scholarly journals Semiannual and annual variations in the height of the ionospheric F2-peak

2000 ◽  
Vol 18 (3) ◽  
pp. 285-299 ◽  
Author(s):  
H. Rishbeth ◽  
K. J. F. Sedgemore-Schulthess ◽  
T. Ulich
Keyword(s):  
Solar Activity ◽  
Computational Models ◽  
Annual Variation ◽  
Late Summer ◽  
Early Summer ◽  
Atmospheric Composition ◽  
Annual Variations ◽  
Composition And Structure ◽  
Semiannual Variation ◽  
Quiet Day

Abstract. Ionosonde data from sixteen stations are used to study the semiannual and annual variations in the height of the ionospheric F2-peak, hmF2. The semiannual variation, which peaks shortly after equinox, has an amplitude of about 8 km at an average level of solar activity (10.7 cm flux = 140 units), both at noon and midnight. The annual variation has an amplitude of about 11 km at northern midlatitudes, peaking in early summer; and is larger at southern stations, where it peaks in late summer. Both annual and semiannual amplitudes increase with increasing solar activity by day, but not at night. The semiannual variation in hmF2 is unrelated to the semiannual variation of the peak electron density NmF2, and is not reproduced by the CTIP and TIME-GCM computational models of the quiet-day thermosphere and ionosphere. The semiannual variation in hmF2 is approximately "isobaric", in that its amplitude corresponds quite well to the semiannual variation in the height of fixed pressure-levels in the thermosphere, as represented by the MSIS empirical model. The annual variation is not "isobaric". The annual mean of hmF2 increases with solar 10.7 cm flux, both by night and by day, on average by about 0.45 km/flux unit, rather smaller than the corresponding increase of height of constant pressure-levels in the MSIS model. The discrepancy may be due to solar-cycle variations of thermospheric winds. Although geomagnetic activity, which affects thermospheric density and temperature and therefore hmF2 also, is greatest at the equinoxes, this seems to account for less than half the semiannual variation of hmF2. The rest may be due to a semiannual variation of tidal and wave energy transmitted to the thermosphere from lower levels in the atmosphere.Key words: Atmospheric composition and structure (thermosphere - composition and chemistry) - Ionosphere (mid-latitude ionosphere)

scholarly journals Seasonal variations of thermospheric mass density at dawn/dusk from GOCE observations

2018 ◽  
Vol 36 (2) ◽  
pp. 489-496 ◽  
Author(s):  
Libin Weng ◽  
Jiuhou Lei ◽  
Eelco Doornbos ◽  
Hanxian Fang ◽  
Xiankang Dou
Keyword(s):  
Solar Activity ◽  
Ocean Circulation ◽  
Seasonal Variations ◽  
Annual Variation ◽  
Mass Density ◽  
High Amplitude ◽  
Atmospheric Composition ◽  
Polar Regions ◽  
Composition And Structure ◽  
Semiannual Variation

Abstract. Thermospheric mass densities from the GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite for Sun-synchronous orbits between 83.5∘ S and 83.5∘ N, normalized to 270 km during 2009–2013, have been used to develop an empirical mass density model at dawn/dusk local solar time (LST) sectors based on the empirical orthogonal function (EOF) method. The main results of this study are that (1) the dawn densities peak in the polar regions, but the dusk densities maximize in the equatorial regions; (2) the relative seasonal variations to the annual mean have similar patterns across all latitudes regardless of solar activity conditions; (3) the seasonal density variations show obvious hemispheric asymmetry, with large amplitudes in the Southern Hemisphere; (4) both amplitude and phase of the seasonal variations have strong latitudinal and solar activity dependences, with high amplitude for the annual variation at higher latitudes and semiannual variation at lower latitudes; (5) the annual asymmetry and effect of the Sun–Earth distance vary with latitude and solar activity. Keywords. Atmospheric composition and structure (pressure, density, and temperature)

scholarly journals Post midnight spread-F occurrence over Waltair (17.7° N, 83.3° E) during low and ascending phases of solar activity

2003 ◽  
Vol 21 (3) ◽  
pp. 745-750 ◽  
Author(s):  
K. Niranjan ◽  
P. S. Brahmanandam ◽  
P. Ramakrishna Rao ◽  
G. Uma ◽  
D. S. V. V. D. Prasad ◽  
...  
Keyword(s):  
Solar Activity ◽  
Atmospheric Composition ◽  
Activity Period ◽  
Sunspot Activity ◽  
Low Latitude ◽  
F Region ◽  
Composition And Structure ◽  
Spread F ◽  
Solar Activity Period ◽  
Night Airglow

