Mechanics and Materials Technology Center: Evaluation and characterization of new materials: metals, alloys, ceramics, polymers and their composites, and new forms of c;u-bon; development and analysis of thin films and depositi m techniques; nondestructive evaluation, component failure analysis and reliability; fracture mechanics and stress corrosion; development and evaluation ':,f hardened components; analysis and evaluation of materials at cryogenic and elevated temperatures; launch vehicle and reentry fluid mechanics, heat trans fer and flight dynamics; chemical and electric propulsion; spacecraft structural mechanics, spacecraft survivability and vulnerability assessment, contamination, thermal and structural control; high temperature thermomechanics, gas kinetics and radiation; lubrication and surface phenomena.Space and Envirunment Technology Center: Magnetospheric, auroral and cosmic ray physics, wave -particle interactions, magnetospheric plasma waves; atmospheric and ionospheric physics, density and composition of the upper atmosphere, remote sensing using atmospheric radiation; solar physics, infrared astronomy, ;nfrared signature analysis; effects of solar activity, magnetic storms and nuclear expiusions on the earth 's atmosphere, ionosphere and magnetosphere; effects of electromagnetic and particulate radiations on space systems; space instrumentation; propellant chef. istry, chemical dynamics, environmental Lhemistry, trace detection; atmospheric chemical reactions, atmospheric optics, light scattering, state-specific cherr ical reactions and radiative signatures of missile plumes, and sensor out-offield-of-view rejection.. . ,^.,..2:Yw ^n .

Magnetometer and HF radar data often indicate the presence of magnetohydrodynamic, field line resonances in the nightside magnetosphere. These resonances have frequencies of about 1.3, 1.9, 2.6, and 3.4 mHz and are due to cavity modes or waveguide modes which form between the magnetopause and turning points on dipolelike magnetic shells. Energy from these cavity modes tunnels to the field line resonances which are seen in the F region by the HF radar and on the ground by the magnetometers. The presence of these field line resonances gives us an excellent diagnostic tool for determining the position of the mechanism leading to the energetic electrons and field-aligned currents associated with substorm intensifications and auroral brightening. Using data from the Canadian CANOPUS array of magnetometers, meridian scanning photometers, riometers, and bistatic auroral radars and data from the Johns Hopkins University/Applied Physics Laboratory HF radar at Goose Bay in Canada, we have identified a number of intervals in which substorm intensifications occurred during times when field line resonances existed in the region of the magnetosphere where the intensification occurred. In the events that we have analyzed in detail, the ionospheric signatures of the substorm intensification began equatorward (earthward) of existing field line resonances. These observations give very strong evidence indicating that at least one component of the substorm mechanism must be active very close to the Earth, probably on dipolelike field lines in regions with trapped and quasi-trapped energetic particles. Furthermore, the auroral intensifications started near the position of one of the equatorward resonances, indicating that the field line resonances may play a role in triggering or producing the substorm intensifications. One possible scenario is mode conversion to kinetic Alfv6n waves in the resonance. Table 1), meridian scanning photometers, a bistatic auroral radar, and a charged couple device (CCD) imager and became fully operational in December of 1989. The CANOPUS meridian scanning photometer array (MPA) uses meridian scanning, eight-channel, filter wheel photometers at Rankin Inlet, Gillam, Pinawa, and Fort Smith. Only the data from the Gillam (GILL) and Rankin Inlet (RANK) instruments are used in this study. Five of the channels measure auroral emissions (4709, 4861 (twice), 5577, and 6300-/•), and three channels measure the background near 4800, 4935, and 6250/•. The photometer scans the meridian at two revolutions per minute with a sampling rate of 510 samples per scan per channel. Data from the scans are averaged into 17 latitudinal bins, centered on the latitude of the station. The data bins are 0.5 ø wide and 0.5 ø apart for the low-altitude (110 kin) emissions (4861, 5577, and 4709 /•) and approximately 1.0 ø wide for the high-altitude (230 kin) emission (6300/•). The magnetometer array uses three-component, ring core, flux gate instruments. Each channel is sampled at 5-s intervals. The magnetometers are aligned in geogra...

