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. (2015). The auroral red line polarisation: modelling and measurements
. Journal of Space Weather and Space Climate, 5, A26.
Abstract: In this work, we model the polarisation of the auroral red line using the electron impact theory developed by Bommier et al (2011). This theory enables the computation of the distribution of the Degree of Linear Polarisation (DoLP) as function of height if the flux of precipitated electrons is provided as input.\\
An electron transport code is used to infer the stationary electron flux at each altitude in the ionosphere as a function of energy and pitch angle. Using adequate cross sections, the integral of this electron flux over energy and pitch angle provides an anisotropy parameter from which the theoretical local DoLP can be computed at each altitude. The modelled DoLP is then derived by integrating along the line-of-sight.\\
Depending on the integration length, the modelled DoLP ranges between 0.6\% for a very long integration length, and 1.8\% for a very short integration length localized around an altitude of 210 km. A parametric study is performed to check how the characteristics of the local DoLP (maximum value, altitude of the maximum, integrated height profile) vary. It is found that the polarisation is highly sensitive to the scattering function of the electrons, to the electron precipitation and the geomagnetic activity.\\
We compare these values to measured ones obtained during an observational campaign performed in February 2012 from Svalbard. The measured DoLP during the campaign was 1.9\% $\pm$ 0.1\%. The comparison between this value and the theoretical one is discussed . Discrepancies may be due to the poor constraint of the input parameters (thermosphere and ionosphere), to the fact that only electron precipitation is considered in this approach (and not proton precipitation for instance), and to the difficulty in constraining the exact width of the emission layer in the thermosphere.
Programme: 1026
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Hanane Marif, Jean Lilensten. (2020). Suprathermal electron moments in the ionosphere (Vol. 10). Bachelor's thesis, , .
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. (2020). On the nightglow polarisation for space weather exploration (Vol. 10).
Abstract: 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 Petit Cru. 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 in several circumstances, this polarisation is linked to the local magnetic activity and to the state of the ionosphere through the electron density measured with EISCAT. However, we also show that the contribution of light pollution from nearby cities via scattering can not be ignored and can play an important role in polarisation measurements. This series of observations questions the geophysical origin of the polarisation. It also leaves open its relation to the magnetic field orientation and to the state of both the upper atmosphere and the troposphere.
Keywords: polarisation / aurora
Programme: 1026
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. (2013). The thermospheric auroral red line polarization: confirmation of detection and first quantitative analysis (Vol. 3). Bachelor's thesis, , .
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Mike Lockwood, Carl Haines, Luke A. Barnard, Mathew J. Owens, Chris J. Scott, Aude Chambodut, Kathryn A. McWilliams. (2021). Semi-annual, annual and Universal Time variations in the magnetosphere and in geomagnetic activity: 4. Polar Cap motions and origins of the Universal Time effect (Vol. 11).
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. (2019). Measurement of the polarisation in the auroral N2+ 427.8 nm band (Vol. 9).
Abstract: In this paper, we provide for the first time polarisation measurements of the N+2 band at 427.8 nm performed with Premier Cru, a dedicated spectropolarimeter to investigate the polarisation of auroral emission lines between 400 and 700 nm. Details about the instrument, the observing conditions and the data analysis procedure are provided. Results obtained during three nights in March 2017 in Skibotn, Norway, indicate that the auroral blue line is polarised with a degree of linear polarisation of a few %. Due to weak Signal-to-Noise Ratios (SNR), these measurements still need to be taken with caution since none of the individual data set has a detection with a 3? confidence level. However, results integrated over the entire observing period each night do show a 3? detection but due to the long integration period, the origin of this polarisation cannot be linked to a specific type of aurora (diffuse vs structured arc) or specific ionospheric or geomagnetic conditions. These observations need to be confirmed with an improved design to increase the SNR and decrease the exposure time. When available, these improved measurements of the blue line polarisation will be important to better understand the physics of auroral processes at altitudes below 100 km where the N2+ emission occurs and possibly for space weather applications if the polarisation varies with ionospheric/geomagnetic conditions.
Programme: 1026
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Sophie Musset, Karl-Ludwig Klein, Nicolas Fuller, Gaelle Khreich, Antonin Wargnier. (2023). The time profile of relativistic solar particle events as observed by neutron monitors (Vol. 13).
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. (2022).
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MAJ Emilie. (2009).1.
Abstract: About the evolution of worlddview and conception of landscape in Yakut culture:
Based on geographical and anthropological litterature and on the field data collected during the missions Ethnoequid 2003-2006 and Festivethno 2009.
Keywords: Landscape, Siberia, Republic Sakha (Yakutia), Sakha, Yakut, Siberian minoritites,Turkic people, semiotic, temporality, space, history, place, taiga, domestication
Programme: 1024
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Chattova B., Van de Vijver B., Lebouvier M., De Smet W., Uher B. (2011). Freshwater diatoms of Ile Amsterdam (TAAF, Southern Indian Ocean) (Vol. 46).
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