ACCELERATION PROFILE OF THE SLOW SOLAR WIND AS INFERRED FROM GRADUAL MASS EJECTIONS OBSERVED BY LASCO NANDITA SRIVASTAVA, RAINER SCHWENN, BERND INHESTER, GUILLERMO STENBORG and BORUT PODLIPNIK Max-Planck-Institut f¨ ur Aeronomie, 37191, Katlenburg-Lindau, Germany Abstract. The slow solar wind ( 400 km s 1 ) appears to initiate from the regions in the corona where magnetic fields are closed, or from the interface between streamers and other coronal regions. The nature of the acceleration of slow solar wind is not yet well known. LASCO observations of gradually evolving mass ejections offer us a good opportunity to study the speed and acceleration profiles of the slow solar wind from a distance of 1.1 up to 30 . We present speed and acceleration profiles of slow solar wind, derived on the basis of measurements of mass flows in several cases of gradual mass ejections and present them in perspective of earlier work. 1. Introduction The fast (700 km s 1 ) and slow solar wind ( 400 km s 1 ) are now well known to originate and accelerate differently. While the fast solar wind is believed to come from the coronal holes and is observed to accelerate close to the sun, the slow solar wind is highly variable and most likely originates from streamers and interfaces between streamers and other coronal regions. Sheeley et al. (1997) suggested that the acceleration of the slowly moving blobs as observed by LASCO starts at 3 to 4 above the cusps of streamers, and they then move radially outward at speeds from 150 km s 1 to 300 km s 1 . Since the features are small and accelerate in a similar fashion, they appear to trace out the slow solar wind. In our quest for slowly moving blobs or blob-like features in the inner corona (i.e., the C1 field of view), no such small-scale features could be detected, although we could identify a distinct class of slow CMEs that were relatively less frequent in occurrence. During its 2.5 years of operation aboard SOHO, LASCO has recorded several of these gradual coronal mass ejections that have been tracked from 1.1 to 30 using its three coronagraphs. These CMEs can be classified as gradually rising balloon-type events. They are structurally distinct and evolve as a low-lying loop for several hours in the C1 field of view before crossing gradually the entire field of view of the C2 and C3 coronagraphs in several hours (of the order of a day). In the past, only a few observations of similar type slow CMEs have been reported by, e.g., Fisher and Garcia (1984), based on data of the K-III coronameter within the range of 1.24 to 2.31 . We present a study of a few cases of slowly evolving or gradual CMEs as observed by LASCO and compare their flow speed and acceleration profiles to those of the slow solar wind as obtained by Sheeley et al. (1997). Space Science Reviews 87: 303–306, 1999. c 1999 Kluwer Academic Publishers. Printed in the Netherlands.