Ice nucleation in cirrus clouds: A model study of the homogeneous and heterogeneous modes

Sassen, Kenneth; Benson, Sally

doi:10.1029/1999gl010883

Cited by 37 publications

(47 citation statements)

References 12 publications

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“…Previous simulations that took both nucleation modes into account (e.g. DeMott et al, 1997;Spice et al, 1999;Sassen and Benson, 2000) agree concluding that heterogeneous nucleation becomes relatively unimportant for updrafts exceeding a few 10 cm s −1 . This expectation is essentially confirmed by the results of the present model.…”

Section: Resultsmentioning

confidence: 99%

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: Resultsmentioning

confidence: 99%

On the transition between heterogeneous and homogeneous freezing

Gierens

2003

Atmos. Chem. Phys.

111

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“…DeMott et al, 1997). However Sassen and Benson (2000) show that heterogeneous nucleation cannot compete with homogeneous nucleation for most atmospheric situations. DeMott et al (1994) concluded that changing size distribution and composition of aerosol particles may have large effects on the onset conditions of cirrus formations and the crystal number density.…”

Section: Discussionmentioning

confidence: 99%

In-situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses

et al. 2003

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Abstract. In-situ observations of aerosol particles contained in cirrus crystals are presented and compared to interstitial aerosol size distributions (non-activated particles in between the cirrus crystals). The observations were conducted in cirrus clouds in the Southern and Northern Hemisphere mid-latitudes during the INCA project. The first campaign in March and April 2000 was performed from Punta Arenas, Chile (54°S) in pristine air. The second campaign in September and October 2000 was performed from Prestwick, Scotland (53°N) in the vicinity of the North Atlantic flight corridor. Size distribution measurements of crystal residuals (particles remaining after evaporation of the crystals) show that small aerosol particles (Dp< 0.1 mm) dominate the number density of residuals. The crystal residual size distributions were significantly different in the two campaigns. On average the residual size distributions were shifted towards larger sizes in the Southern Hemisphere. For a given integral residual number density, the calculated particle volume was on average three times larger in the Southern Hemisphere. This may be of significance to the vertical redistribution of aerosol mass by clouds in the tropopause region. In both campaigns the mean residual size increased slightly with increasing crystal number density. The form of the residual size distribution did not depend on temperature as one might have expected considering different modes of nucleation. The observations of ambient aerosol particles were consistent with the expected higher pollution level in the Northern Hemisphere. The fraction of residual particles only contributes to approximately a percent or less of the total number of particles, which is the sum of the residual and interstitial particles. Excellent agreement between the CVI and FSSP-300 probes was found supporting the assumption that each crystal is associated with only one residual particle.

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“…However, suitable ice nuclei are rare in the upper troposphere, so that it is generally believed that homogeneous nucleation is the dominant pathway for formation of cold cirrus clouds (Sassen and Dodd, 1989;Heymsfield and Sabin, 1989;Kärcher and Ström, 2003). While this may be so, simulations indicate that heterogeneous nucleation can influence the formation of cirrus clouds significantly (Sassen and Benson, 2000;Khvorostyanov and Curry, 2005;DeMott et al, 1997). Box model studies (Gierens, 2003;Ren and Mackenzie, 2005;Liu and Penner, 2005) even suggest that heterogeneous nucleation can suppress homogeneous nucleation if enough heterogeneous ice nuclei are available, depending on environmental conditions, and if the vertical velocity is sufficiently small.…”

Section: Introductionmentioning

confidence: 99%

Modelling of cirrus clouds – Part 2: Competition of different nucleation mechanisms

Spichtinger

Gierens

2009

Atmos. Chem. Phys.

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Abstract.We study the competition of two different freezing mechanisms (homogeneous and heterogeneous freezing) in the same environment for cold cirrus clouds. To this goal we use the recently developed and validated ice microphysics scheme (Spichtinger and Gierens, 2009a) which distinguishes between ice classes according to their formation process. We investigate cases with purely homogeneous ice formation and compare them with cases where background ice nuclei in varying concentration heterogeneously form ice prior to homogeneous nucleation. We perform additionally a couple of sensitivity studies regarding threshold humidity for heterogeneous freezing, uplift speed, and ambient temperature, and we study the influence of random motions induced by temperature fluctuations in the clouds. We find three types of cloud evolution, homogeneously dominated, heterogeneously dominated, and a mixed type where neither nucleation process dominates. The latter case is prone to long-lasting in-cloud ice supersaturation of the order 30% and more.

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Ice nucleation in cirrus clouds: A model study of the homogeneous and heterogeneous modes

Cited by 37 publications

References 12 publications

On the transition between heterogeneous and homogeneous freezing

On the transition between heterogeneous and homogeneous freezing

In-situ observations of aerosol particles remaining from evaporated cirrus crystals: Comparing clean and polluted air masses

Modelling of cirrus clouds – Part 2: Competition of different nucleation mechanisms

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