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31.10.2022: Open PhD position

Interhemispheric differences of the lower stratospheric composition

The composition of the tropopause region and lower stratosphere is highly climate relevant, but driving factors time scales are yet poorly understood. This project will investigate the composition differences  between the northern and southern hemisphere lowermost stratosphere (LMS) and their driving factors. For this we will use data obtained from the HALO and US research aircraft during different missions. This  includes comprehensive data from H2O, O3, CO, N2O to derive the structure and variability of the lower stratosphere of both hemispheres.
The measurements will be complemented by meteorological reanalysis data from ECMWF (ERA5) to put the observations into a global dynamical context. Special focus will be given to shear and potential turbulence occurrence. To link the measurements to regions relevant for turbulence occurrence and to derive transport time scales, the observational data will be connected to ERA-5 meteorological reanalysis data using comprehensive sets of trajectories.
The Lagrangian air parcel analysis will be complemented with age spectral analysis from the CLaMS model (Chemical Lagrangian Model of the Stratosphere) which is provided by FZ Juelich. The final goal is to identify and quantify hemispheric differences of the LMS composition and to identify the processes leading to these differences of transport and time scales.

The position will be embedded in the TPChange collaborative research center TPChange and the HALO consortium. The salary is 75% EG13 with a duration of 36 months.

Contact. Prof. Dr. Peter Hoor

06.10.2022: GRL paper on turbulence analysis in a tropopause relative framework: (Kaluza, Kunkel, Hoor, 2022)

Analysis of Turbulence Reports and ERA5 Turbulence Diagnostics in a Tropopause-Based Vertical Framework

In the tropopause region turbulence exhibits a common feature with posing a threat for aviation as well as presenting a pathway for cross tropopause exchange. However, current numerical weather prediction and in particular climate models still struggle to resolve a large part of the dynamics responsible for turbulence generation. This renders high resolution observations of turbulence to be very valuable to identify the spatio-temporal distribution of turbulence. In this study we use aircraft observations along with reanalysis data over the North Atlantic during winter season to analyze turbulence occurrence. Using a tropopause-based coordinate system, we found that turbulence occurs within a sharp unimodal distribution which maximizes just below the tropopause. Turbulence also significantly affects the first 2  km above the tropopause which highlights its potential impact on the formation of the so called extratropical mixing layer around the tropopause.

08.06.2022: Transport of pollution over the Pacific from MOPITT: (Smoydzin and Hoor 2022)

Contribution of Asian emissions to upper tropospheric CO over the remote Pacific

By analysing the global distribution of the highest 2 % of daily CO mixing ratios at 400 hPa derived from the MOPITT satellite instrument for 20 years (2000–2019), we very regularly detect regions with very high CO values (i.e. mixing ratios belonging to the globally highest 2 %) over the remote Northern Hemispheric (NH) Pacific. Such events of elevated CO over the upper tropospheric NH Pacific occur throughout the year with surprisingly high regularity and frequency (70 % of all days during winter, 80 % of all days during spring). During winter, most of these pollution events are detected over the north-eastern and central NH Pacific, during spring over the central NH Pacific, and during summer over the western NH Pacific. We detect most pollution events during spring.

17.03.2022: Evolution of air mass composition in the arctic polar vortex during 2015/2016: Ziereis et al (2022)

Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016

During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NO_y), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NO_y–N₂O and NO_y–O₃). During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. This indicates the downward transport of air masses that have been denitrified during the earlier winter phase. Using tracer–tracer correlations, missing total reactive nitrogen was estimated to amount to 6 ppb. Further, indications of transport and mixing of these processed air masses outside the vortex have been found, contributing to the chemical budget of the winter lowermost stratosphere (see also Krause et al., 2018).

