scholarly journals Spectrum analysis of short-period <i>K</i> index behaviour at high and mid-latitudes

2015 ◽  
Vol 33 (1) ◽  
pp. 31-37 ◽  
Author(s):  
P. B. Kotzé
Keyword(s):  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Confidence Level ◽  
Solar Minimum ◽  
Solar Maximum ◽  
Coronal Holes ◽  
Activity Levels ◽  
Maximum Phase ◽  
K Index ◽  
Recurrent Activity

Abstract. Geomagnetic activity levels during the declining phase and solar minimum period of the solar cycle are considerably different from those during the solar maximum phase. Previous studies revealed variations in the pattern of recurrent activity from cycle to cycle as well as variations in the average geomagnetic activity levels during a solar cycle. During the declining phase of a solar cycle (and solar minimum), the solar and interplanetary causes of geomagnetic activity are substantially different from those during the solar maximum phase. Co-rotating fast solar wind streams originating from large polar coronal holes, extending towards the Sun's equator, interact with the Earth's magnetosphere, resulting in recurrent geomagnetic activity particularly during solar cycle minimum periods. This is a well-known phenomenon with respect to 27.0- and 13.5-day recurrence geomagnetic activity, and it is well-known to be related to sectorial (non-axial) poloidal magnetic field structure in the Sun. Published results of the recent solar-cycle-23 minimum showed that the presence of 9.0- and 6.7-day recurrent geomagnetic activities can be attributed to the sectorial spherical harmonic structure present in the solar magnetic field. In this study we performed a wavelet and Lomb–Scargle analysis of the geomagnetic activity K index at Lerwick (LER), Hermanus (HER) and Canberra (CNB) for the period between 1960 and 2010, overlapping with solar cycles 20 to 23. Daily mean K indices are used to identify how several harmonics of the 27.0-day recurrent period change during each solar cycle when comparing high and mid-latitude geomagnetic activity, applying a 95% confidence level. In particular the behaviour of the second (13.5-day), third (9.0-day) and fourth (6.7-day) harmonics are investigated by doing a wavelet analysis of each individual year's K indices at each location. Results obtained show that particularly during solar minima the 27.0-day period is no longer detectable above the 95% confidence level, and that geomagnetic activity is in fact dominated by higher harmonics like 13.5-, 9.0- and 6.7-day periods. These findings in fact are in line with previous investigations and confirm the results obtained by researchers using other geomagnetic activity indices like \\textit{aa} and C9. The wavelet-spectrum analysis also reveals that during the downward phase of cycle 23 and the very long minimum of 23–24 between 2002 and 2008, the 27.0-day activity period drops below the 95% confidence level. This is confirmed by Lomb–Scargle analyses of every year's K index activity. Results obtained in this study support evidence by other investigations that this can be attributed to the lack of coronal-mass ejection (CME)-dominated solar activity during solar minima, periods characterized by strong solar dipolar magnetic fields, less sunspot numbers than at solar maxima, and multiple prominent co-rotating solar wind streams present. This analysis further confirms previous studies by other authors that the pattern of recurrent activity is dictated by the configuration of coronal holes which give rise to related high-speed streams during a solar cycle by analysing K indices at both high- and mid-latitude magnetic observatories.

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 Spectral analysis of auroral geomagnetic activity during various solar cycles between 1960 and 2014

2016 ◽  
Vol 34 (12) ◽  
pp. 1159-1164 ◽  
Author(s):  
Pieter Benjamin Kotzé
Keyword(s):  
Spectral Analysis ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
High Speed ◽  
Solar Rotation ◽  
Pearson Correlation ◽  
Coronal Holes ◽  
Rotation Period ◽  
Period Change ◽  
Solar Cycles

