A prediction model for the global distribution of whistler chorus wave amplitude developed separately for two latitudinal zones

Abstract

Whistler mode chorus waves are considered to play a central role in accelerating and scattering electrons in the outer radiation belt. While in situ measurements are usually limited to the trajectories of a small number of satellites, rigorous theoretical modeling requires a global distribution of chorus wave characteristics. In the present work, by using a large database of chorus wave observations made on the Time History of Events and Macroscale Interactions during Substorms satellites for about 5 years, we develop prediction models for a global distribution of chorus amplitudes. The development is based on two main components: (a) the temporal dependence of average chorus amplitudes determined by correlating with the preceding solar wind and geomagnetic conditions as represented by the interplanetary magnetic field (IMF) B z and AE index and (b) the determination of spatial distribution pattern of chorus amplitudes, specifically, the profiles in L in all 2 h magnetic local time zones, which are categorized by activity levels of either the IMF B z or AE index. Two separate models are developed: one based only on the IMF B z and the other based only on AE. Both models predict chorus amplitudes for two different latitudinal zones separately: |magnetic latitude (MLAT)| < 10°, and |MLAT| = 10°-25°. The model performance is measured by the coefficient of determination R 2 and the rank-order correlation coefficient (ROCC) between the observations and model prediction results. When tested for a new data interval of~1.5 years, the AE-based model works slightly better than the IMF B z -based model: for the AE-based model, the mean R 2 and ROCC values are~0.46 and~0.78 for |MLAT| < 10°, respectively, and~0.4 and~0.74 for |MLAT| = 10°-25°, respectively; for the IMF B z -based model, the mean R 2 and ROCC values are~0.39 and~0.74 for |MLAT| < 10°, respectively, and~0.33 and~0.70 for |MLAT| = 10°-25°, respectively. We provide all of the model information in the text and supporting information so that the developed chorus models can be used for the existing outer radiation belt electron models.

Hybrid fluid‐particle simulation of whistler‐mode waves in a compressed dipole magnetic field: Implications for dayside high‐latitude chorus

“…In Figure a, which represents the dayside magnetic field topology, we can see waves being locally generated in a broad range of high latitudes λ c >30° . Figures a–c show for the first time (in a self‐consistent, 2‐D simulation) the generation of wave power at higher latitudes on the dayside than at the nightside, in agreement with observational features discussed in section 1 [see, for example, results from Meredith et al , and Kim et al , ]. These results are consistent with maximum temperature anisotropy off equator and in line with the hypothesis put forward by Tsurutani and Smith [] that high‐latitude dayside chorus is produced at minimum B pockets caused by the solar wind compression of the Earth's magnetic field.…”

“…We show, for the first time, whistler-mode wave generation at high latitudes in the dayside and compare their characteristics to their dawn counterparts. The off-equatorial peak in whistler-mode wave power in the dayside, in contrast to an equatorial one in the nightside, is a salient feature of chorus observations [Meredith et al, 2003;Kim et al, 2015]. The results shown in this paper shed some light on a possible source mechanism that explains this contrasting difference.…”

“…Additionally, the occurrence probability of chorus waves also increases strongly with geomagnetic activity [Meredith et al, 2001]. Equatorial chorus (located within the magnetic latitude range | | < 15 ∘ ) is typically observed between midnight and dawn, while higher-latitude chorus (| | > 15 ∘ ) is mostly observed in the morning sector [Meredith et al, 2003;Kim et al, 2015].…”

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

“…Most statistical studies have grouped the observed chorus wave power into ranges of geomagnetic indices (AE/Kp) to differentiate between geomagnetic activity levels (Agapitov et al, 2013;Kim et al, 2015;Li et al, 2009;Meredith et al, 2001Meredith et al, , 2012. This grouping does not fully capture the transport history of electron drifts during storm times as they combine storm main and recovery phase effects.…”

A unified approach to inner magnetospheric state prediction

“…An extension of this approach was employed by J.‐H. Kim et al [], who fit up to seventh‐order polynomials at every 2 h magnetic local time (MLT) interval to chorus wave intensity, in two latitude ranges and driven by either solar wind conditions or geomagnetic indices. While these functional fits make the models more flexible and dynamic, the functional forms used for fitting are only applicable to the parameter at hand and a new approach will inevitably need to be taken if a different parameter is to be predicted.…”