REVISED FORECAST: The CME launched toward Earth by yesterday's X-flare is moving faster than originally thought. Analysts at the Goddard Space Weather Lab have revised their forecast accordingly, advancing the cloud's expected arrival time to 09:17 UT (5:17 am EDT) on Saturday, July 14th. Weekend auroras are likely.Aurora alerts: text, voice.
X-FLARE! Big sunspot AR1520 unleashed an X1.4-class solar flare on July 12th. Because the sunspot is directly facing Earth, everything about the blast was geoeffective. For one thing, it hurled a coronal mass ejection (CME) directly toward our planet. According to a forecast track prepared by analysts at the Goddard Space Weather Lab, the CME will hit Earth on July 14th around 09:17 UT (+/- 7 hours) and could spark strong geomagnetic storms.
The explosion also strobed Earth with a pulse of extreme UV radiation, shown here in a movie recorded by NASA's Solar Dynamics Observatory:
The UV pulse partially ionized Earth's upper atmosphere, disturbing the normal propagation of radio signals around the planet. Monitoring stations in Norway,Ireland and Italy recorded the sudden ionospheric disturbance.
Finally, solar protons accelerated by the blast are swarming around Earth. The radiation storm, in progress, ranks "S1" on NOAA space weather scales, which means it poses no serious threat to satellites or astronauts. This could change if the storm continues to intensify. Stay tuned.
These are the first noctilucent clouds this year so clearly visible at our latitude in Warsaw (52 N)," says Grudzinska.
When NLCs first appeared in the 19th century, the mysterious clouds were confined to the Arctic, most often seen in the same places as Northern Lights. In recent years, however, their "habitat" has been expanding, rippling as far south as Colorado, Virginia, Kansas, and Utah. (Here are some examples of sightings in the lower United States.) There is growing evidence that the expansion is a sign of climate change, although this remains controversial.
Whatever the reason, noctilucent clouds aren't just at high latitudes anymore, so sky watchers everywhere should be alert for them. Observing tips: Look west 30 to 60 minutes after sunset when the sun has dipped 6o to 16o below the horizon. If you see luminous blue-white tendrils spreading across the sky, you've probably spotted a noctilucent cloud.
