Browsing by Author "Mittal, Nishant"

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    On distribution of CMEs speed in solar cycle 23
    (2009-02-01) Mittal, Nishant; Sharma, Joginder; Tomar, Vivek; et al.
    We have analyzed the data for more than 12900 CMEs which were obtained by SOHO/LASCO during the period of 1996-2007. The online CME catalogue contains all major CMEs detected by LASCO C2 and C3 coronagraphs. Basically we determine the CME speeds from the linear and quadratic fits to the height-time measurements. It is found that linear (constant speed) fit is preferable for 90% of the CMEs. The distribution of speeds of CMEs in solar cycle 23 is presented along with those obtained by others. As expected, the speeds decrease in the decay phase of the cycle 23. There is an unusual drop in speed in the year 2001 and an abnormal increase in speed in the year 2003 due to the high concentration of CMEs, X-class soft X-ray flares, solar energetic particle (SEP) events and interplanetary shocks observed during October-November period called Halloween events.
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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 some properties of coronal mass ejections in solar cycle 23
    (2009-03-01) Mittal, Nishant
    We have investigated the some properties such as speed, apparent width, acceleration, latitude, mass and kinetic energy etc. of all types of CMEs observed during the period 1996-2007 by SOHO/LASCO covering the solar cycle 23. The results are in satisfactory agreement with previous investigations.