Gutenberg Open Science

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Recent Submissions

ZeitschriftenaufsatzAccess status: Open Access ,
Evidence of gravity wave contribution to vertical shear and mixing in the lower stratosphere
(2026)
Umbarkar, Madhuri
;
Kunkel, Daniel
;
Miltenberger, Annette
;
Lachnitt, Hans-Christoph
;
Kaluza, Thorsten
Small-scale dynamics, particularly gravity waves (GWs), modify vertical wind shear and can trigger turbulence in the lowermost stratosphere (LMS), thereby influencing the transport of trace species across the tropopause. Although idealized modeling and observational case studies have demonstrated this link, the contribution of small-scale dynamics to turbulence generation remains poorly understood, particularly under real atmospheric conditions. Here, we investigate the relationship between GWs, vertical wind shear, and clear-air turbulence (CAT) in the LMS over the North Atlantic during a baroclinic life cycle. We combine airborne observations with ERA5 reanalysis and high-resolution forecasts from the IFS and ICON models. To isolate the contribution of small-scale dynamics to turbulence generation, we extract the small-scale divergent component of the modeled wind field. From this, we derive momentum flux, perturbation vertical wind shear, and the turbulence indices TI1 and TI2, and compare these quantities with those calculated from the full wind fields. Trace-species mixing is observed within a region of enhanced GW activity over Iceland that is characterized by increased vertical wind shear and turbulence. ERA5 reproduces the spatial and temporal distribution of enhanced shear and turbulence but underestimates shear magnitudes relative to the forecasts while yielding comparable values of TI1 and TI2. These findings extend previous idealized studies from Umbarkar and Kunkel (2025) to real atmospheric conditions and provide further evidence that GW-induced small-scale dynamics contribute to turbulence generation in the LMS. They also demonstrate the potential of ERA5 for long-term investigations of the role of small-scale dynamics in transport and mixing near the tropopause.
ZeitschriftenaufsatzAccess status: Open Access ,
Fractal characteristics of ice-supersaturated regions in the tropopause region of the northern midlatitudes
(2026)
Schuh, Helena Zoe
;
Reutter, Philipp
;
Niebler, Stefan
;
Spichtinger, Peter
Ice supersaturated regions (ISSRs) are air masses in the upper troposphere and lower stratosphere (UTLS) where saturation ratio over ice (Si) exceeds one, i.e. regions with enhanced water vapor concentrations. These are potential formation regions of cirrus clouds and contrails. While the impact of cloud free regions of enhanced water vapor on the planetary radiation balance is small to negligible, thin cirrus clouds and aircraft induced contrail cirrus formed within them might have a large radiative impact. Understanding the characteristics of ISSRs, including their geometry and seasonal variability, is essential for evaluating atmospheric models in representing ice clouds correctly. While ISSR's pathlength statistics, i.e. 1D characteristics, have already been studied, their geometric properties, particularly fractal properties such as self-similarity, and their seasonal variability remain largely unexplored. We identify ISSRs using ERA5 reanalysis data spanning from 2010 to 2020 at three pressure levels. An area-perimeter method is employed to compute fractal dimensions. The results reveal slopes implying fractal dimensions, strongly suggesting that ISSRs in the UTLS exhibit fractal behavior. A seasonal cycle in total number and area of ISSRs, as well as in the fractal dimension is found, in combination with a strong vertical variation. We hypothesize that this is caused by the seasonal variation of convective and frontal activity. We further analyzed the zonal and meridional extents of ISSRs as well as the pathlengths of modeled flights along commercial flight routes. The results of these horizontal extents are consistent with the fractal properties, and suggest distinct formation processes for ISSRs.
ZeitschriftenaufsatzAccess status: Open Access ,
Impact of South American biomass burning emissions on elevated South Atlantic upper tropospheric ozone
(2026)
Smoydzin, Linda
;
Bense, Vera
;
Bozem, Heiko
;
Joppe, Philipp
;
Kunkel, Daniel
During the SOUTHTRAC mission in autumn 2019 elevated mixing ratios of carbon monoxide (CO), carbon dioxide CO2, nitrogen oxide (NO) and total reactive nitrogen NOy were observed during a flight at the beginning of October. The potential plume extended over more than 1000 km (15° latitude) east of the Brasilian coast at altitudes of 13 km in the upper troposphere. In-situ measurements showed elevated ozone in this plume (≈ 100 ppbv), being 20–40 ppbv higher than during a previous flight in early September at exactly the same flight route. For the plume flight positive correlations of ozone and pollutants (CO, NO, NOy) indicate ozone production in these pollution layers. Lagrangian Analysis shows, that the observed air masses were strongly affected by biomass burning over Amazonia. A combined analysis of a chemical Lagrangian box model and a global chemistry climate model (EMAC) revealed that ozone production from biomass burning predominantly caused the ozone enhancements. The effect is intensified by NOx produced from lightning. Upward transport of the plumes happened ≈ one week before the flight, allowing ozone to be formed and enhanced by 25 % compared to the September flight. Estimate of the potential climate impact show, that the biomass burning produced ozone has an impact on the radiation budget, namely a spatially and regionally localized radiative flux disturbance of up to 250 mW m−2 at the tropopause and 150 mW m−2 at the top of the atmosphere.