Solar cycle and seasonal variations in F-region vertical drifts over Kodaikanal, India

1995 ◽  
Vol 13 (6) ◽  
pp. 633-640 ◽  
Author(s):  
K. B. Ramesh ◽  
J. H. Sastri
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Normal Incidence ◽  
Magnetic Activity ◽  
Solar Flux ◽  
Seasonal Trend ◽  
F Region ◽  
Phase Path ◽  
10.7 Cm Solar Flux

Abstract. Measurements of the changes in phase path of F-region reflections at normal incidence at Kodaikanal (77° 28'E, 10° 14'N, dip 3°N) from February 1991 to February 1993 are used to determine the variation of the equatorial evening F-region vertical drifts (V z) with season, solar and magnetic activity. It is found that on average, at Kodaikanal, the post-sunset peak in Vz(Vzp) is higher in equinox and local winter months than in local summer. The day-to-day variability in V zp is highest in summer and lowest in winter. This seasonal trend persists even on magnetically quiet days (Ap \\leq14). Vzp is found to increase with 10.7 cm solar flux in all three seasons but tends to saturate for large flux values (>230 units) during local summer and winter months. Magnetic activity [represented by Ap as well as the time-weighted accumulations of a p and ap (τ)] does not seem to have any statistically significant effect on Vzp , except during equinoctial months of moderate solar activity, when Vzp decreases as magnetic activity increases.

Characteristics of VHF scintillations in the equatorial anomaly crest region in India

1995 ◽  
Vol 13 (7) ◽  
pp. 730-739 ◽  
Author(s):  
K. N. Pathak ◽  
R. D. Jivrajani ◽  
H. P. Joshi ◽  
K. N. Iyer
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Magnetic Activity ◽  
Summer Season ◽  
Equatorial Anomaly ◽  
Equatorial Station ◽  
F Region ◽  
Ionospheric Scintillations

Abstract. The characteristics of ionospheric scintillations at Rajkot in the equatorial anomaly crest region in India are described for the years 1987–1991 by monitoring the 244-MHz transmission from the satellite FLEETSAT. This period covers the ascending phase of solar cycle 22. Scintillations occur predominantly in the pre-midnight period during equinoxes and winter seasons and in the post-midnight period during summer season. During equinoxes and winter, scintillation occurrence increases with solar activity, whilst in summer it is found to decrease with solar activity. Statistically, scintillation occurrence is suppressed by magnetic activity. The characteristics observed during winter and equinoxes are similar to those seen at the equatorial station, Trivandrum. This, coupled with the nature of the post-sunset equatorial F-region drift and h'F variations, supports the view that at the anomaly crest station, scintillations are of equatorial origin during equinox and winter, whilst in summer they may be of mid-latitude type. The variations in scintillation intensity (in dB) with season and solar activity are also reported.

scholarly journals Shift of effective lightning areas during pre to post period of solar cycle minimum of 2008-2009 as determined from Schumann resonance studies at Agra, India

2015 ◽  
Vol 57 (6) ◽  
Author(s):  
Birbal Singh ◽  
Devbrat Pundhir
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Thunderstorm Activity ◽  
Schumann Resonance ◽  
Cycle Minimum ◽  
Source Distance ◽  
Imaging Sensor ◽  
Post Period ◽  
Effective Source

<p>Employing a set of 3-component search coil magnetometer, Schumann resonance studies have been in progress at Agra (Geograph. lat. 27.2°N, long. 78°E), India since 01 April, 2007. We have analysed the data for two periods; first from 01 April, 2007 to 31 March, 2008 (period-I), and then from 01 March, 2011 to 29 February, 2012 (period-II) which correspond to pre and post periods of solar cycle minimum of 2008-2009. From the diurnal variation of first mode intensity and frequency, we study the seasonal variations of global thunderstorm activity, effective source distance and level of lightning during both the periods. We show that world thunderstorm activity shifts to summer in the northern hemisphere as the effective source distance approaches close to the observer, and the level of intense lightning shifts from the month of July, 2007 in period-I to August, 2011 in period-II. This is supported by Lightning Imaging Sensor (LIS) satellite data also. A possible explanation in terms of increasing solar activity is suggested.</p>

scholarly journals Equatorial ionospheric response to the 10.7 cm radio flux over two sunspot cycles (1969−1991)

