Correction to “Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere”

Abstract

[1] The paper “Pc2 EMIC waves generated high off the equator in the dayside outer magnetosphere” by Y. Liu et al. (Geophys. Res. Letters, 39, L17102, doi:10.1029/2012GL053082, 2012) reported an electromagnetic ion cyclotron (EMIC) wave event detected by the four Cluster spacecraft from ~0820 to ~1400 UT on 16 February 2004, which is believed to be the first observational evidence of EMIC wave activity in the local minimum magnetic field region off the equator. Such a location has been predicted as an EMIC wave source region in previous theoretical work involving Shabansky particle orbits and drift shell splitting [McCollough et al., 2010, 2012]. H+ energy and pitch angle spectra from the Cluster Ion Spectrometry (CIS)-Composition and Distribution Function (CODIF) Analyzer [Rème et al., 2001] onboard Cluster 1 (C1), shown in the bottom two panels of Figure 2 by Liu et al. [2012], are used to confirm that the EMIC waves were locally excited. However, the plotted CODIF H+ energy spectra data from the ESA Cluster Active Archive obtained for the Liu et al. [2012] study some 2 years ago are erroneous and not consistent with the actual data plots now available on the ESA Cluster Active Archive. A CODIF instrument anomaly resulted in unusual features in the H+ pitch angle spectra that were not revealed in the paper. Consequently, descriptions of the plasma properties during the wave event shown in the bottom panel in Figure 2 of Liu et al. [2012] over times before 1029 UT and after 1230 UT are incorrect. Between these two times the pitch angle data are correct. During the event, CODIF on C1 experienced an increase in the high-voltage current across the microchannel plate detectors [Rème et al., 2001]. This type of high-voltage anomaly, taking place a few times throughout the year of 2004, resulted in the complete switch-off of the instrument on 29 October 2004. [2] In this correction, we present the more reliable ion measurements from the other instrument in the CIS package, the Hot Ion Analyzer (HIA), on the same Cluster spacecraft C1. The new results are presented below. It is important to point out that the original conclusions arrived at by Liu et al. [2012] in their summary section are in no way affected by the incorrect plasma data originally published, namely that the source of this wave event in the outer magnetosphere is located off the geomagnetic equator. [3] On Cluster the CODIF sensor measures ion composition, and the HIA sensor measures all ions [Rème et al., 2001]. Figure 1 shows the Cluster/CIS-HIA plasma measurements on C1 in the same period as Figure 2 by Liu et al. [2012], i.e., 0800–1430 UT on 16 February 2004. The top panel shows the HIA ion energy-time flux spectrogram and the bottom panel the pitch angle-time flux spectrogram, both for the full energy range 5.56 eV to 28.90 keV. Data are missing from 1325 UT on the plot, and the vertical magenta dotted lines indicate the start (0820 UT) and end (1400 UT) time of the wave event. The pitch angle observations centered on 90° on the horizontal black dotted line indicates that the strong temperature anisotropies of hot (>10 keV) ions are the likely direct cause of the EMIC wave activity. [4] Research at the UoN was supported by Australian Research Council Discovery Project grant DP0772504 and Linkage International grant LX0882515. Work at PRIC was supported by the Ocean Public Welfare Scientific Research Project (201005017) and the Shanghai Pujiang Talent Project (12PJ1409200). Work at UNH was supported by NASA under grant numbers NNX11AO82G and NNX11AB65G. The authors thank C. G. Mouikis and other Cluster team members for Cluster data preparation and software development.