Jaramillo had been the Cubs' hitting coach since after the 2009 season.
This year, Chicago is 10th in the 16-team National League with a .247 batting average, but 14th in runs (222) and 15th in on-base percentage (.304). The Cubs are 20-40 and in last place in the NL Central, 12 1/2 games behind division-leading Cincinnati.
Rowson has been the Cubs organization minor league hitting coordinator. He previously spent six seasons with the New York Yankees system.
Chicago said Tom Beyers was installed as interim minor league hitting coordinator.