected. The aquaria were maintained at simulated in situ conditions by maintaining a continuous flow of fresh seawater through them. The sediments were exposed to crude oil for periods up to 1.5 years. Sediments exposed to 50‰ fresh crude oil showed significant decreases in nitrogen fixation and denitrification rates and redox potentials. Also observed were increases in CO₂ production rates and methane concentrations. These same changes were observed in sediments exposed to 1‰. When ‘weathered’ crude oil was added to the sediments, the same changes were observed except there was no reduction in nitrogen fixation activity. In most cases, the observed effects were less marked when the sediments were amended with ‘weathered’ crude oil than with the same concentration of fresh crude oil. Untreated sediments that were overlain with treated sediments showed the same changes as those sediments that were thoroughly mixed with crude oil. The presence of fresh crude oil at 50‰ essentially eliminated burrowing activity of the benthic infauna. Under these conditions, there was an accumulation of detritus particles on the oiled sediments that was not present in the untreated controls.  相似文献   

Use of magnetotelluric signals from 50 Hz power lines for resistivity mapping of geothermal fields in New Zealand     

Risk  Caldwell  & Bibby 《Geophysical Prospecting》1999,47(6):1091-1104

Electromagnetic (EM) fields radiated from the transmission lines of the New Zealand electricity grid have been digitally recorded at test sites near the Tokaanu geothermal field. Amplitudes and phases of the 50 Hz signals (and the odd harmonics up to 450 Hz) were determined using a software implementation of a phase-locked filter. These data were then analysed to determine the components of the magnetotelluric impedance tensor and the corresponding apparent resistivities and phases. At most sites, there was sufficient variation in the elliptical polarization of the EM fields to enable the impedance tensors to be determined in full. Sites where the EM data had been affected by near-source effects were identified by having large vertical magnetic field components and by being closer to a power line source than about 3–5 skin depths. With the test measurements, the north-eastern part of the Tokaanu geothermal field was successfully delineated giving low resistivities (< 5 Ωm) on the inside and higher resistivities on the outside, in agreement with the Schlumberger array DC apparent resistivities. The small size of the 50 Hz magnetotelluric equipment and its portable nature make this method of resistivity measurement suitable for reconnaissance resistivity mapping in places with difficult access.  相似文献   

Long-term waves on Cepheid pulsation period trends     

L. N. Berdnikov  V. V. Ignatova  John A. R. Caldwell  C. Koen 《New Astronomy》2000,4(8):587-639

The secular evolution of the pulsation period of δ Cephei, η Aquilae, and ζ Geminorum during a cumulative total of 577 years suggests wave-like departures about the smooth time trends.  相似文献   

Short‐term stream water temperature observations permit rapid assessment of potential climate change impacts          下载免费PDF全文

Peter Caldwell  Catalina Segura  Shelby Gull Laird  Ge Sun  Steven G. McNulty  Maria Sandercock  Johnny Boggs  James M. Vose 《水文研究》2015,29(9):2196-2211

Assessment of potential climate change impacts on stream water temperature (T_s) across large scales remains challenging for resource managers because energy exchange processes between the atmosphere and the stream environment are complex and uncertain, and few long‐term datasets are available to evaluate changes over time. In this study, we demonstrate how simple monthly linear regression models based on short‐term historical T_s observations and readily available interpolated air temperature (T_a) estimates can be used for rapid assessment of historical and future changes in T_s. Models were developed for 61 sites in the southeastern USA using ≥18 months of observations and were validated at sites with longer periods of record. The T_s models were then used to estimate temporal changes in T_s at each site using both historical estimates and future T_a projections. Results suggested that the linear regression models adequately explained the variability in T_s across sites, and the relationships between T_s and T_a remained consistent over 37 years. We estimated that most sites had increases in historical annual mean T_s between 1961 and 2010 (mean of +0.11 °C decade^?1). All 61 sites were projected to experience increases in T_s from 2011 to 2060 under the three climate projections evaluated (mean of +0.41 °C decade^?1). Several of the sites with the largest historical and future T_s changes were located in ecoregions home to temperature‐sensitive fish species. This methodology can be used by resource managers for rapid assessment of potential climate change impacts on stream water temperature. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

