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W. K. Hocking 《Annales Geophysicae》1997,15(9):1111-1122
Radars have been used successfully for many years to measure atmospheric motions over a wide range of altitudes, from ground level up to heights of several hundred kilometres into the ionosphere. In this paper we particularly wish to concentrate on the accuracy of these measurements for winds in the middle atmosphere (i.e. 10–100–km altitude). We begin by briefly reviewing the literature relating to comparisons between radar methods and other techniques. We demonstrate where the radar data are most and least reliable and then, in parallel with a discussion about the basic principles of the method, discuss why these different regimes have the different accuracies and precisions they do. This discussion is used to highlight the strengths and weaknesses of radar methods. Issues like radar volume, aspect sensitivity, gravity wave effects and scatterer intermittency in producing wind biases, and the degree by which the intermittent generation of scatterers at quasi-random points in space could skew the radar measurements, are all considered. We also investigate the possibility that MF radar techniques can be contaminated by E-region scatter to heights as low as 92–95–km altitude (i.e. up to 8–10 km below the ionospheric peak echo). Within all these comments, however, we also recognize that radar methods still represent powerful techniques which have an important future at all levels of the atmosphere. 相似文献
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W. K. Hocking 《Earth, Moon, and Planets》2004,95(1-4):671-679
At altitudes above 93 km in the atmosphere, magnetic and electric fields can affect the modes and rates of non-turbulent diffusion
of ionized meteor trails. Anisotropic diffusion is expected. Most theories of anisotropic diffusion, and indeed most experimental
studies, have concentrated on the effects of the magnetic field in producing this anisotropy, and different rates of expansion
are expected in directions parallel to and perpendicular to the magnetic field lines. In this study, we use interferometric
meteor radars to investigate the dependence of the ambipolar diffusion coefficient on viewing direction relative to the magnetic
field, and show that the dependence is at best weak when daily averages are used. We then demonstrate that the reason for
this effect is that the positions of maximum and minimum diffusion rates varies as a function of time of day, and that daily
averaging masks the anisotropy. One possibility to account for the observations is that this strong diurnal variation is a
consequence of the electric fields in the upper atmosphere, which are often tidally driven. An alternative possibility is
a diurnal cycle in mean meteor entrance speeds. We lean towards the first hypothesis, but both possibilities are discussed.
We demonstrate our results with data from several sites, but particularly using the Clovar radar near London, Ontario, Canada. 相似文献
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Koushik N. Kumar K. Kishore Ramkumar Geetha Subrahmanyam K. V. Kishore Kumar G. Hocking W. K. He Maosheng Latteck Ralph 《Climate Dynamics》2020,54(9):4059-4074
Climate Dynamics - In the present communication, characteristics of mean winds and planetary waves in the mesosphere lower thermosphere (MLT) region during sudden stratospheric warming (SSW) events... 相似文献
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P. W. Haines R. M. Hocking K. Grey M. K. Stevens 《Australian Journal of Earth Sciences》2013,60(3):397-406
The stratigraphy in Vines 1, a 2017.5 m-deep cored stratigraphic hole drilled by the Geological Survey of Western Australia in 2001 near the Western Australian – South Australian border, has been reinterpreted with implications for the Neoproterozoic to Cambrian geological history of the Officer Basin. A previous interpretation considered the intersected succession as a conformable stratigraphic package, the Vines Formation. An assemblage of palynomorphs, found throughout the hole and previously used to infer an age of no older than earliest Cambrian, is now thought to consist of contaminants. An older assemblage, which is considered to be reworked and inherited from underlying rocks, provides a new maximum age constraint of mid-Neoproterozoic. Based on sedimentological interpretations and comparisons with other drillholes in the western Officer Basin, and the succession in the eastern Officer Basin, the Vines 1 succession is reinterpreted as four discrete sedimentary packages, the Pirrilyungka (new name), Wahlgu, Lungkarta and Vines (redefined) Formations, in ascending order. The Pirrilyungka and Wahlgu Formations include glacigenic sediments and may correlate with similar glacial successions in Supersequences 2 and 3 (mid to late Cryogenian) of the Centralian Superbasin, and the Sturt Tillite and Elatina Formation and their equivalents in the Adelaide Rift Complex of South Australia, respectively. The eolian Lungkarta Formation and fluvial Vines Formation are considered, on regional evidence, to be most likely of Ediacaran to earliest Cambrian age. 相似文献
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Analysis of State and Provincial Atlas Reviews* 总被引：1，自引：0，他引：1
Ninety-eight reviews of state and provincial atlases are examined in order to address several questions. Reviews are subjected to content analysis to identify the judgement criteria that experts use in evaluating a provincial or state atlas, and the aspects of each criterion that reviewers praise or condemn. An attempt is made to search for expert consensus and to identify a provincial or state atlas review recipe. The research reported here is part of a larger study undertaken to assist those in the process of planning a new provincial or state atlas initiative. This paper also assists individuals who are searching for rules and guidelines when undertaking an atlas review. 相似文献
