DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near
Space Interactions

Editorial Board (November 2023)
Editor-in-Chief
Takeshi Sagiya, Nagoya University, Japan

Vice Editors-in-Chief
Masahito Nosé, Nagoya City University, Japan

Aitaro Kato, University of Tokyo, Japan

Editors
Koki Aizawa
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Xiaowei ChenPeter Chi
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Journal Scope
Earth, Planets and Space (EPS) is the official journal of Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
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Earth, Planets and Space(2023) 75:137
Stolle et al. Earth, Planets and Space
https://doi.org/10.1186/s40623-023-01893-6

Open Access

PREFACESpecial issue “DynamicEarth: Earth’s interior,surface, ocean, atmosphere, and near spaceinteractions”
C. Stolle1*, J. Baerenzung2, E. A. Kronberg3, J. Kusche4, H. Liu5 and H. Shimizu6

fields requires knowledge of the all these Earth’s components. In turn, observations of the geomagnetic andthe gravitational fields provide a wealth of information
about them. An interdisciplinary approach is thus mosteffective to best exploit new observations and advanced
modelling capabilities. The Priority Programme 1788
“DynamicEarth” funded by the German Research Foundation (DFG) between 2015 and 2021 has established aninternational research framework for gravity, geomagnetism, space and atmospheric sciences to tackle theinterdisciplinary questions. This special issue collects
contributions that exploit data from recent dedicated satellites in low Earth orbit, such as ESA’s Swarm mission
launched in 2013 and the US/German GRACE-FO mission launched in 2018, among others. It also addresses
studies based on ground-based observations and on
empirical and numerical models which concerns one ormore of these geoscientific research areas.
A global geomagnetic field model derived from dataof several satellites, as well as ground, airborne and shipdata is provided by Baerenzung et al. (2022). At well covered regions, the model reaches resolutions up to spherical harmonic degree and order 1000, and temporally
down to 3 h. It thus emphasises on the representationof the lithospheric field. Another model advancement
lies in the joint estimation of the magnetospheric fields
and those induced in the mantle and crust. Oceanic
magnetic signals are expected to provide valuable information on climatological trends in the ocean. Their
extraction from geomagnetic measurements requires,
however, high-precision estimates from other magnetic
field sources. Petereit et al. (2022) used 10 years of geomagnetic ground-based observations to investigate the

The near-Earth’s gravity and magnetic fields are mostimportant to enable terrestrial life. The role of the gravity field is obvious, it reflects the mass distribution of the
Earth’s interior and determines, e.g., the flow of water.
The role of the geomagnetic field is more indirect. It
protects our atmosphere from severe solar and cosmic
radiation. Mankind’s capability to measure the gravity
and geomagnetic fields has been fundamentally important to advance societal development since hundreds ofyears (e.g., navigation) and it has brought scientific breakthroughs in several disciplines of geosciences recently(e.g., response of ground water tables to natural climate
variability and anthropogenic water use, characteristics
of solar–terrestrial interactions in the magnetosphereand space weather).
Variations in Earth’s interior, atmosphere, oceans,and near-Earth space manifest in the gravity and Earth’s
magnetic fields and their changes. Understanding the
spatial and temporal characteristics of these potential*Correspondence:
C. Stolle
cstolle@iap-kborn.de
1
Leibniz Institute of Atmospheric Physics at the University of Rostock,
Schloßstraße 6, 18225 Kühlungsborn, Germany
2
Institute of Geodesy, Technical University of Berlin,
Kaiserin-Augusta-Allee 104, 10553 Berlin, Germany
3
Department of Earth and Environmental Sciences, Ludwig-MaximiliansUniversität Munich, Theresienstraße 41, 80333 Munich, Germany
4
Institute of Geodesy and Geoinformation, Rheinische FriedrichWilhelms-University of Bonn, Nussallee 17, 53115 Bonn, Germany
5
Department of Earth and Planetary Science, Kyushu University,
Fukuoka 819-0395, Japan
6
Earthquake Research Institute, University of Tokyo, Yayoi 1-1-1,
Bunkyo-ku, Tokyo 113-0032, Japan© The Author(s) 2023. Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which
permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to theoriginal author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images orother third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line
to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory
regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of thislicence, visit http://creativecommons.org/licenses/by/4.0/.

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DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions
Stolle et al. Earth, Planets and Space(2023) 75:137

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a comprehensive study of solar and lunar daily geomagnetic variations and their equivalent ionosphericcurrent systems in the E region including their quantification. Only available from ground-based, locally
restricted data so far, this paper provides a global viewon atmospheric tides in the magnetic field based on
Swarm observations. Sporadic-E events are E region
ionospheric irregularities and they, as well as postsunset equatorial F region irregularities, can disturb
trans-ionospheric radio waves used for navigation, suchas GNSS, severely through their strong imprint in local
plasma density gradients. Arras et al. (2022) discussed
generation mechanisms for the rarely observed equatorial Sporadic-E events based on GPS radio occultation
data from multiple satellites, while Sobhkhiz-Miandehi
et al. (2022) identified tidal variations in the occurrenceof mid-latitude Sporadic-E events based on GPS radio
occultation of the FORMOSAT-3/COSMIC mission andcompared the observations with results from a wholeatmosphere General Circulation Model (GCM).
Parameterised imaging of the regular global ionosphericplasma density is provided by Lalgudi Gopalakrishnan andSchmidt (2022). Also their work relies on electron density
profiles derived from GPS observations onboard the GRACE
and the FORMOSAT-3/COSMIC missions supported byin situ electron density data from several missions. Validation with independent ionosonde data revealed a correlation
between observations and their parameterised images of theionospheric F region peak height up to 90%. The variabilityof neutral winds and temperature in the Mesosphere–Lower
Thermosphere (MLT) largely determine the variability ofthe entire ionosphere, e.g., by the propagation of atmospheric tides and waves. Thus, the MLT is a major link invertical atmosphere coupling. Based on globally distributed,
satellite-based neutral temperature data and results from awhole-atmosphere GCM, Siddiqui et al. (2022) described the
reduction of low-latitude solar tides at the MLT during both
Northern and Southern stratospheric warming events. Theysuggested that changes in the latitudinal shear in the MLT
could explain the observed variability. Based on a synthetic
data set for a network of radar stations, He (2023) reviewed
existing analysis schemes and introduced a new scheme forthe derivation of planetary waves in the MLT winds, as wellas compared the implications of the schemes on the analysis
results. Applying a spectral analysis on a data set from a radar
network campaign in northern Germany, Charuvil Asokan
et al. (2022) provided evidence that gravity waves with periods between 2 and 7 h dominate horizontal medium-scale
structures of neutral winds in the MLT.
Several of the works in this special issue rely on amost accurate performance of GCMs of the upper
atmosphere. As a step forward towards a most
realistic representation of neutral and electron

