Vattikuti Rajesh Chowdhary
@ait.ac.th
Asian Institute of Technology, Bangkok, Thailand
Scopus Publications
Scopus Publications
Raghavendra Neeli, J R K Kumar Dabbakuti, V. Rajesh Chowdhary, Nitin K. Tripathi, and Venkata Ratnam Devanaboyina
Springer Science and Business Media LLC
Singular Value Decomposition (SVD) model is implemented to recognize the Total Electron Content (TEC) time series of daily, temporal as well as seasonal characteristics throughout the 24th solar cycle period of the year 2015 in the study. The Vertical (vTEC) analysis has been carried out with Global Positioning System (GPS) data sets collected from five stations from India namely GNT, Guntur (16.44∘ N, 80.62∘ E), and IISC, Bangalore (12.97∘ N, 77.59∘ E), LCK2, Lucknow (26.76∘ N, 80.88∘ E), one station from Thailand namely AITB, Bangkok (14.07∘ N, 100.61∘ E), and one station from South Andaman Island namely PBR, Port Blair (11.43∘ N, 92.43∘ E), located in low latitude region. The first five singular value modes constitute about 98% of the total variance, which are linearly transformed from the observed TEC data sets. So it is viable to decrease the number of modeling parameters. The Fourier Series Analysis (FSA) is carried out to characterize the solar-cycle, annual and semi-annual dependences through modulating the first three singular values by the solar (F10.7) and geomagnetic (Ap) indices. The positive correlation coefficient (0.75) of daily averaged GPS–TEC with daily averaged F10.7 strongly supports the temporal variations of the ionospheric features depends on the solar activity. Further, the significance and reliability of the SVD model is evaluated by comparing it with GPS–TEC data and the standard global model (Standard Plasma-Spherical Ionospheric Model, SPIM and International Reference Ionosphere, IRI 2016).
Puram Sai Suraj, J. R. K. Kumar Dabbakuti, V. Rajesh Chowdhary, Nitin K. Tripathi, and D. Venkata Ratnam
Springer Science and Business Media LLC
This paper proposes a linear time series model to represent the climatology of the ionosphere and to investigate the characteristics of hourly averaged total electron content (TEC). The GPS–TEC observation data at the Bengaluru international global navigation satellite system (GNSS) service (IGS) station (geographic $$13.02^{\\circ }\\hbox {N}$$13.02∘N, $$77.57^{\\circ }\\hbox {E}$$77.57∘E; geomagnetic latitude $$4.4^{\\circ }\\hbox {N}$$4.4∘N) have been utilized for processing the TEC data during an extended period (2009–2016) in the $$24{\\mathrm{th}}$$24th solar cycle. Solar flux F10.7p index, geomagnetic Ap index, and periodic oscillation factors have been considered to construct a linear TEC model. It is evident from the results that solar activity effect on TEC is high. It reaches the maximum value ($$\\sim $$∼ 40 TECU) during the high solar activity (HSA) year (2014) and minimum value ($$\\sim $$∼ 15 TECU) during the low solar activity (LSA) year (2009). The larger magnitudes of semiannual variations are observed during the HSA periods. The geomagnetic effect on TEC is relatively low, with the highest being $$\\sim $$∼ 4 TECU (March 2015). The magnitude of periodic variations can be seen more significantly during HSA periods (2013–2015) and less during LSA periods (2009–2011). The correlation coefficient of 0.89 between the observations and model-based estimations has been found. The RMSE between the observed TEC and model TEC values is 4.0 TECU (linear model) and 4.21 TECU (IRI2016 Model). Further, the linear TEC model has been validated at different latitudes over the northern low-latitude region. The solar component (F10.7p index) value decreases with an increase in latitude. The magnitudes of the periodic component become less significant with the increase in latitude. The influence of geomagnetic component becomes less significant at Lucknow GNSS station $$(26.76^{\\circ }\\hbox {N}, 80.88^{\\circ }\\hbox {E})$$(26.76∘N,80.88∘E) when compared to other GNSS stations. The hourly averaged TEC values have been considered and ionospheric features are well recovered with linear TEC model.
G Sivavaraprasad, Yuichi Otsuka, Nitin Kumar Tripathi, V Rajesh Chowdhary, D Venkata Ratnam, and Mohammed Afzal Khan
IEEE
The study and understanding of the intermittent characteristics of equatorial and low latitude ionosphere is crucial for modelling and forecasting the ionosphere and space weather conditions. The performance of space-based navigation systems such as Global Positioning System (GPS) is affected by the sporadic temporal and spatial variations of ionospheric Total Electron Content (TEC). The variability of ionospheric electron density over Indian low latitude sector is difficult to model due to Equatorial Ionization Anomaly (EIA). In this paper, Multi-fractal aspects of the GPS measured TEC is investigated during both high and low solar activity periods of 24th solar cycle. The vertical TEC (VTEC) data sets are obtained from two Indian low latitude stations namely, Bangalore (Geographical Latitude: 13.020 N, Geographical Longitude: 77.57o E), and Lucknow (Geographical Latitude: 26.830 N, Geographical Longitude: 80.92o E) for two year long period 2013 and 2015. The experimental results shows that the respective geographic sites have important scaling differences as well as similarities when their Multi-fractal signatures for VTEC are compared. These differences and similarities are interpreted in terms of the EIA conditions, where this phenomenon is an important source of intermittence due to the presence of the VTEC peaks at ±300 geomagnetic latitudes. During the high solar activity period, the intermittence characteristics of VTEC over EIA region (Lucknow) are relatively more complex than equatorial (Bengaluru) station, whereas during low solar activity period the scenario is reciprocal.
