Incoherent Scatter Measurements of Ion-Neutral Collision Frequencies and Temperatures in the Lower Thermosphere of the Auroral Region

Incoherent scatter observations performed in March and November 1978 at Chatanika have been used for studying the lower thermosphere in the auroral region. Neutral temperatures and densities have been found during periods without Joule heating. We present mean profiles of temperatures and collision frequencies (approximately proportional to neutral densities) for each month and profiles obtained during four specific nights. Between 93 km and 110 km the mean profiles of temperature are in good agreement with the Jacchia (1971) model, and the profiles of collision frequency are similar to those deduced from the model. Consistency checks between these collision frequencies and temperatures were performed, as were various simulations of the data. Neutral temperature profiles between 90 km and 140 km on the four specific nights show variations from one night to another that are not correlated to magnetic activity. However, there are systematic variations during each night that we suggest are due to atmospheric tides

Impact of the 26-30 May 2003 solar events on the earth ionosphere and thermosphere.

During the last week of May 2003, the solar active region AR 10365 produced a large number of flares, several of which were accompanied by Coronal Mass Ejections (CME). Specifically on 27 and 28 May three halo CMEs were observed which had a significant impact on geospace. On 29 May, upon their arrival at the L1 point, in front of the Earth's magnetosphere, two interplanetary shocks and two additional solar wind pressure pulses were recorded by the ACE spacecraft. The interplanetary magnetic field data showed the clear signature of a magnetic cloud passing ACE. In the wake of the successive increases in solar wind pressure, the magnetosphere became strongly compressed and the sub-solar magnetopause moved inside five Earth radii. At low altitudes the increased energy input to the magnetosphere was responsible for a substantial enhancement of Region-1 field-aligned currents. The ionospheric Hall currents also intensified and the entire high-latitude current system moved equatorward by about 10°. Several substorms occurred during this period, some of them - but not all - apparently triggered by the solar wind pressure pulses. The storm's most notable consequences on geospace, including space weather effects, were (1) the expansion of the auroral oval, and aurorae seen at mid latitudes, (2) the significant modification of the total electron content in the sunlight high-latitude ionosphere, (3) the perturbation of radio-wave propagation manifested by HF blackouts and increased GPS signal scintillation, and (4) the heating of the thermosphere, causing increased satellite drag. We discuss the reasons why the May 2003 storm is less intense than the October-November 2003 storms, although several indicators reach similar intensities

Elevated Electron Temperatures in the Auroral E Layer Measured With the Chatanika Radar

An extensive series of spectral measurements has been made in the auroral E region with the Chatanika incoherent scatter radar. Becasue of the small scale length for variations of electron density, temperatures, and ion-neutral collisions we used the operating mode with the best possible range resolution—9 km. About 5% of the time the data exhibited an unusual spectral shape that was most pronounced at 105 and 110 km. Instead of being almost Gaussian with only a small hint of two peaks, the spectra are much wider, with two well-developed peaks. After carefully considering the validity of the measurements and their interpretation, we conclude that the unusual spectra are due to greatly enhanced electron temperatures. At 110 km, the electron temperature may increase from 250 K to 800 K, while the ion temperature remains near 250 K. This enhancement of the electron temperature extends from 99 km to at least 116 km. We show that the temperature increase is too large to be accounted for by auroral particle precipitation, though it coincides in time with ion temperature enhancements at altitudes above 125 km. Because these latter enhancements are believed to be due to joule heating, we deduce that electric fields of 24-40 mV/m are present and that the electrons are moving through the ions and neutrals at speeds of 500-800 m/s. Despite these velocities, we find that joule heating of the electrons also cannot account for the elevated electron temperatures. Several consequences of the elevated electron temperatures are discussed. One is that the rate constants for molecular recombination are reduced. Another is that during periods of significant joule heating, the deduced electron density profile, when fully corrected for temperatures, has a significantly lower peak altitude and greater density than that deduced under the usual assumption of equal electron and ion temperatures. Since conductivities, currents, ionization rates, and differential energy spectra are dependent upon the density profile, care must be taken to account properly for the temperature effects when deriving these quantities

Progress in space weather modeling in an operational environment

YesThis paper aims at providing an overview of latest advances in space weather modeling in an operational environment in Europe, including both the introduction of new models and improvements to existing codes and algorithms that address the broad range of space weather's prediction requirements from the Sun to the Earth. For each case, we consider the model's input data, the output parameters, products or services, its operational status, and whether it is supported by validation results, in order to build a solid basis for future developments. This work is the output of the Sub Group 1.3 "Improvement of operational models'' of the European Cooperation in Science and Technology (COST) Action ES0803 "Developing Space Weather Products and services in Europe'' and therefore this review focuses on the progress achieved by European research teams involved in the action

Étude du rayonnement diurne émis à 557.7 nm et 630.0 nm par l'atome d'oxygène dans la thermosphère de la terre (analyse de données satellite [i.e satellites] et modélisation numérique)

L'objectif principal de ce travail de thèse est d'analyser les phénomènes de luminescence diurne qui apparaissent dans la thermosphère terrestre, et plus particulièrement les émissions de l'oxygène atomique (raie verte à 557,7 et raie rouge à 630,0 nm). Cette étude met en oeuvre une analyse statistique des mesures de l'interféromètre WINDII qui permet de quantifier l'influence du flux solaire et de l'activité magnétique sur le rayonnement. Il apparaît que l'intensité et l'altitude des deux émissions augmentent quasi-linéairement avec le flux solaire. Nous montrons également que lorsque l'activité magnétique augmente, l'intensité du pic thermosphérique de la raie verte diminue, alors que l'intensité de la raie rouge reste quasiment constante. Cette étude a également permis de reproduire qualitiativement et quantitativement ces résultats statistiques en utilisant le modèle d'ionosphère TRANSCAR, ce qui montre que les phénomènes physiques mis en jeu sont bien compris.GRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

Un exemple de l’évolution du roman arthurien en prose dans la deuxième moitie du xiiie siècle

Le manuscrit 3325 de la Bibliothèque de l'Arsenal, après avoir donné le début de la version commune de Guiron le courtois, jusqu'au f° 47 v°, cl, fournit à partir du f° 48 r, cl, jusqu'à la fin du manuscrit, f° 237 v°, une version particulière de ce roman, incomplète du début et de la fin, soit une masse imposante de 190 ff. à 2 colonnes de 49 lignes. On retrouve ce texte pour l'essentiel dans l'un des volumes du manuscrit de Turin de Guiron le courtois (Bibliothèque Nationale, R. 1622, xve s..