Dynamo Region Research Articles

A machine learning approach for estimating the drift velocities of equatorial plasma bubbles based on All-Sky Imager and GNSS observations

Equatorial Plasma Bubbles (EPBs) are zones characterized by fluctuations in plasma densities which form in the low-latitude ionosphere primarily during the post-sunset. They subject radio signals to amplitude and phase variabilities, affecting the functioning of technological systems that utilize the Global Navigation Satellite Systems (GNSS) signals for navigation. Thus, understanding EPB occurrence patterns and morphological features is vital for mitigating their effects. In this work, we employed two GNSS receivers and an All-Sky Imager (ASI) to conduct simultaneous observations on the morphology of EPBs over Brazil. The main objectives of the study were (1) to develop a Random Forest (RF) machine-learning model to estimate and predict the zonal drift velocities of EPBs, and (2) to compare the model predictions with actual EPB drifts inferred from the two instruments, as well as zonal neutral wind speeds obtained from the Horizontal Wind Model (HWM-14). In the model development, we utilized reliable EPB drift measurements made during geomagnetically quiet days between 2013 and 2017 in Brazil. The model predicted the velocities based on parameters including the day of the year, universal time, critical frequency of the F2 layer (foF2), solar and interplanetary indices. The correlation coefficients of 0.98 and 0.96 and RMSE values of 10.61 m/s and 10.06 m/s were obtained upon training and validation correspondingly. We evaluated the accuracy of the model in predicting EPB drifts on two geomagnetically quiet nights where an average correlation coefficient of 0.89 and an RMSE of 15.74 m/s were obtained. The predicted drifts, the zonal neutral wind velocities, and the GNSS and ASI velocity measurements were put into context for validation purposes. Overall, the velocities were comparable and ranged between ∼100 m/s and ∼30 m/s from the hours of 00 UT to 05 UT. The results confirmed the accuracy and applicability of the model, revealing the ionosphere-thermosphere coupling influence on the nocturnal propagation of EPBs under the full activation of the F region dynamo.

A Statistical Study of the Day‐To‐Day Variability of Diurnal and Semidiurnal Tides in the Ionospheric Dynamo Region From MIGHTI/ICON Observations

AbstractThe statistics of day‐to‐day tidal variability within 35‐day running mean windows is obtained from Michelson Interferometer for Global High‐Resolution Thermospheric Imaging (MIGHTI)/Ionospheric Connection Explorer (ICON) observations in the 90–107 km height region for the year 2020. Temperature standard deviations for 18 diurnal and semidiurnal tidal components, and for four quasi‐stationary planetary waves are presented, as function of latitude, altitude, and day‐of‐year. Our results show that the day‐to‐day variability (DTDV) can be as large as 70% of the monthly mean amplitudes, thus providing a significant source of variability for the ionospheric E‐region dynamo and hence for the F‐region plasma. We further validate our results with COSMIC‐2 ionospheric observations and present an approach to extend the MIGHTI/ICON results to all latitudes using Hough Mode Extension fitting, to produce global tidal fields and their statistical DTDV that are suitable as lower boundary conditions for nudging and ensemble modeling of TIE‐GCM. In the future, this will likely help to establish a data‐driven perspective of space weather variability caused by the tidal weather of the lower atmosphere.

Comparison of the Ionospheric Dynamo Current of Mars Above InSight and Zhurong Landing Sites: A Modeling Study