ACP highlight paper: Observed export from the Asian and American summer monsoon during the WISE campaign: Lauther et al. (2022)

In situ observations of CH₂Cl₂ and CHCl₃ show efficient transport pathways for very short-lived species into the lower stratosphere via the Asian and the North American summer monsoon

(see also special issue for the HALO campaign WISE (Wave-driven isentropic Exchange)

Efficient transport pathways for ozone-depleting very short-lived substances (VSLSs) from their source regions into the stratosphere are a matter of current scientific debate; however they have yet to be fully identified on an observational basis. Understanding the increasing impact of chlorine-containing VSLSs (Cl-VSLSs) on stratospheric ozone depletion is important in order to validate and improve model simulations and future predictions. We report on a transport study using airborne in situ measurements of the Cl-VSLSs dichloromethane (CH₂Cl₂) and trichloromethane (chloroform, CHCl₃) to derive a detailed description of two transport pathways from (sub)tropical source regions into the extratropical upper troposphere and lower stratosphere (Ex-UTLS) in the Northern Hemisphere (NH) late summer. The Cl-VSLS measurements were obtained in the upper troposphere and lower stratosphere (UTLS) above western Europe and the midlatitude Atlantic Ocean in the frame of the WISE (Wave-driven ISentropic Exchange) aircraft campaign in autumn 2017 and are combined with the results from a three-dimensional simulation of a Lagrangian transport model as well as back-trajectory calculations. Compared to background measurements of similar age we find up to 150 % enhanced CH₂Cl₂ and up to 100 % enhanced CHCl₃ mixing ratios in the extratropical lower stratosphere (Ex-LS).

We show that air masses uplifted by hurricanes, the North American monsoon, and general convection above Central America into the tropical tropopause layer to potential temperatures of about 360–370 K are transported isentropically within 5–9 weeks from the boundary layer into the Ex-LS. This transport pathway linked to the North American monsoon mainly impacts the middle and lower part of the LMS with particularly low CH₂Cl₂ and CHCl₃ mixing ratios. The observed CHCl₃ : CH₂Cl₂ ratio further suggests clearly stronger anthropogenic emissions in the region of southern and eastern Asia compared to those in the region of Central America and the tropical Atlantic. Overall, the transport of strongly enhanced CH₂Cl₂ and CHCl₃ mixing ratios from southern and eastern Asia via the ASMA is the main factor in increasing the chlorine loading from the analyzed VSLSs in the Ex-LS during the NH late summer. Thus, further increases in Asian CH₂Cl₂ and CHCl₃ emissions, as frequently reported in recent years, will further increase the impact of Cl-VSLSs on stratospheric ozone depletion.

20.10.2021: New discussion paper on transport from Asia into the UTLS over the remote Pacific: Smoydzin & Hoor (2021)

Contribution of Asian emissions to upper tropospheric CO over the remote Pacific

We use CO data from the MOPITT satellite instrument from 2000–2019 to compose a climatology of severe pollution events in the mid- and upper troposphere over the northern-hemispheric (NH-) Pacific. To link each individual pollution event detected by MOPITT with a CO source region, we performed trajectory calculations using MPTRAC, a lagrangian transport model. To analyse transport pathways and uplift mechanisms we combine MOPITT data, the trajectory calculations and ERA-Interim reanalysis data.

Events of elevated CO which we detect at level between 500 hPa and 300 hPa over the NH-Pacific throughout the year, occur with a surprisingly high regularity and frequency (70 % of all days during winter, 80 % respectively during spring). Our study further indicates, that the spatial coverage of individual upper tropospheric pollution cluster increased in spring time during the 20 years we analysed.

The position of upper tropospheric pollution plumes show a strong seasonal cycle. During winter, most pollution events are detected over the north-eastern and central NH-Pacific, during spring over the central NH-Pacific and during summer over the western NH-Pacific. We detect most pollution episodes during spring. Trajectory simulations reveal China as the major CO-source region throughout the year. The contribution of other source regions shows a strong seasonal cycle: NE-Asia is a significant CO-source region during winter and summer while India and SE-Asia are important source regions mainly during spring.

17.08.2021: New paper on the TSL available in Weather and Climate Dynamics: Kaluza et al. (2021)

On the occurrence of strong vertical wind shear in the tropopause region: a 10-year ERA5 northern hemispheric study

The paper presents an anaylsis of the global occurrence of vertical shear of the horizontal wind in the UTLS, which gives rise to defining a tropopause shear layer (TSL). The vertical distribution reveals that strong vertical wind shear above the threshold occurs almost exclusively at tropopause altitudes, within a vertically confined layer of about 1–2 km in extent directly above the local lapse rate tropopause. The TSL emerges as a distinct feature in the tropopause-based 10-year temporal and zonal mean climatology, spanning from the tropics to latitudes around 70^∘ N, with average occurrence frequencies on the order of 1 %–10 %. Strong wind shear in the tropopause region is of interest because it can generate turbulence, which in turn can lead to cross-tropopause mixing thereby contributing to the formation of the extratropical tropopause layer (ExTL).

