共查询到20条相似文献，搜索用时 15 毫秒
1.
Three-dimensional simulations of the heliospheric modulation of galactic cosmic ray protons show that corotating variations in the intensity can persist to quite high heliographic latitudes. Variations are seen at latitudes considerably higher than the maximum latitude extension of the heliographic current sheet, in regions where the solar wind velocity and magnetic field show no significant variation. Similar conclusions may apply also to lower energy particles, which may be accelerated at lower latitudes. Cosmic ray variations caused by corotating interaction regions present at low heliographic latitudes can propagate to significantly higher latitudes. 相似文献
2.
Stone RG Pedersen BM Harvey CC Canu P Cornilleau-Wehrlin N Desch MD de Villedary C Fainberg J Farrell WM Goetz K Hess RA Hoang S Kaiser ML Kellogg PJ Lecacheux A Lin N Macdowall RJ Manning R Meetre CA Meyer-Vernet N Moncuquet M Osherovich V Reiner MJ Tekle A Thiessen J Zarka P 《Science (New York, N.Y.)》1992,257(5076):1524-1531
The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of aurorallike hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the lo plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the lo torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed. 相似文献
3.
Plasma wave electric field measurements with the solar orbiting Helios spacecraft have shown that intense (approximately 10 millivolts per meter) electron plasma oscillations occur in association with type III solar radio bursts. These observations confirm the basic mechanism, proposed in 1958, that type III radio emissions are produced by intense electron plasma oscillations excited in the solor corona by electrons ejected from a solar flare. 相似文献
4.
Observations of solar p-mode frequency splittings obtained at Big Bear Solar Observatory in 1986 and during 1988-90 reveal small ( approximately 1 percent) changes in the sun's subsurface angular velocity with solar cycle. An asymptotic inversion of the splitting data yields the latitude dependence of the rotation rate and shows that the largest changes in the angular velocity, approximately 4 nanohertz, occurred between 1986 and the later years, at high ( approximately 60 degrees ) solar latitudes. Earlier helioseismic observations suggest that solar cycle changes in the ratio of magnetic to turbulent pressure in the solar convection zone are large enough to account for the magnitude of the observed angular velocity variations but a detailed model of the phenomenon does not exist. 相似文献
5.
Simpson JA Anglin JD Balogh A Burrows JR Cowley SW Ferrando P Heber B Hynds RJ Kunow H Marsden RG McKibben RB Müller-Mellin R Page DE Raviart A Sanderson TR Staines K Wenzel KP Wilson MD Zhang M 《Science (New York, N.Y.)》1992,257(5076):1543-1550
The Ulysses spacecraft made the first exploration of the region of Jupiter's magnetosphere at high Jovigraphic latitudes ( approximately 37 degrees south) on the dusk side and reached higher magnetic latitudes ( approximately 49 degrees north) on the day side than any previous mission to Jupiter. The cosmic and solar particle investigations (COSPIN) instrumentation achieved a remarkably well integrated set of observations of energetic charged particles in the energy ranges of approximately 1 to 170 megaelectron volts for electrons and 0.3 to 20 megaelectron volts for protons and heavier nuclei. The new findings include (i) an apparent polar cap region in the northern hemisphere in which energetic charged particles following Jovian magnetic field lines may have direct access to the interplanetary medium, (ii) high-energy electron bursts (rise times approximately 17 megaelectron volts) on the dusk side that are apparently associated with field-aligned currents and radio burst emissions, (iii) persistence of the global 10-hour relativistic electron "clock" phenomenon throughout Jupiter's magnetosphere, (iv) on the basis of charged-particle measurements, apparent dragging of magnetic field lines at large radii in the dusk sector toward the tail, and (v) consistent outflow of megaelectron volt electrons and large-scale departures from corotation for nucleons. 相似文献
6.
Balogh A Southwood DJ Forsyth RJ Horbury TS Smith EJ Tsurutani BT 《Science (New York, N.Y.)》1995,268(5213):1007-1010
Magnetic field measurements from the Ulysses space mission overthe south polar regions of the sun showed that the structure and properties of the three-dimensional heliosphere were determined by the fast solar wind flow and magnetic fields from the large coronal holes in the polar regions of the sun. This conclusion applies at the current, minimum phase of the 11-year solar activity cycle. Unexpectedly, the radial component of the magnetic field was independent of latitude. The high-latitude magnetic field deviated significantly from the expected Parker geometry, probably because of large amplitude transverse fluctuations. Low-frequency fluctuations had a high level of variance. The rate of occurrence of discontinuities also increased significantly at high latitudes. 相似文献
7.
