scholarly journals One-Day-Shock, Two-Days-Shock and Three-Days-Shocks foF2 Diurnal Variation with Solar Cycle Phases at Ouagadougou Station from 1966 to 1998. Comparison with IRI 2012 Predictions

2019 ◽  
Vol 12 (1) ◽  
pp. 38
Author(s):  
Abdoul-kader SEGDA ◽  
Doua Allain GNABAHOU ◽  
Frédéric OUATTARA
Keyword(s):  
Solar Cycle ◽  
Time Variation ◽  
Solar Minimum ◽  
The Other ◽  
Cycle Phase ◽  
Minimum Phase ◽  
Solar Cycles ◽  
Night Time ◽  
Maximum Phase ◽  
Phase Dependence

The present work concerns foF2 time variation at Ouagadougou station for three solar cycles (from cycle 20 to cycle 22). We not only investigate solar cycle phase dependence under shock activity that is divided into one-shock-activity, two-shock-activity and three-shock-activity but also compare the IRI 2012 model values with the data carried out at Ouagadougou station. This study reveals that there is no one-day-shock during solar minimum phase. For the other solar cycle phases IRI 2012 reproduces the ionosphere electrodynamics at daytime except during the increasing phase. During night time the model is not suitable. The best subroutine under one-day-shock activity is URSI for increasing and decreasing phases. During the maximum phase it is CCIR. For two-days-shock activity IRI 2012 reproduces the ionosphere electrodynamics during the minimum and the increasing phases. The best subroutine is CCIR during the minimum phase and URSI for the other solar cycle phases. For three-days-shock activity IRI 2012 is not suitable. The best model is URSI for all solar cycle phases.

scholarly journals Calcium K Line Profiles as a Function of Latitude and Solar Cycle Phase

1990 ◽  
Vol 142 ◽  
pp. 261-261
Author(s):  
Jagdev Singh
Keyword(s):  
Solar Cycle ◽  
Line Profile ◽  
Solar Minimum ◽  
Active Network ◽  
Cycle Phase ◽  
Line Profiles ◽  
Maximum Phase ◽  
Excess Emission ◽  
Limb Darkening ◽  
Network Component

The sun as a star has been studied by many observers by monitoring the calcium K line profile. Skumanich et al (1984) proposed a three component model of the solar cycle variability of calcium K emission using extant contrast and fractional area parameters for (1) cell (2) network and (3) plage components. The computed line profile agreed well with the observed one at the solar minimum by taking the contribution of only cell and network features and using extant limb-darkening laws. The occurrence of plages during the growth of the solar cycle was found to be insufficient to account for the increase in K emission and therefore, they introduced an additional network component, ‘Active network’ in excess of the quiet sun value to explain the observed excess emission during the maximum phase.

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.

scholarly journals Critical Frequency foF2 Variations at Korhogo Station from 1992 to 2001 Prediction with IRI-2012

2019 ◽  
Vol 2019 ◽  
pp. 1-11
Author(s):  
Karim Guibula ◽  
Jean Louis Zerbo ◽  
M’Bi Kaboré ◽  
Frédéric Ouattara
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Critical Frequency ◽  
Solar Maximum ◽  
Measured Data ◽  
Night Time ◽  
Maximum Phase ◽  
Critical Frequency Fof2

In this paper we report the foF2 data measured at Korhogo station (Lat. 9.3° N; Long. 354.6° E; dip. 0.6° S) compared to predictions with IRI-2012 subroutine URSI and CCIR for different solar cycle phases (minimum, ascending, maximum, descending) and different geomagnetic activity classes (quiet, fluctuating, recurrent, shock). According to our investigations, predictions with IRI are in agreement with the measured data during daytime and show significant differences between them at night-time and especially before sunrise. Except at solar minimum, the gap between predictions and measured data are more appreciable during recurrent and shock conditions compared to quiet and fluctuating conditions. Our results also show that only URSI model expresses the signature of EXB drift phenomenon at solar maximum phase during the recurrent days and at ascending phase for fluctuating activity.

scholarly journals Statistical study of the night-time F-layer dynamics at the magnetic equator in West Africa during the solar minimum period 1995–1997

2015 ◽  
Vol 33 (1) ◽  
pp. 143-157 ◽  
Author(s):  
K. S. Tanoh ◽  
B. J.-P. Adohi ◽  
I. S. Coulibaly ◽  
C. Amory-Mazaudier ◽  
A. T. Kobea ◽  
...  
Keyword(s):  
Solar Minimum ◽  
Transition Process ◽  
The Other ◽  
Winter Period ◽  
Night Time ◽  
Minimum Period ◽  
Bottom Part ◽  
Layer Height ◽  
Northern Summer ◽  
The One

