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11.
A universal formula for the estimation of equilibrium scour depth around a single cylindrical pile under the action of steady currents, tidal and short waves is presented. 相似文献
12.
Particle detection by condensation particle counters (CPCs) is ultimately limited by the onset of homogeneous nucleation. At vapour supersaturations around the homogeneous nucleation limit the diameter of critical clusters is typically about 2 nm. It is widely assumed that only particles larger than critical clusters can be activated by vapour condensation and the general detection limit of CPCs is therefore currently accepted to be around 2 nm particle diameter. Using an expansion type CPC with n-propanol as working fluid we investigated the transition from heterogeneous to homogeneous nucleation, clearly showing that particles are activated much before the onset of homogeneous nucleation, even at particle diameters as small as 1.4 nm. For particle diameters below 2 nm we have usually found condensation particle counting to be influenced by the simultaneous presence of ions as generated in a bipolar diffusion charger. In this paper we illustrate how the presence of ions influences particle number concentration measurement and how ions can be removed in order to obtain accurate seed particle number concentrations for particle diameters down to 1 nm. 相似文献
13.
Summary The effect of clouds on longwave radiation budget at the top and base of the atmosphere is studied by using the HIRS2/MSU-retrieved temperature and humidity fields, and cloud fields and the International Satellite Cloud Climatology Project-produced fields. Detailed studies are carried out at four selected sites: one at Equatorial Eastern Pacific (ITCZ) area, one at Libyan Desert (Libya), one at Ottawa, Montreal (Ottawa), and one at central Europe (Europe). The monthly mean differences in outgoing longwave radiation (OLR) (the ISCCP-based OLR minus the HIRS2-based OLR), ranging from –2.8 Wm–2 at ITCZ to –15.4 Wm–2 at Ottawa, are less than the monthly mean differences in surface downward flux, ranging from –2.7 Wm–2 at Libya to 40.6 Wm–2 at the ITCZ. The large differences in surface downward flux are mainly due to large differences in cloud amount and moisture in the low levels of the atmosphere.Monthly mean OLR and surface downward flux can be derived either (1) from instantaneous temperature, humidity, and cloud fields over a month period or (2) from monthly mean temperature, humidity, and cloud fields. The monthly mean OLR and surface downward flux derived from the first approach is compared with the second. The differences in OLR are small, ranging from –0.05 Wm–2 to 6.2 Wm–2, and the differences in surface downward flux is also small, ranging from 0.4 Wm–2 to 6.4 Wm–2.List of Acronyms AVHRR
Advanced Very High Resolution radiometer
- ERB
Earth Radiation Budget
- ERBE
Earth Radiation Budget Experiment
- FGGE
First Global GARP Experiment
- GARP
Global Atmospheric Research Program
- GCM
General Circulation Model
- GISS
Goddard Institute for Space Studies
- GLA
Goddard Laboratory for Atmospheres
- GMS
Geostationary Meteorological Satellite
- GOES
Geostationary Operational Environmental Satellite
- HIRS2
High Resolution Infrared Radiation Sounder/2
- ISCCP
International Satellite Cloud Climatology Project
- IR
Infrared
- MSU
Microwave Sounding Unit
- NFOV
Narrow Field of View
- NOAA
National Oceanic and Atmospheric Administration
- NESDIS
National Environmental Satellite Data Information Service
- TOVS
TIROS Operational Vertical Sounder
With 4 Figures 相似文献
14.
Eugenio E. Veloso Daniele Tardani Daniel Elizalde Benigno E. Godoy Pablo A. Sánchez-Alfaro Felipe Aron 《International Geology Review》2020,62(10):1294-1318
ABSTRACT Geothermal exploration in the Central Andean Volcanic Zone (CAVZ) focuses on heat capacities of known geothermal systems, yet the role of faults, veins, fractures and folds on the evolution and migration of fluids is far from complete. Here, we present a compilation of He and Sr isotope data and newly generated structural maps to examine if particular tectonic configurations are associated with fluids migrating from different crustal levels. Accordingly, we defined three tectono-geothermal environments (T1–T3) depicting specific structural arrangements and spatial relation with geothermal and volcanic manifestations. T1 is dominated by left-lateral strike-slip NW-striking faults, and geothermal and volcanic manifestations occur along the traces of these structures. T2 is dominated by N-striking thrust faults and parallel fault-propagated folds, cut and displaced by NW-striking faults. Here, geothermal manifestations occur at fault intersections and at fold hinges. T3 is defined by left-lateral/normal NW-striking faults, with geothermal and volcanic manifestations lying along fault traces. Each tectono-geothermal environment yields distinctive isotope ratios and geothermal reservoir temperatures. T1 shows high helium and low strontium ratios, and temperatures between 220° and 310°C. T3 shows low helium and high strontium ratios and temperatures between 260° and 320°C. T2 isotope ratios fall between T1 and T3, with lowest (130°-250°C) reservoir temperatures. We argue that these particular isotope signatures are due to a structural control on reservoir location and orientation. The orientation of the fracture mesh genetically associated with each tectono-geothermal environment is a first-order control on the migration pathway of fluids. Our model shows that T1 allows fluxing of deeper fluids, T2 promotes storage and favors longer residence times and T3 enhances subvertical fluid migration. Results here help to explain the evolution of geothermal systems in a wider context, including fault systems and Sr and He isotope variations, thus providing a framework for geothermal exploration in the CAVZ. 相似文献
15.
