Investigation of CME dynamics in the LASCO field of view

Abstract

Context. The speed-distance profile of CMEs is important for understanding the propagation of CMEs. Aims. Our main aim is to study the initial speed of CMEs in the LASCO field of view and its role in subsequent CME propagation using the acceleration-speed profile. The secondary aim is to obtain the speed growth rate. Methods. We considered the height-time data of 307 CMEs observed by SOHO/LASCO during January−March 2005. To study the CME speed profile, we used only 116 events for which there were at least 10 height-time measurements in the LASCO field of view. Using this data, we obtained their initial speed, extrapolated initial speed, and growth rate. Results. The following results were found from this analysis. (i) The initial speed obtained from the first two data points is in the range 24−1208 km s −1 , which is nearly similar to the range of linear speed (67−920 km s −1 ) obtained from a least squares fit through the entire h-t data set for each CME. (ii) However, the initial speed or extrapolated initial speed is much better correlated with acceleration and growth rate than the linear speed. (iii) Nearly two thirds of the events (74/116) are found to be accelerating. (iv) The speed growth rate is within the range −0.058 to 0.061 × 10 −3 s −1 , and it decreases with the distance. (v) The final observed distance in the LASCO field of view depends very weakly upon the initial speed, or extrapolated initial speed whereas it depends strongly on the linear speed. The above results demonstrate the role played by the initial speed of the CMEs.