Not one, but two coronal mass ejections (CMEs) are headed for Earth and they are expected to have a potent impact on Earth’s magnetic field. Active sunspot region AR2158 – still directly facing the Earth – launched a solar storm cloud on Tuesday, September 9th, and this was then followed by an even stronger explosion on Wednesday, September 10th, that classified as an X-class solar flare (image above). According to NOAA forecasters, there is now an 80% chance of polar geomagnetic storms on Friday, September 12th, when the first of the two CMEs arrives and the second one could arrive on Saturday. Auroras are in the offing – perhaps even visible at mid-latitudes during the next few nights - and there can be intermittent GPS problems. There are currently 7 numbered sunspot regions on the sun, but AR2158 is the largest and most active.
The plot below shows the current extent and position of the “auroral oval” in the northern hemisphere, extrapolated from measurements taken during the most recent polar pass of the NOAA POES satellite [courtesy NOAA Space Prediction Center]. This plot provides an estimate of the location, extent and intensity of aurora on a global basis under the conditions that existed at the time of the most recent polar satellite pass. Notice some aurora activity (blue area on plot) measured as far south as the middle latitudes in the US.
Geomagnetic storms of this magnitude are not uncommon, but the current solar cycle (#24) - now experiencing a "double-peak" type of maximum phase - has been relatively quiet and is on pace to be the weakest solar cycle in a century. Powerful solar storms can, in fact, occur during weak solar cycles. The "superstorm" of all solar storms in recent history known as the Carrington Event of 1859 took place during another weak solar cycle (#10) that somewhat resembles our current cycle.
Bottom line, sky watchers should be on alert for possible northern lights over the next few nights from this pair of incoming CMEs.
(For a detailed discussion on the Carrington Event of 1859 click here: http://thesiweather.com/2014/09/02/300-pm-the-carrington-event-of-1859-a-solar-superstorm-that-took-places-155-years-ago/ and for a detailed discussion on solar cycle 24 click here: http://thesiweather.com/2014/07/16/1045-am-the-sun-has-gone-quiet-solar-cycle-24-continues-to-rank-as-one-of-the-weakest-cycles-more-than-a-century/).