POLSTRACC: Airborne Experiment for Studying the Polar Stratosphere in a Changing Climate with the High Altitude and Long Range Research Aircraft (HALO)

Abstract

The Polar Stratosphere in a Changing Climate (POLSTRACC) mission employed the German High Altitude and Long Range Research Aircraft (HALO). The payload comprised an innovative combination of remote sensing and in situ instruments. The in situ instruments provided high-resolution observations of cirrus and polar stratospheric clouds (PSCs), a large number of reactive and long-lived trace gases, and temperature at the aircraft level. Information above and underneath the aircraft level was achieved by remote sensing instruments as well as dropsondes. The mission took place from 8 December 2015 to 18 March 2016, covering the extremely cold late December to early February period and the time around the major warming in the beginning of March. In 18 scientific deployments, 156 flight hours were conducted, covering latitudes from 25° to 87°N and maximum altitudes of almost 15 km, and reaching potential temperature levels of up to 410 K. Highlights of results include 1) new aspects of transport and mixing in the Arctic upper troposphere–lower stratosphere (UTLS), 2) detailed analyses of special dynamical features such as tropopause folds, 3) observations of extended PSCs reaching sometimes down to HALO flight levels at 13–14 km, 4) observations of particulate NOy and vertical redistribution of gas-phase NOy in the lowermost stratosphere (LMS), 5) significant chlorine activation and deactivation in the LMS along with halogen source gas observations, and 6) the partitioning and budgets of reactive chlorine and bromine along with a detailed study of the efficiency of ClOx/BrOx ozone loss cycle. Finally, we quantify—based on our results—the ozone loss in the 2015/16 winter and address the question of how extraordinary this Arctic winter was.

A convolution of observational and model data to estimate age of air spectra in the northern hemispheric lower stratosphere

“…In contrast to these results, different mass budget analyses of the lowermost stratosphere in both hemispheres show that the net direction of the hemispherically integrated mass flux across the tropopause is downward with a maximum during spring in each hemisphere and a generally weaker seasonality in the SH. The upward component of this net mass flux is shown to reach its maximum during fall and its minimum conversely in spring in each hemisphere (Olsen et al, 2004;Schoeberl, 2004). The contradicting seasonality patterns imply that a hemispherically integrated mass flux might not be a suitable proxy for upward transport across the defined extratropical tropopause sections in this study, especially since the net direction of this flux is downward.…”

“…For the NH tropopause section, the net flux across the section is downward (Olsen et al, 2004), so that tropospheric air mixes with descending stratospheric air, characterized by lower mixing ratios due to the chemical loss regions in the stratosphere. At the extratropical tropopause the mixing ra-tio should thus be lower than in the tropics.…”

“…The upward mass flux in the tropics presents a distinct seasonality with maximum upward transport during northern hemispheric winter, due to a maximum of tropospheric waves (Rosenlof and Holton, 1993;Rosenlof, 1995). Although the TTL is identified as the main entry point to the stratosphere, transport mechanisms across the extratropical tropopause play an important role in air composition in the lowermost stratosphere (LMS) below 380 K potential temperature (Olsen et al, 2004;Boothe and Homeyer, 2017). Those exchange processes exhibit their own distinct seasonality (Appenzeller et al, 1996;Schoeberl, 2004) and geographical distribution (Škerlak et al, 2014;Yang et al, 2016).…”

Airborne measurements and large-eddy simulations of small-scale gravity waves at the tropopause inversion layer over Scandinavia

“…So far, different sources for GWs in the troposphere have been identified, e.g. flow over orography, convection, jets and fronts, as well as secondary generation in the region of GW breaking (Smith, 1979;Gill, 1982;Baines, 1995;Fritts and Alexander, 2003;Sutherland, 2010;Plougonven and Zhang, 2014;Vadas et al, 2003). GWs are propagating from their sources in the troposphere and the tropopause region (Sato et al, 2009;Fritts et al, 2016).…”

Airborne measurements and large-eddy simulations of small-scale Gravity Waves at the tropopause inversion layer over Scandinavia

“…The airborne observations took place during the intensive observing period 6 (IOP 6) on 28 January 2016 in the framework of the combined missions POLSTRACC (The Polar Stratosphere in a Changing Climate), GW-LCYCLE II and SALSA (Seasonality of Air mass transport and origin in the Lowermost Stratosphere using the HALO Aircraft). An overview of the performed HALO research flights can be found in Oelhaf et al (2019). In January 2016, the DLR research aircraft Falcon and HALO operated from the airport of Kiruna (67.82 • N,20.33 • E), northern Sweden, to investigate chemical and dynamical processes 95 in the UTLS region at high latitudes.…”