Context: Recently, an international team of solar physicists, including academics from Northumbria University has measured for the first time the global magnetic field of the outer most layer of the Sun's atmosphere i.e. solar corona.
About Global Magnetic Field of the Solar Corona

• The researchers used observations from the Coronal Multi-channel Polarimeter (CoMP) which an instrument that can provide measurements of infrared radiation coming from the Sun's atmosphere.
• It is the first time that a global map of the coronal magnetic field has been obtained through actual coronal observations.
• The team used a technique known as coronal seismology or magnetoseismology to measure the coronal magnetic field.
• The method requires the measurement of the properties of magnetohydrodynamic (MHD) waves and the density of the corona simultaneously.

• There are two main puzzles about the Sun which this advancement will help address i.e. Coronal heating problem and Mechanisms of eruptions of the Sun.

Coronal Heating Problem

• Though the core of the Sun is at a temperature of about 15 million degrees, its outer layer, the photosphere is a mere 5700 degrees hot.
• However, its corona or outer atmosphere, which stretches up to several million kilometres beyond its surface, is much, much hotter than the surface (reaching temperatures of one million degrees or more).

Mechanisms of eruptions of the Sun

• Solar flares and coronal mass ejections (eruptions of the Sun) are driven by magnetic reconnections happening in the Sun’s corona.
• Magnetic reconnection is a process where oppositely polarity magnetic field lines connect and some of the magnetic energy is converted to heat energy and also kinetic energy which leads to the generation of heating, solar flares, solar jets, etc.

Significance of measurement of Global Magnetic Field of the Solar Corona

• The Sun is a magnetized star, and its magnetic field plays a critical role in shaping the solar atmosphere.
• The magnetic field governs many aspects of the Sun's behaviour, leading to an 11-year solar cycle, spectacular solar eruptions, and the heating of the hot gas (plasma) in the solar corona to millions of degrees Celsius.
• The magnetic field threads through the different layers of the Sun's atmosphere, which means that information on the magnetic field of the whole atmosphere is required in order to understand the interplay between the solar plasma and magnetic field.
• The speed the waves travel at depends on the strength of the magnetic field which means that being able to measure how fast the waves travel enables an estimate of the magnetic field to made.
• The global map of the coronal magnetic field obtained through actual coronal observations will mark a leap towards solving the problem of coronal magnetic field measurements.
• The new technique will provide that global coronal magnetic field maps could now be routinely obtained, filling in the missing part of the measurements of the Sun's global magnetism.
• The synoptic coronal magnetograms will provide critical information to advance the understanding of how the magnetic field couples the different layers of the Sun's atmosphere as well as the physical mechanisms responsible for solar eruptions and solar cycle.

Why study of Global Magnetic Field of the Solar Corona is necessary?

• It is very important to measure the corneal magnetic fields regularly since the solar corona is highly dynamic and varies within seconds to a minute time scale.
• The measurement of global coronal magnetic fields was missing in the past since the coronal magnetic fields are very weak. 

Additional Information
Coronal Multi-channel Polarimeter (CoMP)

• It is located at Mauna Loa Solar Observatory, near the summit of that volcano on the big island of Hawaii.
• It is an instrument operated by High Altitude Observatory, of the U.S.

Aditya-L1 satellite 

• It is India’s first solar mission which is aimed to measure the solar coronal magnetic fields regularly.
• It will help understand the spectacular solar eruptions and predictions of space weather and many more things.
• A Satellite placed in the halo orbit around the Lagrangian point 1 (L1) of the Sun-Earth system has the major advantage of continuously viewing the Sun without any occultation/ eclipses.