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Survey of coherent approximately 1 hz waves in mercury's inner magnetosphere from messenger observations
| Content Provider | NASA Technical Reports Server (NTRS) |
|---|---|
| Author | Slavin, James A. Solomon, Sean C. Anderson, Brian J. Korth, Haje Boardsen, Scott A. Schriver, David |
| Copyright Year | 2012 |
| Description | We summarize observations by the MESSENGER spacecraft of highly coherent waves at frequencies between 0.4 and 5 Hz in Mercury's inner magnetosphere. This survey covers the time period from 24 March to 25 September 2011, or 2.1 Mercury years. These waves typically exhibit banded harmonic structure that drifts in frequency as the spacecraft traverses the magnetic equator. The waves are seen at all magnetic local times, but their observed rate of occurrence is much less on the dayside, at least in part the result of MESSENGER's orbit. On the nightside, on average, wave power is maximum near the equator and decreases with increasing magnetic latitude, consistent with an equatorial source. When the spacecraft traverses the plasma sheet during its equatorial crossings, wave power is a factor of 2 larger than for equatorial crossings that do not cross the plasma sheet. The waves are highly transverse at large magnetic latitudes but are more compressional near the equator. However, at the equator the transverse component of these waves increases relative to the compressional component as the degree of polarization decreases. Also, there is a substantial minority of events that are transverse at all magnetic latitudes, including the equator. A few of these latter events could be interpreted as ion cyclotron waves. In general, the waves tend to be strongly linear and characterized by values of the ellipticity less than 0.3 and wave-normal angles peaked near 90 deg. Their maxima in wave power at the equator coupled with their narrow-band character suggests that these waves might be generated locally in loss cone plasma characterized by high values of the ratio beta of plasma pressure to magnetic pressure. Presumably both electromagnetic ion cyclotron waves and electromagnetic ion Bernstein waves can be generated by ion loss cone distributions. If proton beta decreases with increasing magnetic latitude along a field line, then electromagnetic ion Bernstein waves are predicted to transition from compressional to transverse, a pattern consistent with our observations. We hypothesize that these local instabilities can lead to enhanced ion precipitation and directly feed field-line resonances. |
| File Size | 938855 |
| Page Count | 14 |
| File Format | |
| Alternate Webpage(s) | http://archive.org/details/NASA_NTRS_Archive_20150004119 |
| Archival Resource Key | ark:/13960/t0dv6j508 |
| Language | English |
| Publisher Date | 2012-09-22 |
| Access Restriction | Open |
| Subject Keyword | Ultra-low-frequency Mercury Messenger Plasma Layers Magnetometers Ion Cyclotron Radiation Plasma Pressure Data Processing Frequencies Ellipticity Equators Histograms Wave Propagation Coherent Radiation Spectrograms Bernstein Energy Principle Mercury Planet Eigenvalues Eigenvectors Sky Surveys Astronomy Messenger Spacecraft Polarization Waves Planetary Magnetospheres Analysis of Variance Ntrs Nasa Technical Reports Server (ntrs) Nasa Technical Reports Server Aerodynamics Aircraft Aerospace Engineering Aerospace Aeronautic Space Science |
| Content Type | Text |
| Resource Type | Article |