1996 ◽  
Vol 14 (7) ◽  
pp. 725-732
Author(s):  
L. A. Hajkowicz
Keyword(s):  
Solar Activity ◽  
Correlation Coefficient ◽  
Geomagnetic Latitude ◽  
Correlation Coefficients ◽  
Radio Flux ◽  
Solar Cycles ◽  
Pronounced Difference ◽  
F Region ◽  
Diurnal Distribution ◽  
10.7 Cm Solar Flux

Abstract. It is evident that fluctuations in a standard ionospheric parameter, the minimum (virtual) height (h´F) of the equatorial F-region in the African (Ouagadougou), Asian (Manila) and American (Huancayo) longitudinal sectors, closely resemble changes in solar activity as deduced from the 10.7 cm solar flux index (S), over two solar cycles (1969–91). The monthly median hourly value of h´F, particularly in the post-sunset period (18–20 LT), are positively correlated with the monthly average S. The value of h´F can be deduced from an empirical formula: h´F=0.68S+218.3, with the correlation coefficient (r) between h´F and S being 0.78. The diurnal distribution of r during daytime (06–14 LT) was radically different for the African and Asian longitudinal sectors during 1980-1991, with the most pronounced difference in the post-noon period (12–14 LT) when the correlation coefficients r for the Asian and African sectors are 0.8 and 0.2, respectively. Thus, the daytime F-region in the African sector responded far less to changes in solar activity than the Asian F-region during this cycle. This longitudinal anomaly was however absent in the preceding cycle (1969–1979) when the African and Asian sectors were both characterised by low daytime and pronounced post-sunset correlation coefficient r. The American sector appears to have a high correlation coefficient r in daytime increasing to a small maximum in the post-sunset interval. The post-sunset enhancement in r is a characteristic feature for equatorial stations only (corrected geomagnetic latitude <10°).

scholarly journals Lower-thermosphere response to solar activity: an empirical-mode-decomposition analysis of GOCE 2009–2012 data

2020 ◽  
Vol 38 (3) ◽  
pp. 789-800
Author(s):  
Alberto Bigazzi ◽  
Carlo Cauli ◽  
Francesco Berrilli
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Empirical Mode Decomposition ◽  
Dynamic Range ◽  
Extreme Ultraviolet ◽  
Lower Thermosphere ◽  
European Space Agency ◽  
Solar Flux ◽  
Specific Response ◽  
Mode Decomposition

Abstract. Forecasting the thermosphere (the atmosphere's uppermost layer, from about 90 to 800 km altitude) is crucial to space-related applications, from space mission design to re-entry operations, space surveillance and more. Thermospheric dynamics is directly linked to the solar dynamics through the solar UV (ultraviolet) input, which is highly variable, and through the solar wind and plasma fluxes impacting Earth's magnetosphere. The solar input is non-periodic and non-stationary, with long-term modulations from the solar rotation and the solar cycle and impulsive components, due to magnetic storms. Proxies of the solar input exist and may be used to forecast the thermosphere, such as the F10.7 radio flux and the Mg II EUV (extreme-ultraviolet) flux. They relate to physical processes of the solar atmosphere. Other indices, such as the Ap geomagnetic index, connect with Earth's geomagnetic environment. We analyse the proxies' time series comparing them with in situ density data from the ESA (European Space Agency) GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) gravity mission, operational from March 2009 to November 2013, therefore covering the full rising phase of solar cycle 24, exposing the entire dynamic range of the solar input. We use empirical mode decomposition (EMD), an analysis technique appropriate to non-periodic, multi-scale signals. Data are taken at an altitude of 260 km, exceptionally low for a low-Earth-orbit (LEO) satellite, where density variations are the single most important perturbation to satellite dynamics. We show that the synthesized signal from optimally selected combinations of proxy basis functions, notably Mg II for the solar flux and Ap for the plasma component, shows a very good agreement with thermospheric data obtained by GOCE, during periods of low and medium solar activity. In periods of maximum solar activity, density enhancements are also well represented. The Mg II index proves to be, in general, a better proxy than the F10.7 index for modelling the solar flux because of its specific response to the UV spectrum, whose variations have the largest impact over thermospheric density.

scholarly journals Seasonal Variations of the Optimum Reliable Frequencies During Maximum and Minimum Periods of Solar Cycle 24

2020 ◽  
Vol 31 (4) ◽  
pp. 15
Author(s):  
Samar Abdalkaream Thabit ◽  
Loay E. George ◽  
Khalid A. Hadi
Keyword(s):  
Mathematical Model ◽  
Solar Activity ◽  
Solar Cycle ◽  
Seasonal Variations ◽  
Path Length ◽  
Polynomial Equation ◽  
Ionospheric Parameter ◽  
Solar Cycle 24 ◽  
Path Lengths ◽  
Cycle 24