AbstractPrevious observational studies suggest that the surface time‐varying magnetic field of Mars originates in large part from the dynamo currents in the Martian ionosphere. However, whether there are significant differences in the strength, configuration, diurnal, and seasonal variations of the dynamo currents above different regions need to be further studied. In this study, using the ionospheric parameters from Mars Climate Database version 5.3 (MCD v5.3) and 7 years of MAVEN magnetic field measurements, we compare the ionospheric dynamo currents above the landing sites of InSight (4.50°N, 135.62°E) and Zhurong (25.07°N, 109.90°E) and the resulting surface magnetic variations at the two landing sites by conducting a modeling study. We find that the average dynamo current as well as its diurnal magnetic field amplitude on the Martian surface is significantly stronger at InSight than that at Zhurong due to the stronger background magnetic field strength and more perpendicular angle between magnetic field and neutral wind vectors in the dynamo region, though the conductivities is always weaker over InSight landing site. The seasonal variation of the current intensity (represented by differences between northern winter and summer solstices) is prominent over InSight than that over Zhurong because the heliospheric distance effect‐resulted conductivity difference is the dominate factor for the seasonal variations over InSight while both the heliospheric distance and solar zenith angle (SZA) contribute to the current intensity at different Ls over Zhurong. The two factors partially offset each other and lead to a smaller seasonal variation. The role of crustal field, as well as the latitude effects on dynamo currents is also discussed. This study provides an attempt to promote the understanding of the solar wind‐induced magnetosphere‐ionosphere‐surface coupling process.

Strong Resemblance between Surface and Deep Zonal Winds inside Jupiter Revealed by High-degree Gravity Moments

Jupiter’s atmosphere interior is a coupled fluid dynamical system strongly influenced by the rapid background rotation. While the visible atmosphere features east–west zonal winds on the order of ∼100 m s−1, zonal flows in the dynamo region are significantly slower, on the order of ∼cm s−1 or less, according to the latest magnetic secular variation analysis. The vertical profile of the zonal flows and the underlying mechanism remain elusive. The latest Juno radio tracking measurements afforded the derivation of Jupiter’s gravity field to spherical harmonic degree 40. Here, we use the latest gravity solution to reconstruct Jupiter’s deep zonal winds without a priori assumptions about their latitudinal profile. The pattern of our reconstructed deep zonal winds strongly resemble that of the surface wind within ±35° latitude from the equator, in particular the northern off-equatorial jet (NOEJ) and the southern off-equatorial jet. The reconstruction features larger uncertainties in the southern hemisphere due to the north–south asymmetric nature of Juno's trajectory. The amplitude of the reconstructed deep NOEJ matches that of the surface wind when the wind is truncated at a depth ∼2500 km, and becomes twice that of the surface wind if the truncation depth is reduced to ∼1500 km. Our analysis supports the physical picture in which a prominent part of the surface zonal winds extends into Jupiter’s interior significantly deeper than the water cloud layer.

Jupiter’s cloud-level variability triggered by torsional oscillations in the interior

Jupiter’s weather layer exhibits long-term and quasi-periodic cycles of meteorological activity that can completely change the appearance of its belts and zones. There are cycles with intervals from 4 to 9 years, dependent on the latitude, which were detected in 5-μm radiation, which provides a window into the cloud-forming regions of the troposphere; however, the origin of these cycles has been a mystery. Here we propose that magnetic torsional oscillations arising from the dynamo region could modulate the heat transport and hence be ultimately responsible for the variability of the tropospheric banding. These axisymmetric torsional oscillations are magnetohydrodynamic waves influenced by rapid rotation, which have been detected in Earth’s core, and have been recently suggested to exist in Jupiter by the observation of magnetic secular variations by Juno. Using the magnetic field model JRM33, together with a density distribution model, we compute the expected speed of these waves. For the waves excited by variations in the zonal jet flows, their wavelength can be estimated from the width of the alternating jets, yielding waves with a half-period of 3.2–4.7 years at 14–23° N, consistent with the intervals in the cycles of variability of Jupiter’s North Equatorial Belt and North Temperate Belt identified in the visible and infrared observations. The nature of these waves, including the wave speed and the wavelength, is revealed by a data-driven technique, dynamic mode decomposition, applied to the spatiotemporal data for 5-μm emission. Our results indicate that exploration of these magnetohydrodynamic waves may provide a new window to the origins of quasi-periodic patterns in Jupiter’s tropospheric clouds and to the internal dynamics and the dynamo of Jupiter. Torsional waves extend into the deep interior of Jupiter where they can modulate the outgoing heat flux and couple with Jupiter’s weather layer to generate the observed quasi-periodic oscillations in the cloud deck. Such waves can be used to explore the interior structure of gas giants.

