Modelling of cirrus clouds – Part 1a: Model description and validation

Spichtinger, Peter; Gierens, Klaus

doi:10.5194/acp-9-685-2009

Cited by 109 publications

(205 citation statements)

References 81 publications

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“…This scenario is used quite often in many idealized studies in order to investigate ice formation at constant updraughts under certain conditions (see, e.g. Kärcher and Lohmann, 2002;Hoyle et al, 2005;Barahona and Nenes, 2008;Spichtinger and Gierens, 2009a;Spichtinger and Cziczo, 2010), leading to a one-toone relationship between vertical updraughts and ice crystal number concentrations produced in such cooling events.…”

Section: Homogeneous Freezing Of Solution Droplets: Rhi Variations Anmentioning

confidence: 99%

“…The model is described in detail in Spichtinger and Gierens (2009a) and Spichtinger and Cziczo (2010), thus here only some key properties are briefly described. The double-moment scheme with prognostic equations for ice crystal mass and number concentration is based on general moments of the underlying mass distribution(s) of the ice crystals, which are assumed to be lognormal with a fixed geometric standard deviation of mass σ m = 2.85, corresponding to a geometric standard deviation of length σ L ∼ 1.4-1.6.…”

Section: The Ice Cloud Modelmentioning

confidence: 99%

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Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Spichtinger

Krämer²

2013

Atmos. Chem. Phys.

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Abstract. The occurrence of high, persistent ice supersaturation inside and outside cold cirrus in the tropical tropopause layer (TTL) remains an enigma that is intensely debated as the "ice supersaturation puzzle". However, it was recently confirmed that observed supersaturations are consistent with very low ice crystal concentrations, which is incompatible with the idea that homogeneous freezing is the major method of ice formation in the TTL. Thus, the tropical tropopause "ice supersaturation puzzle" has become an "ice nucleation puzzle". To explain the low ice crystal concentrations, a number of mainly heterogeneous freezing methods have been proposed. Here, we reproduce in situ measurements of frequencies of occurrence of ice crystal concentrations by extensive model simulations, driven by the special dynamic conditions in the TTL, namely the superposition of slow large-scale updraughts with high-frequency short waves. From the simulations, it follows that the full range of observed ice crystal concentrations can be explained when the model results are composed from scenarios with consecutive heterogeneous and homogeneous ice formation and scenarios with pure homogeneous ice formation occurring in very slow (< 1 cm s −1 ) and faster (> 1 cm s −1 ) largescale updraughts, respectively. This statistical analysis shows that about 80 % of TTL cirrus can be explained by "classical" homogeneous ice nucleation, while the remaining 20 % stem from heterogeneous and homogeneous freezing occurring within the same environment. The mechanism limiting ice crystal production via homogeneous freezing in an environment full of gravity waves is the shortness of the gravity waves, which stalls freezing events before a higher ice crystal concentration can be formed.

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Section: Homogeneous Freezing Of Solution Droplets: Rhi Variations Anmentioning

confidence: 99%

Section: The Ice Cloud Modelmentioning

confidence: 99%

Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Spichtinger

Krämer²

2013

Atmos. Chem. Phys.

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“…), cloud internal dynamics (Marsham and Dobbie, 2005;Fusina and Spichtinger, 2010) and background aerosols that are either liquid and freeze homogeneously (Hoyle et al, 2005;Spichtinger and Gierens, 2009a) or contain a solid and may act as heterogeneous ice nuclei (DeMott et al, 2010). Ice in the upper troposphere is known to nucleate via both pathways, homogeneous freezing of aqueous solution droplets (Koop et al, 2000) or heterogeneous nucleation on solid aerosol particles (DeMott et al, 2003).…”

