[1] Using data from the Medium Electrons A instrument on the Combined Release and Radiation Effects Satellite (CRRES), a survey of pitch angle distributions (PADs) of energetic electrons is performed. The distributions are classified into three categories: 90°-peaked, flattop, and butterfly. The categorizations are examined as a function of L-shell and orbit number and at electron energies of 153, 510, and 976 keV. The 90°-peaked distributions dominate at the lowest energy channel, and butterfly distributions are more prevalent at higher L values. The PADs on the dayside are predominately 90°-peaked distributions, while butterfly distributions become more common on the nightside at higher L-shells. Fitting the PADs to a sin n a form, where a is the local pitch angle, a profile of the parameter n versus L-shell is produced for local times corresponding to postnoon and midnight sectors for the 510-keV channel. We then compare the 510-keV data during times of moderate disturbance to the less disturbed case and the average case, and show an increase in butterfly distributions, which occurs at L > 6 for the nightside case and 3.5 < L < 5.5 for the dayside case. Comparing the profiles for n > 1 before and after the great storm on 24 March 1991, we find that there are significant differences before and after this event, the latter orbits being during a time of higher observed geomagnetic activity. Considering only those PADs with a calculated n > 1, the variation of the 90°-peaked distributions versus L-shell and orbit shows increased steepness at lower L-shell. For the lowest energy channel, the low L-shell variation of the steepness of the distributions visually correlates with the average 2-day minimum plasmapause location calculated from a model based on the D st index over the same time period. For the 510-keV electrons, a correlation can be seen with the development of flattop distributions inside of the calculated minimum plasmapause location.

Abstract.A revised version of the storm-time disturbance index D st is calculated using hourly-mean magneticobservatory data from four standard observatories and collected over the years . The calculation algorithm is a revision of that established by Sugiura et al., and which is now used by the Kyoto World Data Center for routine production of D st . The most important new development is for the removal of solar-quiet variation. This is done through time and frequency-domain band-stop filtering -selectively removing specific Fourier terms approximating stationary periodic variation driven by the Earth's rotation, the Moon's orbit, the Earth's orbit around the Sun, and their mutual coupling. The resulting non-stationary disturbance time series are weighted by observatory-site geomagnetic latitude and then averaged together across longitudes to give what we call D , storms are ranked for maximum storm-time intensity, and we show that storm-occurrence frequency follows a power-law distribution with an exponential cutoff. The epicycles of magnetic disturbance are explored: we (1) map low-latitude local-time disturbance asymmetry, (2) confirm the 27-day storm-recurrence phenomenon using autocorrelation, (3) investigate the coupled semi-annual-diurnal variation of magnetic activity and the proposed explanatory equinoctial and Russell-McPherron hypotheses, and (4) illustrate the well-known solar-cycle modulation of stormoccurrence likelihood. Since D 5807−4SH st is useful for a variety of space physics and solid-Earth applications, it is made freely available to the scientific community.

Accurate geomagnetic field models are crucial to the study of radiation belt phenomena. We quantitatively examine the accuracy of several external models widely in use via the Office National d'Etudes et de Recherche Aérospatiales‐Département Environnement Spatial (ONERA‐DESP) libraries. We study 2 years characterized by very different space weather conditions, 1996 and 2003. The year 1996, at solar minimum, exhibited many high‐speed streams and a few corotating interaction regions but was generally quiet. In contrast, 2003 included the Halloween storm, one of the most intense geomagnetic storms on record caused by a coronal mass ejection. The performance of each model, as measured by prediction efficiency and skill score, is evaluated as a function of magnetospheric conditions (reflected by the geomagnetic index Kp) and magnetic local time (MLT). Not surprisingly, the newer models tend to perform better and interesting comparisons arise between the performances of the models during different periods of the solar cycle and across different Kp and MLT values. For Kp < 4, most models show similar performance, but for higher values, there are large differences between newer and older model performance. As a function of MLT, noticeable dips in the performance of older models are observed near dawn. These dips are suspected to be effects of field‐aligned and partial ring currents that are not fully incorporated into the models, but their exact nature is unknown.