Abstract. In this paper we use wavelets and Lomb–Scargle spectral analysis techniques to investigate the changing pattern of the different harmonics of the 27-day solar rotation period of the AE (auroral electrojet) index during various phases of different solar cycles between 1960 and 2014. Previous investigations have revealed that the solar minimum of cycles 23–24 exhibited strong 13.5- and 9.0-day recurrence in geomagnetic data in comparison to the usual dominant 27.0-day synodic solar rotation period. Daily mean AE indices are utilized to show how several harmonics of the 27-day recurrent period change during every solar cycle subject to a 95 % confidence rule by performing a wavelet analysis of each individual year's AE indices. Results show that particularly during the solar minimum of 23–24 during 2008 the 27-day period is no longer detectable above the 95 % confidence level. During this interval geomagnetic activity is now dominated by the second (13.5-day) and third (9.0-day) harmonics. A Pearson correlation analysis between AE and various spherical harmonic coefficients describing the solar magnetic field during each Carrington rotation period confirms that the solar dynamo has been dominated by an unusual combination of sectorial harmonic structure during 23–24, which can be responsible for the observed anomalously low solar activity. These findings clearly show that, during the unusual low-activity interval of 2008, auroral geomagnetic activity was predominantly driven by high-speed solar wind streams originating from multiple low-latitude coronal holes distributed at regular solar longitude intervals.

scholarly journals Extremely low geomagnetic activity during the recent deep solar cycle minimum

2011 ◽  
Vol 7 (S286) ◽  
pp. 200-209 ◽  
Author(s):  
E. Echer ◽  
B. T. Tsurutani ◽  
W. D. Gonzalez
Keyword(s):  
Solar Wind ◽  
Solar Cycle ◽  
Geomagnetic Activity ◽  
Solar Minimum ◽  
Solar Wind Speed ◽  
Sunspot Cycle ◽  
Cycle Minimum ◽  
Current Minimum ◽  
Solar Wind Parameters ◽  
Xix Century

AbstractThe recent solar minimum (2008-2009) was extreme in several aspects: the sunspot number, Rz, interplanetary magnetic field (IMF) magnitude Bo and solar wind speed Vsw were the lowest during the space era. Furthermore, the variance of the IMF southward Bz component was low. As a consequence of these exceedingly low solar wind parameters, there was a minimum in the energy transfer from solar wind to the magnetosphere, and the geomagnetic activity ap index reached extremely low levels. The minimum in geomagnetic activity was delayed in relation to sunspot cycle minimum. We compare the solar wind and geomagnetic activity observed in this recent minimum with previous solar cycle values during the space era (1964-2010). Moreover, the geomagnetic activity conditions during the current minimum are compared with long term variability during the period of available geomagnetic observations. The extremely low geomagnetic activity observed in this solar minimum was previously recorded only at the end of XIX century and at the beginning of the XX century, and this might be related to the Gleissberg (80-100 years) solar cycle.

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.

A Search for Solar Cycle Variability in the Nightside Ionosphere of Mars

2020 ◽  
Author(s):  
Zachary Girazian ◽  
Jasper Halekas
Keyword(s):  
Solar Cycle ◽  
Ion Transport ◽  
Electron Impact ◽  
Solar Minimum ◽  
Impact Ionization ◽  
Solar Maximum ◽  
Electron Impact Ionization ◽  
Mars Atmosphere ◽  
Relative Contribution ◽  
Cyclical Variability

&lt;p&gt;The nightside ionosphere of Mars is mainly produced by a combination of electron impact ionization and day-to-night ion transport. The relative contribution of these two sources, and their variability over the solar cycle, has not been well established. To address this issue, we use Mars Atmosphere and Volatile EvolutioN (MAVEN) observations to search for cyclical variability in nightside ion densities over the solar cycle. We find that nightside densities (O&lt;sup&gt;+&lt;/sup&gt; in particular) were significantly higher during solar maximum (2014) than during solar minimum (2019). Our results suggest that, similar to the nightside ionosphere of Venus, day-to-night transport of O&lt;sup&gt;+&lt;/sup&gt; ions is more prominent during solar maximum.&lt;/p&gt;

scholarly journals Secular trends in storm-level geomagnetic activity

2011 ◽  
Vol 29 (2) ◽  
pp. 251-262 ◽  
Author(s):  
J. J. Love
Keyword(s):  
Geomagnetic Activity ◽  
Linear Trend ◽  
Statistical Significance ◽  
Activity Levels ◽  
Future Trends ◽  
Solar Cycles ◽  
Monotonic Trend ◽  
Secular Evolution ◽  
The Past ◽  
K Index

