TY  - JOUR
AU  - Kunkel, Daniel
AU  - Hoor, Peter
AU  - Kaluza, Thorsten
AU  - Ungermann, Jörn
AU  - Kluschat, Björn
AU  - Giez, Andreas
AU  - Lachnitt, Hans-Christoph
AU  - Kaufmann, Martin
AU  - Riese, Martin
TI  - Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves
JO  - Atmospheric chemistry and physics
VL  - 19
IS  - 19
SN  - 1680-7324
CY  - Katlenburg-Lindau
PB  - EGU
M1  - FZJ-2021-00172
SP  - 12607 - 12630
PY  - 2019
AB  - Stratosphere–troposphere exchange within extratropical cyclones provides the potential for anthropogenic and natural surface emissions to rapidly reach the stratosphere as well as for ozone from the stratosphere to penetrate deep into the troposphere, even down into the boundary layer. The efficiency of this process directly influences the surface climate, the chemistry in the stratosphere, the chemical composition of the extratropical transition layer, and surface pollution levels. Here, we present evidence for a mixing process within extratropical cyclones which has gained only a small amount of attention so far and which fosters the transport of tropospheric air masses into the stratosphere in ridges of baroclinic waves. We analyzed airborne measurement data from a research flight of the WISE (Wave-driven ISentropic Exchange) campaign over the North Atlantic in autumn 2017, supported by forecasts from a numerical weather prediction model and trajectory calculations. Further detailed process understanding is obtained from experiments of idealized baroclinic life cycles. The major outcome of this analysis is that air masses mix in the region of the tropopause and potentially enter the stratosphere in ridges of baroclinic waves at the anticyclonic side of the jet without changing their potential temperature drastically. This quasi-isentropic exchange occurs above the outflow of warm conveyor belts, in regions which exhibit enhanced static stability in the lower stratosphere and a Kelvin–Helmholtz instability across the tropopause. The enhanced static stability is related to radiative cooling below the tropopause and the presence of small-scale waves. The Kelvin–Helmholtz instability is related to vertical shear of the horizontal wind associated with small-scale waves at the upper edge of the jet stream. The instability leads to the occurrence of turbulence and consequent mixing of trace gases in the tropopause region. While the overall relevance of this process has yet to be assessed, it has the potential to significantly modify the chemical composition of the extratropical transition layer in the lowermost stratosphere in regions which have previously gained a small amount of attention in terms of mixing in baroclinic waves.
LB  - PUB:(DE-HGF)16
UR  - <Go to ISI:>//WOS:000489689500005
DO  - DOI:10.5194/acp-19-12607-2019
UR  - https://juser.fz-juelich.de/record/889267
ER  -