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21.
Dr. D. P. Jorgensen T. Matejka J. D. DuGranrut 《Meteorology and Atmospheric Physics》1996,59(1-2):83-104
Summary Two techniques for deriving horizontal and vertical air motions using vertically scanning airborne Doppler radar data are presented and discussed. These techniques make use of the scanning ability of the NOAA P-3 tail-mounted radar antenna to view a region of space from at least two vantage points during a straight-line flight track. The scanning methodology is termed the Fore/Aft Scanning Technique or FAST because the antenna is alternately scanning forward and then aft of the flight track. The major advantages of FAST over flying two quasi-orthogonal flight tracks with the antenna scanning normal to the flight track are that the data are collected in roughly half the time and the aircraft does not have to execute a right-angle turn. However, accuracy of the resulting wind field is compromised slightly because the beam intersection angle is reduced from 90° to about 50°. The reduction of area covered because of large drift angles is also discussed.A three-dimensional wind field can be constructed using the dual-Doppler equations from FAST data using the two radial velocity estimates and vertical integration of the continuity equation with a boundary condition of no vertical motion at cloud top and the Earth's surface. To keep errors in the calculated winds acceptably small, the elevation angles are typically restricted to ±45° from the horizontal to minimize contamination of the horizontal wind by terminal fallspeeds.A different, and perhaps more believable vertical velocity, can be derived using a second technique that utilizes two (or more) airborne Doppler radar equipped aircraft each using FAST to observe the echo-top vertical velocity at common point (e.g., two aircraft flying parallel flight, paths, or by using an L-shaped flight track with a single aircraft). This technique results in 4 (or more) radial velocity estimates at each point (hence is called the quad-Doppler technique). Horizontal winds can be derived using either an overdetermined three-equation solution or an overdetermined dual-Doppler solution, whichever is more accurate. For the calculation of vertical velocity a new approach is proposed that utilizes the overdetermined triple-Doppler solution for vertical particle motion near cloud top, minus an estimate of terminal fallspeeds, as a top boundary condition for the downward vertical divergence integration to derive vertical air velocity elsewhere in the domain. In addition, this approach allows measurements at steep elevation angles allowing for more depth of coverage for a given range.To show the utility of the method, analyses of data collected using FAST are compared to conventional dual-Doppler-derived wind fields constructed from data collected simultaneously by S-band ground-based Doppler radars. An example of the quad-Doppler technique is also presented from the recently completed Tropical Oceans/Global Atmospheres Coupled Ocean/Atmosphere Response Experiment (TOGA/COARE). Comparisons of quad-Doppler vertical velocity are made with in-situ derived vertical air motions collected by the NASA DC-8 to judge the quality of the approach.With 9 Figures 相似文献
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Jorgensen H. Lipunov V. M. Panchenko I. E. Postnov K. A. Prokhorov M. E. 《Astrophysics and Space Science》1995,231(1-2):389-392
Assuming that gamma-ray bursts (GRB) originate from binary neutron star (NS) or black holes (BH) merging in distant galaxies, theoretical logN-logS distributions for gamma-ray bursts (GRB) are calculated using the compact binaries coalescence rates computed for model galaxies with different star formation histories. A flat cosmological model ( = 1) with different values of the cosmological constant is used. The calculated source evolution predicts a 5–10 times increase of the source statistics at count rates 3–10 times lower than the existing BATSE sensitivity limit. The most important parameter in fitting the 2nd BATSE catalogue is the initial redshift of star formation, which is found to bez
* = 2 — 5 depending on a poorly determined average spectral index of GRB. 相似文献
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Colin R. O'Farrell Arjun M. Heimsath Daniel E. Lawson Laura M. Jorgensen Edward B. Evenson Grahame Larson Jon Denner 《地球表面变化过程与地形》2009,34(15):2008-2022
Glacial erosion rates are estimated to be among the highest in the world. Few studies have attempted, however, to quantify the flux of sediment from the periglacial landscape to a glacier. Here, erosion rates from the nonglacial landscape above the Matanuska Glacier, Alaska are presented and compare with an 8‐yr record of proglacial suspended sediment yield. Non‐glacial lowering rates range from 1·8 ± 0·5 mm yr?1 to 8·5 ± 3·4 mm yr?1 from estimates of rock fall and debris‐flow fan volumes. An average erosion rate of 0·08 ± 0·04 mm yr?1 from eight convex‐up ridge crests was determined using in situ produced cosmogenic 10Be. Extrapolating these rates, based on landscape morphometry, to the Matanuska basin (58% ice‐cover), it was found that nonglacial processes account for an annual sediment flux of 2·3 ± 1·0 × 106 t. Suspended sediment data for 8 years and an assumed bedload to estimate the annual sediment yield at the Matanuska terminus to be 2·9 ± 1·0 × 106 t, corresponding to an erosion rate of 1·8 ± 0·6 mm yr?1: nonglacial sources therefore account for 80 ± 45% of the proglacial yield. A similar set of analyses were used for a small tributary sub‐basin (32% ice‐cover) to determine an erosion rate of 12·1 ± 6·9 mm yr?1, based on proglacial sediment yield, with the nonglacial sediment flux equal to 10 ± 7% of the proglacial yield. It is suggested that erosion rates by nonglacial processes are similar to inferred subglacial rates, such that the ice‐free regions of a glaciated landscape contribute significantly to the glacial sediment budget. The similar magnitude of nonglacial and glacial rates implies that partially glaciated landscapes will respond rapidly to changes in climate and base level through a rapid nonglacial response to glacially driven incision. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