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Latitudinal and longitudinal variability of mesospheric winds and temperatures during stratospheric warming events 总被引：1，自引：0，他引：1
P. Hoffmann W. Singer D. Keuer W.K. Hocking M. Kunze Y. Murayama 《Journal of Atmospheric and Solar》2007,69(17-18):2355
Continuous MF and meteor radar observations allow detailed studies of winds in the mesosphere and lower thermosphere (MLT) as well as temperatures around the mesopause. This height region is characterized by a strong variability in winter due to enhanced planetary wave activity and related stratospheric warming events, which are distinct coupling processes between lower, middle and upper atmosphere. Here the variability of mesospheric winds and temperatures is discussed in relation with major and minor stratospheric warmings as observed during winter 2005/06 in comparison with results during winter 1998/99.Our studies are based on MF radar wind measurements at Andenes (69°N, 16°E), Poker Flat (65°N, 147°W) and Juliusruh (55°N, 13°E) as well as on meteor radar observations of winds and temperatures at Resolute Bay (75°N, 95°W), Andenes (69°N, 16°E) and Kühlungsborn (54°N, 12°E). Additionally, energy dissipation rates have been estimated from spectral width measurements using a 3 MHz Doppler radar near Andenes. Particular attention is directed to the changes of winds, turbulence and the gravity wave activity in the mesosphere in relation to the planetary wave activity in the stratosphere.Observations indicate an enhancement of planetary wave 1 activity in the mesosphere at high latitudes during major stratospheric warmings. Daily mean temperatures derived from meteor decay times indicate that strong warming events are connected with a cooling of the 90 km region by about 10–20 K. The onset of these cooling processes and the reversals of the mesospheric circulation to easterly winds occur some days before the changes of the zonal circulation in the stratosphere start indicating a downward propagation of the circulation disturbances from the MLT region to the stratosphere and troposphere during the stratospheric warming events. The short-term reversal of the mesospheric winds is followed by a period of strong westerly winds connected with enhanced turbulence rates and an increase of gravity wave activity in the altitude range 70–85 km. 相似文献
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Thomas Monecke Sven Petersen Mark D. Hannington Marco Anzidei Alessandra Esposito Guido Giordano Dieter Garbe-Sch?nberg Nico Augustin Bernd Melchert Mike Hocking 《Bulletin of Volcanology》2012,74(9):1937-1944
Explosions of hot water, steam, and gas are common periodic events of subaerial geothermal systems. These highly destructive events may cause loss of life and substantial damage to infrastructure, especially in densely populated areas and where geothermal systems are actively exploited for energy. We report on the occurrence of a large number of explosion craters associated with the offshore venting of gas and thermal waters at the volcanic island of Panarea, Italy, demonstrating that violent explosions similar to those observed on land also are common in the shallow submarine environment. With diameters ranging from 5 to over 100?m, the observed circular seafloor depressions record a history of major gas explosions caused by frequent perturbation of the submarine geothermal system over the past 10,000?years. Estimates of the total gas flux indicate that the Panarea geothermal system released over 70?Mt of CO2 over this period of time, suggesting that CO2 venting at submerged arc volcanoes contributes significantly to the global atmospheric budget of this greenhouse gas. The findings at Panarea highlight that shallow submarine gas explosions represent a previously unrecognized volcanic hazard around populated volcanic islands that needs to be taken into account in the development of risk management strategies. 相似文献
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R. Arlt J. Rendtel P. Brown V. Velkov W. K. Hocking J. Jones 《Monthly notices of the Royal Astronomical Society》1999,308(3):887-896
The June Boötid meteor shower (sometimes referred to as the Draconids) surprised a number of regular and casual observers by an outburst with maximum zenithal hourly rates (ZHRs) near 100 on 1998 June 27 after a quiescent period of several decades. A total of 1217 June Boötid meteors were recorded during regular visual meteor observations throughout this outburst. An average population index of r =2.2±0.10 was derived from 1054 shower magnitude estimates. The broad activity profile with ZHR>40 lasting more than 12 h and the large spread of apparent radiants in 1998 resemble the 1916 and 1927 outbursts. The peak time is found to be at about λ ⊙ =95°.7 (2000.0); peak ZHRs are of the order of 200, whereas reliable averages reach only 81±7. The period of high ZHRs covered by a single observer implies a full width at half-maximum of 3–4 h. The resulting maximum flux of particles causing meteors brighter than +6.5 mag is between 0.04 and 0.06 km−2 h−1 . The average radiant from photographic, radar and visual records is α =224°.12, δ =+47°.77. The observed activity outbursts in 1916, 1927 and 1998 are not related to the orbital period or the perihelion passages of the parent comet 7P/Pons–Winnecke. These are probably a consequence of the effects of the 2:1 resonance with Jupiter. 相似文献