The Kepler Mission: Astrophysics and Eclipsing Binaries     

D. Koch  W. Borucki  G. Basri  T. Brown  D. Caldwell  J. Christensen-Dalsgaard  W. Cochran  E. Dunham  T. N. Gautier  J. Geary  R. Gilliland  J. Jenkins  Y. Kondo  D. Latham  J. Lissauer  D. Monet 《Astrophysics and Space Science》2006,304(1-4):391-395

The Kepler Mission is a photometric space mission that will continuously observe a single 100 square degree field of view (FOV) of the sky of more than 100,000 stars in the Cygnus-Lyra region for four or more years with a precision of 14 parts per million (ppm) for a 6.5 hour integration including shot noise for a twelfth magnitude star. The primary goal of the mission is to detect Earth-size planets in the habitable zone of solar-like stars. In the process, many eclipsing binaries (EB) will also be detected. Prior to launch, the stellar characteristics will have been determined for all the stars in the FOV with K<14.5. As part of the verification process, stars with transits (about 5%) will need to have follow-up radial velocity observations performed to determine the component masses and thereby separate grazing eclipses caused by stellar companions from transits caused by planets. The result will be a rich database on EBs. The community will have access to the archive for uses such as for EB modeling of the high-precision light curves. A guest observer program is also planned for objects not already on the target list.  相似文献   

The reliability of Cepheid reddenings based on BVI_C photometry     

C. David Laney  John A. R. Caldwell 《Monthly notices of the Royal Astronomical Society》2007,377(1):147-158

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The X-Ray Telescope (XRT) for the Hinode Mission     

L. Golub  E. DeLuca  G. Austin  J. Bookbinder  D. Caldwell  P. Cheimets  J. Cirtain  M. Cosmo  P. Reid  A. Sette  M. Weber  T. Sakao  R. Kano  K. Shibasaki  H. Hara  S. Tsuneta  K. Kumagai  T. Tamura  M. Shimojo  J. McCracken  J. Carpenter  H. Haight  R. Siler  E. Wright  J. Tucker  H. Rutledge  M. Barbera  G. Peres  S. Varisco 《Solar physics》2007,243(1):63-86

The X-ray Telescope (XRT) of the Hinode mission provides an unprecedented combination of spatial and temporal resolution in solar coronal studies. The high sensitivity and broad dynamic range of XRT, coupled with the spacecraft’s onboard memory capacity and the planned downlink capability will permit a broad range of coronal studies over an extended period of time, for targets ranging from quiet Sun to X-flares. This paper discusses in detail the design, calibration, and measured performance of the XRT instrument up to the focal plane. The CCD camera and data handling are discussed separately in a companion paper.  相似文献   

Further observations of 8-μm polar brightenings of Jupiter     

John Caldwell  Alan T. Tokunaga  Glenn S. Orton 《Icarus》1983,53(1):133-140

North to south scans of Jupiter at 7.8-μm wavelength in early 1981 confirm polar brightening events that correlate with LCM_III, such that a polar limb is bright when the corresponding magnetic pole is tilted eartward. The correlation with magnetic features of the planet suggests that the energy source for the brightenings is magnetospheric particles incident upon the polar regions of the atmosphere. The northern polar events are more prominent and more regular than the southern ones. The polar emission may be indirectly related to the ultraviolet absorber observed near the poles by Voyager 2.  相似文献   

The Jovian stratosphere in the ultraviolet     

Richard Wagener  John Caldwell  Tobias Owen  Therese Encrenaz  Michel Combes 《Icarus》1985,63(2):222-236

The center-of-disk reflectivity of Jupiter in the wavelength range from 1450 to 3150A?has been computed from 30 low-dispersion IUE spectra taken during solar maximum in 1978–1980. A vertically inhomogeneous radiative transfer program is used to compute model reflectivities of various stratospheric compositions for comparison. Ammonia and acetylene are well determined because they show narrow absorption bands in the ultraviolet. Above 1800A?, these two gases provide a good fit to the data, but not below. At shorter wavelengths the fit would be much improved by a small amount (5–15 ppb) of propadiene/allene (C₃H₄). Voyager IRIS spectra show that the IR bands of allene are not strong enough to be detected in such a small amount. Additional absorption around 1600A?can be reproduced best with the presence of cyclopropane (C₃H₆, <15ppb), although other absorbers (e.g., hydrocarbon molecules with more than three carbon atoms, oxygen- or nitrogen-containing molecules, or a high-attitude haze) could also explain the spectrum in this region. The data are too noisy to detect possible CO Cameron band absorption near 2000A?.  相似文献