Tag Archives: solar

Solar wind and real wind

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“Solar wind” is a colloquial term for the stream of charged particles ejected from the surface of the Sun by heat and strong magnetic fields. It is the interaction between the solar wind and Earth’s magnetic field that is responsible for the aurorae.

During solar storms, when larger amounts of material are ejected at higher speeds (a coronal mass ejection) the solar wind can cause damage to satellites and even to power grids on Earth.

But a new paper from South Korean scientists suggests that the solar wind affects the real wind; that the solar wind hitting the atmosphere can affect the pressure at sea level. Their suggestion is that changes in clouds are caused by currents flowing from the ionosphere (a charged upper layer of the atmosphere) to the land/ocean; and that the solar wind affects these currents. They measured a increase in pressure of about 2500 pascals (over a standard pressure of 101325 pascals) in the days following solar winds above 800km/s.

Il-Hyun Cho et al. 2011. “Changes in Sea-Level Pressure over South Korea Associated with High-Speed Solar Wind Events.” arXiv: 1107.1841v1 [astro-ph.EP]

The Northern Lights over the UK

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A sunspot is an area of intense magnetic activity on the surface of the Sun (the photosphere) that causes it to decrease in temperature and darken.

One particular sunspot (imaginatively named “Active Region 1158”, shown above) has been growing in size over the past week and is now wider than the planet Jupiter. At 0156 on Tuesday morning an enormous X-class solar flare, the largest and most powerful type, erupted from AR1158. This was the Sun’s first X-class flare for more than four years.

The X-class flare shown in an image taken by NASA’s Solar Dynamics Observatory at 193Å.

The flare was accompanied by a coronal mass ejection (CME), a plasma of highly energetic electrons and protons propelled outwards at great speed. This CME travelled towards Earth at about 900 kilometres per second and will strike the atmosphere at about 0100 on Friday morning.

Update (2011‑02‑18): the “blow” from the CME seems to have been fairly glancing and will therefore not impact as severely as thought. The solar wind speed on impact has been about 500-600 km/s, peaking at around 700 km/s for brief periods of time.

There is still the risk of further, less powerful, M-class flares from AR1158 in the future.

A CME is essentially a more powerful version of the solar wind. It is the collision of the solar wind and the Earth’s magnetic field that produces aurora (aurora borealis in the northern hemisphere and aurora australis in the southern hemisphere). It is possible, though unlikely, that the increased strength of the solar wind due to the CME from AR1158 will mean that the aurora borealis can be seen from the UK, especially at higher latitudes (e.g. the Hebrides or Shetland Islands) where the Earth’s magnetic field is stronger.

Update (2011‑02‑18): the current NOAA POES auroral oval clearly shows (top-right quadrant) that there is almost no chance of visible aurora anywhere in the UK.

Previously:

What’s up with the Sun?

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The Sun (the big floaty fireball, not the awful “newspaper”) has been in the news lately as it’s been predicted that the Sun may interfere with the 2012 Olympics. It’s been suggested that  solar flares, ejections of material from the Sun’s surface; and the solar wind, a fast-moving stream of charged particles (normally responsible for the Northern and Southern Lights (Aurora Borealis and Aurora Australis)), could affect the satellites that are responsible for relaying television footage from the Games around the globe.

Over the last few years the Sun has been in an unusually quiet mood, but recently it seems to be “waking up”. Looking at images from the Solar and Heliospheric Observatory (SOHO) Large Angle Spectrometric Coronagraph (LASCO) you can see a clear difference between images taken now and images taken in past months.

Tuesday:

Last Month:

December:

October:

SOHO picked up its largest solar flare in two years on January 22nd:

At the time of writing the solar wind is running at somewhere between 300km and 400km per second with between 2 and 4 protons per cubic metre [source]; this is nothing to worry about. The concern is that by the time the Olympics come around we might be experiencing periods of solar weather like in January 2005 during a severe solar storm.