Warwick JW Evans DR Romig JH Alexander JK Desch MD Kaiser ML Aubier M Leblanc Y Lecacheux A Pedersen BM 《Science (New York, N.Y.)》1982,215(4532):582-587
Planetary radio astronomy measurements obtained by Voyager 2 near Saturn have added further evidence that Saturnian kilometric radiation is emitted by a strong dayside source at auroral latitudes in the northern hemisphere and by a weaker source at complementary latitudes in the southern hemisphere. These emissions are variable because of Saturn's rotation and, on longer time scales, probably because of influences of the solar wind and Dione. The electrostatic discharge bursts first discovered by Voyager 1 and attributed to emissions from the B ring were again observed with the same broadband spectral properties and an episodic recurrence period of about 10 hours, but their occurrence frequency was only about 30 percent of that detected by Voyager 1. While crossing the ring plane at a distance of 2.88 Saturn radii, the spacecraft detected an intense noise event extending to above 1 megahertz and lasting about 150 seconds. The event is interpreted to be a consequence of the impact, vaporization, and ionization of charged, micrometer-size G ring particles distributed over a vertical thickness of about 1500 kilometers. 相似文献
8.
Ho GC Krimigis SM Gold RE Baker DN Slavin JA Anderson BJ Korth H Starr RD Lawrence DJ McNutt RL Solomon SC 《Science (New York, N.Y.)》2011,333(6051):1865-1868
The MESSENGER spacecraft began detecting energetic electrons with energies greater than 30 kilo-electron volts (keV) shortly after its insertion into orbit about Mercury. In contrast, no energetic protons were observed. The energetic electrons arrive as bursts lasting from seconds to hours and are most intense close to the planet, distributed in latitude from the equator to the north pole, and present at most local times. Energies can exceed 200 keV but often exhibit cutoffs near 100 keV. Angular distributions of the electrons about the magnetic field suggest that they do not execute complete drift paths around the planet. This set of characteristics demonstrates that Mercury's weak magnetic field does not support Van Allen-type radiation belts, unlike all other planets in the solar system with internal magnetic fields. 相似文献
9.
Phillips JL Bame SJ Feldman WC Gosling JT Hammond CM McComas DJ Goldstein BE Neugebauer M Scime EE Suess ST 《Science (New York, N.Y.)》1995,268(5213):1030-1033
Solar wind plasma observations made by the Ulysses spacecraft through -80.2 degrees solar latitude and continuing equatorward to -40.1 degrees are summarized. Recurrent high-speed streams and corotating interaction regions dominated at middle latitudes. The speed of the solar wind was typically 700 to 800 kilometers per second poleward of -35 degrees . Corotating reverse shocks persisted farther south than did forward shocks because of the tilt of the heliomagnetic streamer belt. Sporadic coronal mass ejections were seen as far south as -60.5 degrees . Proton temperature was higher and the electron strahl was broader at higher latitudes. The high-latitude wind contained compressional, pressure-balanced, and Alfvénic structures. 相似文献
10.
Lunar surface magnetic fields and their interaction with the solar wind: results from lunar prospector 总被引：1，自引：0，他引：1
RP Lin DL Mitchell DW Curtis KA Anderson CW Carlson J McFadden MH Acuna LL Hood A Binder 《Science (New York, N.Y.)》1998,281(5382):1480-1484
The magnetometer and electron reflectometer experiment on the Lunar Prospector spacecraft has obtained maps of lunar crustal magnetic fields and observed the interaction between the solar wind and regions of strong crustal magnetic fields at high selenographic latitude (30 degreesS to 80 degreesS) and low ( approximately 100 kilometers) altitude. Electron reflection maps of the regions antipodal to the Imbrium and Serenitatis impact basins, extending to 80 degreesS latitude, show that crustal magnetic fields fill most of the antipodal zones of those basins. This finding provides further evidence for the hypothesis that basin-forming impacts result in magnetization of the lunar crust at their antipodes. The crustal magnetic fields of the Imbrium antipode region are strong enough to deflect the solar wind and form a miniature (100 to several hundred kilometers across) magnetosphere, magnetosheath, and bow shock system. 相似文献
11.
