What are aurora australis and aurora borealis? How are these triggered?

Auroras are luminous phenomena thatoccur near the North (Aurora Borealis) and South Poles (Aurora Australis).They are caused by the interaction of charged particles from the Sun with the Earth’s magnetic field and atmosphere.

Aurora Borealis:Often called theNorthern Lights,it occursin the northern hemisphere,predominantly in regions near the Arctic Circle. This includes countries likeRussia, Norway, Sweden, Finland, Iceland, Canada, and Alaska.

Aurora Australis:Also known as theSouthern Lights,it occurs in theSouthern Hemisphere, primarily around the Antarctic Circle.It can be seen in countries such asAustralia, New Zealand, Antarctica, and parts of southern South America.

• ## Characteristic features of auroras

• Timing and Frequency:Auroras are most visible during winter and around the equinoxes, with increased activity during periods of high solar activity, such as solar storms or solar flares


• Shapes and Movements:Both auroras exhibit a variety of shapes, including arcs, curtains, rays, and spirals. They often move and change shape rapidly due to interactions with Earth’s magnetic field.

## Colors of Aurora

• Altitude and Atmospheric Composition:Higher altitudes produce red glows from oxygen atoms, while lower altitudes result in the more common green-yellow hues.


• Oxygen and Nitrogen:Oxygen atoms at lower altitudes produce the familiar green-yellow hues, while reddish and bluish light in the lower fringes of auroras is created by ions striking nitrogen atoms.


• Rare Colors:Ions striking hydrogen and helium atoms can produce blue and purple auroras, but these colors are rarely visible to the human eye as they are outside the visible spectrum.

## Trigger and Formation of auroras

• Solar Wind Generation:This solar wind (primarily electrons and protons) is a result of the sun’s intense activity and consists of superheated gases.


• Interaction with Earth’s Magnetic Field:Most of the solar wind is deflected, but some particles become trapped within the magnetosphere and are directed towards the magnetic poles.


• Trapping in the Ionosphere:The trapped ions enter the ionosphere and accumulate in ring-shaped areas around the geomagnetic poles.


• Collisions with Atmospheric Gaseslike oxygen and nitrogen and transfer of energy to these atoms resulting into light.


• Colorful Displays:oxygen at lower altitudes produces green and yellow hues, while higher altitudes can emit red light. Nitrogen can create blue or purple shades.


• Influence of Solar Activity:Geomagnetic storms, triggered by solar events likecoronal mass ejections (CMEs)and solar flares, enhance auroral activity.  Eg- During periods of heightened solar activity, auroras can be seen further south than usual and can exhibit more vibrant colors.

## Significance and importance of Auroras

• Understanding Earth’s upper atmosphere,including its density, composition, flow speeds, and the strength of electrical currents flowing in the upper atmosphere.


• Study of Solar Activity: Auroras are directly linked tosolar activity, including solar flares andcoronal mass ejections (CMEs). Monitoring auroras can help predict and mitigate the effects of solar activity ontechnological infrastructurelike satellites and GPS systems.


• Cultural and Historical Importance: Auroras have been observed and revered by various cultures throughout history, often appearing inmythology and folklore. For example, theInuit peoplebelieved auroras were the spirits of their ancestors.

Due to 4 strong Coronal Mass Ejections (CMEs) Aurora lights in red hues were visible from Ladakh on May 10th 2024.

Auroras are not only breathtaking natural phenomena but also help advance our understanding ofEarth’s magnetosphere,solar activity, and theupper atmosphere, making them an essential subject of study.

Click to Access Full Notes