Phase Coherence on Open Field Lines Associated with FLRs Abiyu Nedie, Frances Fenrich & Robert Rankin University of Alberta Edmonton, Alberta, Canada 2011 SuperDARN Meeting Hanover May 30 – June 3, 2011

Outline of the Talk  Introduction Magnetospheric disturbances Field Line Resonance & Excitation Mechanisms  Events from our Observations  Sources of Pulsations MHD waves in the solar wind  What we ‘ve learnt from this event 2

Outline of the Talk  Introduction Magnetospheric disturbances Field Line Resonance & Excitation Mechanisms  Events from our Observations Phase Coherence on open field lines 1 st & 2 nd order harmonic FLR signatures  Source of Pulsation MHD waves in the solar wind  Conclusions 3

Magnetospheric disturbances  The entire dayside MP & LLBL can map along the magnetic field lines in to a relatively small area of the ionosphere  Disturbances in Magnetosphere can be followed by their signatures in the ionosphere  High latitude ionosphere provides a screen on which to view processes in the Magnetosphere & interactions b/n Magnetosphere, Solar wind, IMF  Ground based radars, magnetometers, optical instruments can be used to study magnetospheric disturbances  Significant advances in understanding the interaction b/n the SW & the Magnetosphere have been made through the study of ionospheric signatures (eg. Geotail & SuperDARN echoes will be used in this talk) 4

Theory of MHD Waves and Field Line Resonance There are two decoupled modes of MHD waves in homogeneous cold plasma. 1. Shear Alfven waves propagate along the magnetic field lines.  and reflect back from the highly conducting ionospheres.  As a result, the standing oscillation of the field lines could be driven 2. Fast compressional waves propagates across the magnetic field.  Fast compressional waves in the outer magnetosphere can couple to shear Alfven Waves to drive the so-called FLRs. FLR Excitation Mechanisms 1.KH surface wave on the Magnetopause, Chen & Hasegawa (1974) 2.Abrupt changes in the solar wind dynamic pressure excites compressional waves, Kivelson & Southwood (1985, 1986) 3.MHD waves in the Solar wind, Walker (2002) 5

Geotail Orbit, 2000/12/26, UT

Oscillations in time domain (Spacecraft and Radar data), UT g=47 g=49 g=17 g=16

Frequency Spectra of Spacecraft and Radar data, UT

Contour plot of 0.8 mHz wave from Kodiak HF radar, b=2-10, g=35-48, UT

Contour plot of 0.8 mHz wave from Hanksalami HF radar, b=5-15, g=38-55, UT

Ultraviolet Imager, OCB ≈ 71/72 ≈ 73/74

SuperDARN swd OCB ≈ 71/72 OCB ≈ 73/74

0.8-mHz FLR from Pykkvibaer b=0-15, g=15-30, UT

Contour plot of the power spectra at 0.8 -mHz from the Pykkvibaer, g=17, b=1-15

Spectral Power and Phase vs Latitude for the 0.8-mHz resonance from Pykkvibaer, g=17, b=1-15

Overlay of Pykkvibaer (b=13, g=16) and Geotail (Bz)

Cross power spectral density and and coherence of Pykkvibaer (b=13, g=16) with Geotail Bz time shifted to (15min)

Comparison of convection flow speed and wave phase velocity H P K VpK ≅ 670m/s 500<Vc<1000 m/s VpP ≅ 600m/s 500<Vc<900m /s VpH ≅ 1440m/s 400<Vc<700m/ s

Conclusions A completely new feature of phase coherence on open field lines at exactly the same resonant frequency is found at the same time. Clear and discernible signatures of 1 st and 2 nd order harmonics at 0.8-mHz are observed Results in this study support the hypothesis that the coherent phase on open field lines and the discrete frequency FLR at 0.8-mHz were being driven at the same time by an external wave source in the solar wind at 0.8-mHz. SuperDARN could be used as a potential tool of providing a direct diagnostics on how MHD waves in the solar wind could enter into magnetosphere right at the boundary -test various theories on how energy is transported into the boundary of the magnetosphere in a global scale view through continuous monitoring of the high latitude ionospheric convection

Conclusions discernible FLR signatures at 0.8-mHz, extended azimuthally along the latitude contour are found to be associated source in the Solar wind. A completely new feature of phase coherence on open field lines at exactly the same resonant frequency is found at the same time. Clear signatures of second harmonics are observed Results in this study support the hypothesis that the coherent phase on open field lines and the discrete frequency FLR at 0.8-mHz were being driven by an external wave source in the solar wind at the same discrete frequency. SuperDARN could be used as a potential tool of providing a direct diagnostics on how MHD waves in the solar wind could enter into magnetosphere right at the boundary -test various theories on how energy is transported into the boundary of the magnetosphere through continuous monitoring of the high latitude ionospheric convection