seasonal variations and long-term trends of oceanic lunar
tide. An increased specification of errors in estimating
oceanic tidal signals by applying the model infrastructure described in Baerenzung et al. (2022) from this special issue is discussed in Saynisch-Wagner et al. (2021).
Differently to oceanic tides, signals from ocean circulation are very challenging to detect in magnetic observations due to their long-term variability combined with
their low amplitude, but still could provide an approach
towards better understanding ocean climate evolution.
To this aim, Hornschild et al. (2022) evaluated a newalgorithm for detecting magnetic signals of ocean circulation on a synthetic data set.
Space- and ground-based geomagnetic observations
combined with, e.g, electric field, plasma density and drift,and solar wind data are crucial to investigate the magnetosphere–ionosphere interactions and, in addition, areessential in characterising signal properties from magnetospheric sources. To complement the Swarm data base ofmagnetic measurements, Michaelis et al. (2022) and StypRekowski et al. (2022) presented calibrated magnetic datafrom non-dedicated instruments onboard ESA’s GOCE
satellite mission by an analytical and by a Machine Learning technique, respectively. Their results demonstrate thehigh value and quality of the data from this low-flying satellite (about 260 km altitude) by successful applications inimaging magnetic signatures of the lithospheric field anddeciphering the local time dependence of magnetosphericring current signals. Xiong et al. (2021) exploited recently
non-dedicated calibrated magnetometer data of the
GRACE-FO twin satellite mission which flies in a stringof-pearls constellation. They derived characteristic correlations lengths of magnetic disturbances due to auroral
field-aligned currents. By the combination of solar wind,
geomagnetic, and ionospheric data and indices, Rout et al.
(2022) identified a global magnetosphere–ionospherequasi-resonant mode of oscillation during long-duration
auroral geomagnetic activity.
At the mid- and low-latitude ionosphere, high-precision satellite-based geomagnetic observations are used
to investigate ionospheric currents which result froma close interaction with neutral dynamics in the lower
thermosphere and atmosphere, and with the geomagnetic field. Rodríguez-Zuluaga et al. (2022) provide thefrontier letter of this special issue identifying the sourceof low-latitude post-sunset F region plasma irregularities to be off-equatorial which is in contrast to earlier
theories suggesting equatorial sources. This observational evidence was achieved by analysing the 3-component Swarm magnetic field measurements and thederived hypothesis was verified with a local physicsbased model of ionospheric irregularities. Concerning
regular, periodic variability, Yamazaki (2022) provides

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Earth, Planets and Space
Stolle et al. Earth, Planets and Space(2023) 75:137

Page 3 of 3

density in GCMs, Corbin and Kusche (2022) and Fernandez-Gomez et al. (2022) proposed data assimilation
approaches of CHAMP, GRACE, and Swarm neutral
density data into a GCM and could demonstrate theimprovement of the model predictions of neutral andelectron density, respectively.
Only a multi-disciplinary approach from disciplines
in geophysics, meteorology, geodesy, and theoreticaldevelopments can reveal a better understanding of thecomplex variability of Earth’s magnetic and gravity fields
including the various sources of this variability, e.g., in
the Earth’s interior, oceans, magnetosphere, and atmosphere. The presented papers give valuable examples offruitful interdisciplinary research in solar–terrestrial
science and provide ground for new approaches.

occultation measurements. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01718-y
Baerenzung J, Holschneider M, Saynisch-Wagner J, Thomas M (2022) Kalmag:
a high spatio-temporal model of the geomagnetic field. Earth Planets
Space. https://doi.org/10.1186/s40623-022-01692-5
Charuvil Asokan H, Chau J, Marino R, Vierinen J, Vargas F, Urco JM, Clahsen M,
Jacobi C (2022) Frequency spectra of horizontal winds in the mesosphereand lower thermosphere region from multistatic specular meteor radarobservations during the SIMONe 2018 campaign. Earth Planets Space.
https://doi.org/10.1186/s40623-022-01620-7
Corbin A, Kusche J (2022) Improving the estimation of thermospheric
neutral density via two-step assimilation of in situ neutral density
into a numerical model. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01733-z
Fernandez-Gomez I, Kodikara T, Borries C, Forootan E, Goss A, Schmidt M,
Codrescu M (2022) Improving estimates of the ionosphere during geomagnetic storm conditions through assimilation of thermospheric massdensity. Earth Planets Space. https://doi.org/10.1186/s40623-022-01678-3
He M (2023) Planetary-scale MLT waves diagnosed through multi-station
methods: a review. Earth Planets Space. https://doi.org/10.1186/
s40623-023-01808-5
Hornschild A, Baerenzung J, Saynisch-Wagner J, Irrgang C, Thomas M (2022)
On the detectability of the magnetic fields induced by ocean circulationin geomagnetic satellite observations. Earth Planets Space. https://doi.
org/10.1186/s40623-022-01741-z
Lalgudi Gopalakrishnan G, Schmidt M (2022) Ionospheric electron density
modelling using B-splines and constraint optimization. Earth Planets
Space. https://doi.org/10.1186/s40623-022-01693-4
Michaelis I, Styp-Rekowski K, Rauberg J, Stolle C, Korte M (2022) Geomagnetic
data from the GOCE satellite mission. Earth Planets Space. https://doi.org/
10.1186/s40623-022-01691-6
Petereit J, Saynisch-Wagner J, Morschhauser A, Pick L, Thomas M (2022)
On the characterization of tidal ocean-dynamo signals in coastal
magnetic observatories. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01610-9
Rodríguez-Zuluaga J, Stolle C, Hysell D, Knudsen DJ (2022) Topside equatorial
spread F-related field-aligned Poynting flux: observations and simulations. Earth Planets Space. https://doi.org/10.1186/s40623-022-01679-2
Rout D, Singh R, Pandey K, Pant TK, Chakrabarty D, Thampi S, Bag T (2022)
Evidence for presence of a global quasi-resonant mode of oscillations
during high-intensity long-duration continuous AE activity (HILDCAA)
events. Earth Planets Space. https://doi.org/10.1186/s40623-022-01642-1
Saynisch-Wagner J, Baerenzung J, Hornschild A, Irrgang C, Thomas M (2021)
Tide-induced magnetic signals and their errors derived from CHAMP and
Swarm satellite magnetometer observations. Earth Planets Space. https://doi.org/10.1186/s40623-021-01557-3
Siddiqui T, Chau J, Stolle C, Yamazaki Y (2022) Migrating solar diurnal
tidal variability during Northern and Southern hemisphere sudden
stratospheric warmings. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01661-y
Sobhkhiz-Miandehi S, Yamazaki Y, Arras C, Miyoshi Y, Shinagawa H (2022)
Comparison of the tidal signatures in sporadic E and vertical ion convergence rate, using FORMOSAT-3/COSMIC radio occultation observations and GAIA model. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01637-y
Styp-Rekowski K, Michaelis I, Stolle C, Baerenzung J, Korte M, Kao O (2022)
Machine learning-based calibration of the GOCE satellite platform
magnetometers. Earth Planets Space. https://doi.org/10.1186/
s40623-022-01695-2
Xiong C, Stolle C, Michaelis I, Lühr H, Zhou Y, Wang H, Kervalishvili G, Rauberg
J (2021) Correlation analysis of field-aligned currents from the magnetic
measurements of GRACE follow-on mission. Earth Planets Space. https://doi.org/10.1186/s40623-021-01540-y
Yamazaki Y (2022) Solar and lunar daily geomagnetic variations and theirequivalent current systems observed by Swarm. Earth Planets Space.
https://doi.org/10.1186/s40623-022-01656-9

