摘要:

The solar corona was observed with an externally occulted White Light Coronagraph carried on the SPARTAN 201‐01 spacecraft for a 47 hour period beginning on April 11, 1993. At this phase of the descending solar magnetic activity cycle there were well developed coronal helmet streamers located over both the east and west limbs of the sun. Of additional interest in the SPARTAN data are the finer scale streamer structures observed in the low latitude corona which are partially resolved by the SP201‐01 instrument. The purpose of this investigation was to determine the physical and morphological characteristics of the streamers and the fine scale ray structures observed in the region between streamers. A comparison of these low latitude rays with the polar rays observed in the north and south polar holes during the same flight suggest that they have similar morphology and physical characterist

ISSN:0094-8276    

DOI:10.1029/95GL01603

年代:1995

数据来源: WILEY

摘要:

A 1.3‐year oscillation in the IMP‐8 and Voyager 2 solar wind plasma radial speed observations for the period of 1987–94 was recently reported [Richardson et al., 1994]. The same periodicity is identified for the same time period in the North‐South component of the interplanetary magnetic field at 1 AU when studied with a dynamic power spectrum. This observation sheds new light on the nature of these unusual oscil

ISSN:0094-8276    

DOI:10.1029/95GL01737

年代:1995

数据来源: WILEY

摘要:

We estimate the location of the reconnection line and plasmoid size in the geomagnetic tail using data from the Plasma Wave Instrument onboard the GEOTAIL spacecraft. We first compare AKR onset events with high energy particle observations at geosynchronous orbit. We determine the plasmoid ejection (reconnection) time by the AKR enhancement only when it corresponds to energetic particle enhancement within five minutes. The traveling time of the plasmoid from theX‐line to the spacecraft is calculated by the difference in time of the AKR onset and that of the plasmoid encounter with GEOTAIL. Assuming the plasmoid propagates with the Alfvén velocity in the tail lobe as MHD simulations predict, we estimate the location of the reconnection line in 11 events. The results show that the most probable location of the plasmoid edge is distributed aroundx= −60 REin the GSE coordinates. The estimated size of the plasmoids ranges from 10 to 50 REin thexdirection. If we apply this result to the alternative plasmoid model in which the evolution of the tearing instability causes the generation of plasmoids, theX‐line should be approximately atx=

ISSN:0094-8276    

DOI:10.1029/95GL01514

年代:1995

数据来源: WILEY

摘要:

The distribution of energetic electrons and ions withL‐value (L≤8) as measured by the Electron‐Proton Angle Spectrometer onboard CRRES over the whole mission lifetime (July 1990 to October 1991) is presented. The outer radiation belt is shown to be highly dynamic, both in position and in strength. Substantial enhancements of electron and ion flux on short timescales are seen throughout most of the magnetosphere sampled by CRRES, and are strongly related to theKpindex and the ring current as measured byDST. These enhancements decay over less than 30 days. There is evidence of a magnetospheric electron and ion acceleration mechanism of considerable strength and efficiency. Very intense periods of activity (such as the March, 1991 storm) can lead to the creation of an additional, high‐energy belt in the slot region, which persists over a period of many

ISSN:0094-8276    

DOI:10.1029/95GL01607

年代:1995

数据来源: WILEY

摘要:

The polar wind is an ambipolar plasma outflow from the terrestrial ionosphere at high latitudes. As the ions drift upward along geomagnetic flux tubes, they move from collision‐dominated (ion barosphere) to collisionless (ion exosphere) regions. A transition layer is embedded between these two regions where the ion characteristics change rapidly. A Monte Carlo simulation was used to study the steady‐state flow of H+ions through a background of O+ions. The simulation domain covered the collision‐dominated, transition, and collisionless regions. The model properly accounted for the divergence of magnetic field lines, the gravitational force, the electrostatic field, and H+‐O+collisions. The H+velocity distribution,f(H+), was found to be very close to Maxwellian at low altitudes (deep in the barosphere). As the ions drifted to higher altitudes,f(H+) formed an upward tail. In the transition layer, the upward tail evolved into a second peak with a kidney bean shape, and hence,f(H+) developed a double‐humped shape. The second peak grew with altitude and eventually became dominant as the ions reached the exosphere. This behavior is due to the interplay between the electrostatic force and the velocity‐dependent Coulomb collisions. Moreover, the H+heat flux,q(H+), was found to change rapidly with altitude in the transition layer from a positive maximum to a negative minimum. This remarkable feature ofq(H+) is closely related to the coincident formation of the double‐humped structure off(H+). The double‐hump distribution might destabilize the plasma or, at least, cause enhanced thermal fluctuations. The double‐humpf(H+), and the associated wave turbulence, have several consequences with regard to our understanding of the polar wind and similar space physics problems. The plasma turbulence can significantly alter the behavior of the plasma in and above the transition region and, therefore, should be considered in future polar wind models. The wave turbulence can serve as a signature for the formation of the double‐humpf(H+). Also, more sophisticated (than the existing bi‐Maxwellian 16‐moment) generalized transport equations might be needed to properly handle problems such as

