Much of what we know about the solar wind’s interaction with the Earth’s magnetosphere has been gained from isolated in-situ measurements by single or multiple spacecraft. Based on their observations, we know that reconnection, whether on the dayside magnetopause or deep within the Earth’s magnetotail, controls the bulk flow of solar wind energy into and through the global system and that nightside activity provides the energized particles that power geomagnetic storms. But by their very nature these isolated in-situ measurements cannot provide an instantaneous global view of the entire system or its cross-scale dynamics. To fully quantify the dynamics of the coupled solar wind-magnetosphere requires comprehensive end-to-end global imaging of the key plasma structures that comprise the magnetosphere which have spatial resolutions that exceeds anything possible with multi-point or constellation situ measurements. Global, end-to-end, imaging provides the pathway to understanding the system as a whole, its constituent parts, and its cross-scale processes on a continuous basis, as needed to quantify the flow of solar wind energy through the global magnetospheric system. This paper describes how a comprehensively-instrumented single spacecraft in a high-altitude, high-inclination orbit coupled with ground-based instruments provides the essential observations needed to track and quantify the flow of solar wind energy through the magnetosphere. This includes observations of the solar wind plasma and magnetic field input, the magnetopause location in soft X-rays, the auroral oval in far ultraviolet, the ring current in energetic neutrals, the plasmasphere in extreme ultraviolet, the exosphere in Lyman-α, and the microstructure of the nightside auroral oval from ground-based all sky cameras.

We present a new technique for reducing the uncertainties inherent in the interpretation of lithospheric magnetic field observations over the Earth. This technique, without involving iterations, provides an improved estimate of the depth-integrated magnetic susceptibility of the crust as compared to previous approaches. Departing from the normal practice of using observations at specific locations, we model directly Gauss coefficients of the lithospheric magnetic field and use an a-priori initial lithospheric thickness model to circumvent magnetic annihilators (i.e. magnetisation distributions that cannot be determined from magnetic data since they have no impact on the lithospheric magnetic field). Of the several initial magnetic layer models tested, we prefer the model where magnetic thickness is based on the Moho or the regional estimate of the Curie depth when it is shallower than the Moho because it is physically reasonable and produces the fewest artefacts. The method is applied to a recent high-degree lithospheric magnetic field model called LCS-1 derived from CHAMP and Swarm magnetic satellite data. The technique is appropriate for regions where induced magnetisation dominates over remanent magnetisation. We show that high degrees of the final depth-integrated magnetic susceptibility variation are dependent only on the corresponding high degrees of the LCS-1 magnetic field model. Thus, the depth-integrated magnetic susceptibility variation is an important quantity derived in the study which enables readily qualitative interpretation of regional geology.

Much of what we know about the solar wind's interaction with the Earth's magnetosphere has been gained from isolated in situ measurements by single or multiple spacecraft.Based on their observations, we know that reconnection, whether on the dayside magnetopause or deep within the Earth's magnetotail, controls the flow of solar wind energy into and through the global system.We know that nightside activity provides the energized particles that power geomagnetic storms.But by their very nature these isolated in situ measurements cannot provide an instantaneous global view of the entire system or its cross-scale dynamics.As a result, we don't know which mode of reconnection prevails on the dayside magnetopause or within the magnetotail as a function of solar wind and geomagnetic conditions.We don't know which mode or modes of nightside activity supply the most energized particles to the ring current.Nor do we know the dominant loss mode for ring current decay: precipitation, magnetopause outflow, or charge exchange with neutrals.Nor do we know how processes deep within the magnetosphere provide feedback to those happening in the outer magnetosphere.The answers to these questions have an impact far beyond magnetospheric physics, as magnetic reconnection, particle acceleration, and charge-exchange are fundamental plasma processes that operate at other planets and throughout the universe.Comprehensive end-to-end global imaging of the key micro, meso-, and macro-scale plasma structures that comprise the magnetosphere will provide the answers to these questions via observations with a spatial resolution that exceeds anything possible with in situ measurements.Each proposed interaction mechanism generates a diagnostic plasma structure or boundary signature.Global, end-to-end, imaging provides the pathway to understanding the system as a whole, its constituent parts, and its cross-scale processes on a continuous basis, as needed to quantify the flow of solar wind energy through the global magnetospheric system.The significance of each mechanism is the product of its amplitude and occurrence rate.This white paper describes how a comprehensively-instrumented single spacecraft in a highlatitude circular polar orbit provides the essential observations needed to track and quantify the flow of solar wind energy through the magnetosphere, including the solar wind plasma and magnetic field input, the magnetopause location in soft X-rays, the auroral oval in far ultraviolet, the ring current in energetic neutrals, the plasmasphere in extreme ultraviolet, the exosphere in Lyman-, the microstructure of the nightside auroral oval in ground-based all sky cameras, and the magnetic perturbations of ionospheric current patterns seen by ground-based magnetometers. Imaging the End-to-End Dynamics of the Global Solar Wind-Magnetosphere Interaction

