AE and DE mass spectrometer observations relevant to the shuttle glow

Recent work suggested that NO2 may be responsible for the observed continuum glow near surfaces of the space shuttle. The observations of atomic nitrogen (N) are reported at shuttle altitudes using mass spectrometers, giving special attention to the surface reactions of N relevant to the production of NO2 on spacecraft surfaces. Data from two semi-open sources mass spectrometers, the OSS instruments on the Atmosphere Explorer-C and -D satellites, and the closed source Neutral Atmospheric Composition Spectrometer (NACS) on the Dynamic Explorer-2 satellite are presented to show the similar behavior of NO in each case and the contrasting behavior of NO2. Although signals of NO and NO2 are highly dependent on surface temperature and surface composition, it appears that direct exposure of ion source surfaces to rammed gas is a necessary condition for the production of large amounts of NO2. Evidence that elevated surface temperatures can significantly reduce the production of NO2, likely by causing more rapid desorption of NO from these surfaces, is presented

Atomic nitrogen densities near the polar cusp

The neutral atmospheric composition spectrometer on board the Dynamics Explorer 2 spacecraft sampled several major and minor thermospheric gases including atomic nitrogen. A selection of passes over the polar cusp that provide a quantitative measure of N densities in this region and provide evidence of localized density increases due to soft particle precipitation is presented. Increases in N densities are frequently observed but are smaller than accompanying increases in N2 densities. The observations support earlier studies suggesting that N densities increase more rapidly than O densities during periods of high solar EUV flux and N densities are larger in the summer hemisphere than in the winter hemisphere. A series of passes in February 1983, late in the lifetime of DE 2, indicated N densities at 200 km altitude were a factor of 2 larger near the southern cusp than near the northern cusp

Analysis of atomic thermospheric nitrogen density

A NASA grant provided support for a research project at Augsbury College, Minneapolis, Minnesota for the analysis of atomic nitrogen density data obtained by the Neutral Atmospheric Composition Spectrometer (NACS) on board the Dynamics Explorer-2 satellite. Initial funding was for an exploratory study of the feasibility of obtaining ambient densities of N from source densities of NO. Funding was continued under the Dynamics Explorer Guest Investigator Program when initial studies indicated probable success in obtaining such ambient densities. The major scientific focus of the later work was to be to characterize the behavior of N densities at high latitudes

Field line distribution of density at \u3ci\u3eL\u3c/i\u3e=4.8 inferred from observations by CLUSTER

For two events observed by the CLUSTER space- craft, the field line distribution of mass density ρ was inferred from Alfve ́n wave harmonic frequencies and compared to the electron density ne from plasma wave data and the oxy- gen density nO+ from the ion composition experiment. In one case, the average ion mass M≡ρ/ne was about 5amu (28 October 2002), while in the other it was about 3 amu (10 September 2002). Both events occurred when the CLUSTER 1 (C1) spacecraft was in the plasmatrough. Nevertheless, the electron density ne was significantly lower for the first event (ne =8 cm−3 ) than for the second event (ne =22 cm−3 ), and this seems to be the main difference leading to a dif- ferent value of M. For the first event (28 October 2002), we were able to measure the Alfve ́n wave frequencies for eight harmonics with unprecedented precision, so that the er- ror in the inferred mass density is probably dominated by factors other than the uncertainty in frequency (e.g., mag- netic field model and theoretical wave equation). This field line distribution (at L=4.8) was very flat for magnetic lati- tude |MLAT|20◦ but very steeply increasing with respect to |MLAT| for |MLAT|40◦. The total variation in ρ was about four orders of magnitude, with values at large |MLAT| roughly consistent with ionospheric values. For the second event (10 September 2002), there was a small local maxi- mum in mass density near the magnetic equator. The in- ferred mass density decreases to a minimum 23% lower than the equatorial value at |MLAT|=15.5◦, and then steeply in- creases as one moves along the field line toward the iono- sphere. For this event we were also able to examine the spa- tial dependence of the electron density using measurements of ne from all four CLUSTER spacecraft. Our analysis in- dicates that the density varies with L at L∼5 roughly like L−4, and that ne is also locally peaked at the magnetic equa- tor, but with a smaller peak. The value of ne reaches a den- sity minimum about 6% lower than the equatorial value at |MLAT|=12.5◦, and then increases steeply at larger values of |MLAT|. This is to our knowledge the first evidence for a local peak in bulk electron density at the magnetic equa- tor. Our results show that magnetoseismology can be a useful technique to determine the field line distribution of the mass density for CLUSTER at perigee and that the distribution of electron density can also be inferred from measurements by multiple spacecraft

