Building the second version of the World Digital Magnetic Anomaly Map (WDMAM)

Abstract

The World Digital Anomaly Map (WDMAM) is a worldwide compilation of near-surface magnetic data. We present here a candidate for the second version of the WDMAM and its characteristics. This candidate has been evaluated by a group of independent reviewers and has been adopted as the official second version of the WDMAM during the 26th general assembly of the International Union of Geodesy and Geomagnetism (IUGG). The way this compilation has been built is described with some details. A global magnetic field model of the lithosphere contribution, parameterised by spherical harmonics, has been derived up to degree and order 800. The model information content has been evaluated by computing local spectra. Further, the compatibility of the anomaly field displayed by the WDMAM with a pure induced magnetisation is tested by comparison with the main field strength. These studies allowed an analysis of the compilation in terms of strength and wavelength content. They confirm the extremely smooth and weak contribution of the magnetic field generated in the lithosphere over Western Europe. This apparent weakness possibly extends to the Northern African continent. However, a global analysis remains difficult to achieve given the sparseness of good quality data over very large area of oceans and continents. The WDMAM and related information can be downloaded at http://www.wdmam.org/.

A New Model of the Crustal Magnetic Field of Mars Using MGS and MAVEN

“…Instead, it possesses very localized magnetic field anomalies. Such anomalies are also found on the Earth (e.g., Lesur et al, ), the Moon (e.g., Purucker & Nicholas, ), and Mercury (Hood, ; Johnson et al, ), but the Martian anomalies are 1 or 2 orders of magnitude more intense than on these bodies.…”

“…In the ESD scheme, the magnetization is estimated over a relatively large area, nearly 10,000 km 2 in our case. This is much larger than the meter to kilometer spatial scale at which the Earth's crustal magnetic field is known to vary (e.g., Lesur et al, 2016;Théebault et al, 2010). Because there is no reason that the Martian and terrestrial crustal field would be associated with different spatial scales, we can extrapolate they also exist on Mars.…”

Diffuse Extension of the Southern Mariana Margin

“…To further minimize artifacts created by short wavelength discrepancies, we excluded the regional data from within 3.7 km of the dense R/V Thompson data as it already has high density and addition of regional data added artifacts without increasing resolution. Remaining gaps in ship magnetic coverage were filled with a 3 min global grid of ship anomaly data (Lesur et al, 2016).…”

Global Centroid Distribution of Magnetized Layer From World Digital Magnetic Anomaly Map

“…WDMAM is an international scientific joint effort to compile a reliable world map of magnetic anomalies that provide a new generation of high‐resolution global lithospheric field models, including wavelengths shorter than about 2,600 km. The first and second versions of WDMAM were released in 2007 (Korhonen et al, ) and in 2016 (Dyment et al, ; Lesur et al, ). WDMAM version 2.0 has been upgraded using the new available data and approach, resulting in a better representation of the anomalies.…”

“…A detailed description of this data sets is found in Dyment et al () and Lesur et al (). These data result from a worldwide compilation of magnetic anomaly information of various time, scales, and spacings from many sources, which causes data quality problems.…”