Hemispheric distributions and interannual variability of NO_y produced by energetic particle precipitation in 2002–2012

Abstract

We investigate the interannual variability and hemispheric differences of reactive odd nitrogen produced by energetic particle precipitation (EPP‐NOy) and transported into the stratosphere and lower mesosphere during polar winters in 2002–2012. For this purpose, EPP‐NOy amounts derived from observations of the Michelson Interferometer for Passive Atmospheric Sounding by means of a tracer correlation method have been used. Southern hemispheric (SH) seasonal maximum EPP‐NOy amounts transported below the 0.02 hPa level range from 0.5GM to 2.5GM in the 2009 and 2003 winters, respectively. Northern hemispheric (NH) amounts were typically 2–5 times smaller, with the exception of the 2003/2004 winter. This interhemispheric asymmetry is primarily caused by a reduction of the mesospheric descent rates in NH midwinter, as opposed to the SH. Hemispherically integrated NOy fluxes through given pressure levels reach up to 0.07GM/day at 0.1 hPa. A multilinear regression of the EPP‐NOy evolution to the Ap index of the preceding months indicates that a large fraction of the SH interannual variability of EPP‐NOy (excluding direct contributions by solar protons) can be linked to geomagnetic activity variations. This relationship holds throughout the winter and at all vertical levels where EPP‐NOy is present. In the NH, a similar correlation is found until midwinter, however, breaking down afterward above 2 hPa in years with elevated stratopause occurrence. As an exception, EPP‐NOy amounts in the Arctic winter 2004/2005 were much higher than in other NH winters with similar geomagnetic activity. We attribute this behavior to the unusually stable polar vortex in that winter, otherwise typical for the SH.

NO<sub><i>y</i></sub> production, ozone loss and changes in net radiative heating due to energetic particle precipitation in 2002–2010

“…These values are higher than in previous studies summarized in , which provide a range of zero to 1.5 Gmol per winter based on HALOE (Siskind et al, 2000;Randall et al, 2007) observations, but are in good agreement with studies based on MIPAS data Reddmann et al, 2010;Funke et al, 2014b). In Funke et al (2014b), the wintertime increase in EPP NO y due to the indirect effect is derived from MIPAS observations for every Northern Hemisphere and Southern Hemisphere winter covered by MIPAS observations (mid-2002-early 2012). To make these observations directly comparable to our model results, the increase in every Northern Hemisphere and Southern Hemisphere winter is derived from the model results by subtracting the lowest value in the preceding summer.…”

“…Additionally, there are sporadic increases of more than 1 Gmol per event Table 2. Comparison of modeled EPP NO y (Gmol) with data derived from MIPAS (Funke et al, 2014b). For the models, the difference between the highest value of this winter minus the lowest value of the preceding summer is given; in brackets, the maximal value of the winter is given.…”

“…To make these observations directly comparable to our model results, the increase in every Northern Hemisphere and Southern Hemisphere winter is derived from the model results by subtracting the lowest value in the preceding summer. Results for all winters and all model runs are summarized together with the MIPAS observations (Funke et al, 2014b, their …”

A semi-empirical model for mesospheric and stratospheric NO<sub><i>y</i></sub> produced by energetic particle precipitation

“…However, since below 50 km NO x is partly converted into its reservoirs (Stiller et al, 2005) In a recent paper, Funke et al (2014a) provide quantitative estimates of the total amount of EPP-NO y for the years 2002-2012, also inferred from MIPAS measurements. In a subsequent paper, Funke et al (2014b) showed that the EPP IE, i.e., the descended EPP-NO y , is highly correlated with geomagnetic activity, as indicated by the A p index, in Southern Hemisphere (SH) winters and dynamically unperturbed Northern Hemisphere (NH) winters. This suggests that the indirect effect during those winters is driven by the EPP source strength rather than by variations of subsidence.…”

Validation of ACE-FTS version 3.5 NO<sub><i>y</i></sub> species profiles using correlative satellite measurements

“…The IMK-IAA algorithm is described by von Clarmann et al (2009) and Funke et al (2014), and the most recent version of the level 2 data (used in this study) is version 5. The IMK-IAA algorithm uses an iterative variant of Tikhonov regularization (Tikhonov, 1963) on species-dependent sets of microwindows.…”