Height-Time Diagrams Of The July 25Th (1999) Halo Coronal Mass Ejection Obtained From Lasco Observations

In this paper we present height-time diagrams of the<br>halo coronal mass ejection observed in July 25th<br>(1999) from the Large Angle and Spectroscopic Coronagraph<br>(LASCO), which is an instrument on board<br>of Solar and Heliopheric Observatory (SOHO) able to<br>observe the solar corona from 2 to 32 solar radii. To<br>obtain these diagrams we used a new technique in<br>which we divide the LASCO images in angular slices<br>and place side by side the same slice in different<br>observation times, producing height-time diagrams.<br>With this method we were able to identify a small<br>deceleration of the July 25th halo CME in several<br>directions around the sun. We propose that this technique<br>is appropriated to identify whether there is<br>acceleration or deceleration on halo CMEs near the<br>sun which is an important parameter that can be used<br>to predict the time of arrival and the velocity of these<br>structures near the earth.