Observations of Co-variation of Ice Properties at Tops of Thick Ice Clouds with Cloud-Top Temperature and Humidity
Abstract
A better understanding of the many interacting processes governing the formation of complex mixtures of ice of various shapes and sizes in natural ice clouds is required to improve the representation of ice clouds in global models. Polarimetric satellite retrievals over thick ice clouds globally have recently revealed systematic variations of ice size and shape with cloud top temperature, which show a remarkable agreement with simplified ice crystal vapor growth theory and in situ and laboratory data. This agreement suggests that the temperature dependence of the cloud top ice sizes and shapes could be dominated by the vapor growth process, which is somewhat surprising given the many processes involved and the large variation in dynamical variables. To shed more light on this matter, here we turn to airborne remote sensing observations of subtropical convective clouds with a spatial resolution of about 50-100 m, combined with reanalysis data of relative humidity and temperature to estimate vapor growth rates at cloud tops. Airborne multi-angle polarimeter data over ocean and land show that effective radii, aspect ratios of hexagonal components of complex crystals, crystal distortion parameters and scattering asymmetry parameters vary with cloud top temperature in a manner consistent with our previous results. Moreover, for supersaturated conditions at cloud top, the effective radii are well correlated with estimated vapor growth rates at cloud top. Furthermore, significant differences in aspect ratios, crystal distortion and asymmetry parameters between sub- and supersaturated conditions at cloud top are seen that are consistent with laboratory observations, again pointing to a greater effect of vapor growth processes than might be expected. Contrasting cases over land and ocean with different dynamics, we explore possible explanations of these observations. Furthermore, we discuss possible implications for the dependence of the radiative properties of such clouds on environmental conditions.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2020
- Bibcode:
- 2020AGUFMA011.0006V
- 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