• H Chandra

      Articles written in Journal of Earth System Science

    • Effect of filtering on drift and anisotropy parameters determined by full correlation analysis

      H Chandra

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      The effect of low-pass filtering on the various drift and anisotropy parameters obtained by full correlation analysis of spaced receiver records is studied theoretically, assuming Gaussian correlation functions. A decrease in the characteristic velocityVcis shown with increasing filtering, unlessV ≫ Vv, whenVcincreases with filtering. The ratioVc/V however shows an increase as the decrease in the true drift velocityV is steeper thanVc. An increase in the size of the ground pattern with increasing filtering is also shown, while the axial ratio for anisotropic patterns shows a decrease. The results are verified with experimental data recorded earlier at Tiruchirapalli.

    • Equatorial electrojet in east Brazil longitudes

      R G Rastogi H Chandra K Yumuto

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      This paper describes the morphology of the equatorial electrojet (EEJ) along 45°W longitude in east Brazil, where the ground magnetic (dip) equator is associated with the largest declination in the world. Daily range of the horizontal field (𝛿 𝐻), as expected, was largest at the station in the chain closest to the dip equator, Sao Luiz (inclination $−$0.25°S). 𝛿 𝑍 was largest positive at Eusebio (inclination 9.34°S) and largest negative at Belem (inclination 7.06°N); both near the fringe of EEJ belt. 𝛿 𝑍 at Sao Luiz during the daytime was unexpectedly large negative in-spite of a small dip and also located south of the dip equator where 𝛿 𝑍 should be positive. Center of EEJ was found to be shifted southward of the dip equator by about 1° in latitude. During southern summer, 𝛥 𝑌 started decreasing from 00 h and reached a minimum value in the afternoon, an abnormal feature not discussed for any station so far. The mid-day value of the direction of 𝛥 𝐻 vector was 22°-24°W compared to the declination of 19°$–$21°W in the region.

    • Equatorial electrojet in the south Atlantic anomaly region

      R G Rastogi H Chandra N B Trivedi V Doumbia

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      Features of the equatorial electrojet are studied at Sao Luiz (2.6°S, 44.2°W, inclination $−$0.25°) in eastern Brazil and Sikasso (11.3°N, 5.7°W, inclination 0.1°) in the western African sector. The stations are situated on either side of the lowest magnetic field intensity in the region of rapid changes in the declination. The daily variations of 𝛥 X at the two stations are almost similar with the peak around noon with maximum values during equinoxes and minimum values during J-solstices. Daily variations of 𝛥 Y differ with the maximum deviation of about −35 nT around noon at Sao Luiz and much smaller value of about −10 nT around 14 h LT for Sikasso. The direction of the 𝐻 vector varies from 15°W of north at 08 h to more than 30°W of north at 17 h for Sao Luiz and from 14°E of north to 25°W of north at 18 h for Sikasso. The plot of the deviations in 𝛥 X and 𝛥 Y at different hours for the two stations shows the points along narrow ellipses with major axis aligned along 22°W of north for Sao Luiz and along 3°W of north for Sikasso as compared to declination of 20°W for Sao Luiz and 6°W for Sikasso. The deviations in 𝛥 X at the two stations are fairly well correlated.

    • Abnormally large magnetospheric electric field on 9 November 2004 and its effect on equatorial ionosphere around the world

      R G Rastogi H Chandra Louis Condori M A Abdu B Reinisch R T Tsunoda D S V V D Prasad T K Pant T Maruyama

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      There was a solar event around 1850 UT on 9th November 2004, associated with an abnormally large solar wind flow pressure and large southward interplanetary magnetic field, causing an abnormally large prompt penetration electric field between 1850 and 2100 UT. Abnormally large vertical F-region drifts by Jicamarca backscatter radar were reported associated with the event. The F-region over Jicamarca, Peru (14–16 LT) and Sao Luis, Brazil (16–18 LT) was lifted upward, broken into two portions and the upper one was blown out of the range of the ionosonde. At Fortaleza, an off-equatorial station in Brazil, the F-region was also lifted up but later the $f_\circ F_2$ increased due to the flow of ionization from upper layer blown up over the equatorial region. The F-region at Ascension Island (19–21 LT), an off-equatorial station, was lifted up without any deformations till 1915 LT but descended at 1930 LT due to reversal of electric field polarity. At Indian stations, Trivandrum and Waltair (00–02 LT), the F-region was pushed down and later disappeared as a consequence of enhanced westward ionospheric electric field in the night sector. The ionosonde did not receive any echo for a couple of hours till the next sunrise. The F-region at Kototaban (03–05 LT), Indonesia also disappeared after a rapid descend. At Kwajelien (06–08 LT) there was no equatorial type of sporadic-E at 07 to 09 LT due to the westward electric field.

    • Spread-F during the magnetic storm of 22 January 2004 at low latitudes: Effect of IMF-Bz in relation to local sunset time

      R G Rastogi H Chandra P Janardhan Thai Lan Hoang Louis Condori T K Pant D S V V D Prasad B Reinisc

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      The paper describes the results of spread-F at low latitude stations around the world during the magnetic storm starting at 0130 UT on 22 January 2004. The storm can be divided into two phases, first phase up to 1000 UT when interplanetary magnetic field IMF-Bz was highly fluctuating around a small positive value and the second phase after a sudden large southward turning of IMF-Bz at 1030 UT. The first phase produced strong spread-F at Jicamarca, Sao Luis, and Ascension Island and caused complete inhibition of spread-F at Thumba and Waltair in India. It generated weak spread-F at Ho Chi Minh City in Vietnam and strong spread-F at Hainan and Chung Li. The strong spread-F at Hainan and Chung Li were caused by the positive IMF-Bz during the first phase of the storm and not by the negative pulse of IMF-Bz at 1000 UT.

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