St. Patrick’s Day night, 2015, the northerly reaches of the Northern Hemisphere were showered with a startling array of auroral lights. In the US, they could be seen as far south as Kansas and Virginia. Had these been the normal aurora borealis, the sight would have been spectacular.
March 17, 2015
On March 17, a huge coronal mass ejection (CME) ripped loose from the corona of the Sun and flung itself into interplanetary space, making it an interplanetary coronal mass ejection (ICME).
CMEs are masses of plasma heated to such extreme temperatures that extensive ionization occurs. CME plasma comprises electrons, protons and magnetic field lines that have been ripped free from the Sun’s corona.
Solar astronomers who were watching would have seen a halo form around the Sun as the CME, the largest CME of this solar maximum (the most active time of an 11-year cycle that has a low activity minimum and a high activity maximum). The hurtling CME would have given the appearance of a halo around the Sun because it was hurtling directly toward Earth so it gained relative size as it drew nearer in space and perspective.
CME Hits Earth’s Magnetosphere
At around 4:25 GMT the CME hit the day side of Earth’s magnetosphere. The magnetosphere wraps around Earth. Once thought to be a spherical magnetic shield (hence, magnetosphere), the day side is rounded like a bullet nose while the night side is extended into a tail, blown backward by the stream of photons from solar wind that always pummels the magnetosphere.
CME is one of the solar events that have the potential to interact with Earth in some way, thus CMEs are classified geoeffective: CMEs have an effect on Earth’s magnetosphere and, potentially, on Earth’s atmosphere. When the CME hit Earth’s magnetosphere, a small magnetic storm, or geomagnetic storm, was generated.
The magnetosphere is magnetic. CMEs carry loose magnetic field lines. To show the potential of an meeting between CME and magnetosphere, when two downed electrical power lines interact with each other, sparks fly. The same sort of thing happens when two magnetic fields interact in interplanetary space, sparks fly. The impact of solar photons, coronal plasma and magnetic field lines on Earth’s magnetic shield stirred up a storm, even though initially it was a mild, G-1 class storm. But a surprise was in store.
The CME was so powerful and fast that there was a sea of magnetic charge rushing onward in it’s wake. When this magnetic field also hit Earth, a fearsome geomagnetic storm of G-4 class was unleashed. Persons at high altitudes, like in military aircraft, airplanes and space stations, are in danger of health risks and even fatalities if exposed at such levels, as demonstrated by scientists at the Mullard Space and Science Laboratory in England.
March 18, 2015
While there was much concern about power utility grids, satellite functionality, military communications, global positioning satellites and myriad scientific satellites, no serious reports have made the news.
The auroral display on March 18 was less but still quite active although confined more to the traditional aurora borealis circle. The latest space weather report from NOAA and the Space Weather Prediction Center (solarham.net) is that “solar activity returned to low levels” with no Earth directed CMEs observed.