Section: A Cirisan Et Al: Balloon-borne Match Measurementsmentioning

confidence: 99%

Balloon-borne match measurements of midlatitude cirrus clouds

et al. 2014

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Abstract.Observations of high supersaturations with respect to ice inside cirrus clouds with high ice water content (> 0.01 g kg −1 ) and high crystal number densities (> 1 cm −3 ) are challenging our understanding of cloud microphysics and of climate feedback processes in the upper troposphere. However, single measurements of a cloudy air mass provide only a snapshot from which the persistence of ice supersaturation cannot be judged. We introduce here the "cirrus match technique" to obtain information about the evolution of clouds and their saturation ratio. The aim of these coordinated balloon soundings is to analyze the same air mass twice. To this end the standard radiosonde equipment is complemented by a frost point hygrometer, "SnowWhite", and a particle backscatter detector, "COBALD" (Compact Optical Backscatter AerosoL Detector). Extensive trajectory calculations based on regional weather model COSMO (Consortium for Small-Scale Modeling) forecasts are performed for flight planning, and COSMO analyses are used as a basis for comprehensive microphysical box modeling (with grid scale of 2 and 7 km, respectively). Here we present the results of matching a cirrus cloud to within 2-15 km, realized on 8 June 2010 over Payerne, Switzerland, and a location 120 km downstream close to Zurich. A thick cirrus cloud was detected over both measurement sites. We show that in order to quantitatively reproduce the measured particle backscatter ratios, the smallscale temperature fluctuations not resolved by COSMO must be superimposed on the trajectories. The stochastic nature of the fluctuations is captured by ensemble calculations. Possibilities for further improvements in the agreement with the measured backscatter data are investigated by assuming a very slow mass accommodation of water on ice, the presence of heterogeneous ice nuclei, or a wide span of (spheroidal) particle shapes. However, the resulting improvements from these microphysical refinements are moderate and comparable in magnitude with changes caused by assuming different regimes of temperature fluctuations for clear-sky or cloudysky conditions, highlighting the importance of proper treatment of subscale fluctuations. The model yields good agreement with the measured backscatter over both sites and reproduces the measured saturation ratios with respect to ice over Payerne. Conversely, the 30 % in-cloud supersaturation measured in a massive 4 km thick cloud layer over Zurich cannot be reproduced, irrespective of the choice of meteorological or microphysical model parameters. The measured supersaturation can only be explained by either resorting to an unknown physical process, which prevents the ice particles from consuming the excess humidity, or -much more likely -by a measurement error, such as a contamination of the sensor housing of the SnowWhite hygrometer by a precipitation drop from a mixed-phase cloud just below the cirrus layer or from some very slight rain in the boundary layer. This uncertainty calls for in-flight checks or calibrations of hygrom...

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“…For masses below m split , a geo,con = 526.1 and b geo,con = 3.0 is prescribed which defines quasispherical hexagonal columns with aspect ratio 1 (see derivation in Spichtinger and Gierens, 2009). The upper limit is set to a relatively small value of m max = 2 × 10…”

Section: The Contrail Ice Classmentioning

confidence: 99%

“…For this, we use a piece-wise definition of a geo and b geo (Spichtinger and Gierens, 2009;Heymsfield and Iaquinta, 2000). For masses above m split = 2.15×10…”

Section: The Contrail Ice Classmentioning

confidence: 99%

Contrails and Their Impact on Shortwave Radiation and Photovoltaic Power Production – A Regional Model Study

Gruber¹,

Unterstraßer²,

Bechtold³

et al. 2017

Preprint

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Abstract. A high resolution regional-scale numerical model was extended by a parameterization that allows for both the generation and the life cycle of contrails and contrail cirrus to be calculated. The life cycle of contrails and contrail cirrus is described by a two-moment cloud microphysical scheme that was extended by a separate contrail ice class for a better representation of the high concentration of small ice crystals that occur in contrails. The basic input data set contains the spatially and temporally highly resolved flight trajectories over Central Europe derived from real time data. The parameterization provides 5 aircraft-dependent source terms for contrail ice mass and number. A case study was performed to investigate the influence of contrails and contrail cirrus on the radiative fluxes at the earth's surface. Accounting for contrails produced by aircraft enabled the model to simulate high clouds that were otherwise missing on this day. The effect of these extra clouds was to reduce the incoming shortwave radiation at the surface as well as the production of photovoltaic power by up to 10 %.

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Modelling of cirrus clouds – Part 1a: Model description and validation

Cited by 109 publications

References 81 publications

Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Tropical tropopause ice clouds: a dynamic approach to the mystery of low crystal numbers

Balloon-borne match measurements of midlatitude cirrus clouds

Contrails and Their Impact on Shortwave Radiation and Photovoltaic Power Production – A Regional Model Study

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