Gyroresonant wave particle interactions with whistler mode chorus play a fundamental role in the dynamics of the Earth's radiation belts and inner magnetosphere, affecting both the acceleration and loss of radiation belt electrons. Knowledge of the variability of chorus wave power as a function of both spatial location and geomagnetic activity, required for the computation of pitch angle and energy diffusion rates, is thus a critical input for global radiation belt models. Here we present a global model of lower band (0.1fce < f < 0.5fce) and upper band (0.5fce < f < fce) chorus, where fce is the local electron gyrofrequency, using data from five satellites, extending the coverage and improving the statistics of existing models. From the plasmapause out to L* = 10 the chorus emissions are found to be largely substorm dependent with the largest intensities being seen during active conditions. Equatorial lower band chorus is strongest during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 between 2300 and 1200 MLT. Equatorial upper band chorus is both weaker and less extensive with peak intensities of the order a few hundred pT2 during active conditions between 2300 and 1100 MLT from L* = 3 to L* = 7. Moving away from the equator midlatitude chorus is strongest in the lower band during active conditions with peak intensities of the order 2000 pT2 in the region 4 < L* < 9 but is restricted to the dayside between 0700 and 1400 MLT.

A number of modes of oscillations of particles and fields can exist in space plasmas. Since the early 1970s, space missions have observed noise-like plasma waves near the geomagnetic equator known as ‘equatorial noise'. Several theories were suggested, but clear observational evidence supported by realistic modelling has not been provided. Here we report on observations by the Cluster mission that clearly show the highly structured and periodic pattern of these waves. Very narrow-banded emissions at frequencies corresponding to exact multiples of the proton gyrofrequency (frequency of gyration around the field line) from the 17th up to the 30th harmonic are observed, indicating that these waves are generated by the proton distributions. Simultaneously with these coherent periodic structures in waves, the Cluster spacecraft observes ‘ring' distributions of protons in velocity space that provide the free energy for the waves. Calculated wave growth based on ion distributions shows a very similar pattern to the observations.

We present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22-14 magnetic local time (MLT) the boundary between plasmaspheric hiss and chorus moves to lower L * values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200 to 500 Hz frequency band during active conditions, 400 < AE < 750 nT, with an average intensity of 1,128 pT 2 in the region 05-17 MLT from 1.5 < L * < 3.5. In the prenoon sector, waves in the 100 to 200 Hz frequency band peak near the magnetic equator and decrease in intensity with increasing magnetic latitude, inconsistent with a source from chorus outside the plasmapause, but more consistent with local amplification by substorm-injected electrons. At higher frequencies the average wave intensities in this sector exhibit two peaks, one near the magnetic equator and one at high latitudes, 45 ∘ < | m | < 60 ∘ , with a minimum at intermediate latitudes, 30 ∘ < | m | < 40 ∘ , consistent with a source from chorus outside the plasmapause. In the premidnight sector, the intensity of plasmaspheric hiss in the frequency range 50 < f < 1,000 Hz decreases with increasing geomagnetic activity. The source of this weak premidnight plasmaspheric hiss is likely to be chorus at larger L * in the postnoon sector that enters that plasmasphere in the postnoon sector and subsequently propagates eastward in MLT.

Abstract. The Whisper instrument yields two data sets: (i) the electron density determined via the relaxation sounder, and (ii) the spectrum of natural plasma emissions in the frequency band 2-80 kHz. Both data sets allow for the threedimensional exploration of the magnetosphere by the Cluster mission. The total electron density can be derived unambiguously by the sounder in most magnetospheric regions, provided it is in the range of 0.25 to 80 cm −3 . The natural emissions already observed by earlier spacecraft are fairly well measured by the Whisper instrument, thanks to the digital technology which largely overcomes the limited telemetry allocation. The natural emissions are usually related to the plasma frequency, as identified by the sounder, and the combination of an active sounding operation and a passive survey operation provides a time resolution for the total density determination of 2.2 s in normal telemetry mode and 0.3 s in burst mode telemetry, respectively. Recorded on board the four spacecraft, the Whisper density data set forms a reference for other techniques measuring the electron population. We give examples of Whisper density data used to derive the vector gradient, and estimate the drift velocity of density structures. Wave observations are also of crucial interest for studying small-scale structures, as demonstrated in an example in the fore-shock region. Early results from the Whisper instrument are very encouraging, and demonstrate that the four-point Cluster measurements indeed bring a unique and completely novel view of the regions explored.Correspondence to: P. Décréau (pdecreau@cnrs-orleans.fr)

We present a global model of plasmaspheric hiss, using data from eight satellites, extending the coverage and improving the statistics of existing models. We use geomagnetic activity dependent templates to separate plasmaspheric hiss from chorus. In the region 22-14 magnetic local time (MLT) the boundary between plasmaspheric hiss and chorus moves to lower L * values with increasing geomagnetic activity. The average wave intensity of plasmaspheric hiss is largest on the dayside and increases with increasing geomagnetic activity from midnight through dawn to dusk. Plasmaspheric hiss is most intense and spatially extended in the 200 to 500 Hz frequency band during active conditions, 400 < AE < 750 nT, with an average intensity of 1,128 pT 2 in the region 05-17 MLT from 1.5 < L * < 3.5. In the prenoon sector, waves in the 100 to 200 Hz frequency band peak near the magnetic equator and decrease in intensity with increasing magnetic latitude, inconsistent with a source from chorus outside the plasmapause, but more consistent with local amplification by substorm-injected electrons. At higher frequencies the average wave intensities in this sector exhibit two peaks, one near the magnetic equator and one at high latitudes, 45 ∘ < | m | < 60 ∘ , with a minimum at intermediate latitudes, 30 ∘ < | m | < 40 ∘ , consistent with a source from chorus outside the plasmapause. In the premidnight sector, the intensity of plasmaspheric hiss in the frequency range 50 < f < 1,000 Hz decreases with increasing geomagnetic activity. The source of this weak premidnight plasmaspheric hiss is likely to be chorus at larger L * in the postnoon sector that enters that plasmasphere in the postnoon sector and subsequently propagates eastward in MLT.