Solar Xrays Oscillate D Layer Ionosphere

K3GAU · Nov 21, 2017

KQ6XA said: ↑

A team of scientists led by solar physicist Laura Hayes, investigated a connection between solar flares and Earth's ionosphere. They discovered oscillating pulses in the D layer of the ionosphere at Low Frequency [transatlantic propagation at 24 kHz LF] mirrored X-ray and Extreme Ultraviolet (EUV) oscillations during a July 24, 2016 flare. It has now become clear that solar flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies; it had not been previously known that the ionosphere is sensitive to this variability. Their results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought. Modeling of the ionosphere shows that the D region electron density varies by up to an order of magnitude over the timescale of the pulsations (approximately 20 minutes). Their research article appears in Space Physics, The Journal of Geophysical Research.

Solar Physicist Laura Hayes

NASA Detects Solar Flare Pulses at Sun and Earth
When our Sun erupts with giant explosions — such as bursts of radiation called solar flares — we know they can affect space throughout the solar system as well as near Earth. But monitoring their effects requires having observatories in many places with many perspectives, much the way weather sensors all over Earth can help us monitor what’s happening with a terrestrial storm.

NASA’s Solar Dynamics Observatory captured these images of an X-class flare on Feb. 15, 2011.
Credits: NASA's Goddard Space Flight Center/SDO

By using multiple observatories, two recent studies show how solar flares exhibit pulses or oscillations in the amount of energy being sent out. Such research provides new insights on the origins of these massive solar flares as well as the space weather they produce, which is key information as humans and robotic missions venture out into the solar system, farther and farther from home.

The first study spotted oscillations during a flare — unexpectedly — in measurements of the Sun’s total output of extreme ultraviolet energy, a type of light invisible to human eyes. On Feb. 15, 2011, the Sun emitted an X-class solar flare, the most powerful kind of these intense bursts of radiation. Because scientists had multiple instruments observing the event, they were able to track oscillations in the flare’s radiation, happening simultaneously in several different sets of observations.

“Any type of oscillation on the Sun can tell us a lot about the environment the oscillations are taking place in, or about the physical mechanism responsible for driving changes in emission,” said Ryan Milligan, lead author of this first study and solar physicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Glasgow in Scotland. In this case, the regular pulses of extreme ultraviolet light indicated disturbances — akin to earthquakes — were rippling through the chromosphere, the base of the Sun’s outer atmosphere, during the flare.

What surprised Milligan about the oscillations was the fact that they were first observed in extreme ultraviolet data from NOAA’s GOES — short for Geostationary Operation Environmental Satellite, which resides in near-Earth space. The mission studies the Sun from Earth’s perspective, collecting X-ray and extreme ultraviolet irradiance data — the total amount of the Sun’s energy that reaches Earth’s atmosphere over time.

This wasn’t a typical data set for Milligan. While GOES helps monitor the effects of solar eruptions in Earth’s space environment — known collectively as space weather — the satellite wasn’t initially designed to detect fine details like these oscillations.

When studying solar flares, Milligan more commonly uses high-resolution data on a specific active region in the Sun’s atmosphere to study the physical processes underlying flares. This is often necessary in order to zoom in on events in a particular area — otherwise they can easily be lost against the backdrop of the Sun’s constant, intense radiation.

“Flares themselves are very localized, so for the oscillations to be detected above the background noise of the Sun’s regular emissions and show up in the irradiance data was very striking,” Milligan said.

There have been previous reports of oscillations in GOES X-ray data coming from the Sun’s upper atmosphere, called the corona, during solar flares. What’s unique in this case is that the pulses were observed in extreme ultraviolet emission at frequencies that show they originated lower, in the chromosphere, providing more information about how a flare’s energy travels throughout through the Sun’s atmosphere.

To be sure the oscillations were real, Milligan and his colleagues checked corresponding data from other Sun-observing instruments on board NASA’s Solar Dynamics Observatory or SDO, for short: one that also collects extreme ultraviolet irradiance data and another that images the corona in different wavelengths of light. They found the exact same pulses in those data sets, confirming they were a phenomenon with its source at the Sun. Their findings are summarized in a paper published in The Astrophysical Journal Letters on Oct. 9, 2017.

These oscillations interest the scientists because they may be the result of a mechanism by which flares emit energy into space — a process we don’t yet fully understand. Additionally, the fact that the oscillations appeared in data sets typically used to monitor larger space patterns suggests they could play a role in driving space weather effects.

In the second study, scientists investigated a connection between solar flares and activity in Earth’s atmosphere. The team discovered that pulses in the electrified layer of the atmosphere — called the ionosphere — mirrored X-ray oscillations during a July 24, 2016, C-class flare. C-class flares are of mid-to-low intensity, and about 100 times weaker than X-flares.

Stretching from roughly 30 to 600 miles above Earth’s surface, the ionosphere is an ever-changing region of the atmosphere that reacts to changes from both Earth below and space above. It swells in response to incoming solar radiation, which ionizes atmospheric gases, and relaxes at night as the charged particles gradually recombine.

In particular, the team of scientists — led by Laura Hayes, a solar physicist who splits her time between NASA Goddard and Trinity College in Dublin, Ireland, and her thesis adviser Peter Gallagher — looked at how the lowest layer of the ionosphere, called the D-region, responded to pulsations in a solar flare.

“This is the region of the ionosphere that affects high-frequency communications and navigation signals,” Hayes said. “Signals travel through the D-region, and changes in the electron density affect whether the signal is absorbed, or degraded.”