Abstract. Analysis is made of K-index data from groups of ground-based geomagnetic observatories in Germany, Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. Methods include nonparametric measures of trends and statistical significance used by the hydrological and climatological research communities. Among the three observatory groups, German K data systematically record the highest disturbance levels, followed by the British and, then, the Australian data. Signals consistently seen in K data from all three observatory groups can be reasonably interpreted as physically meaninginful: (1) geomagnetic activity has generally increased over the past 141 years. However, the detailed secular evolution of geomagnetic activity is not well characterized by either a linear trend nor, even, a monotonic trend. Therefore, simple, phenomenological extrapolations of past trends in solar and geomagnetic activity levels are unlikely to be useful for making quantitative predictions of future trends lasting longer than a solar cycle or so. (2) The well-known tendency for magnetic storms to occur during the declining phase of a sunspot-solar cycles is clearly seen for cycles 14–23; it is not, however, clearly seen for cycles 11–13. Therefore, in addition to an increase in geomagnetic activity, the nature of solar-terrestrial interaction has also apparently changed over the past 141 years.

scholarly journals Long-term biases in geomagnetic <i>K</i> and <i>aa</i> indices

2011 ◽  
Vol 29 (8) ◽  
pp. 1365-1375 ◽  
Author(s):  
J. J. Love
Keyword(s):  
Geomagnetic Activity ◽  
Estimation Methods ◽  
Activity Levels ◽  
Solar Cycles ◽  
K Value ◽  
K Index ◽  
Medium Level ◽  
Value Estimation ◽  
Aa Index

Abstract. Analysis is made of the geomagnetic-activity aa index and its source K-index data from groups of ground-based observatories in Britain, and Australia, 1868.0–2009.0, solar cycles 11–23. The K data show persistent biases, especially for high (low) K-activity levels at British (Australian) observatories. From examination of multiple subsets of the K data we infer that the biases are not predominantly the result of changes in observatory location, localized induced magnetotelluric currents, changes in magnetometer technology, or the modernization of K-value estimation methods. Instead, the biases appear to be artifacts of the latitude-dependent scaling used to assign K values to particular local levels of geomagnetic activity. The biases are not effectively removed by weighting factors used to estimate aa. We show that long-term averages of the aa index, such as annual averages, are dominated by medium-level geomagnetic activity levels having K values of 3 and 4.

scholarly journals Linking solar minimum, space weather, and night sky brightness

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Albert D. Grauer ◽  
Patricia A. Grauer
Keyword(s):  
Magnetic Field ◽  
Time Series ◽  
Solar Cycle ◽  
Space Weather ◽  
Solar Minimum ◽  
Coronal Holes ◽  
Planetary Science ◽  
Sky Brightness ◽  
Night Sky ◽  
Night Sky Brightness

AbstractThis paper presents time-series observations and analysis of broadband night sky airglow intensity 4 September 2018 through 30 April 2020. Data were obtained at 5 sites spanning more than 8500 km during the historically deep minimum of Solar Cycle 24 into the beginning of Solar Cycle 25. New time-series observations indicate previously unrecognized significant sources of broadband night sky brightness variations, not involving corresponding changes in the Sun's 10.7 cm solar flux, occur during deep solar minimum. New data show; (1) Even during a deep solar minimum the natural night sky is rarely, if ever, constant in brightness. Changes with time-scales of minutes, hours, days, and months are observed. (2) Semi-annual night sky brightness variations are coincident with changes in the orientation of Earth's magnetic field relative to the interplanetary magnetic field. (3) Solar wind plasma streams from solar coronal holes arriving at Earth’s bow shock nose are coincident with major night sky brightness increase events. (4) Sites more than 8500 km along the Earth's surface experience nights in common with either very bright or very faint night sky airglow emissions. The reason for this observational fact remains an open question. (5) It is plausible, terrestrial night airglow and geomagnetic indices have similar responses to the solar energy input into Earth's magnetosphere. Our empirical results contribute to a quantitative basis for understanding and predicting broadband night sky brightness variations. They are applicable in astronomical, planetary science, space weather, light pollution, biological, and recreational studies.

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