Time-resolved ferromagnetic resonance in epitaxial Fe1-xCox films

Magnetodynamics in epitaxial Fe1-xCox films on GaAs (100) are studied using time-resolved ferromagnetic resonance, in which the free precession of the magnetization after an impulsive excitation is measured using the polar Kerr effect. The sample is rotated with respect to the static and pulsed field directions, providing a complete mapping of the free energy surface and characteristic relaxation times. The magnetic response can be simulated with a simple coherent rotation model except in the immediate vicinity of switching fields. Bulk and surface anisotropies are identified, and unusual dynamics associated with the coexistence of cubic and uniaxial anisotropies are observed.Comment: PDF - 4 figure

Simultaneous traveling convection vortex events and Pc1 wave bursts at cusp latitudes observed in Arctic Canada and Svalbard

Traveling convection vortices (TCVs), which appear in ground magnetometer records at near‐cusp latitudes as solitary ~5 mHz pulses, are a signature of dynamical processes in the ion foreshock upstream of the Earth's bow shock that can stimulate transient compressions of the dayside magnetosphere. These compressions can also increase the growth rate of electromagnetic ion cyclotron (EMIC) waves, which appear in ground records at these same latitudes as bursts of Pc1 pulsations. In this study we have identified TCVs and simultaneous Pc1 burst events in two regions, Eastern Arctic Canada and Svalbard, using a combination of fluxgate magnetometers and search coil magnetometers in each region. By looking for the presence of TCVs and Pc1 bursts in two different sequences, we have found that the distribution of Pc1 bursts was more tightly clustered near local noon than that of TCV events, that neither TCVs nor Pc1 bursts were always associated with the other, and even when they occurred simultaneously their amplitudes showed little correlation. Magnetometer data from GOES‐12 were also used to characterize the strength of the magnetic compressions at geosynchronous orbit near the magnetic equator. Compressions > 2 nT at GOES‐12 occurred during 57% of the Canadian TCV events, but during ~85% of the simultaneous TCV/Pc1 burst events. There was again little evident correlation between TCV and GOES‐12 compression amplitudes. We have also documented unusually low EMIC wave activity during this deep solar minimum interval, and we attribute the low occurrence percentage of combined events in this study to this minimum. Key Points TCVs and Pc1 bursts often occur together in high‐latitude magnetometer data Pc1 events were more tightly clustered near local noon than TCV events Pc1 activity was unusually low during the solar activity minimum in 2008–2010.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/101826/1/jgra50604.pd

First simultaneous measurements of waves generated at the bow shock in the solar wind, the magnetosphere and on the ground

On 5 September 2002 the Geotail satellite observed the cone angle of the Interplanetary Magnetic Field (IMF) change to values below 30° during a 56 min interval between 18:14 and 19:10 UT. This triggered the generation of upstream waves at the bow shock, 13 <I>R<sub>E</sub></I> downstream of the position of Geotail. Upstream generated waves were subsequently observed by Geotail between 18:30 and 18:48 UT, during times the IMF cone angle dropped below values of 10°. At 18:24 UT all four Cluster satellites simultaneously observed a sudden increase in wave power in all three magnetic field components, independent of their position in the dayside magnetosphere. We show that the 10 min delay between the change in IMF direction as observed by Geotail and the increase in wave power observed by Cluster is consistent with the propagation of the IMF change from the Geotail position to the bow shock and the propagation of the generated waves through the bow shock, magnetosheath and magnetosphere towards the position of the Cluster satellites. We go on to show that the wave power recorded by the Cluster satellites in the component containing the poloidal and compressional pulsations was broadband and unstructured; the power in the component containing toroidal oscillations was structured and shows the existence of multi-harmonic Alfvénic continuum waves on field lines. Model predictions of these frequencies fit well with the observations. An increase in wave power associated with the change in IMF direction was also registered by ground based magnetometers which were magnetically conjunct with the Cluster satellites during the event. To the best of our knowledge we present the first simultaneous observations of waves created by backstreaming ions at the bow shock in the solar wind, the dayside magnetosphere and on the ground

Investigation of EMIC wave scattering as the cause for the BARREL 17 January 2013 relativistic electron precipitation event: A quantitative comparison of simulation with observations

Abstract Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution, and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date. Key PointsQuantitative analysis of the first balloon REP with closely conjugate EMIC wavesOur simulation suggests EMIC waves to be a viable cause for the REP eventThe adopted model is proved to be applicable to simulating the REP event