12.
Warwick JW Pearce JB Riddle AC Alexander JK Desch MD Kaiser ML Thieman JR Carr TD Gulkis S Boischot A Harvey CC Pedersen BM 《Science (New York, N.Y.)》1979,204(4396):995-998
We report results from the first low-frequency radio receiver to be transported into the Jupiter magnetosphere. We obtained dramatic new information, both because Voyager was near or in Jupiter's radio emission sources and also because it was outside the relatively dense solar wind plasma of the inner solar system. Extensive radio spectral arcs, from above 30 to about 1 megahertz, occurred in patterns correlated with planetary longitude. A newly discovered kilometric wavelength radio source may relate to the plasma torus near Io's orbit. In situ wave resonances near closest approach define an electron density profile along the Voyager trajectory and form the basis for a map of the torus. Detailed studies are in progress and are out-lined briefly. 相似文献
13.
Levy GS Sato T Seidel BL Stelzried CT Ohlson JE Rusch WV 《Science (New York, N.Y.)》1969,166(3905):596-598
Pioneer 6, which was launched into orbit around the sun on 16 December 1965, was occulted by the sun in the last half of November 1968. During the period in which the spacecraft was occulted by the solar corona, the S-band telemetry carrier underwent Faraday rotation as a result of this anisotropic plasma. The NASA-Jet Propulsion Laboratory 210-foot (64-meter) antenna of the Deep Space Network at Barstow, California, which was equipped with an automatic polarization tracking system, was used to measure this effect. Three large-scale transient phenomena were observed. The measurement of these phenomena indicated that Faraday rotation on the order of 40 degrees occurred. The duration of each phenomenon was approximately 2 hours. These phenomena appear to be correlated with observations of solar radio bursts with wavelengths in the dekametric region. 相似文献
14.
Rea N Esposito P Turolla R Israel GL Zane S Stella L Mereghetti S Tiengo A Götz D Göğüş E Kouveliotou C 《Science (New York, N.Y.)》2010,330(6006):944-946
Soft gamma repeaters (SGRs) and anomalous x-ray pulsars form a rapidly increasing group of x-ray sources exhibiting sporadic emission of short bursts. They are believed to be magnetars, that is, neutron stars powered by extreme magnetic fields, B ~ 10(14) to 10(15) gauss. We report on a soft gamma repeater with low magnetic field, SGR 0418+5729, recently detected after it emitted bursts similar to those of magnetars. X-ray observations show that its dipolar magnetic field cannot be greater than 7.5 × 10(12) gauss, well in the range of ordinary radio pulsars, implying that a high surface dipolar magnetic field is not necessarily required for magnetar-like activity. The magnetar population may thus include objects with a wider range of B-field strengths, ages, and evolutionary stages than observed so far. 相似文献
15.
Pearce JB Riddle AC Warwick JW Alexander JK Desch MD Kaiser ML Thieman JR Carr TD Gulkis S Boischot A Leblanc Y Pedersen BM Staelin DH 《Science (New York, N.Y.)》1979,206(4421):991-995
The Voyager 2 Planetary Radio Astronomy experiment to Jupiter has confirmed and extended to higher zenomagnetic latitudes results from the identical experiment carried by Voyager 1. The kilometric emissions discovered by Voyager 1 often extended to 1 megahertz or higher on Voyager 2 and often consisted of negatively or, less frequently, positively drifting narrowband bursts. On the basis of tentative identification of plasma wave emissions similar to those detected by Voyager 1, the plasma torus associated with Io appeared somewhat denser to Voyager 2 than it did to Voyager 1. We report here on quasiperiodic sinusoidal or impulsive bursts in the broadcast band range of wavelengths (800 to 1800 kilohertz). A Faraday effect appears at decametric frequencies, which probably results from propagation of the radiation near its sources on Jupiter. Finally, we discuss the occurrence of decametric emission in homologous arc families. 相似文献
16.
