First In-Situ Observations of Waveguide Modes in the Dayside Magnetosphere by Cluster

Details First In-Situ Observations of Waveguide Modes in the Dayside Magnetosphere by Cluster First In-Situ Observations of Waveguide Modes in the Dayside Magnetosphere by Cluster

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsm33a1746c&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SM33A-1746

Physics

2712 Electric Fields (2411), 7836 Mhd Waves And Instabilities (2149, 2752, 6050), 7868 Wave/Wave Interactions

Scientific paper

We present for the first time convincing evidence that the Cluster satellites observed a waveguide mode in the dayside magnetosphere following a minor enhancement in the solar wind dynamic pressure. The wave was observed in the vicinity of the spacecraft's perigee outside the plasmasphere. The waveguide mode lasted for at least one hour and had a frequency of 14 mHz. Poynting flux measurements show that at the beginning of the observations 50% of the wave's energy was reflected at some boundary in the inner magnetosphere. An hour later, when the last satellite observed the wave, only about 10% were reflected, i.e. the wave's character changed from partially reflected to almost purely propagating radially inwards in the course of the event. The theory of waveguide modes predicts that energy of the compressional wave is converted to standing Alfvénic waves where the frequency of the compressional driver matches the local fundamental eigenfrequency of the field line. Ground based magnetometers in the vicinity of the resonant field line indeed registered several pulsations during the event. Latitude profiles of Fourier power and phase show that these are Field Line Resonances (FLRs), supporting the model predictions. We show that the small amplitudes of the FLRs are consistent with the energy input of the compressional mode into the dayside magnetosphere. From considerations about the location of the turning point of the compressional wave we are able to estimate the azimuthal wave number to be small, between 1 and 2.

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