10 Years of SOHO - Nasa

SOHOdynamics of Earth’s upper atmosphere.Water vapour and ozone are especiallysensitive to changes in the Sun’s UVoutput. Fortunately, Earth’s atmosphereprotects us from this harmful radiation.This also means that we have to leaveEarth’s atmosphere behind and observethe Sun from space.SOHO’s Extreme ultraviolet ImagingTelescope (EIT) provides us with stunningimages of the Sun’s corona, showingdelicate coronal loops, bright flares andintriguing coronal holes. EIT and the UVspectrometers SUMER and CDS show usthat the outer solar atmosphere isextremely dynamic and changing, and thatplasma flows play an extremely importantrole.Gone With the Solar WindThe solar wind is a stream of mainlyelectrons and protons flowing from theUsing advanced analysis techniques, SOHO/MDI can reveal the temperature and flow structure beneath sunspotsJust a little over 4 years after the launchof SOHO, scientists published anastonishing result: the first successfulholographic reconstruction of features onthe far side of the Sun. An active regionon the far side reveals itself because itsstrong magnetic fields speed up the soundwaves. The difference becomes evidentwhen sound waves shuttling back andforth fall out of step with one another. Inthe meantime, the astonishing has becomeroutine, and MDI offers daily far-sideimages online, at http://soi.stanford.edu/data/full_farside/.Violent solar activity occasionallydisrupts satellites, radio communicationsand power systems. Advancewarning of magnetic storms brewing onthe far side that could rotate with theSun and threaten Earth is therefore ofvital importance for space weatherforecasting.The Sun’s Dynamic CoronaThe outer atmosphere of the Sun, thecorona, has a typical temperature of about1 million K and emits light mainly in theultraviolet (UV) part of the spectrum. It isthis radiation from the Sun’s hot coronathat controls the composition andHolographically reconstructed side view of the Sun showing thetwo large active regions 10486 and 10488 as they rotate fromthe far side (left) to the hemisphere visible from Earth (right).During the previous rotation, these two active regions were thesource of the powerful ‘Halloween’ storms in 2003, whichincluded the largest ever recorded X-ray flarewww.esa.int esa bulletin 126 - may 2006 27