Tuesday, 17 May 2011

Wind Fluctuations During Pulsating Aurora at Tromsø

It's Tuesday, and time for another blog post about EISCAT-related science results. This time we look at a study combining radar measurements with a rocket campaign and optical observations. If you want to increase visibility for your science results, please let us know!

Simultaneous observations were conducted with a Fabry-Perot Interferometer (FPI) and an all-sky camera, both at a wavelength of 557.7 nm, as well as the EISCAT UHF radar during the Dynamics and Energetics of the Lower Thermosphere in Aurora 2 (DELTA-2) rocket campaign in January 2009. This paper concentrates on two events during periods of pulsating aurora. The lower-thermospheric wind velocity measured with the FPI showed obvious fluctuations in both vertical and horizontal components. Of particular interest is that the location of the fluctuations was found to be in a darker area that appeared within the pulsating aurora.

During the same time period, the EISCAT radar observed sporadic enhancements in the backscattered power from the F region, which suggests the presence of low-energy electron precipitation (<=1 keV) coinciding with the increase of the amplitude of the electromagnetic wave (order of 10 Hz or higher). While we have not yet identified the dominant mechanism causing the fluctuations in FPI-derived wind velocity during pulsating aurora, the frictional heating energy dissipated by the electric-field perturbations may be responsible for the increase in ionospheric thermal energy thus modifying the local wind dynamics in the lower thermosphere.

Figure: Top panels show the temporal variations in vertical wind speed and fringe peak count at zenith, respectively, measured with the FPI (557.7 nm) on 26 January 2009. Vertical bars are 2σ uncertainty. Bottom panels show images taken with the ASC at 557.7 nm during pulsating aurora, which are mapped in geographic co-ordinates at a height of 110 km. Black dots and red crosses indicate the location of the FPI and the EISCAT UHF observation positions, respectively. Black arrows correspond to the horizontal component of the FPI-derived neutral wind velocity (scale in image of 01:15 UTC).

Original article: S. Oyama, K. Shiokawa, J. Kurihara, T. T. Tsuda, S. Nozawa, Y. Ogawa, Y. Otsuka, and B. J. Watkins, Lower-thermospheric wind fluctuations measured with an FPI in pulsating aurora at Tromsoe, Norway, Ann. Geophys.28, 1847-1857, 2010.

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