Transport versus energetic particle precipitation: Northern polar stratospheric NO_x and ozone in January–March 2012

摘要

In early 2012, a strong sudden stratospheric warming (SSW) took place, accompanied by several medium-scale solar proton events (SPEs). Here we use a chemistry transport model (CTM) in order to assess the relative contributions of (1) intensified downward transport of odd nitrogen (NO_x ) and (2) in situ production of NO_x by protons, on stratospheric NO_x and ozone during January–March 2012. The CTM is constrained by an upper boundary condition for reactive nitrogen (NO_y) species, based on satellite observations from Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board Envisat, and includes a new parameterization of the SPE-caused effects on NO_y and odd hydrogen (HO_x ) species. We found that the amount of NO_x increases due to both transport and in situ production effects, the intensified descent of NO_x dominating the middle and upper stratospheric impact. The model results indicate NO_x enhancements of 120–3300% (5–48 ppbv) between 38 and 50 km, caused by the transport of mesosphere/lower thermosphere NO_x down to the stratosphere following the SSW. The SPEs increase NO_x by up to 820–1200% (14–21 ppbv) at 33 to 50 km. The effect on the stratospheric ozone is larger following the downward transport of NO_x than during and after the SPEs. The model predicts ozone losses of up to 17% and 9% at around 40 km due to transport and SPE effects, respectively.