PP UTCSStatus Report

Dmitrii Mironov

German Weather Service, Offenbach am Main, Germany

dmitrii.mironov@dwd.de

COSMO General Meeting, Offenbach am Main, Germany 7-11 September 2009

Outline

• Overview of project results, plan for the next COSMO year (Dmitrii Mironov, 25 min)

• Testing of the moist second-order turbulence-convection model including transport equations for the scalar variances (Ekaterina Machulskaya, 25 min)

Task 1: Ekaterina Machulskaya and Dmitrii Mironov

Work Content • Consolidation of a two-equation closure model (transport equations for TKE

and for the temperature variance) of a temperature-stratified PBL

• Development and coding of a second-order closure model of a moist PBL, including transport equations for the TKE and for the scalar variances and an SGS statistical cloud scheme for non-precipitating clouds

• Testing of a new model, comparison with a one-equation model (prognostic equation for the TKE only)

Expected Outcome • Improved representation of mixing within dry and moist PBL

• Improved representation of entrainment at the PBL top

• Stable performance of a new model

Task 1: Results

• A two-equation turbulence closure model (prognostic equations for the TKE and for the temperature variance) is favourably tested through single-column numerical experiments.

• A skewness-dependent parameterisation of the temperature-variance turbulent transport is implemented and tested (physically, the skewness-dependent formulation is a mass-flux formulation for the scalar transport due to shallow convection recast in terms of ensemble-mean turbulence moments).

• The model reveals a stable performance on a relatively coarse grid (zmin=10 m, t well over 40 sec).

• Results from testing of moist scheme including transport equations for the scalar variances are reported by Ekaterina Machulskaya.

Budget of Potential-Temperature Variance in Convective PBL One-Equation and Two-Equation Models vs. LES Data

Dotted curves – LES data, solid curves – model results. Left panel – one-equation model, right panel – two-equation model. Red – mean-gradient production/destruction, green – third-order transport, blue – dissipation. The budget terms are made dimensionless with w**

2/h.

Counter-gradient heat flux

Task 2a: Balazs Szintai and Matthias Raschendorfer

Work Content

• Comprehensive component testing against LES and observational data of the current COSMO-model turbulence scheme

Expected Outcome

• Improved understanding of the COSMO-model turbulence scheme

• Recommendations towards the scheme improvement

• Whenever possible, improved formulations of various components of the scheme

Task 2a: Results

• 3D COSMO-model simulations of the LITFASS-2003 case are performed, results are compared to surface meteorological measurements (wind, temperature) and to radiosonde data. TKE budget terms are analysed and compared with previously studied idealised convective case (using LES data). The 3D COSMO runs show results similar to those from single-column runs. (i) TKE is overestimated during night time and is fairly well predicted during daytime. (ii) The transport term in the TKE budget is strongly underestimated.

• TKE budget terms are estimated on the basis of data from the tower turbulence measurements and compared with the COSMO results. It is found that, although the TKE time series are in good agreement with the tower measurements during the daytime, it is not the case for individual budget terms.

• An implicit treatment of the TKE diffusion is implemented into the COSMO model (Oliver Fuhrer and Balazs Szintai), it improves the vertical TKE transport and the scheme performance in terms of numerical stability.

• The work is somewhat delayed, further results will be available by December 2009.

COSMO-3D at 1 km for LITFASS-2003

• COSMO runs at 1 km horizontal resolution

• Timestep: 10 s

• Soil analysis produced with TERRA standalone

• Case study: 2003-05-30 : convective day, calm winds, no clouds

• Simulation of the whole diurnal cycle

• Testing of: – Vertical level distribution– Horizontal numerical diffusion

COSMO-7 COSMO-1

20 k

m20 km

Area of interest

COSMO-3D at 1 km for LITFASS-2003

Sensitivity to horizontal diffusion:

Validation of turbulence scheme:

100

km

Without hor. diff. With hor. diff.

Vertical wind at 800 m AGL

• Without horizontal diffusion the results are not very realistic wavelength is on the order of the mesh size

• Horizontal diffusion reduces the amplitude of waves and increases the wavelength

• Maximum of TKE is earlier in the Model

• Night time TKE is overestimated by the model

• Fairly accurate results for TKE with overestimated surface heat flux

Turbulence Kinetic Energy at 90 m AGL

Task 2a: Results (Matthis Raschendorfer)

• COSMO-SC is extended towards a flexible tool for component testing, including

- Introduction of the option to force the atmosphere (and the soil) by measured surface heat fluxes,

- Consolidation of the calculation of 3D corrections.

• First test simulations for a stable case with snow cover are performed (GABLS_3 in which COSMO is participating).

