Eigil Friis-Christensen

Swarm : A constellation to study the Earth's magnetic field

The Swarm mission was selected as the 5th mission in ESA’s Earth Explorer Programme in 2004. The mission will provide the best ever survey of the geomagnetic field and its temporal evolution that will lead to new insights into the Earth system by improving our understanding of the Earth’s interior and its effect on Geospace, the vast region around the Earth where electrodynamic processes are influenced by the Earth’s magnetic field. Scheduled for launch in 2010, the mission will comprise a constellation of three satellites, with two spacecraft flying sideby- side at lower altitude (450 km initial altitude), thereby measuring the East-West gradient of the magnetic field, and the third one flying at higher altitude (530 km). High-precision and high-resolution measurements of the strength, direction and variation of the magnetic field, complemented by precise navigation, accelerometer and electric field measurements, will provide the necessary observations that are required to separate and model the various sources of the geomagnetic field. This results in a unique “view” inside the Earth from space to study the composition and processes of its interior. It also allows analysing the Sun’s influence within the Earth system. In addition practical applications in many different areas, such as space weather, radiation hazards, navigation and resource management, will benefit from the Swarm concept.

The Swarm Satellite Constellation Application and Research Facility (SCARF) and Swarm data products

Swarm, a three-satellite constellation to study the dynamics of the Earth’s magnetic field and its interactions with the Earth system, is expected to be launched in late 2013. The objective of the Swarm mission is to provide the best ever survey of the geomagnetic field and its temporal evolution, in order to gain new insights into the Earth system by improving our understanding of the Earth’s interior and environment. In order to derive advanced models of the geomagnetic field (and other higher-level data products) it is necessary to take explicit advantage of the constellation aspect of Swarm. The Swarm SCARF (SatelliteConstellationApplication andResearchFacility) has been established with the goal of deriving Level-2 products by combination of data from the three satellites, and of the various instruments. The present paper describes the Swarm input data products (Level-1b and auxiliary data) used by SCARF, the various processing chains of SCARF, and the Level-2 output data products determined by SCARF.

Ørsted satellite captures high‐precision geomagnetic field data

Space-based, high-precision magnetometry is essential for understanding a variety of phenomena ranging from secular variation of the Earths main field, through the signatures of crustal magnetism and the effects of plasma currents flowing externally to the Earth. Orsted, Denmarks first satellite, was launched on February 23, 1999 into a polar, low-Earth orbit to provide the first near-global set of high-precision geomagnetic observations since the Magsat mission of 1979–1980 (see Magsat Special Issue of Geophysical Research Letters., vol. 9, no. 4, pp. 239–379, 1982). With the new mapping of the Earths magnetic field, the International Geomagnetic Reference Field model (IGRF), a standard model used for navigation, prospecting, and other practical purposes, has been determined with improved precision for epoch 2000 [Olsen et al., 2000a; Mandea and Langlais, 2000]. The satellite has routinely provided high-precision vector data since August 1999, and the mission is continuing well beyond its nominal 14-month lifetime into 2001.

The Swarm Initial Field Model for the 2014 geomagnetic field

Data from the first year of ESAs Swarm constellation mission are used to derive the Swarm Initial Field Model (SIFM), a new model of the Earths magnetic field and its time variation. In addition to the conventional magnetic field observations provided by each of the three Swarm satellites, explicit advantage is taken of the constellation aspect by including east-west magnetic intensity gradient information from the lower satellite pair. Along-track differences in magnetic intensity provide further information concerning the north-south gradient. The SIFM static field shows excellent agreement (up to at least degree 60) with recent field models derived from CHAMP data, providing an initial validation of the quality of the Swarm magnetic measurements. Use of gradient data improves the determination of both the static field and its secular variation, with the mean misfit for east-west intensity differences between the lower satellite pair being only 0.12 nT.

What do we really know about the Sun-climate connection?

Abstract The Earths climate has always been changing. This is documented in historical as well as in geological records. The reasons for these changes, however, have always been subject to discussions and are still not well understood. In addition to natural climate changes the risk of human influence on climate has recently been seriously considered by the Intergovernmental Panel on Climate Change. Any factor that alters the radiation received from the Sun or lost to Space will affect climate. The Suns output of energy is known to change over an 11-year cycle, and variations over longer periods occur as well. A number of correlations between solar activity variations and climate changes, some more significant than others, have been reported but they have traditionally been accompanied by a considerable skepticism among scientists because a plausible physical mechanism to account for these correlations has not yet been found. The most immediate cause of climate changes would be changes in the total irradiance of the Sun. This, however, would either imply unrealistically large variations in total solar irradiance or a higher climate sensitivity to radiative forcing than normally accepted. Therefore other mechanisms have to be invoked. The most promising candidate is a change in cloud formation because clouds have a very strong impact on the radiation balance and because only little energy is needed to change the cloud formation process. One of the ways to influence cloud formation might be through the cosmic ray flux that is strongly modulated by the varying solar activity.

