Velocity of E-region HF echoes under strongly-driven electrojet conditions
Data collected by the Stokkseyri SuperDARN HF radar simultaneously at short and far ranges are used to investigate the relationship between the velocity of E-region HF echoes, <I><B>E</I></B>×<I><B>B</I></B> electron drift and the isotherm...
Main Authors: | , , , , |
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Format: | Article |
Language: | English |
Published: |
Copernicus Publications
2012-01-01
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Series: | Annales Geophysicae |
Online Access: | https://www.ann-geophys.net/30/235/2012/angeo-30-235-2012.pdf |
Summary: | Data collected by the Stokkseyri SuperDARN HF radar simultaneously at short
and far ranges are used to investigate the relationship between the velocity
of E-region HF echoes, <I><B>E</I></B>×<I><B>B</I></B> electron drift and the
isothermal ion-acoustic speed <I>C</I><sub>S</sub>. The work targets large <I><B>E</I></B>×<I><B>B</I></B> drifts of >1000 m s<sup>−1</sup> and observations predominantly along the
flow. By considering the EISCAT temperature and electric field data, an
empirical relationship between the <I><B>E</I></B>×<I><B>B</I></B> drift velocity and <I>C</I><sub>S</sub> is
established for a number of ionospheric heights. For the Stokkseyri HF radar
beams oriented roughly along the <I><B>E</I></B>×<I><B>B</I></B> direction, the observed
E-region HF velocities are consistent with the <I>C</I><sub>S</sub> values at the bottom
of the electrojet but not at its center. For a subset of the data with
smooth and consistent velocity variation with the beam azimuth at both short
and far radar ranges the velocity varies according to the cosine law. For
the E-region echoes, the proportionality coefficient in the cosine law is
consistent with the <I>C</I><sub>S</sub> values at the bottom of the electrojet. For these
events, the E-region velocity maximum is shown to be between the <I><B>E</I></B>×<I><B>B</I></B>
and electric field directions. The statistically average shift is ~20° and it increases slightly with the <I><B>E</I></B>×<I><B>B</I></B> magnitude. |
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ISSN: | 0992-7689 1432-0576 |