Options
Venkatesh, K.
Loading...
Preferred name
Venkatesh, K.
5 results
Now showing 1 - 5 of 5
- PublicationRestrictedBottom side profiles for two close stations at the southern crest of the EIA: Differences and comparison with IRI-2012 and NeQuick2 for low and high solar activity(2018-01)
; ; ; ; ; ; ; ;; ; ; ; ;Bottom side electron density profiles for two stations at the southern crest of the Equatorial Ionization Anomaly (EIA), Sao José dos Campos (23.1°S, 314.5°E, dip latitude 19.8°S; Brazil) and Tucuman (26.9°S, 294.6°E, dip latitude 14.0°S; Argentina), located at similar latitude and separated by only 20° in longitude, have been compared during equinoctial, winter and summer months under low (year 2008, minimum of the solar cycle 23/24) and high solar activity (years 2013–2014, maximum of the solar cycle 24) conditions. An analysis of parameters describing the bottom side part of the electron density profile, namely the peak electron density NmF2, the height hmF2 at which it is reached, the thickness parameter B0 and the shape parameter B1, is carried out. Further, a comparison of bottom side profiles and F-layer parameters with the corresponding outputs of IRI-2012 and NeQuick2 models is also reported. The variations of NmF2 at both stations reveal the absence of semi-annual anomaly for low solar activity (LSA), evidencing the anomalous activity of the last solar minimum, while those related to hmF2 show an uplift of the ionosphere for high solar activity (HSA). As expected, the EIA is particularly visible at both stations during equinox for HSA, when its strength is at maximum in the South American sector. Despite the similar latitude of the two stations upon the southern crest of the EIA, the anomaly effect is more pronounced at Tucuman than at Sao José dos Campos. The differences encountered between these very close stations suggest that in this sector relevant longitudinal-dependent variations could occur, with the longitudinal gradient of the Equatorial Electrojet that plays a key role to explain such differences together with the 5.8° separation in dip latitude between the two ionosondes. Furthermore at Tucuman, the daily peak value of NmF2 around 21:00 LT during equinox for HSA is in temporal coincidence with an impulsive enhancement of hmF2, showing a kind of ‘‘elastic rebound” under the action of the EIA. IRI-2012 and NeQuick2 bottom side profiles show significant deviations from ionosonde observations. In particular, both models provide a clear underestimation of the EIA strength at both stations, with more pronounced differences for Tucuman. Large discrepancies are obtained for the parameter hmF2 for HSA during daytime at Sao José dos Campos, where clear underestimations made by both models are observed. The shape parameter B0 is quite well described by the IRI-2012 model, with very good agreement in particular during equinox for both stations for both LSA and HSA. On the contrary, the two models show poor agreements with ionosonde data concerning the shape parameter B1.252 8 - PublicationRestrictedIonospheric disturbances in a large area of the terrestrial globe by two strong solar flares of September 6, 2017, the strongest space weather events in the last decade(2020-07)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; On September 6, 2017, the solar active region AR 2673 emitted two solar flares: the first at 08:57 UT (X2.2) and the second at 11:53 UT (X9.3); both were powerful enough to black-out high and low frequency radio waves (where UT is universal time). The X9.3 was the strongest solar flare event in the past decade. In this study, we took the advantage of these two extreme flare events to investigate corresponding effects on the ionosphere using multi-instrument observations from magnetometers, Global Positioning System – Total Electron content (GPS-TEC) receivers, ionosondes and Swarm satellites over a large geographical extent covering South American, African and European sectors. During the X2.2 flare, European and African sectors were sunlit and during X9.3 European, African, and South American sectors were sunlit and exposed to the solar flare radiation. During the X2.2 flare, there was an ionosonde blackout for a duration of about 45 min, while during the X9.3 flare this blackout lasted for 1 h and 30 min. The blackout are seen over a large global extent which demonstrates the severity of solar flare events in disrupting the radio communication. The horizontal component of Earth’s geomagnetic field has shown ripples and enhancements during these flare events. The ionospheric Vertical Total Electron Content (VTEC) showed a positive phase along with an intensification of the Equatorial Ionization Anomaly (EIA) over the South American and African sectors. The dynamical and physical processes associated with the TEC and EIA variabilities due to solar flare are discussed.217 4 - PublicationOpen AccessStudy of the F3 and StF4 Layers at Tucumán Near the Southern Crest of the Equatorial Ionization Anomaly in Western South America(2018-03)
