Transient production of F-region irregularities associated with TCV passage

Abstract

Abstract. Transient production of F-region plasma irregularities due to traveling convection vortices (TCVs) was investigated using the Super Dual Auroral Radar Network (SuperDARN) combined with ground magnetometer networks and the POLAR ultraviolet imager. We selected two largeamplitude (100-200 nT) TCV events that occurred on 22 May 1996 and 24 July 1996. It is found that the TCVassociated HF backscatter arises in blobs with spatial scale of a few hundreds km. They traveled following tailward bulk motion of the TCV across the three fields-of-view of the SuperDARN HF radars in the prenoon sector. The spectra in the blobs showed unidirectional Doppler velocities of typically 400-600 m/s, with flow directions away from the radar. These unidirectional velocities correspond to the poleward and/or eastward convective flow near the leading edge of upward field-aligned current. The backscatter blobs overlapped the poleward and westward part of the TCV-related transient aurora. It is likely that the transient backscatter blobs are produced by the three-dimensional gradient drift instabilities in the three-dimensional current system of the TCV. In this case, nonlinear rapid evolution of irregularities would occur in the upward field-aligned current region. The spectral width of the backscatter blob is typically distributed between 50 and 300 m/s, but sometimes it is over 400 m/s. This suggests that the temporal broad spectra over 400 m/s are produced by Pc1-2 bursts, while the background spectral width of 50-300 m/s are produced by the velocity gradient structure of convection vortices themselves.

Transient response of the Earth's magnetosphere to a localized density pulse in the solar wind: Simulation of traveling convection vortices

“…In the interval of 6.0–7.0 min, the negative potential peak moves from 1200 LT to 1100 LT at the latitude of ∼75°, giving an averaged propagation speed of ∼7 km/s. The propagation speeds of the simulated TCVs are comparable with magnetometer observations [ Murr et al , 2002; Kataoka et al , 2001, 2002, 2003a; Amm et al , 2002]. The skew of the simulated TCVs as moving away from noon is also consistent with magnetometer observations [e.g., Friis‐Christensen et al , 1988; Lühr and Blawert , 1994; Moretto et al , 1997; Murr et al , 2002].…”

Statistical identification of solar wind origins of magnetic impulse events

“…Consequently, the results in this paper are remarkably consistent with previous results in the literature. Our list consists of 825 MIEs over the 8 years and includes “typical” MIEs analyzed in past papers such as 24 January 1996 [ Clauer and Petrov , 2002], 22 May 1996 [ Kataoka et al , 2002, 2003], 24 July 1996 [ Sitar et al , 1998; Sibeck et al , 1999; Kataoka et al , 2003], 6 June 1997 [ Kataoka et al , 2001], and 27 May1998 [ Kataoka et al , 2002]. Also, 8 of 32 events analyzed by Murr and Hughes [2003] are included in our list.…”

Effects of sudden commencement on the ionosphere: PFISR observations and global MHD simulation

“…Smaller‐scale magnetic disturbances sometimes occur on the dayside high‐latitude magnetosphere, and they are often called magnetic impulse event [ Lanzerotti et al , ; Sibeck and Korotova , ], which are associated with smaller‐scale ionospheric convection vortices (traveling convection vortices, or TCVs) and FACs systems [ Friis‐Christensen et al , ; Glassmeier et al , ]. These smaller‐scale features are suggested to arise from localized solar wind dynamic pressure enhancement or dynamic processes in the foreshock region [e.g., Moretto et al , ; Zesta et al , ; Zesta , ; Murr et al , ; Sibeck et al , ; Murr and Hughes , ; Kataoka et al , ]. Kataoka et al [] simulated the FACs systems associated with TCVs by introducing a localized density perturbation and found that the FACs produced have the same polarities as those induced by large‐scale solar wind dynamic pressure enhancement but with much smaller‐scale sizes.…”

“…These smaller‐scale features are suggested to arise from localized solar wind dynamic pressure enhancement or dynamic processes in the foreshock region [e.g., Moretto et al , ; Zesta et al , ; Zesta , ; Murr et al , ; Sibeck et al , ; Murr and Hughes , ; Kataoka et al , ]. Kataoka et al [] simulated the FACs systems associated with TCVs by introducing a localized density perturbation and found that the FACs produced have the same polarities as those induced by large‐scale solar wind dynamic pressure enhancement but with much smaller‐scale sizes.…”

“…Ground‐based coherent scatter radar requires field‐aligned density irregularities in the F region in order to scatter the radar signals back. There have been a few studies on the effects of the SC on the radar performance [ Kataoka et al , ; Kane and Makarevich , ; Gillies et al , ]. Kataoka et al [] found enhanced F region irregularities excited due to local and strong F region density gradient within the convection flow vortex.…”