Time changes in the geomagnetic transfer functions at Chengdu, Xichang and Chongqing stationsfrom May 2007 to December 2013

This paper discusses the method for computing geomagnetic transfer functions in detail and introduces the error formulae of the real and imaginary parts of complex transfer functions. And then the transfer functions A and B as well as Parkinson vectors are calculated by using the digital geomagnetic data recorded at the stations Chengdu, Xichang and Chongqing from May 2007 to December 2013. The results show that there are perceptible small bulges at Chengdu station before and after the 2008 Wenchuan MS8.0 earthquake, but the other two stations do not exhibit perceptible anomalies. Comparison with the results in the 1980s indicates that obvious long-term variations of the b value as well as the length and direction of Parkinson vectors are observed at the station Chengdu.