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1.
Douglas O. ReVelle Elizabeth A. Sukara Wayne N. Edwards Peter G. Brown 《Earth, Moon, and Planets》2008,102(1-4):337-344
We have recently digitized and partially reanalyzed the historic bolide infrasonic database. These 10 events were originally
detected by the U.S. Air Force Technical Applications Center (AFTAC) from ∼1960 to 1974. In this paper we present the first
preliminary reanalysis results for two of the 10 bolide events, namely the Revelstoke bolide of 3/31/1965 as well as the Prince
Edward Islands (P.E.I). S. African bolide of 8/03/1963, which were among the largest bolides detected during this time period.
These bolides have been investigated initially since they are most likely to have had a significant effect on the computed
global influx rate of ReVelle (Global Infrasonic Monitoring of Large Bolides, pp 483–490, 2001) as indicated in Brown et al. (Nature, 420:314–316, 2002). We are in the process of recomputing all relevant infrasonic propagation quantities such as plane wave back azimuth, signal
velocities, power spectra, spectrograms, as well as energy estimates using multiple techniques. In a future paper we will
present a complete digital reanalysis of the AFTAC bolide infrasonic data and its final resulting global bolide influx implications. 相似文献
2.
Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):345-356
We have developed a new approach to modeling the acoustic-gravity wave (AGW) radiation from bolide sources. This first effort
involves entry modeling of bolide sources that have available satellite data through procedures developed in ReVelle (Earth
Moon Planets 95, 441–476, 2004a; in: A. Milani, G. Valsecchi, D. Vokrouhlicky (eds) NEO Fireball Diversity: Energetics-based Entry Modeling and Analysis Techniques, Near-earth Objects: Our Celestial Neighbors
(IAU S236), 2007b). Results from the entry modeling are directly coupled to AGW production through line source blast wave theory for the initial
wave amplitude and period at (at 10 blast wave radii and perpendicular to the trajectory). The second effort involves the prediction of the formation
and or dominance of the propagation of the atmospheric Lamb, edge-wave composite mode in a viscous fluid (Pierce, J. Acoust.
Soc. Amer. 35, 1798–1807, 1963) as a function of the source energy, horizontal range and source altitude using the Lamb wave frequency that was deduced
directly during the entry modeling and that is used as a surrogate for the source energy. We have also determined that Lamb
wave production by bolides at close range decreases dramatically as either the source energy decreases or the source altitude
increases. Finally using procedures in Gill (Atmospheric-Ocean Dynamics, 1982) and in Tolstoy (Wave Propagation, 1973), we have analyzed two simple dispersion relationships and have calculated the expected dispersion for the Lamb edge-wave
mode and for the excited, propagating internal acoustic waves. Finally, we have used the above formalism to fully evaluate
these techniques for four large bolides, namely: the Tunguska bolide of June 30, 1908; the Revelstoke bolide of March 31,
1965; the Crete bolide of June 6, 2002 and the Antarctic bolide of September 3, 2004. Due to page limitations, we will only
present results in detail for the Revelstoke bolide. 相似文献
3.
D.O. ReVelle 《Journal of Atmospheric and Solar》2010,72(2-3):241-261
We have incorporated horizontal winds into ray-mode theory including the full spectrum of acoustic–gravity waves for a perfectly stratified, range-independent, steady-state model atmosphere for frequencies from 10?4 to ～10 Hz. This approach has also been applied to a specific atmospheric propagation problem that has long defied a solution, namely counter-wind propagation arrivals at a location ～300 km up-wind of the source. Our modified ray-mode theory predicts reliable up-wind solutions, but only if small-scale sound speed fluctuations were added to the mean seasonal sound speed profiles. Since full-waveguide theory and modified ray-mode mode theory incorporate diffraction and scattering propagation effects, we have performed additional analyses to determine the mechanism through which these fluctuations produce the up-wind signals. We have concluded that the dominant mechanism is through diffraction due to the presence of semi-permanent turbulence and internal gravity waves located near the stratopause. 相似文献
4.
