Global model of low-frequency chorus (f_LHR< f<0.1 f_ce) from multiple satellite observations

Whistler mode chorus is an important magnetospheric emission, playing a dual role in the acceleration and loss of relativistic electrons in the Earth's outer radiation belt. Chorus is typically generated in the equatorial region in the frequency range 0.1-0.8 f_ce, where f_ce is the local electron gyrofrequency. However, as the waves propagate to higher latitudes, significant wave power can occur at frequencies below 0.1f_ce. Since this wave power is largely omitted in current radiation belt models, we construct a global model of low-frequency chorus, f_LHR<f<0.1f_ce, using data from six satellites. We find that low-frequency chorus is strongest, with an average intensity of 200 pT², in the prenoon sector during active conditions at midlatitudes (20°<|λ_m |<50°) from 4<L^∗<8. Such midlatitude, low-frequency chorus wave power will contribute to the acceleration and loss of relativistic electrons and should be taken into account in radiation belt models.

Key points: Strong chorus waves can extend below 0.1 times local electron gyrofrequencyLow frequency chorus strongest at mid-latitudes in pre-noon sector for L*=4 to 8Low frequency chorus should be included in radiation belt models.