Abstract. A study carried out on the occurrence of post midnight spread-F events at a low-latitude station, Waltair (17.7° N, 83.3° E), India revealed that its occurrence is maximum in the summer solstice months of the low solar activity period and decreases with an increase in the sunspot activity. The F-region virtual height variations show that 80% of these spread-F cases are associated with an increase in the F-region altitude. It is suggested with the support of the night airglow 6300 A zenith intensity data obtained with co-located ground-based night airglow photometer and electron temperature data from the Indian SROSS C2 satellite that the seasonal variation of the occurrence and probable onset times of the post midnight spread-F depend on the characteristics of the highly variable semipermanent equatorial Midnight Temperature Maximum (MTM).Key words. Ionosphere (ionospheric irregularities; ionosphere atmosphere interactions) Atmospheric composition and structure (airglow and Aurora)

scholarly journals Seasonal features of geomagnetic activity: a study on the solar activity dependence

2021 ◽  
Vol 39 (5) ◽  
pp. 929-943
Author(s):  
Adriane Marques de Souza Franco ◽  
Rajkumar Hajra ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Geomagnetic Activity ◽  
Annual Variation ◽  
Geomagnetic Storms ◽  
Solar Wind Speed ◽  
Solar Cycles ◽  
Annual Variations ◽  
Long Duration ◽  
Activity Dependence

Abstract. Seasonal features of geomagnetic activity and their solar-wind–interplanetary drivers are studied using more than five solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1296 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75 863 substorms identified from the SuperMAG AL/SML index from January 1976 to December 2019 and a total of 145 high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events identified using the AE index from January 1975 to December 2017. The occurrence rates of the substorms and geomagnetic storms, including moderate (-50nT≥Dst>-100nT) and intense (-100nT≥Dst>-250nT) storms, exhibit a significant semi-annual variation (periodicity ∼6 months), while the super storms (Dst≤-250 nT) and HILDCAAs do not exhibit any clear seasonal feature. The geomagnetic activity indices Dst and ap exhibit a semi-annual variation, while AE exhibits an annual variation (periodicity ∼1 year). The annual and semi-annual variations are attributed to the annual variation of the solar wind speed Vsw and the semi-annual variation of the coupling function VBs (where V = Vsw, and Bs is the southward component of the interplanetary magnetic field), respectively. We present a detailed analysis of the annual and semi-annual variations and their dependencies on the solar activity cycles separated as the odd, even, weak and strong solar cycles.

scholarly journals Annual and semiannual variations in the ionospheric F2-layer. I. Modelling

2000 ◽  
Vol 18 (8) ◽  
pp. 927-944 ◽  
Author(s):  
L. Zou ◽  
H. Rishbeth ◽  
I. C. F. Müller-Wodarg ◽  
A. D. Aylward ◽  
G. H. Millward ◽  
...  
Keyword(s):  
Molecular Nitrogen ◽  
Companion Paper ◽  
Field Configuration ◽  
Atmospheric Composition ◽  
Vibrationally Excited ◽  
Composition And Structure ◽  
Hemisphere Difference ◽  
Semiannual Variation ◽  
Layer I ◽  
Magnetic Poles

Abstract. Annual, seasonal and semiannual variations of F2-layer electron density (NmF2) and height (hmF2) have been compared with the coupled thermosphere-ionosphere-plasmasphere computational model (CTIP), for geomagnetically quiet conditions. Compared with results from ionosonde data from midlatitudes, CTIP reproduces quite well many observed features of NmF2, such as the dominant winter maxima at high midlatitudes in longitude sectors near the magnetic poles, the equinox maxima in sectors remote from the magnetic poles and at lower latitudes generally, and the form of the month-to-month variations at latitudes between about 60°N and 50°S. CTIP also reproduces the seasonal behaviour of NmF2 at midnight and the summer-winter changes of hmF2. Some features of the F2-layer, not reproduced by the present version of CTIP, are attributed to processes not included in the modelling. Examples are the increased prevalence of the winter maxima of noon NmF2 at higher solar activity, which may be a consequence of the increase of F2-layer loss rate in summer by vibrationally excited molecular nitrogen, and the semiannual variation in hmF2, which may be due to tidal effects. An unexpected feature of the computed distributions of NmF2 is an east-west hemisphere difference, which seems to be linked to the geomagnetic field configuration. Physical discussion is reserved to the companion paper by Rishbeth et al.Key words: Atmospheric composition and structure (thermosphere-composition and chemistry) - Ionosphere (mid-latitude ionosphere; modelling and forecasting)

scholarly journals Seasonal variations of O<sub>2</sub> atmospheric and OH(6−2) airglowand temperature at mid-latitudes from SATI observations

