Compatibility of seasonal variations in mid-latitude thermospheric models at solar maximum and low geomagnetic activity

1978 ◽  
Vol 83 (A3) ◽  
pp. 1141 ◽  
Author(s):  
D. Alcaydé ◽  
P. Bauer ◽  
A. Hedin ◽  
J. E. Salah
Keyword(s):  
Geomagnetic Activity ◽  
Seasonal Variations ◽  
Solar Maximum

Seasonal variations in statistical distributions of geomagnetic activity indices

2015 ◽  
Vol 55 (4) ◽  
pp. 493-498 ◽  
Author(s):  
A. A. Nusinov ◽  
N. M. Rudneva ◽  
E. A. Ginzburg ◽  
L. A. Dremukhina
Keyword(s):  
Geomagnetic Activity ◽  
Seasonal Variations ◽  
Statistical Distributions ◽  
Activity Indices

scholarly journals Solar cycle variation in radar meteor rates

2019 ◽  
Vol 485 (3) ◽  
pp. 4446-4453 ◽  
Author(s):  
M D Campbell-Brown
Keyword(s):  
Solar Activity ◽  
Geomagnetic Activity ◽  
Negative Correlation ◽  
Solar Maximum ◽  
Radar Data ◽  
Scale Height ◽  
Seasonal Effects ◽  
Strong Negative Correlation ◽  
Solar Cycle Variation ◽  
Transmitter Power

ABSTRACT 16 yr of meteor radar data from the Canadian Meteor Orbit Radar (CMOR) were used to investigate the link between observed meteor rates and both solar and geomagnetic activity. Meteor rates were corrected for transmitter power and receiver noise, and seasonal effects were removed. A strong negative correlation is seen between solar activity, as measured with the 10.7 cm flux, and observed meteor rates. This lends support to the idea that heating in the atmosphere at times of elevated solar activity changes the scale height and therefore the length and maximum brightness of meteors; a larger scale height near solar maximum leads to longer, fainter meteors and therefore lower rates. A weaker negative correlation was observed with geomagnetic activity as measured with the K index; this correlation was still present when solar activity effects were removed. Meteor activity at solar maximum is as much as 30 per cent lower than at solar minimum, strictly due to observing biases; geomagnetic activity usually affects meteor rates by less than 10 per cent.

scholarly journals Solar cycle and seasonal variations of the GPS phase scintillation at high latitudes

2018 ◽  
Vol 8 ◽  
pp. A48 ◽  
Author(s):  
Yaqi Jin ◽  
Wojciech J. Miloch ◽  
Jøran I. Moen ◽  
Lasse B.N. Clausen
Keyword(s):  
Solar Cycle ◽  
Seasonal Variations ◽  
Solar Maximum ◽  
Occurrence Rate ◽  
Local Minima ◽  
Magnetic Latitude ◽  
Latitude Range ◽  
Gps Scintillation ◽  
Gps Scintillations ◽  
The Impact

We present the long-term statistics of the GPS phase scintillation in the polar region (70°–82° magnetic latitude) by using the GPS scintillation data from Ny-Ålesund for the period 2010–2017. Ny-Ålesund is ideally located to observe GPS scintillations modulated by the ionosphere cusp dynamics. The results show clear solar cycle and seasonal variations, with the GPS scintillation occurrence rate being much higher during solar maximum than during solar minimum. The seasonal variations show that scintillation occurrence rate is low during summer and high during winter. The highest scintillation occurrence rate is around magnetic noon except for December 2014 (solar maximum) when the nightside scintillation occurrence rate exceeds the dayside one. In summer, the dayside scintillation region is weak and there is a lack of scintillations in the nightside polar cap. The most intriguing features of the seasonal variations are local minima in the scintillation occurrence rate around winter solstices. They correspond to local minima in the F2 peak electron density. The dayside scintillation region migrates equatorward from summer to winter and retreats poleward from winter to summer repetitively in a magnetic latitude range of 74°–80°. This latitudinal movement is likely due to the motion of the cusp location due to the tilt of the Earth’s magnetic field and the impact of the sunlight.

scholarly journals The importance of solar illumination for discrete and diffuse aurora

2005 ◽  
Vol 23 (11) ◽  
pp. 3481-3486 ◽  
Author(s):  
M. Hamrin ◽  
P. Norqvist ◽  
K. Rönnmark ◽  
D. Fellgård
Keyword(s):  
Northern Hemisphere ◽  
Geomagnetic Activity ◽  
Seasonal Variations ◽  
Pitch Angle ◽  
Seasonal Effects ◽  
Comprehensive Overview ◽  
Diffuse Aurora

