A Localized Lithospheric Magnetic Model of Australia Incorporating Spectrally Diverse Aeromagnetic and Satellite Observations
1Kongju National University, Korea, Republic of (South Korea); 2The Ohio State Univesity, Columbus, Ohio, USA
A localized lithospheric magnetic anomaly model of Australia was developed from aeromagnetic total intensity data and CHAMP satellite vector observations. This joint inversion model was based on spherical Slepian functions that maximize power over a 20o-radius spherical cap centered on Australia. The spherical Slepian model to degree 360 was used to represent anomaly features of 1o (~111 km) and longer. Relative to global spherical harmonic modeling, localized Slepian modeling requires significantly fewer harmonic coefficients to represent the anomaly features. For the Australian study area, some 6,104 Slepian coefficients were used to model the near-surface and satellite altitude magnetic anomaly vectors and gradients to all orders within the working precision of the observations. This study also considers the use of spherical Slepian functions for combining spectrally diverse compilations of near-surface and satellite magnetic observations over spatially restricted spherical patches of the Earth. This approach is being developed for the next Antarctic Digital Magnetic Anomaly Project phase (ADMAP-2) that is compiling near-surface and satellite magnetic data for the Antarctic region south of 60o S. In this application, the gradient-like observations from the Swarm mission’s satellite constellation are being investigated to augment regional gaps in the aeromagnetic data coverage.
Localized Crustal Magnetic Vector and Gradient Anomaly Components of the Antarctic from a Global Spherical Harmonic Model of the Swarm Observations
1Kongju National University, Korea, Republic of (South Korea); 2Korea Polar Research Institute, Songdo, In-choen, Korea, Republic of (South Korea); 3The Ohio State Universtiy, Columbus, Ohio, USA; 4Goddard Space and Flight Center, NASA, Greenbelt, Maryland, USA; 5Geomatics Engineering, Univ. of Calgary, Alberta, Canada
Crustal magnetic vector and gradient components are modeled by spherical Slepian functions over the 20o-radius spherical cap centered on the South Pole. The orbital configuration of the three Swarm satellites provides additional constraints for modeling the crustal magnetic gradient components by spherical Slepian functions for regional studies of the Antarctic crust south of 70oS. The advantages in localized Slepian versus spherical harmonic modeling include avoiding the need for a global distribution of data, far fewer numbers of spherical harmonic coefficients are required, and significantly more efficient computation of the higher degree components. In addition, spherical Slepian basis functions are orthogonal, and thus can be transformed into global spherical harmonic coefficients. In this study, localized spherical Slepian functions are developed to represent the three vector and six gradient magnetic anomaly components over the Antarctic from a global spherical harmonic model of the crustal magnetic anomalies of Swarm measurements. The role of Slepian functions for joint modeling of the Antarctic’s near-surface terrestrial, marine, and airborne magnetic data with satellite altitude magnetic observations is also considered.
A Regional Geomagnetic Secular Variation Model of East Asia Using Spherical Slepian Functions
1Kongju National University, Korea, Republic of (South Korea); 2The Ohio State University, Columbus, Ohio, USA; 3Goddard Space and Flight Center, NASA, Greenbelt, Maryland, USA
A regional secular variation model of the geomagnetic field for East Asia was made by fitting geomagnetic observatory data with spherical Slepian functions. This method is widely used in modeling the spherical coordinate attributes of spatially limited distributions or patches of geopotential field anomalies. The localized Slepian method is particularly efficient for updating the conventional global spherical harmonic secular model with new data. The annual means of vector components observed from 1997 to 2011 by four East Asia INTRAMAGNET observatories (i.e., Kakioka, Kanoya, Memambetsu, and Beijing) were modeled and compared with the global CHAOS-4 model. Cubic splines were adapted to produce secular coefficients at half-year intervals to maximum degree 8. Statistical and graphical comparisons with the global CHAOS-4 model illustrate the effectiveness of localized spherical Slepian functions for geomagnetic secular field modeling.
Distribution of the Magnetic Anomaly for the Swarm Satellite in China and Adjacent Area
1IGP Institute of Geophysics, China Earthquake Administration, Beijing, China; 2China Earthquake Administration of Xinjiang
The three-satellite constellation mission Swarm was launched by the European Space Agency (ESA) on22 November 2013.The mission provided reliable measurements from which the global lithospheric magnetic field. Based on 3 years (2004~2006) of Swarmsatellitemagnetic field data, we derive themagnetic anomaly in China and adjacent area.
