F-region seasonal and magnetic-storm behaviour

Duncan, R. A.

doi:10.1016/0021-9169(69)90081-6

Cited by 148 publications

(98 citation statements)

References 30 publications

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“…and O 2 • Our results show that the electron density in the F 2 region could decrease up to about a factor of three at high and mid latitudes and slightly increase at low latitudes, a result which verifies the hypothesis of Seaton (1956), Duncan (1969), Chandra and Herman (1969), and Obayashi and Ma1¥ura (1972), who postulated this kind of composition changes in interpreting the magnetic storm response of the ionosphere. Obayashi and Matuura (1972) also suggested that the composition effect could be induced by the thermospheric circulation.…”

Section: Magnetic Storm Synthesissupporting

confidence: 87%

Magnetic storm characteristics of the thermosphere

Mayr¹,

Volland²

1973

J. Geophys. Res.

143

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Energy and diffusive mass transport associated with the thermospheric circulation are considered in a self-consistent, though mathematically relatively simple form to describe in a three-dimensional two-constituent model magnetic storm characteristics in composition (N 2' 0, and He), temperature and massdensity. It is shown that during disturbed conditions the latitudinal variations of composition and gas temperature Tg reflect the local nature of the magnetic storm heat input assumed to be primarily confined to the auroral zones. Thereby T g and N2 increase, He decreases and°remains constant through the auroral zones at exospheric heights (due to the superposition of temperature and diffusioneffects) in agreement with OGO-6 mass spectrometer measurements.In contrast, the magnetic storm response in the total mass density is characterized by a strong world-wide component and a relatively insignificant increase toward the poles with the density peak occurring between two (poles) and eight (equator) hours after the maximum energy input, in substantial agreement with satellite drag data. While in situ composition and satellite drag mass-density measurements can thus be reconciled it must, however, be emphasized that the temperature derivation from the satellite drag data cannot be justified during disturbed conditions.

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Section: Magnetic Storm Synthesissupporting

confidence: 87%

Magnetic storm characteristics of the thermosphere

Mayr¹,

Volland²

1973

J. Geophys. Res.

143

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“…King attributed the composition change to the progressive dissociation of O 2 molecules as the air travels from the summer to the winter hemisphere, thus increasing the atomic/molecular ratio (it being thought at the time that O 2 plays a major part in the loss of ionization). The role of the circulation in producing both the seasonal and storm e ects in the F2-layer was further discussed by Duncan (1969). Our modelling supports the following picture, essentially that envisaged by Duncan (1969).…”

Section: Wind Patterns and Their E Ectssupporting

confidence: 79%

“…The role of the circulation in producing both the seasonal and storm e ects in the F2-layer was further discussed by Duncan (1969). Our modelling supports the following picture, essentially that envisaged by Duncan (1969). Upwelling in the summer hemisphere and in the tropics causes upward transport of gases rich in molecular nitrogen.…”

Section: Wind Patterns and Their E Ectssupporting

confidence: 77%

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion

et al. 2000

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Abstract. The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external in¯uences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric ®elds play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions a ect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual e ect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the e ect of the composition changes is modi®ed by the large solar zenith angle at midwinter. The zenith angle e ect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle e ect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/ molecular ratio. This leads to a semiannual variation of NmF2. A di erent situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations.

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“…less ionization in winter than in summer, because of the different solar zenith angle), but to also create enhanced values of N m F 2 in winter relative to summer [Rishbeth and Setty, 1962]. King [1964] and Duncan [1969] indicated that seasonal neutral composition differences could result from the summer to winter circulation. These wind-driven composition changes result primarily from the vertical winds, rather than the horizontal ones, although horizontal winds are important in the early morning hours [Burns et al, 1989].…”

Section: Introductionmentioning

confidence: 99%

On the solar cycle variation of the winter anomaly

et al. 2014

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Constellation Observing System for Meteorology, Ionosphere and Climate, Ionosonde, and Global Ultraviolet Imager data have been used to investigate the solar cycle changes in the winter anomaly (the winter anomaly is defined as the enhancement of the F 2 peak electron density in the winter hemisphere over that in the summer hemisphere) in the last solar cycle. There is no winter anomaly in solar minimum, and an enhancement of about 50% in winter over summer ones on the same day of the year at solar maximum. This solar cycle variation in the winter anomaly is primarily due to greater winter to summer differences of [O]/[N 2 ] in solar maximum than in solar minimum, with a secondary contribution from the effects of temperature on the recombination coefficient between O + and the molecular neutral gas. The greater winter increases in electron density in the Northern Hemisphere than in the Southern Hemisphere appear to be related to the greater annual variation of [O]/[N 2 ] in the north than in the south.

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F-region seasonal and magnetic-storm behaviour

Cited by 148 publications

References 30 publications

Magnetic storm characteristics of the thermosphere

Magnetic storm characteristics of the thermosphere

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion

On the solar cycle variation of the winter anomaly

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