Inferred electric field variability in the polarization jet from Millstone Hill E region coherent scatter observations

Abstract

[1] We investigate the fine-scale structure of the subauroral electric field in the vicinity of the polarization jet and subauroral ion drift (SAID) using coherent E region backscatter observed with the Millstone Hill 440 MHz UHF radar during a moderately disturbed period (K p = 5) on 13 November 1998. We use a combination of data obtained at high time and spatial resolution and radar response modeling, incorporating magnetic aspect angle sensitivity and radar antenna beam shape. The modeled radar response function depends not only on the magnetic and radar pointing geometry but also on the altitude and extent of the irregularity layer. In addition to modeling of the radar system response, an optimal, regularized deconvolution technique is used to resolve fine-scale spatial structure from the relatively long pulse length used. At the 440 MHz Millstone radar frequency, coherent backscattered power is a linear function of electric field amplitude, and we are able to relate changes in the range variation of deconvolved power to spatial/temporal structure in the electric field. We observe the polarization jet to have superimposed multiple instances of narrow (0.1°) intense SAID configuration electric fields having lifetimes as short as 1.5 min and gradients on their equatorward edge as large as 4 mV/m per kilometer. Simultaneous DMSP satellite observations of westward ion drift across our experimental field of view confirms our interpretion of the radar data in terms of a subauroral polarization jet structure spanning over 3°latitude moving poleward at 250 -400 m/s velocity (cross-L-shell) past the radar beam with superimposed intense SAID-like electric fields.

Millstone Hill coherent‐scatter radar observations of electric field variability in the sub‐auroral polarization stream

“…Foster and Tetenbaum [1991, Figures 2, 5, 6, and 7] present additional observations of near-periodic variations of the coherent scatter intensity seen from Millstone Hill. It is suggested, in agreement with Erickson et al [2002], that such localized electric field intensifications, which exhibit many of the characteristics of the narrow SAID features described in the literature, arise as wavelike perturbations within the broader SAPS channel. Figure 5.…”

“…[8] Erickson et al [2002] used a 'slit-camera' experiment to provide a detailed look at the structure and variability of the polarization stream (SAPS) electric fields as the SAPS channel receded poleward past the radar beam. Their observations indicate that the spatial extent of the SAPS electric field can change in under one minute from a widespread, structureless, distributed field, to a system of very narrow features (less than 0.1 degrees latitude; $10 km range extent), which exhibit the observational characteristics of SAID events.…”

“…Foster and Tetenbaum [1991] have described a number of coherentscatter experiments run in this pointing position and have described the near-sinusoidal variations in coherent amplitude which often have been observed. In this case, a short pulse was used with the fast sampling and deconvolution technique described by Erickson et al [2002]. Figure 1 presents high-resolution observations of the spatial/temporal variation of the sub-auroral electric field magnitude during an interval when the SAPS convection channel progressed equatorward.…”

Electromagnetic Wave Structures Within Subauroral Polarization Streams

“…However, observations from Defense Meteorological Satellite Program (DMSP) satellites and Millstone Hill radar [Erickson et al, 2002] often indicate the presence of irregular substructures with scale size of order tens km within SAPS. While Maynard et al [1980] mentioned that storm time electric fields adjacent to the plasmapause were strongly variable, consequences of their observations were not pursued.…”

Observations of high-velocity SAPS-like flows with the King Salmon SuperDARN radar

“…In the past, the Millstone Hill (MH) incoherent scatter radar has been successfully used to study SAPS (Yeh et al, 1991;Foster and Vo, 2002;Erickson et al, 2002;Foster et al, 2005). Another opportunity to study SAPS is to utilize the Super Dual Auroral Radar Network (SuperDARN) HF radars (Greenwald et al, 1995).…”