Mantle-driven north–south dichotomy in geomagnetic polar minima

The geomagnetic field on the core-mantle boundary (CMB) is characterized by weak or even reversed field in the polar regions and intense flux patches at the edges of the intersection of the inner-core tangent cylinder (TC) with the CMB. This high-latitude field morphology is in agreement with thermal wind theory inside the TC in which polar upwellings disperse magnetic field lines. Furthermore, inferences from the geomagnetic secular variation hint to the presence of a westward jet at high latitudes of the northern hemisphere, also in agreement with the TC dynamical theory, but not in the southern hemisphere. Here we study polar minima in an ensemble of geomagnetic field models that span the historical era and in a set of numerical dynamo simulations with a heterogeneous outer boundary heat flux inferred from a tomographic model of lowermost mantle seismic anomalies. We quantified the polar minima using a previously-proposed expression as well as a new measure which may better capture this phenomenon. We found that throughout the historical era the geomagnetic field is characterized by stronger polar minima and more reversed flux inside the northern TC than inside the southern TC. Likewise, almost all dynamo models exhibit on average stronger polar minima in the northern hemisphere. This north/south dichotomy is explained in terms of the pattern of lowermost mantle seismic anomalies, in particular the southern centers of the two Large Low Shear-wave Velocity Provinces below Africa and the Pacific. We also investigated polar minima in planets where magnetic field models at the top of the dynamo region are available. We speculate that the absence of polar minima in Mercury’s field is likely due to the thick stratified layer at the top of its core, while the strong polar minima in Jupiter’s field might have a different dynamical origin than the geomagnetic polar minima.

Imprint of Mesospheric Quasi 2‐Day Wave in the Ground Geomagnetic Field Variations at Low Latitudes

AbstractThe strong quasi 2‐day wave (Q2DW) event that occurred during January 2015 was studied by employing medium frequency and meteor radar observations of winds from three different locations at low latitudes with considerable longitudinal separation. The large‐amplitude wave activity that occurred in mid‐January is the focus of this study. Using the advantage offered by the longitudinal separation among the stations, the zonal structure of the Q2DW has been examined. The presence of a dominant westward propagating zonal wavenumber 3 (W3) mode was revealed in the analysis. The availability of geomagnetic field data from a number of stations at low latitudes enabled us to observe the wave event at ionospheric dynamo region heights. The phase‐longitude cross‐section of the quasi 2‐day oscillation in the Y component of the geomagnetic field reiterates the presence of the dominant W3 mode observed at lower altitudes. Similar zonal characteristics and periods of the wave signatures found at mesospheric altitudes and in the manifestation of quiet‐time ionospheric currents in geomagnetic field are in conformity with the notion of the wave coupling of the atmosphere‐ionosphere system.

Theoretical study of the ionospheric dynamo region inside the South Atlantic Anomaly

The South Atlantic Anomaly (SAA) is a region where the geomagnetic field is significantly lower than that of the surrounding area. On the basis of the models of CHAOS-7.8, Mass Spectrometer Incoherent Scatter Model (NRLMSISE-00), and International Reference Ionosphere 2016 (IRI-2016), we theoretically investigated the lower and upper boundaries of the ionospheric dynamo region inside the SAA. In the ionospheric dynamo region, electrons are coupled with magnetic field lines, whereas ions are decoupled from magnetic field lines. Our results showed that the ionospheric dynamo region inside the SAA is higher and larger than that outside the SAA. We also studied the boundary variations of the dynamo region inside the SAA depending on the seasons and solar activities. We found that the dynamo region inside the SAA is the highest and largest in the summer of the southern hemisphere at solar maximum. The larger and higher altitude range of the ionospheric dynamo region in the SAA can contribute to the stronger ionospheric currents in this region.

