The northern lights, a weather phenomenon rarely seen on the West Coast, briefly danced on the horizon in Yreka (Siskiyou County) around 10 p.m. on March 23.
Anthony EdwardsMissed seeing the northern lights last weekend? There should be at least a couple of more sighting opportunities in the next few years, according to space weather experts.
Last Sunday’sunusual northern lightswere because of what’s known as a severe geomagnetic storm — the largest in the last seven years — according to UCLA space physics Professor Vassilis Angelopoulos.
For any enthusiasts hoping to catch a glimpse of the next one, there should be one or two similarly sized storms every year in the next few years, and up to several per year could cause northern lights to be visible in Northern California, Angelopoulos said.
Intense auroras are most likely to occur at lower latitudes near the equinox around March, April, September and October, around 11 p.m. local time, Angelopoulos said.
During those months, Angelopoulos suggested following theNational Oceanic and Atmospheric Administration’s space weather forecaststo see the geomagnetic K-index, a measure of the strength of the storms, hit 7.
Interested watchers should try to get as far away from city lights as possible to a dark area for the best views of the northern lights. Clouds could block the lights, but on a clear night, viewers will be in for a sight to remember.
“It takes some patience, but after a few tries, you will not be disappointed,” Angelopoulos said.
The NOAA Space Weather Prediction Center is typically able to issue forecasts two days in advance, though sometimes the center is only able to give about提前30分钟通知, said Lt. Bryan Brasher with the NOAA Space Weather Prediction Center.
Northern lights occur because of a type of space weather known as coronal mass ejections, said Mark Miesch, a space scientist with the NOAA Space Weather Prediction Center. Coronal mass ejections are expulsions of millions of tons of plasma, a fourth state of matter formed by superheating gas from the sun’s outer atmosphere (the corona), that then travels 1 million to 2 million mph to reach Earth.
“When that big ball of plasma hits the Earth, the Earth has a magnetic bubble around it, the magnetosphere, and that squeezes the magnetic bubble all around us,” Miesch said. “That squeezing of the magnetic field around the Earth sends particles streaming in towards the north and south pole.”
Some of those particles, mostly electrons, then cause the northern lights that are visible to the human eye, Miesch said.
“The more you squeeze that magnetic bubble, the more the disruption, the lower (in latitude) it can extend,” Miesch said, explaining how the northern lights can sometimes be visible in places such as California.
The sun has its own magnetic field, which is generated and gradually disappears as part of an 11-year cycle, Angelopoulos said.
The number of geomagnetic storms becomes more frequent as the cycle approaches its maximum, Miesch said — boding well for more northern lights sightings at lower latitudes in the next few years.
Severe geomagnetic storms such as coronal mass ejections can disrupt power grids, pipelines, railroad tracks, satellites, radio communications and GPS navigation systems, Miesch said. This is because changes in Earth’s magnetic field can induce currents — a phenomenon science enthusiasts will recognize asFaraday’s law, Miesch said.
No disruptions from last weekend’s storm were reported to NOAA, Miesch said. However, Angelopoulos said he knew of some satellites that were turned off because of the storms. “Thankfully, the ones I’m talking about are not critical, they’re for scientific exploration,” he said.
“有很大的潜力,和then that could be catastrophic,” Angelopoulos said. “Hopefully, we’ll be able to predict them well enough so we can know in advance and take precautions.”
Reach Claire Hao: claire.hao@sfchronicle.com; Twitter: @clairehao_