V. Chowdhary, N. Tripathi, Sanit Arunpold and D. Raju
This paper presents the first results of vertical total electron content (VTEC) data from (1) a dual-frequency GPS receiver installed at the Chiang Mai University in Chiang Mai (CHGM, 18.480 N, 98.570 E) as part of SCINDA (Scintillation Network and Decision Aid) and (2) the International GNSS Service (IGS) station Pathum Wan ( CUSV, 13.735 N, 100.533 E ) with magnetic latitude of 8.69°N and 3.92°N respectively in Thailand, from August 2010 to July 2012. In the equatorial ionization anomaly (EIA) region, these two stations are separated at a distance of 668 km. Observed GPS-TEC values were found to be the highest between 1500 and 1900 Local Time (LT) throughout the study period at both the stations. The GPS-TEC data from both the stations was plotted diurnal, monthly and seasonal analyses were performed. The equinox (March, April, September, and October) and solstice (January, February, June, July, and December) periods had maximum and minimum diurnal peak variations, respectively, of the GPS-TEC. High TEC values are attributed to extreme solar ultra-violet ionization coupled with upward vertical E×B drift. A comparison of the GPS-TEC data from both the stations for the study period shows that the CHGM station recorded higher values of TEC than the CUSV station because of the formation of an ionization crest over the CHGM station. The GPS-TEC values also exhibited an increasing trend-because of the approach of solar cycle 24. For data validation, the diurnal, monthly, and seasonal variations in the measured TEC were compared with the TEC modelled in the International Reference Ionosphere (IRI) models (IRI-2007 and the recently released IRI-2012 model). The IRI-2007 shows good agreement with the data from 2010 to 2011 from both stations and IRI-2012 agrees well with the data from 2012 onwards compared to IRI-2007.
V. Rajesh Chowdhary, N.K. Tripathi, Sanit Arunpold, and Durairaju Kumaran Raju
Elsevier BV
Abstract This paper presents the first results of total electron content (TEC), derived by analyzing dual frequency Novatel GSV4004 GPS receiver’s data which were installed by the SCINDA project, located at the Asian Institute of Technology, Bangkok (AITB, 14.079N, 100.612E) and Chiang Mai University, Chiang Mai (CHGM, 18.480N, 98.570E) with magnetic latitude of 4.13°N and 8.61°N respectively in Thailand, for the year 2011. These two stations are separated by 657 km in the equatorial anomaly region. The highest TEC values occurred from 1500 to 1900 LT throughout the study period. The diurnal, monthly and seasonal GPS-TEC have been plotted and analyzed. The diurnal peaks in GPS-TEC is observed to be maximum during equinoctial months (March, April, September and October) and minimum in solstice months (January, February, June, July and December). These high TEC values have been attributed to the solar extreme ultra-violet ionization coupled with the upward vertical E × B drift. A comparison of both station’s TEC has been carried out and found that CHGM station experiences higher values of TEC than AITB station, due to formation of ionization crest over the CHGM station. Also, TEC values have shown increasing trend due to approaching solar maximum. These results from both stations were also compared with the TEC derived from the International Reference Ionosphere’s (IRI) recently released, IRI-2012 model. Results have shown positive correlation with IRI-2012 model. Although, IRI-model does not show any response to geomagnetic activity, the IRI model normally remains smooth and underestimates TEC during a storm.
Sanit Arunpold, Nitin K. Tripathi, V. Rajesh Chowdhary, and Durairaju Kumaran Raju
Elsevier BV
This paper presents the first vertical total electron content (VTEC) data derived from a dual-frequency GPS receiver installed at the Asian Institute of Technology in Bangkok, as part of project SCINDA (Scintillation Network and Decision Aid) with a magnetic dip latitude of 14°N, The diurnal, monthly, and seasonal variation in TEC, measured between August 2010 and July 2012, was compared with values derived from two International Reference Ionosphere (IRI) models: the IRI-2007 and the recently released IRI-2012. The highest diurnal TEC always occurred between 08:00 and 12:00 Universal Time (UT). The diurnal pattern of GPS-TEC reached its maximum values during equinoctial months (March, April, September, and October) and minimum values during solstice months (June, July, December, and January), which can be attributed to the solar extreme ultra-violet ionization coupled with the upward vertical E×B drift. The modeled TEC was underestimated in 2010 and 2011 and overestimated in 2012, especially with the IRI-2007 model. The measured values were better correlated with the IRI-2012 model, especially in 2012. However, neither of the IRI models responded to geomagnetic activity, despite the selection of the “storm” option, generally showing a smooth curve and underestimating TEC during a storm. To verify this phenomenon, the impacts of geomagnetic storms were considered.