Space physics

Website of the space physics research team

Space weather briefly

Space weather refers to changing conditions in the near-Earth space environment. Northern lights are perhaps the best known consequence of space weather, but space weather may also significantly affect the reliability and operation of many technological systems in space and on ground, such as telecommunication, power transmission and navigation systems. During strong radiation storms transpolar flights are occasionally rerouted and increased radiation levels may also damage satellites and endanger the health of astronauts. In addition, the Earth's atmosphere expands during space weather disturbances and the satellites on low-Earth orbits experience increased drag. For example, the orbit of the international space station ISS is regularly adjusted as it decays during space weather storms.

Figure 1.

(Left) During space weather storms the residents on the northern latitudes can frequently admire spectacular auroral displays (image: Jouni Jussila) Right) Coronal mass ejections (CMEs) drive nearly all largest space weather storms. The image shows a CME captured by the COR2 coronagraph on-board the STEREO-A spacecraft. (image: NASA).

The ultimate source of space weather is the Sun. Solar activity varies cyclically with a period of about 11 years. In the activity minimum the Sun is calm and space weather disturbances are weak and infrequent, while during the maximum the Sun and the near-Earth space are stormy. At this time solar magnetic field is very complex and in continuous change. Strong eruptions occur daily. The most important solar eruptions are coronal mass ejections (CMEs) and flares.

CMEs are huge ejections of magnetized plasma in which billions of tons of solar material is hurled into interplanetary space. Fastest CMEs are expelled with speeds up to several thousands of kilometers per second and they reach the orbit of the Earth in less than two days. CMEs expand significantly in the heliosphere and when they arrive to the distance of the Earth their dimensions are on average nearly one-third of the Sun-Earth distance. It takes about one day for a CME to pass the Earth. The strong and prolonged southward magnetic field within the CME couples effectively with the geomagnetic field and CMEs cause the majority of strong space storms.

Flares are abrupt and powerful energy releases at the Sun that are observed in nearly all wavelengths of the electromagnetic spectrum. Flares accelerate protons to extremely high energies. These protons arrive to the Earth nearly as fast as the light, in about 30 minutes and they cause radiations storms. However, flares do not cause disturbances to the interplanetary plasma and magnetic field.

Our research

Our space research group at the Department of Physics studies the solar-terrestrial physics and space weather in collaboration with the Finnish Meteorological Institute and Aalto University within the Kumpula Space Centre. The emphasis of our research is on understanding the formation of CMEs and their evolution in the heliosphere and consequences in the near-Earth space. We aim at a profound understanding of the physics behind space weather phenomena and at using this knowledge to develop services for the society.

The philosophy of the group is to pursue a diversity of research methodologies including data analysis and interpretation, theoretical modeling and numerical simulation. An emphasis is on actively participating in the design and implementation of instrumentation for scientific space missions.

Instrument design and implementation

The space research group is involved in the development and scientific planning of several space-borne instruments.

The XSM instruments onboard Smart-1 and Chandrayaan-1, implemented by our high energy astrophysics group, conducted X-ray spectroscopy of the solar corona. A similar instrument is currently operating on-board NASA's Messenger, and is also under study for future application as a standard X-ray Flux Monitor for ESA missions as well as commercial satellites.

BepiColombo is an ESA-led mission to Mercury scheduled for launch in 2017. The SIXS instrument on-board BepiColombo is developed by UH, FMI as well as several Finnish companies. It will measure solar X-rays, electrons and protons. The particle detector system of SIXS is also under study for future application as a standard Energetic Particle Spectrometer (EPS) for ESA and commercial satellites.

Modeling and data analysis

The key focus areas of our current research are - Analyzing and modeling of CME eruption and evolution in the corona - Quantifying how CME properties change during the journey from Sun to Earth - Investigating the solar wind-magnetosphere coupling during different CME structures - Investigating how different CME structures affect the Earth's radiation belts (Van Allen belts)

Today there are many spacecraft observing the Sun. Our group employs in particular observations from the joint ESA and NASA SOHO spacecraft, and from NASA's twin STEREO and Solar Dynamic Observatory (SDO) spacecraft. For instance, using these observations we produce 3-dimensional models of CMEs (Figure 2). ESA's Solar Orbiter and NASA's Solar Probe missions will provide the most compelling future observations of the Sun. Solar Orbiter will be send to an orbit with the perigee at 60 Solar radii from the Sun. Solar Probe will travel even closer. It will approach the Sun within only about 10 solar radii. These missions are expected to answer many open questions on the formation and evolution of the solar wind and CMEs.