A Global Simulation of the Dynamo, Zonal Jets, and Vortices on Saturn

Abstract The fluid dynamics planet Saturn gives rise to alternating east–west jet streams, large cyclonic and anticyclonic vortices, and a dipole-dominant magnetic field that is highly axisymmetric about the planetary rotation axis. Modeling these features in a self-consistent manner is crucial for understanding the dynamics of Saturn’s interior and atmosphere. Here we report a turbulent high-resolution dynamo simulation in a spherical shell that produces these features simultaneously for the first time. A crucial model ingredient is a long-hypothesized stably stratified layer (SSL), sandwiched between a deep metallic hydrogen layer and an outer low-conductivity molecular layer, born out of the limited solubility of helium inside metallic hydrogen at certain depths. The model spontaneously produces polar cyclones and significant low-latitude and midlatitude jet stream activity in the molecular layer. The off-equatorial low-latitude jet streams partially penetrate into the SSL and interact with the magnetic field. This helps to axisymmetrize the magnetic field about the rotation axis and convert some of the poloidal magnetic field to a toroidal field, which appears as two global magnetic energy rings surrounding the deeper dynamo region. The simulation also mimics a distinctive dip in the fifth spherical harmonic in Saturn’s magnetic energy spectrum as inferred from the Cassini Grand Finale measurements. Our model highlights the role of an SSL in shaping the fluid dynamical and magnetic features of giant planets, as exemplified at Saturn.

Thermal Evolution and Magnetic History of Rocky Planets

We present a thermal evolution model coupled with a Henyey solver to study the circumstances under which a rocky planet could potentially host a dynamo in its liquid iron core and/or magma ocean. We calculate the evolution of planet thermal profiles by solving the energy-balance equations for both the mantle and the core. We use a modified mixing length theory to model the convective heat flow in both the magma ocean and solid mantle. In addition, by including the Henyey solver, we self-consistently account for adjustments in the interior structure and heating (cooling) due to planet contraction (expansion). We evaluate whether a dynamo can operate using the critical magnetic Reynolds number. We run simulations to explore how the planet mass (M pl), core mass fraction (CMF), and equilibrium temperature (T eq) affect the evolution and lifetime of possible dynamo sources. We find that the T eq determines the solidification regime of the magma ocean, and only layers with melt fraction greater than a critical value of 0.4 may contribute to the dynamo source region in the magma ocean. We find that the mantle mass, determined by M pl and CMF, controls the thermal isolating effect on the iron core. In addition, we show that the liquid core lasts longer with increasing planet mass. For a core thermal conductivity of 40 Wm−1 K−1, the lifetime of the dynamo in the iron core is limited by the lifetime of the liquid core for 1 M ⊕ planets and by the lack of thermal convection for 3 M ⊕ planets.

Effect of the Non‐Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

AbstractThe annual mean (Sq0), annual (Sq1), and semiannual (Sq2) components of the monthly averaged daily amplitude of the geomagnetic Y component during quiet period over several solar cycles at 25 mid‐low latitudes observatories were separated by means of Fourier analysis. No obvious distinction is found for the morphology of the spatial distribution of these Sq(Y) components during solar quiet and active periods, except that they are more intense in high solar activity. We found that the longitudinal variations in the Southern Hemisphere were primarily attributed to the differences in the annual component (Sq1), which is stronger at the Eurasia and Australia anomaly zones than at the South Atlantic Ocean anomaly (SAA) zones. The positive correlation between Sq0 and geomagnetic vertical component Z suggests that the convection electric fields in the dynamo region play a key role in controlling the annual mean (Sq0). On the other hand, the Sq1 exhibits a positive correlation with geomagnetic horizontal component H, implying the interhemispheric field‐aligned currents (IHFACs) may contribute to difference of the annual variation amplitude at the different observatories. Sq2 is most prominent in the SAA region while rather weak at other positive anomaly zones (in total field), which indicates there is a negative correlation between the total field anomaly and the semiannual variations.

