Simultaneous observation of chorus and hiss near the plasmapause

On 4 August 2010 a moderate geomagnetic storm occurred with minimum Dst of −65 nT and maximum Kp of 7−. Shortly after the onset of this storm, VLF chorus was observed at Marion Island (L= 2.6). Over time the spectral structure of the chorus transformed into a hiss band spanning the same frequency range. The observation of overlapping chorus and hiss suggests that Marion Island was close to the plasmapause at the time of this event, and provides ground-based observational confirmation of the generation mechanism of plasmaspheric hiss from chorus waves outside of the plasmasphere. Chorus observations at Marion Island were not common during this period of the solar cycle and so this event was investigated in detail. The geomagnetic conditions are discussed and geosynchronous particle data and broadband data from two other stations are presented. Empirical models are employed to predict the location of the plasmapause, and its location is inferred from a knee whistler recorded at Dunedin, New Zealand. These show that Marion Island is in the vicinity of the plasmapause during the event. The event is also compared to chorus observed at similarL after the Halloween storms of 2003. The rarity of the chorus observation is quantified using DEMETER VLF data. The DEMETER data, along with the various ground based VLF measurements, allows us to infer temporal and spatial variations in the chorus source region

Storm/substorm signatures in the outer belt

The response of the ring current region is compared for periods of storm and substorm activity, with an attempt to isolate the contributions of both processes. The authors investigate CRRES particle data in an overview format that allows the display of long-term variations of the outer radiation belt. They compare the evolution of the ring current population to indicators of storm (Dst) and substorm (AE) activity and examine compositional changes. Substorm activity leads to the intensification of the ring current at higher L (L {approximately} 6) and lower ring current energies compared to storms (L {approximately} 4). The O{sup +}/H{sup +} ratio during substorms remains low, near 10%, but is much enhanced during storms (can exceed 100%). They conclude that repeated substorms with an AE {approximately} 900 nT lead to a {Delta}Dst of {approximately} 30 nT, but do not contribute to Dst during storm main phase as substorm injections do not form a symmetric ring current during such disturbed times

The derivation of bi-Maxwell distribution variables from chorus emissions detected on the ground

“ACHDANet” (Automatic Chorus and Hiss Detector and Analyzer Network) project is an analogy to, and additional product of the well-known AWDANet. Our mission is to create a monitoring system which nowcast the source population in the Radiation Belts based on ground-detected chorus emissions by the AWDANet stations at L > Lpp . In our recent paper, we introduced a direct method to derive the approximate biMaxwellian parameters of the source population from the starting frequency and frequency sweep rate of individual chorus emissions. The chorus inversion method was tested successfully on Van Allen Probes EMFISIS and ECT-HOPE data. That chorus inversion method fulfill the requirements of a future automatic detector and analyzer system: a robust technique which inputs are spectrogram of chorus emissions recorded on the ground, fce gyrofrequency and fpe plasmafrequency at the assumed source region. As a next step, the effects of propagation is under investigation. In this paper we examine the application domain of the most robust propagation model, namely, propagation with a group velocity quasi-parallel to the magnetic field. In this model we apply an empirical density model for plasmatrough and the critical frequency of F2 region f0F2 for ionosphere. We present the first results of Van Allen Probes EMFISIS and AWDANet chorus emissions which were simultaneously detected and analyzed