Solar activity variations of equatorial spread F occurrence and sustenance during different seasons over Indian longitudes: Empirical model and causative mechanisms

2018 ◽  
Vol 61 (10) ◽  
pp. 2585-2592 ◽  
Author(s):  
M.K. Madhav Haridas ◽  
G. Manju ◽  
T. Arunamani
Keyword(s):  
Solar Activity ◽  
Empirical Model ◽  
Equatorial Spread F ◽  
Different Seasons ◽  
Spread F

scholarly journals Radar and satellite investigations of equatorial evening vertical drifts and spread <i>F</i>

2015 ◽  
Vol 33 (11) ◽  
pp. 1403-1412 ◽  
Author(s):  
J. M. Smith ◽  
F. S. Rodrigues ◽  
E. R. de Paula
Keyword(s):  
Local Time ◽  
Empirical Model ◽  
Sufficient Condition ◽  
Satellite Measurements ◽  
Equatorial Spread F ◽  
Annual Variability ◽  
F Region ◽  
Plasma Drifts ◽  
Spread F ◽  
Coherent Backscatter

Abstract. We analyzed pre-midnight equatorial F region observations made by the 30 MHz coherent backscatter radar of São Luis, Brazil between August 2010 and February 2012. These measurements were processed, and used to create monthly maps of the echo occurrence as a function of local time and height. The maps show the inter-annual variability associated with equatorial spread F (ESF) occurrence in the Brazilian longitude sector. We also constructed monthly curves of the evening vertical drifts, for the Brazilian sector, using measurements by the ion velocity meter (IVM) onboard the C/NOFS satellite. The IVM evening drifts show a good overall agreement with the Scherliess and Fejer (1999) empirical model. Measured and model drifts show the development of the pre-reversal enhancement (PRE) of the vertical plasma drifts during ESF season. Using joint radar and satellite measurements, we found that evening (18:00–18:30 LT) mean non-negative drifts provide a necessary but not sufficient condition for the occurrence of topside ESF echoes. Evening downward (negative) drifts preceded the absence of topside ESF irregularities.

scholarly journals On the seasonal variations of the threshold height for the occurrence of equatorial spread F during solar minimum and maximum years

2007 ◽  
Vol 25 (4) ◽  
pp. 855-861 ◽  
Author(s):  
G. Manju ◽  
C. V. Devasia ◽  
R. Sridharan
Keyword(s):  
Solar Minimum ◽  
Solar Maximum ◽  
Decisive Role ◽  
Meridional Wind ◽  
Equatorial Spread F ◽  
Clear Cut ◽  
Meridional Winds ◽  
Different Seasons ◽  
Spread F ◽  
Bottom Side

Abstract. A study has been carried out on the occurrence of bottom side equatorial spread F (ESF) and its dependence on the polarity and magnitude of the thermospheric meridional wind just prior to ESF occurrence during summer, winter and equinox seasons of solar maximum (2002) and minimum years (1995), using ionosonde data of Trivandrum (8.5° N, 76.5° E, dip=0.5° N) and SHAR (13.7° N, 80.2° E, dip ~5.5° N) in the Indian longitude sector. In this study, we have examined the changes in the threshold height of the base of the F layer for the triggering of ESF, irrespective of the magnitude and polarity of the meridional winds during the above periods. The study indicates that the threshold height above which ESF triggering is entirely controlled only by the collisional R-T instability is least for summer months, with higher values for winter and equinox, during the solar minimum period, whereas for the solar maximum period the threshold height is least for winter, with higher values for summer and equinox. But the range over which the threshold height varies is very narrow (<15 km) for solar minimum in relation to the large range of variation (>50 km) in the solar maximum epoch. Further to this, the study also reveals a clear-cut increase in threshold height with solar activity for all seasons. Clear-cut seasonal variability is also observed in the threshold height, especially for solar maximum. The study quantifies the level of the base of the F layer below which neutral dynamical effects play a decisive role in the triggering of ESF during different seasons and solar epochs.

scholarly journals Geomagnetic storm and equatorial spread-F

2004 ◽  
Vol 22 (9) ◽  
pp. 3231-3239 ◽  
Author(s):  
F. Becker-Guedes ◽  
Y. Sahai ◽  
P. R. Fagundes ◽  
W. L. C. Lima ◽  
V. G. Pillat ◽  
...  
Keyword(s):  
Case Studies ◽  
Geomagnetic Storm ◽  
Geomagnetic Storms ◽  
Equatorial Spread F ◽  
University Center ◽  
Different Seasons ◽  
Spread F ◽  
Salient Features ◽  
The University ◽  
Ionospheric Sounding

