# Special issue "Swarm science results after 2 years in space"

Nils Olsen, Claudia Stolle, Rune Floberghagen, Gauthier Hulot, Alexey Kuvshinov

► To cite this version:

Nils Olsen, Claudia Stolle, Rune Floberghagen, Gauthier Hulot, Alexey Kuvshinov. Special issue "Swarm science results after 2 years in space". Earth Planets and Space, 2016, 68, 3 pp. 10.1186/s40623-016-0546-6. insu-03581273

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# Special issue "Swarm science results after 2 years in space"

Nils Olsen<fnref n="1" />*, Claudia Stolle², Rune Floberghagen³, Gauthier Hulot⁴ and Alexey Kuvshinov⁵

Swarm is a three-satellite constellation mission launched by the European Space Agency (ESA) on 22 November 2013. It consists of three identical spacecraft, two of which (Swarm Alpha and Swarm Charlie) are flying almost side-by-side in polar orbits at lower altitude (about 470 km in September 2016) with an East-West separation of 1.4° in longitude corresponding to 155 km at the equator. The third satellite (Swarm Bravo) is in a slightly higher orbit (about 520 km altitude in September 2016). Each of the three satellites carry a magnetometry package (consisting of absolute scalar magnetometer, fluxgate vector magnetometer, and star imager) for measuring the direction and strength of the magnetic field, and instruments to measure plasma and electric field parameters as well as gravitational acceleration. Time and position are provided by on-board GPS. The configuration of the various instruments on each of the three Swarm spacecraft is shown in Fig. 1. More information about the mission can be found at http://earth.esa.int/swarm.

The 21 articles collected in this special issue were stimulated by the Joint Inter-Association Symposium “JA4 Results from Swarm, Ground Based Data and Earlier Satellite Missions” at the 26th General Assembly of the International Union of Geodesy and Geophysics (IUGG) held in Prague in July 2015.

Toffner-Clausen et al. (2016) report on the advanced calibration of the magnetometry package of the Swarm satellites. Finlay et al. (2016) and Olsen et al. (2016) present models of Earth's core magnetic field, while Thébault et al. (2016) and Kotsiaros (2016) determine models of the lithospheric field. The importance of high-resolution magnetic field models for studying external magnetic

field contributions, in particular during geomagnetic quiet conditions, is discussed by Stolle et al. (2016).

Five contributions discuss the magnetic field produced by ionospheric and magnetospheric currents: Chulliat et al. (2016) present a climatological model of the ionospheric currents responsible for geomagnetic daily variations at non-polar latitudes, while the work of Laundal et al. (2016) concentrates on a consistent description of horizontal ionospheric and field-aligned currents in the polar ionosphere, in particular regarding their dependence on solar irradiation that controls ionospheric conductivity. A scheme for estimating the polar ionospheric currents that form the Polar Electrojets on an orbit-by-orbit basis is presented by Aakjaer et al. (2016), while Tozzi et al. (2016) discuss unmodelled magnetic field contributions in satellite-based magnetic field models. Michelis et al. (2016) present a study of high-latitude magnetic field variations during the St. Patrick's Day Storm.

The same event is investigated by Pignalberi et al. (2016) using Swarm plasma density measurements, and by Cherniak and Zakharenkova (2016) using GPS data from ground and Swarm.

Calibration of the electric field instrument of Swarm is presented by Fiori et al. (2016). A combination of electric, magnetic, and TEC observations has been used by Astafyeva et al. (2016) to investigate the magnetic storm of 22–23 June 2015. Aoyama et al. (2016) combine ground magnetic data and Swarm TEC observations to study possible ionospheric effects of the 2015 eruption of a volcano in Chile, Zakharenkova et al. (2016) used GPS and Swarm plasma observations to study equatorial plasma density irregularities in the topside ionosphere, and Xiong et al. (2016) performed a scale analysis of equatorial plasma irregularities.

