Earth's magnetic field

About: Earth's magnetic field is a research topic. Over the lifetime, 20360 publications have been published within this topic receiving 446747 citations. The topic is also known as: magnetic field of Earth & geomagnetic field.

Zonal winds in the equatorial upper thermosphere: Decomposing the solar flux, geomagnetic activity, and seasonal dependencies

Abstract: Using 3 years (2002–2004), over 16,400 orbits of measurements from the accelerometer on board the CHAMP satellite, we have studied the climatology of the equatorial zonal wind in the upper thermosphere. Several main features are noticed. The most prominent one is that the solar flux significantly influences both the daytime and nighttime winds. It overrides the geomagnetic activity effect, which is found to be rather limited to the nightside. An elevation of the solar flux level from F10.7 ? 100 × 10?22 W m?2 Hz?1 to F10.7 ? 190 × 10?22 W m?2 Hz?1 produces an eastward disturbance wind up to ?110 m s?1. This consequently enhances the nighttime eastward wind but suppresses the daytime westward wind. A seasonal variation with weaker wind (by over 50 m s?1 at night) around June solstice than in other seasons has been observed regardless of solar flux and geomagnetic activity levels. The zonal wind is eastward throughout the night except around June solstice, where it ebbs to almost zero or turns even westward in the postmidnight sector at low solar flux level. The daytime wind is found to be generally more stable than the nighttime wind, particularly unresponsive to geomagnetic activities. Predictions from the Horizontal Wind Model find good agreement with the CHAMP?observed wind at high solar flux levels during nighttime. At low solar flux levels, however, the model strongly underestimates the westward wind during morning hours by 50–120 m s?1 depending on season. The major difference between the HWM?predicted and the CHAMP?observed wind is seen in the phase of its diurnal variation. The CHAMP?observed wind turns eastward around 1200–1300 MLT instead of 1600–1700 MLT predicted by the model. Comparisons with ground FPI observations and the NCAR Thermosphere?Ionosphere?Electrodynamics General Circulation Model (TIEGCM) predictions show that the solar flux effect obtained from CHAMP is consistent with that modeled by TIEGCM. The solar flux dependence of zonal wind found here together with that of the zonal ion drift found in previous studies reflect the relative importance of the E? and F?region wind dynamo in the thermosphere?ionosphere coupling process. Furthermore, these wind measurements indicate that the Earth's atmosphere superrotates. The average superrotation speed amounts to about 22 m s?1 for a solar flux level of F10.7 ? 100 × 10?22 W m?2 Hz?1 but increases to 63 m s?1 for F10.7 ? 190 × 10?22 W m?2 Hz?1. Finally, the wind behavior presented in this study is longitudinally averaged and may differ from wind measurements at a certain longitude.

Global positioning system phase fluctuations at auroral latitudes

Abstract: Using observations of a diversity of propagation paths of Global Positioning System satellites from each of 11 high-latitude stations, it was possible to determine the behavior pattern for the development of phase fluctuations in the auroral and subauroral irregularity regions. The coverage comprised a large range of longitudes and latitudes with all data measuring the same parameter, i.e., phase fluctuations. Starting with characteristics of the irregularity development on magnetically quiet days, it was noted that the start and stop times of phase fluctuations correlated with the entry and exit into the irregularity oval. Maximum occurrence of phase fluctuation took place near magnetic midnight. During magnetic storms the irregularity oval expands equatorward and poleward and phase fluctuations increase in intensity. Using the time difference of the development of irregularities between stations considerably separated in longitude, the conclusion was reached that during a magnetic storm there is a long time feeding of the turbulent energy that develops irregularities in the oval. While the geographic position of the station relevant to the oval is important during storms, the dynamics of each storm modifies the simple behavior shown during quiet times. Observations at corrected geomagnetic latitudes >80° indicate that phase scintillation intensities were lower than those in the oval during both quiet and disturbed conditions in years of low solar flux. Since the technique yields a measure of total irregularity intensity for the total propagation path, it was not possible solely from these data to determine the altitude of the irregularities. In case studies it was found that during magnetically quiet periods when irregularities are noted on propagation paths in the irregularity oval, F layer critical frequencies and thicknesses were greater than those of the E layer. During magnetic storm periods, E layer critical frequencies are for various periods of time greater than those of the F layer. During storms, there are probably contributions from both layers with different mechanisms for the development of irregularities operating as a function of time, storm development, and latitude.

Interaction between the solar plasma wind and the geomagnetic cavity

Abstract: If the quiet-time interplanetary magnetic field near the earth is parallel to the solar wind, the flow of this "collision-free" plasma over the geomagnetic cavity is reducible to an equivalent hypersonic "blunt-body problem" in ordinary gasdynamics. The shape of the converging "tail" portion of the geomagnetic cavity is determined by an equivalent gasdynamic (PrandtlMeyer) expansion along the surface streamline. The length of the tail measured from the earth's center is about 54 earth-radii. At the aft end of the cavity, the converging plasma flow is deflected back to the axial direction across an oblique tail or "wake" shock, which decays to an Alfven wave in a distance of some 10-20 cavity diameters downstream, or about 300 earth-radii. The geomagnetic cavity leaves a wake of hot plasma in the solar wind, and a corresponding defect in magnetic field intensity. The effects of a transverse component of the interplanetary magnetic field are illustrated by considering the flow along the stagnation line between the bow shock and the stagnation point on the magnetosphere. The axial velocity and plasma density both vanish at the stagnation point, whereas the transverse magnetic field reaches its maximum value there. This discussion furnishes the necessary first step for the analysis of the flow and magnetic field around the magnetosphere.