In this research, the seasonal Optimal Reliable Frequency (ORF) variations between different transmitter/receiver stations have been determined. Mosul, Baghdad, and Basra have been chosen as tested transmitting stations that located in the northern, center, and southern of Iraqi zone. In this research, the minimum and maximum years (2009 and 2014) of solar cycle 24 have been chosen to examine the effect of solar activity on the determined seasonal ORF parameter. Mathematical model has been proposed which leads to generate the Optimal Reliable Frequency that can maintain the seasonal connection links for different path lengths and bearings. The suggested ORF parameter represented by a different orders polynomial equation. The polynomial equation has been determined depending on different selected parameters (path length, bearing, time (day), months and BUF values). The suggested seasonal ORF parameter was examined for the three stations of the adopted years. The value of the seasonal ORF ionospheric parameter increased with the increase of path length and varies with the bearing between the transmitting and receiving stations also, the seasonal ORF values were higher at maximum solar cycle (2014) than the minimum solar cycle (2009).

scholarly journals Effect of solar cycle on topside ion temperature measured by SROSS C2 and ROCSAT 1 over the Indian equatorial and low latitudes

2012 ◽  
Vol 30 (12) ◽  
pp. 1645-1654 ◽  
Author(s):  
A. Borgohain ◽  
P. K. Bhuyan
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Significant Negative Correlation ◽  
Solar Flux ◽  
High Solar Activity ◽  
Topside Ionosphere ◽  
Ion Temperature ◽  
Ion Density ◽  
Positive Correlation ◽  
June Solstice

Abstract. The effect of solar activity on the diurnal, seasonal and latitudinal variations of ion temperature Ti and its relationship with corresponding ion density Ni over the Indian low and equatorial topside ionosphere within 17.5° S to 22.5° N magnetic latitudes are being investigated, combining the data from SROSS C2 and ROCSAT 1 for the 9-year period from 1995 to 2003 during solar cycle 23. Ti varies between 800 K and 1100 K during nighttime and rises to peak values of ~1800 K in the post sunrise hours. Daytime Ti varies from 1000 K to 1500 K. The time of occurrence, magnitude and duration of the morning enhancement show distinct seasonal bias. For example, in the June solstice, Ti increases to ~1650 K at ~06:00 h and exhibits a daytime plateau till 17:00 LT. In the equinoxes, enhanced ion temperature is observed for a longer duration in the morning. There is also a latitudinal asymmetry in the ion temperature distribution. In the equinoxes, the daytime Ti is higher at off equatorial latitudes and lower over the Equator, while in the solstices, Ti exhibits a north–south gradient during daytime. Nighttime Ti is found to be higher over the Equator. Daytime ion temperature exhibits insignificant positive correlation with F10.7 cm solar flux, while nighttime ion temperature decreases with increase in solar flux. Daytime ion temperature and ion density are negatively correlated during solar minimum, while nighttime Ti does not exhibit any correlation. However, during high solar activity, significant positive correlation of Ti with Ni has been observed over the Equator, while at 10° S and 10° N temperature and density exhibit significant negative correlation. The neutral temperature Tn derived from the MSISE 90 model is found to be higher than measured Ti during nighttime, while daytime Ti is higher than model Tn.

Observation of Hysteresis between Solar Activity Indicators and p-mode Frequency Shifts for Solar Cycle 22

2000 ◽  
Vol 179 ◽  
pp. 357-360
Author(s):  
S. C. Tripathy ◽  
Brajesh Kumar ◽  
Kiran Jain ◽  
A. Bhatnagar
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Magnetic Activity ◽  
Mode Frequency ◽  
Hysteresis Phenomenon ◽  
Data Sets ◽  
Frequency Data ◽  
Frequency Shifts ◽  
Intermediate Degree

AbstractUsing intermediate degreep-mode frequency data sets for solar cycle 22, we find that the frequency shifts and magnetic activity indicators show a “hysteresis” phenomenon. It is observed that the magnetic indices follow different paths for the ascending and descending phases of the solar cycle while for radiative indices, the separation between the paths are well within the error limits.