Abbreviations
CHAMP
CHAllenging Minisatellite Payload
COSMIC
Constellation Observing System for Meteorology, Ionosphere,
and Climate
ESA
European Space Agency
GCM
General Circulation Model
GNSS
Global Navigation Satellite Systems
GOCE
Gravity field and steady-state OCean circulation Explorer
GPS
Global Positioning System
GRACE(-FO) GRavity Recovery and Climate Experiment (-Follow-On)
MLT
Mesosphere–lower thermosphereAcknowledgements
We express our sincere gratitude to the authors who contributed to thisspecial issue and the reviewers who evaluated the contributions and gavethoughtful comments and suggestions. We also thank Editor-in-Chief Takeshi
Sagiya for his support in editing the issue. Particular acknowledgement isgiven to the German Research Foundation (DFG) for the installation of the Priority Programme 1788 “Dynamic Earth” supporting many of the joint research
activities and published works, as well as to the external review panel for theirthorough and constructive evaluation of the research project proposals.
Author contributions
All authors of this article served as guest editors for this special issue. All
authors read and approved the final manuscript.
Funding
This initiative has been partly supported by projects in the Priority Programme
1788 “Dynamic Earth” funded by the German Research Foundation (DFG).
Availability of data and materials
Not applicable.

Declarations
Competing interests
The authors declare that they have no competing interests.
Received: 7 July 2023 Accepted: 29 August 2023

References
Arras C, Resende L, Kepkar A, Senevirathna G, Wickert J (2022) Sporadic E
layer characteristics at equatorial latitudes as observed by GNSS radio

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions

FRONTIER LETTER

Open Access

Topside equatorial spread F-related field-aligned Poynting
flux: observations and simulations
J. Rodríguez-Zuluaga*, C. Stolle, D. Hysell and D. J. Knudsen
Earth, Planets and Space 2022, 74:119 DOI: 10.1186/s40623-022-01679-2
Received: 5 April 2022, Accepted: 14 July 2022, Published: 29 July 2022

Abstract
Electric and magnetic field data from the Swarm constellation mission are used to report on the Poynting flux associated withpostsunset topside equatorial spread F. A three-dimensional numerical simulation of plasma density irregularities in the Fregion ionosphere leading to spread F is used to interpret and support the satellite observations. Here, we focus on quasistatic magnetic and electric fields nearby equatorial plasma depletions (EPDs). The observations show a correlation of the
Poynting flux with the plasma number density when background densities are larger than105 cm−3—typical of pre-midnight
hours. In other words, the Poynting flux increases as EPDs get more depleted. As time passes, both plasma density andPoynting flux decay. For the latter, however, this temporal dependence is evident in the pre-midnight sector only. Concerning
spatial variations, the Poynting flux is observed to enhance inside EPDs as a function of magnetic latitude mainly due to thestrengthening of field-aligned currents as they flow away from the dip equator. The Poynting flux follows the dynamo theory,
wherein the winds in the F region act as the generator at night and theE region conductivity on shared magnetic field lines as the load. Thatsaid, the Poynting flux is generally expected to flow along the field lines
away from a dynamo source at the dip equator. Nevertheless,observations show unidirectional flows from one magnetic hemisphereto another, suggesting a generator below the satellites’ altitude. The
numerical simulations confirm these observations and show that suchlatitudinal shifts of the generator are due almost entirely to the winds.

Keywords: Equatorial spread F, Plasma density depletions, Poynting
flux, Swarm, Spread F simulation

Graphical abstract*Corresponding author: J. Rodríguez-Zuluaga, juanrz@gfz-potsdam.de

FULL PAPER

Open AccessCorrelation analysis of field-aligned currents from the magnetic
measurements of GRACE follow-on mission
Chao Xiong*, Claudia Stolle, Ingo Michaelis, Hermann Lühr, Yunliang Zhou, Hui Wang,
Guram Kervalishvili and Jan Rauberg
Earth, Planets and Space 2021, 73:206 DOI: 10.1186/s40623-021-01540-y
Received: 7 September 2021, Accepted: 3 November 2021, Published: 15 November 2021

Abstract
In this study we performed a detailed analysis on the scale-size of field-aligned currents (FACs) at auroral latitudes, using the well-calibrated
magnetic data from the non-dedicated magnetic field mission, Gravity Recovery and Climate Experiment Follow-On (GRACE-FO). With two
spacecraft following each other, the GRACE-FO provides a good opportunity to identify the variation of FACs with different scale lengths. The
results show that the auroral FACs can be classified into two groups: the small-scale ones, shorter than some tens of kilometers, dominated bykinetic Alfvén waves, are quite dynamic; and the large-scale ones, typically larger than 150 km, can be considered as quasi-static and persist
longer than 1 min. The GRACE-FO observations also reveal that the small-scale FACs at the same location sometimes can persist over 25 s, e.g.,around dusk and dawn hours, which is longer than the typical persistent period (10 s) of kinetic Alfvén waves as earlier reported. The FAC
structures show clear magnetic local time dependence, with higher correlations between the spacecraft around dusk and dawn hours; lower
correlations are found around midnight and lowest correlations around noon, implying that the small-scale FACs most frequently appear at thenoon cusp region. Slightly better correlations of FACs between two spacecraft are found during local summer, and such seasonal dependence isdominated by the correlations ofsmall-scale FACs at noon.
However, further analysis showsthat the small-scale FACs at noon
have largest occurrence andintensity during local summer,
which reveals that wheninterpreting the cross-correlation
analysis the intensity of FACs
needs to be taken into account.
Graphical abstract*Corresponding author: Chao Xiong, xiongchao@whu.edu.cn
4Earth, Planets and Space

FULL PAPER

Open AccessTide-induced magnetic signals and their errors derived
from CHAMP and Swarm satellite magnetometer
observations
Jan Saynisch-Wagner*, Julien Baerenzung, Aaron Hornschild, Christopher Irrgang
and Maik Thomas
Earth, Planets and Space 2021, 73:234 DOI: 10.1186/s40623-021-01557-3
Received: 15 September 2021, Accepted: 8 December 2021, Published: 20 December 2021

Abstract
Satellite-measured tidal magnetic signals are of growing importance. These fields are mainly used to infer Earth’s mantle
conductivity, but also to derive changes in the oceanic heat content. We present a new Kalman filter-based method to derivetidal magnetic fields from satellite magnetometers: KALMAG. The method’s advantage is that it allows to study a precisely
estimated posterior error covariance matrix. We present the results of a simultaneous estimation of the magnetic signals of 8
major tides from 17 years of Swarm and CHAMP data. For the first time, robustly derived posterior error distributions arereported along with the reported tidal magnetic fields. The results are compared to other estimates that are either based on
numerical forward models or on satellite inversions of the same data. For all comparisons, maximal differences and thecorresponding globally averaged RMSE are reported. We found that the inter-product differences are comparable with the
KALMAG-based errors only in a global mean sense. Here, allapproaches give values of the same order, e.g., 0.09 nT-0.14
nT for M2. Locally, the KALMAG posterior errors are up to
one order smaller than the inter-product differences, e.g.,
0.12 nT vs. 0.96 nT for M2.

