Chantal Lathuillere

Modeling the OI 630.0 and 557.7 nm thermospheric dayglow during EISCAT‐WINDII coordinated measurements

The 630.0 and 557.7 nm thermospheric dayglow was modeled at high-latitude using an eight-moment fluid model, from measurements coordinated between the European Incoherent Scatter (EISCAT) radar and the Wind Imaging Interferometer (WINDII). The emission computation in particular included the electron (suprathermal and thermal) impact whose cross sections have been updated, the dissociative recombination of O2+ ion described for the first time by a theoretical rate coefficient, the photodissociation of molecular oxygen, and some relevant chemical reactions. The neutral atmosphere was adjusted by calibrating the ionospheric model outputs to EISCAT data. Slight adjustments were needed in order to reach a good agreement. The results were successfully compared to WINDII observations. Our present study shows that simultaneous EISCAT-WINDII measurements can be used to reduce uncertainties due to the neutral composition and that new observations of the EUV solar spectrum are still needed.

The Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite: A 20 year perspective

The Wind Imaging Interferometer (WINDII) was launched on the NASAs Upper Atmosphere Research Satellite on 12 September 1991 and operated until 2003. Its role in the mission was to measure vector winds in the Earths atmosphere from 80 to 110 km, but its measurements extended to nearly 300 km. The approach employed was to measure Doppler shifts from a suite of visible region airglow lines emitted over this altitude range. These included atomic oxygen O(1S) and O(1D) lines, as well as lines in the OH Meinel (8,3) and O2 Atmospheric (0,0) bands. The instrument employed was a Doppler Michelson Interferometer (DMI) that measured the Doppler shift as a phase shift of the cosinusoidal interferogram generated by single airglow lines. An extensive validation program was conducted after launch to confirm the accuracy of the measurements. The dominant wind field, the first one observed by WINDII, was that of the migrating diurnal tide at the equator. The overall most notable WINDII contribution followed from this; determining the influence of dynamics on the transport of atmospheric species. Currently, non-migrating tides are being studied in the thermosphere at both equatorial and high latitudes. Other aspects investigated included solar and geomagnetic influences, temperatures from atmospheric scale heights, nitric oxide concentrations and the occurrence of polar mesospheric clouds. The results of these observations are reviewed from a perspective of twenty years. A future perspective is then projected, involving more recently developed concepts. It is intended that this description will be helpful for those planning future missions.

Neutral atmosphere studies in the altitude range 90–110 km using EISCAT

Abstract In this paper we describe measurements by the incoherent scatter technique in the low thermosphere and compare the results to models. We find that the observed neutral temperature in winter at 100 km is lower by about 15K than predicted by the MSIS model and closer to the temperature predicted by the Jacchia 71 model. We also show that the neutral mass, which we inferred from the temperature and scale height, is about 26–28 a.m.u. and that this value is also lower than that used in the MSIS model. Finally, we show data for a very disturbed day, with very strong anomalous heating, for which the assumption of thermal equilibrium between electrons and ions is not correct.

A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes

[1] From one year (2004) of thermosphere total density data inferred from CHAMP/ STAR accelerometer measurements, we calculate the global thermosphere response to auroral magnetic activity forcing at middle and low latitudes using a method based on a singular value decomposition of the satellite data. This method allows separating the large-scale spatial variations in the density, mostly related to altitude/latitude variations and captured by the first singular component, from the time variations, down to timescales on the order of the orbital period, which are captured by the associated projection coefficient. This projection coefficient is used to define a disturbance coefficient that characterizes the global thermospheric density response to auroral forcing. For quiet to moderate magnetic activity levels (Kp < 6), we show that the disturbance coefficient is better correlated with the magnetic am indices than with the magnetic ap indices. The latter index is used in all empirical thermosphere models to quantify the auroral forcing. It is found that the NRLMSISE-00 model correctly estimates the main features of the thermosphere density response to geomagnetic activity, i.e., the morphology of Universal Time variations and the larger relative increase during nighttime than during daytime. However, it statistically underestimates the amplitude of the thermosphere density response by about 50%. This underestimation reaches 200% for specific disturbed periods. It is also found that the difference between daytime and nighttime responses to auroral forcing can statistically be explained by local differences in magnetic activity as described by the longitude sector magnetic indices. Citation: Lathuillere, C., M. Menvielle, A. Marchaudon, and S. Bruinsma (2008), A statistical study of the observed and modeled global thermosphere response to magnetic activity at middle and low latitudes,

Meridional wind in the auroral thermosphere : Results from EISCAT and WINDII-O(1D) coordinated measurements

Neutral thermospheric winds calculated from European incoherent scatter (EISCAT) radar data have been compared with winds measured by wind imaging interferometer (WINDII) in O(1D) emission during 11 passes of the WINDII fields of view near the radar facility. For the eight occasions when geomagnetic activity was low the average difference in the meridional winds measured by the two methods is less than 10 m/s. The EISCAT calculations were done with and without a “Burnside factor” of 1.7, and agreement with WINDII is somewhat better when the Burnside factor is not included. The three passes corresponding to disturbed conditions show poor agreement. In addition, agreement between EISCAT and WINDII is better when unfiltered EISCAT winds are used, rather than the 2-hour running mean used in earlier work. This finding suggests that the short-term oscillations seen by EISCAT are real oscillations of the neutral atmosphere.

