The SERAnt Action Group (Sun Earth Relationships and Antarctica) was formed in 2014. Its purpose was to determine the Terms of Reference for a Task Group on solar terrestrial physics to be proposed at the XXXIV SCAR Meetings in Kuala Lumpur, Malaysia. The proposed group is intended to replace ICESTAR, which ended in 2014.
SERAnt will lead to representation within the Physical Sciences Group of the research effort in Antarctica that aims on quantifying effects of the solar activity on the near-Earth environment (Geospace) and the planet's geomagnetic, plasma, and atmospheric domains.
- The main science objectives of the SERAnt activtities fall under the general framework of the “space weather” and “space climate” studies. Everlasting sophistication of human-built infrastructure on the Earth and in Geospace makes the effects of solar activity, both at the average level and with large and strong impulsive events, more and more relevant to the infrastructure proper protection and uninterrupted operation, as well as to better understanding of the long-term changes in the Earth magnetic field and solar irradiance. Such studies will be important through the solar activity minimum that is expected within the next five years, 2016 to 2020.
- The Antarctic continent offers an excellent vantage point and platform for the SERAnt-coordinated studies as being unique with its location at high Southern geomagnetic latitudes (that provides access to the regions where geomagnetic field lines directly interact with the solar wind) given the significant number of ground stations that are equipped with modern instrumentations providing continuous data streams on relevant parameters. These Antarctic observations of Geospace parameters and respective research occurs in parallel with similar research done over the Arctic, making the SERAnt effort bi-hemispheric in nature.
SERAnt will complement and parallel its coordination activtities with the joint Physical Sciences Task Group GRAPE (GNSS Research and Application for Polar Environment), which deals with monitoring, investigation and modelling of neutral and ionized atmospheric phenomena at bi-polar latitudes impacting on a variety of GNSS-based technology in several fields of application from space weather to the solid Earth. Thus, SERAnt and GRAPE are synergetic with the goals and objectives of the former SCAR Scientific Research Programme ICESTAR (Interhemispheric Conjugacy Effects in Solar Terrestrial and Aeronomy Research). The programmes of SERAnt and GRAPE are also in line as well with the SCOSTEP-sponsored 5-year coordination programme VarSITI (Variability of the Sun and Its Terrestrial Impact), 2014-2018.
A comprehensive description of the general Solar-Terrestrial Physics (STP) research goals and objectives related to respective available resources in Antarctica can be found in the recent report from the U.S. Antarctic community workshop “Solar Terrestrial Research: Past, Present and Future”, Proceedings of the polar research meeting, 2014, ed. M. Lessard, A. Gerrard and A. Weatherwax.
Proposed SERAnt research fields
Space weather and space climate have become common terms to relate studies of the Sun's activities and solar wind interaction to the Earth magnetosphere, depositing respective energy and momentum in the Earth geomagnetic, ionospheric, and atmospheric domains. The outstanding questions of that field are:
- What features may appear on the solar surface that may lead to solar flares and coronal mass ejections that might affect the Earth?
- What are mechanisms are involved in the respective propagation of the solar wind perturbations to near-Earth space (Geospace), and what evolutions might these perturbations experience during the transit?
- What are the effects that determine coupling between the solar wind perturbations and the Earth's magnetosphere?
- Which Geospace domains are affected by the above interaction, and how may they influence or modify/impact on the Earth's climate and human technological systems?
All these questions and many more will be examined through studies of several specific phenomena that range from cosmic ray interaction with the Earth's atmosphere, magnetospheric charged precipitation from the magnetosphere to the ionosphere, geomagnetic field disturbances in all frequency ranges, auroral phenomena, and general effects on the upper atmospheric layers, even weather and climate in the Earth’s lower atmosphere. These will be briefly addressed individually in the following sections.