Large-scale current systems in the ionosphere and the magnetosphere are intimately controlled by the solar wind-magnetosphere interaction and the magnetosphere-ionosphere coupling. During space weather events, these currents reconfigure and intensify significantly in response to enhanced solar wind-magnetosphere interaction, facilitating explosive energy input from the magnetosphere into the ionosphere-thermosphere system and inducing electric current surges in electric power systems on the ground. Therefore, measurements of magnetic manifestations associated with the dynamic changes of the current systems are crucial for specifying the energy input into the ionosphere-thermosphere system, understanding energy dissipation mechanisms, and predicting the severity of their space weather impacts. We investigate the potential uses of high-quality magnetic field data for space weather operations and propose real-time data products from next generation constellation missions that enable improved space weather forecasting and mitigation.

We report on magneto-optical resonances observed in sodium fluorescence from D2 manifold with an intensity-modulated light. Fluorescence resonances are measured in the perpendicular (90°) and backward (180°) directions to the light propagation in laboratory experiments using a sodium cell containing neon buffer gas. Properties of these resonances are studied by varying the magnetic field at fixed-light modulation frequency, and vice-versa. Modulation with low-duty cycle shows higher-harmonic resonances of the modulation frequency and sub-harmonic resonances of the Larmor frequency. A dark resonance with maximum amplitude for laser wavelength closer to the crossover peak is observed. The origin of this dark resonance observed in Na D2 line is discussed using a theoretical model. Present study is aimed towards improving the understanding of magneto-optical resonances for remote magnetometry applications with mesospheric sodium.

We use L1‐norm model regularization of |Br| component at the surface on magnetic monopoles bases and along‐track magnetic field differences alone (without vector observations) to derive high quality global magnetic field models at the surface of the Moon. The practical advantages to this strategy are the following: monopoles are more stable at closer spacing in comparison to dipoles, improving spatial resolution; L1‐norm model regularization leads to sparse models which may be appropriate for the Moon which has regions of localized magnetic field features; and along‐track differences reduce the need for ad‐hoc external field noise reduction strategies. We examine also the use of Lunar Prospector and SELENE/Kaguya magnetometer data, combined and separately, and find that the Lunar Prospector along‐track vector field differences lead to surface field models that require weaker regularization and, hence, result in higher spatial resolution. Significantly higher spatial resolution (wavelengths of roughly 25–30 km) and higher amplitude surface magnetic fields can be derived over localized regions of high amplitude anomalies (due to their higher signal‐to‐noise ratio). These high‐resolution field models are also compared with the results of Surface Vector Mapping approach of Tsunakawa et al. (2015, https://doi.org/10.1002/2014JE004785). Finally, the monopoles‐ as well as dipoles‐based patterns of the Serenitatis high amplitude magnetic feature have characteristic textbook patterns of Br and Bθ component fields from a nearly vertically downwardly magnetized source region and it implies that the principal source of the anomaly was formed when the region was much closer to the north magnetic pole of the Moon.

