English
norskBlar i forfatter "Brändström, Urban"
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The 3‐D Distribution of Artificial Aurora Induced by HF Radio Waves in the Ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-03-21)We present 3‐D excitation rate estimates of artificial aurora in the ionospheric F layer, induced by high‐frequency radio waves from the European Incoherent Scatter heating facility. Simultaneous imaging of the artificial aurora was done with four separate Auroral Large Imaging System stations, permitting tomography‐like 3‐D auroral reconstruction of the enhanced atomic oxygen emissions at 6,300, ... -
Eastward-expanding auroral surges observed in the post-midnight sector during a multiple-onset substorm
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-11-09)We present three eastward-expanding auroral surge (EEAS) events that were observed intermittently at intervals of about 15 min in the post-midnight sector (01:55–02:40 MLT) by all-sky imagers and magnetometers in northern Europe. It was deduced that each surge occurred just after each onset of a multiple-onset substorm, which was small-scale and did not clearly expand westward, because they were ... -
On mechanisms for high-frequency pump-enhanced optical emissions at 557.7 and 630.0gnm from atomic oxygen in the high-latitude F-region ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-13)The EISCAT (European Incoherent Scatter Scientific Association) Heating facility was used to transmit powerful high-frequency (HF) electromagnetic waves into the Fregion ionosphere to enhance optical emissions at 557.7 and 630.0 nm from atomic oxygen. The emissions were imaged by several stations of ALIS (Auroral Large Imaging System) in northern Sweden, and the EISCAT UHF incoherent scatter radar ... -
Reconstruction of electron precipitation spectra at the top of the upper atmosphere using 427.8 nm auroral images
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-12-13)We present an innovative method to reconstruct the characteristics of precipitated electrons in auroral regions from optical measurements. This method is based on an optimization implemented between numerical simulations of the Transsolo code and tomographic maps made from the Auroral Large Imaging System (ALIS) network. We focus on the Volume Emission Rate (VER) of the blue line 1NG 427.8 nm, which ... -
Reconstruction of precipitating electrons and three-dimensional structure of a pulsating auroral patch from monochromatic auroral images obtained from multiple observation points
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-07-12)In recent years, aurora observation networks using high-sensitivity cameras have been developed in the polar regions. These networks allow dimmer auroras, such as pulsating auroras (PsAs), to be observed with a high signal-to-noise ratio. We reconstructed the horizontal distribution of precipitating electrons using computed tomography with monochromatic PsA images obtained from three observation ... -
Solar illumination dependence of the auroral electrojet intensity: Interplay between the solar zenith angle and dipole tilt
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-18)The present study investigates the dependence of the local auroral electrojet (AEJ) intensity on solar illumination by statistically examining northward geomagnetic disturbances in the auroral zone in terms of the solar zenith angle χ. It is found that on the dayside, both westward and eastward electrojets (WEJ and EEJ) are more intense for smaller χ, suggesting that the solar extreme ultraviolet‐induced ...
