Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012

Abstract

Abstract. Dehydration in the Antarctic winter stratosphere is a well-known phenomenon that is annually observed by satellites and occasionally observed by balloon-borne measurements. However, in situ measurements of dehydrated air masses in the Antarctic vortex are very rare. Here, we present detailed observations with the in situ and GLO-RIA remote sensing instrument payload aboard the German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv of water vapor were observed as far north as 47 • S in an altitude between 12 and 13 km in the lowermost stratosphere. The dehydration can be traced back to individual ice formation events above the Antarctic Peninsula and Plateau, where ice crystals sedimented out and water vapor was irreversibly removed. Within these dehydrated stratospheric air masses, filaments of moister air reaching down to the tropopause are detected with the high-resolution limb sounder, GLORIA. Furthermore, dehydrated air masses are observed with GLORIA in the Antarctic lowermost stratosphere down to 7 km. With the help of a backward trajectory analysis, a midlatitude origin of the moist filaments in the vortex can be identified, while the dry air masses down to 7 km have stratospheric origins. Antarctic stratospheretroposphere exchange (STE) and transport of dehydrated air masses into the troposphere are investigated. Further, it is shown that the exchange process can be attributed to several successive Rossby wave events in combination with an isentropic exchange of air masses across the thermal tropopause.The transport into the troposphere is caused by air masses that are detached from the potential vorticity (PV) structure by Rossby wave breaking events and subsequently transported diabatically across the dynamical tropopause. Once transported to the troposphere, air masses with stratospheric origin can reach near-surface levels within several days.

The novel HALO mini-DOAS instrument: inferring trace gas concentrations from airborne UV/visible limb spectroscopy under all skies using the scaling method

“…3b), indicating in-mixing of tropospheric air from more NO x -rich air masses. Rolf et al (2015) also infer in-mixing of moister midlatitude air into the bottom of the polar vortex, albeit not at the same time during the flight, since the used instrument (GLORIA) was switched off during the dive. At altitudes below 9 and 10 km, respectively, retrieved [NO] and [NO 2 ] are near their detection limits of 7 and 10 ppt, indicating very pristine air.…”

“…8c and 9g). For both flight sections measurements indicate air mass ages up to 4.5 years in combination with strong dehydration (Rolf et al, 2015) and denitrification . However, the subsidence of O 3 appears to be overestimated in the CLaMS model, since the vertical profile of measured O 3 concentrations is more accurately represented by EMAC (Fig.…”

“…The lower edge of the Antarctic polar vortex was penetrated during the flight between approximately 08:00 and 13:00 UTC, i.e. south of 49 • S. More information on the flight, in particular the transport of dehydrated air masses forming the Antarctic vortex into the upper and middle troposphere, can be found in the publication of Rolf et al (2015). The shielding effect of low-and mid-level aerosols and clouds is investigated by additional RT calculations considering an uniform cloud cover (optical thickness τ = 20) located at 4-8 km altitude.…”

Airborne limb-imaging measurements of temperature, HNO<sub>3</sub>, O<sub>3</sub>, ClONO<sub>2</sub>, H<sub>2</sub>O and CFC-12 during the Arctic winter 2015/16: characterization, in-situ validation and comparison to Aura/MLS

“…For an overview of comparisons of GLORIA high-spectralresolution retrieval results to in situ measurements for all PGS flights, the median difference and the median absolute deviation (Rousseeuw and Croux, 1993) are presented in Table 2. The median difference gives a measure of the accuracy of the match between the data sets, and the median absolute deviation is a method for describing the spread around this median value.…”

Seasonal impact of biogenic VSL bromine on the evolution of mid-latitude lowermost stratospheric ozone during the 21<sup>st</sup> century

“…S2). Additionally, the favourable conditions for isentropic exchange of young 25 subtropical air with extremely old winter polar vortex air masses within the SH-ML (Spang et al 2015;Rolf et al 2015), could drive an additional chlorine heterogeneous reactivation and thus enhance hemispheric asymmetry.…”