scholarly journals Solar cycles: the past evolution influence

2009 ◽  
Vol 5 (S264) ◽  
pp. 155-157
Author(s):  
Alexis Klutsch ◽  
Rubens Freire Ferrero
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Magnetic Activity ◽  
Measured Data ◽  
Physical Models ◽  
Periodic Pattern ◽  
Solar Cycles ◽  
Future Evolution ◽  
The Past ◽  
Physical Phenomena

AbstractThe so-calledsolar cycleis generally characterized by the quasi-periodic oscillatory evolution of the photospheric spots number. This quasi-periodic pattern has always been an intriguing question. Several physical models were proposed to explain this evolution and many mathematical data analysis were employed to determine the principal frequencies noticeable in the measured data. Both approaches try to predict the future evolution of the solar activity and to understand the physical phenomena producing these cycles. Here we present the analysis of the sunspots number evolution using the time-delay approach. Our results show than the solar cycle can also be characterized by this behavior implying the influence of the past evolution over the present one, suggesting an histeresis mechanism, linked probably with magnetic activity.

scholarly journals Multi-station investigation of spread F over Europe during low to high solar activity

2018 ◽  
Vol 8 ◽  
pp. A27 ◽  
Author(s):  
Krishnendu Sekhar Paul ◽  
Haris Haralambous ◽  
Christina Oikonomou ◽  
Ashik Paul ◽  
Anna Belehaki ◽  
...  
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Geomagnetic Storms ◽  
Occurrence Rate ◽  
High Solar Activity ◽  
Solar Cycle Variation ◽  
F Region ◽  
Perkins Instability ◽  
Spread F ◽  
Triggering Mechanisms

Spread F is an ionospheric phenomenon which has been reported and analyzed extensively over equatorial regions on the basis of the Rayleigh-Taylor (R-T) instability. It has also been investigated over midlatitude regions, mostly over the Southern Hemisphere with its generation attributed to the Perkins instability mechanism. Over midlatitudes it has also been correlated with geomagnetic storms through the excitation of travelling ionospheric disturbances (TIDs) and subsequent F region uplifts. The present study deals with the occurrence rate of nighttime spread F events and their diurnal, seasonal and solar cycle variation observed over three stations in the European longitude sector namely Nicosia (geographic Lat: 35.29 °N, Long: 33.38 °E geographic: geomagnetic Lat: 29.38 °N), Athens (geographic Lat: 37.98 °N, Long: 23.73 °E geographic: geomagnetic Lat: 34.61 °N) and Pruhonice (geographic Lat: 50.05 °N, Long: 14.41 °E geographic: geomagnetic Lat: 47.7 °N) during 2009, 2015 and 2016 encompassing periods of low, medium and high solar activity, respectively. The latitudinal and longitudinal variation of spread F occurrence was examined by considering different instability triggering mechanisms and precursors which past literature identified as critical to the generation of spread F events. The main findings of this investigation is an inverse solar cycle and annual temporal dependence of the spread F occurrence rate and a different dominant spread F type between low and high European midlatitudes.

scholarly journals Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

2004 ◽  
Vol 22 (8) ◽  
pp. 2849-2860 ◽  
Author(s):  
R. P. Singh ◽  
R. P. Patel ◽  
A. K. Singh
Keyword(s):  
Solar Activity ◽  
Solar Cycle ◽  
Electric Fields ◽  
Recovery Phase ◽  
Magnetic Activity ◽  
Magnetic Storms ◽  
High Solar Activity ◽  
Equatorial Anomaly ◽  
Probability Of Occurrence

Abstract. The VHF amplitude scintillation recorded during the period January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3°, long.=83.0°, dip=37°N) have been analyzed to study the behavior of ionospheric irregularities during active solar periods and magnetic storms. It is shown that irregularities occur at arbitrary times and may last for <30min. A rise in solar activity increases scintillations during winter (November-February) and near equinoxes (March-April; September-October), whereas it depresses the scintillations during the summer (May-July). In general, the role of magnetic activity is to suppress scintillations in the pre-midnight period and to increase it in the post-midnight period during equinox and winter seasons, whilst during summer months the effect is reversed. The pre-midnight scintillation is sometimes observed when the main phase of Dst corresponds to the pre-midnight period. The annual variation shows suppression of scintillations on disturbed days, both during pre-midnight and post-midnight period, which becomes more effective during years of high solar activity. It is observed that for magnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time. If the magnetic storm occurred during daytime, then the probability of occurrence of scintillations during the night hours is decreased. The penetration of magnetospheric electric fields to the magnetic equator affects the evolution of low-latitude irregularities. A delayed disturbance dynamo electric field also affects the development of irregularities.

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