Statistical studies of impulsive events at high latitudes

A statistical study has been made of the high-latitude impulsive events that were observed during the 1985–1986 South Pole Balloon Campaign. The events were selected by searching for unipolar pulses ≥ 10 nT above background in the vertical component of the magnetic field on the ground and/or pedestal or “W” shaped horizontal electric field perturbations ≥ 10 mV/m in amplitude and accompanied by perturbations in the vertical electric field at balloon altitude. A main event list comprising 112 events was compiled from the 468 hours of data available. Three aspects of the events were examined: the solar wind conditions prior to the event, local time of observation, and intrinsic properties of the events. The local time distribution was obtained from the 112 entry main event list and was found to be nearly uniform across the dayside, with no midday gap. The event rate found using our low-amplitude selection criteria was 0.7 event/hr, comparable to expectations based on in situ studies of the magnetopause. A total of 42 events were found for which data were available from Interplanetary Monitoring Platform (IMP) 8. Of these events, 12 occurred when the ZGSM component (BZ) of the interplanetary magnetic field (IMF) was northward and 30 occurred when BZ was southward or fluctuating. Only three of the BZ northward cases and only five of the BZ southward cases were preceded by pressure pulses greater than 0.4 nPa in amplitude. Ten of the events were studied in detail by means of a model-fitting method discussed elsewhere. This method infers values of several parameters, including the total current flowing in a coaxial or monopole system and a two-dimensional dipole system. The intrinsic properties of the events showed that only ∼ 10% of the total current contributed to momentum transfer to the high-latitude ionosphere, that the direction of the motion depended more on local time of observation than IMF By, and that events were usually several hundred kilometers in size. The observed Bz control found in the 42 event list and the prevalence of coaxial current dominated events are inconsistent with the predictions of the pressure pulse model.

Geomagnetic Research From Space

The Decade of Geopotential Field Research, inaugurated in 1999 with the launch of the Danish satellite Orsted on 23 February, was designed as an international effort to promote and coordinate continuous monitoring of geopotential field variability in the near-Earth environment. Since 1999, the Challenging Minisatellite Payload (CHAMP), the Gravity Recovery and Climate Experiment (GRACE), the Satelite de Aplicaciones Cientificas-C (SAC-C), and most recently, the Gravity field and steady-state Ocean Circulation Explorer (GOCE) satellites have combined with Orsted to generate an unprecedented wealth of data on Earths magnetic and gravity fields.

The Swarm Magnetometry Package

The Swarm mission under the ESA’s Living Planet Programme is planned for launch in 2010 and consists of a constellation of three satellites at LEO. The prime objective of Swarm is to measure the geomagnetic field with unprecedented accuracy in space and time. The magnetometry package consists of an extremely accurate and stable vector magnetometer, which is co-mounted in an optical bench together with a start tracker system to ensure mechanical stability of the measurements.

Call for Papers: Special Issue of Earth, Planets and Space (EPS) “Swarm Science Data Processing and Products—the Swarm Satellite Constellation Application and Research Facility, SCARF”

In order to take optimal advantage of the unique three-satellite constellation aspect of the European Space Agency’s Swarm mission, implemented as part of the Agency’s Living Planet programme and targeted for launch within the next months, considerably advanced data analysis tools have been developed. Scientific users of data from the Swarm mission will therefore benefit significantly from free and open access to such derived products, so-called Level 2 data, that take due account the constellation features. This facility, called “Satellite Constellation Application and Research Facility” (SCARF), has been developed, tested and validated by a European consortium of six research institutions under a contractual agreement with ESA. A number of Level-2 data products will be generated by this service, including various models of the core and lithospheric part of the geomagnetic field as well as of the ionospheric and magnetospheric field contribution. In addition, derived parameters like three-dimensional electrical conductivity of the mantle, thermospheric mass density and winds, field-aligned currents, an ionospheric plasma bubble index, the ionospheric total electron content and the dayside equatorial ionospheric electrical field will be provided. This service is planned to be operational for a period of 5 years after the launch of the Swarm Mission, including processing of 4 years nominal mission data. ESA will provide all data products through the archiving and dissemination infrastructure of the Swarm mission. Considering the scientific potential of the unique set of data from the constellation of three spacecraft and to foster an enhanced discussion within and across scientific disciplines it has been decided to publish in a special issue a selection of papers that describe or discuss a number of new scientific results, algorithms, and methods, which have been obtained and developed for this facility and which will be of high interest to the wider scientific community. All submitted manuscripts will go through a peer review process before publication. Contributors to this special issue should submit their papers online through “http://www.editorialmanager.com/eps/”, and select the article type: “Swarm Satellite Constellation Application and Research Facility, SCARF”. For details, please visit the EPS website: