Transcript Slide 1
New software for the World Magnetic Model (WMM) GP13A-0766 Adam Woods(1, 2), Manoj Nair(1,2), Stefan Maus(1,2), Susan McLean(1) 1. NOAA’s National Geophysical Data Center, Boulder, CO 2.CIRES, University of Colorado, Boulder, CO The WMM is a large spatial-scale representation of the Earth's magnetic field. It consists of a degree and order 12 spherical-harmonic expansion of the magnetic potential of the geomagnetic main field generated in the Earth’s core. Apart from the 168 spherical-harmonic “Gauss” coefficients, the model also has an equal number of spherical-harmonic Secular-Variation (SV) coefficients predicting the temporal evolution of the field over the upcoming five-year epoch. The WMM is produced by the U.S. National Geophysical Data Center (NGDC) in collaboration with the British Geological Survey (BGS). The current WMM is valid up to December 2009. We present the new software for the nextgeneration WMM (2010-2015). The software and WMM2010 model are available for download at: http://www.ngdc.noaa.gov/geomag/WMM/ Display WMM Magnetic declination at sea level for 2010 information, limitations I no At poles ? Continue ? yes yes no Read WMM Model file, Geoid file, set the Spherical Harmonic Spherical Harmonic Default parameters summation Summation - special Secular variation Secular variation User input : Location & time Summation -special summation no Convert the geomagnetic Valid ? field elements to geodetic coordinates Total magnetic field strength at sea level for 2010 yes Calculate all the geomagnetic field Convert height above MSL Elements and their time variations. To height above WGS84 ellipsoid Latitude above 55º ? Convert geodetic yes Locations to geocentric Time change the coefficients no Grid variation in polar Grid variation in Universal stereographic projection Traverse Mercator proj. Print results Compute Spherical harmonic Variables yes Compute Associated Legendre Functions More points ? no •The new software exactly follows the algorithm outlined in the technical report Free memory Degree > 16 ? yes •The new WMM software has been written from scratch in C no End of the program Use high Use low degree ALF degree ALF •Uses a modular programming approach to facilitate reuse in other applications •Conforms to industry standards. Flow chart of WMM Software to compute magnetic field elements at a single point •The core functions are optimized for speed and efficiency III II Use of WMM software for high degree geomagnetic models: The software accurately computes the associated Legendre functions up to degree 2800, making it adaptable for high-degree geomagnetic models. Here we demonstrate the use of the new WMM software to compute NGDC’s new degree 720 Enhanced Magnetic Model (EMM). The figure shows the difference between EMM and WMM for the year 2010. The majority of the differences are due to the difference in spatial resolution between the WMM and EMM. The EMM covers about one third of the crustal field strength. Typical radii for the magnetic deviations are on the order of 50 km. These small deviations represent the contribution of frozen-in magnetic fields in the Earth’s crust, compared to the large scale contribution of the internally generated magnetic field of the Earth. Geoid implementation in WMM software: The new version of the WMM software allows the user to enter their altitude above the mean sea level (MSL) rather than their height above the WGS-84 ellipsoid. Conversion between heights referenced to MSL and WGS-84 ellipsoid has been implemented using the EGM-96 geoid. This correction results in a difference of magnetic field strength of about 1-3 nT. The largest differences in magnetic field strength coincide with the largest deviations of the geoid from the WGS-84 ellipsoid. The new WMM software and WMM2010 model is available for download at: http://www.ngdc.noaa.gov/geomag/WMM/