Saturday, 3 October 2015

Solar Observing Space Missions (Past, Present and Future)

Our studies of solar global oscillations require validation against observational data from both ground and space based observations. One such observatory is the Solar dynamics observatory  which continues to produce huge quantities of data inspiring much public interest and used to discern the mysteries of our star.  Before we consider future solar observing missions we shall consider the development over the last 60 years.  Shrouded in secrecy some of the first space based observations of the sun were made in the late 40's using rockets based on designs of the V2 and carrying payloads upto altitudes achieved by the space shuttle.  The earlier "sounding rockets" carried instrumentation for around 10 minutes before re-entering the atmosphere. Using the techniques developed for high resolution imaging of the solar corona the skylab mission in 1974 undertook some of the first ground breaking observations of solar phenomena. By making observations situated above the earths atmosphere it is possible to extend the wavelength range over which observations can be made. Such observations reduce the atmospheric scattering/distortion which occurs. They also make continuous observations possible. Continuous observations allow for the possibility of studying long duration events and oscillatory phenomena. Space weather monitoring is important for the protection of satellites, airborne aircraft safety, power systems and for the safety of astronauts. Our increasing dependence on global communications and monitoring systems requires an array of space borne monitoring and detection systems to provide reliable space weather forecasts. The diversity of measurements required for space weather forecasting can be seen on sites such as;
Examples of solar wind prediction from NOAA are shown above. It should be noted that modern space weather studies is dependent on an armoury of computational modelling tools a key topic of this blog.
There have been many other missions including
  1. Solwind launched in 1979
  2. Orbiting Solar Observatories (1962-1975)
  3. GOES  Geo-stationary operational environmental satellites (1975-2016)
  4. The solar maximum mission  launched in 1980
  5. Yohkoh launched in 1991
  6. Hinode launched in 2006
  7. Ace launched in 1997
  8. Cluster II mission, launched 2000
  9. RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager), launched 2002
  10. Solar and Heliospheric Observatory, launched 1995
  11. Transition Region and Coronal Explorer (TRACE), launched 1998
  12. Stereo (Solar Terrestrial Relations Observatory) launched 2006
  13. Solar Dynamics Observatory  launched 2010
  14. Proba2 launched 2009
We have included in this list satellites monitoring the near earth environment, the magnetosphere and the solar wind. The list of instruments used is huge including spectrometers, coronagraphs, charge analysers, mass spectrometers, telescopes and magnetometers.

The solar dynamics observatory (SDO) features three main sets of instruments
  • Helioseismic and magnetic imager (HMI)
  • Extreme ultraviolet variability experiment (EVE)
  • Atmospheric Imaging Assembly (AMI)
SDOs purpose is to study solar variability and the space weather which results from that. Whilst the HMI are the main instruments for monitoring magnetic variability the AIA provide views of the solar corona extending to 1.3 solar diameters. The AIA covers 10 wavelengths and provides a resolution of 1 arcsecond with a cadence of approximately 10seconds. This level of data provides excellent opportunities to improve our understanding of the activities and dynamics of the solar atmosphere. The range of wavelengths covered by the AIA provides opportunities to study the propagation of phenomena through the layers of the solar atmosphere.

AIA wavelength channel Source Region of solar atmosphere Characteristic
White light continuum Photosphere 5000 K
170 nm continuum Temperature minimum, photosphere 5000 K
30.4 nm He II Chromosphere & transition region 50,000 K
160 nm C IV + continuum Transition region & upper photosphere 105 & 5000 K
17.1 nm Fe IX Quiet corona, upper transition region 6.3×105 K
19.3 nm Fe XII, XXIV Corona & hot flare plasma 1.2×106 & 2x107 K
21.1 nm Fe XIV Active region corona 2×106 K
33.5 nm Fe XVI Active region corona 2.5×106 K
 9.4 nm Fe XVIII Flaring regions 6.3×106 K
13.1 nm Fe VIII, XX, XXIII Flaring regions 4×105, 107 & 1.6×107 K

Live Imagery from SDO AIA
As well as the fourth generation GOES-R missions planned for 2016, future missions include
  The solar orbiter  is an ESA mission partnering with NASA one of the objectives is to perform close observations of the polar regions of the sun. Observations would be made from distances as close as 45 solar radii (0.22AU).  Solar orbiter has a range of instrumentation for solar remote sensing, including EUV imagers covering different depths through the solar atmosphere, high resolution and full disk imagers.  The METIS coronagraph will provide imaging of the corona at 121.6nm. An important feature is that observations willl be coordinated with those of the solar probe plus mission.  The solar  probe plus mission will use gravity assist from Venus to acheive increasingly close distances to the sun to approximately 8.5 solar radii. The range of instruments it includes is as follows SWEAP for analysing the composition of the solar wind. A suite of magnetometers and antennae for modelling the characteristics of the electromagnetic fields. The Thor mission is part of the ESA Cosmic Vision 2015-2025 the purpose of Thor is to investigate plasma heating and energy dissipation.

Turbulence formation at shock, Vlasiator
The figure above shows the formation of turbulence at the bow shock as seen by the global hybrid-Vlasov simulation code VlasiatorThe figure shows a zoomed in cut from the full simulation, where zooming has been done on the quasi-parallel part of the shock where the strongest turbulent fluctuations are observed.  The full simulation box extends from -10 Re to +50 Re in X, and +-50 Re in Y. The ordinary space resolution in this run was set to 227 km (of the order of the ion skin depth), while the velocity space resolution is 30 km/s. Color-scaling depicts density, solar wind flows from the right-hand-side-of the simulation box, while the interplanetary magnetic field forms a 30 degree angle with respect of the Sun-Earth line. The waves in the lower part are the foreshock waves due to solar wind ion reflection at the bow shock surface.

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