Monday, January 6, 2014

ALERT: Proton Event 10MeV Integral Flux exceeded 10pfu


(Explanation of chart below)
Long-range communications using high frequency (HF) radio waves (3 - 30 MHz) depend on reflection of the signals in the ionosphere. Radio waves are typically reflected near the peak of the F2 layer (~300 km altitude), but along the path to the F2 peak and back the radio wave signal suffers attenuation due to absorption by the intervening ionosphere.

Absorption is the process by which the energy of radio waves is converted into heat and electromagnetic (EM) noise through interactions between the radio wave, ionospheric electrons, and the neutral atmosphere (for a more extensive description of the absorption process see Davies, 1990). Most of the absorption occurs in the ionospheric D region (50–90 km altitude) where the product of the electron density and the electron-neutral collision frequency attains a maximum. Within this region the neutral density is relatively constant over time, so variations in the local electron density drive the total amount of absorption. The electron density is a function of many parameters and normally varies with local time, latitude, season, and over the solar cycle. These "natural" changes are predictable, and affect absorption only moderately at the lowest HF frequencies. Much more significant changes to the absorption strength are seen as a result of sudden increases of electron density in the D region (the classic short wave fade) due to, for example, solar X-ray flares on the dayside or solar proton precipitation in the polar regions.

Solar X-ray flares have significant emission in the 0.1-0.8 nm [1-8 Å] wavelength range. This is important because these wavelengths ionize the D region, dramatically increasing local electron density, and hence the total EM absorption. The flares, which can last from a few minutes to several hours, are rated C, M, or X according to the 0.1-0.8 nm flux as measured by instruments on the GOES satellites. To qualify as a C-class flare the flux, F, must fall within the range 10-6 ≤ F < 10-5 W·m-2, for M-class 10-5 ≤ F < 10-4 W·m-2, and X-class F ≥ 10-4 W·m-2. In standard notation the letters act as multipliers, for example C3.2 equates to a flux of 3.2 x 10-6 W·m-2. The C, M, and X classification is based on the full-disk X-ray emission from the sun. During periods of high solar activity, such as solar maximum, the background flux may increase to C-class levels for days at a time, even without flare activity. The D region electron density is directly driven by the total X-ray flux regardless of the source, so these periods of high background flux are equally important to radio absorption. Due to geometric effects, D region ionization by solar X-rays is greatest at the sub-solar point, where the sun is directly overhead. The amount of ionization and absorption falls with distance away from the sub-solar point, reaching zero at the day/night terminator. The night-side of the Earth is unaffected.

Significant Eruption
Old sunspot 1936 now located just beyond the west limb produced a strong solar flare this morning. STEREO Ahead captured the bright flash of the flare, and the Solar Dynamics Observatory (SDO) observed the eruption that took place just beyond the west limb. A minor S1 level radiation storm remains in progress following an increase in Earth directed proton levels. Unfortunately for us sky watchers, the bright coronal mass ejection (CME) it generated is likely directed away from our planet. More information to follow if necessary.
ALERT: Proton Event 10MeV Integral Flux exceeded 10pfu
Begin Time: 2014 Jan 06 0915 UTC
NOAA Scale: S1 - Minor
Potential Impacts: Radio - Minor impacts on polar HF (high frequency) radio propagation resulting in fades at lower frequencies.
Updated 01/06/2014 @ 11:20 UTC
Solar Update
Good morning. Below is an updated look at the visible solar disk on Monday morning. Solar activity, at least on the Earth facing side of the sun, is currently at low levels with only minor C-Class flares detected. Most detectable X-Ray activity is being observed around massive sunspot 1944. Despite possessing a weak delta signature within the trailing section of the group, 1944 remains fairly stable due to a rather non compact overall magnetic structure of the entire region. Regardless of this, there will remain a chance for at least moderate M-Class solar flares. Sunspot 1937 located in the southwest quadrant is now about to rotate onto the west limb. All other visible regions, including sunspot 1946, remain stable. New sunspots 1947 and 1948 were numbered overnight

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