CIRRUS in High Latitudes

Mission status: Currently ongoing

Mission Website:

HALO Deployment Base

Time Period

Feb 1, 2021 – Sep 17, 2021

Mission phaseDates
Flight testing of ext. config01.02.2021-18.04.2021
Integration phase19.05.2021-02.06.2021
Instrument tests and preparations03.06.2021-23.06.2021
EMI test flight24.06.2021
Mission phase25.06.2021-29.07.2021
Dismlount of payload30.07.2021-17.09.2021

Project description


The CIRRUS-HL campaign is a joint atmospheric research project by German research centres and universities within the DFG HALO-SPP 1294 framework. The experiment deploys the research aircraft HALO together with satellites and models to gain new insights into nucleation, properties, and climate impact of ice clouds in high latitudes, hence in a region of the world with strongest anthropogenic increase in surface temperatures. Aviation effects on clouds and contrail impact on climate will be studied in flight above Central Europe and the North Atlantic flight corridor.

Most rapid climate change occurs in high latitudes. Here, ice clouds exert a substantial positive forcing onto surface temperatures. However, direct observations of cirrus properties in high latitudes and their variability are sparse, and ice clouds and related aerosol effects are not adequately represented in today’s climate models which currently limits our understanding of cirrus effects on climate.

Aviation at present contributes with 3 to 4 % to the total anthropogenic effective radiative forcing (Lee et al., 2021). More than half of the effective forcing results from contrail cirrus, about a third from aviation’s CO2 emissions, together contributing more than 90 % to the total climate impact from aviation. Only a low number of flights in so-called contrail hot spots have large share on the energy forcing and the related warming by contrail cirrus. As a demo experiment, it is a goal of the CIRRUS-HL mission to investigate the contrail hot spots and the potential for climate impact reduction by avoiding those regions. Also the effect of day time contrail cooling will be investigated.

CIRRUS-HL, the only HALO cloud mission combining in situ and remote sensing cloud instrumentations since 2014, uses state-of-the-art cloud probes, and novel ice residual, aerosol, trace gas and radiation instruments to investigate nucleation, life cycle and radiative impact of ice clouds in high latitudes and of anthropogenic contrail cirrus. The aircraft observations are accompanied by remote sensing from satellite and by numerical simulations with global and process-based models. The campaign is complementary linked to international polar research activities by focusing on the physics of ice clouds and anthropogenic perturbations.

From June to July 2021, HALO performs flights in the Arctic and Northern Europe with a focus on high-latitude cirrus induced by different meteorological regimes including synoptic cirrus with slow updrafts, frontal or warm conveyor belt cirrus with moderate updrafts and orographic or convective cirrus characterized by high updrafts. A differentiation is made between in situ cirrus which formed homogeneously or heterogeneously at temperatures below 238 K and liquid origin cirrus. To get more insight into liquid origin cirrus and ice nucleation, mixed phase and ice clouds are also probed at temperatures above 238 K.

In addition microphysical and optical properties of contrail cirrus will be investigated and the diurnal evolution of the radiative impact will be measured.

Hence, CIRRUS-HL provides

  1. comprehensive observations of microphysical properties of ice clouds and their variability in the poorly probed high latitudes for process studies as well as satellite and model evaluation,
  2. new insights into aerosol transport into the Arctic and heterogeneous ice nucleation,
  3. observations of radiative properties of ice clouds in high latitudes in summer,
  4. novel observation on contrail cirrus properties in contrail hot spots, and
  5. first airborne experimental data on soot effects on cirrus

Summarized, CIRRUS-HL provides a comprehensive data set on contrail cirrus and ice clouds in high latitudes to enhance our understanding of their climate impact.

Science Goals

  1. Investigate distributions of microphysical, optical and radiative properties of cirrus clouds to better understand and more accurately quantify their climate impact
  2. Study cirrus properties, lifetime, ambient conditions (updraft, RHI, aerosol load) in meteorological regimes typical for high latitudes → focus in-situ cirrus
  3. Validate satellite products and ground-based observations and evaluate advanced cloud models
  4. Assess cirrus and contrail cirrus predictability → Contrail avoidance demo
  5. Directly observe contrail cirrus and investigate differences between contrail and natural cirrus
  6. Quantify an aviation effect on cirrus

Scientific questions

Cirrus at high and mid latitudes
  • Are cirrus clouds adequately represented in climate models? Convection? Mixed phase clouds? → What is the related uncertainty in their climate impact?
  • Do weather models underestimate/overestimate water vapor and RHi in cirrus regions, in the upper troposphere and in the lower stratosphere?
  • What is the role of clouds for the Arctic amplification?
  • Are Arctic cirrus observations from Calipso real?
  • Process studies: Convection, WCB, ridge cirrus, high pressure cirrus, leewave cirrus
Aviation cirrus
  • Do contrails significantly modify microphysical, optical and radiation effect on cirrus in mid-latitudes?
  • Do cirrus properties in regions with high air traffic differ from cirrus in regions with low airtraffic?
  • Is there an aviation impact on cirrus (in addition to contrails)?
  • Do we understand the daily cycle of cirrus radiative effects (LW/SW/Net)?
  • Is there a distinguishable anthropogenic effect on cirrus (compared to e.g. BLUESKY 2020, ML-CIRRUS 2014)?

Persons in Charge


Christiane Voigt

Mission coordinator

Tina Jurkat-Witschas

Contact point at DLR-FX for this mission:

Thomas Sprünken


    • DLR, Institute of Atmospheric Physics
    • Karlsruhe Institute of Technology
    • University Leipzig
    • Johannes Gutenberg University Mainz
    • Max Planck Institute for Chemistry
    • Ludwig Maximilians University Munich
    • Forschungszentrum Jülich
    • Goethe University Frankfurt
    • University Heidelberg
    • Leibniz Institute for Tropospheric Research

Cabin and exterior configuration of HALO for the mission

HALO cabin configuration for CIRRUS-HL

HALO exterior configuration for CIRRUS-HL

Press releases, media etc

Press release about CIRRUS-HL from 22 July 2021