European Repeat Station Workshop Bucharest May 2007 UK repeat station programme Tom Shanahan and Susan Macmillan

European Repeat Station Workshop Bucharest May 2007 The Earth’s magnetic field Most of the field is from the Earth’s core  varies slowly with time (months to years) Local fields from magnetized rocks in Earth’s crust  relatively stable with time Fields due to currents in the ionosphere (from about 100 km altitude) and the magnetosphere (several earth radii)  variations from seconds to years Repeat station observation and reduction programmes aimed at monitoring the core field but they also include the crustal field

European Repeat Station Workshop Bucharest May 2007 Regional model - provides magnetic north data for 200 topographic and 30 geological maps in UK every year

European Repeat Station Workshop Bucharest May 2007 Grid Magnetic Angle convergence = difference between true north and grid north declination - convergence = grid magnetic angle

European Repeat Station Workshop Bucharest May 2007 Regional model

European Repeat Station Workshop Bucharest May 2007 Rate of change does change!

European Repeat Station Workshop Bucharest May 2007 Regional model declination residuals

European Repeat Station Workshop Bucharest May 2007 UK crustal field from aeromagnetic & marine surveys

European Repeat Station Workshop Bucharest May 2007 Other work done with the UK repeat station data inducing field changed by almost 20° Jackson, A., Study of crustal magnetic anomalies of the British Isles, Astronomy and Geophysics 48(2): an attempt to separate induced and remanent magnetisation using dense repeat station data collected in and airborne surveys done in