In this paper, we analyze 91 coronal mass ejection (CME) events studied by Manoharan et al. (2004) and Gopalswamy and Xie (2008). These earthdirected CMEs are large (width > 160• ) and cover a wide range of speeds (∼120-2400 kms −1 ) in the LASCO field of view. This set of events also includes interacting CMEs and some of them take longer time to reach 1 AU than the travel time inferred from their speeds at 1 AU. We study the link between the travel time of the CME to 1 AU (combined with its final speed at the Earth) and the effective acceleration in the Sun-Earth distance. Results indicate that (1) for almost all the events (85 out of 91 events), the speed of the CME at 1 AU is always less than or equal to its initial speed measured at the near-Sun region, (2) the distributions of initial speeds, CME-driven shock and CME speeds at 1 AU clearly show the effects of aerodynamical drag between the CME and the solar wind and in consequence, the speed of the CME tends to equalize to that of the background solar wind, (3) for a large fraction of CMEs (for ∼50% of the events), the inferred effective acceleration along the Sun-Earth line dominates the above drag force. The net acceleration suggests an average dissipation of energy ∼10
31−32ergs, which is likely provided by the Lorentz force associated with the internal magnetic energy carried by the CME.
We analyzed the physical characteristics of 40 halo coronal mass ejections (CMEs) and their geo-effective parameters observed during the period 2011 to 2013 in the rising phase of Solar Cycle 24. Out of all halo CMEs observed by SOHO/LASCO, we selected 40 halo CMEs and investigated their geomagnetic effects. In particular, we estimated the CME direction parameter (DP) from coronagraph observations, and we obtained the geomagnetic storm disturbance index (Dst) value corresponding to each event by following certain criteria. We studied the correlation between near-Sun parameters of CMEs such as speed and DP with Dst. For this new set of events in the current solar cycle, the relations are found to be consistent with those of previous studies. When the direction parameter increases, the Dst value also increases for symmetrical halo CME ejections. If DP > 0.6, these events produce high Dst values. In addition, the intensity of geomagnetic storm calculated using an empirical model with the near-Sun parameters is nearly equal to the observed values. More importantly, we find that the geo-effectiveness in the rising phase of Solar Cycle 24 is much weaker than that in Cycle 23.
Static and ultrasonic methods are described for the determination of the piezo-optic coefficients, q11-qlz and q44, and the strain-optic ratios, plz/p11 and @11 +p12-2p44)/@11 "~"P12-[-2p44), for NaC1, KC1, KBr and KI. Dispersion of the absolute elasto-optical constants, p11, p12 and p44 is evaluated. Comparison is made with predictions of Bansigir & Iyengar's theory of the piezo-optic effect in cubic crystals. The occurrence of isotropy of birefrigence for uniaxial stress and uniaxial strain at different wavelengths of light is explained.
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