2004 ◽  
Vol 22 (3) ◽  
pp. 819-828 ◽  
Author(s):  
M. J. López-González ◽  
E. Rodríguez ◽  
R. H. Wiens ◽  
G. G. Shepherd ◽  
S. Sargoytchev ◽  
...  
Keyword(s):  
Seasonal Variation ◽  
Key Words ◽  
Sierra Nevada ◽  
Seasonal Variations ◽  
Annual Variation ◽  
Emission Rate ◽  
Atmospheric Composition ◽  
Emission Rates ◽  
Composition And Structure ◽  
Instruments And Techniques

Abstract. More than 3 years of airglow observations with a Spectral Airglow Temperature Imager (SATI) installed at the Sierra Nevada Observatory (37.06°N, 3.38°W) at 2900m height have been analyzed. Values of the column emission rate and vertically averaged temperature of the O2 atmospheric (0–1) band and of the OH Meinel (6–2) band from 1998 to 2002 have been presented. From these observations a clear seasonal variation of both emission rates and rotational temperatures is inferred at this latitude. It is found that the annual variation of the temperatures is larger than the semi-annual variation, while for the emission rates the amplitudes are comparable. Key words. Atmospheric composition and structure (airglow and aurora; pressure density and temperature; instruments and techniques)

scholarly journals Solar activity effects in the ionospheric D region

1998 ◽  
Vol 16 (12) ◽  
pp. 1527-1533 ◽  
Author(s):  
A. D. Danilov
Keyword(s):  
Solar Activity ◽  
Middle Atmosphere ◽  
Activity Cycle ◽  
Solar Activity Cycle ◽  
Atmospheric Composition ◽  
Ion Chemistry ◽  
Theoretical Concepts ◽  
Rotation Method ◽  
Composition And Structure ◽  
D Region

Abstract. Variations in the D-region electron concentration within the solar activity cycle are considered. It is demonstrated that conclusions of various authors, who have analyzed various sets of experimental data on [e], differ significantly. The most reliable seem to be the conclusions based on analysis of the [e] measurements carried out by the Faraday rotation method and on the theoretical concepts on the D-region photochemistry. Possible QBO effects in the relation of [e] to solar activity are considered and an assumption is made that such effects may be the reason for the aforementioned disagreement in conclusions on the [e] relation to solar indices.Key words. Atmospheric composition and structure · Ion chemistry of the atmosphere · Middle atmosphere

scholarly journals Seasonal features of geomagnetic activity: evidence for solar activity dependence?

2021 ◽  
Author(s):  
Adriane Marques de Souza Franco ◽  
Rajkumar Hajra ◽  
Ezequiel Echer ◽  
Mauricio José Alves Bolzan
Keyword(s):  
Solar Wind ◽  
Solar Activity ◽  
Geomagnetic Activity ◽  
Annual Variation ◽  
Geomagnetic Storms ◽  
Solar Wind Speed ◽  
Solar Cycles ◽  
Annual Variations ◽  
Long Duration ◽  
Activity Dependence

Abstract. Seasonal features of geomagnetic activity and their solar wind-interplanetary drivers are studied using more than 5 solar cycles of geomagnetic activity and solar wind observations. This study involves a total of 1239 geomagnetic storms of varying intensity identified using the Dst index from January 1963 to December 2019, a total of 75863 substorms identified from the SML index from January 1976 to December 2019, a total of 145 high-intensity long-duration continuous auroral electrojet (AE) activity (HILDCAA) events identified using the AE index from January 1975 to December 2017. The occurrence rates of the substorms, geomagnetic storms, including moderate (−50 nT ≥ Dst > −100 nT) and intense (−100 nT ≥ Dst > −250 nT), exhibit a significant semi-annual variation (periodicity ~ 6 months), while the super storms (Dst ≤ −250 nT) and HILDCAAs do not exhibit any clear seasonal feature. The geomagnetic activity indices Dst and ap exhibit a semi-annual variation while AE exhibits an annual variation (periodicity ~ 1 year). The annual and semi-annual variations are found to be driven by the annual variation of the solar wind speed Vsw and the semi-annual variation of the coupling function V Bs (where V = Vsw, and Bs is the southward component of the interplanetary magnetic field), respectively. We present a detailed analysis of the annual and semi-annual variations and their dependencies on the solar activity cycles separated as the odd, even, weak and strong solar cycles.