Energetic Particles Studies
The Earth’s particle radiation environment consists of several components of ionizing radiation, among which there are galactic cosmic rays (GCRs), solar cosmic rays (also called solar energetic particles (SEPs) or solar proton events (SPEs)), energetic electrons from the Earth’s outer radiation belt and auroral electrons. The GCR flux in near-Earth space is controlled by solar magnetic activity and follows an 11-year cycle that is in anticorrelation with the main solar activity indices (e.g., the sunspot number). In addition, the GCR flux responds to solar-wind variations on both long and short time scales. SEPs, on the other hand, comprise events that are associated with coronal mass ejections (CMEs) and solar flares (e.g., Reames 1999). Thus, the somewhat sporadic occurrence of SEPs is in positive correlation with ongoing solar activity.
It follows that the radiation environment of the Earth is very dynamic. Even the most stable component of the radiation (i.e., the GCRs) varies by an order of magnitude at energies below a few hundred MeV per nucleon due to heliospheric modulation. SEP events can produce increases of several orders of magnitude in the fluxes of energetic ions (above 1 MeV per nucleon) and electrons (above 100 keV), which can last from a few hours to a week.
Navigation and radio communication performance failure are well documented since the discovery of the PCA effect (Polar Cap Absorption). Radiobiological damage is similar to that described in manned space flights, but now also affects aeroplane flights, especially over polar areas (Dosimetry is strongly improved). In particular, secondary neutrons are the major component of the total dose of the human radiation exposure at high altitude (mountains, flights) and high latitudes (polar and sub-polar).
Space-based observations are essential to estimate EPP-induced ionization but are subject to limitation (shortness of time series, inter-satellite calibration issues, proton contamination etc.). In this framework, the possibility of using geomagnetic indices (e.g. Ap, Kp, AE), recorded at ground-based observatories, as EPP proxy (Randall et al., 2007; Funke et al., 2014) opened new scenarios for investigating the EPP role in past and, potentially, future climate. Indeed, work is on-going to include the EPP forcing within multi-model initiatives. In this respect, it is important to mention that, for the first time, data on this forcing will be provided to the modelling groups taking part in the next CMIP-6 (Coupled Model Intercomparison Project Phase 6), i.e. the scientific basis for the IPCC (Intergovernmental Panel on Climate Change), allowing the opportunity for an unprecedented evaluation of the EPP impact on climate.
Upper Atmospheric Studies
Among the various research programmes conducted in the VarSITI initiative of SCOSTEP, ROSMIC (Role Of the Sun and the Middle atmosphere/thermosphere/ionosphere In Climate) appears to be connected with Antarctic observations; initiatives within SERAnt will have to be coordinated and represented there.
Cosmic Rays can lead to chemical changes in the atmosphere (e.g., Chapter 13 in Dorman 2004; Section 4 in Kudela et al. 2000). Important for the terrestrial environment, particularly for climate, is the destruction of ozone (Thorne 1977; Baker et al. 1987) and the formation of minor atmospheric components (e.g., OHx and NOy) (Damiani et al. 2006; Jackman and McPeters 2004; Krivolutsky 2003).
These changes can be quite dramatic during SEP events in the polar upper atmosphere (Verronen et al., 2006; Damiani et al., 2008; Jackman et al., 2008; Storini et al., 2008). Intense SEP events are also able to greatly increase the concentration of NOx (NO + NO2) and HOx (H + OH + HO2) in mesosphere and stratosphere, hence destruction of ozone and therefore disturbance of temperature and wind. The potential descent of NOx during the polar winter, produced by energetic particle precipitation (EPP, due to SEPs, auroral particles and particles from outer radiation belts), and its impact on the ozone could be an important climate forcing. Modelling of such effects is in progress. The role of GCRs still has several controversies, for example that of polar particle precipitations.
Galactic Cosmic Rays, which come continuously into the upper layers of the atmosphere, interact primarily with atmospheric nitrogen and oxygen nuclei and produce secondary particles (such as protons, neutrons and mesons), that can penetrate deeper into the atmosphere and undergo further collisions, generating the particle shower. This phenomenon induces major physical and chemical effects in the atmosphere. The most important effect is cosmic ray induced ionization (CRII) in the atmosphere. CRs form the principal source of ionization in the low and middle atmosphere, except in the near-to-ground layer, where natural radioactivity in the soil may play a role. The permanent ionization of the atmosphere has numerous consequences for various aspects of the terrestrial environment, even for human life.
