摘要:

A bright feature observed on Jan. 24–26, 1992 with the soft X‐ray telescope on the YOHKOH spacecraft and with the coronameter at the Mauna Loa Solar Observatory assumed the appearance of a coronal helmet streamer as it slowly expanded. Mauna Loa observations from Jan. 22–24 indicate that a prominence eruption and coronal mass ejection occurred before this feature was seen. We interpret the Jan. 24–26 observations as evidence for “reformation” of a magnetically closed helmet structure as a consequence of magnetic reconnection that proceeded along a vertical magnetic neutral sheet formed by the ma

ISSN:0094-8276    

DOI:10.1029/93GL01449

年代:1993

数据来源: WILEY

摘要:

Ulysses‧ initial transit to high heliographic latitudes at a heliocentric distance of ∼5 AU has revealed systematic effects in the latitudinal evolution of corotating interaction regions (CIRs). At a latitude corresponding roughly to, but slightly less than, the inferred tilt of the coronal streamer belt and embedded heliospheric current sheet, the strong forward shocks commonly associated with CIRs at lower latitudes disappeared almost entirely; however, the reverse shocks associated with these CIRs persisted to latitudes ∼ 10° above the streamer belt. Systematic meridional flow deflections observed in association with the forward and reverse waves bounding the CIRs demonstrate that the above effect is the result of the fact that the forward waves propagate to lower latitudes and the reverse waves to higher latitudes with increasing heliocentric distance. These observational results are in excellent agreement with the predictions of a three‐dimensional model of corotating solar wind flows that originate in a tilted dipole geometry back at

ISSN:0094-8276    

DOI:10.1029/93GL03116

年代:1993

数据来源: WILEY

摘要:

We have examined the time series of hourly values of cosmic ray intensity over the years 1974–1990, observed by neutron monitors at Calgary and Lomnicky Stit, for the scaling properties. The scaling is shown to exist in intervals of 32–256 hours in data over several years. Fractal structure is deduced with statistically insignificant evidence of multifractal behaviour. The higher moments of the distribution have, in many years, symmetric properties, i.e., the scaling is similar for the same order (positive and negati

ISSN:0094-8276    

DOI:10.1029/93GL00090

年代:1993

数据来源: WILEY

摘要:

There was a succession of major solar flares in late‐May to mid‐June 1991. Their effects on cosmic ray intensity were observed by six spacecraft at various points in the heliosphere and by terrestrial neutron monitors. Study of these observations is summarized as follows: (a) An abrupt and extraordinarily large Forbush decrease in intensity occurred at the Earth on DOY 164/1991 (13 June) and ones of similar magnitude (≈ 20 percent) occurred in an orderly sequence of timing thereafter over ranges of heliocentric ecliptic longitude of essentially 360 degrees; of heliographic latitude +32 degrees to −5 degrees; and of radial distance 1.0 to 53 AU. (b) The apparent radial speed of propagation of the presumably causative blast wave was 865 (±75) km s−1(c) It appears likely that the distinctive solar flare of DOY 162/1991 (11 June) was the dominant cause of the blast wave. (d) Two different representations of the subsequent recoveries of intensity yield substantially different numerical values of “recovery time” but either set of values shows an increase by a factor of about three between

ISSN:0094-8276    

DOI:10.1029/93GL03119

年代:1993

数据来源: WILEY

摘要:

VLF plasma wave measurements obtained from the Pioneer Venus Orbiter Electric Field Detector (OEFD) have been used to construct statistical images of the Venus foreshock. Our data set contains all upstream measurements from an entire Venus year (∼200 orbits). Since the foreshock VLF characteristics vary with IMF orientation we restrict the study to IMF orientations near the nominal Parker spiral angle (25° to 45°). Our results show a strong decrease in 30 kHz wave intensity with both foreshock depth and distance. There is also an asymmetry in the 30 kHz emissions from the upstream and downstream foreshocks. The ion foreshock is characterized by strong emissions in the 5.4 kHz OEFD channel which are positioned much deeper in the fore‐shock than expected from terrestrial observations. No activity is observed in the region where field aligned ion distributions are expected. ULF wave activity, while weaker than at Earth, shows similar behavior and may indicate the presence of similar ion distribu

ISSN:0094-8276    

DOI:10.1029/93GL01258

年代:1993

数据来源: WILEY

摘要:

The large offset of Neptune's magnetic field in an offset tilted dipole (OTD) approximation allows some fraction of magnetospheric field lines to have monotonically increasing field magnitude over their entire length in the magnetosphere. The usual magnetic trapping is impossible on such field lines, meaning that all charged particles on these field lines will precipitate after mirroring at most once. These field lines can be thought of as the part of the global magnetic anomaly where no particles on the corresponding drift shells remain trapped for an entire rotation of the planet. In this paper we examine both the morphology and size of the affected surface area in the OTD2 and O8 magnetic field models. For regions where there are indications that part of the aurora could be due to monotonic field line precipitation we analyze whether these field lines could be sufficiently populated to produce auroral signatures by considering photoelectron production rates and radial diffusion. We conclude that monotonic field line precipitation may contribute to the observed Neptune aurora but does not explain the global phenomenon.

ISSN:0094-8276    

DOI:10.1029/93GL02430

年代:1993

数据来源: WILEY

摘要:

A novel viewpoint of the magnetosphere as a lens for MHD waves is presented. Using a simple model of the variation of the Alfven speed as proportional to the local magnetic field value given by the Earth's dipole field and that due to the magnetopause currents represented by a current loop, it is found that the near‐Earth magnetotail, in the range 8–16 RE, is the focus of the magnetospheric lens. This location is found to be quite insensitive to a wide variation of parameters. By using simple diffraction theory analysis it is found that the focal region extends about 1 REabout the neutral sheet in the north‐south plane and 0.2–0.5 REalong the Sun‐Earth line. Compressive MHD waves carried by the solar wind or created by the interaction of the wind with the magnetopause can be amplified by a factor of about 100 in the focal region and this has potentially important implications to substorm

ISSN:0094-8276    

DOI:10.1029/93GL03011

年代:1993

数据来源: WILEY

摘要:

No high‐speed flows or discernible counterstreaming ion beams were observed during a series of plasma sheet boundary encounters resulting from solar wind‐driven plasma sheet motions. We conclude that the boundary may be active primarily during plasma sheet “recovery”. A temporal onset of flows in the inner plasma sheet (IPS) was associated with the appearance of counterstreaming beams embedded in an already isotropic plasma sheet distribution, suggesting that high speed flows at the plasma sheet boundary and close to the neutral sheet may have a common generation me

ISSN:0094-8276    

DOI:10.1029/93GL01979

年代:1993

数据来源: WILEY

摘要:

Recently there as been much interest in determining if the global geomagnetic system, as characterized by AE and AL indices, can be described by a low dimensional, possibly chaotic, non‐linear dynamical system. By using a statistical method for detecting nonlinearity, we show that for one interval which has been previous analyzed (the first 8192 minutes of January 1983) there is no evidence for low dimensional behavio

ISSN:0094-8276    

DOI:10.1029/93GL03012

年代:1993

数据来源: WILEY

摘要:

Numerical solutions to the time‐dependent kinetic equation, which describes the transport of superthermal electrons in the plasmasphere between the two conjugate ionospheres, are presented. The model calculates the distribution function as a function of time, field‐aligned distance, energy, and pitch‐angle. The processes of refilling, depleting, and establishing steady‐state conditions of super‐thermal electrons in the plasmasphere are

ISSN:0094-8276    

DOI:10.1029/93GL03121

年代:1993

数据来源: WILEY