Weather Clim. Dynam., 2, 631–651, https://doi.org/10.5194/wcd-2-631-2021, 2021.

25.05.2021 New Collaborative Research Center TPChange funded

Our new Collaborative Research Center (CRC) named The Tropopause in a Changing Atmosphere will start on 01 July 2021. Peter Hoor is the speaker of the CRC with JGU Mainz being the coordinating university along with Goethe University in Frankfurt.
More infomation about the CRC can be found under the following links (all German):

• IPA Mitteilung
• DFG Pressemitteilung
• JGU Pressemitteilung

More information can be found on the CRC's homepage: https://tpchange.de and also on Twitter (@trr301). In particular, many PhD and PostDoc positions wait to be filled (https://tpchange.de/open-positions/)

13.-14.02.2020 Group seminar in Bacharach

In mid February the group met in Bacharach for the traditional group seminar. Usually, this meeting takes place at the end of the year. However, due to the long SouthTRAC campaign this event was shifted about two months. This meeting provides the chance to present the current status of the individual projects and to discuss the achievements of the last year and even more important the plans of the next months. And of course to have chats not directly related to work. We finally managed to update our group photo on the inner yard of Stahleck castle with the river Rhine well below us.

13.12.2019: New paper available in ACP: Bozem et al. (2019)

Characterization of transport regimes and the polar dome during Arctic spring and summer using in situ aircraft measurements

The paper presents empirical trace gas based evidence on the location of the polar dome in the Canadian high Arctic. For this purpose airborne measurements of CO and CO2 during the NETCARE campaigns were analyzed to identify the transport barrier of the polar dome. It could be shown, that gradients of these species in isentropic and vertical direction mark the transport barrier of the polar dome. This clearly separates isolated innerarctic air masses from mid-latitude air. The distribution of 10-day backward trajectories confirms the existence of different air mass regimes as identified from the chemical composition. The trajectories further allow to identify characteristic transport processes for the air masses encountered during the different meteorological regimes. Based on the correlation between trace species an intermediate mixed regime could be identified during the summer campaign indicating exchange between the high arctic and mid latitudes.

10.12.2019: New paper available in Tellus B: Zanatta et al. (2019)

A new study led by Marco Zanatta (AWI) on trace gas and aerosol measurements over the Southern Baltic Sea is available in Tellus B. Our group contributed with airborne trace gas (CO2, O3) measurements and FLEXPART simulations.

28.11.2019: End of HALO SouthTRAC campaign

HALO is back in Oberpfaffenhofen which marks the end of the second phase and the entire SouthTRAC campaign. In total 25 science flights have been completed on the Northern and Southern Hemisphere shedding in particular new light into the structure of the UTLS on the Southern Hemisphere.
Unfortunately, the second phase could not be completed as planned due to technical issues which, however, should not diminish the overall success of the campaign.

11.11.2019: HALO SouthTRAC campaign article in DFG magazine

An article about the SouthTRAC mission as part of the SPP 1294 has been published in the DFG magazine. The article mainly covers the topics to be addressed in the second phase of the SouthTRAC mission.

29.10.2019: Special issue in ACP/AMT/WCD about isentropic exchange

Following the WISE campaign a special issue dedicated to the WISE mission and related topics is now available in ACP/AMT/WCD. Go and submit!

More information: The Wave-driven ISentropic Exchange (WISE) mission is a collaborative research project to investigate transport and mixing processes in the upper troposphere and the lower stratosphere (UTLS) over the Atlantic. Headed by Forschungszentrum Jülich GmbH and the Johannes Gutenberg University of Mainz, 14 measurement flights were conducted with the high-altitude research aircraft HALO in September and October 2017 from Shannon, Ireland. Further partners providing instrumentation were the Karlsruhe Institute for Technology (KIT), the German Aerospace Center (DLR), the universities of Heidelberg, Frankfurt am Main, and Wuppertal, and the German National Metrology Institute. The scientific flights were supported by a team of about 90 persons.

