By using the AL index for one year as well as some of the IMS meridian chain records, the longitudinal center of the substorm westward electrojet is examined. Although on the average AL is most often dominated by stations located near 0300 MLT, the westward electrojet during the expansion and maximum phase of substorms tends to be centered in the premidnight to early morning sector, and, during the recovery phase, it is most intense in morning hours. It is suggested that the substorm-associated westward electrojet consists of two components which have different characteristic times; one produced mainly by Hall condutivity enhancements which dominate in the midnight sector and the other one by southward electric fields in the morning sector.