On seasonality of stratomesospheric CO above midlatitudes: New insight from solar FTIR spectrometry at Zugspitze and Garmisch

摘要

1] A significant seasonality in stratomesospheric CO (24-100 km) above mid-latitudes is derived from FTIR via a new regularization scheme. Half hourly means from the Zugspitze (47.42°N, 10.98°E, 2964 m a.s.l.) and nearby Garmisch (745 m a.s.l.) measurements show excellent agreement (R = 0.94, slope 0.91, standard deviation 12%). Mean seasonality of the Zugspitze series (1999-2008) shows a November–April enhancement (February maximum 3.63 x 10~(16) cm~(-2)) and a summer background (1.64 x 10~(16) cm~(-2)) which agrees with the WACCM model. Measured monthly means reveal a year-to-year variability of up to 32% ( 1-sigma) in winter not reproduced by WACCM (R = -0.13). Frequency distributions of daily means are right skewed in winter due to enhancements by vortex air transport (1-3 days duration) which typically reflect CO levels of the vortex border and may even reach vortex-center levels (≈300% of the multi-annual monthly median).