Title: Regime dependence of ice cloud heterogeneity – a convective life‐cycle effect?

Abstract

Cloud condensate varies on scales smaller than those typically resolved by global weather and climate models. In order to accurately predict the radiative and microphysical process rates representative of the entire model grid box, the effect of the subgrid‐scale heterogeneity of cloud must be taken into account. In this study, observed ice water content retrieved from A‐Train satellite observations is used to explore how spatial ice condensate variability, characterized by the fractional standard deviation (FSD, the standard deviation divided by the mean), varies with cloud regime. FSD is generally lower for overcast cloud scenes, but an additional predictor based on convective activity is needed to capture the high FSD associated with more turbulent clouds and reproduce the observed latitudinal and height variations of FSD. Convective clouds that extend only a few kilometres above the freezing level are likely to be smaller at an earlier stage in their life cycle, and actively growing with a higher FSD. In contrast, more mature clouds reaching the tropopause are larger and generally have a lower variability and smaller FSD. To capture this life‐cycle effect, a new parametrization is tested which uses the ratio of a model's convectively detrained condensate to the existing cloud condensatemore » mass as a proxy for the cloud's convective life stage to highlight areas with enhanced condensate variability. The parametrization is scale‐adaptive, situation‐dependent and captures seasonally varying global patterns and the zonal mean vertical structure of observed ice condensate variability well. Ground‐based observations obtained from five Atmospheric Radiation Measurement sites provide independent confirmation that the parametrization satisfactorily captures condensate variability in high‐altitude ice clouds.« less

Authors:

Ahlgrimm, Maike ^[1]; Forbes, Richard M. ^[1]

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+ Show Author Affiliations

1. European Centre For Medium‐range Weather Forecasts Reading UK

Publication Date:

Wed Dec 27 00:00:00 EST 2017

Sponsoring Org.:

USDOE

OSTI Identifier:

1414966

Grant/Contract Number:  

DE‐SC0005259

Resource Type:

Publisher's Accepted Manuscript

Journal Name:

Quarterly Journal of the Royal Meteorological Society

Additional Journal Information:

Journal Name: Quarterly Journal of the Royal Meteorological Society Journal Volume: 143 Journal Issue: 709; Journal ID: ISSN 0035-9009

Publisher:

Wiley Blackwell (John Wiley & Sons)

Country of Publication:

United Kingdom

Language:

English