SHARAD CHANDRA TRIPATHI
@vitbhopal.ac.in
Assistant Professor, School of Advanced Sciences and Languages
VIT Bhopal University
RESEARCH INTERESTS
Space Weather, Solar Physics, Ionospheric Physics, Earth System Science
Scopus Publications
Scholar Citations
Scholar h-index
Scopus Publications
B Suresh Babu, Pradeep Kayshap, Sharad C Tripathi, P Jelínek, and B N Dwivedi
Oxford University Press (OUP)
ABSTRACT Statistically, the cool loop’s footpoints are diagnosed using Si iv resonance lines observations provided by Interface Region Imaging Spectrograph (IRIS). The intensity and full width at half-maximum (FWHM) of the loop’s footpoints in β–γ active regions (ARs) are higher than the corresponding parameters of footpoints in β ARs. However, the Doppler velocity of footpoints in both ARs are almost similar to each other. The intensities of footpoints from β–γ AR is found to be around nine times that of β AR when both ARs are observed nearly at the same time. The same intensity difference reduces nearly to half (four times) when considering all ARs observed over 9 yr. Hence, the instrument degradation affects comparative intensity analysis. We find that Doppler velocity and FWHM are well correlated while peak intensity is neither correlated with Doppler velocity nor FWHM. The loop’s footpoints in β–γ ARs have around four times more complex Si iv spectral profiles than that of β ARs. The intensity ratios (Si iv 1393.78 Å/1402.77 Å) of the significant locations of footpoints differ, marginally, (i.e. either less than 1.9 or greater than 2.10) from the theoretical ratio of 2, i.e. 52 per cent (55 per cent) locations in β (β–γ) ARs significantly deviate from 2. Hence, we say that more than half of the footpoint locations are either affected by the opacity or resonance scattering. We conclude that the nature and attributes of the footpoints of the cool loops in β–γ ARs are significantly different from those in β ARs.
Bhupendra Malvi, Sharad C. Tripathi, and P. K. Purohit
Cambridge University Press (CUP)
AbstractAn analysis of geomagnetic disturbances and global ionospheric electron density perturbations during the 2015 St. Patrick’s Day geomagnetic storm is presented in this paper. GPS observations from worldwide IGS stations are used and analysed through GPS-TEC analysis application developed by Gopi Seemala to get VTEC profiles. The St. Patrick’s geomagnetic storm covers the interval of 15-23 March 2015, when transient solar eruptions (a prolonged C9-class solar flare and associated CMEs on 15 March) and a strong geomagnetic storm during 16-18 March (Dst dropped to -223 nT) were reported. This geomagnetic storm led to complex effects on the ionosphere. The global maps have been created after analysing VTEC profiles at Low, Mid and High-latitudes over different longitudinal sectors. Major features of the positive and negative ionospheric storm development are observed in Asian, European and American Low, Mid and High-latitudes.
Pradeep Kayshap, Rajdeep Singh Payal, Sharad C Tripathi, and Harihara Padhy
Oxford University Press (OUP)
ABSTRACT Surges have regularly been observed in mostly H α 6563 Å and Ca ii 8542 Å. However, surge responses to other prominent lines of the interface region (Mg ii k 2796.35 Å and h 2803.52 Å, O iv 1401.15 Å, Si iv 1402.77 Å) are not well studied. Here, the evolution and kinematics of six homologous surges are analysed using IRIS and AIA observations. These surges were observed on 2014 July 7 and were located very close to the limb. A differential emission measure analysis is performed on these surges where the coexistence of cool (log T/K = 6.35) and relatively hot (log T/K = 6.95) components has been found at the base. This demonstrates that the bases of surges undergo substantial heating. During the emission of these surges in the above-mentioned interface-region lines, reported here for the first time, two peaks have been observed in the initial phase of emission, where one peak is found to be constant while other one varies; i.e. is non-constant (observed red- to blueshifts across the surge evolution) in nature. This suggests the rotational motion of surge plasma. The heated base and rotating plasma suggest the occurrence of magnetic reconnection as the most likely trigger for homologous surges. During the emission of these surges, it is found that, despite them being optically thick (i.e. Rkh < 2.0), central reversal was not observed for the Mg ii k and h lines. Further, Rkh increases with surge emission in time and it is found to have a positive correlation with Doppler velocity and negative with Gaussian width.