Keywords: Tides, Electromagnetic induction, Error
covariance, Satellite magnetometer
observations

Graphical abstract*Corresponding author: Jan Saynisch-Wagner, saynisch@gfz-potsdam.de

FULL PAPER

Open AccessOn the characterization of tidal ocean-dynamo signals incoastal magnetic observatories
Johannes Petereit*, Jan Saynisch-Wagner, Achim Morschhauser, Leonie Pick and Maik Thomas
Earth, Planets and Space 2022, 74:67 DOI: 10.1186/s40623-022-01610-9
Received: 22 September 2021, Accepted: 23 March 2022, Published: 29 April 2022

Abstract
Periodic tidal ocean currents induce electric currents and, therefore, magnetic field signals that are observable using spaceborne and groundbased observation techniques. In theory, the signals can be used to monitor oceanic temperature and salinity variations. Tidal magnetic field
amplitudes and phases have been extracted from magnetometer measurements in the past. However, due to uncertainties caused by aplentitude of influencing factors, the shape and temporal variation of these signals are only known to a limited extent. This study uses past
extraction methods to characterize seasonal variations and long-term trends in the ten year magnetometer time series of three coastal island
observatories. First, we assess data processing procedures used to prepare ground-based magnetometer observations for tidal ocean dynamo
signal extraction to demonstrate that existing approaches, i.e., subtraction of core field models or first-order differencing, are unable toreliably remove low-frequency contributions. We hence propose low-frequency filtering using smoothing splines and demonstrate theadvantages over the existing approaches. Second, we determine signal and side peak magnitudes of the M2 tide induced magnetic fieldsignal by spectral analysis of the processed data. We find evidence for seasonal magnetic field signal variations of up to 25% from the annual
mean. Third, to characterize the long-term behavior of tidal ocean dynamo signal
amplitudes and phases, we apply different signal extraction techniques to identify
tidal ocean-dynamo signal amplitudes and phases in sub-series of the ten-year timeseries with incrementally increasing lengths. The analyses support three main
findings: (1) trends cause signal amplitude changes of up to ≈1 nT and phasechanges are in the order of O(10°) within the observation period; (2) at least four
years of data are needed to obtain reliable amplitude and phase values with theextraction methods used and (3) signal phases are a less dependent on the chosen
extraction method than signal amplitudes.

Keywords: Ocean-tide induced magnetic fields, Tidal ocean dynamo, EMOTS,
Signal extraction, Magnetometer Observations, Data Processing*Corresponding author: Johannes Petereit, petereit@gfz-potsdam.de5Petereit et al. Earth, Planets and Space, April 2022

Graphical abstract

DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions

FULL PAPER

Open AccessFrequency spectra of horizontal winds in the mesosphere andlower thermosphere region from multistatic specular meteor
radar observations during the SIMONe 2018 campaign
Harikrishnan Charuvil Asokan*, Jorge L. Chau, Raffaele Marino, Juha Vierinen, Fabio Vargas,
Juan Miguel Urco, Matthias Clahsen and Christoph Jacobi
Earth, Planets and Space 2022, 74:69 DOI: 10.1186/s40623-022-01620-7
Received: 7 July 2021, Accepted: 2 April 2022, Published: 11 May 2022

Abstract
In recent years, multistatic specular meteor radars (SMRs) have been introduced to study the Mesosphere and Lower Thermosphere (MLT) dynamics
with increasing spatial and temporal resolution. SMRs, compared to other ground-based observations, have the advantage of continuously measuring
the region between 80 and 100 km independent of weather, season, or time of day. In this paper, frequency spectra of MLT horizontal winds are
explored through observations from a campaign using the SIMONe (Spread-spectrum Interferometric Multistatic meteor radar Observing Network)
approach conducted in northern Germany in 2018 (hereafter SIMONe 2018). The 7-day SIMONe
2018 comprised of fourteen multistatic SMR links and allows us to build a substantial database of(a)specular meteor trail events, collecting more than one hundred thousand detections per day withina geographic area of ~500 km × 500 km. We have implemented two methods to obtain thefrequency spectra of the horizontal wind components: (1) Mean Wind Estimation (MWE) and (2)Wind field Correlation Function Inversion (WCFI), which utilizes the mean and the covariances of theline of sight velocities, respectively. Monte Carlo simulations of a gravity wave spectral model were
implemented to validate and compare both methods. The simulation analyses suggest that theTime period (hour)
WCFI helps us to capture the energy of smaller scale wind fluctuations than those capture with(b)(c)
MWE. Characterization of the spectral slope of the horizontal wind at different MLT altitudes has
been conducted on the SIMONe 2018, and it provides evidence that gravity waves with periods
ωω
smaller than 7 h and greater than 2 h dominate with horizontal structures significantly larger than
500 km. In the future, these analyses can be extended to understand the significance of small-scale
fluctuations in the MLT, which were not possible with conventional MWE methods.
100.0

100

λz (km)

0
200.

15

30

0.0

10

50

40

0.0

0.0

70

60

0.0

0.0

0.0

900.
0

800

.0

1200
.0
1100
.0

1600
.0
1500
.0
1400
.0
1300
.0

170

1200
1000
800
600

λH (km)

20

400

5

200

Power spectral density(m2s−2/ (rad/s))

102

Keywords: Frequency spectra, Mesosphere and lower thermosphere, Specular meteor

radar, Horizontal winds, Wind field Correlation Function Inversion, SIMONe 2018

1

2

8h

4h

3

4

2h

1h

101

5

102

6

8h

7

4h

8

2h

1h

101

−2

100

−2

100

WCFI50 km

WCFI500 km

Input
MWE

10−1

10−4

10−1

ω (rad/s)

10−3

10−4

Input
MWE

ω (rad/s)

10−3Graphical abstract*Corresponding author: Harikrishnan Charuvil Asokan, hari@iap-kborn.de

FULL PAPER

Open AccessComparison of the tidal signatures in sporadic E andvertical ion convergence rate, using FORMOSAT-3/COSMIC
radio occultation observations and GAIA model
Sahar Sobhkhiz-Miandehi*, Yosuke Yamazaki, Christina Arras, Yasunobu Miyoshi
and Hiroyuki Shinagawa
Earth, Planets and Space 2022, 74:88 DOI: 10.1186/s40623-022-01637-y
Received: 1 November 2021, Accepted: 29 April 2022, Published: 7 June 2022

Abstract
Sporadic E or Es is a transient phenomenon where thin layers of enhanced electron density appear in the ionospheric E region(90–120 km altitude). The neutral wind shear caused by atmospheric tides can lead ions to converge vertically at E-region
heights and form the Es layer. This research aims to determine the role of atmospheric solar and lunar tides in Es occurrence.
For this purpose, radio occultation data of FORMOSAT-3/COSMIC have been used, which provide complete global coverage ofEs events. Moreover, GAIA model simulations have been employed to evaluate the vertical ion convergence induced by solar
tides. The results show both migrating and non-migrating solar tidal
signatures and the semidiurnal migrating lunar tidal signature
mainly in low and mid-latitude Es occurrence. The seasonal variationof the migrating solar tidal components of Es is in good agreementwith those in the vertical ion convergence derived from GAIA athigher altitudes. Furthermore, some non-migrating components ofsolar tides, including semidiurnal westward wavenumbers 1 and 3
and diurnal eastward wavenumbers 2 and 3, also significantly affectthe Es occurrence rate.