No abstract

[1] The equatorward boundary of the proton aurora corresponds to a transition from strong pitch angle scattering to bounce trapped particles. This transition has been identified as the b2i boundary in Defense Meteorological Satellite Program (DMSP) ion data [Newell et al., 1996]. We use ion data from 29 DMSP overflights of the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) Meridian Scanning Photometer (MSP) located at Gillam, Canada, to develop a simple algorithm to identify the b2i boundary in latitude profiles of proton auroral (486 nm) brightness. Applying this algorithm to a ten year set of Gillam MSP data, we obtain $250,000 identifications of the ''optical b2i,'' the magnetic latitude of which we refer to as b2i à . We intercompare $1600 near-simultaneous optical and in situ b2i à , concluding that the optical b2i à is a reasonable basis for an optical equivalent to the MT-index put forward by Sergeev and Gvozdevsky [1995]. Using $17,000 simultaneous measurements, we demonstrate a strong correlation between the optical b2i à and the inclination of the magnetic field as measured at GOES 8. We develop an empirical model for predicting the GOES 8 inclination, given theuniversal time, dipole tilt, and the optical b2i à , as determined at Gillam. We also show that in terms of information content, the b2i boundary is an optimal boundary upon which to base such an empirical model.

Data from the Canadian Auroral Network for the OPEN Unified Study (CANOPUS) array in Canada are used to analyze the magnetic fields and auroral structures which were associated with a field line resonance which occurred near local midnight and in the early morning sector. The electric fields of this resonance, which have a frequency of about 1.95 mHz, were observed by the Johns Hopkins University, Applied Physics Laboratory HF radar at Goose Bay and had a maximum at about 70.7° invariant latitude. Effects of the field line resonance were seen in the 5577 Å, meridian scanning photometer data and the magnetometer data from the CANOPUS array. The field line resonance was accompanied by precipitating energetic electrons (energies greater than 3 keV) in a narrow auroral arc which was 3°–4° equatorward of the resonance structure seen in the radar data and approximately 1° equatorward of field lines threading the inner boundary of the proton plasma sheet. The electron precipitation in this arc was modulated at the frequency of the field line resonance. The effects of the resonance are also seen as pulsations in the magnetometer data, and the horizontal polarization of the pulsations showed a change in sense of rotation across the arc. The oscillations in the precipitating electrons might have been caused by modulation in the ELF/VLF growth rates due to the presence of the magnetohydrodynamic waves associated with the resonance, by mode conversion to kinetic Alfvén waves, or by the formation of electrostatic ion cyclotron waves due to field‐aligned currents associated with a second field line resonance collocated with the arc. The evidence presented here suggests that the modulation of ELF/VLF by magnetohydrodynamic waves on field lines near the plasmapause was the most likely cause of the auroral oscillations.

Abstract. The objective of the present study is to examine the timing of various onsetassociated signatures and address the cause-and-effect relationship between the formation of a near-Earth neutral line (NENL) and the trigger of tail current disruption. An event selected for this study took place on December 31, 1995. In this event the Geotail satellite was located at X = -30.3 R e in the midnight sector at a local time between the GOES 8 and 9 geosynchronous satellites. The timing of the Geotail observation of a fast (950-km/s) tailward convection flow accompanied with southward B z (< -10 nT) indicates that the near-Earth reconnection process started at least 4 min before the ground substorm onset, which was identified by various signatures such as an auroral expansion, a Pi2 onset, a positive bay onset, and a negative bay onset. Both GOES satellites observed dipolarization. GOES 9 was located closer to the onset meridian and observed a sudden recovery (dipolarization) of the local magnetic field but with a noticeable (=1 min) delay from the ground onset. This delay can be interpreted in terms of the earthward expansion of tail current disruption initiated outside of geosynchronous orbit. The timing of all these features is consistent with the idea that dipolarization is a pileup of magnetic flux conveyed from the NENL. However, a sharp decrease in the H component at GOES 9 prior to the local dipolarization onset and the sudden start of a substorm are difficult to explain in terms of this idea. It is asserted that tail current disruption is a unique process rather than a direct consequence of the NENL formation, although it is possible that the reconnection process sets up a favorable condition for triggering tail current disruption. The fast plasma flow in the plasma sheet ceased soon after the substorm onset, suggesting that during the expansion phase, the tail current disruption took over the near-Earth reconnection process as a major role in the substorm dynamics.