ISSN:0094-8276    

DOI:10.1029/95GL01519

年代:1995

数据来源: WILEY

摘要:

Using DE 2 data of ion drift velocities and magnetic fields, we have calculated the field‐aligned Poynting flux (S∥) for 576 orbits over the satellite lifetime. This is the first application over an extended data set of Poynting flux observations from in situ measurements. The data has been sorted by interplanetary magnetic field conditions (northward or southward IMF) and geomagnetic activity (Kp≤3 and Kp>3) and binned by invariant latitude and magnetic local time. Our general results may be summarized as 1) the averaged S∥is everywhere directed into the ionosphere, indicating that electric fields of magnetospheric origin generally dominate, and 2) the distribution of S∥for southward IMF can be well explained in terms of an average two cell convection pattern, while for northward IMF a multiple cell convection pattern may be inferred. We have addressed the interesting question of the distribution of upward Poynting flux by binning only upward observations and found that average upward Poynting flux of less than 3 mW/m² may occur anywhere across the high latitude ionosphere. We have also observed a region at high latitudes in the predawn sector where the average upward Poynting flux is of significant size and occurrence frequency during southward IMF and high Kp

ISSN:0094-8276    

DOI:10.1029/95GL00570

年代:1995

数据来源: WILEY

摘要:

It is well known that lightning‐generated whistlers propagate along the Earth's magnetic field lines within a cone that at low frequencies makes an angle of 19°28′ with respect to the local magnetic field. This angle turns out to be exactly the same as the half‐angle of the bow wave of a ship in deep water. Both problems are complicated by the fact that the wave propagation is dispersive. In this paper we show that these two seemingly unrelated problems can be understood using the same basic approach, which is to analyze the direction of the group velocity as a function of the wave normal angle. This approach may have applications to other problems of geophysical interest, such as the bow wave generated by the interaction of a large object with a moving

ISSN:0094-8276    

DOI:10.1029/95GL01728

年代:1995

数据来源: WILEY

摘要:

Using a simple photochemical model we derive the mixing ratio profile of ClO in the altitude range 20–38 km from simultaneous measurements of HO2, OH, HOCl, temperature, pressure, and ozone. The measurements were made with the FIRS‐2 far‐infrared spectrometer during a balloon flight on September 29, 1992. We compare the derived ClO with the ClO profile obtained by the SLS instrument while flying on the same gondola. The good agreement between the two profiles validates our simple model and confirms the relevant rate constants and photolysis cross sec

ISSN:0094-8276    

DOI:10.1029/95GL01249

年代:1995

数据来源: WILEY

摘要:

Nitrogen trifluoride is found to be stable towards photo‐oxidation reactions that limit the atmospheric lifetimes of many gaseous species. Reactions with species such as OH and HO2are thermodynamically unfavorable. The reaction with O3, while thermodynamically favorable, is found to be too slow to be of atmospheric importance. Measurements of the NF3absorption cross‐sections from 180 to 250 nm yield values that are smaller than those previously reported, and indicate an atmospheric lifetime against photodissociation in the stratosphere of about seven hundred years. In addition, the infrared band strengths were determined in order to enable estimates of greenhouse warming potentials. A slow reaction with aqueous Fe2+was observed at room temperature; it could provide an additional destruction mechanism in the environm

ISSN:0094-8276    

DOI:10.1029/95GL01669

年代:1995

数据来源: WILEY

摘要:

An analytic expression is given for the composition and volume of stratospheric HNO3‐H2SO4‐H2O aerosols in terms of the temperature and total amounts of H2O, HNO3and H2SO4, taking into account conservation of HNO3. In contrast to previous parameterisations of equilibrium vapour pressures, the present scheme for calculating the aerosol composition does not require an iteration procedure, thus computation times are significantly reduced, making it ideal for inclusion in large‐scale atmospheric models. Calculated compositions are compared with the results of a comprehensive thermodynamic model for all stratospheric conditions and maximum deviations are pres

ISSN:0094-8276    

DOI:10.1029/95GL01668

年代:1995

数据来源: WILEY