van den IJssel et al. (2016) describe improvements of Swarm GPS antenna settings to enhance high-precision positioning of the spacecraft, and da Encarnação et al. (2016) discuss various attempts to determine monthly

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<footnote>*Correspondence: nio@space.dtu.dk</footnote>

<footnote n="1">¹ Division of Geomagnetism, DTU Space, Technical University of Denmark, Diplomvej 371, 2800 Kongens Lyngby, Denmark
Full list of author information is available at the end of the article</footnote>
<figure><img src="image_5.png" /><figcaption>**Fig. 1** Various scientific instruments on board each of the three *Swarm* satellites (ESA/AOES Medialab)</figcaption></figure>

snapshot models of the large-scale part of Earth's gravity field from *Swarm* GPS observations.

Finally, the processing of the *Swarm* accelerometer data is described by Siemes et al. (2016).

The work reported in this issue could not have been achieved without the unfailing support of our deeply regretted friend and colleague Gernot Plank (Fig. 2), to which we wish to dedicate this special issue of *Earth Planets Space*. Gernot has been one of the major contributors to the success of the *Swarm* mission. With great enthusiasm he played a considerable role in the establishment of *Swarm SCARF*, the *Swarm* Level-2 data processing facility. *Swarm SCARF* was key to the project and all scientific results presented in the present special issue (as well as in a previous issue, see *Earth Planets Space*, Vol. 65, Issue 11) heavily rely on the success of this facility. Gernot's

energy and enthusiastic spirit, from beginning to end of even the most intense meetings, was extremely appreciated. He had a remarkable ability to help solve problems and convince anyone to do the right thing in the interest of the project and science, sometimes even very late in the evening, and always in his unique and particularly cheerful way, whatever the circumstances.

Gernot passed away in March 2016 after a lengthy, hard, and unfair fight against cancer. He, and his legendary laugh, will be sorrowfully missed by his friends and colleagues.

**Authors' contributions**

All authors of this article served as guest editors for this special issue. All authors read and approved the final manuscript.

**Author details**

¹ Division of Geomagnetism, DTU Space, Technical University of Denmark, Diplomvej 371, 2800 Kongens Lyngby, Denmark. ² Helmholtz-Zentrum Potsdam, Deutsches GeoForschungsZentrum GFZ, 14473 Potsdam, Germany.

³ Directorate of Earth Observation Programmes, ESRIN, Via Galileo Galilei 2, 00044 Frascati, Italy. ⁴ Equipe de Géomagnétisme, Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, 1 rue Jussieu, 75005 Paris, France. ⁵ Institute of Geophysics, ETH Zürich, Sonneggstrasse 5, 8092 Zürich, Switzerland.

**Acknowledgements**

We thank the authors of the papers in this special issue, and the referees who served to evaluate the contributions and gave helpful comments and suggestions.

Received: 10 October 2016 Accepted: 10 October 2016

Published online: 04 November 2016

**References**

Aakjær CD, Olsen N, Finlay CC (2016) Determining polar ionospheric electrojet currents from Swarm satellite constellation magnetic data. *Earth Planets Space* 68:140. doi:10.1186/s40623-016-0509-y

Aoyama T, Iyemori T, Nakanishi K, Nishioka M, Rosales D, Veliz O, Safor EV (2016) Localized field-aligned currents and 4-min TEC and ground magnetic oscillations during the 2015 eruption of Chile's Calbuco volcano. *Earth Planets Space* 68:148. doi:10.1186/s40623-016-0523-0

Astafyeva E, Zakharenkova I, Alken P (2016) Prompt penetration electric fields and the extreme topside ionospheric response to the June 22–23, 2015 geomagnetic storm as seen by the Swarm constellation. *Earth Planets Space* 68:152. doi:10.1186/s40623-016-0526-x

<figure><img src="image_6.png" /><figcaption>**Fig. 2** Gernot Plank (1967–2016)</figcaption></figure>
Cherniak I, Zakharenkova I (2016) High-latitude ionospheric irregularities: differences between ground- and space-based GPS measurements during the 2015 St. Patrick's Day Storm. Earth Planets Space 68:136. doi:10.1186/s40623-016-0506-1

