排序方式： 共有17条查询结果，搜索用时 62 毫秒
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Yukimasa Ishida Tsutomu Hariu Junichi Yamashiro Skip McKinnell Takeshi Matsuda Hiromasa Kaneko 《Progress in Oceanography》2001,49(1-4)
Archeological evidence of Pacific salmon in Hokkaido is reviewed and compared with results from western North America. Salmon remains have been found at 24 sites in Hokkaido from the Early Jomon Period to the Ainu Period (6000–100 years ago). Fish remains at three archeological sites in the Kushiro River basin indicated that Pacific salmon (Oncorhynchus spp.) were distributed and utilized from 6000 years ago. The present Kushiro Wetland was formerly covered with seawater and called the Paleo Kushiro Bay 5000–6000 years ago. Based on the molluscan fossil fauna, seawater temperature at Paleo Kushiro Bay was about 5°C warmer than at present. Warmer conditions for salmon in Kushiro 5000–6000 years ago corresponded with the poor conditions for salmon in the Columbia River basin 6000–7000 years ago. If the future global warming is similar to the conditions that prevailed 5000–6000 years ago, the southern limit of salmon distribution will shift northwards and the salmon production will decrease. However, they will not disappear from either Hokkaido or southwestern North America. 相似文献
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Recent events concerning Atlantic salmon escapees in the Pacific 总被引：1，自引：0，他引：1
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John Bosco Habarulema Lee-Anne McKinnell Ben D.L. Opperman 《Journal of Atmospheric and Solar》2010,72(5-6):509-520
This paper presents the results from a study designed to investigate the ability of a newly developed neural network (NN) based model to follow total electron content (TEC) dynamics over the Southern African region. The investigation is carried out by comparing results from the NN model with actual TEC data derived from Global Positioning System (GPS) observations and TEC values predicted by the International Reference Ionosphere (IRI-2007) model during magnetic storm periods over Southern Africa. The magnetic storm conditions chosen for the study presented in this paper occurred during the periods 16–21 April 2002, 1–6 October 2002, and 28 October–01 November 2003. A total of six South African GPS stations were used for the validation of the two models during these periods. A statistical analysis of the comparison between the actual TEC behaviour and that predicted by the two models is shown. In addition, ionosonde measurements from the South African Louisvale (28.5°S, 21.2°E) station, located close to one of the validation GPS stations used, are also considered during the Halloween storm period of 28–31 October 2003. The generalisation of TEC behaviour by the NN model is demonstrated by producing predicted TEC maps during magnetic storm periods over South Africa. Presented results demonstrate the ability of NNs in predicting TEC variability over South Africa during magnetically disturbed conditions, and highlight areas for improvement. 相似文献
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The international reference ionosphere today and in the future 总被引：5，自引：0，他引：5
Dieter Bilitza Lee-Anne McKinnell Bodo Reinisch Tim Fuller-Rowell 《Journal of Geodesy》2011,85(12):909-920
The international reference ionosphere (IRI) is the internationally recognized and recommended standard for the specification
of plasma parameters in Earth’s ionosphere. It describes monthly averages of electron density, electron temperature, ion temperature,
ion composition, and several additional parameters in the altitude range from 60 to 1,500 km. A joint working group of the
Committee on Space Research (COSPAR) and the International Union of Radio Science (URSI) is in charge of developing and improving
the IRI model. As requested by COSPAR and URSI, IRI is an empirical model being based on most of the available and reliable
data sources for the ionospheric plasma. The paper describes the latest version of the model and reviews efforts towards future
improvements, including the development of new global models for the F2 peak density and height, and a new approach to describe
the electron density in the topside and plasmasphere. Our emphasis will be on the electron density because it is the IRI parameter
most relevant to geodetic techniques and studies. Annual IRI meetings are the main venue for the discussion of IRI activities,
future improvements, and additions to the model. A new special IRI task force activity is focusing on the development of a
real-time IRI (RT-IRI) by combining data assimilation techniques with the IRI model. A first RT-IRI task force meeting was
held in 2009 in Colorado Springs. We will review the outcome of this meeting and the plans for the future. The IRI homepage
is at . 相似文献
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David A. KRING Dolores H. HILL James D. GLEASON Daniel T. BRITT Guy J. CONSOLMAGNO Mike FARMER Skip WILSON Robert HAAG 《Meteoritics & planetary science》1999,34(4):663-669
Abstract— A shower of meteorite fragments fell at ～0730 h local time on 1998 June 13 near the town of Portales, New Mexico. Thus far, 51 pieces of the Portales Valley (H6) meteorite have been recovered. This meteorite has an unusually large number of metallic veins. Some of these veins are also unusually thick, having widths on the order of centimeters. These wide veins have fine Widmanstätten structure, which is the first time it has been seen in an ordinary chondrite. This structure indicates the metallic veins and the host chondrite cooled slowly. These veins appear to have been produced by shock-metamorphic processes, which we infer produced a >20 km diameter impact crater on an H-chondrite planetesimal. 相似文献
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The monthly means of the ionospheric F2 peak parameters (foF2 and hmF2) over three stations in South Africa (Grahamstown, 33.3°S, 26.5°E, Madimbo, 22.4°S, 26.5°E, and Louisvale, 28.5°S, 21.2°E) were analyzed and compared with IRI-2001, using CCIR (Comité Consultatif International des Radio communications) and URSI (Union Radio-Scientifique Internationale coefficients) options. The analysis covers a few selected quiet and disturbed days during various seasons represented by the months of January, April, July and October 2003. IRI-2001 generally overestimates hmF2 for both quiet and disturbed days and it overestimates and underestimates foF2 at different times for all the stations. In general, foF2 is predicted more accurately by IRI-2001 than hmF2, and on average, the CCIR option performed better than the URSI option when predicting both foF2 and hmF2.In general, the model generates good results, although some improvements are still necessary to be implemented in order to obtain better predictions. There are no significant differences in the model predictions of hmF2 and foF2 for quiet and disturbed days. 相似文献
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Chigomezyo M. Ngwira Lee-Anne McKinnell Pierre J. Cilliers 《Journal of Atmospheric and Solar》2010,72(9-10):718-725
Radio wave scintillation due to the presence of ionospheric irregularities can cause fading and phase variation of L-band navigation signals such as those used by the Global Positioning System (GPS). The high-latitude regions experience increased scintillation events under geomagnetically disturbed conditions, particularly during solar maximum. This paper presents phase scintillation measurements observed at the South African Antarctic polar research station during solar minimum conditions. In addition, a multi-instrument approach is shown in which the scintillation events are associated with auroral electron precipitation. Furthermore, it is shown that external energy injection into the ionosphere is an important factor in the development of irregularities producing scintillation. 相似文献