While devoid of an active magnetic dynamo field today, Mars possesses a remanent magnetic field that may reach several thousand nanoteslas locally. The exact origin and the events that have shaped the crustal magnetization remain largely enigmatic. Three magnetic field data sets from two spacecraft collected over 13 cumulative years have sampled the Martian magnetic field over a range of altitudes from 90 up to 6,000 km: (a) Mars Global Surveyor (MGS) magnetometer (1997–2006), (b) MGS Electron Reflectometer (1999–2006), and (c) Mars Atmosphere and Volatile EvolutioN (MAVEN) magnetometer (2014 to today). In this paper we combine these complementary data sets for the first time to build a new model of the Martian internal magnetic field. This new model improves upon previous ones in several aspects: comprehensive data coverage, refined data selection scheme, modified modeling scheme, discrete‐to‐continuous transformation of the model, and increased model resolution. The new model has a spatial resolution of ∼160 km at the surface, corresponding to spherical harmonic degree 134. It shows small scales and well‐defined features, which can now be associated with geological signatures.

Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text R. Grewal, R. Tripathi, G. S. Pati, A. W. Yu, M. Krainak, and M. Purucker, "Optical Magnetometry using Fluorescence Resonance in Sodium D2 Manifold," in Frontiers in Optics + Laser Science APS/DLS, OSA Technical Digest (Optica Publishing Group, 2019), paper JTu4A.35. Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article

We demonstrate a new correlation technique for detecting magneto-optical resonances, which are produced by exciting 87Rb atoms in a vapor medium with modulated light. The technique can be used to improve the performance of remote magnetometry.

Introduction: Results from different combinations of vector and vector gradients (along-track differences) from Lunar Prospector (LP) and SELENE/Kaguya (S/K) spacecrafts suggest that the use of LP vector gradients data alone leads to the best quality crustal magnetic field models at the surface of the Moon using global and local sets of equivalent sources (monopoles) [1, 2]. We use the scheme of iteratively reweighted least squares to account for non-Gaussian data errors. The amplitudes of the monopoles are determined by minimizing the misfit to the components together with the average of |Br| at the ellipsoid surface (i.e. applying a L1 model regularization of |Br|). When vector fields are used, external field contamination leads to spurious N-S features in the downward continued field models even with stringent data selection criteria and ad-hoc noise removal techniques (e.g., selection criteria of satellite’s position in the Moon’s wake w.r.t. the solar wind and in the Earth’s magnetotail, internal/external dipoles fields removal, and ad-hoc low-order polynomial removal, equivalent source based cross-validation of nearby passes, and visual removal of remaining anomalous segments). In our present effort, we excluded S/K spacecraft data because orbital positioning of the extended mission (low-altitude) suffers from positioning inaccuracies of several meters to kilometers [3]. When better extended mission S/K orbits are available, we will attempt to improve models in and near the South Pole – Aitken (SPA) basin where low altitude S/K data are available. In the region of Von Kármán crater in the SPA basin, the landing site of Chang’E-4, our high resolution local models show greater detail than global models of the magnetic field of the Moon. Global Models: We derived global models using only LP along-track gradients with 35000 1° equalarea-spacing monopoles in a single subset and 100000 monopoles (0.66° spacing) in 84 overlapping subsets (Figure 1). Regularization parameters were derived based on visual stable appearance of the fields at the surface of the ellipsoid representing the Moon. In general, the optimum regularization parameter depends on the level of noise in the data as well as the monopole spacing. In regions of high amplitude, high S/N ratio magnetic fields such as Reiner Gamma swirl, we can obtain localized models with higher resolution. Figure 1. Total field model at the surface of the Moon from monopoles model constrained with L1 regularization (0.66° or 20 km spacing and equivalent monopoles placed at 20 km depth). Note the logarithmic scale of the anomalies to emphasize small amplitude features. The map shows extensive strong magnetic fields in the SPA basin (central part of the map) and localized anomaly features associated with melt sheets within impact craters, other near-surface to deep geologic sources and possibly large impact ejecta formed during the epoch of a strong core field dynamo.

