Hanane Marif, Jean Lilensten. (2020). Suprathermal electron moments in the ionosphere (Vol. 10). Bachelor's thesis, , .
Abstract: The ionospheric electron population is divided into two groups. The ambient electrons are thermalized. Their energy is usually smaller than one electron volt. Their densities and temperatures are the usual ones measured by incoherent scatter radars, or modeled by international codes such as International Reference Ionosphere (IRI). There is however a second population called the suprathermal electrons. This one is either due to photoionization or to electron impact between the thermosphere and the precipitation in the high latitude zone. In the frame of space weather, it may be the source of scintillations, plasma bulks and other physical phenomena. The suprathermal electron population can only indirectly be measured through the plasmaline and had never been modeled. Its modeling requires the computation of the electron stationary flux by solving the Boltzmann transport equation. This flux is multiplied by various powers of the velocity v and integrated to obtain the different order moments. By integrating f over v0dv, one deduces the suprathermal electron density. An integration of v1fdv allows the computation of their mean velocity. Higher moments give access to their temperature and finally to their heat flux. In this work, we demonstrate for the first time the full and rigorous calculation of the ionospheric electron moments up to three. As two case studies, we focus on high latitude in the auroral oval and low magnetic latitude over Algiers for different solar and geophysical conditions. We compare the suprathermal densities and temperatures to the thermal electron parameters. Our results highlight that – as expected – the suprathermal density is small compared to the thermal one. Although it is close to 3 × 103 m−3 at 180 km during the day, it drops drastically at night, to hardly reach 3 m−3. Contrarily to the density, the velocity is about 10 times more important during the nighttime when precipitation occurs than during the daytime under the electromagnetic solar flux. At 400 km, it varies during the day between 700,000 m s−1 (active solar conditions) and 900,000 m s−1 (quiet Sun). At night, the velocity varies between 3 × 106 m s−1 (low mean energy precipitation) and 3 × 107 m s−1 (high mean energy precipitation) at 400 km. The suprathermal temperature increases as the solar activity decreases or as the mean energy of the electron precipitation increases. It may reach values close to 3 × 108 K. The heat flux may be fully oriented downward or experiences a reversal with some flux going up depending on the forcing.
Programme: 1026
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Jean Lilensten, Mathieu Barthélémy, Pierre-Olivier Amblard, Hervé Lamy, Cyril Simon Wedlund, Véronique Bommier, Joran Moen, Hanna Rothkaehl, Julien Eymard, Jocelyn Ribot. (2013). The thermospheric auroral red line polarization: confirmation of detection and first quantitative analysis (Vol. 3). Bachelor's thesis, , .
Abstract: The thermospheric atomic oxygen red line is among the brightest in the auroral spectrum. Previous observations in Longyearbyen, Svalbard, indicated that it may be intrinsically polarized, but a possible contamination by light pollution could not be ruled out. During the winter 2010/2011, the polarization of the red line was measured for the first time at the Polish Hornsund polar base without contamination. Two methods of data analysis are presented to compute the degree of linear polarization (DoLP) and angle of linear polarization (AoLP): one is based on averaging and the other one on filtering. Results are compared and are in qualitative agreement. For solar zenith angles (SZA) larger than 108° (with no contribution from Rayleigh scattering), the DoLP ranges between 2 and 7%. The AoLP is more or less aligned with the direction of the magnetic field line, in agreement with the theoretical predictions of . However, the AoLP values range between ±20° around this direction, depending on the auroral conditions. Correlations between the polarization parameters and the red line intensity I were considered. The DoLP decreases when I increases, confirming a trend observed during the observations in Longyearbyen. However, for small values of I, DoLP varies within a large range of values, while for large values of I, DoLP is always small. The AoLP also varies with the red line intensity, slightly rotating around the magnetic field line.
Programme: 1026
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Masson-Delmotte V. (2008). Climate evolution in polar regions. Houille blanche-revue internationale de l eau, , 24–29.
Abstract: Revue internationale de l'Eau – Houille Blance
Programme: 458
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Minier V., G. Durand, P.-O. Lagage, M. Talvard, T. Travouillon, M. Busso and G. Tosti. (2007). Submillimetre/TeraHertz Astronomy at Dome C with CEA Filled Bolometer Array (Vol. 25).
Abstract: Abstract Submillimetre/TeraHertz (e.g. 200, 350, 450 m) astronomy is the prime technique to unveil the birth and early evolution of a broad range of astrophysical objects. A major obstacle to carry out submm observations from ground is the atmosphere. Preliminary site testing and atmospheric transmission models tend to demonstrate that Dome C could offer the best conditions on Earth for submm/THz astronomy. The CAMISTIC project aims to install a filled bolometer-array camera with 1616 pixels on IRAIT at Dome C and explore the 200-m windows for potential ground-based observations.
Programme: 1040
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Dommergue, A., Vogel, N., Ferrari, C.P., Magand, O., Barret, M. (2013). Preliminary results from a continuous record of atmospheric gaseous mercury at the coastal station Dumont d’Urville in Antarctica. (Vol. 1). Bachelor's thesis, , .
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Barret M, Dommergue A, Ferrari CP, Magand O, . (2013). The monitoring of atmospheric mercury species in the Southern Indian Ocean at Amsterdam Island (38°S)
(Vol. 1). Bachelor's thesis, , .
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Dommergue A, Ferrari C P, Magand O, Barret M, Gratz L E, Pirrone N, Sprovieri F, . (2013). Monitoring of gaseous elemental mercury in central Antarctica at Dome Concordia
(Vol. 1). Bachelor's thesis, , .
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Hamilton J-Ch, Charlassier R, Cressiot C, Kaplan J, Piat M, Rosset C, . (2008). Sensitivity of a bolometric interferometer to the cosmic microwave backgroud power spectrum
. A&A, 491(3), 923–927.
Abstract: Context. The search for B-mode polarization fluctuations in the Cosmic Microwave Background is one of the main challenges of modern cosmology. The expected level of the B-mode signal is very low and therefore requires the development of highly sensitive instruments with low systematic errors. An appealing possibility is bolometric interferometry. Aims. We compare in this article the sensitivity on the CMB angular power spectrum achieved with direct imaging, heterodyne and bolometric interferometry. Methods. Using a simple power spectrum estimator, we calculate its variance leading to the counterpart for bolometric interferometry of the well known Knox formula for direct imaging. Results. We find that bolometric interferometry is less sensitive than direct imaging. However, as expected, it is finally more sensitive than heterodyne interferometry due to the low noise of the bolometers. It therefore appears as an alternative to direct imagers with different and possibly lower systematic errors, mainly due to the absence of an optical setup in front of the horns.
Programme: 915
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Ziad, E. Aristidi, A. Agabi, J. Borgnino, F. Martin, E. Fossat. (2008). First statistics of turbulence outer scale at Dome C. Astronomy & astrophysics, 491, 917–921.
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Aristidi E., Agabi K., Fossat E., Azouit M., Martin F., Sadibekova T., Travouillon T., Vernin J. & Ziad A. (2005). Site testing in summer at Dome C, Antarctica. Astronomy & astrophysics, 444(2), 651–659.
Abstract: We present summer site testing results based on DIMM data obtained at Dome C, Antarctica. These data were collected on the bright star Canopus during two 3-months summer campaigns in 2003-2004 and 2004-2005. We performed continuous monitoring of the seeing and the isoplanatic angle in the visible. We found a median seeing of 0.54'' and a median isoplanatic angle of 6.8''. The seeing appears to have a deep minimum around 0.4'' almost every day in late afternoon.
Keywords: site testing
Programme: 908
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