Browsing by Author "Pandey, Kumud"

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    On properties of narrow CMEs observed with SOHO/LASCO
    (2009-07-01) Mittal, Nishant; Pandey, Kumud; Udit, Narain, et al.
    We have investigated properties such as speed, angular width, location, acceleration and occurrence rate of narrow CMEs (defined as having angular width ≤ 20°) observed during 1996–2007 by SOHO/LASCO. The results obtained are compared with those of normal CMEs (angular width > 20°) from the same time interval to find whether there are any real differences between the two populations. Our study of 3464 narrow CMEs from the online SOHO/LASCO, CME catalogue leads us to conclude that (1) the fraction of narrow CMEs during solar minimum is 38% and during solar maximum 19%, (2) during solar maximum narrow CMEs are generally faster than normal CMEs, (3) the maximum speed of narrow CMEs is much smaller than that of the normal CMEs, (4) during solar maximum narrow CMEs appear at all latitudes similar to normal CMEs, (5) narrow and normal CMEs have unequal deceleration and (6) the occurrence rate of narrow CMEs remain constant after 1998 until the beginning of 2006 while the normal CMEs occurrence rate seems to follow solar cycle variation until 2004. Thus narrow CMEs and normal CMEs have some differences, in disagreement with previous studies.
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    On tripolar magnetic reconnection and coronal heating
    (2011-07-05) Pandey, Kumud; Narain, Udit; Lohani, N. K.
    Using recent data for the photosphere-chromosphere region of the solar atmosphere the magnetic reconnection in tripolar geometry has been investi- gated through the procedure of Sturrock (1999). Particular attention has been given to the width of the reconnecting region, wave number of the rapidly growing tearing mode, island length scales, frequency of MHD fluctuations, tearing mode growth rate, energy dissipation rate and minimum magnetic field strength required to heat chromospheric plasma to coronal temperatures. It is found that small length scales are formed in the upper chromosphere. The maximum growth rate of tearing mode instability coincides with the peak in the energy dissipation rate both of which occur in the upper chromo- sphere at the same height. It is realized that the distribution of magnetic field with height is essential for a better understanding of the coronal heating problem.