Parameterization and Regression Analysis of Off-Equatorial Chorus Waves for Inclusion in Radiation Belt Models

Outer radiation belt fluxes vary by orders of magnitude on time scales of hours to days (Li et al., 2001). Wave-particle interactions involving lower band chorus waves are thought to play a major role in acceleration and loss of energetic electrons in the outer belt. Wave particle interactions involving chorus and the highest energy electrons (>MeV) is possible only at latitudes above about 20° (Shprits and Ni, 2009). Despite their perceived importance in controlling energetic electron populations in the radiation belts, relatively insubstantial statistical characterization exists from which to base radiation belt model inputs for chorus. Recent investigations employing a database of chorus events observed by the Polar spacecraft have begun to characterize chorus waves at 20° magnetic latitude and above (Bunch et al., 2011). This study utilizes the Polar wave database to parameterize wave intensities as a function of spatial location and geomagnetic driving conditions (e.g. AE, Vsw, Kp, etc.). The relative correlation of chorus occurrence and amplitude with geomagnetic conditions is also examined using an auto regressive moving average (ARMA) technique for non-independent observations, such as those made by orbiting spacecraft. Regression analysis shows significant correlation of chorus with increased AE, Vsw, and Kp, and much lower correlations with proton density, and pressure. Wave parameterizations show, for fixed range in L, an increase in chorus amplitude with magnetic latitude in the dawn sector. Amplitudes appear more constant over a range of latitudes at noon, particularly for increased activity levels. These results represent significant steps forward toward a more complete characterization of the chorus wave environment and understanding the role chorus plays in regulation of the radiation belt environment.