Abstract. In this paper, we report on the night-time equatorial F-layer height behaviour at Korhogo (9.2° N, 5° W; 2.4° S dip lat), Ivory Coast, in the West African sector during the solar minimum period 1995–1997. The data were collected from quarter-hourly ionograms of an Ionospheric Prediction Service (IPS) 42-type vertical sounder. The main focus of this work was to study the seasonal changes in the F-layer height and to clarify the equinox transition process recently evidenced at Korhogo during 1995, the year of declining solar flux activity. The F-layer height was found to vary strongly with time, with up to three main phases. The night-to-night variability of these morphological phases was then analysed. The early post-sunset slow rise, commonly associated with rapid chemical recombination processes in the bottom part of the F layer, remained featureless and was observed regardless of the date. By contrast, the following event, either presented like the post-sunset height peak associated with the evening E × B drift, or was delayed to the midnight sector, thus involving another mechanism. The statistical analysis of the occurrence of these events throughout the solar minimum period 1995–1997 revealed two main F-layer height patterns, each characteristic of a specific season. The one with the post-sunset height peak was associated with the northern winter period, whereas the other, with the midnight height peak, characterized the northern summer period. The transition process from one pattern to the other took place during the equinox periods and was found to last only a few weeks. We discuss these results in the light of earlier works.

Solar Cycle Phase Dependence of Supergranular Fractal Dimension

2011 ◽  
Vol 32 (1-2) ◽  
pp. 265-268
Author(s):  
U. Paniveni ◽  
V. Krishan ◽  
J. Singh ◽  
R. Srikanth
Keyword(s):  
Fractal Dimension ◽  
Solar Cycle ◽  
Cycle Phase ◽  
Phase Dependence

Number of Sunspot Groups and Individual Sunspots Recorded by Tevel for the Period 1816–1836 in the Dalton Minimum

2021 ◽  
Vol 922 (1) ◽  
pp. 58
Author(s):  
V. M. S. Carrasco
Keyword(s):  
Solar Cycle ◽  
Sunspot Number ◽  
Sunspot Group ◽  
Maunder Minimum ◽  
The Other ◽  
Solar Cycles ◽  
Group Number ◽  
The One ◽  
Dalton Minimum ◽  
Sunspot Groups

Abstract Cornelis Tevel made sunspot observations during the period 1816–1836, including the Dalton Minimum. In this work, the first revision of these observations since Wolf incorporated them into his database is presented. On the one hand, the number of individual sunspots from Tevel’s drawings was counted. This is of special interest for the sunspot number reconstruction because this kind of information is not as common in historical sunspot records as the number of groups. Thus, Tevel could be considered for the future reconstruction of the sunspot number index. On the other hand, the number of groups counted according to modern sunspot group classifications finding significant misinterpretations with the number of groups assigned to Tevel in the existing databases. Tevel was a relevant sunspot observer in the Dalton Minimum. In fact, he was the observer with the highest number of groups observed in Solar Cycles 6 and 7 according to the existing sunspot group number databases. According to the raw group number recount in this work, the maximum amplitudes for Solar Cycles 6 and 7 are, respectively, 27% and 7% lower than those previously determined. Moreover, Solar Cycle 6 is the weakest solar cycle since the Maunder Minimum after applying these new counts. Group counts from Tevel’s observations were compared with those from relevant contemporary astronomers, demonstrating that Schwabe and Tevel systematically recorded a higher number of groups than Flaugergues and Derfflinger. In addition, sunspot areas and positions recorded by Tevel should be used with caution for scientific purposes.

scholarly journals Probable Value for the Next Sunspot Minimum

2014 ◽  
Vol 2014 ◽  
pp. 1-4
Author(s):  
Virginia Mabel Silbergleit
Keyword(s):  
Solar Cycle ◽  
Solar Minimum ◽  
The Sun ◽  
Solar Cycles ◽  
Additional Insight ◽  
Sunspot Minimum ◽  
Sunspot Numbers ◽  
Solar Cycle 24 ◽  
Cycle 24

Gumbel’s first distribution is applied to smoothed monthly mean sunspot numbers for solar cycles 10 to 24. According to that, the next minimum for solar cycle 24-25 transition would be the deepest solar minimum of the last 150 years. This study provides an additional insight about changes in the Sun which are currently happening.

scholarly journals Cosmic ray recovery and solar minimum phase of solar cycle 22: An interim report

1998 ◽  
Vol 103 (A1) ◽  
pp. 373-379 ◽  
Author(s):  
Frank B. McDonald ◽  
Nand Lal ◽  
Robert E. McGuire
Keyword(s):  
Solar Cycle ◽  
Solar Minimum ◽  
Cosmic Ray ◽  
Minimum Phase ◽  
Interim Report
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