At satellite altitude the amplitude of the lithospheric field is very small, in particular that of the small-scale features. To isolate this signature, the first step is therefore to select the least-disturbed data. High and low latitudes exhibit very different properties in terms of ionospheric current intensities, we only selected and processed the middle-latitude data as ranging from 55°to 55°magnetic latitude. We are interested in night side effects, we have limited our study to the hours 22 to 03 local time (LT), during which the influence of F region currents can be neglected. Furthermore, we took only data from periods of lowgeomagnetic activity(Kp ≤2+ and DST ≤|30| ). Contaminated tracks were identified here by an automatic detection process and have been discarded. Then the main magnetic field, magnetospheric field, ionospheric field and induction fields were removed from the scalar data by subtracting the field model CHAOS, and finally some unrealistic observed data were deleted.
The Swarm magnetic anomalies show that satellite magnetic anomalies we obtained correspond quite well to characteristics of the large scale structure in China and adjacent area. Four magnetic anomaly areas formed by all the positive and negative anomalies, they are Songliao magnetic anomaly, Sichuan magnetic anomaly, Tarim magnetic anomaly , and Tibet magnetic anomaly, each of them have one or more magnetic anomaly centers.
Balloon Gradient Magnetic Research at Altitudes of 20-40 Km in Addition to the Project "Swarm"
1Moscow Aviation Institute (National Research University), Russian Federation; 2Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Academy of Sciences (IZMIRAN), Russian Federation
The stratospheric balloon magnetic gradiometer at the Pushkov Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation of Russian Academy of Sciences (IZMIRAN) and the Moscow Aviation Institute (MAI) is developed. It has two-stage measuring base of 6 km general length, oriented along the vertical line by means of the gravity. Balloon gradient magnetic research expands design possibilities "Swarm" for the geomagnetic field (GMF). The problem dealing with an investigation of the interior structure of the Earth crust by means of remote sensing methods is under consideration. This problem can be reliably solved on the base of the Earth magnetic field (EMF) data obtained at two space altitudes (30 and 500 km). The validation of the main global analytical models of the main EMF is examined by means of the gradient magnetic surveys executed on the stratospheric balloon flights at altitude of 30 km. The opportunity to use these models for the magnetic anomaly detection from the balloon surveys data derived at the altitude of 30 km is investigated. The stratospheric balloon gradient geomagnetic data of IZMIRAN-2010 experiment are used. Normal (main) and regional (crust) geomagnetic fields are separately considered. Daily mean spherical harmonious model (DMSHAM) derived from CHAMP data is used for study of the normal EMF. In this case the secular variations of EMF can be considered with accuracy up to 0.1nT. Regional EMF is investigated by means of comparison of the experimental data with ground base data and EMM2010 model data derived from satellite and ground base data. It is shown that the EMM2010 model limited of 13 spherical harmonics have mistakes up to 15 nT. The balloon data show that EMM/720 model unsatisfactorily displays the EMF at 30 km altitudes. Regional EMF (anomaly geomagnetic field) derived from EMM2010 model differs (70%) from the measured one on the balloon. Improved model of the EMF derived from the satellite and balloon magnetic survey data could show the reliable information about the regional crust magnetic field and could give the way to see deep magnetic structure of the Earth's crust. The qualitative model of the main geomagnetic field cannot be constructed by means of satellite and ground base data only. It is shown, that an adequate global model of magnetic anomalies must be constructed only in accordance with the data obtained at satellite and stratospheric altitudes.
Using Variable Quad Geometry to Better Characterize the Field-Aligned Currents with Swarm
1Institute for Space Sciences, Romania; 2Jacobs University Bremen, Germany
The algorithm used to generate the L2 dual-sat Field-Aligned Current (FAC) product is based on data provided by the lower satellite pair, i.e. SwA and SwC, and relies on a rigid geometry of the four-point quad configuration (regular trapezoid, with fixed, i.e. 5s, along track separation). Depending on the FAC geographic location and inclination, other configurations are expected to provide a more accurate current density estimation.
During the cal/val activities a dual-sat least squares (LS) method [Vogt et al. 2013] developed for a Swarm-like mission was shown to offer some advantages by allowing a more flexible geometry and by providing a framework for error assessment. The results supported the idea of using variable parameters for the quad configuration along the orbit, e.g. a smaller along track separation in the regions close to the geographic poles and a larger separation at lower latitudes, in order to increase the accuracy of FAC density estimation, as specified by the level of errors dependent on the geometry. In addition, since at least at the beginning of the mission, the orbital plane of SwB was close enough to the lower satellites' orbital planes, the LS dual-sat method can be successfully applied also to the combination SwB-SwA or SwB-SwC. In such events, the standard SwA-SwC FAC density estimate can be complemented with one (or sometimes two) additional estimate(s).