Neutral dynamics of the high latitude E region from EISCAT measurements : a new approach

Abstract We have analysed the EISCAT data from two long campaigns, in October 1992 and in January 1993, in order to derive the three components (N-S, E-W, vertical) of the neutral wind in the E region. The winds are derived using the simultaneously measured ion-neutral collision frequency. We calculate the tidal parameters of the measured winds and compare them with models. In addition the CP2 experiment allows us to determine the vertical wind in two independent ways. During the disturbed day of the October campaign we derived a very large vertical wind. Such large values are not reproduced in any model. In this article we discuss the validity of our results.

“Non-Maxwellian” studies in the auroral F region: a new analysis of incoherent scatter spectra

Abstract When large electric fields occur in the auroral F region, the ion-velocity distribution-function becomes non-Maxwellian. Therefore the incoherent spectra are distorted from their normal shape. Up to now, analyses of the distorted spectra have been done with Ramans model of the distribution function (Winser et al., 1989 Geophys. Res., Lett. 94, 1439–1449; Lockwood and Winser, 1988 Planet. Space Sci. 36, 1295–1384; Suvanto et al., 1989 J. atmos. terr. Phys. 51, 483–495). We have chosen here to use the distribution function calculation based on the polynomial series expansion approximation of Hubert (1983). This needs a model of ion-neutral interactions: the model B of St Maurice and Schunk (1977) Planet. Space Sci. 25, 243–260 is used. This new analysis procedure works with a mixture of ions (O+ and NO+ ions) in a neutral atmosphere composed of O, N2 and O2 (Hubert and Kinzelin, 1992 J. geophys. Res. 97, 4053–4059). Simulations using noise perturbed correlation functions have been performed to test our new non-Maxwellian analysis. Results are presented that include three and four-parameter regressions. These parameters have been selected from electron density, neutral and electron temperatures, ion composition, ion-neutral differential velocity and neutral composition. These simulations allows us to propose a strategy for the analysis of real data. We have studied the well-known 27 August 1986 EISCAT CP-3-E experiment that shows a large electric field (100 mV m−1) for the scan between 13h00 and 13h30 UT (Winser et al., 1987 Geophys. Res., Lett. 14, 957–960). Assuming Tn, we are able to deduce ionospheric plasma parameters including the ion composition, which is mainly molecular around 275 km altitude.

A statistical model of ion composition in the auroral lower F region

Abstract 32 EISCAT experiments from October 1981 trough August 1986, have been analyzed for ion composition in the altitude region between 150 and 300 km. At each altitude, the ion composition was deduced from 5-minute integrated autocorrelation functions by the method of Lathuillere et al. /1/ and averaged for 3 hours to obtain profiles corresponding to the three-hour Kp magnetic index. Statistical analysis was performed on this data base, which is much bigger than any previously studied. The diurnal variation of the transition altitude between molecular and oxygen ions is found to be 26 km, which is much larger than the seasonal variation —8 km between summer and winter— and the magnetic activity variation —10 km for Kp ranging from 0 to 4. In addition, it is found that the extent of the transition region increases with the transition altitude. These results confirm and extend previous. Finally a simple analytical model of ion composition, including only diurnal variation, is proposed for use in EISCAT incoherent-scatter data analysis.

Storm effects on the ion composition

Abstract It is well known that the ion composition of the F1-region is strongly affected by electric fields, electron precipitations and change in the neutral atmosphere composition. The transition altitude between molecular and oxygen ions can therefore be raised or lowered depending on local conditions. Ion composition measurements by the EISCAT facility during a substorm are presented. Emphasis is put on results obtained during a period of high electric field with a new analysis program of incoherent scatter spectra that allows for non-Maxwellian ion velocity distribution functions. These results are discussed in the light of numerical simulation, using TRANSCAR 1D-ionospheric model. This model couples a kinetic description of precipitating electrons with a fluid description of the thermal plasma (6 ions and electrons) and is therefore well adapted to a quantitative description of storm effects on the transition altitude between molecular and oxygen ions.

Incoherent scatter measurements in the F1-region

Abstract In the F 1-region, temperature and ion composition measurements at EISCAT are usually obtained with a transmitted pulse of 360 μs, corresponding to a diffusive volume much larger than the ionospheric scale height. A special correlator program has been used in order to estimate the errors due to the smearing effect of the diffusive volume. We show that these errors can be as large as 50% in electron temperature and 20% in ion temperature and that they depend on electron density gradients in the diffusive volume. From ion composition results, we deduce that the transition altitude between molecular ions and oxygen ions is correctly estimated when using a 360 μs pulse, and that a diffusive volume of the order of ± 25 km would be good for obtaining correct composition values above 200 km altitude.