Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate

Jensen, E. J.; Toon, O. B.

doi:10.1029/94gl01287

Cited by 94 publications

(90 citation statements)

References 17 publications

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“…Thus the consumption of supersaturation proceeds slowly and the nucleation processes can act longer and at a higher rate, producing more crystals than in the warmer case. This effect has been observed earlier in simulations by Jensen and Toon (1994). Second, one observes that already the curve for SNF = 0.3 bears signs of homogeneous nucleation, such that in this case the critical soot concentration is one order of magnitude larger (i.e.…”

Section: The Box Modelsupporting

confidence: 59%

On the transition between heterogeneous and homogeneous freezing

Gierens

2003

Atmos. Chem. Phys.

111

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Abstract. Box model simulations of an uplifting and adiabatically cooling cloud of aerosol have been performed in order to study the transition between cirrus formation dominated by homogeneous nucleation of ice to that dominated by heterogeneous nucleation. The aerosol was assumed to consist of an internal mixture of sulfuric acid solution droplets with inclusions of soot. The parametrisation of DeMott et al. (1997) was used to simulate the heterogeneous nucleation of ice in such droplets with soot inclusions. The simulations show that the transition from heterogeneous to homogeneous nucleation occurs over a narrow range of soot concentration. Thus it seems to be possible to fix critical concentrations of heterogeneous ice nuclei which must be exceeded if heterogeneous freezing dominates cirrus formation. A formula has been derived that allows to compute the critical concentrations of heterogeneous ice nuclei as a function of temperature, updraft speed, ambient pressure, and supersaturation at which heterogeneous freezing occurs. Generally, homogeneous nucleation dominates in regions with updrafts stronger than 20 cm s −1 , with the exception of heavily polluted areas which could be common in the northern hemisphere due to air traffic, where updrafts of the order 1 m s −1 may be necessary to render heterogeneous nucleation unimportant. According to the present results it cannot be excluded that heterogeneous nucleation plays a more important role for cirrus formation in the northern midlatitudes than anywhere else. A possible consequence of these results is that air pollution may lead to a higher coverage of cirrus clouds, but then these clouds will be optically thinner than clouds formed by homogeneous freezing, with the exception of regions where condensation trails are frequent.

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Section: The Box Modelsupporting

confidence: 59%

On the transition between heterogeneous and homogeneous freezing

Gierens

2003

Atmos. Chem. Phys.

111

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“…A number of modeling studies have shown that if ice nucleation occurs via homogeneous freezing, the resulting ice concentration is primarily controlled by cooling rate, with aerosol abundance having a minor effect (e.g., Jensen and Toon, 1994;Kärcher and Lohmann, 2002). At low temperatures and with moderate-to-rapid cooling rates, the ice concentration could become comparable to the concentration of aerosols available, in which case ice concentration could be controlled by aerosol abundance (Kay and Wood, 2008).…”

Section: Ttl Cirrus Microphysical Properties Predicted By Homogeneousmentioning

confidence: 99%

Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

et al. 2010

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Abstract.In past modeling studies, it has generally been assumed that the predominant mechanism for nucleation of ice in the uppermost troposphere is homogeneous freezing of aqueous aerosols. However, recent in situ and remotesensing measurements of the properties of cirrus clouds at very low temperatures in the tropical tropopause layer (TTL) are broadly inconsistent with theoretial predictions based on the homogeneous freezing assumption. The nearly ubiquitous occurence of gravity waves in the TTL makes the predictions from homogeneous nucleation theory particularly difficult to reconcile with measurements. These measured properties include ice number concentrations, which are much lower than theory predicts; ice crystal size distributions, which are much broader than theory predicts; and cloud extinctions, which are much lower than theory predicts. Although other explanations are possible, one way to limit ice concentrations is to have on the order of 50 L −1 effective ice nuclei (IN) that could nucleate ice at relatively low supersaturations. We suggest that ammonium sulfate particles, which would be dry much of the time in the cold TTL, are a potential IN candidate for TTL cirrus. However, this mechanism remains to be fully quantified for the size distribution of ammonium sulfate (possibly internally mixed with organics) actually present in the upper troposphere. Possible implications of the observed cloud microphysical properties for ice sedimentation, dehydration, and cloud persistence are also discussed.

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“…Depending on optical thickness and altitude, as well as on the albedo of the surface or lower clouds, the net effect on climate can either be a cooling or warming (Chen et al, 2000;Fusina et al, 2007;Corti and Peter, 2009), but quantifying the magnitude of this effect is difficult because of uncertainties in these or other quantities characterizing the cirrus life cycle (Lynch et al, 2002). Furthermore, microphysical properties such as number density, size and shape of the ice crystals affect the cloud lifetime and radiative properties and thus the humidity of the upper troposphere and lower stratosphere (Jensen and Toon, 1994).…”

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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Ice nucleation in the upper troposphere: Sensitivity to aerosol number density, temperature, and cooling rate

Cited by 94 publications

References 17 publications

On the transition between heterogeneous and homogeneous freezing

On the transition between heterogeneous and homogeneous freezing

Ice nucleation and cloud microphysical properties in tropical tropopause layer cirrus

Balloon-borne match measurements of midlatitude cirrus clouds

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