The Internal Structure and Dynamics of Jupiter Unveiled by a High‐Resolution Magnetic Field and Secular Variation Model

AbstractUnique information about the dynamo process acting at Jupiter can be inferred by modeling and interpreting its magnetic field. Using the fluxgate magnetometer measurements acquired during the 4 years of the Juno mission, we derive a magnetic field model which describes simultaneously the main field and the secular variation (SV) up to spherical harmonic degrees 16 and 8, respectively. Apart from the Earth's, this is the first time another planetary magnetic field along with its time variation is described to such a high degree. We use properties of the power spectrum of the static field to infer the upper boundary of the dynamo convective region at 0.830 ± 0.022 Jupiter radius. The SV and correlation times are relatively comparable to the Earth's and indicate that the field is dominated by advection. The field and SV morphologies suggest zonal as well as non‐zonal deep fluid motions.

Solar Cycle and Seasonal Variability of Martian Ionospheric Irregularities from Mars Atmosphere and Volatile Evolution Observations

Spacecraft observations around Mars show that ionospheric irregularities occur frequently in the Martian ionosphere. In this study, Mars Atmosphere and Volatile Evolution data (the region is below ∼200 km) during 2015 January to 2021 March were used to revisit the statistical characteristics of ionospheric irregularities and the comparison of irregularities in Martian years with higher or lower solar activity phase of solar cycle. Results show that the characteristics of the irregularities with a larger length scale associated with the magnetic field and solar zenith angle are similar to the previous studies. Moreover, our results show that the occurrence rate of irregularities exhibits dawn and dusk asymmetry, and the occurrence rate at dusk is higher than that at dawn. In addition, results demonstrate that the occurrence rate of irregularities is higher in Martian years with higher solar activity than Martian years with lower solar activity, which means that the solar cycle might play an important role in the formation of irregularity events. Further studies show that the solar zenith angle (SZA) and altitude at the maximum occurrence rate depend on the level of solar activity. The SZA and altitude of the maximum occurrence rate are smaller in the Martian year with higher solar activity than the lower. We also found that the rate of events is lower during the day than the terminator in the ionospheric dynamo region. By contrast, in the regions where both electrons and ions are magnetized, events have a higher rate during the day than the terminator. Furthermore, the seasonal variation of the irregularity events was also presented in this study. Results show that the occurrence rate in the dynamo region with 80° < SZA < 150° in MY34 and MY35 show an incremental trend from spring to winter, but this trend is not obvious in MY33.

Remote Sensing of Mid‐Latitude Ionospheric Magnetic Field Fluctuations Using Cosmic Radio Sources

AbstractThis paper describes a new method for remote sensing of magnetic field fluctuations at ionospheric altitudes using a relatively long‐baseline interferometer and exceptionally bright cosmic radio sources at 35 MHz. The technique uses sensitive measurements of the difference in phase between two phased array telescopes separated by about 75 km and between the right and left circular polarizations to measure the amount of differential Faraday rotation. Combined with estimates of the background magnetic field and total electron content, these can be converted to measurements of fluctuations in the differential magnetic field parallel to the line of sight, ΔB‖. The temporal gradient in ΔB‖ roughly follows the diurnal pattern expected for B‖ due to the vertical gradient in the background electric field, but at roughly 25% the magnitude and offset by ∼50 nT hr−1. This suggests that the diurnal variation in the electric fields observed by the two telescopes are similar but slightly different (|ΔE| ≲ 0.1 mV m−1). Fluctuations in ΔB‖ were typically ∼10–30 nT with wavelike fluctuations often apparent. These typically have oscillation periods of about 10–30 min, similar to traveling ionospheric disturbances (TIDs). Simultaneous observations toward two sources separated by 25.4° on the sky (∼140 km in the F‐region) show a few detections of wavelike disturbances with lags of ±10–30 min between them. These imply speeds on the order of 100–200 m s−1, also similar to TIDs. We estimate that gravity waves with amplitudes within the dynamo region of ∼10 m s−1 could generate the observed fluctuations in ΔB‖.

