We analyze observations of three bow shock crossings which occurred during 2007,using upstream data from STEREO A/B,ACE and WIND,combined with multi-point THEMIS and Cluster data,and TC-1 data located near noon.During the crossing of 7 May 2007,we find that following a rapid reduction in solar wind ram pressure and subsequent pressure pulse seen by ACE and WIND upstream,the bow shock responds asymmetrically from dawn to dusk.Cluster data on the dawn-side suggest the bow shock is significantly flared and responds rapidly to the pulse arrival,while TC-1 at noon,and THEMIS on the dusk-side,are well matched to the model bow shock,but show a delayed response.The crossings observed on 21 May and 2 June show contrasting response matching the model boundary for northward Interplanetary Magnetic Field (IMF).The IMF and solar wind plasma data suggest that the bow shock crossing at dawn-dusk side and subsolar point were mainly caused by large and smaller scale features of the solar wind ram pressure rise rather than the influence of IMF.
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