AJP	ISSN : 0971 – 3093 Vol 24, No. 6, June, 2015

 

Vol. 24, No 6 (2015) 785-792

Seasonal variations in the ionospheric F-region parameters during the recent low solar activity in the Brazilian sector: Comparison with ionospheric models

Y Sahai^a, R de Jesus^a P R Fagundes^a, A J de Abreu^a, G Crowley^b, V G Pillat^a, J R Abalde^a, and J A Bittencourt^c

Routine ionospheric sounding observations in Brazil at S J Campos (23.2 S, 45.9 W; dip latitude 18.0 S), and a low latitude station under the southern crest of the equatorial ionospheric anomaly, and Palmas (10.2 S, 48.2 W; dip latitude 6.1 S), a near equatorial station use Canadian Advanced Digital Ionosondes (CADIs). The S J Campos and Palm as soundings were started under the UNIVAP network in August 2000 and April 2002, respectively. In this paper, we present seasonal variations in the following ionospheric F-region parameters: critical frequency of the F-region (foF2), minimum virtual height of reflection (h’F), and virtual height at 0.834 foF2 (hpF2, which is approximately equal to the peak height of the F-region – hmF2) during the low solar activity period (December 2007 to October 2008). We scaled the three ionospheric parameters every 15 minutes for a few geomagnetically quiet days in the four seasons; viz. summer (December 2007 and January 2008), autumn (March and April 2008), winter (June and July 2008), and spring (September and October 2008). Large inter-seasonal and day-to-day variations were observed in all the ionospheric parameters. The observed ionospheric parameters (hpF2 and/or foF2) are compared with the TIME-GCM simulations and IRI-2007 model results. The model results show both similarities and differences from the observed results. ©Anita Publications. All rights reserved.

 

Vol. 24, No 6 (2015) 793-805

Use of All-sky imaging systems to study plasma processes in the low and midlatitude ionosphere

 

C Martinis, M Mendillo, J Baumgardner, P Zablowski and C Sullivan

Center for Space Physics- Boston University, Boston, MA 02215, USA 

Vol. 24, No 6 (2015) 807-810

Optical and ionosonde range/time observations of plasma depletions over Darwin

 

K J W Lynn^a*, K Shiokawa^b, Y Otsuka^b and P Wilkinson^c

 ^aIonospheric Systems Research, Noosaville, Australia 4056

 ^bSolar-Terrestrial Environment Laboratory, Nagoya University, Toyokawa 442-8507, Japan

Ionosonde range-time displays have recently been used to identify the effect of overhead optical plasma depletions on ionograms received at Darwin. Since the initial two identifications, a greater number of examples have been obtained over the period October 2001 to May 2002. Optical plasma depletions ceased to reach overhead at Darwin as the sunspot cycle moved towards minimum, the equatorial ionospheric electron density decreased, the peak height dropped and the driving electric field weakened. The associated ra++nge-time plots disappeared. Optical plasma depletions were once more visible at Darwin in 2011 as the sunspot cycle moved towards maximum. The variety of events observed has shown that the optical measurements can pick up plasma depletions up to some 500 km north of Darwin. However the optical plasma depletions have to reach the overhead position before the Darwin ionosonde can see them, even though the ionosonde can identify their presence at such times as satellite traces while they are some 400 km away in the East-West direction. This indicates that the off-angle ionosonde reflections require a propagation path orthogonal to the depletion. As the optical depletion drifts overhead, the ionosonde receives multiple echoes as it sees reflections from within and outside the bubble. Bubbles are normally seen to branch as their height increases so that the ionosonde sees a complex of range-spread echoes typical of equatorial spread F when the multi-pronged bubble passes overhead. ©Anita Publications. All rights reserved.

 Vol. 24, No 6 (2015) 811-820

Study of GPS based ionospheric scintillation during low solar activity period
(2009–2010) at an Indian low latitude station-Surat

 

H J Tanna, S P Karia and K N Pathak

The present paper investigates the characteristics of ionospheric scintillation at Surat  station near the northern crest of equatorial anomaly in India (21.16 ^°N, 72.78 ^°E; Geomagnetic: 12.90^°N, 147.35^°E) during the low solar activity years 2009 and 2010. As expected in the low latitude region, scintillations were found to occur predominantly during the nighttime. However, occurrences were also noted of daytime scintillation activity especially in the April, May, June months of the year 2009. The duration of the daytime scintillation were found to be considerably less than that of the nighttime scintillation especially in March-June of the year 2009 and equinoctial period of 2010. ©Anita Publications. All rights reserved.

 Vol. 24, No 6 (2015) 821-827

Comparison of GPS based TEC measured at Surat (India) with IRI – 2007 Models

 

Sheetal P Karia and Kamlesh N Pathak

The measurements of Total Electron Content (TEC) are made at Surat (Geographic Lat. 21.16 N, Long. 72.78 E,) in the equatorial ionization anomaly region in India, for a period of 11 months from 01 February to 31 December, 2009 using a Global Positioning System (GPS) receiver. These results are compared with the TEC derived from IRI-2007 using three different options of topside electron density, NeQuick, IRI01-corr, and IRI-2001. A good agreement is found between the TEC obtained at Surat and those derived from IRI01-corr and NeQuick ©Anita Publications. All rights reserved.