The main objective of this project is to study the relation between chemical composition and the dynamical structure of the UTLS with a focus on the following topics: (i) interrelation of the tropopause inversion layer (TIL) and trace gas distribution, (ii) role of planetary wave breaking for water vapor transport into the extratropical lower stratosphere, (iii) role of halogenated substances for ozone and radiative forcing in the UTLS region, and (iv) occurrence and effects of sub-visual cirrus (SVC) in the lowermost stratosphere.

The special issue mainly includes papers from the airborne measurement campaign itself but is also open to other studies close to the topic. This includes both advanced scientific analyses of observational and measured data during the campaign as well as related climatological studies, but also manuscripts based on instrumental developments.

09.10.2019: New paper available in ACP: Kunkel et al. (2019)

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

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.

05.08.2019: Start of HALO SouthTRAC campaign

The next field project of the AG Hoor just started with the integration of the measurement equipment in the research aircraft HALO in the last week.

The project SouthTRAC (Southern Hemisphere Transport, Composition and Dynamics) will lead us together with several partners from FZ Jülich, KIT, DLR, University of Frankfurt, University of Wuppertal and University of Heidelberg and with funding from DFG to the southern tip of South America. Our destination and ground base in Argentina will be Rio Grande (53°47' S, 67°42' W).

We will have two intensive measurement periods in Rio Grande, one in September and the other in November. In between HALO will fly back to Oberpfaffenhofen/Germany. The goals of the mission are to study the composition of the UTLS over the Southern Hemisphere, gravity wave dynamics, as well as processes related to the Antarctic vortex.

More information on SouthTRAC can be found

• on our field project website
• in our research blog (in German)
• and on the public SouthTRAC homepage.

 

20.5.2019: New paper available in ACP Kaluza et al. (2019)

Composite analysis of the tropopause inversion layer in extratropical baroclinic waves

The evolution of the tropopause inversion layer (TIL) during cyclogenesis in the North Atlantic storm track is investigated using operational meteorological analysis data (Integrated Forecast System from the European Centre for Medium-Range Weather Forecasts). For this a total of 130 cyclones have been analysed during the months August through October between 2010 and 2014 over the North Atlantic. Their paths of migration along with associated flow features in the upper troposphere and lower stratosphere (UTLS) have been tracked based on the mean sea level pressure field. Subsets of the 130 cyclones have been used for composite analysis using minimum sea level pressure to filter the cyclones based on their strength.

The composite structure of the TIL strength distribution in connection with the overall UTLS flow strongly resembles the structure of the individual cyclones. Key results are that a strong dipole in TIL strength forms in regions of cyclonic wrap-up of UTLS air masses of different origin and isentropic potential vorticity. These air masses are associated with the cyclonic rotation of the underlying cyclones. The maximum values of enhanced static stability above the tropopause occur north and northeast of the cyclone centre, vertically aligned with outflow regions of strong updraft and cloud formation up to the tropopause, which are situated in anticyclonic flow patterns in the upper troposphere. These regions are co-located with a maximum of vertical shear of the horizontal wind. The strong wind shear within the TIL results in a local minimum of Richardson numbers, representing the possibility for turbulent instability and potential mixing (or air mass exchange) within regions of enhanced static stability in the lowermost stratosphere.

15.4.2019: Kunkel et al. 2019: Paper on WISE mission at ACPD

One of the key topics of the WISE mission has been addressed by the Paper of D.Kunkel, who analyzes the occurrence of turbulence and mixing directly at the tropopause above the ridge region of an extratropical cyclone (https://www.atmos-chem-phys-discuss.net/acp-2019-342/). The paper bridges the in-situ observations with the fundamental process view from idealized simulations of baroclinic life cycles. These indicate that strong shear in regions of high static stability at the tropopause may lead to tracer exchange and mixing.

29.3.2019: Rhine-Main Universities undertake research on transport processes in the tropopause region

The Initiative Funding for Research of the Rhine-Main Universities (RMU) is currently supporting a cross-university project in the field of meteorology and climatology. The objective is to determine the time scales of transport processes in the tropopause, a region in the Earth's atmosphere at an elevation of 10 to 20 kilometers. The processes and composition in the tropopause region strongly affect surface temperatures and climate.