Keywords: Sporadic E, Es, Wind shear, Solar tide, Lunar tide, GAIA,Radio occultation*Corresponding author: Sahar Sobhkhiz-Miandehi, sahar@gfz-potsdam.de
6

Graphical abstract

Earth, Planets and Space

FULL PAPER

Open AccessSolar and lunar daily geomagnetic variations and theirequivalent current systems observed by Swarm
Yosuke Yamazaki
Earth, Planets and Space 2022, 74:99 DOI: 10.1186/s40623-022-01656-9
Received: 14 February 2022, Accepted: 2 June 2022, Published: 23 June 2022

Abstract
This paper describes solar and lunar daily variations of the geomagnetic field over low- and mid-latitude regions, using vector
magnetometer data from Swarm satellites at altitudes of ~500 km during the solar minimum years of 2017–2020. The average
solar variation of the geomagnetic field is within the range of ±14 nT, while the lunar variation is within ±2 nT. The latter iscomparable to the ocean tidal field. A spherical harmonic analysis is performed on the solar and lunar variations to evaluate
their internal and external equivalent current systems. The results show that both the solar and lunar variations are mainly ofinternal origin, which can be attributed to
combined effects of ionospheric dynamo currents
and induced underground currents. Global patternsof the internal solar and lunar current systems are
consistent with the corresponding external current
systems previously reported based on groundobservations. The Swarm external currents aremainly in the meridional direction, and are likely
associated with interhemispheric field-aligned
currents. Both the internal and external current
systems depend on the season and longitude.

Keywords: Geomagnetic field, Sq, L, Daily

variation, Ionospheric currents, Swarm
Graphical abstract

Corresponding author: Yosuke Yamazaki, yamazaki@iap-kborn.de

FULL PAPER

Open Access

Migrating solar diurnal tidal variability during Northern andSouthern Hemisphere Sudden Stratospheric Warmings
Tarique A. Siddiqui*, Jorge L. Chau, Claudia Stolle and Yosuke Yamazaki
Earth, Planets and Space 2022, 74:101 DOI: 10.1186/s40623-022-01661-y
Received: 16 February 2022, Accepted: 9 June 2022, Published: 24 June 2022

Abstract
In this study, the variability of the migrating solar diurnal (DW1) tide in the mesosphere-lower thermosphere (MLT) region
during Northern and Southern Hemisphere (NH & SH) Sudden Stratospheric Warmings (SSWs) is investigated using Soundingof the Atmosphere using Broadband Emission Radiometry (SABER) temperatureobservations and reanalysis-driven Whole Atmosphere Community Climate
Model with thermosphere and ionosphere extension (WACCM-X) simulations.
The periods examined include four major NH SSWs that occurred in 2006, 2009,2010 and 2013 and two SH SSWs that were observed in 2002 and 2019. Our
analysis shows that the DW1 tide in both observations and simulations displays areduction of amplitude at low-latitudes after the onset of NH and SH SSWs. As
WACCM-X simulations qualitatively reproduce this feature of DW1 tidal variability
common to both NH and SH SSWs, they have been used to examine the possible
mechanism that could explain these observations in the DW1 tide. It is known
that changes in the latitudinal shear of zonal winds at low-latitudes strongly
affect the seasonal variation of the DW1 tide in the MLT. We show that SSWassociated changes in the latitudinal shear in the MLT could explain the observed
variability of the DW1 tide during NH and SH SSWs.

Keywords: SSW, Migrating solar tide, Mesosphere-lower thermosphere (MLT),
Atmospheric coupling

Graphical abstract*Corresponding author: Tarique A. Siddiqui, siddiqui@iap-kborn.de7

DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions

FULL PAPER

Open Access

Improving estimates of the ionosphere during geomagnetic
storm conditions through assimilation of thermosphericmass density
Isabel Fernandez-Gomez*, Timothy Kodikara, Claudia Borries, Ehsan Forootan, Andreas Goss,
Michael Schmidt and Mihail V. Codrescu
Earth, Planets and Space 2022, 74:121 DOI: 10.1186/s40623-022-01678-3
Received: 10 February 2022, Accepted: 14 July 2022, Published: 6 August 2022

Abstract
Dynamical changes in the ionosphere and thermosphere during geomagnetic storm times can have a significant impact on our communication andnavigation applications, as well as satellite orbit determination and prediction activities. Because of the complex electrodynamics coupling processes
during storms, which cannot be fully described with the sparse set of thermosphere–ionosphere (TI) observations, it is crucial to accurately model thestate of the TI system. The approximation closest to the true state can be obtained by assimilating relevant measurements into physics-based models.
Thermospheric mass density (TMD) derived from satellite measurements is ideal to improve the thermosphere through data assimilation. Given the
coupled nature of the TI system, the changes in the thermosphere will also influence the ionosphere state. This study presents a quantification of thechanges and improvement of the model state produced by assimilating TMD not only for thethermosphere density but also for the ionosphere electron density under storm conditions. TMD
estimates derived from a single Swarm satellite and the Coupled Thermosphere Ionosphere
Plasmasphere electrodynamics (CTIPe) physics-based model are used for the data assimilation. The
results are presented for a case study during the St. Patricks Day storm 2015. It is shown that the TMD
data assimilation generates an improvement of the model’s thermosphere density of up to 40%(measured along the orbit of the non-assimilated Swarm satellites). The model’s electron density
during the course of the storm has been improved by approximately 8 and 22% relative to Swarm-A
and GRACE, respectively. The comparison of the model’s global electron density against a highquality 3D electron density model, generated through assimilation of total electron content, showsthat TMD assimilation modifies the model’s ionosphere state positively and negatively during storm
time. The major improvement areas are the mid-low latitudes during the storm’s recovery phase.