There is scientific work/debate on the ability of cosmic rays to activate cloud formation. Atmospheric ionization caused by cosmic rays may affect aerosol formation/growth, specifically in the polar stratosphere (e.g., Mironova et al, Space Sci. Rev., 194, 1, 2015) but the exact mechanism is still debated.
This topic includes the whole neutral atmosphere, since many of the aspects of sun-earth connection impacting the upper atmosphere have either direct impacts also lower down, or propagate down towards the stratosphere and troposphere via atmospheric coupling mechanisms (such as those discussed in the cosmic ray section). The atmospheric coupling from the bottom upwards (e.g., various wave couplings from the troposphere to the middle and upper atmosphere) is also an important part of the sun-earth connection because it drives global circulation of the atmosphere as well as ionospheric disturbances and irregularities that affect GNSS positioning and satellite communication. Polar atmosphere is one of the key regions of this coupling, such as driving polar stratospheric sudden warmings through planetary waves. This is also in line with the VarSITI/ROSMIC programme.
Ultra Low Frequency (ULF)
In the study of STP, it is extremely important to measure the geomagnetic field fluctuations in the polar regions, and thus in Antarctica. The availability of long data series allows the study, at different time scales, of the processes which control the energy transfer from the solar wind to the magnetosphere, and the investigation of open issues and recent challenging problems. In particular, Ultra Low Frequency (ULF, 1 mHz-1 Hz) waves in the magnetosphere:
- Low-frequency range (1-10 mHz)
Wave activity in this frequency range shows correlation with the fluctuations of the solar wind speed and dynamic pressure (Takahashi et al., 2012). In addition, it has been evidenced that these waves play a role in the acceleration of magnetospheric energetic electrons in the radiation belts, through a resonant interaction of the ULF waves with the electron drift motion (Millan and Baker, 2012).
- Mid-frequency range (10-100 mHz)
Recent studies, based on ULF fluctuations simultaneously observed in the solar wind by cluster satellites and on the ground in Antarctica, at Dome C and Terra Nova Bay (Francia et al., 2012; Regi et al., 2013; Regi et al., 2014), showed that ULF waves generated in the solar wind can penetrate through the lobes of the geomagnetic tail and propagate along the outermost open field lines to the polar cap. Such studies need further analyses, particularly with regard to the properties of the propagating waves.
- ULF activity and the atmosphere
During intense ULF activity, energetic electrons precipitate into the atmosphere at high latitudes, producing changes in the chemistry and electrical conductivity of the stratosphere, with detectable effects also at ground (Tinsley et al., 2007; Seppala et al., 2009). Through the analysis of geomagnetic field fluctuations in Antarctica, it is possible to study the short and long term variations of the magnetospheric activity and to investigate their correlation with the temperature and atmospheric dynamics changes (Francia et al., 2015).
- The magnetospheric and ionospheric current systems
In general, the extreme latitude measurements of the geomagnetic field variations are useful also in the Space Weather context in that, compared with lower latitude measurements, spacecraft observations in the magnetosphere, and model representations of the magnetospheric field, may allow to discriminate between the influence of the different magnetospheric and ionospheric current system during magnetic storms.
Very Low Frequency (VLF)
Very Low Frequency (VLF) electromagnetic waves are generally taken to span the range from a few kHz through to a few tens of kHz. For most locations on Earth, the dominant source of VLF waves are generated by lightning discharges, except at narrow frequency bands where manmade VLF transmitters dominate. At mid- and high- latitudes VLF waves naturally generated in space can be received on the ground. Examples of such waves are whistlers (generated by lightning), plasmaspheric hiss and chorus. The occurrence and properties of these waves tell us about the nature of the space around the Earth, and can be continuously monitored from high-latitude polar sites at comparatively low cost. All of the waves, along with ULF-band EMIC waves, are thought to be important drivers of loss of energetic electrons from the radiation belts. Whistler-mode chorus is increasingly accepted to be a highly important driver of acceleration processes in the radiation belts, energising electrons with tens of keV energy to hundreds or thousands of keV. In SCOSTEP's VarSITI programme, radiation belt dynamics and the nature and processes of inner magnetosphere processes is studied inside the SPeCIMEN project, while the impact of the loss on the atmosphere is part of the focus of ROSMIC. The joint URSI/IAGA working group VERSIM supports collaboration in the VLF community.
