The morphology of spread-<i>F</i>occurrence over half a sunspot cycle

Singleton, D. G.

doi:10.1029/ja073i001p00295

Cited by 42 publications

(39 citation statements)

References 21 publications

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“…Ionograms with spread F traces have been extensively used for indirect studies of ionospheric irregularities. Singleton [1968] and Shirnazaki [1959,1962] have discussed the morphology of spread F, and Herman [1966] has reviewed the subject of spread F and F region irregularities. The similarity •Now at the University of Oxford, Engineering Science Department, Oxford, England.…”

Section: Introductionmentioning

confidence: 99%

Plasma density irregularities in the high-latitude top side ionosphere

Phelps¹,

Sagalyn²

1976

J. Geophys. Res.

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Thermal plasma density measurements obtained by using the spherical electrostatic analyzer probe carried by the polar orbiting satellite Isis 1 have been spectrally analyzed to provide quantitative results on the amplitude and scale size distribution of the plasma irregularities in the high‐latitude top side ionosphere. The range of scale sizes examined, 200 m to over 100 km under normal conditions, is more than an order of magnitude greater than that available from ground‐based measurements. Data in the altitude range 574–3523 km and from the period February 1969 to April 1972 have been analyzed. Irregularities in the high‐latitude region from 40° invariant latitude up to the invariant L pole have been studied. In over 90% of the cases examined, the power spectra are found to fit a power law of the form P = P0f−β, where the index β varies within the range 1.5–2.5. The power spectral density was integrated over the scale size range 1–10 km in order to analyze quantitatively latitudinal variations of the irregularity amplitude. While the boundaries of the high‐latitude irregularity zone on particular orbits examined by using this technique are in agreement with earlier morphological studies, it is also evident that the amplitude of the irregularities within the high‐latitude irregularity region itself shows irregular enhancements above a generally raised amplitude level.

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Section: Introductionmentioning

confidence: 99%

Plasma density irregularities in the high-latitude top side ionosphere

Phelps¹,

Sagalyn²

1976

J. Geophys. Res.

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“…Small-scale thermal charged particle irregularities in the ionosphere have been examined by several techniques. Knowledge of the spatial and temporal characteristics of these irregularities has been obtained primarily from ground-based measurements of spread F [Shimazaki, 1959[Shimazaki, , 1962Singleton, 1960Singleton, , 1968 and radio scintillations [Aarons et al, 1969;Aarons an Allen, 1971]. Ground-based measurements give an excellent description of the temporal behavior of irregularities at a given location.…”

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confidence: 99%

High-latitude irregularities in the top side ionosphere based on Isis 1 Thermal Ion Probe data

Sagalyn¹,

Smiddy²,

Ahmed³

1974

J. Geophys. Res

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Thermal ion density irregularities at high latitudes have been investigated by using results from the spherical electrostatic analyzer flown on the polar‐orbiting satellite Isis 1. The size of the irregularities is found to be highly variable, dimensions typically ranging from 1 to 140 km. Results from 3500 orbits in the top side ionosphere during the first year of operation have been examined. The daily and seasonal behavior of the equatorial boundary of the high‐latitude irregularity zone and its dependence on magnetic activity have been established for the northern and southern hemispheres. The daily variation in the location of the boundary of the irregularity zone is found to be 14°±2° for any level of magnetic activity; the boundary is at the highest latitude near local noon. The irregularities consistently extend across the pole; there is no upper boundary. Systematic differences are found in the mean location of the equatorial boundary in the northern and southern hemispheres. In the south the boundary is on the average 4.8°±0.6° closer to the pole than in the north. Good agreement is found between the direct measurements of the irregularity boundary and scintillations, severe top side spread F and ≤300‐eV electron precipitation boundaries, and trough and plasmapause positions on the night side. Significant differences found to exist between the irregularity boundary and plasmapause positions on the day side are considered to be due to their different origins.

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“…The distribution of ionosondes around the world is very uneven. Thus maps of the global occurrence of spread F [e.g., Shirnazaki, 1959;Tao, 1965;Singleton, 1968] must be interpreted with care. Often contours of occurrence show peaks and troughs based on little or no data.…”

Section: Introductionmentioning

confidence: 99%

“…Other reviews also show a reduced occurrence of spread F during years of low solar flux for the auroral region [Shimazaki, 1959;Singleton, 1968].…”

Section: Introductionmentioning

confidence: 99%

The sunspot cycle and “auroral” F layer irregularities

Aarons¹,

Kersley²,

Rodger³

1995

Radio Science

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The use of the word “aurora” for many different observations at high latitudes has limited the concepts involved; this is particularly true for F region irregularities. Observations setting the position of the auroral oval (Starkov and Fel'dshtein, 1970) were made using primarily the 555.7‐nm green line, which is emitted predominantly at E layer heights. These observations have shown that the change in position of the auroral oval for low values of Kp as a function of sunspot cycle is of the order of 1° to 2° between sunspot maximum and sunspot minimum. However, irregularities in the F region show much larger solar cycle variations in the locations of the equatorward boundary, typically 10°. A review of scintillation data indicates that at a given auroral latitude, the scintillation activity increases with sunspot number. In addition, for a constant scintillation intensity, the equatorward boundary moves to lower latitudes as sunspot maximum is approached. We review existing spread F studies and show that for quiet geomagnetic conditions, there is lower occurrence during years of low sunspot numbers than during years of high sunspot numbers. However, the spread F index, related to Δ ƒ/ƒ0F2, is higher during years of low sunspot number than during years of high sunspot number. We demonstrate that this apparent dichotomy can be reconciled by using a new method of normalizing the spread F index by the maximum electron concentration of the F layer. We briefly discuss the possible explanations for the observed solar cycle variations of irregularity occurrence in terms of the absolute values and gradients of electron concentration and the E region conductivity.

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The morphology of spread-Foccurrence over half a sunspot cycle

Cited by 42 publications

References 21 publications

Plasma density irregularities in the high-latitude top side ionosphere

Plasma density irregularities in the high-latitude top side ionosphere

High-latitude irregularities in the top side ionosphere based on Isis 1 Thermal Ion Probe data

The sunspot cycle and “auroral” F layer irregularities

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