Abstract. We present a comprehensive overview of the occurrence of discrete and diffuse aurora in the nightside Northern Hemisphere at invariant latitudes 55°-75°. Twenty-one months of Freja observations (1 January 1993 to 30 September 1994) from the Northern Hemisphere, obtained at altitude, are included in this investigation. We investigate the importance of seasonal effects, solar illumination and geomagnetic activity for the auroral precipitation. The seasonal variations in the occurrence of discrete aurora are separated from the dependence on solar illumination of the ionosphere. When the effects of sunlight are eliminated, aurora is found to be more common during the summer. The occurrence of diffuse, as well as discrete aurora, is suppressed by solar illumination of the ionosphere. This dependence of diffuse auroral precipitation on ionospheric conditions is not predicted by theories that attribute diffuse aurora to equatorial pitch-angle diffusion of hot magnetospheric electrons.

scholarly journals ESTIMATED RELATIONS BETWEEN THE MAIN THERMOSPHERIC NEUTRAL COMPONENTS AT IONOSPHERIC F1-LAYER HEIGHTSABOVE IRKUTSK IN 2014–2017

2020 ◽  
Vol 6 (3) ◽  
pp. 90-93
Author(s):  
Galina Kushnarenko ◽  
Olga Yakovleva ◽  
Galina Kuznetsova
Keyword(s):  
Solar Activity ◽  
Molecular Oxygen ◽  
Electron Density ◽  
Oxygen Content ◽  
Geomagnetic Activity ◽  
Seasonal Variations ◽  
Molecular Component ◽  
Geomagnetic Disturbances ◽  
Density Measurements ◽  
Atomic Component

We have estimated seasonal variations in the main thermospheric gas components [O]/[N₂] and [O₂]/[O] for the period 2014–2017. We have used the well-known authoring technique and electron density measurements made with the Irkutsk digisonde (52° N, 104° E) at ionospheric F1-layer heights under different geomagnetic activity conditions. We have found that at these heights during geomagnetic disturbances in all seasons the molecular component of the neutral composition of the thermosphere increases and the atomic component decreases. In comparison with 2014, [O₂]/[O] values increased by 2017 under quiet and disturbed geomagnetic conditions: up to 30 % and 20 % in summer and spring respectively; up to 10 % in winter and autumn. The [O]/[N₂] ratio decreased by an average of 15 % by 2017. The assumption has been confirmed that in summer under quiet geomagnetic conditions the relative molecular oxygen content [O₂]/[O] increases with decreasing solar activity.

scholarly journals foF2 Seasonal Asymmetry Diurnal Variation Study during Very Quiet Geomagnetic Activity at Dakar Station

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Sibri Alphonse Sandwidi ◽  
Doua Allain Gnabahou ◽  
Frédéric Ouattara
Keyword(s):  
Solar Cycle ◽  
Solar Radiation ◽  
Diurnal Variation ◽  
Geomagnetic Activity ◽  
Vertical Velocity ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Solar Cycles ◽  
Maximum Phase ◽  
Vertical Drift

This paper aims to study the foF2 seasonal asymmetry diurnal variation at Dakar station from 1976 to 1995. We show that equinoctial asymmetry is less pronounced and somewhere is absent throughout 21 and 22 solar cycles. The absence of equinoctial asymmetry may be due to Russell-McPherron mechanism and the vertical drift E × B . The solstice anomaly or annual anomaly is always observed throughout both 21 and 22 solar cycles as measured at Dakar ionosonde. The maximum negative value of σfoF2, fairly equal to -65%, is observed during the decreasing phase at solstice time; this value appeared usually at 0200 LT except during the maximum phase during which it is observed at 2300 LT. The maximum positive value, fairly equal to +94%, is observed at 0600 LT during solar minimum at solstice time. This annual asymmetry may be due to neutral composition asymmetric variation and solar radiation annual asymmetry with the solstice time. The semiannual asymmetry is also observed during all solar cycle phases. The maximum positive value (+73%) is observed at 2300 LT during solar maximum, and its maximum negative (-12%) is observed during the increasing phase. We established, as the case of annual asymmetry, that this asymmetry could not be explained by the asymmetry in vertical velocity E × B phenomenon but by the axial mechanism, the “thermospheric spoon” mechanism, and the seasonally varying eddy mixing phenomenon.

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