The Hα radiation from solar flares in relation to sudden enhancements of atmospherics on frequencies near 27 Kc/s

Ellison, M. A.

doi:10.1016/0021-9169(53)90057-9

Cited by 25 publications

(14 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…1). About one-third of the same signals that have frequency changes during solar flares and subflares also exhibit changes in the azimuthal angle The majority of workers who have studied the effects of solar flares upon the ionosphere suggest that the radiation affects mainly the lower part (the D region) [Dellinter, 1937;Bracewell and Straker, 1949;Ellison, 1953;Mitra and Jones, 1954]. Others have maintained that the E region is sometimes affected also [Findlay, 1951;Bibl, 1951;Burkard, 1938], and that the region above the E level is very seldom or never affected.…”

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

“…The points are scattered below i cps because it is very difficult to pick up the exact magnitude of the changes from the Sanborn records when the frequency change is below i cps (the com- The ionizing energy that affects the instantaneous frequency of the HF waves must be different from that producing ionization in the lower D region, that is, ultraviolet radiation rather than X rays. The maxima of the D-region effects such as sudden enhancement of atmospherics (SEA) [Ellison, 1953], sudden phase anomalies (SPA) [Bracewell and Straker, 1949], and short-wave fadeouts (SWF) [Dellinger, 1937] For the purpose of locating the approximate height of ionization production we will assume that a narrow region (region II in Fig. 6) absorbs the ionizing energy during solar flares.…”

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

“…First we will assume that the ionization that affects the instantaneous frequency is the same as the ionization producing the SPA and SEA effects. Under these conditions the ionization is produced in a thin layer of about 2 km in the 70-km region [Ellison, 1953;Mitra and Jones, 1954]. The resulting frequency and absorption changes will be assumed that are due to the change in N in region II through which N does not vary appreciably with height.…”

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

See 2 more Smart Citations

On the altitude at which some solar-flare-induced lonization is released

Kanellakos¹,

Chan²,

Villard³

1962

J. Geophys. Res.

View full text Add to dashboard Cite

During the occurrence of certain solar flares and subflares (about 20 to 25 per cent of those optically observed), the instantaneous frequency of a highly stable, CW, HF signal transmitted obliquely through the ionosphere, over distances of the order of 5000 km, is momentarily changed by a few cycles. The change consists of an increase in the frequency, followed by a decrease and, subsequently, a gradual return toward the original received frequency. The rapidly changing portion of the frequency variation lasts only a few minutes (usually less than 5). In addition, the frequency change varies inversely with the operating frequency and proportionally with the path length. Paths separated by many hundreds of kilometers are simultaneously affected. It is of interest that these pronounced frequency shifts invariably occur prior to the loss of signal characteristic of a short-wave fadeout, and hence could conceivably be used to warn of impending signal loss in modern HF communication systems affording continuous feedback of propagation conditions over the path. In certain cases, however, the flare-induced frequency shift is not followed by a fadeout. The azimuthal angle of arrival of the same signals that have frequency changes during solar flares and subflares also deviates in about one-third of the cases. The fact that a I-IF wave exhibits bearing deviations signifies that a horizontal gradient of ionization, capable of bending the wave, exists. Electron-density gradients are probably produced as a result of solar-flare-induced ionization, especially at times when the sun's energy falls at a grazing angle on the path. The angle usually deviated to the south (toward the subsolar point) of the great-circle path for the Puerto Rico-Palo Alto (PR-SU) path during the season at which these measurements were made. These observations of instantaneous frequency and angle-of-arrival changes during solar flares suggest that new ionization is introduced initially somewhere just above the E region, very probably in the height region 120 to 200 km, although even greater heights are possible. This initial ionization may or may not be followed by the generation of ionization in the absorbing D region. The time variation of height at which solar-flare-induced ionization is released suggests that the ionization-producing radiant energy is initially soft, and then 'hardens' as the flare progresses. released, Fall URSI-IRE Meeting, Austin, Texas, October 1961, TR 45, Radioscience Lab., Stanford Univ., December 4, 1961. Kanellakos, D. P., and O. G. Villard, Jr., Some relationships between frequency and azimuth angle of arrival of I-IF waves propagated over long distances, URSI-IRE meeting