Peter G. Brown Douglas O. ReVelle Edward Tagliaferri Alan R. Hildebrand 《Meteoritics & planetary science》2002,37(5):661-675
Abstract— We present instrumental observations of the Tagish Lake fireball and interpret the observed characteristics in the context of two different models of ablation. From these models we estimate the pre‐atmospheric mass of the Tagish Lake meteoroid to be ?56 tonnes and its porosity to be between 37 and 58%, with the lowest part of this range most probable. These models further suggest that some 1300 kg of gram‐sized or larger Tagish Lake material survived ablation to reach the Earth's surface, representing an ablation loss of 97% for the fireball. Satellite recordings of the Tagish Lake fireball indicate that 1.1 times 1012 J of optical energy were emitted by the fireball during the last 4 s of its flight. The fraction of the total kinetic energy converted to light in the satellite pass band is found to be 16%. Infrasonic observations of the airwave associated with the fireball establish a total energy for the event of 1.66 ± 0.70 kT TNT equivalent energy. The fraction of this total energy converted to acoustic signal energy is found to be between 0.10 and 0.23%. Examination of the seismic recordings of the airwave from Tagish Lake have established that the acoustic energy near the sub‐terminal point is converted to seismic body waves in the upper‐most portion of the Earth's crust. The acoustic energy to seismic energy coupling efficiency is found to be near 10?6 for the Tagish Lake fireball. The resulting energy estimate is near 1.7 kT, corresponding to a meteoroid 4 m in diameter. The seismic record indicates extensive, nearly continuous fragmentation of the body over the height intervals from 50 to 32 km. Seismic and infrasound energy estimates are in close agreement with the pre‐atmospheric mass of 56 tonnes established from the modeling. The observed flight characteristics of the Tagish Lake fireball indicate that the bulk compressive strength of the pre‐atmospheric Tagish Lake meteoroid was near 0.25 MPa, while the material compressive strength (most appropriate to the recovered meteorites) was closer to 0.7 MPa. These are much lower than values found for fireballs of ordinary chondritic composition. The behavior of the Tagish Lake fireball suggests that it represents the lowest end of the strength spectrum of carbonaceous chondrites or the high end of cometary meteoroids. The bulk density and porosity results for the Tagish Lake meteoroid suggest that the low bulk densities measured for some small primitive bodies in the solar system may reflect physical structure dominated by microporosity rather than macroporosity and rubble‐pile assemblages. 相似文献
5.
Stephen J. Arrowsmith Doug ReVelle Wayne Edwards Peter Brown 《Earth, Moon, and Planets》2008,102(1-4):357-363
We present the infrasonic observations of three large bolides that were observed at numerous International Monitoring System
(IMS) infrasound arrays on a global scale. First, a simple procedure for the global association of infrasound detections from
large infrasound events is outlined. Infrasound signals are associated with large events based on arrival time, backazimuth
and uniqueness at a given IMS array. Next, we apply the algorithm to three bolides and investigate some of the factors affecting
the detectability of infrasound from large events. Our findings suggest that site-noise effects significantly degrade the
capability of the IMS infrasound network, suggesting that more effort is required to reduce ambient site noise. These results
have implications for the use of infrasound measurements (in particular those from IMS stations) as a tool for evaluating
the global flux of near-Earth objects. 相似文献
6.
Wayne N. Edwards Peter G. Brown Robert J. Weryk Douglas O. ReVelle 《Earth, Moon, and Planets》2008,102(1-4):221-229
Recent observations using the newly installed Elginfield infrasound array in coordination with the Southern Ontario all-sky
meteor camera network and Canadian Meteor Orbit Radar (CMOR) has shown that the number of meteors producing infrasound at
the Earth’s surface is more frequent than previously thought. These data show the flux of meteoroids capable of producing
infrasound at the ground is at least 1/month and is limited to meteors with peak visual brightness above −2. Comparisons to
current meteor infrasound theory show excellent agreement with amplitude and period predictions for weakly non-linear shock
waves using a realistic vertically inhomogeneous atmosphere. Similar predictions show isothermal assumptions underestimate
the amplitude by orders of magnitude. 相似文献
7.
8.
SURAKSHA M PEDNEKAR S G PRABHU MATONDKAR HELGA DO R GOMES JOAQUIM I GOES SUSHMA PARAB VIJAYA KERKAR 《Journal of Earth System Science》2011,120(3):545-556
In May of 2007, a study was initiated by the National Institute of Oceanography (NIO), Goa, India, to investigate the influence
of monsoonal rainfall on hydrographic conditions in the Mandovi River of India. The study was undertaken at a location ∼2 km
upstream of the mouth of this estuary. During the premonsoon (PreM) in May, when circulation in the estuary was dominated
by tidal activity, phytoplankton communities in the high saline (35–37 psu) waters at the study site were largely made up
of the coastal neritic species Fragilaria oceanica, Ditylum brightwellii and Trichodesmium erythraeum. During the later part of the intermonsoon (InterM) phase, an abrupt decline in salinity led to a surge in phytoplankton
biomass (Chlorophyll a ∼14 mg m − 3), of a population that was dominated by Thalassiosira eccentricus. As the southwest monsoon (SWM) progressed and the estuary freshened salinity and Chlorophyll a (Chl a) concentrations decreased during the MoN, Skeletonema costatum established itself as the dominant form. Despite the low biomass (Chl a <2 mg m − 3), the phytoplankton community of the MoN was the most diverse of the entire study. During the postmonsoon (PostM), the increase
in salinity was marked by a surge in dinoflagellate populations comprising of Ceratium furca, Akashiwo sanguinea, and Pyrophacus horologium. 相似文献
9.
提出了多光谱图像像元特征矢量之间的极小互相关系数，极大互相关系数及互相关差值和相关密度的概念，在对模拟图像进行矢量相关分析及其对边缘提取的有效性分析基础上，提出对多光谱图像采取像元特征矢量相关分析并提取边缘信息的方法，对TM图像进行试验分析的结果说明了此方法的有效性。 相似文献
10.