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.

Modeling ring current proton precipitation by electromagnetic ion cyclotron waves during the May 14-16, 1997, storm

Abstract: We study mechanisms contributing to proton precipitation from the ring current during the May 14–16, 1997, geomagnetic storm. This storm was caused partly by Bz< 0 fields in the sheath region behind an interplanetary shock and partly by the magnetic cloud driving the shock. The storm was characterized by a maximum Kp=7− and a minimum Dst=−115 nT and had a distinctive two-phase decay related to the passage of the ejection at the Earth. We model the ring current development caused by adiabatic drifts and losses due to charge exchange, Coulomb collisions, wave-particle interactions, and atmospheric collisions at low altitudes. The nightside magnetospheric inflow is simulated using geosynchronous Los Alamos National Laboratory data, whereas the dayside free outflow corresponds to losses through the dayside magnetopause. We calculate the equatorial growth rate of electromagnetic ion cyclotron waves with frequencies between the oxygen and helium gyrofrequencies and their integrated wave gain as the storm progresses. The regions of maximum wave amplification compare reasonably well to satellite observations. A time-dependent global wave model is constructed, and the spatial and temporal evolution of precipitating proton fluxes during different storm phases is determined. We find that the global patterns of proton precipitation are very dynamic: located at larger L shells during prestorm conditions, moving to lower L shells as geomagnetic activity increases during storm main phase, and receding back toward larger L shells with storm recovery. However, the most intense fluxes are observed along the duskside plasmapause during the main and early recovery phase of the storm and are caused by plasma wave scattering. This study is relevant to the analysis of the anticipated new data sets from the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) and Thermosphere Ionosphere Mesosphere Energetics Dynamics (TIMED) missions.

Association between Geotail plasma flows and auroral poleward boundary intensifications observed by CANOPUS photometers

Abstract: Poleward boundary intensifications are nightside geomagnetic disturbances that have an auroral signature that moves equatorward from the poleward boundary of the auroral zone. They occur repetitively, so that many individual disturbances can occur during time intervals of ∼1 hour, and they appear to be the most intense auroral disturbance at times other than the expansion phase of substorms. We have used data from three nightside conjunctions of the Geotail spacecraft in the magnetotail with the Canadian Auroral Network for the OPEN Program Unified Study (CANOPUS) ground-based array in central Canada to investigate the relation between the poleward boundary intensifications and bursty plasma sheet flows and to characterize the bursty flows associated with the disturbances. We have found a distinct difference in plasma sheet dynamics between periods with, and periods without, poleward boundary intensifications. During periods with identifiable poleward boundary intensifications, the plasma sheet has considerable structure and bursty flow activity. During periods without such poleward boundary intensifications, the plasma sheet was found to be far more stable with fewer and weaker bursty flows. This is consistent with the intensifications being the result of the mapping to the ionosphere of the electric fields that give rise to bursty flows within the plasma sheet. Two different types of plasma sheet disturbance have been found to be associated with the poleward boundary intensifications. The first consists of plasma sheet flows that appear to be the result of Speiser motion of particles in a localized region of thin current sheet. The second, seen primarily in our nearest-to-the-Earth example, consists of energy-dispersed ion structures that culminate in bursts of low-energy ions and isotropic low-energy electrons and are associated with minima in magnetic field and temperature and maxima in ion density and pressure. Both types of plasma sheet disturbance are associated with localized regions of enhanced dawn-to-dusk electric fields and appear to be associated with localized enhanced reconnection. Our analysis has shown that poleward boundary intensifications are an important aspect of geomagnetic activity that is distinct from substorms. In addition to their very distinct auroral signature, we have found them to be associated with a prolonged series of ground magnetic Pi 2 pulsations and ground X component perturbations, which peak at latitudes near the ionospheric mapping of the magnetic separatrix, and with a series of magnetic Bz oscillations near synchronous orbit. Like substorms, the tail dynamics associated with the poleward boundary intensifications can apparently extend throughout the entire radial extent of the plasma sheet. Color versions of figures are available at http://www.atmos.ucla.edu/∼larry/geotail.html.

The boundary of the geomagnetic field

Abstract: Determination of the geomagnetic field boundary using data obtained from a magnetometer on the explorer xii

Predicting interplanetary magnetic field (IMF) propagation delay times using the minimum variance technique

Abstract: [1] It has been known that the fluctuations in the interplanetary magnetic field (IMF) may be oriented in approximately planar structures that are tilted with respect to the solar wind propagation direction along the Sun-Earth line. This tilting causes the IMF propagating from a point of measurement to arrive at other locations with a timing that may be significantly different from what would be expected. The differences between expected and actual arrival times may exceed an hour, and the tilt angles and subsequent delays may have substantial changes in just a few minutes. A consequence of the tilting of phase planes is that predictions of the effects of the IMF at the Earth, on the basis of IMF measurements far upstream in the solar wind, will suffer from reduced accuracy in the timing of events. It has recently been shown how the tilt angles may be determined using multiple satellite measurements. However, since the multiple satellite technique cannot be used with real-time data from a single sentry satellite, then an alternative method is required to derive the phase front angles, which can then be used for more accurate predictions. In this paper we show that the minimum variance analysis (MVA) technique can be used to adequately determine the variable tilt of the plane of propagation. The number of points that is required to compute the variance matrix has been found to be much higher than expected, corresponding to a time period in the range of 7 to 30 min. The optimal parameters for the MVA were determined by a comparison of simultaneous IMF measurements from four satellites. With use of the optimized parameters it is shown that the MVA method performs reasonably well for predicting the actual time lags in the propagation between multiple spacecraft, as well as to the Earth. Application of this technique can correct for errors, on the order of 30 min or more, in the timing of predictions of geomagnetic effects on the ground.

Mirror and azimuthal drift frequencies for geomagnetically trapped particles

Abstract: For charged particles trapped in the geomagnetic field, the frequencies of the mirror oscillations ωm and the azimuthal drift ωd are defined as appropriate averages over the helical motion around the field lines and the mirror motion between reflection points in the two magnetic hemispheres. These integrals for ωm and ωd are evaluated numerically. Results are tabulated, illustrated, and represented by approximate analytical expressions.