Keywords: Global Positioning System (GPS), Total Electron Content (TEC)

 Vol. 24, No 6 (2015) 829-841

On the TEC variability during 24^th solar cycle near northern anomaly crest

 

Himanshi Rajyaguru, Nimit Godhani, H P Joshi and K N Iyer

Department of Physics

Saurashtra University, Rajkot-360 005, India

The dual frequency signals from the GPS satellites recorded at Rajkot (22.29 °N, 70.74 °E, geographic, 14.03 °N geomagnetic) near the Equatorial Ionization Anomaly (EIA) crest in India are analysed to derive the Total Electron Content (TEC) for the years 2006 to 2014 covering extremely low to high solar activity period during the 24th solar cycle. The subtle differences are found in diurnal variation pattern of TEC from low to high solar activity. The seasonal behaviour shows that TEC is maximum for equinox months. The winter anomaly is observed during the high solar activity period only for the year 2014. It is found that the EUV flux is most suitable for solar activity dependence of ionization with correlation coefficient of 0.83. The EUV flux and 10.7 cm flux also show the saturation in ionization production. © Anita publications. All rights reserved.

Total Refs : 23

Vol. 24, No 6 (2015) 843-850

Electromagnetic precursor in the ionosphere associated with the Bhuj Earthquake of 26 January, 2001

 

Som Sharma and H Chandra

Physical Research Laboratory, Ahmedabad- 380 009, India

There have been several studies reporting perturbations in the ionosphere prior to the onset of major earthquakes. However, the monitoring of the ionosphere as a precursor to seismic activity is yet to be established. There was a major earthquake with a magnitude of 7.7 in Richter scale, in Bhuj in Gujarat, India at 0825 LT of January 26, 2001. The epicenter of the seismic activity was in Bhuj (23.3o N, 70.3o E), situated around 250 km west of Ahmedabad (23.1o N, 72.4o E). Physical Research Laboratory (PRL) regularly operates an ionosonde at Ahmedabad with quarter hourly recordings. We have examined critical frequency (f_oF₂) of the F₂ region and f_oE_s during the period January 16-26, 2001 to investigate perturbations and anomalies prior to the seismic activity. Normalized devations in f_oF₂ during this period revealed ~ 50 % fluctuation on 22 January 2001 which is about 25 % higher than the normal days variations. Strong spread in the sporadic E layers in the morning hours on 22 January has been found with increased f_oE_s. The observed changes are likely due to the seismic effects. © Anita Publications. All rights reserved.

Keywords: Earthquakes, Ionosphere, Geo-stationary satellites, GPS

 Vol. 24, No 6 (2015) 851-867

VHF scintillations at the Indian low latitudes

 

VHF scintillations were recorded at a chain of low-latitude stations in India as part of the All India Coordinated Program of Ionospheric and Thermospheric Studies (AICPITS), using the 244 MHz radio beacon from the geo-stationary satellite FLEETSAT which was located at 73º E longitude. In addition to regular operation at each of the stations, data were collected during three campaigns of March-April 1991, September-October 1991 and February-March 1993. The campaign data were analyzed jointly by the participating investigators. The nocturnal variations of the mean occurrence of scintillations and the latitudinal variations of the mean occurrence at different local times were studied and the latitudinal extent of the equatorial belt of scintillation estimated. Maximum monthly mean occurrence was highest at stations close to dip equator and decreased with increasing latitude. The onset times of scintillation at pairs of stations at similar latitude but different longitudes were used to estimate the eastward drift of the scintillation patches and its E-W extent. The delays in the onset time of scintillation at different latitudes were used to estimate the vertical bubble rise velocities at different altitude ranges near magnetic equator. Dependence of scintillation occurrence on geomagnetic activity and effects on individual geomagnetic storms were also studied. From the digital data recorded at some stations, spectral indices of the ionospheric irregularities causing scintillations were obtained. © Anita Publications. All rights reserved.

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  Vol. 24, No 6 (2015) 869-873

Effect of interplanetary magnetic field on ionospheric drift

 

M Mittal¹, H Chandra² and P Sharma¹

¹Govt. Holkar Science College, Indore-452 017, India

² Physical Research Laboratory, Ahmedabad -380 009, India

Ionospheric drift measurements made at Thumba, close to magnetic equator, Udaipur a low latitude station and Irkutsk, a high latitude station during 1973-1975 are examined for the effect of interplanetary magnetic field. Results show that the effect of interplanetary magnetic field on the midday E-region as well as midnight F-region drift speed shows decrease of zonal drift at low/equatorial latitudes and increase of zonal drift at high latitudes with increasing southward IMF-Bz. ©Anita Publications. All rights reserved.

Keywords: Magnetic field, Geomagnetic activity index

  Vol. 24, No 6 (2015) 875-883

Stydy of the sporadic E layer during low and high sunspot activity  years over Ahmedabad

 

Som Sharma, H Chandra and Rajesh Vaishnav

Physical Reseasrch Laboratory, Ahmedabad-380 009, India

Sporadic E layers are mainly formed by wind shear mechanism in the presence of sufficient ionozation and ions and electrons of meterioc orgin, but their formation and dynamics are governed also by ionospheric electrodynamic processes. A study of sporadic E has been carried out using critical frequency, f_oE_s, over Ahmedabad (23.1°N, 72.7°E), India utilizing Ionosonde observations. Association between occurrence of Es, f_oE_s and solar activity (low sunspot years and high sunspot years) have also been examined. The occurrence of E_s layer is solar activity dependent, with the E_s occurrence being high during the low sunspot activity years and low during high sunspot activity years. It is found that the value of f_oE_s is higher during noon time than in the morning and evening hours. Seasonally higher percentage occurrence is found during December than in July. Minimum occurrence is found during the month of April. The f_oE_s < 3MHz has been observed before sunrise for all the months during low and high sunspot activity years. © Anita publications. All rights reserved.

Key Words: Low and high sunspot activity, Sporadic E layers

Total Refs: 43