Impact of Ice Particle Shape Effects on Arctic Mixed-Phase Cloud Presence
Abstract
Mixed-phase clouds are defined as clouds containing both supercooled and ice water particles. Since at sub-freezing temperatures (< 0 °C) the saturation vapor pressure over ice is less than that over liquid, one would expect mixed-phase conditions presence to be short-lived; however, Arctic conditions may allow these clouds to persist for longer periods. Observations suggest a high prevalence of mixed-phase clouds in the Arctic with the probability of finding supercooled water being dependent on temperature. Using data collected at Utqiagvik, Alaska, the probability of finding supercooled water given cloud temperature was calculated. This probability density has local minima at temperatures around -7°C and -15°C indicating that mixed-phase clouds are less likely to exist at these temperatures. A parcel model with Lagrangian microphysics and a one-dimensional single-column model with habit-dependent bulk microphysics were used to investigate reasons for the observed minima in the supercooled water probability. It was found that the rate at which liquid is depleted by ice crystal growth has local maxima at -7°C and -15°C where the growth of needles and dendrites, respectively, are prevalent. The maxima in growth at these temperatures produce local minima in the fraction of supercooled water. When ice crystals are treated as spheres, which is a common assumption in numerical models, the maxima in the liquid depletion rates, and minima in supercooled water cloud fraction disappear and the curve monotonically decreases commensurately with temperature. These results suggest that the observed local minima in the probability of finding supercooled water at temperatures around -7°C and -15°C are a result of habit-dependent ice crystal growth.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA011.0005M
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3337 Global climate models;
- ATMOSPHERIC PROCESSES;
- 3359 Radiative processes;
- ATMOSPHERIC PROCESSES;
- 3360 Remote sensing;
- ATMOSPHERIC PROCESSES