[1] Determining the global distribution of chorus wave power in the off-equatorial region (i.e., magnetic latitude l > 15 ) is a crucial component of understanding the contribution of chorus to radiation belt acceleration and loss. In this paper we use a database of chorus power spectral density observations from the Plasma Wave Instrument (PWI) Sweep Frequency Receiver (SFR) on the Polar spacecraft to generate separate distributions of wave occurrence rate and magnetic field amplitude as a function of space and geomagnetic activity. Previous studies focused on a band-integrated and time-averaged data product to characterize the global distribution of wave power. Using a slightly different technique, we first estimate the wave amplitude from the peak wave power spectral density for times when chorus is observed. The mean wave amplitude at a given location is then multiplied by the wave occurrence rate to yield the time-averaged amplitude. We present the spatial distributions of wave occurrence rate, mean amplitude, and time-averaged amplitude in the region of maximum statistics, l > 15 and R = 4À8 R E . We find that waves of significant amplitude (>10 pT) can be observed in all local time sectors, but significant wave occurrence (>20%) is confined to the dawn and noon local time sectors. Wave mean and time-averaged amplitudes are also highest in the dawn and noon sectors. The spatial extent of regions with high time-averaged amplitude is primarily defined by regions of high occurrence rate. Time-averaged amplitudes exceeding $6 pT are observed up to a magnetic latitude of 40 at dawn and 50 at noon, while at midnight and dusk the time-averaged amplitude tends to be below that value. We also examine the geomagnetic and solar wind dependence of the spatial distribution of wave occurrence, mean amplitude, and time-averaged amplitude. In the off-equatorial region (l > 15 ), wave amplitude and occurrence on the nightside increase dramatically during disturbed geomagnetic and solar wind conditions. In contrast, waves on the dayside occur over a wider range of activity, and even during quiet conditions, mean and time-averaged amplitudes at noon significantly exceed amplitudes at midnight for disturbed times. In the dusk sector, observation of waves is mostly limited to quiet conditions, and during those times, mean amplitudes at dusk exceed those at midnight and approach amplitudes observed in the dawn sector. Parallel investigation of the independent variability of occurrence and amplitude provides a more complete picture of the chorus wave environment, particularly for application to modeling radiation belt dynamics on both short and long time scales.

The Student Dust Counter (SDC) experiment of the New Horizons Mission is an impact dust detector to map the spatial and size distribution of dust along the trajectory of the spacecraft across the solar system. The sensors are thin, permanently polarized polyvinylidene fluoride (PVDF) plastic films that generate an electrical signal when dust particles penetrate their surface. SDC is capable of detecting particles with masses m > 10 −12 g, and it has a total sensitive surface area of about 0.1 m 2 , pointing most of the time close to the ram direction of the spacecraft. SDC is part of the Education and Public Outreach (EPO) effort of this mission. The instrument was designed, built, tested, integrated, and now is operated by students.

[1] The statistical distribution of chorus wave power in the off-equatorial region is evaluated using data from the Plasma Wave Instrument (PWI) Sweep Frequency Receiver (SFR) on board the Polar spacecraft. Maps of average wave power in the meridional plane divided into four local time sectors are presented. The geomagnetic dependence of wave power is examined, and substorm activity and enhanced solar wind speed result in distinctly different wave distributions. The maximum latitudinal extent of chorus as a function of latitude and L* is estimated within the orbit constraints of the spacecraft, and on the basis of this the corresponding minimum resonant energy for first-order relativistic cyclotron resonance is calculated using a realistic magnetic field model.

[1] Magnetospheric chorus waves are a major driver of acceleration and loss in the Earth's outer electron radiation belt. The spectral extent of chorus is a key parameter in quantifying the global effect of chorus on energetic particle populations by determining the range of resonant electron energies. However, statistics of spectral properties are sparse, particularly in the off-equatorial magnetosphere. We use a database of chorus observations from the Polar spacecraft to generate statistics on the normalized chorus frequency (with the respect to the minimum field line gyrofrequency, Ω min ) as a function of magnetic local time (MLT) (0 < MLT < 24), L-shell (3 < L < 11), and magnetic latitude (|l|< 65 ). We find that, on average, the chorus spectrum peaks in the range of 0.1-0.4 Ω min , varying significantly with l, R 0 and MLT. The normalized chorus peak frequency is found to decrease with increasing R 0 , and decreases with increasing latitude below $ 25 . When fit to a Gaussian spectral model, lower band chorus is found to have a bandwidth < 0.1 Ω min , which is narrower than assumed in most diffusion models. Diffusion coefficients calculated using the University of California at Los Angeles (UCLA) Full Diffusion Code show that wave-particle interactions on the nightside are highly sensitive to both the peak frequency and bandwidth of chorus, yet on the dayside scattering is mostly sensitive to the peak frequency as a result of the wider latitudinal extent of the waves. We also find that fitting a Gaussian to the logarithm of the spectrum reduces fit errors by over 60%, indicating that inclusion of arbitrary spectral forms may improve the accuracy of wave models within radiation belt simulations.