Monitoring of naturally occurring VLF waves allows remote sensing of the space environment. Ground-based observations of waves are complementary to space-based, providing a stationary platform to measure the VLF wave activity. In some parts of Antarctica, ground-based observations of whistlers can be used to provide continuous plasmasphere monitoring (the cold plasma environment is a vital component of describing how the processes in space couple waves and particles). Because lightning activity is extremely low in the Antarctic, this region is also very well suited to remote sensing lightning activity - the lower background noise levels and longer propagation paths provide high accuracy timing observations of lightning-generated radio pulses (sferics) which can be used in lightning location systems (e.g., WWLLN).
Monitoring of man-made VLF waves (generally from military transmitters) allows low-cost continuous remote sensing of the lower ionosphere. Either communication transmitters or lightning provide powerful sources of VLF waves which propagate many thousands of kilometres, trapped between the lower edge of the ionosphere and the conducting ground/sea. Networks of narrow-band transmitter monitors have been deployed to the polar region, particularly focused on highly energetic electrons and protons lost into the polar atmosphere. These include solar proton events (rare, and very very large), radiation belt precipitation (common, highly variable), and substorm precipitation (very common, highly variable). One example of such a network is AARDDVARK.
Current efforts in the scientific community focus on a wide range of topics in auroral studies. Auroras associated with substorms are the most dynamic and historically have received the most attention. Other questions have revolved around the connection between fast earthward-moving plasma flows from the magnetotail and north-south oriented auroral forms. The relationship between auroras and ion beams flowing out from the ionosphere is also important. Pulsating auroras have been observed to cover a great extent both in space and time, and are linked to Earth’s equatorial magnetosphere, providing an important path by which energy is transferred from the magnetosphere to the ionosphere and thermosphere. Proton aurora has been used to help understand substorm development and is associated with electromagnetic ion cyclotron waves; theory has been developed to show how these waves scatter radiation belt magnetospheric protons into the ionosphere.
- Actions to bring together presently available data, including harmonisation of data formats, also considering the provisions of the SCAR data specialists;
- Planning for integration of resources, coordinating observation plans, defining time intervals for joint studies;
- Coordinated presentation of Antarctic results at disciplinary meetings, and at SCAR Open Science Conferences;
- Due attention will be devoted to the efforts of GRAPE to estabilsh a task force for the SRP proposal on which the URSI Commission G and SCAR-GRAPE communities agreed at the URSI AT RASC meeting 2015. Representatives from other communities (e.g. SuperDARN) will be involved in the task force as well as SERAnt.
The group will act for four years, starting in Kuala Lumpur 2016, and will coordinate with GRAPE, the leading task force devoted to the preparation of a Scientific Researcy Programme that will be presented and discussed during the SCAR OSC in Kuala Lumpur 2016. This is in response to one of the six SCAR Horizon Scan priorities, namely "the near Earth space and beyond". Horizontal coordination between the SRP with other programmes of interest are envisaged (e.g. SCOSTEP’s VarSITI, 2014-18).
Further details are given in the SERAnt Proposal.
Terms of Reference
In 2014 the SERAnt Action Group was established to determine the Terms of Reference for an Expert Group on solar terrestrial physics, with the following objectives:
- Identify the science to be addressed, and the groups worldwide that are already active in research in the field;
- Formulate a proposal for its structure and composition;
- Analyze the interaction with GRAPE EG and avoid duplication, while promoting synergy; and
- Bridge over gap between ICESTAR, closed at Auckland, and future EG to be formed in Kuala Lumpur.