Keywords: Data assimilation, Geomagnetic storm, Neutral density, Thermosphere–
ionosphere system

Graphical abstract*Corresponding author: Isabel Fernandez-Gomez, Isabel.FernandezGomez@dlr.de

FULL PAPER

Open Access

Machine learning-based calibration of the GOCE satellite
platform magnetometers
Kevin Styp-Rekowski*, Ingo Michaelis, Claudia Stolle, Julien Baerenzung, Monika Korte
and Odej KaoEarth, Planets and Space 2022, 74:138 DOI: 10.1186/s40623-022-01695-2
Received: 6 May 2022, Accepted: 24 August 2022, Published: 13 September 2022

Abstract
Additional datasets from space-based observations of the Earth’s magnetic field are of high value to space physics andgeomagnetism. The use of platform magnetometers from non-dedicated satellites has recently successfully provided
additional spatial and temporal coverage of the magnetic field. The Gravity and steady-state Ocean Circulation Explorer(GOCE) mission was launched in March 2009 and ended in November 2013 with the purpose of measuring the Earth’s gravity
field. It also carried three platform magnetometers onboard. Careful calibration of the platform magnetometers can remove
artificial disturbances caused by other satellite payload systems, improving the quality of the measurements. In this work, amachine learning-based approach is presented that uses neural networks toachieve a calibration that can incorporate a variety of collected information
about the satellite system. The evaluation has shown that the approach isable to significantly reduce the calibration residual with a mean absoluteresidual of about 6.47nT for low- and mid-latitudes. In addition, the calibrated
platform magnetometer data can be used for reconstructing the lithosphericfield, due to the low altitude of the mission, and also observing othermagnetic phenomena such as geomagnetic storms. Furthermore, theinclusion of the calibrated platform magnetometer data also allows
improvement of geomagnetic field models. The calibrated dataset ispublished alongside this work.

Keywords: Machine learning, Calibration, Platform magnetometer, GOCE
satellite, Magnetic field model*Corresponding author: Kevin Styp-Rekowski, styp-rekowski@tu-berlin.de
8

Graphical abstract

Earth, Planets and Space

FULL PAPER

Open AccessKalmag: a high spatio-temporal model ofthe geomagnetic field
Baerenzung Julien*, Holschneider Matthias, Jan Saynisch-Wagner and Maik Thomas
Earth, Planets and Space 2022, 74:139 DOI: 10.1186/s40623-022-01692-5
Received: 2 April 2022, Accepted: 19 August 2022, Published: 16 September 2022

Abstract
We present the extension of the Kalmag model, proposed as a candidate for IGRF-13, to the twentieth century. The dataset serving its derivation
has been complemented by new measurements coming from satellites, ground-based observatories and land, marine and airborne surveys. As
its predecessor, this version is derived from a combination of a Kalman filter and a smoothing algorithm, providing mean models and associateduncertainties. These quantities permit a precise estimation of locations where mean solutions can be considered as reliable or not. The temporal
resolution of the core field and the secular variation was set to 0.1 year over the 122 years the model is spanning. Nevertheless, it can be shown
through ensembles a posteriori sampled, that this resolution can be effectively achieved only by a limited amount of spatial scales and duringcertain time periods. Unsurprisingly, highest accuracy in both space and time of the core field and the secular variation is achieved during the
CHAMP and Swarm era. In this version of Kalmag, a particular effort was made for resolving the small-scale lithospheric field. Under specificstatistical assumptions, the latter was modeled up to spherical harmonic
degree and order 1000, and signal from both satellite and survey
measurements contributed to its development. External and induced
fields were jointly estimated with the rest of the model. We show that theirlarge scales could be accurately extracted from direct measurements
whenever the latter exhibit a sufficiently high temporal coverage.
Temporally resolving these fields down to 3 hours during the CHAMP and
Swarm missions, gave us access to the link between induced andmagnetospheric fields. In particular, the period dependence of the driving
signal on the induced one could be directly observed. The model isavailable through various physical and statistical quantities on a dedicatedwebsite at https://ionocovar.agnld.uni-potsdam.de/Kalmag/.

Keywords: Geomagnetic field, Lithospheric field, Secular variation,

Magnetospheric field, Induced field, Assimilation, Kalmanfilter, Machine learning

Graphical abstract*Corresponding author: Baerenzung Julien, baerenzung@gmx.de

FULL PAPER

Open Access

Ionospheric electron density modelling using B-splines
and constraint optimization
Ganesh Lalgudi Gopalakrishnan* and Michael Schmidt
Earth, Planets and Space 2022, 74:143 DOI: 10.1186/s40623-022-01693-4
Received: 5 April 2022, Accepted: 21 August 2022, Published: 19 September 2022

Abstract
Many modern applications, such as precise point positioning, autonomous driving or precision agriculture would benefit
significantly if a high-precision and high-resolution model of electron density in the ionosphere and the plasmasphere would
be globally available. Since the development of such a model still relies on data with insufficient and uneven global coverage,
the consideration of background information and the introduction of equality and inequality constraints on Chapman key
parameters are essential. In this work, we develop a multi-layer
Chapman model based on B-spline expansions of selected key
parameters of the electron density. The unknown series coefficients of
the key parameters are subject to equality and inequality constraints.
Finally, the developed model is applied to a combination of real andsemi-simulated input data; the results are validated through ionosondemeasurements.

Keywords: Ionosphere layers, Multi-layer Chapman model, Inequality
constraints, B-spline expansions, Optimization approach

Graphical abstract*Corresponding author: Ganesh Lalgudi Gopalakrishnan, ganesh.lalgudi-gopalakrishnan@tum.de9

DynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions

FULL PAPER

Open AccessSporadic E layer characteristics at equatorial latitudes as
observed by GNSS radio occultation measurements
Christina Arras*, Laysa Cristina Araújo Resende, Ankur Kepkar, Gethmini Senevirathna
and Jens Wickert
Earth, Planets and Space 2022, 74:163 DOI: 10.1186/s40623-022-01718-y
Received: 31 March 2022, Accepted: 10 October 2022, Published: 7 November 2022

Abstract
Scintillations in the signal-to-noise (SNR) profiles of GNSS radio occultation (RO) measurements at lower ionospheric altitudes
are caused by compact layers of high ionization also known as sporadic E (Es) layers. It is widely accepted that Es layers areformed by the wind shear mechanism at northern and southern midlatitudes.
However, approaching the equatorial regions, electric fields also control theformation and dispersal of these layers. In this paper we concentrate, inparticular, on the occurrence rate and on the altitudes of Es layers appearing ina narrow band along the Earth’s magnetic equator. We analyzed several millionof RO profiles concerning sporadic E occurrence as well as altitude andobserved a high daily, seasonal and longitudinal variability which is controlled
partly by zonal winds and electric fields. Especially Es layers at higher altitudes
show a clear anticorrelation with the zonal electric field intensity measured by
the Swarm satellites. Further, we solve the existing contradiction of Es layer
signatures being present in equatorial ionosonde measurements while they are
only rarely seen in RO recordings.

