How stratospheric are deep stratospheric intrusions?

Abstract

Abstract. Preliminary attempts of quantifying the stratospheric ozone contribution in the observations at the Zugspitze summit (2962 m a.s.l.) next to GarmischPartenkirchen in the German Alps had yielded an approximate doubling of the stratospheric fraction of the Zugspitze ozone during the time period 1978 to 2004. These investigations had been based on data filtering by using low relative humidity (RH) and elevated 7 Be as the criteria for selecting half-hour intervals of ozone data representative of stratospheric intrusion air. To quantify the residual stratospheric component in stratospherically influenced air masses, however, the mixing of tropospheric air into the stratospheric intrusion layers must be taken into account. In fact, the dewpoint mirror instrument at the Zugspitze summit station rarely registers RH values lower than 10 % in stratospheric air intrusions. Since 2007 a programme of routine lidar sounding of ozone, water vapour and aerosol has been conducted in the Garmisch-Partenkirchen area. The lidar results demonstrate that the intrusion layers are drier by roughly one order of magnitude than indicated in the in situ measurements. Even in thin layers RH values clearly below 1 % have frequently been observed. These thin, undiluted layers present an important challenge for atmospheric modelling. Although the ozone values never reach values typical of the lower-stratosphere it becomes, thus, obvious that, without strong wind shear or convective processes, mixing of stratospheric and tropospheric air must be very slow in most of the free troposphere. As a consequence, the analysis the Zugspitze data can be assumed to be more reliable than anticipated. Finally, the concentrations of Zugspitze carbon monoxide rarely drop inside intrusion layers and normally stay clearly above full stratospheric values. This indicates that most of the CO, and thus the intrusion air mass, originates in the shallow "mixing layer" around the thermal tropopause. The CO mixing ratio in these descending layers between 1990 and 2004 exhibits a slightly positive trend indicating some Asian influence on the lowermost stratosphere in the high-latitude source region of most intrusions reaching the station.

Stratospheric ozone in boreal fire plumes – the 2013 smoke season over central Europe

“…Also, parts of the 2004 ICARTT boreal plumes proceeded within a layer descending from the tropopause region (Methven et al, 2006;Real et al, 2007). On the other hand, we have rarely seen strong mixing of stratospheric and tropospheric air in our lidar results (Trickl et al, 2014).…”

“…The vertical resolution is dynamically varied between 50 m and a few hundred metres, depending on the signal-to-noise ratio decreasing with altitude. The lidar has been used in numerous atmospheric transport studies (e.g., Eisele et al, 1999;Seibert et al, 2000;Carnuth et al, 2002;Trickl et al, 2003Trickl et al, , 2010Trickl et al, , 2011Trickl et al, , 2014Zanis et al, 2003). The Oberschleißheim ("Munich", station number 10868) radiosonde data have been used for calculating the atmospheric density and, subsequently, both the ozone mixing ratio and the Rayleigh optical coefficients.…”

Tropospheric Ozone Assessment Report: Assessment of global-scale model performance for global and regional ozone distributions, variability, and trends

“…While most extreme events in polluted regions are fueled by regional anthropogenic emissions, extreme ozone events are in some cases produced by wildfire emissions (e.g., Jaffe and Wigder, 2012), transport from the lower stratosphere to the lower troposphere (e.g., Langford et al, 2009;Lin et al, 2012a;Trickl et al, 2014), and intercontinental transport (e.g., Jaffe et al, 1999;Jacob and Winner, 2009). Impacts from these sources vary in space and time and models differ in their level of process representation and estimates of the relative importance of these background sources (e.g., Fiore et al, 2014aFiore et al, , 2014b.…”

Spatio-Temporal Variability of Water Vapor in the Free Troposphere Investigated by Dial and Ftir Vertical Soundings

“…This is particularly pronounced for stratospheric intrusions that descend from the Arctic to Central Europe. These intrusion layers occasionally become the main source of short-term variability of water vapor in the altitude range between 3 km and 5 km [5]. However, such events occur predominantly during the winter season and are accompanied with nonconvective weather conditions.…”