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We present new models of Jupiter's internal magnetic field and secular variation from all available direct measurements from three decades of spacecraft observation. A regularized minimum norm approach allows the creation of smooth, numerically stable models displaying a high degree of structure. External field from the magnetodisk is modeled iteratively for each orbit. Jupiter's inner magnetosphere is highly stable with time, with no evidence for variation with solar activity. We compare two spherical harmonic models, one assuming a field constant in time and a second allowing for linear time variation. Including secular variation improves data fit with fewer additional parameters than increasing field complexity. Our favored solution indicates a ∼0.012% yr −1 increase in Jupiter's dipole magnetic moment from 1973 to 2003; this value is roughly one quarter of that for Earth. Inaccuracies in determination of the planetary reference frame cannot explain all the observed secular variation. Should more structure be allowed in the solutions, we find the northern hemispherical configuration resembles recent models based on satellite auroral footprint locations, and there is also evidence of a possible patch of reversed polar flux seen at the expected depth of the dynamo region, resembling that found at Earth and with implications for the Jovian interior. Finally, using our preferred model, we infer flow dynamics at the top of Jupiter's dynamo source. Though highly speculative, the results produce several gyres with some symmetry about the equator, similar to those seen at Earth's core-mantle boundary, suggesting motion on cylinders aligned with the rotation axis.

[1] We present a review of seismological constraints on deep crustal structures underlying large igneous provinces (LIPs), largely from wide-angle seismic refraction surveys. The main purpose of this review is to ascertain whether this seismic evidence is consistent with, or contrary to, petrological models for the genesis of flood basalt lavas. Where high-quality data are available beneath continental flood basalt (CFB) provinces (Emeishan, Columbia River, Deccan, Siberia), high-velocity structures (V p ∼ 6.9-7.5 km/sec) are typically found immediately overlying the Moho in layers of order ∼5-15 km thick. Oceanic plateau (OP) LIPs exhibit similar layers, with a conspicuous layer of very high crustal velocity (V p ∼ 7.7 km/sec) beneath the enormous Ontong-Java plateau. These structures are similar to inferred ultramafic underplating structures seen beneath active hot spots such as Hawaii, the Marquesas, and La Reunion. Petrogenetic models for flood basalt volcanism based on hot plume melting beneath mature lithosphere suggest that these deep seismic structures may consist in large part of cumulate bodies of olivine and clinopyroxene which result from ponding and deep-crustal fractionation of ultramafic primary melts. Such fractionation is necessary to produce basalts with typical MgO contents of ∼6-8%, as observed for the vast bulk of observed flood basalts, from primary melts with MgO contents of order ∼15-18% (or greater) such as result from hot, deep melting beneath the lithosphere. The volumes of cumulate bodies and ultramafic intrusions in the lowermost crust, often described in the literature as "underplating," are comparable to those of the overlying basaltic formations, also consistent with petrological models. Further definition of the deep seismic structure beneath such prominent LIPs as the Ontong-Java Plateau could place better constraints on flood basalt petrogenesis by determining the relative volumes of ultramafic bodies and basaltic lavas, thereby better constraining the overall process of LIP emplacement.

We describe the candidate models submitted by the British Geological Survey for the 12th generation International Geomagnetic Reference Field. These models are extracted from a spherical harmonic 'parent model' derived from vector and scalar magnetic field data from satellite and observatory sources. These data cover the period 2009.0 to 2014.7 and include measurements from the recently launched European Space Agency (ESA) Swarm satellite constellation. The parent model's internal field time dependence for degrees 1 to 13 is represented by order 6 B-splines with knots at yearly intervals. The parent model's degree 1 external field time dependence is described by periodic functions for the annual and semi-annual signals and by dependence on the 20-min Vector Magnetic Disturbance index. Signals induced by these external fields are also parameterized. Satellite data are weighted by spatial density and by two different noise estimators: (a) by standard deviation along segments of the satellite track and (b) a larger-scale noise estimator defined in terms of a measure of vector activity at the geographically closest magnetic observatories to the sample point. Forecasting of the magnetic field secular variation beyond the span of data is by advection of the main field using core surface flows.