A Dynamo Simulation Generating Saturn‐Like Small Magnetic Dipole Tilts

AbstractAmong planetary dynamos, the magnetic field of Saturn stands out in its exceptional level of axisymmetry. One of its peculiar features is that the magnetic dipole mode is tilted with respect to the planetary rotation axis by only ≈0.007° or less. Numerical dynamo simulations performed in this context have had great difficulty in producing such small dipole tilt angles without introducing ad hoc ingredients such as a latitudinally varying heat flux pattern in the outer layers or stably stratified layers (SSLs). Here we present a numerical dynamo simulation that generates a highly axisymmetric dynamo with a dipole tilt of about ≈0.0008° on average. The model consists of a deep dynamo layer and an overlying low‐conductivity layer but without any SSLs. We highlight a novel mechanism where strong differential rotation generated in the atmospheric layer penetrates into the dynamo region, helping to maintain a very small magnetic dipole tilt.

Conductivities of Titan's Dusty Ionosphere

AbstractTitan's ionosphere hosts a globally distributed non‐trivial dusty ion‐ion plasma, providing an environment for studies of dusty ionospheres that is in many aspects unique in our solar system. Thanks to the Cassini mission, Titan's ionosphere also features one of the largest dusty plasma data sets from 126 flybys of the moon over 13 years, from 2004 to 2017. Recent studies have shown that negatively charged dust dramatically alters the electric properties of plasmas, in particular planetary ionospheres. Utilizing the full plasma content of the moon's ionosphere (electrons, positive ions, and negative ions/dust grains), we derive the electric conductivities and define the conductive dynamo region. Our results show that using the full plasma content increases the Pedersen conductivities at ∼1,100–1,200 km altitude by up to 35% compared to the estimates using only electron densities. The Hall conductivities are in general not affected but several cases indicate a reverse Hall effect at ∼900 km altitude (closest approach) and below. The dayside conductivities are shown to be factor ∼7–9 larger than on the nightside, owing to higher dayside plasma densities.

On the source of the quasi Carrington Rotation periodic magnetic variations on the Martian surface: InSight Observations and Modelling

In a recent paper (Luo H et al., 2022), we found that the peak amplitudes of diurnal magnetic variations, measured during martian days (sols) at the InSight landing site, exhibited quasi Carrington-Rotation (qCR) periods at higher eigenmodes of the natural orthogonal components (NOC); these results were based on ~664 sols of magnetic field measurements. However, the source of these periodic variations is still unknown. In this paper we introduce the neutral-wind driven ionospheric dynamo current model (e.g., Lillis et al., 2019) to investigate the source. Four candidates — the draped IMF, electron density/plasma density, the neutral densities, and the electron temperature in the ionosphere with artificial qCR periodicity, are applied in the modeling to find the main factor likely to be causing the observed surface magnetic field variations that exhibit the same qCR periods. Results show that the electron density/plasma density, which controls the total conductivity in the dynamo region, appears to account for the greatest part of the surface qCR variations; its contribution reaches about 67.6%. The draped IMF, the neutral densities, and the electron temperature account, respectively, for only about 12.9%, 10.3%, and 9.2% of the variations. Our study implies that the qCR magnetic variations on the Martian surface are due primarily to variations of the dynamo currents caused by the electron density variations. We suggest also that the time-varying fields with the qCR period could be used to probe the Martian interior's electrical conductivity structure to a depth of at least 700 km.

On the horizontal currents over the Martian magnetic cusp

Localized crustal magnetization over heavily cratered southern hemisphere at Mars gives rise to open magnetic field configurations which interact with the solar wind magnetic field to form magnetic cusp. The downward acceleration of energetic electrons in these cusps can produce aurora and an extended topside ionospheric structure over regions of magnetic anomalies. We report plasma collisions with the neutral atmosphere at one of the Martian cusps located at 82 o S and 180 o E, where the crustal field is strong with a radial component ~35° from the local zenith. We find that the dynamo region in the upper ionosphere of Mars is located between altitudes of 102 km and 210 km. The electrons in this region are constrained to gyrate along magnetic field lines while ions are dragged by neutrals and move along the direction of applied force. In the absence of the electric field, the horizontal current in the Martian dynamo is generated by the differential motion of ions and electrons. We find that the bulk of the current density is equatorward and confined within the Martian dynamo near the ionospheric peak with a magnitude of ~3.5 µA/m 2 . We also find that the eastward current density of magnitude ~0.4 µA/m 2 peaking near the upper boundary of the Martian dynamo is generated by magnetized ions in the F × B direction.

