Importance of Ground Magnetometers to NASA Heliophysics Missions

1. Importance of Ground Magnetometersto NASA Heliophysics Missions • Several U.S. projects have established over four dozen ground magnetometers in North America. • These ground stations can provide invaluable measurements to support NASA Heliophysics missions (e.g. RBSP). • Continued operation and maintenance of these networks is required if they are to contribute to RBSP science investigations. • Many of the current operating programs are winding down. Acknowledgement: Much of the material presented here provided by Peter Chi RBSP SWG, Redondo Beach, CA

2. US-sponsored Ground Magnetometer Arrays in North America • UCLA-built: • THEMIS: 22 (NASA, since 2004) • IGPP-LANL: 6 (UC, since 1997) • MEASURE: 10 (NSF, since 1999) • McMAC: 9 (NSF, since 2004) • Falcon: 6 (Air Force, since 2008) • Other US-sponsored arrays: • MACCS (NSF): In Arctic territory of Canada; Focusing on cusp latitudes • GIMA: In Alaska only RBSP SWG, Redondo Beach, CA

3. Distribution of North American Magnetometers RBSP SWG, Redondo Beach, CA

4. Examples of Ground Magnetometer Observations Useful to RBSP • Measuring ULF waves across a wide region in space (North America has the widest span in magnetic latitude) • Remote sensing of the magnetospheric mass density through field line resonance (FLR) sounding • Remote sending of the location of the plasmapause • Determine the time and location of substorm onsets RBSP SWG, Redondo Beach, CA

5. Observations of Ultra-Low-Frequency (ULF) Waves • “The global ULF wave distribution is required for individual event analysis and for first-principles models of radiation belts” [The LWS Geospace Storm Investigations, NASA, 2002]. • “Recently, data from ground-based magnetometer chains have been used to derive the global distribution of ULF waves. It is expected that this important data source will remain available through the RBSP mission” [ibid.]. ULF waves are one of the important mechanisms responsible for particle energization in radiation belts. (Figure taken from Reeves [2007]) RBSP SWG, Redondo Beach, CA

6. Global Distribution of ULF Waves • Pc 5 waves during magnetic storms can appear very differently at different locations. • Narrow-band enhancement in spectral power (e.g., due to field line resonance) can be localized but important in accelerating particles • A need to have a magnetometer network rather than a few stations Right: Correlations between Pc 5 wave power and solar wind parameters reveal significant variability across the magnetometer network. Each symbol represents the correlation with a particular solar wind parameter [circles: log(Vsw), triangles: log(Psw), open symbols: log variance, Posch et al., 2003]. RBSP SWG, Redondo Beach, CA

7. Ground Observations of Plasmapause • The plasmapause location is one of the important inputs to radiation belt models. • The existing magnetometer network in North America can remotely detect the plasmapause through field line resonance (FLR) sounding. • The measurements can also be useful for studying the interconnecting regions in the inner magnetosphere and the coupling with the ionosphere. Right: Ground observations of FLR and an example of phase-difference spectrogram showing FLR harmonics FLR harmonics RBSP SWG, Redondo Beach, CA

8. FLR Sounding by Meridian Chain of Magnetometers October 28, 2003 Plasmapause (Black curves) Above: Equatorial mass density inferred from one day of data from a meridian chain of magnetometers RBSP SWG, Redondo Beach, CA

9. THEMIS EPO Ground Magnetometers Local newspaper reports showing strong school and community college interest.

10. Ground Magnetometer Network Maintenance • Ground magnetometers require regular maintenance to ensure consistent performance. • From past experience ~10-20% of ground magnetometers were damaged by either natural (e.g. lightning) or man-made mishaps (e.g. cutting through cables or sensors) within 5 years of operation. • Most site operators are non-scientists and they rely on an experienced instrument team to cope with any unpredictable events. • Routine inspection of data are needed to ensure normal operation. • Without maintenance and oversight by an experienced team, a significant portion of the US-built magnetometer network in North America may be lost during the prime phase of RBSP (~2011-2016). RBSP SWG, Redondo Beach, CA

11. Conclusions • Continued operation of ground magnetometers in North America will increase the science return of RBSP and future NASA missions. • At present support for all US-run ground magnetometers does not extend beyond 2011. • Recognition of the benefit of ground magnetometer networks for enhancing and extending RBSP science investigations may help in obtaining additional support for continued operations into the RBSP era. RBSP SWG, Redondo Beach, CA