Read more

20. - 21. March 2019

The WISE group will meet for a data meeting from 20. - 21. March 2019 at Johannes Gutenberg University in Mainz.

22.2.2019: New Paper in ACP

A new study led by Hannes Schulz (AWI) on the vertical variability of black carbon (BC) in high Arctic spring and summer is available in ACP (https://www.atmos-chem-phys.net/19/2361/2019/). Our group contributed airborne carbon monoxide (CO) measurements and LAGRANTO kinematic back trajectories.

12.2.2019: Bozem et al. 2019 in ACPD

A new diagnostic for the determination of the polar dome boundary is presented using airborne in-situ CO and CO2 data as well as 10-day kinematic back trajectories in the European and Canadian Arctic in July 2014 and April 2015. Using the tracer derived boundary the analysis of the recent transport history of air masses within the polar dome reveals significant differences of dome extent and transport properties between spring and summer (https://www.atmos-chem-phys-discuss.net/acp-2019-70/).

19.11.2018: Kaluza et al., 2018 in ACPD

A new view on the static stability structure of extratropical cyclones is presented using a composite analysis of cyclones identified from ECMWF operational analysis data. The analysis shows, that even in regions of high static stability conditions favorable for cross tropopause exchange exist, which are linked to the occurrence of strong vertical shear of horizontal winds (https://www.atmos-chem-phys-discuss.net/acp-2018-1100/)

7 - 9 November 2018, OCTAV-UTLS workshop in Mainz

The 2nd meeting of the SPARC activity OCTAV-UTLS took place at the Helmholtz Institute (HIM) in Mainz. Speakers from the United States, UK, France and Gernany discussed new approaches and potential methods to account for the dynamical induced variability of ozone observations from different observations systems. These include radio sondes, LIDAR, aircraft measurements and satellite observations. The group defined a set of common diagnostic approaches to be applied to the different data sets, which allow to directly compare distributions and trends of ozone from different platforms and observational geometries consistently in the UTLS region. The comparison will be done at the next meeting in the United States at the Table Mountain lidar site.

13.10.2018: New discussion paper in ACPD

A summary paper about the advances of our understanding in the processes controlling Arctic aerosols during the NETCARE project led by Jonathan Abbatt (University of Toronto) and W. Richard Leaitch (Environment and Climate Change, Toronto) has been published for discussion in ACPD.
Our group contributed with airborne measurements during NETCARE 2014 and NETCARE 2015 as well as with FLEXPART simulations to analyze air mass histories.

02.10.2018: New discussion paper in ACPD

A new study led by Meng Si (University of British Columbia) on ice-nucleating particles in the Canadian High Arctic during spring 2016 is available in ACPD.
Our group provided FLEXPART results for a source attribution of the ice-nucleating particles.

01.-05.10.2018: SPARC General Assembly in Kyoto, Japan

This week the SPARC GA takes place in Kyoto, Japan.
Peter Hoor will present first results on the WISE campaign and an overview on the OCTAV-UTLS activities.

31.08.2018: OCTAV-UTLS workshop, 7 - 9 November 2018, Mainz

The SPARC OCTAV - UTLS working group will meet for a data meeting from 7 - 9 November 2018 at the Johannes Gutenberg University in Mainz. We will host this meeting which will take place at the Helmholtz Institute Mainz (HIM).

More information can be found here.

24.08.2018: New discussion paper in ACPD

A new study led by Megan Willis (University of Toronto) on the vertical distribution of aerosols in the high Arctic is available now in ACPD.
Our group contributed airborne measurement data, ECMWF analysis data as well as results from FLEXPART simulations.

07.08.2018: HALO mission CAFE AFRICA started

Two member of our group, Franziska Köllner and Oliver Eppers, participate in the current HALO mission CAFE-AFRICA (lead: MPIC, Mainz) which is based on Cap Verde and studies the influence of the massive biomass burning emissions from southern Africa on the atmospheric oxidation capacity over the tropical and South Atlantic Ocean.

More information can be found here.