Dynamo constraints on the long-term evolution of Earth’s magnetic field strength

SUMMARY Elucidating the processes in the liquid core that have produced observed palaeointensity changes over the last 3.5 Gyr is crucial for understanding the dynamics and long-term evolution of Earth’s deep interior. We combine numerical geodynamo simulations with theoretical scaling laws to investigate the variation of Earth’s magnetic field strength over geological time. Our approach follows the study of Aubert et al., adapted to include recent advances in numerical simulations, mineral physics and palaeomagnetism. We first compare the field strength within the dynamo region and on the core–mantle boundary (CMB) between a suite of 314 dynamo simulations and two power-based theoretical scaling laws. The scaling laws are both based on a Quasi-Geostropic (QG) force balance at leading order and a Magnetic, Archimedian, and Coriolis (MAC) balance at first order and differ in treating the characteristic length scale of the convection as fixed (QG-MAC-fixed) or determined as part of the solution (QG-MAC-free). When the data set is filtered to retain only simulations with magnetic to kinetic energy ratios greater than at least two we find that the internal field together with the root-mean-square and dipole CMB fields exhibit power-law behaviour that is compatible with both scalings within uncertainties arising from different heating modes and boundary conditions. However, while the extrapolated intensity based on the QG-MAC-free scaling matches Earth’s modern CMB field, the QG-MAC-fixed prediction shoots too high and also significantly overestimates palaeointensities over the last 3.5 Gyr. We combine the QG-MAC-free scaling with outputs from 275 realizations of core–mantle thermal evolution to construct synthetic true dipole moment (TDM) curves spanning the last 3.5 Gyr. Best-fitting TDMs reproduce binned PINT data during the Bruhnes and before inner core nucleation (ICN) within observational uncertainties, but PINT does not contain the predicted strong increase and subsequent high TDMs during the early stages of inner core growth. The best-fitting models are obtained for a present-day CMB heat flow of 11–16 TW, increasing to 17–22 TW at 4 Ga, and predict a minimum TDM at ICN.

An experimental investigation into the possible connections between the zonal neutral wind speeds and equatorial plasma bubble drift velocities over the African equatorial region

There is increasing interest to understand thermospheric neutral wind and ionized plasma coupling, especially by using empirical observations. This is the first study that reports simultaneous measurements of thermospheric neutral wind and equatorial plasma bubble (EPB) speeds over the African equatorial region. Neutral wind speeds were obtained using a Fabry-Perot interferometer (FPI), while EPB speeds were obtained using an all-sky optical imager. Both instruments are co-located in Abuja (Geographic: 8.99°N, 7.38°E; Geomagnetic: 1.60°S). Data for 11 nights of coincident neutral wind and EPB speed observations were used. The neutral wind speeds were in the range of about −30 to 300 m/s, while EPB speeds were in the range of about 15–400 m/s. The speeds of both neutral winds and EPBs were generally observed to be faster during the early night hours and to slow down towards midnight. In some instances, the neutral wind and EPB speeds were comparable, an observation that is in agreement with full development of the F region dynamo. There were also instances in which the EPBs were faster or slower than the neutral winds. In one of the nights, a southward turning of the IMF-Bz was observed to cause a sudden increase in the EPB speed. For some nights, the neutral winds were faster than the EPBs during earlier hours of the nights, and the disparity reduced during the later hours of the nights. This was attributed to the possibility that the F region dynamo was yet to be fully developed during the earlier hours.