lais, E. Thébault, M.E. Purucker, R.J. Lillis, S. Bouley, C.L. Johnson, A. Mittelholz, C.T. Russell, S. P. Joy, Y. Yu, S.E. Smrekar and W.B. Banerdt. 1 Lab. Planet. Geodyn., Univ. Nantes, Univ. Angers, CNRS, UMR 6112, 44000 Nantes, France, Benoit.langlais@univ-nantes.fr). 2 Planet. Magnetospheres Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA. 3 Space Sci. Lab., U. California, Berkeley, CA, USA. 4 Geosci. Paris Sud, Univ. Paris-Sud, CNRS, Univ. Paris-Saclay, Orsay, France. Earth, Ocean, Atm. Sci., Univ. Brit. Columbia, Vancouver, Canada. 6 Planet. Sci. Inst., Tucson, AZ, USA. 7 Earth Planet. Spa. Sci., U. California, Berkeley, CA, USA. 8 JPL, Pasadena, CA, USA.

This paper summarizes recent advances in our understanding of geomagnetism, and its relevance to terrestrial space weather. It also discusses specific core magnetic field features such as the dipole moment decay, the evolution of the South Atlantic anomaly, and the location of the magnetic poles that are of importance for the practice of space weather.

SMALLSAT INVESTIGATION OF HYDRATION AND SPACE WEATHERING PROCESSES AT THE MOON. T. J. Stubbs, B. K. Malphrus, R. Hoyt, M. A. Mesarch, M. Tsay, D. J. Chai, M. K. Choi, M. R. Collier, J. W. Keller, W. M. Farrell, J. R. Espley, J. S. Halekas, A. P. Zucherman, R. R. Vondrak, P. E. Clark, D. C. Folta, T. E. Johnson, G. Y. Kramer, S. Fatemi, J. Deca, J. R. Gruesbeck, J. L. McLain, M. E. Purucker, NASA Goddard Space Flight Center, Greenbelt, MD, USA, Morehead State University, Morehead, KY, USA, Tethers Unlimited, Inc., Bothell, WA, USA, Busek Co. Inc., Natick, MA, USA, University of Iowa, Iowa City, IA, USA, NASA Jet Propulsion Laboratory, Pasadena, CA, USA, NASA Wallops Flight Facility, Wallops, VA, USA, Lunar and Planetary Institute, Houston, TX, USA, Swedish Institute of Space Physics, Kiruna, Sweden, University of Colorado, Boulder, CO, USA, University of Maryland, College Park, MD, USA. Timothy.J.Stubbs@NASA.gov

We derived new vector gradients based models of crustal magnetic field at the lunar surface with data from the Lunar Prospector (LP) satellite using two model parameterization approaches: a global set of 35820 1° spaced (~30 km) equal area monopoles at 20 km below the surface (O’Brien and Parker, 1994; Olsen et al., 2017) and combined results of subsets of 100000 0.66° spaced monopoles at the same depth. We use the scheme of iteratively reweighted least-squares inversion to compute the initial model. Then the amplitudes of these monopoles are determined by minimizing the misfit to the components together with the global average of |Br| at the ellipsoid surface (i.e. applying a L1 model regularization of Br). In previous approaches using vector fields for modeling, we found that external field contamination leads to spurious anomalies in the downward continued field models even with stringent data selection criteria and ad-hoc noise removal techniques (e.g., satellite’s position in the Moon’s wake w.r.t. the solar wind and in the Earth’s magnetotail, internal/external dipoles fields removal, low-order polynomial removal, joint equivalent source cross-validation technique and visually removing remaining anomalous segments). On the other hand, with the use of gradients-only data (along-track first finite differences), we were able to completely bypass the ad-hoc techniques. Similar processing of Kaguya magnetic data, which have only higher altitude coverage over the most of the Moon except in the region of the South Pole–Aitken (SPA) basin, completely misses some of the anomalies seen in the Lunar Prospector data. The combined Lunar Prospector and Kaguya gradient-based models also severely degrade the derivation of the anomaly fields in many regions. Euler analysis of isolated anomaly features from the Reiner Gamma swirl suggests top depths of about 0.3 to 1.5 km and center depths of 10-14 km; in the region between Stein and Vallier craters north of the SPA basin our analysis suggests top depths of around 1.5 km and center depths of 13-15 km. With the spectral depth determination techniques, the SPA basin region yields depths to the base of magnetization ranging between 15 and 40 km. Three-dimensional modeling and the bulk magnetization determinations of the sources constrained by the Euler and spectral methods is underway.

