Abstract
Rocket‐based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere
Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
Department of Physics and Astronomy, University of Calgary, Calgary, Alberta, Canada
Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
Department of Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
The JOULE‐II sounding rocket salvo was launched from Poker Flat Rocket Range into weak pulsating aurora following a moderate
substorm at 0345 LT on 19 January 2007. We present in situ measurements of ion flow velocity and electric and magnetic fields
combined with neutral wind observations derived from ground observations of in situ chemical tracers. Measured ion drifts
in the 150–198 km and 92–105 km altitude ranges are consistent with
×
motion to within 16 m s−1 rms and with neutral wind velocity to within 20 m s−1, respectively. From these measurements we have calculated the ratio
of the ion cyclotron and ion collision frequencies, finding
= 1 at an altitude of 118 ± 0.3 km. Using direct measurements of ion current, we calculate the Joule heating rate and Pedersen
and Hall conductivity profiles for this moderately active event and find height‐integrated values of 390 W km−2 and 0.59 and 2.22 S, respectively. We also find that these values would have errors of up to tens of percent without coincident
neutral wind measurements, and presumably more so during more active conditions. Ion flow vectors were measured at a rate
of 125 s−1; however, no significant fluctuations were observed at spatial/temporal scales below ∼350 m and 0.5 s. Observational limits
were 5.5 m and 0.016 s.
Received 16 September 2008; accepted 6 February 2009; published 7 April 2009.
Citation: (2009), Rocket‐based measurements of ion velocity, neutral wind, and electric field in the collisional transition region of the auroral ionosphere, J. Geophys. Res., 114, A04306, doi:10.1029/2008JA013757.
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