"Exploding Aurora": What caused these flashes?

The high-speed video of the Northern Lights reveals why the brilliant sky sometimes flashes like lightning: it's all because of gas.

A team from the University of Tokyo and the Japan Polar Research Institute spent three years filming the high-speed video of the Northern Lights. They are looking for photos of "explosive aurora", which flashes intermittently, instead of forming a curtain like what most aurora photographers are looking for. They found it.

It is not only a well-known flicker that occurs every tenth of a second, but also a faster pulse. They found that some aurora flashes 50 to 60 times per second, and some aurora flashes 80 times per second. [Aurora Photo: See the amazing Northern Lights]

Aurora occurs when charged particles from the sun hit the earth's magnetic field for thousands of miles. These charged particles move at high speed along the magnetic field lines and collide with gas atoms in the highest atmosphere of the earth, the so-called outer atmosphere. According to the website of the National Oceanic and Atmospheric Administration, oxygen and nitrogen atoms in the air will glow when they collide. According to NASA, oxygen emits green, yellow or red light, while nitrogen usually emits blue light.

The Northern Lights don't always produce colorful curtains. Sometimes they flash like flashlights. They say that by watching video clips, researchers can track faster light pulses to understand their regular frequencies, which shows that flicker occurs because some atoms have so-called cyclotron frequencies. The cyclotron frequency is the frequency at which an ion-an atom that has lost one or more electrons-rotates around the magnetic field lines in a spiral motion. Take oxygen as an example. Atoms rotate at the speed of 10 times per second. This produces an electromagnetic ion cyclotron, or electromagnetic wave, which propagates through a gas (called plasma) with charged particles. Electromagnetic waves begin to propagate in the atmosphere from a height of 1800 miles to 900 miles (3,000 to 1500 kilometers). Wave is an oscillation phenomenon in which electrons of various gas atoms (oxygen, hydrogen and nitrogen) move back and forth near the magnetic field lines. It's like a large group of people doing radio waves in the stadium. )

Electron waves generate electric waves in plasma and interact with charged particles. These charged particles-mainly free electrons-reach the low-altitude atmosphere at an altitude of about 250 to 60 miles (400 to 100 km), hitting gas molecules in the atmosphere and forming aurora. At the same time, when the wave propagates along the magnetic field lines, the ions in its plasma will emit light with characteristic frequency. When charged particles move synchronously under electromagnetic waves, the radiation they emit can be regarded as a flicker, and its "beat" matches the cyclotron frequency. Careful examination of scintillation can reveal which gases are in the plasma.

"Detailed observation of scintillation helps us diagnose the plasma environment around space," Ryuho Kataoka, co-author of the study, told Live Science in an email.

The observation results show that the scintillation energy is greater than that of oxygen, and the cyclotron frequency of oxygen is 10 times per second. On the other hand, the faster flicker may be due to hydrogen. "The cyclotron frequency of hydrogen ions is 16 times that of oxygen ions, while the cyclotron frequency of helium ions is four times that of oxygen ions," Kataoka said. Therefore, if the oxygen frequency of 10 Hz is taken as the baseline, the "hydrogen band" electromagnetic wave appears in the frequency range of 40 Hz to 160 Hz. "This is the place where the flash speed is faster.

In the video, you can see the unique green color of oxygen at 60 to 120 miles (100 to 200 kilometers). At higher altitudes, oxygen is released in the red wavelength range.

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