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Rasmus Heltberg Paul Bennett Siegel Steen Lau Jorgensen 《Global Environmental Change》2009,19(1):89-99
This paper presents and applies a conceptual framework to address human vulnerability to climate change. Drawing upon social risk management and asset-based approaches, the conceptual framework provides a unifying lens to examine links between risks, adaptation, and vulnerability. The result is an integrated approach to increase the capacity of society to manage climate risks with a view to reduce the vulnerability of households and maintain or increase the opportunities for sustainable development. We identify ‘no-regrets’ adaptation interventions, meaning actions that generate net social benefits under all future scenarios of climate change and impacts. We also make the case for greater support for community-based adaptation and social protection and propose a research agenda. 相似文献
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J.F. Gransden J.G. Jorgensen N. Manery J.T. Price N.J. Ramey 《International Journal of Coal Geology》1991,19(1-4)
A Canadian perspective of the petrographic, thermal rheological and grade of metallurgical coals required to make coke with high strength and strength after reaction (CSR) properties is presented. The development of automated microscopic techniques to obtain reproducible and reliable petrographic data to predict coke quality is discussed. The amount of “altered vitrinite” in the microscopic coke textures has been used as a reference to quantifiy in situ coal oxidation. Relationships between coke microscopy, coal petrography and thermal rheological data show that FSI can be used to estimate the amount of oxidized vitrinite plus petrographic inert contents of coal. Plastic temperature ranges determined from microscopic examination of the coal/coke transformations for Appalachian and Canadian coals show that standard thermal rheological tests underestimate the plastic range for high inertinite coals. 相似文献
27.
Optical properties of benthic photosynthetic communities: fiber-optic studies of cyanobacterial mats
A fiber-optic microphobe was used to analyze the spectral light gradients in benthic cyanobacterial mats with 50-micrometer depth resolution and 10-nm spectral resolution. Microcoleus chthononplastes mats were collected from hypersaline, coastal ponds at Guerrero Negro, Baja California. Gradients of spectral radiance, L, were measured at different angles through the mats and the spherically integrated scalar irradiance, Eo, was calculated. Maximal spectral light attenuation was found at the absorption peaks for the dominant photosynthetic pigments: chlorophyll a at 430 and 670 nm, carotenoids at 450-500 nm, phycocyanin at 620 nm, and bacteriochlorophyll a at 800-900 nm. Scattered light had a marked spectral effect on the scalar irradiance which near the mat surface reached up to 190% of the incident irradiance. The spherically integrated irradiance thus differed strongly from the incident irradiance both in total intensity and in spectral composition. These basic optical properties are important for the understanding of photosynthesis and light harvesting in benthic and epiphytic communities. 相似文献
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Rachel Winterton Andrew Butt Bradley Jorgensen John Martin 《The Australian geographer》2019,50(1):111-128
Within the policy and academic literature, the impact of rural retirement migration (RRM) on community sustainability has been questioned. This qualitative study investigated the perceived impact of retirement migration on rural social sustainability from a local government perspective. Focus groups were conducted with local government senior managers and community services staff (n = 39) across six rural local government areas in one Australian state. Data were analysed against the three components of rural social sustainability (equity, community and rurality) proposed by Jones and Tonts [1995. “Rural Restructuring and Social Sustainability: Some Reflections on the Western Australian Wheatbelt.” Australian Geographer 26: 133–140]. While RRM is perceived to benefit rural community capacity to facilitate or maintain equity, community and rurality, it also presents challenges for local government. Participants suggested that capacity to facilitate equity, community and rurality in contexts of RRM was impacted by uncertainty around future impacts of RRM on population ageing, increasing advocacy and expectations of older in-migrants, and the impact of RRM on rural heterogeneity. These issues required local governments to think critically about how to accommodate and manage the needs and expectations of older in-migrants, while mediating potential impacts associated with RRM. 相似文献
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Deep-ocean predation by a high Arctic cetacean 总被引：2，自引：0，他引：2
Laidre K.L.; Heide-Jorgensen M.P.; Jorgensen O.A.; Treble M.A. 《ICES Journal of Marine Science》2004,61(3):430-440