; ; ; ; ; ; ; ; ; ; ; ; ; The present investigation reports for the first time seasonal and solar activity variations of F3 and StF4 layers at the low-latitude station of Tucumán (26.9°S, 65.4°W; dip latitude 13.9°S), Argentina, by considering ionograms recorded from 2007 to 2015 by an Advanced Ionospheric Sounder-Istituto Nazionale di Geofisica e Vulcanologia (AIS-INGV) digital ionosonde. Occurrences of F3 and StF4 layers are found to be higher during summer months, while they are almost nil in winter. Moreover, occurrences of F3 and StF4 layers show a solar activity dependence with higher values during high solar activity. The solar activity dependence of F3 over Tucumán is similar to that reported earlier for the low-latitude station of São José dos Campos, Brazil (dip latitude 14.1°S), but different than that reported for the near-equatorial station of Palmas (dip latitude 6.6°S), Brazil. On the other hand, the solar cycle dependence of StF4 layer is consistent with the one obtained at Palmas. This highlights the complex nature of electrodynamics characterizing the ionosphere from the magnetic equatorial to low latitudes. Moreover, as shown in previous studies, the StF4 layer is always preceded and followed by the F3 layer, and it shows a shorter lifetime than that of the F3 layer. During the considered period, 1812 days were analyzed and the F3 layer was found in 370 days (20.4%), while the StF4 layer was found in 41 days (2.3%). This means that the StF4 stratification is seen during 11% of F3 layer days.165 88 - PublicationOpen AccessIonospheric response to the 2009 sudden stratospheric warming over the equatorial, low, and middle latitudes in the South American sector(2015)
; ; ; ; ; ; ; ; ; ;Fagundes, P. R.; Universidade do Vale do Paraíba (UNIVAP) ;Goncharenko, L. P.; Massachusetts Institute of Technology ;de Abreu, A. J.; Universidade do Vale do Paraíba (UNIVAP) ;Venkatesh, K.; Universidade do Vale do Paraíba (UNIVAP) ;Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;de Jesus, R.; Universidade do Vale do Paraíba (UNIVAP) ;Gende, M.; Universidad Nacional de La Plata ;Coster, A. J.; Massachusetts Institute of Technology ;Pillat, V. G.; Universidade do Vale do Paraíba (UNIVAP) ;; ; ; ; ; ; ; The present study investigates the ionospheric total electron content (TEC) and F-layer response in the Southern Hemisphere equatorial, low, and middle latitudes due to major sudden stratospheric warming (SSW) event, which took place during January–February 2009 in the Northern Hemisphere. In this study, using 17 ground-based dual frequency GPS stations and two ionosonde stations spanning latitudes from 2.8°N to 53.8°S, longitudes from 36.7°W to 67.8°W over the South American sector, it is observed that the ionosphere was significantly disturbed by the SSW event from the equator to the midlatitudes. During day of year 26 and 27 at 14:00 UT, the TEC was two times larger than that observed during average quiet days. The vertical TEC at all 17 GPS and two ionosonde stations shows significant deviations lasting for several days after the SSWtemperature peak. Using one GPS station located at Rio Grande (53.8°S, 67.8°W, midlatitude South America sector), it is reported for the first time that the midlatitude in the Southern Hemisphere was disturbed by the SSW event in the Northern Hemisphere.419 281 - PublicationOpen AccessSeasonal and solar activity variations of F3 layer and quadruple stratification (StF-4) near the equatorial region(2016-12-20)
; ; ; ; ; ;Tardelli, A.; Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, Brazil ;Fagundes, P. R.; Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, Brazil ;Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Pillat, V. G.; Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, Brazil ;Venkatesh, K.; Universidade do Vale do Paraíba (UNIVAP), São José dos Campos, Brazil; ;; ; The study of multiple stratification of the F layer has the initial records in the midtwentieth century. Since then, many studies were focused on F3 layer. The diurnal, seasonal, and solar activity variations of the F3 layer characteristics have been investigated by several researchers. Recently, investigations on multiple stratifications of F layer received an important boost after the quadruple stratification (StF-4) was observed at Palmas (10.3°S, 48.3°W; dip latitude 6.6°S—near-equatorial region), Brazil. The present study reports the latest findings related with the seasonal and solar activity characteristics of the F3 layer and StF-4 near the equatorial region during the period from 2002 to 2006. A significant connection between StF-4 and F3 layer has been noticed, since the StF-4 is always preceded and followed by a F3 layer appearance. However, the F3 layer and the StF-4 present different seasonal and solar cycle variations. At a near-equatorial station Palmas, the F3 layer shows the maximum and minimum occurrences during summer and winter seasons, respectively. On the contrary, the StF-4 presents the maximum and minimum occurrences during winter and summer seasons, respectively. While the F3 layer occurrence is not affected by solar cycle, the StF-4 appearance is instead more frequent during high solar activity.124 180