Chulliat A, Vigneron P, Hulot G (2016) First results from the Swarm dedicated ionospheric field inversion chain. Earth Planets Space 68:104. doi:10.1186/s40623-016-0481-6

da Encarnação JT et al (2016) Gravity field models derived from Swarm GPS data. Earth Planets Space 68:127. doi:10.1186/40623-016-0499-9

Finlay CC, Olsen N, Kotsiaros S, Gillet N, Tøffner-Clausen L (2016) Recent geomagnetic secular variation from Swarm and ground observatories as estimated in the CHAOS-6 geomagnetic field model. Earth Planets Space 68:112. doi:10.1186/s40623-016-0486-1

Fiori RAD, Koustov AV, Boteler DH, Knudsen DJ, Burchill JK (2016) Calibration and assessment of Swarm ion drift measurements using a comparison with a statistical convection model. Earth Planets Space 68:100. doi:10.1186/s40623-016-0472-7

Kotsiaros S (2016) Toward more complete magnetic gradiometry with the Swarm mission. Earth Planets Space 68:130. doi:10.1186/s40623-016-0498-x

Laundal KM, Finlay CC, Olsen N (2016) Sunlight effects on the 3D polar current system determined from low earth orbit measurements. Earth Planets Space 68:142. doi:10.1186/s40623-016-0518-x

Michelis PD, Consolini G, Tozzi R, Marcucci MF (2016) Observations of high-latitude geomagnetic field fluctuations during St. Patrick's Day Storm: Swarm and SuperDARN measurements. Earth Planets Space 68:105. doi:10.1186/s40623-016-0476-3

Olsen N, Finlay CC, Kotsiaros S, Tøffner-Clausen L (2016) A model of earth's magnetic field derived from 2 years of Swarm satellite constellation data. Earth Planets Space 68:124. doi:10.1186/s40623-016-0488-z

Pignalberi A, Pezzopane M, Tozzi R, Michelis PD, Coco I (2016) Comparison between IRI and preliminary Swarm langmuir probe measurements during the St. patrick storm period. Earth Planets Space 68:93. doi:10.1186/s40623-016-0466-5

Siemes C et al (2016) Swarm accelerometer data processing from raw accelerations to thermospheric neutral densities. Earth Planets Space 68:92. doi:10.1186/s40623-016-0474-5

Stolle C, Michaelis I, Rauberg J (2016) The role of high-resolution geomagnetic field models for investigating ionospheric currents at low earth orbit satellites. Earth Planets Space 68:110. doi:10.1186/s40623-016-0494-1

Thébault E, Vigneron P, Langlais B, Hulot G (2016) A Swarm lithospheric magnetic field model to SH degree 80. Earth Planets Space 68:126. doi:10.1186/s40623-016-0510-5

Tøffner-Clausen L, Lesur V, Olsen N, Finlay CC (2016) In-flight scalar calibration and characterisation of the Swarm magnetometry package. Earth Planets Space 68:129. doi:10.1186/s40623-016-0501-6

Tozzi R, Mandea M, Michelis PD (2016) Unmodelled magnetic contributions in satellite-based models. Earth Planets Space 68:108. doi:10.1186/s40623-016-0484-3

van den Ijssel J, Forte B, Montenbruck O (2016) Impact of Swarm GPS receiver updates on POD performance. Earth Planets Space 68:85. doi:10.1186/s40623-016-0459-4

Xiong C, Stolle C, Lühr H, Park J, Fejer BG, Kervalishvili GN (2016) Scale analysis of equatorial plasma irregularities derived from Swarm constellation. Earth Planets Space 68:121. doi:10.1186/s40623-016-0502-5

Zakharenkova I, Astafyeva E, Cherniak I (2016) GPS and in situ Swarm observations of the equatorial plasma density irregularities in the topside ionosphere. Earth Planets Space 68:120. doi:10.1186/s40623-016-0490-5

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