Category Archives: Alerts

Solar Flare and CME promt G1 Storm Watch March 11

Northern Lights Now – At Solar minimum, solar flares and active regions are infrequent, but they still happen. Active Region 2734 provides a case in point with a C1.3 solar flare eruption on March 8th that produced an earth-directed CME. As that CME arrives, aurora hunters can expect a chance for storming on March 11, and so SWPC has issued a G1 geomagnetic storm watch.

This flare had a strong “dimming” signature which is indicative of coronal propagation and a CME. What does that mean? Imagine blowing up an M-80 above the surface of a pond, you would see ripples moving out across the surface of the pond. Now imagine that the pond is boiling, you’d need a big M-80 (or a stick of dynamite!) to make ripples big enough to cross the surface. The image below shows the ripples from the flare explosion propagating across the surface of the Sun. Each frame is generated by subtracting one frame from the next, light areas show where there has been a change in brightness – or where the ripple arrived.

Notice that the ripples move out from the eruptive source in multiple directions. Because the eruption sent energy in all directions across the Sun, forecasters can assume energy was also sent off the surface of the Sun and towards Earth. This indicates the the flare was eruptive and sent a Coronal Mass Ejection (CME) into space away from the Sun and towards Earth.

The speed estimates show that the shock wave from this CME should arrive at Earth around midday on March 11 – that translates to early afternoon in Europe, late morning in the US and pre-sunrise in Australia and NZ. As a result, the forecast is for a period of G1 storming in the second half of the day. A C-class flare, even a very eruptive one, isn’t huge so the so the storming is expected to wane by early on the 12th.

G1 storming is predicted for the second half of the day on March 11, 2019
G1 storming is predicted for the second half of the day on March 11, 2019

Harder to Predict than Coronal Holes

Regular readers have become used to most activity recently being from coronal holes. The profile of a CME from a flare is different so we can expect a different kind of forecast. Coronal holes are fairly stable and rotate predictably with the Sun. They often last multiple rotations so Space Weather Forecasters can use data from previous rotations and from STEREO-A to make fairly detailed predictions. Solar flares are different, they happen at a point source on the Sun and the CME from each flare is oriented differently. Forecasters can make estimates of the speed of an ejection and the size, but knowing the orientation is still nearly impossible with current data.

The impact at Earth is also very different between Coronal Holes and CMEs. CH events have a distinctive signature which plays out slowly, sometimes over days, and often matches what was recorded on STEREO-A. CMEs hit with a shock, data shows a spike in solar wind speed and proton density then Bz and Bt can be used to determine the orientation of the storm. Sometimes the CME is oriented such that Bz dives deeply south for the duration of the storm providing aurora hunters a treat, sometimes is pegs north and aurora hunters get a no-show. It total though a CME related storm tends to be stronger than a coronal hole sourced storm, so forecasts will reflect a stronger storm, but it is more likely that there will be a no show. That can be frustrating for anyone who wants to plan on space weather events.

Happy Hunting

G1 Storm Watch Posted For Possible Aurora Jan 24

Northern Lights Now – SWPC has posted a G1 storm watch for January 24. Active space weather could make for an aurora display starting on the 23rd as high speed winds from a coronal hole buffet Earth’s magnetosphere.

The northern hemisphere coronal hole was directed towards Earth on January 21 as shown below in an image from the SDO satellite. Coronal holes emit higher solar wind speeds and it takes 2-4 days for those winds to arrive at Earth.

The dark area is a coronal hole in this image from SDO in AIA 193
The dark area is a coronal hole in this image from SDO in AIA 193

The timing of this storm is expected to be at the beginning of the UTC on the 24th. For people in the UK, the storm should start around midnight and go into the wee hours. For north american hunters, it should start just after Sunset. These forecasts can be off by as much as 6 hours. If the wind speed is higher than expected, the storm will start earlier as the wind arrives sooner (but the show should be better)

NLN Clock shows the storm arriving just after midnight UTC on the 24th
NLN Clock shows the storm arriving just after midnight UTC on the 24th

Here is the official graphic from SWPC (Space Weather Prediction Center)

SWPC notification timeline showing storm watch
SWPC notification timeline showing storm watch

January 2019 Super Blood Wolf Moon Eclipse Expected

Northern Lights Now – On the night of January 20-21 sky watchers anywhere in the Americas and Western/Northern Europe are in for a treat as they have an opportunity to watch a full lunar eclipse. Weather permitting, viewers should be able to see the moon slowly edge into the Earth’s shadow, then turn red as it enters an hour long phase of full eclipse.

This eclipse also aligns with a super moon. That means the Moon is closer than normal or “at perigee.” The Moon has an elliptical orbit, so there are times when it is closer and and times when it is farther from Earth. Occasionally perigee aligns with a full moon or a new moon, when it does, the full moon is labeled “Super.”

Tides are higher and lower than normal during perigee because the Moon is closer and exerts more gravitational force on the oceans. Tides are also higher (and lower) during full moons because the gravity of the Earth and Sun pull together. When these align, as they will be this weekend, it is called a King tide.

You may also see this full moon referred to as a Wolf Blood Moon. Each of the full moons throughout the year are given names. The January full Moon is often referred to as the Wolf Moon. It’s easy to imagine wolves howling at the moon in the dead of winter when clear dry air will make their howls carry farther.

Why does the Blood Moon Turn Red?

Great Question – once the moon is fully in the shadow of the Earth, the only light reflecting off the Moon has been refracted through the edges of the Earths Atmosphere. The atmosphere filters out most other wavelengths or colors of light. Red is the majority of the light that reaches the Moon and reflects back, so the eclipsed Moon will look Red (or Pink, or Orange). This is actually the same process that makes sunsets look red on Earth. In fact, you can imagine that if you were standing on the Moon during a lunar eclipse, the sun would “set” behind the Earth, then you would see a ring of sunset that is mostly red from every part of the horizon of Earth. Yep – Cool!

Why does it always seem like an eclipse happens during a full moon?

Because it does! The only time the Moon can fall into the shadow behind the Earth is when it is exactly opposite the Sun. That can only happen during a full Moon because the Moon is full when it is opposite the Sun. Similarly, Solar eclipses can only happen during new moons, when the moon is directly between the Sun and the Earth. In a solar eclipse, the Moon casts it’s shadow on a portion of Earth. If you are in that shadow, you see a full eclipse.

It’s actually slightly more likely you will see an eclipse if it falls during perigee. During perigee, the Earths shadow is slightly bigger at the Moon. That makes for a longer transit, and more of the Earth will be in a position to see the Moon completely eclipse.

Happy Hunting!