Recent sophisticated global data compilations and magnetic surveys have been used to investigate the nature of magnetization in the lower crust and upper mantle. Two approaches to constraining magnetizations are developed, providing minimum (0.01 SI) and maximum (0.04 SI) susceptibility estimates, given some assumed thickness (15+ km here). These values are higher than are found in many continental rocks. Are there rocks deeper in the crust or upper mantle that are more magnetic than expected, or are the model assumptions incomplete? What is the magnetic behavior of deep crustal and upper mantle rocks, when slightly cooler than the Curie or Néel temperatures of their magnetic minerals, after being exhumed from locations of high-grade metamorphism at greater depth? Different sets of equilibrium metamorphic minerals can be considered that would form under different conditions. Results on 1501 samples from the Western Gneiss Region (WGR) Norway, mainly from mafic and ultramafic bodies subducted to depths of 60-200 km and temperatures of 750 up to 950°C at the very highest pressures, show that rocks did not fully equilibrate to the dominant metamorphic-facies conditions. There is a large variation in petrophysical properties, oxide minerals, and mineral assemblages in WGR samples, though they cannot explain the broad high-amplitude (deep-seated) anomalies measured in this region. The presence of magnetite, and exsolved titanohematite and hemo-ilmenite in samples, shows those magnetic phases are preserved even at eclogite-facies conditions, in part because complete eclogite-facies equilibrium was rarely achieved.

We have demonstrated a remote magnetometer based on sodium atoms in the Earth's mesosphere, at a 106-kilometer distance from our instrument. A 1.33-watt laser illuminated the atoms, and the magnetic field was inferred from back-scattered light collected by a telescope with a 1.55-meter-diameter aperture. The measurement sensitivity was 162 nT/$\sqrt{Hz}$. The value of magnetic field inferred from our measurement is consistent with an estimate based on the Earth's known field shape to within a fraction of a percent. Projected improvements in optics could lead to sensitivity of 20 nT/$\sqrt{Hz}$, and the use of advanced lasers or a large telescope could approach 1-nT/$\sqrt{Hz}$ sensitivity. All experimental and theoretical sensitivity values are based on a 60$^\circ$ angle between the laser beam axis and the magnetic field vector; at the optimal 90$^\circ$ angle sensitivity would be improved by about a factor of two.

Both magnetic and seismic techniques can provide information about the Moho (Mohorovicic discontinuity). We develop a new technique that provides a better estimate of the magnetic thickness of the crust, as compared with previous approaches. It uses prior knowledge from seismology (Crust 1.0), a new high-degree model from CHAMP (CHAllenging Mini-satellite Payload) and Swarm (LCS-1 - a model of Earth's lithospheric field) and a newly developed technique. The technique is appropriate for regions where induced magnetization dominates over remanent magnetization. We compare the predictions from LCS-1 with those from Crust 1.0, with some simple assumptions, and find that the correlations increase until about spherical harmonic degree 30, and then decrease globally. Spatially, the correlations between the seismic and magnetic techniques are strongest over North America and Australia, and weakest over South America and northern Africa. Strong correlations also exist between the two approaches over the Antarctic, northern Europe, and Greenland. While we might expect the seismic and magnetic approaches to correlate over well-characterized regions (i.e. North America), and show weaker correlations over poorly-characterized regions (i.e. South America and north Africa), the strong correlation in the Antarctic and Greenland is puzzling, because both of these regions are poorly-characterized. We discuss some possible explanations, and implications, of this attempt to correlate seismic and magnetic approaches to characterizing the lithosphere.