Cloud microphysics, radiation and vertical velocities in two- and three-dimensional simulations of deep convection

Summary, in English

This study investigates the importance of dimensionality for the characteristics of simulations performed with cloud-system resolving models (CSRMs). In addition to intrinsic questions related to dimensionality in CSRMs, the issue has gained added interest since CSRMs can be utilized instead of conventional cloud parametrizations to represent deep convection within global climate models. Such CSRMs may be either two- or three-dimensional. CSRM simulations of five observed cases of deep convection are performed in both two and three dimensions (2D and 3D) with the aim of elucidating the impact of dimensionality on overall cloud statistics. Observed profiles of the large-scale average of advection of temperature and humidity are applied to initiate and maintain the convection. Two of the cases are from tropical oceanic regions. The other three cases are continental. The average ascent rate in deep convective, cloudy updraughts is about 20-50% higher at mid-levels of the troposphere in 3D than in 2D, for all cases. This corresponds to an increase by a similar percentage in the vertical mass flux of deep updraughts in the oceanic cases. Furthermore, the weak ascent (0. 1 < w < 1 m s(-1)) outside the deep convective updraughts is much less prevalent in 3D than in 2D, with vertical velocities being about 20% lower for a given cumulative frequency and a lower vertical mass flux. Downdraughts are weaker in 3D, for most cases. There is a substantial sensitivity of the vertical profiles of cloud liquid and cloud ice, and of other microphysical species, to dimensionality. This is consistent with the sensitivity of the dynamics of convection. Corresponding changes in radiative transfer, especially in the short-wave band, result from the cloud-radiative interactions. In particular, the peak in domain-averaged cloud liquid content in the melting layer is about 50% higher in most of the 2D simulations. The land cases display more sensitivity of the short-wave radiative flux to the choice of orientation of the vertical plane of 2D simulations.

• Author: Vaughan Phillips; Leo J. Donner
• Publishing year: 2006
• Language: English
• Pages: 3011-3033
• Publication/Series: Quarterly Journal of the Royal Meteorological Society
• Volume: 132
• Issue: 621
• Links: http://dx.doi.org/10.1256/qj.05.171
• Document type: Journal article
• Publisher: Royal Meteorological Society
• Topic: Physical Geography
• Keywords: cloud-radiation interactions; cloud-system resolving model
• Status: Published
• ISBN/ISSN/Other: ISSN: 0035-9009