Keywords: GNSS radio occultation, Sporadic E layers, Equatorial ionosphere
Graphical abstract*Corresponding author: Christina Arras, arras@gfz-potsdam.de

FULL PAPER

Open AccessOn the detectability of the magnetic fields induced by ocean
circulation in geomagnetic satellite observations
Aaron Hornschild*, Julien Baerenzung, Jan Saynisch-Wagner, Christopher Irrgang
and Maik Thomas
Earth, Planets and Space 2022, 74:182 DOI: 10.1186/s40623-022-01741-z
Received: 16 May 2022, Accepted: 10 November 2022, Published: 9 December 2022

Abstract
Due to their sensitivity to conductivity and oceanic transport, magnetic signals caused by the movement of the ocean are a beneficial
source of information. Satellite observed tidal-induced magnetic fields have already proven to be helpful to derive Earth’s
conductivity or ocean heat content. However, magnetic signals caused by ocean circulation are still unobserved in satellite
magnetometer data. We present a novel method to detect these magnetic signals from ocean circulation using an observing systemsimulation experiment. The introduced approach relies on the assimilation of satellite magnetometer data based on a Kalman filter
algorithm. The separation from other magnetic contributions is attained by predicting the temporal behavior of the ocean-induced
magnetic field through presumed proxies. We evaluate the proposed method in different test case scenarios. The results demonstrate
a possible detectability of the magnetic signal in large parts of the ocean. Furthermore, we point out the crucial dependence on themagnetic signal’s variability and show that our approach is robust to slight spatial and temporal deviations of the presumed proxies.
Additionally, we showed that including simple prior spatial constraints could further improve the assimilation results. Our findings
indicate an appropriate sensitivity of the detection method for
an application outside the presented observing systemsimulation experiment. Therefore, we finally discussed potential
issues and required advances toward the method’s application
on original geomagnetic satellite observations.

Keywords: Electromagnetic induction, Ocean circulation,

Satellite magnetometer observations, Kalmanfilter, Assimilation, Observing system simulation
experiment

Graphical abstract*Corresponding author: Aaron Hornschild, aaron.hornschild@gfz-potsdam.de10Earth, Planets and Space

FULL PAPER

Open Access

Improving the estimation of thermospheric neutral
density via two-step assimilation of in situ neutral
density into a numerical model
Armin Corbin* and Jürgen Kusche
Earth, Planets and Space 2022, 74:183 DOI: 10.1186/s40623-022-01733-z
Received: 5 May 2022, Accepted: 3 November 2022, Published: 9 December 2022

Abstract
Neutral thermospheric density is an essential quantity required for precise orbit determination of satellites, collision avoidance of satellites, re-entry
prediction of satellites or space debris, and satellite lifetime assessments. Empirical models of the thermosphere fail to provide sufficient estimatesof neutral thermospheric density along the orbits of satellites by reason of approximations, assumptions and a limited temporal resolution. At highsolar activity these estimates can be off by 70% when comparing to observations at 12-hourly averages. In recent decades, neutral density isregularly observed with satellite accelerometers on board of low Earth orbiting satellites like CHAMP, GOCE, GRACE, GRACE-FO, or Swarm. Whenassimilating such along-track information into global models of thermosphere–ionosphere dynamics, it has been often observed that only a very
local sub-domain of the model grid around the satellite’s position is updated. To extend the impact to the entire model domain we suggest a new
two-step approach: we use accelerometer-derived neutral densities from the CHAMP mission in a first step to calibrate an empirical thermospheredensity model (NRLMSIS 2.0). In a second step, we assimilate—for the first time—densities predicted for a regular three-dimensional grid into the
TIE-GCM (Thermosphere Ionosphere Electrodynamics General Circulation Model). Data assimilation is performed using the Local Error-Subspace
Transform Kalman Filter provided by the Parallel Data Assimilation Framework (PDAF). We test the new approach using a 2-week-long period
containing the 5 April 2010 Geomagnetic storm. Accelerometer-derived neutral densities from the GRACE mission are used for additional
evaluation. We demonstrate that the two-step approach globally improves thesimulation of thermospheric density. We could significantly improve the density
prediction for CHAMP and GRACE. In fact, the offset between the accelerometerderived densities and the model prediction is reduced by 45% for CHAMP and 20%
for GRACE when applying the two-step approach. The implication is that ourapproach allows one to much better ’transplant’ the precise CHAMP
thermospheric density measurements to satellites flying at a similar altitude.

Keywords: Thermosphere, Neutral mass density, Data assimilation,
Geomagnetic storm

Graphical abstract*Corresponding author: Armin Corbin, corbin@geod.uni-bonn.de

FULL PAPER

Open Access

Planetary-scale MLT waves diagnosed throughmulti-station methods: a review
Maosheng He
Earth, Planets and Space 2023, 75:63 DOI: 10.1186/s40623-023-01808-5
Received: 18 March 2022, Accepted: 21 March 2023, Published: 28 April 2023

Abstracteoh jing
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Keywords: Mesosphere and lower thermosphere

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rd es hba n ru
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Sv A JuliCol

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Most experimental investigations on planetary-scale waves in the mesosphere and lower thermosphere (MLT) region are
based on single-station or -satellite spectral analysis methods, which suffer from intrinsic spectral aliasing/ambiguity. To
overcome the aliasing, the author has developed and utilized dual- and multi-station spectral methods in a series of recent
works. These methods were implemented on meteor radar observations and surface magnetometer observations. In theimplements, a variety of waves were discovered or investigated in terms of seasonal variations and responses to sudden
stratospheric warming events, such as lunar and solar tides (migrating and non-migrating), Rossby wave normal modes,
ultra-fast Kelvin waves, and secondary waves of wave–wave nonlinear interactions between the previous waves. The current
paper illustrates these methods using synthetic data, comparatively reviews the methods and results in plain language, andproposes a new representation, termed theadjusted Feynman diagram, to summarize thenonlinear interactions and explain theirimplications.

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Graphical abstract

Corresponding author: Maosheng He, hmq512@gmail.com
11

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(MLT) region, Solar and lunar tide,
Planetary wave, Wave–wave nonlinear
interaction, Adjusted Feynman
diagram, Sudden stratosphericwarmingDynamicEarth: Earth’s Interior, Surface, Ocean, Atmosphere, and Near Space Interactions

EXPRESS LETTER

Open Access

Evidence for presence of a global quasi-resonant mode ofoscillations during high-intensity long-duration continuous
AE activity (HILDCAA) events
Diptiranjan Rout*, Ram Singh, K. Pandey, T. K. Pant, C. Stolle, D. Chakrabarty, S. Thampi and T. Bag
Earth, Planets and Space 2022, 74:91 DOI: 10.1186/s40623-022-01642-1
Received: 5 January 2022, Accepted: 4 May 2022, Published: 13 June 2022

Abstract
The responses of two High-Intensity Long-Duration Continuous AE Activity(HILDCAA) events are investigated using solar wind observations at L1,
magnetospheric measurements at geosynchronous orbit, and changes in the
global ionosphere. This study provides evidence of the existence of quasiperiodic oscillations (1.5–2 h) in the ionospheric electric field over low latitudes,
total electron content at high latitudes, the magnetic field over the globe,
energetic electron flux and magnetic field at geosynchronous orbit,
geomagnetic indices (SYM-H, AE, and PC) and the Y-component of theinterplanetary electric field (IEFy) during the HILDCAA events at all local times.
Based on detailed wavelet and cross-spectrum analyses, it is shown that thequasi-periodic oscillation of 1.5–2 h in IEFy is the most effective one that controls
the solar wind–magnetosphere–ionosphere coupling process during the
HILDCAA events for several days. Therefore, this investigation for the first time,shows that the HILDCAA event affects the global magnetosphere–ionospheresystem with a “quasi-resonant” mode of oscillation.

