This study of crustal monthly biases' temporal evolution at 42 geomagnetic observatories over 9 years of the CHAMP satellite mission reveals short-period variations and long-term trends in the bias time series, signature of the induced magnetic fields, annual trends in most bias series, distinct oscillatory pattern over the whole time span, and semi-annual variations in all components. Swarm mission data and analysis of these findings will allow a better understanding of crustal bias evolution.