The Role of Semi-annual Cycle in Modulating Seasonality Changes of Surface Air Temperature over China and its Mechanism

Seminar by Prof. Qimin Deng from China University of Geosciences

08 February 2023
KST 14:00 – 15:00

The Seminar is being held in Room 1010 (Jasmin) – Integrated mechanical engineering building. Click here for the campus map.

Taking the semiannual cycle of surface air temperature (SAT) into account in fitting the finer structure of the seasonal cycle, this study reveals the specific role of the semiannual cycle in modulating variations of the season onsets and lengths for the first time. The results show that the phase differences between the two harmonics remain essentially unchanged, while the amplitude ratio of the semiannual to annual harmonics tends to increase after 1988. This enhanced semiannual cycle together with the global warming and annual cycle changes jointly led to a much longer summer with an average speed of 7.45 days/10 years and shorter spring, autumn, and winter with speeds of -2.43, -1.63, and -4.26 days/10 years, respectively. Such obvious asymmetry cannot be found in fitting seasonal cycles by only annual harmonics. The average absolute percentages of the linear trends of season onsets and lengths caused by the intensification of the semiannual cycle are 52.63% and 78.66%. The time evolutions of semiannual cycle strength in China are found to be significantly correlated to the meridional temperature advection. The anomalous stronger southward wind in December can result in colder temperature and hence intensify the semiannual component.