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Natural electron cyclotron harmonic emissions in the outer magnetosphere are often cited as the electron scattering mechanism which results in the diffuse auroral precipitation. A survey is presented of the characteristics of these waves using data from both the SCATHA and Active Magnetospheric Particle Tracer Explorers (AMPTE) IRM plasma wave instruments. The emissions were observed most often in the 0300–0600 LT sector at L ∼ 4–8 and magnetic latitudes in the range ±10°. In this region, emissions exceeding 35 µV m−1 were detected only 25% of the time, and those exceeding 12 µV m−1 were detected 60% of the time. In agreement with Belmont et al. (1983), these amounts are grossly insufficient to account for the diffuse auroral electron precipitation by quasi‐linear pitch angle diffusion.

A neural network has been developed to model the temporal variations of relativistic (>3 MeV) electrons at geosynchronous orbit based on model inputs consisting of 10 consecutive days of the daily sum of the planetary magnetic index ΣKp. The neural network (in essence, a nonlinear prediction filter) consists of three layers of neurons, containing 10 neurons in the input layer, 6 neurons in a hidden layer, and 1 output neuron. The output is a prediction of the daily‐averaged electron flux for the tenth day. The neural network was trained using 62 days of data from July 1, 1984, through August 31, 1984, from the SEE spectrometer on the geosynchronous spacecraft 1982‐019. The performance of the model was measured by comparing model outputs with measured fluxes over a 6‐year period from April 19, 1982, to June 4, 1988. For the entire data set the rms logarithmic error of the neural network is 0.76, and the average logarithmic error is 0.58. The neural network is essentially zero biased, and for accumulation intervals of 3 days or longer the average logarithmic error is less than 0.1. The neural network provides results that are significantly more accurate than those from linear prediction filters. The model has been used to simulate conditions which are rarely observed in nature, such as long periods of quiet (ΣKp = 0) and ideal impulses. It has also been used to make reasonably accurate day‐ahead forecasts of the relativistic electron flux at geosynchronous orbit.

Strong enhancements of whistler mode hiss emissions have been observed to correlate with plasma density enhancements in the outer plasmasphere between L = 4 and L = 6. This indicates that these density enhancements are acting as whistler mode wave ducts. The wave and density observations were made simultaneously by the Aerospace swept frequency receiver aboard the AMPTE IRM spacecraft. The plasma density is determined from a narrow‐band line near the plasma frequency. The hiss emissions generally occur below 2 kHz. The ducts consist of density enhancements of more than 40%. Density gradients on the sides of the ducts range from 0.10 to 0.24 el cm−3 km−1. The half width of each duct is typically 250 km. The wave intensity maximizes about 15 km from the center of the duct toward the outside, i.e., the side with a negative density gradient with increasing distance. The wave intensity near the center of a duct is an order of magnitude higher than the wave intensity at the density minimum between ducts.

The extreme values of many parameters measured by the space science community are important because they have a significant impact on human activities. For example, estimates of extreme radiation belt fluxes, plasma temperatures, and solar particle events must be considered when designing spacecraft, and extreme auroral currents must be considered when designing ground-based electric power systems. The mathematical tools that have been developed to address such problems are known as the statistics of extreme values. Here these tools have been applied to three data sets in order to determine if extreme value parametric models can accurately describe space weather parameters. The three examples chosen are (1) the annual maxima of the magnetic index Ap for the years from 1932 to 1997, (2) the annual maxima of the daily average flux of >60 MeV protons measured by the Interplanetary Monitoring Platform spacecraft from 1973 to 1998, and (3) the exceedances of the flux over a threshold of 104 el cm -2 s -1 sr -1 of >2 MeV electrons at geosynchronous orbit measured by the GOES spacecraft from 1986 to 1999. The parameters for each model were determined using the maximum likelihood estimate. The validity of each model was tested using a quantile-quantile (Q-Q) plot. In each case an excellent fit to the extremes of the sample distribution function is given by an appropriate extreme value distribution function. These extreme value distribution functions were also used to estimate the 50-and 100-year values for each data set. The results show that the extreme values observed to date are not unusual in that they are well fit by extreme value models. They also show that larger values than observed to date can be expected for each of the parameters during any 100-year period. 10,915 10,916