Imaging Interplanetary Disturbances Causing Forbush Decreases
AIR FORCE RESEARCH LAB HANSCOM AFB MA
Pagination or Media Count:
Forbush decreases FDs in neutron monitor NM counting rates are caused by enhanced magnetic fields in interplanetary shocks and solar ejecta that shield the Earth from galactic cosmic rays GCRs. The solar origins of those ejecta can be observed as coronal mass ejections CMEs in coronagraphs, but their propagation through interplanetary space near or past the Earth has not been previously observable. The Solar Mass Ejection Imager SMEI, launched into polar Earth orbit in January 2003, now allows us to search for the white light signatures of interplanetary CMEs ICMEs responsible for FDs. SMEI is unique in that it can monitor the progress of CMEs through the inner heliosphere out to distances beyond 1 AU and distinguish those which hit the Earth from those that do not. For comparison with SMEI observations, we selected all FDs of greater than or equal 2 observed with the Oulu, Finland, NM. We find an excellent association of SMEI CMEs with those FDs and for each of the associated SMEI CMEs a good candidate associated LASCO CME was also found. The SMEI observations provide information on the approximate spatial locations and trajectories of large ICMEs that may result in FDs and hence can be useful as a space weather tool.