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Howard and Simnett (HS) employed a new technique for associating LASCO CMEsto SMEI ICMEs. In order to extrapolate the SMEI data back to the LASCO field ofview they used nonlinear trajectories, dependent on a speed and direction, whatis more realistic than the linear extrapolation with only one parameter (aspeed). However, there are two errors and one mistake in their procedure: (1)HS used two free parameters of the direction, whereas only one can be freelyselected, because the second is provided by SMEI data. As a result, thedirections determined by HS are incorrect. (2) HS overlooked that, since thetrajectory depends on more than one parameter, there is a broad set oftrajectories, for various speeds and directions, matching the event, and thus abroad range of the onset times. HS select only one trajectory for each SMEIevent. Therefore the associations made by them are incomplete, and they shouldbe reexamined. As long as it is not done any conclusion about CMEs undetectedby solar coronagraphs are premature. (3) HS made some mistake in determinationof the SMEI speeds. The speeds given in their Table 1 are about twice as highas those demanded to obtain the onset times given in the table. It explains whythe SMEI speed distribution is excessively shifted toward high speeds ; hence,there is no reason to search for a physical explanation.

Comment on "Interplanetary coronal mass ejections that are undetected by solar coronagraphs" by T. A. Howard and G. M. Simnett