scholarly journals Electron density in the F1 layer over Norilsk in 2007–2014

2019 ◽  
Vol 5 (2) ◽  
pp. 124-128
Author(s):  
Галина Кушнаренко ◽  
Galina Kushnarenko ◽  
Ольга Яковлева ◽  
Olga Yakovleva ◽  
Галина Кузнецова ◽  
...  
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Solar Minimum ◽  
Annual Variation ◽  
Data Approximation ◽  
Annual Variations ◽  
Ionospheric Station ◽  
Different Seasons ◽  
Semi Empirical ◽  
Maximum Solar Activity

We report the results of the analysis of annual variations in daily electron density (N) for various solar activity conditions — minimum, rise, and maximum (2007–2014) — obtained from digisonde measurements at the ionospheric station Norilsk (69.4° N, 88.1° E). New coefficients of the known semi-empirical model (SEM) describing the connection between N and thermosphere characteristics are calculated to identify regularities of these variations exactly at Norilsk station. The height changes of annual variations in the noon electron density N are obtained in the F1 region (120–200 km). The experimental data approximation describes N quite satisfactorily at these heights in the daytime of different seasons under different solar activity conditions. It is shown that in the years of solar minimum at all heights of the F1 layer the tendency remains for maximum N in summer and for minimum N in winter. In later years and in the year of maximum solar activity, a characteristic feature of the behavior of N is the change in the phase of the annual variation by 180° in the range of heights from 170 to180 km: maximum N is observed in winter; and minimum, in summer.

scholarly journals Electron density in the F1 layer over Norilsk in 2007–2014

2019 ◽  
Vol 5 (2) ◽  
pp. 109-112
Author(s):  
Галина Кушнаренко ◽  
Galina Kushnarenko ◽  
Ольга Яковлева ◽  
Olga Yakovleva ◽  
Галина Кузнецова ◽  
...  
Keyword(s):  
Solar Activity ◽  
Electron Density ◽  
Solar Minimum ◽  
Annual Variation ◽  
Data Approximation ◽  
Annual Variations ◽  
Ionospheric Station ◽  
Different Seasons ◽  
Semi Empirical ◽  
Maximum Solar Activity

We report the results of the analysis of annual variations in daily electron density (N) for various solar activity conditions — minimum, rise, and maximum (2007–2014) — obtained from digisonde measurements at the ionospheric station Norilsk (69.4° N, 88.1° E). New coefficients of the known semi-empirical model (SEM) describing the connection between N and thermosphere characteristics are calculated to identify regularities of these variations exactly at Norilsk station. The height changes of annual variations in the noon electron density N are obtained in the F1 region (120–200 km). The experimental data approximation describes N quite satisfactorily at these heights in the daytime of different seasons under different solar activity conditions. It is shown that in the years of solar minimum at all heights of the F1 layer the tendency remains for maximum N in summer and for minimum N in winter. In later years and in the year of maximum solar activity, a characteristic feature of the behavior of N is the change in the phase of the annual variation by 180° in the range of heights from 170 to180 km: maximum N is observed in winter; and minimum, in summer.

scholarly journals Characterization of GPS total electron content (GPS-TEC) in Antarctica from 2004 to 2011

2013 ◽  
Vol 56 (2) ◽  
Author(s):  
Emília Correia ◽  
Amanda Junqueira Paz ◽  
Mauricio A. Gende
Keyword(s):  
Solar Activity ◽  
Total Electron Content ◽  
Electron Content ◽  
Vertical Total Electron Content ◽  
Total Electron ◽  
Annual Variations ◽  
Solar Radiation Intensity ◽  
Winter Anomaly ◽  
Semiannual Variation ◽  
The Mean

<p>The vertical total electron content (VTEC) obtained from 2004 to 2011 at Comandante Ferraz Brazilian Antarctic Station (62.1°S, 58.4°W) is analyzed to study the mean diurnal, seasonal and annual variations. The maximum daytime VTEC had an annual variation that decreased from 2004 to 2008, and then starting to increase in 2009, which followed the variation of the solar activity. The daily VTEC shows good linear correlation with solar radiation intensity, which is also dependent on the solar zenithal angle. The mean diurnal VTEC shows a semiannual variation, with larger peaks in equinoxes for all years; no winter anomaly was observed, and in summer, there was no clear diurnal variation. The semiannual variation of the VTEC is also modulated by solar activity, with larger VTEC peaks when the solar activity was higher.</p>

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