Modification of Potential Vorticity near the Tropopause by Nonconservative Processes in the ECMWF Model

Spreitzer, Elisa; Attinger, Roman; Boettcher, Maxi; Forbes, R. M.; Wernli, Heini; Joos, Hanna

doi:10.1175/jas-d-18-0295.1

Cited by 42 publications

(74 citation statements)

References 68 publications

(99 reference statements)

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“…Analyzing cross-tropopause transport in the UKMO model, Gray (2006) found similar results, with cloud and radiative processes being more important for STE than processes related to turbulence. In contrast, a recent study by Spreitzer et al (2019) shows that turbulent processes are mainly responsible for changing the PV around the tropopause in a ridge of an extratropical baroclinic wave. They used high-resolution ECMWF forecast data and conclude that turbulence is evident around the jet stream.…”

mentioning

confidence: 68%

“…For instance warm conveyor belts, i.e., airstreams ahead of cold fronts associated with extratropical cyclones in which strong diabatic heating by latent heat release occurs (e.g., Wernli and Davies, 1997), can reach the upper troposphere and modify the PV, consequently allowing for exchange between tropospheric and stratospheric air (Wirth, 1995;Wernli and Bourqui, 2002). According to Spreitzer et al (2019) clouds are more likely to change PV in regions with lower tropopause altitudes, e.g., in the trough. Similarly, rapid transfer from the boundary layer D. Kunkel et al: Mixing in the ExTL 12609 into the UTLS is evident in convective systems, which sometimes have the potential to overshoot into the stratosphere (e.g., Poulida et al, 1996;Stenchikov et al, 1996;Homeyer et al, 2014;Homeyer, 2015;Tang et al, 2011).…”

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confidence: 99%

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Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves

et al. 2019

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Abstract. 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.

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confidence: 68%

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confidence: 99%

Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves

et al. 2019

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“…Similar to Spreitzer et al . (), who examined the influence of non‐conservative processes on the PV distribution at the tropopause, this term can be written as

\frac{1}{ρ} false(\nabla \times {bold-italicF}_{i} \cdot \nabla θ false) = \frac{1}{ρ} ({}, \nabla \times true(\begin{matrix} \dot{u} \\ \dot{v} \\ 0 \end{matrix})_{i} \cdot \nabla θ),

where

\overset{u}{true} = \partial u false/ \partial t

and

\overset{v}{true} = \partial v false/ \partial t

. Note that the momentum tendency F only contains horizontal components because the IFS model physics only impose changes to the u and v wind components.…”

Section: Methodsmentioning

confidence: 99%

“…() and Spreitzer et al . (), the accumulated PV tendency (APV) due to an individual process i along the trajectory x ( t ) can be computed by integrating PVR i over the trajectory from time t to t 0 , where t 0 is the start time of the backward trajectory:

{APV}_{i} false[bold-italicx false(t_{0} false), t false] = \int_{t}^{t_{0}} {PVR}_{i} false[bold-italicx false(τ false), τ false] normald τ .

When evaluating subsection for each process, insight into the detailed modification of PV at the location x ( t 0 ) and time t 0 can be gained. The integral can be approximated by interpolating the hourly PVR fields onto the trajectory position and calculating the sum along the trajectory:

{APV}_{i} false[bold-italicx false(t_{0} false), t false] \approx true \sum_{k = 0}^{n - 1} {PVR}_{i} false[bold-italicx false(t_{k} false), t_{k} false] normalΔ t .

The hourly values of PVR i are considered as representative for the previous hour and therefore the time step t n is not included in the summation.…”

Section: Methodsmentioning

confidence: 99%

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Quantifying the role of individual diabatic processes for the formation of PV anomalies in a North Pacific cyclone

Attinger

Spreitzer

Boettcher

et al. 2019

Quart J Royal Meteoro Soc

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Processes that do not conserve potential vorticity (PV) have a profound impact on the intensity, evolution, and mesoscale details of extratropical weather systems. This study aims at quantifying and improving the understanding of how and when physical processes modify PV in cyclones. To this end, a 6-day forecast of a North Pacific cyclone is performed using a recent operational version of the ECMWF global numerical weather prediction model. Hourly instantaneous temperature and momentum tendencies of each parametrized process are used to compute the corresponding PV tendencies. By integrating these diabatic PV rates along backward trajectories, the relative contribution of individual processes for the PV budget can be assessed. The cold front is characterized by an elongated filament of increased PV, generated by latent heating due to condensation at the front as well as long-wave radiative cooling at the surface. Turbulent mixing at the interface of the boundary layer decreases PV behind the cold front during the early stage of the cyclone, while sublimation of snow produces negative PV in the mature phase. A broad region of enhanced PV is found along the warm front, generated by condensation and turbulence at the front as well as long-wave radiative cooling at the surface. The region of decreased PV north of the warm front is mainly modified by snow melting and sublimation. Finally, high values of PV along the bent-back front and the cyclone centre are generated by condensation, convection, snow melting and sublimation. In general, turbulent mixing offsets intense PV modification induced by the other processes. This study highlights the relevance of condensation, melting and sublimation of snow, long-wave radiative cooling, turbulence, and convection for the production of low-level PV anomalies and underlines the importance of correctly representing these processes in weather prediction models. K E Y W O R D Sconvection, diabatic processes, extratropical cyclone, IFS, microphysics, potential vorticity, radiation, turbulence Q J R Meteorol Soc. 2019;145:2454-2476.wileyonlinelibrary.com/journal/qj

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Higher-resolution tropopause folding accounts for more stratospheric ozone intrusions

Bartusek

Ting

et al. 2022

Preprint

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Ozone in the troposphere is a pollutant and greenhouse gas, and it is crucial to better understand its transport from the ozonerich stratosphere. Tropopause folding, wherein stratospheric air intrudes downward into the troposphere, enables stratosphereto-troposphere ozone transport (STT). However, systematic analysis of the relationship between folding and tropospheric ozone, using data that can both capture folding's spatial scales and accurately represent tropospheric chemistry, is lacking. Here, we compare folding in both high-resolution (0.25°) reanalysis ERA5 and low-resolution (0.75°) chemical reanalysis CAMSRA over one year. High-resolution folding is dramatically more frequent and significantly better-correlated with tropospheric ozone. In particular, folding of deep tropospheric extent is nearly 100% missing at low resolution, and folding-ozone correlations increase most with resolution along midlatitude storm tracks, where deep folding is most common. Our results imply that STT is more attributable to tropopause folding than implied by low-resolution analysis, likely associated with resolving filamentary, deep folding.

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Modification of Potential Vorticity near the Tropopause by Nonconservative Processes in the ECMWF Model

Cited by 42 publications

References 68 publications

Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves

Evidence of small-scale quasi-isentropic mixing in ridges of extratropical baroclinic waves

Quantifying the role of individual diabatic processes for the formation of PV anomalies in a North Pacific cyclone

Higher-resolution tropopause folding accounts for more stratospheric ozone intrusions

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