P K Purohit, Azad A Mansoori, Parvaiz A Khan, Roshni Atulkar, Purushottam Bhawre, Sharad C Tripathi, Prakash Khatarkar, Shivangi Bhardwaj, A M Aslam, Malik A Waheed,et al.
IOP Publishing
The geomagnetic storm represents the most outstanding example of solar wind- magnetospheric interaction, which causes global disturbances in the geomagnetic field as well as triggers ionospheric disturbances. We study the behaviour of ionospheric Total Electron Content (TEC) during the geomagnetic storms. For this investigation we have selected 47 intense geomagnetic storms (Dst ≤ -100nT) that were observed during the solar cycle 23 i.e. during 1998- 2006. We then categorized these storms into four categories depending upon their solar sources like Magnetic Cloud (MC), Co-rotating Interaction Region (CIR), SH+ICME and SH+MC. We then studied the behaviour of ionospheric TEC at a mid latitude station Usuda (36.13N, 138.36E), Japan during these storm events produced by four different solar sources. During our study we found that the smooth variations in TEC are replaced by rapid fluctuations and the value of TEC is strongly enhanced during the time of these storms belonging to all the four categories. However, the greatest enhancements in TEC are produced during those geomagnetic storms which are either caused by Sheath driven Magnetic cloud (SH+MC) or Sheath driven ICME (SH+ICME). We also derived the correlation between the TEC enhancements produced during storms of each category with the minimum Dst. We found the strongest correlation exists for the SH+ICME category followed by SH+MC, MC and finally CIR. Since the most intense storms were either caused by SH+ICME or SH+MC while the least intense storms were caused by CIR, consequently the correlation was strongest with SH+ICME and SH+MC and least with CIR.
P. K. Purohit, Azad A. Mansoori, Parvaiz A. Khan, Purushottam Bhawre, Sharad C. Tripathi, A. M. Aslam, Malik A. Waheed, and A. K. Gwal
IEEE
The geomagnetic storm represents the most outstanding example of solar wind- magnetospheric interaction, which causes global disturbances in the geomagnetic field as well as the trigger ionospheric disturbances. Under this problem we study the behaviour of ionospheric Total Electron Content (TEC) during the geomagnetic storms. For the present investigation we have selected 47 intense geomagnetic storms (Dst ≤ -100nT) that during the solar cycle 23 i.e. during 1998- 2006. We then categorized these storms into four categories depending upon their solar sources like Magnetic Cloud (MC), Co-rotating Interaction Region (CIR), SH+ICME and SH+MC. We then studied the behaviour of ionospheric TEC at a mid latitude station Usuda (), Japan during these storm events. During our study we found that the smooth variations in TEC are replaced by rapid fluctuations and the value of TEC is strongly enhanced during the time of these storms belonging to all the four categories. However, the greatest enhancements in TEC are produced during those geomagnetic storms which are either caused by Sheath driven Magnetic cloud (SH+MC) or Sheath driven ICME (SH+ICME). We also derived the correlation between the TEC enhancements produced during storms of each category with the minimum Dst. We found the the strongest correlation exists for the SH+ICME category followed by SH+MC, MC and finally CIR. Since the most intense storms were either caused by SH+ICME or SH+MC while the least intense storms were caused by CIR, consequently the correlation was strongest with SH+ICME and SH+MC and least with CIR.
