Arctic Springtime Chemistry Climate Investigations

Mission status: scheduled

Persons in Charge


  • Andreas Engel (Univ. Frankfurt)
  • Björn-Martin Sinnhuber (KIT)

Contact point at DLR-FX for this mission:


HALO Deployment Base

Time Period

January – April 2025

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Project description

Scientific Rationale

The Arctic is the region that experiences the largest and most rapid climate change on earth. In addition to the increase in long-lived greenhouse gases, short lived climate pollutants such as ozone and aerosols play an important role in Arctic warming, but many uncertainties about processes and impacts remain with large differences between models and observations of Arctic tropospheric chemistry and composition. Substantial ozone depletion in the Arctic lowermost stratosphere has been observed in several recent winter/spring seasons as a result of anthropogenic ozone depleting substances, not well captured by current earth system models. The expected Arctic ozone recovery in the coming decades will exert a positive radiative forcing, the magnitude of which is still uncertain.

Knowledge on the vertical profile and the latitudinal distribution of trace gas and aerosol changes is critical for assessing the associated radiative forcing. Additional aircraft campaigns providing vertically resolved features of short-lived climate pollutants should be given a top priority for future studies. Both emission sources outside the Arctic and within the Arctic contribute to Arctic pollution. Climate pollutants from mid-latitude sources are primarily transported into the Arctic mid- and upper troposphere due to uplift along sloping isentropic surfaces, impacting on free tropospheric ozone. Emission within the Arctic are largely confined to the Arctic lower troposphere at low potential temperatures (“Polar Dome”). Ozone in the Arctic boundary layer during springtime is strongly influenced by “bromine explosion” and ozone depletion events. Despite progress in understanding of the chemical processes involved in the bromine explosion events, there is still little knowledge on their larger scale impacts.

The HALO campaign POLSTRACC was successfully conducted in the unusually cold Arctic winter 2015/16 and provided important information on transport and chemistry under these conditions. However, observations during the unusually cold stratospheric Arctic winter 2015/16 are not necessarily representative and call for a follow up study in another winter to capture inter-annual variability and changes. In addition to the different year (different meteorological conditions, 7-9 years after POLSTRACC), modified measurement capabilities and refined flight strategies to meet the focus of the current proposal will expand the observational base of the 2015/16 POLSTRACC campaign with a stronger focus on composition changes from the lower stratosphere to the mid troposphere at high Arctic latitudes.

In addition to probing the Arctic during the late winter, we suggest to extend the campaign into later spring (e.g. early May) and mid-latitudes to investigate the impact of stratospheric ozone and ozone anomalies onto upper tropospheric and lower stratospheric ozone in the mid latitude lower stratosphere and upper troposphere during spring time. It has been shown that interannual variability of stratospheric ozone are the largest cause for interannual variability in southern hemispheric upper tropospheric ozone. We suggest to provide a database for investigation of this linkage in the northern hemisphere, by extending the measurements into spring and also by using ozone sonde stations and satellite data.

Specific Objectives
1.Inter-annual variability of Arctic lower stratospheric ozone depletion and the implications for radiative forcing and surface climate impacts of ozone recovery
  • How much does ozone and ozone depletion processes differ in the Arctic lowermost stratosphere relative to the cold POLSTRACC winter of 2015/16? Sensitivity to different meteorological conditions should help to further constrain modelled sensitivities.
  • What is the impact of Arctic ozone depletion on mid-latitude airmasses later in spring?
2. High latitude stratosphere-troposphere exchange and the structure of the high latitude tropopause
  • By how much is ozone (and other trace gases) in the high Arctic troposphere influenced by transport from the stratosphere? What is the relative contribution of tropopause folding events relative to large scale radiative subsidence?
3. Short-lived climate pollutants (ozone, aerosols) and their precursors in the Arctic mid and upper troposphere
  • How well do models reproduce pollutants in the Arctic mid and upper troposphere? Observations from POLSTRACC and other campaigns indicate large discrepancies. Is this due to unknown sources, transport pathways or missing chemical processes?
Deployment and flights patterns

ASCCI/POLSTRACC-2 will focus on the high Arctic during spring. We plan an approximately 3 week deployment in Kiruna, Sweden (69°N) with about 6 science flights, plus transfers. The capabilities of HALO will enable science flights into the high Arctic up to the North Pole and possibly even beyond.

Flights will be tailored to sample the high Arctic troposphere and lower stratosphere. Maximum flight altitudes will be used for the remote sensing instruments and for probing the Arctic stratosphere, together with deep dives at high latitudes and stacked flights for in-situ probing of the mid/upper Arctic troposphere. Dropsondes will be primarily used over the data poor Arctic ocean. Quasi-Lagrangian flight patterns will be employed to investigate transformation of airmasses along transport pathways.

Additional flights performed from Oberpfaffenhofen later in spring will focus on the impact on mid-latitudes. We plan to perform 3 flights to probe the large scale distribution of trace species in the UTLS of the Northern Hemisphere. During these flight we will also target remnants of polar vortex air, which could e.g. be tracked by
using specific origin tracers in the CLaMS model for flight planning.

Chemistry transport and earth system models will play an important role for flight planning and analysis.Coordination with ozone sonde, ground based (in particular from the Network for the Detection of Atmospheric Composition Change, NDACC) and satellite observations will provide important context for the HALO observations. In addition we plan to launch several small balloons with AirCores on them to provide information on selected tracers, mean age and ozone on the stratosphere above Kiruna during the spring time.


    • Goethe University Frankfurt
    • Karlsruhe Institute of Technology (KIT)
    • Johannes Gutenberg University Mainz
    • Heidelberg University
    • University of Wuppertal
    • Forschungszentrum Jülich (FZ Jülich)
    • German Aerospace Center, Institute of Atmospheric Physics (DLR-IPA)

Scientific instruments and payload configuration

  • List of scientific instruments for the mission:

DescriptionPrincipal investigatorInstitution
GLORIAGimballed Limb Observer for Radiance Imaging
of the Atmosphere
Felix Friedl-Vallon,
Peter Preuße
FZ Jülich
WALESWater Vapour Lidar Experiment in SpaceMartin WirthDLR-IPA
FISHFast In-situ Stratospheric HygrometerMartina KrämerFZ Jülich
FAIROFast ozone measurementAndreas ZahnKIT
AENEASNOY measurementHelmut ZiereisDLR-IPA
AIMSAtmospheric Chemical Ionization Mass SpectrometerChristiane Voigt, Tina JurkatDLR-IPA
UMAQSQuantum cascade laser absorption spectroscopyPeter Hoor, Heiko BozemUniv. Mainz
HAGAR-VHigh Altitude Gas AnalyzeRMichael VolkUniv. Wuppertal
GhOSTGaschromatograph for Observation of Stratospheric TracersAndreas Engel, Harald BönischUniv. Frankfurt
KIT DropsondesMeteorological dropsondesAndreas WieserKIT
miniDOASDifferential Optical Absorption Spectroscopy Klaus PfeilstickerUniv. Heidelberg
BAHAMASHALO basic data acquisition systemAndreas GiezDLR-FX

Cabin and exterior configuration of HALO for the mission

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HALO flights for this mission

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More information

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Press releases, media etc

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