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A. Chulliat, E. Thébault Institut de Physique du Globe de Paris Sorbonne Paris Cité

Application of quasi-definitive observatory data to the detection of geomagnetic jerks and the validation of IGRF-11 candidate models. A. Chulliat, E. Thébault Institut de Physique du Globe de Paris Sorbonne Paris Cité. Quasi-definitive data.

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A. Chulliat, E. Thébault Institut de Physique du Globe de Paris Sorbonne Paris Cité

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  1. Application of quasi-definitive observatory data to the detection of geomagnetic jerks and the validation of IGRF-11 candidate models A. Chulliat, E. Thébault Institut de Physique du Globe de Paris Sorbonne Paris Cité IAGA Workshop 2010

  2. Quasi-definitive data • The idea of fast baseline corrected data emerged within the geomagnetic field modeling community around 2008. It was later endorsed by: • the Swarm « Mission Advisory Group » (June 2008) • INTERMAGNET (June 2008, September 2009) • an official IAGA resolution (Sopron, August 2009) IAGA Workshop 2010

  3. Methods • As of today, two methods have been proposed: • BGS : the baseline is extrapolated over one month; quasi-definitive data are produced on a next day basis (Baillie et al., IAGA Sopron, 2009). • IPGP : a new baseline is calculated every month; quasi-definitive data are produced at the beginning of the following month, with a latency of a few days (Peltier & Chulliat, EPS, 2010; see poster by Peltier et al.) IAGA Workshop 2010

  4. The difference with definitive data is less than 1nT, even for observatories having irregular baselines (for ex. BOX), provided there is enough absolute measurements. At IPGP, we have been doing it routinely since July 2009 for 9 observatories: AAE, BOX, CLF, KOU, LZH, MBO, PHU, PPT, TAM IAGA Workshop 2010

  5. Is it feasible? • Yes, and it is even relatively easy! • Plus: • It helps detecting problems with the data and absolute measurements in a timely manner. • Producing definitive data at the end of the year is greatly simplified. • Is it useful? • Let’s have a look at two examples of recent use. IAGA Workshop 2010

  6. The 2007 geomagnetic jerk Quasi-definitive data Jan 2009 – Mar 2010 • CHAOS-2 model • observatory monthly means (annual differences) 20 nT/yr2 (4 times the 1979 jerk at NGK!) IAGA Workshop 2010

  7. IAGA Workshop 2010

  8. Signature at the Earth’s surface Using the CHAOS-2 model, we calculate the acceleration change between t1 = 2005.5 and t2 = 2008.5 => The 2007 jerk is not worldwide in occurrence. IAGA Workshop 2010

  9. Signature at the CMB 2003 2007 2005 The maximum jerk (at the Earth’s surface) occurs under St Helena Island The maximum jerk (at the Earth’s surface) occurs under Cocos Islands IAGA Workshop 2010

  10. The 2006 secular acceleration pulse The 2003 and 2007 jerks are Earth’s surface signatures of a single phenomenon at the core surface : a global acceleration pulse peaking between around 2006. Degrees n = 5 or 6 are attenuated at the Earth’s surface IAGA Workshop 2010

  11. IGRF model, the 11th generation • Under the auspices of IAGA Working Group V-MOD (chair: S. Maus; vice-chair: Chris Finlay) • Used by scientists, commercial organizations and private individuals (mostly for orientation purpose). • Three types of models: • main field 2005 (definitive) 7 candidates • main field 2010 (preliminary) 7 candidates • secular variation 2010-2015 8 candidates • Evaluation process took place in November-December 2009. Several participants contributed evaluations with various methods. IAGA Workshop 2010

  12. As part of the IGRF-11 evaluation process, candidate secular variation models were tested against observatory data, i.e., an independent dataset. Black = observatories providing definitive data until 12/2008. Red = observatories providing definitive data until 12/2008 and quasi-definitive data from 01 to 10/2009 IAGA Workshop 2010

  13. Tests against quasi-definitive data • Some models are much closer to the SV measured by observatory quasi-definitive data than others. IAGA Workshop 2010

  14. Means an standard deviations of model-data differences Quasi-definitive data (9 obs) until Oct. 2009 Definitive data (87 obs) until Dec. 2008 IAGA Workshop 2010

  15. Conclusions • Producing quasi-definitive data on a regular basis proved easier than expected, even at “difficult” observatories, and paid off when preparing the 2009 definitive data. • The quasi-definitive data produced by IPGP since July 2009 were used for detecting the 2007 jerk and for testing IGRF-11 candidate SV models. • Extensive use of quasi-definitive data is expected during the Swarm mission, starting 2012. • Chulliat, A., E. Thébault and G. Hulot, Core field acceleration pulse as a common cause of the 2003 and 2007 geomagnetic jerks, Geophys. Res. Lett., 37, L07301, doi:10.1029/2009GL042019, 2010. • Chulliat, A. and E. Thébault, Testing IGRF-11 candidate models against CHAMP data and quasi-definitive observatory data, Earth Planets Space, in press. IAGA Workshop 2010

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