Keywords: HILDCAA, CIR, Prompt penetration electric field, Global oscillation,
Magnetosphere–ionosphere coupling

Graphical abstract*Corresponding author: Diptiranjan Rout, diptiprl89@gmail.com

TECHNICAL REPORT

Open AccessGeomagnetic data from the GOCE satellite mission
I. Michaelis*, K. Styp-Rekowski, J. Rauberg, C. Stolle and M. Korte
Earth, Planets and Space 2022, 74:135 DOI: 10.1186/s40623-022-01691-6
Received: 8 April 2022, Accepted: 13 August 2022, Published: 13 September 2022

Abstract
The Gravity field and steady-state Ocean Circulation Explorer (GOCE) is part of ESA’s Earth Explorer Program. The satellite
carries magnetometers that control the activity of magnetorquers for navigation of the satellite, but are not dedicated as
science instruments. However, intrinsic steady states of the instruments can be corrected by alignment and calibration, andartificial perturbations, e.g. from currents, can be removed by their characterisation correlated to housekeeping data. The
leftover field then shows the natural evolution and variability of the Earth’s magnetic field. This article describes the preprocessing of input data as well as calibration and characterisation steps performed on GOCE magnetic data, using a highprecision magnetic field model as reference. For geomagnetic quiet times, the standard deviation of the residual is below 13
nT with a median residual of (11.7, 9.6, 10.4) nT for the three magnetic field components (x, y, z). For validation of thecalibration and characterisation performance, we selected a geomagnetic storm event in March 2013. GOCE magnetic fielddata show good agreement with results from a ground magnetic observation network. The GOCE mission overlaps with the
dedicated magnetic field satellite mission CHAMP for a short time at the beginning of 2010, but does not overlap with the
Swarm mission or any other mission flying at low altitudeand carrying high-precision magnetometers. We expect
calibrated GOCE magnetic field data to be useful for
lithospheric modelling and filling the gap between the
dedicated geomagnetic missions CHAMP and Swarm.

Keywords: Earth’s magnetic field, Geomagnetism,

Ionospheric currents, Magnetospheric ring
current, Satellite-based magnetometers,
Platform magnetometers, GOCE

Graphical abstract*Corresponding author: I. Michaelis, ingo.michaelis@gfz-potsdam.de12

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Contents
Special issue “DynamicEarth: Earth’s interior, surface, ocean, atmosphere, and near space interactions”. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . C. Stolle, J. Baerenzung, E. A. Kronberg, J. Kusche, H. Liu and H. Shimizu
Topside equatorial spread F-related field-aligned Poynting flux: observations and simulations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . J. Rodríguez-Zuluaga, C. Stolle, D. Hysell and D. J. Knudsen
Correlation analysis of field-aligned currents from the magnetic measurements of GRACE follow-on mission. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chao Xiong, Claudia Stolle, Ingo Michaelis, Hermann Lühr, Yunliang Zhou,
Hui Wang, Guram Kervalishvili and Jan Rauberg

Tide-induced magnetic signals and their errors derived from CHAMP and Swarm satellite magnetometer observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Jan Saynisch-Wagner, Julien Baerenzung, Aaron Hornschild, Christopher Irrgang and Maik Thomas
On the characterization of tidal ocean-dynamo signals in coastal magnetic observatories. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Johannes Petereit, Jan Saynisch-Wagner, Achim Morschhauser, Leonie Pick and Maik Thomas
Frequency spectra of horizontal winds in the mesosphere and lower thermosphere region from multistatic specularmeteor radar observations during the SIMONe 2018 campaign. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Harikrishnan Charuvil Asokan, Jorge L. Chau, Raffaele Marino, Juha Vierinen,
Fabio Vargas, Juan Miguel Urco, Matthias Clahsen and Christoph Jacobi

Comparison of the tidal signatures in sporadic E and vertical ion convergence rate, using FORMOSAT-3/COSMIC radio
occultation observations and GAIA model . . . . . . . . . . . . . . . . . . . . . . . . . Sahar Sobhkhiz-Miandehi, Yosuke Yamazaki, Christina Arras,
Yasunobu Miyoshi and Hiroyuki Shinagawa

Solar and lunar daily geomagnetic variations and their equivalent current systems observed by Swarm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Yosuke Yamazaki
Migrating solar diurnal tidal variability during Northern and Southern Hemisphere Sudden Stratospheric Warmings. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tarique A. Siddiqui, Jorge L. Chau, Claudia Stolle and Yosuke Yamazaki
Improving estimates of the ionosphere during geomagnetic storm conditions through assimilation of thermosphericmass density . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isabel Fernandez-Gomez, Timothy Kodikara, Claudia Borries, Ehsan Forootan,
Andreas Goss, Michael Schmidt and Mihail V. Codrescu

Machine learning-based calibration of the GOCE satellite platform magnetometers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Kevin Styp-Rekowski, Ingo Michaelis, Claudia Stolle, Julien Baerenzung, Monika Korte and Odej Kao
Kalmag: a high spatio-temporal model of the geomagnetic field. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Baerenzung Julien, Holschneider Matthias, Jan Saynisch-Wagner and Maik Thomas
Ionospheric electron density modelling using B-splines and constraint optimization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ganesh Lalgudi Gopalakrishnan and Michael Schmidt
Sporadic E layer characteristics at equatorial latitudes as observed by GNSS radio occultation measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Christina Arras, Laysa Cristina Araújo Resende, Ankur Kepkar,
Gethmini Senevirathna and Jens Wickert

On the detectability of the magnetic fields induced by ocean circulation in geomagnetic satellite observations. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aaron Hornschild, Julien Baerenzung, Jan Saynisch-Wagner,
Christopher Irrgang and Maik Thomas

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Improving the estimation of thermospheric neutral density via two-step assimilation of in situ neutral density into a
numerical model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Armin Corbin and Jürgen Kusche 11
Planetary-scale MLT waves diagnosed through multi-station methods: a review . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Maosheng He 11
Evidence for presence of a global quasi-resonant mode of oscillations during high-intensity long-duration continuous
AE activity (HILDCAA) events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diptiranjan Rout, Ram Singh, K. Pandey, T. K. Pant,
C. Stolle, D. Chakrabarty, S. Thampi and T. Bag
Geomagnetic data from the GOCE satellite mission . . . . . . . . . . . . . . I. Michaelis, K. Styp-Rekowski, J. Rauberg, C. Stolle and M. Korte

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Cover image: Rodríguez-Zuluaga, J. et al., Earth, Planets and Space 2022, 74:119 DOI: 10.1186/s40623-022-01679-2