Gurnett DA Kurth WS Poynter RL Granroth LJ Cairns IH Macek WM Moses SL Coroniti FV Kennel CF Barbosa DD 《Science (New York, N.Y.)》1989,246(4936):1494-1498
The Voyager 2 plasma wave instrument detected many familiar plasma waves during the encounter with Neptune, including electron plasma oscillations in the solar wind upstream of the bow shock, electrostatic turbulence at the bow shock, and chorus, hiss, electron cyclotron waves, and upper hybrid resonance waves in the inner magnetosphere. Low-frequency radio emissions, believed to be generated by mode conversion from the upper hybrid resonance emissions, were also observed propagating outward in a disklike beam along the magnetic equatorial plane. At the two ring plane crossings many small micrometer-sized dust particles were detected striking the spacecraft. The maximum impact rates were about 280 impacts per second at the inbound ring plane crossing, and about 110 impacts per second at the outbound ring plane crossing. Most of the particles are concentrated in a dense disk, about 1000 kilometers thick, centered on the equatorial plane. However, a broader, more tenuous distribution also extends many tens of thousands of kilometers from the equatorial plane, including over the northern polar region. 相似文献
17.
The first inbound Voyager 2 crossing of Saturn's bow shock [at 31.7 Saturn radii (RS), near local noon] and the last outbound crossing (at 87.4 RS, near local dawn) had similar plasma wave signatures. However, many other aspects of the plasma wave measurements differed considerably during the inbound and outbound passes, suggesting the presence of effects associated with significant north-south or noon-dawn asymmetries, or temporal variations. Within Saturn's magnetosphere, the plasma wave instrument detected electron plasma oscillations, upper hybrid resonance emissions, half-gyrofrequency harmonics, hiss and chorus, narrowband electromagnetic emissions and broadband Saturn radio noise, and noise bursts with characteristics of static. At the ring plane crossing, the plasma wave instrument also detected a large number of intense impulses that we interpret in terms of ring particle impacts on Voyager 2. 相似文献
18.
Gurnett DA Kurth WS Roux A Gendrin R Kennel CF Bolton SJ 《Science (New York, N.Y.)》1991,253(5027):1522-1525
During the Galileo flyby of Venus the plasma wave instrument was used to search for impulsive radio signals from lightning and to investigate locally generated plasma waves. A total of nine events were detected in the frequency range from 100 kilohertz to 5.6 megahertz. Although the signals are weak, lightning is the only known source of these signals. Near the bow shock two types of locally generated plasma waves were observed, low-frequency electromagnetic waves from about 5 to 50 hertz and electron plasma oscillation at about 45 kilohertz. The plasma oscillations have considerable fine structure, possibly because of the formation of soliton-like wave packets. 相似文献
19.
Skin-pigment regulation of vitamin-D biosynthesis in man 总被引：11，自引：0，他引：11
W F Loomis 《Science (New York, N.Y.)》1967,157(788):501-506
The known correlation between the color of human skin and latitude (Fig. 2) is explainable in terms of two opposing positive adaptations to solar ultraviolet radiation, weak in northern latitudes in winter yet powerful the year around near the equator. In northern latitudes there is selection for white skins that allow maximum photoactivation of 7-dehydrocholesterol into vitamin D at low intensities of ultraviolet radiation. In southern latitudes, on the other hand, there is selection for black skins able to prevent up to 95 percent of the incident ultraviolet from reaching the deeper layers of the skin where vitamin D is synthesized. Selection against the twin dangers of rickets on the one hand and toxic doses of vitamin D on the other would thus explain the world-wide correlation observed between skin pigmentation and nearness to the equator. 相似文献
20.
Sunspots, dark magnetic regions occurring at low latitudes on the Sun's surface, are tracers of the magnetic field generated by the dynamo mechanism. Recent solar dynamo models, which use the helioseismically determined solar rotation, indicate that sunspots should form at high latitudes, contrary to observations. We present a dynamo model with the correct latitudinal distribution of sunspots and demonstrate that this requires a meridional flow of material that penetrates deeper than hitherto believed, into the stable layers below the convection zone. Such a deep material flow may have important implications for turbulent convection and elemental abundance in the Sun and similar stars. 相似文献