The present contribution reports on the progress made by the ESA project SIFACIT, towards using the full capability of Swarm to better characterize the FAC system. Dual-sat FAC density estimations that rely on flexible SwA-SwC quad configuration, tailored to the FAC location, are presented and compared with the official dual-sat L2 product. At the same time, examples are shown when the use of SwB-SwA or SwB-SwC configuration provides valuable and complementary results, like in the region near the geographic poles or when the difference in orbital phase between SwB and SwA or SwC is smaller than between SwA and SwC.
A New Approach for Retrieving Time Series of External and Internal Spherical Harmonic Coefficients Describing Signals of Magnetospheric Origin
1ETH Zurich, Switzerland; 2NASA Goddard Space Flight Center, Greenbelt, USA; 3National Space Institute, Technical University of Denmark, Lyngby, Denmark
3-D electrical conductivity distribution at mid mantle depths (400-1500 km) was envisaged to be one of the Swarm Cat-1 L2 products. In order to detect 3-D variations of conductivity it was planned to exploit Swarm and observatory magnetic field signals of magnetospheric origin and to invert the so-called matrix Q-responses. These responses relate spherical harmonic (SH) coefficients of internal (induced) and external (inducing) parts of the magnetic potential. Time series of these coefficients are estimated within Comprehensive Inversion framework using potential method. Interpretation of Q-responses estimated from more than 3 years of Swarm and observatorydata did not reveal, however, any meaningful 3-D variations of mid mantle conductivity, most probably due to a poor recovery of the induced coefficients responsible for 3-D effects.
We propose an alternative approach for retrieving time series of induced (and inducing) coefficients. It is based, in particular, on the fact that the horizontal magnetic field components are much less influenced by effects from 3-D inhomogeneities of the Earth compared to the vertical component. This suggests a two-step procedure for retrieving time series of the inducing and induced coefficients: First, by analysing horizontal component and assuming that the Earth’s background conductivity is known, one determines time series of inducing coefficients. Second, with the retrieved time series of inducing coefficients one determines induced coefficients by analysing vertical component only. This study discusses challenges and numerical details of the proposed approach.
On the Role of Fine-Scale Non-Stationary Magnetic Field Perturbations in FAC Systems: Swarm Satellite Observations
1University of Alberta, Edmonton, Alberta, Canada; 2University of Calgary, Calgary, Alberta, Canada; 3John Hopkins University Applied Physics Laboratory, Laurel, MD, USA; 4Mullard Space Science Laboratory, University College London, London, UK; 5NASA Goddard Space Flight Center, Greenbelt, MD, USA; 6National Observatory of Athens, Athens, Greece; 7National and Kapodistrian University of Athens, Athens, Greece
The orbital configuration of the Swarm satellites, with along-track and cross-track separations on the scales of tens of kilometers, allows for the estimation of field-aligned current (FAC) density during traversals of the auroral zones. However, such FAC estimates rely on the assumption that the magnetic field perturbations are quasi-stationary on the temporal scales of the crossings. Past work has focused on elucidating large-scale current features employing techniques such as low-pass filtering to remove any large-amplitude Alfven waves and/or azimuthally localised current filaments which might invalidate these assumptions. In the new work presented here, we present evidence that in a significant proportion of auroral zone crossings the quasi-stationarity assumption may be violated and that the scales at which is it violated are energetically significant and cannot be easily discounted as small scale filamentations. Large-amplitude non-stationarities appear to be ubiquitous in the FAC associated with the coupled magnetosphere-ionosphere system and may have the potential to account for a significant part of the total energy budget. The non-stationarities are analysed statistically with relation to season, meridian and IMF Bz to further elucidate the nature of these dynamics and the potential extend of their energetic significance.
