We investigate a quiet time event of magnetospheric Pc5 ultralow-frequency (ULF) waves and their likely external drivers using multiple spacecraft observations. Enhancements of electric and magnetic field perturbations in two narrow frequency bands, 1.5–2 mHz and 3.5–4 mHz, were observed over a large radial distance range from r ~ 5 to 11 RE. During the first half of this event, perturbations were mainly observed in the transverse components and only in the 3.5–4 mHz band. In comparison, enhancements were stronger during the second half in both transverse and compressional components and in both frequency bands. No indication of field line resonances was found for these magnetic field perturbations. Perturbations in these two bands were also observed in the magnetosheath, but not in the solar wind dynamic pressure perturbations. For the first interval, good correlations between the flow perturbations in the magnetosphere and magnetosheath and an indirect signature for Kelvin-Helmholtz (K-H) vortices suggest K-H surface waves as the driver. For the second interval, good correlations are found between the magnetosheath dynamic pressure perturbations, magnetopause deformation, and magnetospheric waves, all in good correspondence to interplanetary magnetic field (IMF) discontinuities. The characteristics of these perturbations can be explained by being driven by foreshock perturbations resulting from these IMF discontinuities. This event shows that even during quiet periods, K-H-unstable magnetopause and ion foreshock perturbations can combine to create a highly dynamic magnetospheric ULF wave environment.
Bibliographical noteFunding Information:
We thank Xiaoyan Xing, Jacob Bortnik, and Wen Li at University of California, Los Angeles, for helpful discussions. The work by C.-P. Wang and R. Thorne has been supported by JHU/APL contracts 967399 and 921647 under NASA's prime contract NAS5-01072. The analysis at UCLA was supported by the EMFISIS subaward 1001057397:01, and the ECT subaward 13-041. The work by M. Hartinger has been supported by NSF AGS-1049403. The work by C. Kletzing was performed under on JHU/APL contract 921647 under NASA Prime contract NAS5-01072. The work by S.G. Claudepierre was supported by RBSP-ECT funding provided by JHU/APL contract 967399 under NASA's prime contract NAS5-01072. All the data used in this study are available for free. Geotail data are provided through the DARTS system by ISAS. We thank T. Mukai at ISAS for the use of the Geotail LEP data. The THEMIS and ARTEMIS data and GOES 13 magnetic field are obtained with the Space Physics Environment Data Analysis System (SPEDAS) software (http://themis.igpp.ucla.edu/software.shtml). We acknowledge NASA contract NAS5-02099 for THEMIS and ARTEMIS, and C.W. Carlson and J.P. McFadden for the use of ESA data and K.H. Glassmeier, U. Auster, and W. Baumjohann for the use of FGM data provided under DLR contract 50-OC-0302. Van Allen Probes (RBSP) electric field data are obtained from http://www.space.umn.edu/rbspefw-data/, magnetic field data from http://emfisis.physics.uiowa.edu/data, and HOPE and MagEIS data from http:// www.rbsp-ect.lanl.gov/rbsp_ect.php. We thank J.H. King, N. Papatashvilli at AdnetSystems, NASA GSFC, and CDAWeb for providing the OMNI data. For the ground magnetometer data we gratefully acknowledge SuperMAG PI Jesper W. Gjerloev. We thank the national institutes that support the magnetic observatories and INTERMAGNET (www.intermagnet.org) and SuperMAG (http://supermag.jhuapl.edu/) projects for promoting high standards of magnetic observatory practice. We acknowledge Andre Balogh and Elizabeth Lucek at Imperial College, H. Reme at CESR, and CDAWeb for providing Cluster data.
- IMF discontinuity
- Kelvin-Helmholtz vortices
- Pc5 waves
- inner magnetosphere
- plasma sheet