June 19, 2009 R. J. Strangeway – 1 RBSP SWG, Redondo Beach, CA

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

June 19, 2009 R. J. Strangeway – 2 RBSP SWG, Redondo Beach, CA

US-sponsored Ground Magnetometer Arrays in North America

• UCLA-built:• THEMIS: 22 (NASA, since 2004)THEMIS: 22 (NASA, since 2004)

• IGPP-LANL: 6 (UC, since 1997)IGPP-LANL: 6 (UC, since 1997)

• MEASURE: 10 (NSF, since 1999)MEASURE: 10 (NSF, since 1999)

• McMAC: 9 (NSF, since 2004)McMAC: 9 (NSF, since 2004)

• Falcon: 6 (Air Force, since 2008)Falcon: 6 (Air Force, since 2008)

• Other US-sponsored arrays:• MACCS (NSF): In Arctic territory of MACCS (NSF): In Arctic territory of Canada; Focusing on cusp latitudesCanada; Focusing on cusp latitudes

• GIMA: In Alaska onlyGIMA: In Alaska only

June 19, 2009 R. J. Strangeway – 3 RBSP SWG, Redondo Beach, CA

Distribution of North American Magnetometers

June 19, 2009 R. J. Strangeway – 4 RBSP SWG, Redondo Beach, CA

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

June 19, 2009 R. J. Strangeway – 5 RBSP SWG, Redondo Beach, CA

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])

June 19, 2009 R. J. Strangeway – 6 RBSP SWG, Redondo Beach, CA

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].

June 19, 2009 R. J. Strangeway – 7 RBSP SWG, Redondo Beach, CA

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 harmonicsFLR harmonics

June 19, 2009 R. J. Strangeway – 8 RBSP SWG, Redondo Beach, CA

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

THEMIS EPO Ground Magnetometers

Local newspaper reports showing strong school and community college interest.

June 19, 2009 R. J. Strangeway – 10 RBSP SWG, Redondo Beach, CA

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).

June 19, 2009 R. J. Strangeway – 11 RBSP SWG, Redondo Beach, CA

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.