An Investigation of the Winter Polar Climate in the Stratosphere and Mesosphere Using V1.06 SABER/TIMED Nighttime Measurements

Satellite-derived nitric oxide volume emission rate(NOver), ozone and kinetic temperature vertical profiles are used to investigate the polar winter climate northward/southward of 70N/S between 25 km and 105 km for the years from 2003 to 2006. NOver is function of nitric oxide(NO) concentration and temperature, and is used as the proxy to NO concentration. Caution should be taken to separate NOver changes from changes due to temperature variability. Calculations from a Band-Pak model suggest that for temperature that is lower than 205 K (regularly at around 70 km) NOver is extremely low and varies only slightly with the increase or decrease of NO concentration. Nevertheless, there are winters(e.g., 2004 and 2006 boreal winters) during which the polar temperature between 60 km and 80 km is much higher (240-260 K) due to the warming associated to the strongly elevated stratopause, and hence the high NO layer can be distinctly reflected. In such winters NOver, ozone, and temperature coherently exhibit drastic descending pattern towards spring, suggesting the strong downward transport of NO, the corresponding ozone depletion, and the large excursion(25-30 km) of the stratopause. This is probably due to the elevated gravity wave drag and the corresponding strong downwelling in the polar middle atmosphere (mesosphere and upper stratosphere) in the earlier season. Rather, in other likely regular winters (e.g., 2003 and 2005 austral winters) the descending is significantly milder(confined below 60 km). As a result the downward transport of NO and associated ozone depletion is much weaker.