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L.J. Lanzerotti T.J. Rosenberg A. Wolfe C.G. Maclennan 《Planetary and Space Science》1985,33(3):253-262
Hydromagnetic wave and modulated particle precipitation data are reported from conjugate areas near the particledrift shell L ～ 4. A modulation of electrons precipitating from the magnetosphere is observed in the conjugate regions when the accompanying hydromagnetic wave period is ~ 90 s and the wave polarization is linear. When the wave period changes abruptly to ~ 30 s and the polarizations at the observing stations are no longer linear, the modulation of the precipitating electrons is no longer observed. The change in hydromagnetic wave characteristics does not appear to be related to interplanetary plasma and magnetic field conditions. Rather, it is proposed to arise from a change in the wave generation mechanism from an internal magnetospheric source near the inner edge of the plasmapause (lower frequency) to an externally driven source outside the magnetosphere (higher frequency). This observation of a change in the wave characteristics (frequency and polarization) associated with modulated electron precipitation appears to be related to two previous examples wherein modulated electron precipitation was reported to be closely associated with the existence of a wave resonance region near the observing site. 相似文献
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Maclennan David N.; Fernandes Paul G.; Dalen John 《ICES Journal of Marine Science》2002,59(2):365-369
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Lanzerotti L.J. Medford L.V. Maclennan C.G. Kraus J.S. Kappenman J. Radasky W. 《Solar physics》2001,204(1-2):351-359
The large solar activity in mid-July 2000 produced a severe geomagnetic storm at Earth during the last half of 15 July universal
time. The enhancements and changes in the ionosphere electrical current systems caused large geopotentials to be induced over
oceanic distances. Across the northern Atlantic, from New Jersey to near the French coast, a geopotential as large as 0.05 V km−1 (a peak-to-peak voltage of about 300 V) was measured during the geomagnetic storm. While large, this was not among the four
largest such geopotentials that have been recorded in the last 60 years across AT&T telecommunications cable routes, ocean
and continental. The geomagnetic and geopotential data that were measured during the storm event are presented and discussed. 相似文献
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L.J. Lanzerotti T.P. Armstrong C.G. Maclennan G.M. Simnett A.F. Cheng R.E. Gold D.J. Thomson S.M. Krimigis K.A. Anderson S.E. Hawkins III M. Pick E.C. Roelof E.T. Sarris S.J. Tappin 《Planetary and Space Science》1993,41(11-12)
This paper presents an overview of a number of the principal findings regarding the hot plasmas (E 50 keV) in Jupiter's magnetosphere by the HISCALE instrument during the encounter of the Ulysses spacecraft with the planet in February 1992. The hot plasma ion fluxes measured by HI-SCALE in the dayside magnetosphere are similar to those measured in the same energy range in this region by the Voyager spacecraft in 1979. Within the dayside plasma sheet, the hot-ion energy densities are comparable with, or larger than, the magnetic field energy densities; these hot ions are found to corotate at about one-half the planetary corotational speed. For ions of energies 500 keV/nucleon, the protons contributed from 50–60% to as much as 80% of the energy content of these plasmas. Strong, magnetic-field-aligned streaming was found for both the ions and electrons in the high-latitude duskside magnetosphere. The ion and electron pitch-angle distributions could be characterized by cos25 α throughout many of the high anisotropy intervals of the outbound pass. There is some evidence in the ion pitch-angle distributions for a corotational component in the hot plasmas at high Jovian latitudes. While there are limitations owing to the finite geometries of the detector telescope systems on the determination of the angular spreads of the ion and electron beams, the measurements show that there are intervals when the particle distributions are not bidirectional. At such times, locally the hot plasmas could be carrying currents of 10−4μAm−2. The temporal variations in the streaming electron fluxes are substantially larger than the variations measured for the fluxes that are more locally mirroring. The temporal variations contain periodicities that may correspond to hydromagnetic wave frequencies in the magnetosphere as well as to larger scale motions of magnetospheric plasmas. On nearly half of the days for about a 130 day interval around the time of the Ulysses encounter with the planet, particles of Jovian origin were measured in the interplanetary medium. An event discussed herein shows evidence of an energy dependence of the particle release process from the planetary magnetosphere into the interplanetary medium. 相似文献
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Margaret?E.?HartleyEmail authorView author&#;s OrcID profile Enik??Bali John?Maclennan David?A.?Neave S?mundur?A.?Halldórsson 《Contributions to Mineralogy and Petrology》2018,173(2):10
The 2014–2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine–plagioclase–augite–melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1?±?0.7 kbar (7.5?±?2.5 km), which is in agreement with the depths of earthquakes (6?±?1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1–12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12–0.29 m s?1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions. 相似文献
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Maclennan LJ 《The Astrophysical journal》2000,534(1):L109-L112
Anomalous cosmic-ray (ACR) oxygen (O) fluxes in the energy range 0.5-5.0 MeV nucleon-1 were measured in the ecliptic plane at 1 and 5 AU in 1997 and 1998. Using measurements from essentially identical instruments on the Advanced Composition Explorer (ACE) and Ulysses spacecraft, we were able to monitor the decrease with time of the ACR O fluxes in the inner heliosphere during the onset of solar cycle 23. The data obtained from three time intervals that are relatively undisturbed by solar activity during this period show that the e-folding time is approximately 140+/-40 days for the disappearance of 2-5 MeV nucleon-1 ACR oxygen from the ecliptic plane at 5 AU. 相似文献
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U. Villante M. Vellante M. De Lauretis P. Cerulli-Irelli L.J. Lanzerotti L.V. Medford C.G. Maclennan 《Geophysical Prospecting》1998,46(2):121-140
Geomagnetic fluctuations in the frequency band 2–70 mHz recorded simultaneously at a depth of about 1200 m in the underground Gran Sasso Laboratory (central Italy) and on the earth's surface (approximately along the Laboratory vertical) are compared using multivariate spectral analysis. Experimental problems and analytical techniques adopted for the signal processing are discussed. In particular, a modification of the standard least-squares method for estimating multiple-input transfer functions is proposed. The results show apparent different skin effects for each magnetic field component and a significant coherence between the underground vertical signal and the horizontal signals, suggesting the presence of lateral inhomogeneities in the underground conductivity structure. The results are also consistent with an average resistivity of the intervening medium of the order of 10–20 Ωm and with the presence of a more conductive layer at greater depth. 相似文献
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洋壳是由地幔熔融物在扩张洋脊处的结晶作用形成的，熔融物携带的热会在传导和热液循环中消除掉。虽然热液流为海洋提供了一个莺要的地球化学通量，但是人们对洋壳内热液冷却的分布了解得并不多（Schultz和Elder—field，1997；Mottl，2003）。我们对活动扩张脊进行地球物理、地质、岩石学研究，将研究结果用来研制快速扩张脊洋壳增生的概念模式（Quick和Denlinger,1993；Boudier等，1996；Kelemen等，1997）。 相似文献
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