The Revised Time-Frequency Analysis (R-TFA) Tool of the Swarm Mission
1National Observatory of Athens, Greece; 2University of Athens, Greece
The IAASARS/NOA team has developed versatile signal processing tools suitable for the verification and validation of Swarm Level 1b products of the magnetic field [vector fluxgate magnetometer (VFM) and absolute scalar magnetometer (ASM) measurements] as well as of the electric field and electron density [Electric Field Instrument (EFI) measurements]. These tools can be used for the study of magnetospheric Ultra Low Frequency (ULF) waves and ionospheric Equatorial Spread-F (ESF) events, which are phenomena of space weather with effects on technology infrastructure. They are also useful for deriving sets of data suitable for lithospheric and main magnetic field modelling. These tools have the capability to extract information needed to detect space weather events as well as to complement other validation tools used on Swarm mission. Developed to derive the characteristics of ULF waves, the Time-Frequency Analysis (TFA) methodology, based on wavelet transforms, has proven to be effective when applied to the Swarm data to retrieve, on an operational basis, new information about the near-Earth electromagnetic environment. Processing Swarm measurements with the TFA tools helps elucidate the physical processes influencing the generation and propagation of ULF waves, which in turn play a crucial role in magnetospheric dynamics. Here, we present the Revised TFA (R-TFA) tool introducing a new user friendly "web" interface. The main advantage of the R-TFA tool is that is available publicly via a web browser to the scientific community without any software/hardware requirements and tedious installation processes. The new web interface is designed in a way to provide the user all the scientific information (data, products) via a number of user friendly fields and forms.
In Situ Measurements in Perturbed Plasma
University of Alberta, Canada
Humanity relies more on space technology now than it ever did. The optimal use of space technology must be based on a good understanding of the interaction between hardware and space environment. Previous work1 has suggested that this interaction may cause aberration for in situ measurements. Since the presence of instruments perturbs the space plasma, measurement devices collect information of a modified state of the environment. The preliminary purpose of this work is to study the role of the earth magnetic field on in situ measurements obtained with a Langmuir probe. A 3D-particle-in-cell, fully electrostatic code is used to simulate the interaction between the Langmuir Probe and the space environment. The code provides detailed diagnostics, such as the particle flux and current for both species, electric field and potential, and velocity distributions. These parameters are used to construct the current-voltage characteristic of the Langmuir probe. From this electrostatic relation, the temperature and density of the plasma are calculated. Preliminary results show that the orientation of the magnetic field yields to a discrepancy in the measured temperature that is in agreement with reported data1. The preliminary simulations suggest that the earth magnetic field connects the Langmuir probe with other parts of the spacecraft by driving currents that modify the particle flux collected by the probe. Since the space plasma temperature is strongly related to the collection of particles, the electron temperature inferred from probe characteristics is directly affected by the earth magnetic field’s orientation. Further research needs to be done in order to have a better understanding of all the physical processes involved.
Magnetic Remote Sensing of Ocean Heat Content
NASA GSFC, United States of America
Understanding and predicting climate and sea level change requires monitoring the amount of heat stored in the ocean. A primary concern is that the extent of global warming may currently be masked by unaccounted heat increases in the ocean. Despite the recognized importance, adequate monitoring of ocean heat content has remained elusive using established in situ observational methods.
Here we demonstrate that monitoring of ocean heat content may be performed by satellite magnetometers by exploiting a phenomenon whereby ocean flow generates weak magnetic-field fluctuations that reach far outside of the ocean, even passing through sea ice. These magnetic fluctuations are modulated by the ocean’s electrical conductance (i.e. depth-integrated electrical conductivity) which we show to be linearly related to depth-integrated ocean temperature and thereby depth-integrated heat content. Inversion of magnetic data using the electromagnetic induction equation and appropriate methodology might then provide a means of remotely monitoring ocean heat content. Demonstration of this opportunity is made timely by the global magnetic survey underway by the recently launched ESA Swarm constellation of satellites that provides for the first time two-component gradiometric remote measurements of the magnetic field. Although we discuss here an example using just one ocean tidal constituent (the semi-diurnal M2), the larger opportunity allows joint inversions of a variety of induced and motionally induced ocean magnetic signals.
Our research actively underway so far specifically shows (a) a strong linear relationship between conductance and heat content; (b) a proof in concept that a highly accurate description of conductance can be recovered from synthetic (i.e. numerically modeled) ocean tidal (M2) magnetic data as would be observable remotely; (c) an M2 tidal magnetic field extracted from observations that agrees well with the synthetic prediction; and (d) that despite this agreement conductance obtained by inverting the observed M2 magnetic data can show disproportionate differences that are sensitive to the inversion method currently used (a factor of the well-known ill-posedness in inverse problems) such that observational noise and/or modeling errors presently limit the practical reliability of results. Addressing this challenge are the improved observational data being collected by Swarm, and continuing efforts at NASA GSFC to extract further oceanic signals to be used jointly in the inversions while also improving the data processing, modeling, and inversion methodologies.