HEPPA-II model–measurement intercomparison project: EPP indirect effects during the dynamically perturbed NH winter 2008–2009

Abstract

Abstract. We compare simulations from three high-top (with upper lid above 120 km) and five medium-top (with upper lid around 80 km) atmospheric models with observations of odd nitrogen (NO x = NO + NO 2 ), temperature, and carbon monoxide from seven satellite instruments (ACE-FTS on SciSat, GOMOS, MIPAS, and SCIAMACHY on Envisat, MLS on Aura, SABER on TIMED, and SMR on Odin) dur- Larger discrepancies of a few model simulations could be traced back either to the impact of the models' gravity wave drag scheme on the polar wintertime meridional circulation or to a combination of prescribed NO x mixing ratio at the uppermost model layer and low vertical resolution. In March-April, after the ES event, however, modelled mesospheric and stratospheric NO x distributions deviate significantly from the observations. The too-fast and early downward propagation of the NO x tongue, encountered in most simulations, coincides with a temperature high bias in the lower mesosphere (0.2-0.05 hPa), likely caused by an overestimation of descent velocities. In contrast, uppermesospheric temperatures (at 0.05-0.001 hPa) are generally underestimated by the high-top models after the onset of the ES event, being indicative for too-slow descent and hence too-low NO x fluxes. As a consequence, the magnitude of the simulated NO x tongue is generally underestimated by these models. Descending NO x amounts simulated with mediumtop models are on average closer to the observations but show a large spread of up to several hundred percent. This is primarily attributed to the different vertical model domains in which the NO x upper boundary condition is applied. In general, the intercomparison demonstrates the ability of stateof-the-art atmospheric models to reproduce the EPP indirect effect in dynamically and geomagnetically quiescent NH winter conditions. The encountered differences between observed and simulated NO x , CO, and temperature distributions during the perturbed phase of the 2009 NH winter, however, emphasize the need for model improvements in the dynamical representation of elevated stratopause events in order to allow for a better description of the EPP indirect effect under these particular conditions.

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

“…A clear negative downwelling signal of 5-30 % is observed in Antarctic winter 2003 from the lower mesosphere (≈ 0.3 hPa) in mid-winter to the lower stratosphere (below 10 hPa) in spring, preceded by a weaker (5-10 %) positive signal. The structure and strengths of this signal are similar to the downwelling anomalies derived from global satellite observations for the Southern Hemisphere (Fytterer et al, 2015a;Damiani et al, 2016) when comparing composites of years with high minus low geomagnetic activity, and are interpreted as particle impacts there. In the Northern Hemisphere, a similar negative downwelling signal starts in the lower mesosphere in early winter [2003][2004], but is interrupted by a strong (> 40 %) positive anomaly in late 2003 and early 2004 that is probably related to the onset of the sudden stratospheric warming.…”

“…We use results from three different models in this study which have been used to determine the impact of energetic particle precipitation in the past (e.g., Funke et al, 2011Funke et al, , 2017 to analyze differences in the model results due to the implementation of the particle impact and the model transport schemes, and to derive a range of possible model results. The models used are 3dCTM (M. Sinnhuber et al, 2012), KASIMA (Reddmann et al, 2010), and EMAC (Joeckel et al, 2010).…”

“…Previous studies based on observations have compared observations of ozone in situations with and without elevated amounts of NO y on the same day and in the same latitude range (Natarajan et al, 2004), the evolution of ozone in years with high energetic particle fluxes compared to years with low particle fluxes (Randall et al, 2005), and the composite difference of years with high minus years with low particle fluxes (Fytterer et al, 2015a;Damiani et al, 2016). All methods have yielded lower values of ozone in the upper stratosphere presumably related to the energetic particle precipitation; the composite method also shows negative ozone anomalies proceeding downwards from the stratopause to the mid-stratosphere during polar winter.…”

“…Lower values of ozone in the upper stratosphere are observed during winters characterized by large particle forcing or enhanced values of NO y (Natarajan et al, 2004;Randall et al, 2005), and downwelling negative ozone anomalies were observed for the first time by Fytterer et al (2015a) and Damiani et al (2016). However, quantification of the particle-induced ozone loss by observations is difficult, because (a) MIPAS observations of EPP NO x show that EPP-induced ozone loss must occur in every year, so only relative differences can be obtained from observations; (b) stratospheric ozone is quite variable anyway; and (c) a much longer time series than used by (Fytterer et al, 2015a) would be necessary to attribute the observed anomalies clearly to the particle precipitation. Model studies are more suited to studying the ozone loss, as models can do onoff experiments with and without particle precipitation in a clearly defined way.…”

“…Observations from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS, Fischer et al, 2008), which also covered the polar night region, show that NO x produced by energetic particle precipitation (called EPP NO x in the following) reaches down to altitudes below 30 km in both hemispheres, in nearly all winters observed (Funke et al, 2014a). Particularly high values of EPP NO x are observed in Northern Hemisphere late winters after the strong sudden stratospheric warming events in winters (Randall et al, 2006Funke et al, 2014a;Sinnhuber et al, 2014;Funke et al, 2017). These warmings were followed by long-lasting downwelling in the mesosphere and upper stratosphere enabled by a strong polar vortex re-forming after the event.…”