Parvaiz A. Khan, Sharad C. Tripathi, O. A. Troshichev, Malik A. Waheed, A. M. Aslam, and A. K. Gwal
Springer Science and Business Media LLC
Geomagnetic field variations during five major Solar Energetic Particle (SEP) events of solar cycle 23 have been investigated in the present study. The SEP events of 1 October 2001, 4 November 2001, 22 November 2001, 21 April 2002 and 14 May 2005 have been selected to study the geomagnetic field variations at two high-latitude stations, Thule (77.5∘ N, 69.2∘ W) and Resolute Bay (74.4∘ E, 94.5∘ W) of the northern polar cap. We have used the GOES proton flux in seven different energy channels (0.8–4 MeV, 4–9 MeV, 9–15 MeV, 15–40 MeV, 40–80 MeV, 80–165 MeV, 165–500 MeV). All the proton events were associated with geoeffective or Earth directed CMEs that caused intense geomagnetic storms in response to geospace. We have taken high-latitude indices, AE and PC, under consideration and found fairly good correlation of these with the ground magnetic field records during the five proton events. The departures of the H component during the events were calculated from the quietest day of the month for each event and have been represented as ΔHTHL and ΔHRES for Thule and Resolute Bay, respectively. The correspondence of spectral index, inferred from event integrated spectra, with ground magnetic signatures ΔHTHL and ΔHRES along with Dst and PC indices have been brought out. From the correlation analysis we found a very strong correlation to exist between the geomagnetic field variation (ΔHs) and high-latitude indices AE and PC. To find the association of geomagnetic storm intensity with proton flux characteristics we derived the correspondence between the spectral indices and geomagnetic field variations (ΔHs) along with the Dst and AE index. We found a strong correlation (0.88) to exist between the spectral indices and ΔHs and also between spectral indices and AE and PC.
Sharad C. Tripathi, Parvaiz A. Khan, A. M. Aslam, A. K. Gwal, P. K. Purohit, and Rajmal Jain
Springer Science and Business Media LLC
We probe the spectral hardening of solar flares emission in view of associated solar proton events (SEPs) at earth and coronal mass ejection (CME) acceleration as a consequence. In this investigation we undertake 60 SEPs of the Solar Cycle 23 along with associated Solar Flares and CMEs. We employ the X-ray emission in Solar flares observed by Reuven Ramaty Higly Energy Solar Spectroscopic Imager (RHESSI) in order to estimate flare plasma parameters. Further, we employ the observations from Geo-stationary Operational Environmental Satellites (GOES) and Large Angle and Spectrometric Coronagraph (LASCO), for SEPs and CMEs parameter estimation respectively. We report a good association of soft-hard-harder (SHH) spectral behavior of Flares with occurrence of Solar Proton Events for 16 Events (observed by RHESSI associated with protons). In addition, we have found a good correlation (R=0.71) in SEPs spectral hardening and CME velocity. We conclude that the Protons as well as CMEs gets accelerated at the Flare site and travel all the way in interplanetary space and then by re-acceleration in interplanetary space CMEs produce Geomagnetic Storms in geospace. This seems to be a statistically significant mechanism of the SEPs and initial CME acceleration in addition to the standard scenario of SEP acceleration at the shock front of CMEs.
Rajmal Jain, Arun K. Awasthi, Sharad C. Tripathi, Nipa J. Bhatt, and Parvaiz A. Khan
Elsevier BV
Sharad C. Tripathi, Parwaiz A. Khan, Azad Ahmad, Purushottam Bhavre, P.K. Purohit, and A.K. Gwal
IEEE
When the Sun starts flaring, the Earth's atmosphere receives increased amounts of X-ray and EUV fluxes. Consequently ionospheric ionization/absorption gets increased in a cause-effect relation during solar flares and CMEs. Moreover the extent of impact is different in different regions of the ionosphere. To establish the magnitude of correlation and extent of impact in different layers, data of X-ray intensity from geostationary satellite GOES and ionospheric parameter data (D & F layer) from Ionosonde over Okinawa (Japan) station (lat.26.3°N, long.158.7°E) were examined for ten X-class flares that occurred during the maximum phase of solar cycle 23 from 2000 to 2004. The data analysis revealed a positive and good correlation between fmin and X-ray intensity for D layer and NmF2 for F layer. However the correlation coefficient between fmin and X-ray intensity was found to be greater than between NmF2 and X-ray intensity. Which suggest that X-rays play a dominant role in D layer ionization than that in F layer.