CHARACTERISATION OF ARCTIC CIRRUS BY
AIRBORNE WATER VAPOR AND HIGH
SPECTRAL RESOLUTION LIDAR
Martin Wirth and Silke Groß, German Aerospace Center, LIDAR Department
Institute of Atmospheric Physics (IPA) | Münchener Str. 20 | 82234 Wessling | Germany

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Ice Clouds in the Arctic▪ Ice clouds in the Arctic have different radiative impact
compared to Mid-Latitudes▪ T, q and aerosol profiles are different, resulting in different
number concentration, size and shape distributions▪ Sign of net radiative impact depend on details▪ In a changing climate warm air intrusions are expected to be morefrequent, which may also change the radiative impact of ice clouds in highlatitudes▪ Ice cloud observations have to be classified according to the backgroundatmospheric state, the formation mechanism and the state of the cloudwithin its life-cycle▪ RHice is one key parameter, but difficult to measure by remote sensing
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HALO-(AC)3 Airborne Campaign▪ Field experiment in March/April 2022 out of Kiruna
northern Sweden▪ Deployment of the German Research Aircraft HALO
with a remote sensing payload: H2O-DIAL/HSRL,
Cloud Radar, Microwave Radiometers, Passive
imaging and integration radiation measurements invarious spectral bands and a drop-sonde system▪ A total of 19 research flights over the sea between
Svalbard and Greenland and up to nearly 90°N

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Determination of Relative Humidity from DIAL
Measurements of q and Model Data of T

▪ From comparison with 339 dropsondes: T-bias ≈ 0.2 K, precision ≈ 0.4 K▪ Translates to a T-induced RHice error of: 2% bias and 4% precision▪ No relevant bias in pressure (important for correct geometrical altitude assignment)
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HALO-(AC)3 RF03 13.03.2022: Warm Air Intrusion▪ Strong intrusion of warm and moist mid-latitude air up to the pole
▪ Cloud tops reach 12 km altitude (4 km more than typical)▪ Cirrus is strongly structured with imbedded regions of high super-saturation (> 140%)
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HALO-(AC)3 RF15 08.04.2022: Arctic Origin Cirrus▪ Cloud tops only up to 6-7 km. Low optical thickness of cirrus part
▪ Very smooth RHi-field with only moderate supersaturation
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HALO-(AC)3: Warm Air Intrusion vs. Arctic Origin
RF03 compared to RF15

▪ Higher backscatter and depolarization ratios in the intrusion case (more available H2O → larger crystals)▪ Significantly higher super-saturations in the intrusion (freshly formed cirrus ↔ aged clouds?)

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Mixed Scene Case on 30. March 2022…

SR

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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic▪ Airborne Lidar shows extend aerosol layer between 6-8 km altitude▪ Depolarization, color ratio (and lidar ratio) point to aerosols of desert dust type
▪ Backward trajectories link to previous strong Saharan dust outbreak
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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
Dust Layer

Cirrus formed under
dust free condiditons

Dust Layer

Cirrus formed under dust influence▪ Ice clouds embedded in the aerosol layer show higher backscatter▪ Particle depolarization has comparable median but higher peak-value for the dust-case10

HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
Comparison of pristine cirrus vs. dust influenced cirrus
Out of cloud dust

▪ Dust influenced cirrus shows lower supersaturations, higher backscatter and depol. ratios▪ Points to domination of nucleation process by heterogenous freezing on dust particles→ Fewer, but larger ice crystals show different radiative properties
11HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic▪ Cirrus for No Dust case represented
quite well in ECMWF IFS analyses▪ Model RHi for Dust Case is slightly lower
which seems to suppress cloud formationin the model▪ Missing Elements could be:heterogenous nucleation on dustparticles and/or subscale T fluctuations(e.g. in gravity waves)

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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
What would see ATLID?

▪ Vertical resolution set to 100 m▪ Horizontal resolution set to 10 km (1.4 s integration) for S/N reasons
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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
What would see ATLID?

▪ Noise data from ATLID ground validation(Pereira do Carmo et al. https://doi.org/10.3390/atmos12010076)▪ Equivalent noise level for 532 nm applied (with color ratio of 1.5 for aerosol)
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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
Comparison of pristine cirrus vs. dust influenced cirrus with IFS H2O▪ In-Cloud Rhi clamped to 100% → no distinction wrt nucleation processpossible!!!
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HALO-(AC)3 RF11 30.03.2022: Aerosol Trapped in the Arctic
Comparison of pristine cirrus vs. dust influenced cirrus with IFS H2O + ATLID data

▪ Very hard to draw conclusion wrt. to cloud microphysics…

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Summary & OutlookThis Talk
▪ Joint 2-d measurements of optical properties of ice clouds and humidity enable the detailed
characterization of cirrus clouds▪ RH-ice determined form DIAL and Model-T give reliable results▪ Similar studies may be possible using EarthCARE data, provided adaptive signal smoothing isapplied and better RHi data is available

Next Steps▪ Combination with radar to retrieve eff. radius and ice water content▪ Comparison with in-situ measurements for verification (joint flights with FAAM)▪ Combination of trajectories and satellite images to link optical properties to life-cycle of clouds▪ Statistical analyses of all flights

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