Abstract. In August 2000, a new ionospheric sounding station was established at Sao Jose dos Campos (23.2° S, 45.9° W; dip latitude 17.6° S), Brazil, by the University of Vale do Paraiba (UNIVAP). Another ionospheric sounding station was established at Palmas (10.2° S, 48.2° W; dip latitude 5.5° S), Brazil, in April 2002, by UNIVAP in collaboration with the Lutheran University Center of Palmas (CEULP), Lutheran University of Brazil (ULBRA). Both the stations are equipped with digital ionosonde of the type known as Canadian Advanced Digital Ionosonde (CADI). In order to study the effects of geomagnetic storms on equatorial spread-F, we present and discuss three case studies, two from the ionospheric sounding observations at Sao Jose dos Campos (September and November 2000) and one from the simultaneous ionospheric sounding observations at Sao Jose dos Campos and Palmas (July 2003). Salient features from these ionospheric observations are presented and discussed in this paper. It has been observed that sometimes (e.g. 4-5 November 2000) the geomagnetic storm acts as an inhibitor (high strong spread-F season), whereas at other times (e.g. 11-12 July 2003) they act as an initiator (low strong spread-F season), possibly due to corresponding changes in the quiet and disturbed drift patterns during different seasons.

scholarly journals Spread F occurrence features at different longitudinal regions during low and moderate solar activity

2019 ◽  
Author(s):  
Abimbola O. Afolayan ◽  
Singh J. Mandeep ◽  
Mardina Abdullah ◽  
Suhaila M. Buhari ◽  
Tatsuhiro Yokoyama ◽  
...  
Keyword(s):  
Solar Activity ◽  
Time Lag ◽  
Onset Time ◽  
Longitudinal Distribution ◽  
Time Duration ◽  
Range Type ◽  
Different Seasons ◽  
Spread F ◽  
The Difference ◽  
Perturbation Effect

Abstract. A comparative study of the equatorial spread F occurrence was conducted at different longitudes during 2009 or 2010 and 2011 or 2013 which represents the low (LSA) and moderate (MSA) solar activity periods respectively. The ionogram data were recorded at low latitude stations including Jicamarca (JIC; 75.76° W, 8.17° S), Peru; Fortaleza (FZA; 38.52° W, 3.73° S), Brazil; Ilorin (ILR; 7.55° E, 9.93° N), Nigeria; Chumphon (CPN; 88.46° E, 11° N), Thailand and Kwajalein (KWA; 167.73° E, 8.72° N), Marshal Island. The range type spread F (RSF) occurrence was manually recorded at an hour interval between 18:00–06:00 LT and a monthly average of the RSF occurrence was estimated for each of the seasons. The observed features of the RSF occurrence and its longitudinal distribution at different seasons include the difference in the onset time, duration and peak of occurrence. The significant observations include the asymmetric RSF occurrence distribution during the equinoctial season at most of the longitudes, while during the solstice seasons there are cases of discrepancy in the RSF occurrence with respect to the sunset terminator-magnetic field alignment. The inconsistent pattern of the RSF occurrence percentage and the post-sunset rise of the F layer in relation to the sunset time lag were analyzed. While the possible role of the seed perturbation effect was discussed with respect to some of the peculiar features observed in the longitudinal/seasonal distribution of the spread F occurrence percentage.

scholarly journals The persistence of equatorial spread F – an analysis on seasonal, solar activity and geomagnetic activity aspects

2009 ◽  
Vol 27 (2) ◽  
pp. 503-510 ◽  
Author(s):  
V. Sreeja ◽  
C. V. Devasia ◽  
R. Sridharan ◽  
Keyword(s):  
Geomagnetic Activity ◽  
Communication Systems ◽  
Activity Index ◽  
Magnetic Activity ◽  
Activity Levels ◽  
Equatorial Spread F ◽  
Vertical Drift ◽  
Different Seasons ◽  
Spread F ◽  
Advance Information

Abstract. The persistence (duration) of Equatorial Spread F (ESF), which has significant impact on communication systems, is addressed. Its behavior during different seasons and geomagnetic activity levels under the solar maximum (2001) and minimum (2006) conditions, is reported using the data from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip 0.5° N) in India. The study reveals that the persistence of the irregularities can be estimated to a reasonable extent by knowing the post sunset F region vertical drift velocity (Vz) and the magnetic activity index Kp. Any sort of advance information on the possible persistence of the ionospheric irregularities responsible for ESF is important for understanding the scintillation morphology, and the results which form the first step in this direction are presented and discussed.

Equatorial spread-F and solar activity

1964 ◽  
Vol 26 (9) ◽  
pp. 871-878 ◽  
Author(s):  
S. Rangaswamy ◽  
K.B. Kapasi
Keyword(s):  
Solar Activity ◽  
Equatorial Spread F ◽  
Spread F
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