A powerful M-class solar flare erupted on the sun at 5:48 AM, EDT (01:48 UTC), July 18 2023.
In this video obtained from the Solar Dynamics Observatory, the powerful M-5.7 solar flare is clearly visible at the 4:00 position. The video is a composite produced from 3 discrete wavebands in the extreme ultraviolet region of the spectrum at 94, 193 and 335 nanometers. Observing the sun in these wavebands allows us to peer into the hot layers just below the photosphere where the million-degree gas originates, gas that is ultimately ejected from the sun. The SDO continuously monitors the sun in 10 wavebands, allowing us to prepare for geomagnetic events that could adversely affect our near-earth environment. This video is also hosted at our YouTube channel as a “short” here.
In fact, much of July has seen an increase in the frequency and strength of these solar storms, an indication that the sun is becoming more active internally. Although the sun is quite stable, it does vary slightly in output, behavior that is associated with increased sunspot and solar flare activity. This variation occurs in 11-year cycles, with the activity currently on the rise.
Some conditions in space have the potential to seriously affect us on Earth. We call these conditions “Space Weather”. The effects of the solar wind, either as the continuous, daily stream of charged particles bombarding the Ionosphere, the upper, tenuous region of the Earth’s atmosphere or as the result of a solar flare, can be measured. An aspect of Space Weather, this interaction with the Ionosphere above 85 kilometers in altitude produces the beautiful auroral displays we observe as the Northern and Southern Lights.
Another aspect of Space Weather, and one that is central to this research, is the response of the E and F layers of the Ionosphere to the daily irradiance of high-energy solar radiation, predominantly solar ultraviolet. In short, the lower D layer of the Ionosphere is produced by the ionization of the E and F layers during the day. At night, the electrons and ions quickly recombine in the absence of solar irradiance and the D layer disappears.
This ionization and its effects can be measured and quantified by the interaction of VLF (very low frequency) radio waves with these layers and is at the heart of this research. Compared to the charged particles of the solar wind which take 2 or 3 days to reach the Earth, X-rays and ultraviolet radiation travel at the speed of light and thus, take a little over 8 minutes to reach the Earth. Their effects on the Ionosphere can thus be measured and observed within minutes of occurring on the sun.
The Sun and All Stars
The Sun and all stars are dynamic, self-regulating systems, each powered by a huge nuclear fusion reactor in their core. These cores of the sun and other stars in a similar evolutionary state currently produce helium and a tremendous amount of energy, consuming 600 million metric tons of hydrogen per second in the process. From the 15 million-degree core plasma produced by these nuclear fusion reactors flows a stream of protons, electrons and helium nuclei, collectively referred to as the solar wind.
Sunspot numbers are an indicator of internal solar activity. Their increased numbers are an indicator of increased solar output and activity. Our home star has an 11-year activity cycle. Considering the sun’s nature as a giant, roiling, super-heated, self-regulating ball of plasma modeled as a fluid, we expect certain irregularities. These irregularities in the sun’s behavior and activity, aspects of solar dynamics that give rise to solar storms and outbursts, are phenomena whose frequency is directly linked to the solar cycle.
Solar Flares vs Coronal Mass Ejections
While they are both indicative of a dynamic and changing environment, they are, at the same time, quite different in nature, yet have certain commonalities. A CME is a huge bubble of magnetized gas that is ejected into space, an event that may take several hours to complete. A solar flare is far more temporal and short-lived and much smaller in scale. They both have associated with them streams of high-energy protons, electrons and alpha particles (helium nuclei). Hence, the large difference between solar flares and CMEs is mostly one of size. Both can occur together but can also occur in the absence of the other.
Why does the Sun appear dark and unfamiliar?
The video is a composite produced from 3 discrete wavebands in the extreme ultraviolet region of the spectrum at 94, 193 and 335 nanometers. Observing the sun in these wavebands allows us to peer into the hot layers just below the photosphere where the million-degree gas originates, gas that is ultimately ejected from the sun. We only see the superheated gas emitting UV light, superheated to the million-degree range. What appears “dark” are regions of the sun that are cooler, much in the same way that “Sunspots” appear “dark” because they’re cooler.
Million-degree gas produces X-rays. Solar flares, short-lived and temporal, are often associated with sunspots. These are cooler regions of the sun’s photosphere (the solar “disk” we see) resulting from magnetic anomalies that cause a breach in energy transmission from the solar interior. A large sunspot group, known as AR3363, is associated with the July 18th solar flare.
Solar flares emit radiation in the visible, ultraviolet, x-ray and gamm-ray regimes of the electromagnetic spectrum. The X-rays and gamma rays are of highest energy and are associated with localized, super-heated gas. Solar flares are thus categorized according to a logarithmic x-ray intensity scale, from A being the weakest to X being the strongest. We were witness to a powerful (magnitude 5.7) M-class solar flare last week. Please see the following x-ray flux chart for one week beginning on 18 July from the GOES satellite.
The measured flux at the Earth/Sun distance
- A = 1.0×10-8 (Watts m-2)
- B = 1.0×10-7 (Watts m-2)
- C = 1.0×10-6 (Watts m-2)
- M = 1.0×10-5 (Watts m-2)
- X = 1.0×10-4 (Watts m-2)
The SID (Sudden Ionospheric Disturbance) Effect
A SID is the result of a rapid influx of high-energy ultraviolet or x-ray radiation. Although this radiation is most often attributed to the sun, the source could theoretically originate in deep space from supernovae or a Gamma Ray Burst. One method of detecting SIDs involves measuring the effect Ionospheric changes have on reflected VLF (3 – 30 Khz) radio signals. When a solar flare occurs, high-energy X-rays irradiate the sunlit side of the Earth, striking the E and F layers of the Ionosphere. These X-rays penetrate to the D-layer, releasing electrons that rapidly increase absorption, causing VLF (very-low frequency. 3 – 30 kHz) signals to be reflected by that layer where the increased atmospheric density will usually increase the absorption of the signal and thus dampen it.
For a more detailed explanation, to get involved in the ongoing research or to set up your own solar SID station, visit sid.stanford.edu. For the Stanford Solar Center’s home page, visit: solar-center.stanford.edu.
We invite you to view our full-featured video explaining much of what was discussed here and highlighting the famous Anemone Solar flare, made famous by its appearance as a “Sea Anemone”.
Astronomy For Change: https://astronomyforchange.org
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