Global model of low-frequency chorus (f(LHR)<f<0.1f(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 pT(2), 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: 1. Strong chorus waves can extend below 0.1 times local electron gyrofrequency. 2. Low frequency chorus strongest at mid-latitudes in pre-noon sector for L*=4 to 8. 3. Low frequency chorus should be included in radiation belt models;