Observations of polar patches generated by solar wind Alfvén wave coupling to the dayside magnetosphere

Abstract

Abstract. A long series of polar patches was observed by ionosondes and an all-sky imager during a disturbed period (K p 7-and IMF B z < 0). The ionosondes measured electron densities of up to 9´10 11 m A3 in the patch center, an increase above the density minimum between patches by a factor of $4.5. Bands of F-region irregularities generated at the equatorward edge of the patches were tracked by HF radars. The backscatter bands were swept northward and eastward across the polar cap in a fan-like formation as the afternoon convection cell expanded due to the IMF B y > 0. Near the north magnetic pole, an all-sky imager observed the 630-nm emission patches of a distinctly band-like shape drifting northeastward to eastward. The 630-nm emission patches were associated with the density patches and backscatter bands. The patches originated in, or near, the cusp footprint where they were formed by convection bursts (¯ow channel events, FCEs) structuring the solar EUV-produced photoionization and the particle-produced auroral/cusp ionization by segmenting it into elongated patches. Just equatorward of the cusp footprint Pc5 ®eld line resonances (FLRs) were observed by magnetometers, riometers and VHF/HF radars. The AC electric ®eld associated with the FLRs resulted in a poleward-progressing zonal¯ow pattern and backscatter bands. The VHF radar Doppler spectra indicated the presence of steep electron density gradients which, through the gradient drift instability, can lead to the generation of the ionospheric irregularities found in patches. The FLRs and FCEs were associated with poleward-progressing DPY currents (Hall currents modulated by the IMF B y ) and riometer absorption enhancements. The temporal and spatial characteristics of the VHF backscatter and associated riometer absorptions closely resembled those of poleward moving auroral forms (PMAFs). In the solar wind, IMP 8 observed large amplitude Alfve n waves that were correlated with Pc5 pulsations observed by the ground magnetometers, riometers and radars. It is concluded that the FLRs and FCEs that produced patches were driven by solar wind Alfve n waves coupling to the dayside magnetosphere. During a period of southward IMF the dawn-dusk electric ®eld associated with the Alfve n waves modulated the subsolar magnetic reconnection into pulses that resulted in convection¯ow bursts mapping to the ionospheric footprint of the cusp.

Temporal Variation of Solar Wind in Controlling Solar Wind‐Magnetosphere‐Ionosphere Energy Budget

“…Presumably, magnetic reconnection between the southward component of the IMF and magnetospheric magnetic fields during these events is the dominant process for the energy transfer from the solar wind to the magnetosphere. Quasiperiodic or pulsed magnetic reconnection in this case may lead to quasiperiodic or pulsed ionospheric convective flows and joule heating, as well as quasiperiodic cusp particle precipitation, polar cap patches, and periodic penetration electric fields in the equatorial ionosphere (e.g., Prikryl et al, ; Rae et al, ; Rodríguez‐Zuluaga et al, ; Wei et al, ).…”

Polar Ion Temperature Variations During the 22 January 2012 Magnetic Storm

“…Due to these modulating effects, there is a direct correspondence between the B z maxima and E y minima and oppositely, between the B z minima and E y maxima (Prikryl et al, ). Furthermore, the similar amplitudes of the oscillating IEF E y and E z components and their opposite phase imply that these Alfven waves coupled to the subsolar magnetopause—the region of transient reconnection—and modulated the dayside magnetopause reconnection (Prikryl et al, ) leading to mass, momentum, and energy injections from the solar wind to the coupled M‐I‐T system. Solar wind plasma injections into the ring current via magnetic reconnections are indicated by the sudden variations seen in the SYM‐H and ASY data (see shaded intervals).…”

“…Figure is constructed with IMF, solar wind velocity, and SYM‐H data in order to further demonstrate the presence of solar wind Alfven waves and to identify their directions of propagation based on the methodology of Prikryl et al (, ).…”

“…Then, the fluctuating B y and B z components were anticorrelated with their respective fluctuating solar wind V y and V z components. These anticorrelations imply the presence of solar wind Alfven waves propagating antisunward or earthward (Prikryl et al, ) and carrying antisunward (or earthward) Poynting flux from the interplanetary generator to the coupled I‐T system via large‐scale FACs (Cowley, ). During 1200–1800 UT, when Sc‐3 and Sc‐6 occurred, the positive B x pointed toward the Sun.…”

Imaging meso‐scale ionospheric structures

“…Some physical mechanism must be occurring that causes the smooth large scale electron concentration to be disrupted, forming the smaller scale irregularities, as they are known. In the case of polar cap patches the current dominant theory is that the Gradient Drift Instability causes these irregularities but alternative mechanisms exist [ Carlson , 2007; Carlson et al , 2004; Coley and Heelis , 1995, 1998; Dandekar , 2002; Milan et al , 2002; Prikryl et al , 1999; Rodger et al , 1994; Valladares et al , 1994, 1996, 1998; Walker et al , 1999; Wood and Pryse , 2010; Zhang et al , 2011].…”