Cirrus Clouds and Their Response to Anthropogenic Activities

Kärcher, B.

doi:10.1007/s40641-017-0060-3

Cited by 66 publications

(74 citation statements)

References 111 publications

(112 reference statements)

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“…There are discussions if cirrus clouds are mainly formed by homogeneous nucleation as we assume in our reference simulation or are nucleated heterogeneously (Cziczo et al, 2013;Spichtinger and Krämer, 2012;Kärcher, 2017). We investigate the impact of homogeneous vs. heterogeneous freezing in cirrus clouds by performing one simulation in which all cirrus clouds form heterogeneously (simulation HET) instead of homogeneous nucleation in simulation REF.…”

Section: Model Set-up and Experimentsmentioning

confidence: 99%

The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

Lohmann

Neubauer

2018

Atmos. Chem. Phys.

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Abstract. How clouds change in a warmer climate remains one of the largest uncertainties for the equilibrium climate sensitivity (ECS). While a large spread in the cloud feedback arises from low-level clouds, it was recently shown that mixed-phase clouds are also important for ECS. If mixedphase clouds in the current climate contain too few supercooled cloud droplets, too much ice will change to liquid water in a warmer climate. As shown by Tan et al. (2016), this overestimates the negative cloud-phase feedback and underestimates ECS in the CAM global climate model (GCM). Here we use the newest version of the ECHAM6-HAM2 GCM to investigate the importance of mixed-phase and ice clouds for ECS.Although we also considerably underestimate the fraction of supercooled liquid water globally in the reference version of the ECHAM6-HAM2 GCM, we do not obtain increases in ECS in simulations with more supercooled liquid water in the present-day climate, different from the findings by Tan et al. (2016). We hypothesize that it is not the global supercooled liquid water fraction that matters, but only how well low-and mid-level mixed-phase clouds with cloud-top temperatures in the mixed-phase temperature range between 0 and −35 • C that are not shielded by higher-lying ice clouds are simulated. These occur most frequently in midlatitudes, in particular over the Southern Ocean where they determine the amount of absorbed shortwave radiation. In ECHAM6-HAM2 the amount of absorbed shortwave radiation over the Southern Ocean is only significantly overestimated if all clouds below 0 • C consist exclusively of ice. Only in this simulation is ECS significantly smaller than in all other simulations and the cloud optical depth feedback is the dominant cloud feedback. In all other simulations, the cloud optical depth feedback is weak and changes in cloud feedbacks associated with cloud amount and cloud-top pressure dominate the overall cloud feedback. However, apart from the simulation with only ice below 0 • C, differences in the overall cloud feedback are not translated into differences in ECS in our model. This insensitivity to the cloud feedback in our model is explained with compensating effects in the clear sky.

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Section: Model Set-up and Experimentsmentioning

confidence: 99%

The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

Lohmann

Neubauer

2018

Atmos. Chem. Phys.

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“…While high-level ice clouds are a key component of the changing climate system, there remains an absence of wellcharacterised observational constraints of ice cloud microphysics that are desired for climate model evaluation (Kärcher, 2017). The Atmospheric Infrared Sounder (AIRS) instrument, launched in May of 2002, is radiometrically stable within ±3-4 mK yr −1 (Pagano et al, 2012).…”

Section: Summary Conclusion and Outlookmentioning

confidence: 99%

“…The areal extent of cloud anvils are correlated to upper tropospheric lapse rate (Bony et al, 2016) and additionally ice hydrometeor fall speed, with larger (smaller) anvils for smaller (larger) r ei (Satoh and Matsuda, 2009). The radiometrically stable AIRS instrument (Pagano et al, 2012) may provide constraints on ice cloud microphysical properties that are highly desired (Kärcher, 2017).…”

Section: Introductionmentioning

confidence: 99%

“…While not the focus of this investigation, aerosols modulate ice clouds through numerous indirect and direct pathways (Liu et al, 2007;Gettelman et al, 2010;Kärcher, 2017). Variable magnitudes of r ei at convective tops result from variations in cloud condensation nuclei (CCN) or ice nuclei (IN); these responses are highly nonlinear because of complex liquid and ice phase microphysical processes as a function of updraft velocity, concentration and composition of CCN and IN (Phillips et al, 2007;Van Weverberg et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder

et al. 2018

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Abstract. We use the Atmospheric Infrared Sounder (AIRS) version 6 ice cloud property and thermodynamic phase retrievals to quantify variability and 14-year trends in ice cloud frequency, ice cloud top temperature (T ci ), ice optical thickness (τ i ) and ice effective radius (r ei ). The trends in ice cloud properties are shown to be independent of trends in information content and χ 2 . Statistically significant decreases in ice frequency, τ i , and ice water path (IWP) are found in the SH and NH extratropics, but trends are of much smaller magnitude and statistically insignificant in the tropics. However, statistically significant increases in r ei are found in all three latitude bands. Perturbation experiments consistent with estimates of AIRS radiometric stability fall significantly short of explaining the observed trends in ice properties, averaging kernels, and χ 2 trends. Values of r ei are larger at the tops of opaque clouds and exhibit dependence on surface wind speed, column water vapour (CWV) and surface temperature (T sfc ) with changes up to 4-5 µm but are only 1.9 % of all ice clouds. Non-opaque clouds exhibit a much smaller change in r ei with respect to CWV and T sfc . Comparisons between DARDAR and AIRS suggest that r ei is smallest for singlelayer cirrus, larger for cirrus above weak convection, and largest for cirrus above strong convection at the same cloud top temperature. This behaviour is consistent with enhanced particle growth from radiative cooling above convection or large particle lofting from strong convection.

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“…The relative importance of these different processes is relevant for determining the ICNC and the ice crystal size distribution (e.g. Kärcher, 2017), which can affect the reflectivity, extent and lifetime of a cirrus cloud.…”

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confidence: 99%

Technical note: An automated cirrus classification

Gryspeerdt¹,

Quaas²,

Goren³

et al. 2017

Preprint

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Abstract. Cirrus clouds play an important role in determining the radiation budget of the earth, but many of their properties remain uncertain, particularly their response to aerosol variations and to warming. Part of the reason for this uncertainty is the dependence of cirrus clouds on the mechanism of formation, which itself is strongly dependent on the local meteorological conditions. In this work, a classification system (Identification and Classification of Cirrus or IC-CIR) is introduced to identify cirrus 5clouds by their formation mechanisms. Using re-analysis and satellite data, cirrus clouds are separated in four main types: orographic, frontal, convective and in-situ. Through a comparison to convection-permitting model simulations and back-trajectory based analysis, it is shown that the regimes can provide extra information on the properties and origin of cirrus that could not be provided by the retrieved cloud properties or reanalysis data alone. This classification is designed to be easily implemented in GCMs, helping improve future model-observation comparisons and leading to improved parametrisations of cirrus cloud 10 processes.

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Cirrus Clouds and Their Response to Anthropogenic Activities

Cited by 66 publications

References 111 publications

The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

The importance of mixed-phase and ice clouds for climate sensitivity in the global aerosol–climate model ECHAM6-HAM2

Ice cloud microphysical trends observed by the Atmospheric Infrared Sounder

Technical note: An automated cirrus classification

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