English
norskBlar i forfatter "Johnsen, Magnar Gullikstad"
Viser treff 21-32 av 32
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On the correction of temperatures derived from meteor wind radars due to geomagnetic activity
(Journal article; Tidsskriftartikkel; Peer reviewed, 2021-08-12)Radars used to observe meteor trails in the mesosphere deliver information on winds and temperature. Use of these radars is becoming a standard method for determining mesospheric dynamics and temperatures worldwide due to relatively low costs and ease of deployment. However, recent studies have revealed that temperatures may be overestimated in conditions such as high geomagnetic activity. The effect ... -
On the nightglow polarisation for space weather exploration
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-07-28)We present here observations of the polarisation of four auroral lines in the auroral oval and in the polar cusp using a new ground polarimeter called <i>Petit Cru</i>. Our results confirm the already known polarisation of the red line, and show for the first time that the three other lines observed here (namely 557.7 nm, 391.4 nm and 427.8 nm) are polarised as well up to a few percent. We show that ... -
On the relation between ionospheric parameters and sunspot number
(Journal article; Tidsskriftartikkel; Peer reviewed, 2020-05-27)In a recent study, mid-latitude ionospheric parameters were compared with solar activity; it was suggested that the relationship between these, earlier assumed stable, might be changing with time (Lastovicka, 2019). Here, the information is extended to higher latitude (69.6°N, 19.2E) and further back in time. For the ionospheric F-region (viz. the critical frequency, FoF2) the same behaviour is seen ... -
The polarisation of auroral emissions: A tracer of the E region ionospheric currents
(Journal article; Tidsskriftartikkel; Peer reviewed, 2022-05-20)It is now established that auroral emissions as measured from the ground are polarised. The question of the information given by this polarisation is still to be explored. This article shows the results of a coordinated campaign between an optical polarimeter and several ground-based instruments, including magnetometers, the EISCAT VHF radar, and complementary luminance meters in the visible ... -
Possible influence of variations in the geomagnetic field on migration paths of snow buntings
(Journal article; Tidsskriftartikkel; Peer reviewed, 2019-07-24)A hypothesis is proposed wherein changes in the Earth’s magnetic field affect the migratory paths of snow buntings (Plectrophenax nivalis), and in particular from wintering grounds in the Russian/Ukrainian steppes to breeding grounds on Svalbard and with a typical stopover in Finnmark in northern Norway. If one were to assume ignorance of the secular movement of the magnetic north pole approximately ... -
Real-time determination and monitoring of the auroral electrojet boundaries
(Journal article; Tidsskriftartikkel; Peer reviewed, 2013)A method for nowcasting of the auroral electrojet location from real-time geomagnetic data in the European sector is presented. Along the auroral ovals strong electrojet currents are flowing. The variation in the geomagnetic field caused by these auroral electrojets is observed on a routine basis at high latitudes using ground-based magnetometers. From latitude profiles of the vertical component of ... -
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 ... -
Seasonal and solar cycle variations of thermally excited 630.0 nm emissions in the polar ionosphere
(Journal article; Tidsskriftartikkel; Peer reviewed, 2018)Solar cycle and seasonal variations have been found in the occurrence of strong thermally excited 630.0 nm emissions in the polar ionosphere. Measurements from the European Incoherent Scatter Svalbard Radar have been used to derive the thermal emission intensity. Thermally excited emissions have been found to maximize at solar maximum with peak occurrence rate of ∼40% compared to ∼2% at solar minimum. ... -
Simple Minimalistic Offline Plotting of CADI Data Files
(Research report; Forskningsrapport, 2020)A critical element in any observational program is to remotely monitor instrument health and performance. Simple real-time plots provide this type of information and in addition they contain valuable space weather information for nowcasting and acquisition of situational awareness. Several software packages exist for plotting and scaling (analysis) of ionospheric soundings [1,2] using the Canadian ... -
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 ... -
A statistical study of convective and dynamic instabilities in the polar upper mesosphere above Tromsø
(Journal article; Tidsskriftartikkel; Peer reviewed, 2023-02-15)We have studied the convective (or static) and dynamic instabilities between 80 and 100 km above Tromsø (69.6° N, 19.2° E) using temperature and wind data of 6 min and 1 km resolutions primarily almost over a solar cycle obtained with the sodium lidar at Tromsø. First, we have calculated Brunt–Väisälä frequency (N) for 339 nights obtained from October 2010 to December 2019, and the Richardson ... -
Wavelet-based analogous phase scintillation index for high latitudes
(Journal article; Tidsskriftartikkel; Peer reviewed, 2015-07-14)The Global Positioning System (GPS) performance at high latitudes can be severely affected by the ionospheric scintillation due to the presence of small-scale time-varying electron density irregularities. In this paper, an improved analogous phase scintillation index derived using the wavelet-transform-based filtering technique is presented to represent the effects of scintillation regionally at ...
