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[en] Over 100 crossings were made of the magnetosphere's sunward surface for the purpose of determining whether a distinct region of magnetosheath-like plasma could be identified earthward of the magnetopause in these most rapid transitions. It was found that a distinct region of magnetosheath-like plasma can be identified earthward of the magnetopause layer in even the most rapid magnetopause crossings. The results support a model of plasma, momentum, and energy transfer across the magnetopause layer. 3 references
[en] Complete text of publication follows. Very Low Frequency (VLF) waves propagate with insignificant attenuation in the Earth-ionosphere waveguide. Attenuation is, however, appreciably higher on illuminated paths due to the presence of the ionospheric D region. Propagation conditions may be monitored using a narrow-band receiver tuned to the stable signals from numerous VLF transmitters distributed across the surface of the Earth. The passage of the day-night terminator across the transmitter-receiver path has a characteristic signature on the amplitude and phase of the signal. Principal Component Analysis (PCA) has been applied to distinguish between the regular diurnal signal variation and exogenous perturbations.
[en] Complete text of publication follows. There may exist questions concerning the agreement between temperature retrieved from satellites monitoring the upper stratosphere and mesosphere. The indication is that they do provide reasonably similar temperature profiles, i.e., differences exist but may be insignificant. It is unavoidable that the satellite soundings are not coincidental in time or in location and as a result comparison of these profiles are inexact. We will compare early comparisons of conjunctive inflatable falling sphere and satellite measurements, e.g., HALOE, AIRS, SABER, and possibly others as a surrogate method to infer accuracy between temperature retrievals. Comparison of measurements mainly in polar latitudes will establish the retrieval comparability. Our emphasis is to illustrate how well the retrievals representative the polar summer mesosphere. Whether large differences between remotely sensed temperatures are within expected accuracy bounds will be discussed using profiles between 60-90 km.
[en] Complete text of publication follows. The influence of solar activity on the dynamical and thermal state of the mesosphere is studied on the basis of long-term measurements of wind variances. The data base comprises time series of mesospheric winds at mid latitudes (Juliusruh, 54 deg N, 13 deg E), available since 1990, and at high latitudes (Andenes, 69 deg N, 16 deg E ) since 1998. The seasonal variations and interannual variability of gravity wave activity are examined with regard to the filtering by background winds, tides, and planetary waves. Particular attention is directed to the influence of solar activity on gravity waves during the summer months when the mesospheric winds show a strong correlation with the solar cycle. The observed mean gravity wave amplitudes in the mesosphere and lower thermosphere at mid and high latitudes are also compared to model estimations from the KMCM (Kuehlungsborn Mechanistic Circulation Model) which resolves gravity waves in the extratropical mesosphere/lower thermosphere.
[en] Complete text of publication follows. The thermospheric zonal wind forms a fast wind jet at the Earth's dip equator instead of the geographic equator. This remarkable feature is revealed in two sets of independent observations made two decades apart. One is from the CHAMP satellite during the year of 2002 and the other is from the DE-2 satellite during Aug. 1981 - Feb. 1983. Both observations show that this wind jet is eastward at night with speed reaching 150 m/s, and westward around noon with speed over 75 m/s. The fast wind jets are observed during local times of fully developed equatorial ionization anomaly (EIA). On the other hand, a channel of slow wind is found on the dip equator during the period of 05 - 08 LT, which corresponds to local times before the EIA develops. These features strongly suggest the ionosphere / thermosphere coupling by the ion drag being the principle cause for shifting the wind jet from the geographic equator to the dip equator.
[en] Complete text of publication follows. The electric field is a major driver of low latitude ionospheric dynamics. Quantifying the impact of the storm time electric fields on redistributing the low latitude ionospheric plasma has been challenging, mostly because of the degree of variability in the storm time electric fields, which tends to make it difficult to interpret the individual observations. Two sources of the storm time electric fields have been understood, prompt penetration and disturbance dynamo. However, their roles and relative contribution in the low latitude ionosphere throughout different phases of magnetically disturbed periods are yet to be separated. We have developed a self-consistent first-principles model that accounts for the two sources of the storm time electric fields. Modeling of the storm time electric fields requires, as a first ingredient, the field-aligned currents that connect the magnetosphere and ionosphere and that are responsible for the penetration and shielding processes. The second set of ingredients is the global ionospheric conductivity and neutral winds that are responsible for the disturbance dynamo. By including both processes of prompt penetration and disturbance dynamo into the model, the storm time electric fields are reproduced in reasonable agreement with observations. In this paper, we will demonstrate that our model can help us identify the two sources of the storm time electric fields when interpreting the observations. Furthermore, we will attempt to quantify the impact of the storm time electric fields on restructuring the low latitude ionosphere and thermosphere, by taking into consideration the time scales, magnitudes and the relative importance of prompt penetration and disturbance dynamo.
[en] Due to the numerical calculations conducted using the global model of the thermospheric and ionospheric parameters it is shown that the longitudinal variations in the lower thermosphere may be induced by the solar-migrating tides propagating from the middle atmosphere. Non migrating tides whose time variation is determined by the universal time only are induced at presence of such tides at the altitudes over 90 km
[en] Geotail plasma and field measurements at -95 RE are compared with extensive ground-based, near-Earth, and geosynchronous measurements to study relationships between auroral activity and magnetotail dynamics during the expansion phases of two substorms. The studied intervals are representative of intermittent, moderate activity. The behavior of the aurora and the observed effects at Geotail for both events are harmonized by the concept of the activation of near-Earth X lines (NEXL) after substorm onsets with subsequent discharges of one or more plasmoids down the magnetotail. The plasmoids must be viewed as three-dimensional structures which are spatially limited in the dawn-dusk direction. Also, reconnection at the NEXL must proceed at variable rates on closed magnetic field lines for significant times before beginning to reconnect lobe flux. This implies that the plasma sheet in the near-Earth magnetotail is relatively thick in comparison with an embedded current sheet and that both the NEXL and distant X line can be active simultaneously. Until reconnection at the NEXL engages lobe flux, the distant X line maintains control of the poleward auroral boundary. If the NEXL remains active after reaching the lobe, the auroral boundary can move poleward explosively. The dynamics of high-latitude aurora in the midnight region thus provides a means for monitoring these processes and indicating when significant lobe flux reconnects at the NEXL.copyright 1997 American Geophysical Union