Radiocarbon dating of well-preserved, in-place vegetation exposed by the retreating Quelccaya Ice Cap of southeastern Peru constrains the last time the ice cap's extent was smaller than at present. Seventeen plant samples from two sites along the central western margin collectively date to 4700 and 5100 cal yr BP and strongly indicate that current ice cap retreat is unprecedented over the past ∼ 5 millennia. Seventeen vegetation samples interbedded in a nearby clastic sedimentary sequence suggest ice-free conditions at this site from ∼ 5200 to at least ∼ 7000 cal yr BP, and place minimum constraint on early- to mid-Holocene ice cap extent. 相似文献
16.
Jacob D. Hosen George H. Allen Giuseppe Amatulli Sara Breitmeyer Matthew J. Cohen Byron C. Crump YueHan Lu Jérôme P. Payet Brett A. Poulin Aron Stubbins Byungman Yoon Peter A. Raymond 《水文研究》2021,35(5):e14124
Most terrestrial allochthonous organic matter enters river networks through headwater streams during high flow events. In headwaters, allochthonous inputs are substantial and variable, but become less important in streams and rivers with larger watersheds. As allochthonous dissolved organic matter (DOM) moves downstream, the proportion of less aromatic organic matter with autochthonous characteristics increases. How environmental factors converge to control this transformation of DOM at a continental scale is less certain. We hypothesized that the amount of time water has spent travelling through surface waters of inland systems (streams, rivers, lakes, and reservoirs) is correlated to DOM composition. To test this hypothesis, we used established river network scaling relationships to predict relative river network flow-weighted travel time (FWTT) of water for 60 stream and river sites across the contiguous United States (3090 discrete samples over 10 water years). We estimated lentic contribution to travel times with upstream in-network lake and reservoir volume. DOM composition was quantified using ultraviolet and visible absorption and fluorescence spectroscopy. A combination of FWTT and lake and reservoir volume was the best overall predictor of DOM composition among models that also incorporated discharge, specific discharge, watershed area, and upstream channel length. DOM spectral slope ratio (R2 = 0.77) and Freshness Index (R2 = 0.78) increased and specific ultraviolet absorbance at 254 nm (R2 = 0.68) and Humification Index (R2 = 0.44) decreased across sites as a function of FWTT and upstream lake volume. This indicates autochthonous-like DOM becomes continually more dominant in waters with greater FWTT. We assert that river FWTT can be used as a metric of the continuum of DOM composition from headwaters to rivers. The nature of the changes to DOM composition detected suggest this continuum is driven by a combination of photo-oxidation, biological processes, hydrologically varying terrestrial subsidies, and aged groundwater inputs. 相似文献
17.
18.
Robert Aron 《自然地理学》2013,34(6):553-558
Sound travels faster at higher temperatures and relative humidities. It can be heard at a greater distance with a temperature inversion or when the wind direction is toward the listener. Snow and water vapor absorb sound and thus decrease the intensity and distance over which sound can be heard. [Key words: atmospheric acoustics, temperature, relative humidity, temperature lapse rate, wind speed and direction, absorption, snow.] 相似文献
19.
The Federal Aviation Administration (FAA) is developing the wide-area augmentation system (WAAS) to supplement the Global
Positioning System (GPS) and serve as a single en-route navigation aid. The program traveled a rocky road so far. We compare
the original concept of WAAS with its current scaled down version, analyze the changed perspectives with respect to the utility
of GPS for air navigation and the concomitant role of WAAS, and explore the future of GPS/WAAS. ? 2000 John Wiley & Sons,
Inc. 相似文献
20.
Abdolali Ali van der Westhuysen Andre Ma Zaizhong Mehra Avichal Roland Aron Moghimi Saeed 《Ocean Dynamics》2021,71(2):217-235
Ocean Dynamics - Various uncertainties exist in a hindcast due to the inabilities of numerical models to resolve all the complicated atmosphere-sea interactions, and the lack of certain ground... 相似文献