Open AccessAcceleration mechanism of high‐speed neutral wind observed in the polar lower thermosphere
Author(s) -
Tsuda T. T.,
Nozawa S.,
Oyama S.,
Motoba T.,
Ogawa Y.,
Shinagawa H.,
Nishitani N.,
Hosokawa K.,
Sato N.,
Lester M.,
Fujii R.
Publication year - 2009
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2008ja013867
Subject(s) - thermosphere , pressure gradient force , pressure gradient , wind speed , physics , atmospheric sciences , solar wind , drag , geophysics , ionosphere , wind gradient , meteorology , mechanics , wind direction , plasma , quantum mechanics
We analyzed data obtained with the European incoherent scatter (EISCAT) Svalbard Radar (ESR) at Longyearbyen (78.2°N, 16.0°E in geographic coordinates, 75.2°Λ in invariant latitude) to advance our understanding of the acceleration mechanism of the lower thermospheric neutral wind when the ionospheric convection becomes enhanced. The Advanced Composition Explorer satellite observed a southward turning in the interplanetary magnetic field at 0843 UT on 16 June 2005. At 0900 UT, the F region ion velocity and the lower thermospheric neutral wind (at 118‐km altitude) observed with the ESR began to accelerate significantly in the westward and northwestward directions, respectively. The neutral wind was remarkably accelerated within 1 hour from 0900 UT, and its speed became a value of ∼500 m s −1 at 1000 UT. The wind speed was significantly higher than a typical wind speed at 118 km. We evaluated the ion drag contribution on the generation of the high‐speed neutral wind. Our evaluation verifies that the ion drag force could not generate the high‐speed neutral wind within such a short time (∼1 hour). This result implies that the major driving force was the horizontal pressure gradient force induced by the Joule heating. We deduced the contribution of the pressure gradient force based on a quantitative estimation of the Joule‐heating‐induced pressure gradient from the ESR and the Super Dual Auroral Radar Network data. We concluded that the pressure gradient force was the most probable force in this event.