Evolution of spicules in the North Pole

Interface Region Imaging Spectrograph (IRIS)

This is probably not a typical movie of the Sun to the untrained eye. What we see here are observations recorded during 5 hours on August 29, 2015 by the IRIS satellite. IRIS sees the Sun at ultraviolet wavelengths (UV, from 1330 to 2830 Å) not attainable from ground-based telescopes.

When looking at UV images and spectra from the Sun we are looking high up in the Sun's atmosphere, at two layers called chromosphere and transition region. In particular we are looking anywhere between 2000 and 5000 km over the solar surface. In these layers the Sun looks very different! This movie was recorded in the Si IV line at 1400 Å. The field of view shows the North Pole of the Sun and a portion of the limb (the edge of the star). The region shown in this movie does not have much solar activity, but that does not mean that this is a boring place: lots of dynamic phenomena are observed during these 5 hours.

At the limb one can see spicules, which are thin chromospheric dynamic short-lived jets of gas that shoot out towards the corona. They live only for some minutes and have a swaying and torsional motion. They are believed to transfer mass from the chromosphere to the transition region and corona. They loosely follow the magnetic field lines sticking out of the Sun. At any one time more than 100,000 spicules are present in the solar atmosphere. Looking more onto the disk loops are observed everywhere. These loops are in fact magnetic field lines connecting patches of opposite polarities. We "see" the field lines because plasma gets trapped in them and traces their existence. Finally, a very dynamic "boiling" pattern is seen in the form of ubiquitous brightenings. Those small brightenings are not caused by magnetic fields, but by acoustic shocks (waves) coming from the photosphere.

The sparkles (noise) that saturate the images from time to time are due to the South Atlantic Anomaly (SSA). IRIS traverses the SSA several times every day. The SAA is an area where the inner Van Allen radiation belt comes closest to the Earth's surface. When the satellite crosses the SSA it encounters an increased flux of energetic particles and radiation. The impact of this energetic particles on the CCD camera causes bright pixels.

To download the movie, click HERE

Movie credit: Ada Ortiz (ITA, University of Oslo), Luis Bellot Rubio (IAA-CSIC)

Text credit:  Ada Ortiz (ITA, University of Oslo)

Observations: IRIS (NASA, LMSAL)