A buoyancy-based turbulence mixing length technique for cloudless and cloudy boundary layers in the COSMO model Veniamin Perov and Mikhail Chumakov Hydrometcentre of Russia

Blackadar formula, local l

z TKE Schematic view of a turbulent length scale (mixing length)scheme based on a parcel displacement (BL89) for a boundary layer scheme of the COSMO model

Turbulent length scale based on a parcel displacement scheme , Turbulent length scale based on a parcel displacement scheme Non-cloudy case Cloudy case ,

Subgrid condensation scheme Calculations of Partial cloudiness in cloudy boundary layers follows Sommeria and Deardorf (1977)

Potential temperature profiles for non-cloudy L (blue) and cloudy L(red), Moscow 12h, 170711

Difference of Temperatures at the level 35 (Cl - NC), 12h, 170711

Difference of Temperatures at the level 30 (Cl - NC) 12h, 170711

Difference of total cloud cover (Cl - NC), 12h, 170711

Difference of total precipitation (Cl - NC), 12h, 170711

Difference of T2M fields (NC – Cl), 12h, 190711

Differences for T2M fields (Cl - NC), 12h, 170711,

Differences for T2M fields (Cl - NC), left and total cloud cover, right, 9h, 170711

Differences for TD2M fields (Cl - NC), 12h, 170711, Moscow area

Differences for U10M fields (nonlocal L minus local L), 12h, 170711, Moscow area

Main results Algorithm for computing the nonlinear turbulence length scale based on displacement method of air parcel (BL89) was developed for cloudy boundary layers. A new algorithm for calculation turbulence length scale has a more rigorous physical basis in comparison with the algorithm for dry boundary layers and currently used (Blackadar formulae). Algorithm was impact in module TUBDIFF of main COSMO program Calculations were performed for convective situations (July 2009) by full 3-D COSMO model (version 4.13). Results showed differences in fields of temperature, humidity, clouds and wind between variants with L for cloudy boundary layers and L for non-cloudy BL .

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Turbulence and convection in mountain region

Mesoscale modeling in mountain region Mesoscale modeling in mountain area should include simulations of main processes in this domain. These are formation of the regional slope winds, blocked flow, deviated flow, sheltering effect after obstacle, generation of turbulence by wind shear at the lower part of flow. In the upper part of flow it will be generation of turbulence by roughness, mountain waves and generation of turbulence by mountain wave breaking. For high mountains we need also to take into account a tropopause perturbation. All these processes require the use of three-dimensional turbulence and the non-use of simple diagnostic formulas for turbulence length scale (mixing length). In this case, together with the equation for the turbulent kinetic energy (TKE) will have to use the equation for mixing length ( for example equation for dissipation of TKE).

Turbulent length scale based on a parcel displacement scheme Blackadar formula, local l