show abstract

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

Section: Experimental Observations O1 Solar-flare Effectsmentioning

confidence: 99%

See 1 more Smart Citation

On the altitude at which some solar-flare-induced lonization is released

Kanellakos¹,

Chan²,

Villard³

1962

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…Ever since Appleton first developed the theory of ionospheric sluggishness most of the observational VLF studies have considered the peak of solar SRX irradiance as the reference time for estimating sluggishness (Ellison, 1953; Křivský, 1962; Palit et al., 2015), under the assumption that solar SRX irradiance is the best proxy for photoionization. However, photoionization at different altitudes is regulated by solar irradiance wavebands, which peak at different times during a solar flare (Huang et al., 2014).…”

Section: Resultsmentioning

confidence: 99%

“…where θ, ϕ, h, max n e T , and max electron density. Appleton and his contemporaries tried to measure and characterize sluggishness in terms of the time delay between peak solar irradiance (  max I ) and peak radio wave absorption (β) in the ionosphere (Appleton, 1953;Ellison, 1953), as described in Equation 2:…”

Section: Introductionmentioning

confidence: 99%

Ionospheric Sluggishness: A Characteristic Time‐Lag of the Ionospheric Response to Solar Flares

et al. 2021

View full text Add to dashboard Cite

The term "sluggishness" was coined by E. V. Appleton in the 1950s to describe the time delay between peak irradiance at solar noon and the resulting peak in ionospheric electron density. Sluggishness can be understood as an inertial property of the ionosphere that manifests as a lag of the ionospheric response to a solar driver. As shown by Appleton, estimates of sluggishness can be used to study the chemistry of the lower ionosphere, of the D-region in particular. In this study, for the first time, we have examined ionospheric sluggishness in terms of the time delay between the peak irradiance during a solar flare and the resulting peak in ionospheric electron density using HF instruments. Estimates of the delay are obtained using HF observations from riometers and SuperDARN radars that are primarily sensitive to absorption in the D-region. Two new methods for measuring delay are introduced. Sluggishness is shown to be anti-correlated with peak solar X-ray flux and positively correlated with zenith angle and latitude. The choices of instrument, method, and reference solar waveband affect the sluggishness estimation. A simulation study was performed to estimate the effective recombination coefficient in the D-region. The coefficient was found to vary by orders of magnitude with peak flare intensity. We argue that the variation in effective recombination coefficient with peak flare intensity is highly sensitive to changes in the negative and positive ion chemistry of the D-region, which is sensitive to the incoming solar X-ray and EUV radiation. Plain Language Summary A systematic time delay between peak incoming solar radiation during a solar flare and peak electron density in the ionosphere is known as ionospheric sluggishness. Ionospheric sluggishness is known to be maximized around D-region heights (∼60-90 km altitude). This article is our first attempt to estimate ionospheric sluggishness using high frequency (3-30 MHz) instruments. In addition, we statistically characterize the observed sluggishness and provide an insight into D-region photochemical processes. In this article, we also demonstrate how to extract the D-region's recombination coefficient using a theoretical model and measured sluggishness. CHAKRABORTY ET AL.

show abstract

The chromospheric flare effect in atmospherics (IGY 1957)

Krivsky

Råžičková

1959

Stud Geophys Geod

View full text Add to dashboard Cite

The Hα radiation from solar flares in relation to sudden enhancements of atmospherics on frequencies near 27 Kc/s

Cited by 25 publications

References 9 publications

On the altitude at which some solar-flare-induced lonization is released

On the altitude at which some solar-flare-induced lonization is released

Ionospheric Sluggishness: A Characteristic Time‐Lag of the Ionospheric Response to Solar Flares

The chromospheric flare effect in atmospherics (IGY 1957)

Contact Info

Product

Resources

About