The scientists used data from very low frequency, or VLF, radio signals to probe the flare’s effects on the D-region. These were standard communication signals transmitted from Maine and received in Ireland. The denser the ionosphere, the more likely these signals are to run into charged particles along their way from a signal transmitter to its receiver. By monitoring how the VLF signals propagate from one end to the other, scientists can map out changes in electron density.

Pooling together the VLF data and X-ray and extreme ultraviolet observations from GOES and SDO, the team found the D-region’s electron density was pulsing in concert with X-ray pulses on the Sun. They published their results in the Journal of Geophysical Research on Oct. 17, 2017.

“X-rays impinge on the ionosphere and because the amount of X-ray radiation coming in is changing, the amount of ionization in the ionosphere changes too,” said Jack Ireland, a co-author on both studies and Goddard solar physicist. “We’ve seen X-ray oscillations before, but the oscillating ionosphere response hasn’t been detected in the past.”

Hayes and her colleagues used a model to determine just how much the electron density changed during the flare. In response to incoming radiation, they found the density increased as much as 100 times in just 20 minutes during the pulses — an exciting observation for the scientists who didn’t expect oscillating signals in a flare would have such a noticeable effect in the ionosphere. With further study, the team hopes to understand how the ionosphere responds to X-ray oscillations at different timescales, and whether other solar flares induce this response.

“This is an exciting result, showing Earth’s atmosphere is more closely linked to solar X-ray variability than previously thought,” Hayes said. “Now we plan to further explore this dynamic relationship between the Sun and Earth’s atmosphere.”

Both of these studies took advantage of the fact that we are increasingly able to track solar activity and space weather from a number of vantage points. Understanding the space weather that affects us at Earth requires understanding a dynamic system that stretches from the Sun all the way to our upper atmosphere — a system that can only be understood by tapping into a wide range of missions scattered throughout space.

Article Source NASA Press Release: By Lina Tran
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Last Updated: Nov. 16, 2017 , Editor: Rob Garner

Paper:

Research Article
Pulsations in the Earth's Lower Ionosphere Synchronized With Solar Flare Emission
Authors
Laura A. Hayes,
Peter T. Gallagher,
Joseph McCauley,
Brian R. Dennis,
Jack Ireland,
Andrew Inglis
First published: 17 October 2017
DOI: 10.1002/2017JA024647
Abstract
Solar flare emission at X-ray and extreme ultraviolet (EUV) energies can cause substantial enhancements in the electron density in the Earth's lower ionosphere. It has now become clear that flares exhibit quasi-periodic pulsations with timescales of minutes at X-ray energies, but to date, it has not been known if the ionosphere is sensitive to this variability. Here using a combination of very low frequency (24 kHz) measurement together with space-based X-ray and EUV observations, we report pulsations of the ionospheric D region, which are synchronized with a set of pulsating flare loops. Modeling of the ionosphere show that the D region electron density varies by up to an order of magnitude over the timescale of the pulsations (∼ 20 min). Our results reveal that the Earth's ionosphere is more sensitive to small-scale changes in solar soft X-ray flux than previously thought and implies that planetary ionospheres are closely coupled to small-scale changes in solar/stellar activity.
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K3GAU · Nov 21, 2017

I don't know what is so "new" about solar xray flares affecting propagation and not just at VLF. A British ham wrote a program some years ago (SBSpectrum) and there are other pieces of software available as well that will allow you to look at the effects of flares, etc. on transmitted signals. I have used SBSprectrum for several years. All you need is a frequency stable rig or receiver and a computer with some sort of an audio card or interface. I usually monitor WWV or CHU signals. You can definitely see doppler shift on their carriers when there is a solar xray flare.

I am sure their measurements are much more accurate, etc. but you don't need a NASA budget to see the solar flares effect on propagation.

Dave K3GAU

W1YW · Nov 21, 2017

K3GAU said: ↑

I don't know what is so "new" about solar xray flares affecting propagation and not just at VLF. A British ham wrote a program some years ago (SBSpectrum) and there are other pieces of software available as well that will allow you to look at the effects of flares, etc. on transmitted signals. I have used SBSprectrum for several years. All you need is a frequency stable rig or receiver and a computer with some sort of an audio card or interface. I usually monitor WWV or CHU signals. You can definitely see doppler shift on their carriers when there is a solar xray flare.

I am sure their measurements are much more accurate, etc. but you don't need a NASA budget to see the solar flares effect on propagation.

Dave K3GAU
Click to expand...

The oscillations are unexpected.

W4HM · Nov 22, 2017

W1YW said: ↑

D REGION Bonnie; not LAYER

Yes, Danilov's book shows the reaction rate for the dominant NOx chemical reactions is capable of manifesting rapid changes. It's cool that we see it demonstrated 45 years later
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I first heard about this possibility in the early 1980's and it's good to see it now demonstrated. There is allot of knowledge about the ionosphere that was first discovered beginning in the 1970's by Uncle Sam but has been lost to the annals of time because it became classified when first discovered and is still classified in 2017. stupid.

You can see similar things happening in our hamateur radio hobby. I have an ARRL antenna handbook published in 1968. I also have a 1988 version and the two barely resemble each other with much more useful information about antennas in the 1968 version.

One book series that has allot of great MF and HF radio wave propagation science and of course antennas for the hamateur is ON4UN's Low Band DXing.

For many years it was taught in hamateur radio that the D region disappeared after the sun set but that's totally incorrect. It's weaker at night than day but still there and absorbs RF signals on 160 meters in varying degrees. Energetic galactic cosmic rays stoke up the D region at both day and night and things will only get worse as solar cycle 24 fades away and more galactic cosmic rays penetrate into the inner solar system.

And the E region also still exists after sunset and blocks low TOA MF radio signals keeping the RF from reaching the F region.

Solar Xrays Oscillate D Layer Ionosphere

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