Figure 2.

CME seen from three different viewing angles. The bottom row shows a 3-dimensional modeling wireframe.

The quality of long-term space weather forecasts is still very modest. One of the most significant problems is that there is currently no method to predict the magnetic field properties of Earth-impacting CMEs. Our group is in particular tackling this problem. We are developing a novel data-driven coupled simulation, which uses SDO magnetograms to model self-consistently erupting coronal magnetic fields (Figure 2). In addition, we will combine X-ray, EUV and visible-light observations and magnetograms from Hinode, SDO and STEREO to quantify CME magnetic properties and evolution in the corona.

Figure 3.

(Left) MHD-model of erupting CME. Right) Twisted coronal flux rope, which is a precursor for a CME eruption captured by the Japanese Hinode spacecraft. Combining Hinode observations with SDO and STEREO EUV observations and magnetograms will give indirect information on magnetic configuration of the erupting CME.

Among our active research focii are extreme solar and space storms. For example, a super fast and strong CME hit the STEREO A spacecraft on July 2012. This event allowed us to determine how the most extreme eruptions form and what are the worst-case space weather scenarios. We are also participating in the European Commission funded HELCATS project (led by Rutherford Appleton Laboratory, UK). Within HELCATS we are developing new tools to analyze and interpret STEREO heliospheric imager observations on CMEs and the solar wind.

Fast CMEs drive interplanetary shock waves, which accelerate particles to dangerously high energies and when impacting the Earth they can shake violently the whole magnetosphere. Our group is building a comprehensive heliospheric shock database. This database includes shocks and their key parameters from a large number of past and present heliospheric missions. The database offers the scientific community the access to these shocks gathered under the same webpage, identified and analyzed with the same methods and straightforward search options.

Our magnetospheric studies focus on the analysis of energy transport from solar wind to the magnetosphere within the Academy of Finland funded SWIFT project with the Aalto University (Figure 4). The goal of the project is in particular to quantify how solar wind turbulence affects the solar wind-magnetosphere coupling efficiency and how different structures within the CME (sheath and the ejecta) drive activity in the near Earth space. Our research has recently also covered the Van Allen radiation belts. Van Allen belts are composed of high-energy electrons and protons trapped in the geomagnetic field. During space weather storms the electron population in the belts can change dramatically. How and why such changes occur is one of the most current questions in space weather research. Van Allen belts reach out to geostationary orbit, which is populated by several hundred communication, commercial, military and scientific satellite. NASA's Van Allen Probes, launched in late 2012, provide unprecedented comprehensive and detailed information on the radiation belt particles fluxes and dynamics. Our group is investigating how particles that constitute the Van Allen belts reach their high energies and how they are lost from the belts during different solar wind structures.

Figure 4.

(Left) Statistical maps of the flow speed in the geomagnetic tail combined from observations of five THEMIS spacecraft during a five year period. The map on the left shows the flow pattern during southward solar wind magnetic field, while the map on the right shows the flow speed during northward field. Right) Van Allen probe observations of electron fluxes in the Earth radiation belts. The L-parameter gives the distance from the Earth (in Earth radii). The low energies (~ 60 keV) are shown on the top and the highest energies (> 2 MeV) at the bottom. The figure shows how the impact of a CME to the magnetosphere leads to the enhancement of the lower energy electrons.

Lis├Ątietoja

Kumpula Space Centre

MHD Simulations of CMEs at UH

Poster about our activities


Personnel

Hannu Koskinen, Head of department
Physicum C227
(+358) 50 4155356
hannu e koskinen (at) helsinki fi

Emilia Kilpua, University lecturer
Physicum D324
(+358) 50 4155358
Emilia Kilpua (at) helsinki fi

Alexey Isavnin, Post-doc
Physicum D326
(+358) 50 4155514
alexey isavnin (at) helsinki fi

Jens Pomoell, Post-doc
Physicum

jens pomoell (at) helsinki fi

Minna Myllys, PhD student
Physicum A219
(+358) 50 4486267
minna myllys (at) helsinki fi

Erika Palmerio, PhD student
Physicum D315

erika palmerio (at) helsinki fi