Optical aurora and magnetometer data from the Canadian Auroral Network for the OPEN Unified Study (CANOPUS) array in Canada are used in the study of the modulation of optical aurora in the 5577-Jk and 4709-]k emission lines, by resonant shear Alfvtn waves, in the frequency range of 1-4 mHz. A total of four events, carefully chosen to represent different characteristics of timing and location, are analyzed. Typical of these events, the power spectra featured discrete spectral peaks usually near 1.3, 1.9, and 3.1 mHz. Furthermore, latitudinal phase shifts of about 180 ø were typically observed across the latitudinal maximum of a given frequency peak. These observations point irrevocably to the field line resonance as a major factor in the modulation of precipitation and possibly in the acceleration of electrons in forming auroral arcs. Our study demonstrates that the modulation phenomena are common features occurring in the auroral oval, observable in an extensive latitude range, from 66 ø to 73 ø invariant latitude. Of the events, one shows the modulation process accompanied by an inverted V structure of electron precipitation in the evening sector near 72 ø. Two events are observed in the equatorward region of the auroral oval just before substorms onset, and maybe related to the energetic electron arcs which are the precursor of substorm intensification. The fourth event is seen in the morning sector at an equatorward latitude and occurs in the recovery phase of a substorm. The diversity of these modulation events allows us to further infer that resonant Alfvtn waves play a direct role in controlling the luminosity variation of the optical aurora. 1. INTRODUCTION Ultralow frequency (ULF) magnetohydrodynamic (MHD) waves are important energy carriers in the process leading to the coupling of the Earth's magnetosphere and ionosphere [Goertz and Boswell, 1979]. In addition to magnetosphere-ionosphere coupling and the transmission of energy to the auroral ionosphere, a number of authors have suggested that MHD waves might also contribute directly to the energization of electrons which produce optical aurora [Hasegawa, 1976; Goertz, 1984; Samson et al., 1991]. MHD field line resonances have very thin latitudinal scale sizes [Walker et al., 1992] which are comparable with the latitudinal scale size of some discrete arcs, on the order of 50 km or less. If the transverse (latitudinal) scale sizes of these resonances in the upper ionosphere or magnetosphere become comparable to the ion gyroradius or the electron skin depth, then the resonances produce parallel (to the geomagnetic field) electric fields which can accelerate electrons to several hundred eV [HasegawaPaper number 93JA00435. 0148-0227/93/93 JA-00435505.00 important to note that MHD waves can modulate electron precipitation by a number of other mechanisms, in addition to electron inertia and kinetic Alfvtn waves. These additional mechanisms include modulation of the growth rates of ELF/ VLF waves which might be produced by compressional MHD waves [Sato et al., ...

In a substorm event of August 14, 1996, the Geotail satellite was at XGSM ∼ −10 RE aligned with the GOES 8 satellite in the X direction in the premidnight sector. Two Pi2 onsets were identified. Whereas the first onset was associated with a pseudobreakup, an auroral bulge developed following the second onset. At the pseudobreakup Geotail observed a fast (>900 km/s) plasma flow along with dipolarization, but the geosynchronous magnetic field became stretched subsequently. In contrast, for the main onset, the magnetic field dipolarized at GOES 8, although the associated total (time‐integrated) transport of magnetic flux at Geotail was no stronger than that for the pseudobreakup. It is suggested that the braking of the fast flow does not necessarily cause tail current disruption in a large scale, and there is an additional (or alternative) condition to suffice for an initial brightening to develop to a global substorm.