{"id":318,"date":"2016-09-06T13:28:39","date_gmt":"2016-09-06T13:28:39","guid":{"rendered":"http:\/\/wp.lancs.ac.uk\/aurorawatchuk\/?p=318"},"modified":"2016-09-20T08:25:47","modified_gmt":"2016-09-20T08:25:47","slug":"coronal-hole-drives-recent-aurora","status":"publish","type":"post","link":"http:\/\/wp.lancs.ac.uk\/aurorawatchuk\/2016\/09\/06\/coronal-hole-drives-recent-aurora\/","title":{"rendered":"Coronal hole drives recent aurora"},"content":{"rendered":"

This is the first blog post from Dan Billett, a Ph.D. student in Lancaster’s Space and Planetary Physics group. Dan has just joined the AuroraWatch UK team<\/a> and is interested in public outreach so you will, no doubt, be hearing more from him in the future! — Nathan.<\/em><\/p>\n

On Monday 5th September, NOAA\u2019s Space Weather Prediction Center<\/a> posted this update<\/a> referring to a coronal hole<\/a> high speed\u00a0stream (CS HSS); a fast\u00a0stream of solar material which formed a good connection with the Earth’s magnetic field. What has this connection meant for us? Aurora sightings from the UK, of course!<\/p>\n

\"2_coronal_holes\"

Coronal holes are distinguished by the dark regions on the sun which are relatively cold compared to the rest. Image provided by the NASA SDO spacecraft.<\/p><\/div>\n

AuroraWatch UK alert status<\/h2>\n

Over the last few days we have had a few spots of geomagnetic activity (we wrote about the first here<\/a>) with activity reaching our amber level<\/a> on more than one occasion, suggesting that aurora might have been visible in Scotland, the north of England and possibly elsewhere. As of writing this post (5th Sept), activity has spiked yet again to the amber level.<\/p>\n

\"AW

AW UK activity from 00:00 (UT) on 01\/09 to 24:00 (UT) on 05\/09.<\/p><\/div>\n

 <\/p>\n

The K index (a measure of geomagnetic fluctuations) managed to get all the way up to 5 on the 4th Sept, indicating the presence of a geomagnetic storm.<\/p>\n

\"crk2_20160904_k\"

K index measured by AW UK on 5th September.<\/p><\/div>\n

Solar Wind data<\/h2>\n

Now we come to looking at what the solar wind has been doing over the last few days. Although the z (north-south) component of the interplanetary magnetic field (IMF) shown by the red line has not been that strongly negative (which is one of the best indicators of aurora) for long, notice that the solar wind speed (given by the purple line) has nearly doubled over the course of barely a\u00a0day, reaching a top speed of around 800km\/s (typically around 300-400km\/s).<\/p>\n

\"Capture\"

Solar wind data recorded by NOAA\u2019s DSCOVR mission from the 30-08 to 06-09 . Data provided by NOAA\u2019s SWPC.<\/p><\/div>\n

This significant uptick in speed is because of\u00a0the fast material being ejected out of the\u00a0CS HSS\u00a0arriving at Earth, after its 93 million mile journey. It’s slowed up a little bit now, but these high speeds make up for the short periods of negative IMF Bz to make some aurora\u00a0still happen.<\/p>\n

UK sightings<\/h2>\n

Not the best few days recently with rain and clouds being much the norm throughout the UK, but the force of the coronal hole high speed stream seems to have pushed some aurora\u00a0through anyway during times of clear skies:<\/p>\n

Shetland, Scotland<\/strong><\/p>\n

\n

Kicking-off nicely #Shetland<\/a> #Aurora<\/a> @metoffice<\/a> @aurorawatchuk<\/a> https:\/\/t.co\/vN3vaiOBLF<\/a> pic.twitter.com\/ndF94FsFdV<\/a><\/p>\n

— Promote Shetland (@PromoteShetland) September 3, 2016<\/a><\/p><\/blockquote>\n