Task 2b: Veniamin Perov

Work Content

• Implementation into the existing COSMO-model turbulence scheme and testing against observational and LES data of the non-local parameterisation of the turbulence length (time) scale

Expected Outcome

• Improved representation of mixing within dry and moist PBL

Task 2b: Results

• Work on the alternative treatment of the turbulence length scale based on a parcel displacement is performed. The new parameterisation allows the turbulence length scale at any level to be affected not only by static stability at that level, but also by the effect of remote levels (”non-local” length scale).

• The new algorithm has been included into the 3-D COSMO model.

• Numerical experiments show a difference in T2m, RH2m, and Pmsl between the reference COSMO version and the version with the new length-scale parameterisation.

• Verification of results from numerical experiments is being performed.

z

TKE

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

Difference of T2M fields (new – ref), COSMO-RU, 19.07.2009

Task 2c: Matthias Raschendorfer

Work Content

• Consolidation of the current COSMO-model moist turbulence scheme (incl. numerical stability with refined vertical resolution and without minimum diffusion coefficients, implicit vertical diffusion of TKE, numerical treatment of turbulence in stable stratification, numerical efficiency, alternative treatment of the explicit correction terms in the formulation of the sub-grid scale condensation effects, reorganisation of the code and documentation)

Expected Outcome

• Improved representation of the stably stratified PBL

• Improved numerical stability of the turbulence scheme

• Removal of numerical artefacts

Task 2c: Results

• Corrected version of “implicit vertical TKE diffusion” in accordance with the present formulation of the “circulation term” is implemented. SC tests with 80 layers are performed [only stable when explicit TKE diffusion is stronger limited ('secur'=0.85->0.5) or when implicit version is used].

• A revised “positive definite solver for the prognostic TKE” equation has recently been introduced, the effect is going to be tested soon using the SC diagnostic tool.

• A theoretical analysis of the “explicit correction terms due to sub grid scale condensation” is performed. 3D tests show that these effects influence the model significantly with changing value of forecast quality. A version without these corrections does not produce an additional numerical artefact and is more efficient. A parallel experiment showed a slightly better verification.

• Following the concept of scale separation, additional TKE production terms through the shear by non-turbulent sub-grid scale circulations (scale interaction terms due to non-turbulent horizontal wind shear modes and orographic wake modes) are introduced and first tests are performed (within the framework of the “Clear Air Turbulence” project of DWD).

Task 2c: Results (cont’d)

• Analytical work is performed in order to - reformulate the “circulation term” being a further scale interaction term in the TKE equation due to thermal inhomogeneity at the surface, - introduce a scale interaction term with the convection scheme and a combination of turbulent and convective statistical (cloud) condensation (adjustment).

• A “mixed water/ice cloud phase” is introduced into the moist turbulence scheme (in particular into the sub grid scale condensation scheme).

• A new version of the turbulence scheme with “implicit TKE diffusion”, “horizontal shear mode” and “SSO-interaction”, including a “stability correction of turbulent MLS” and the “mixed water/ice phase”, is ready.

• In relation to a reformulated surface-to-atmosphere transfer scheme (WG3) a reorganisation of the code is started.

• The internal documentation is partially updated.

COSMO Offenbach 2009Matthias Raschendorfer

But there are differences … … due do numerical effects with the Exner-factor treatment of the T-equation

Time series of model domain averages

less low level clouds

explicit TKE-diffusion with restriction proper for 50 layer configuration

SC simulations with 80 layers and “implicit TKE diffusion”:

numerically unstable!

COSMO Offenbach 2009Matthias Raschendorfer

Dew point profiles 50 layers

considerable difference

Dew point profiles 80 layers

implicit TKE-diffusion being unconditional stable

almost no difference

Task 3a: Matthias Raschendorfer

Work Content

• Development (based, to a large extent, on the available recipes), implementation into the COSMO-model code and testing of an advanced SGS statistical cloud scheme that accounts for the non-symmetric (skewed) PDF of the SGS temperature and humidity fluctuations and for the enhancement of mixing due to shallow cumuli

Expected Outcome

• Improved parameterisation of unresolved shallow cumuli

• Improved representation of mixing within moist PBL

Task 3a: Results

• Some literature review and and analytical investigations are performed, leading to the belief that an approach towards a generalized statistical cloud condensation scheme is sufficiently easy to implement soon. The approach proposed is consistent with both (i) a separate mass flux scheme interacting with a pure turbulence scheme, and with (ii) a generalized non local 2-nd order turbulence scheme considering 3-rd order moments. A generalised scheme can be developed by applying a scale separation concept (cf. Task 2.c). (Details can be found in the progress report at the COSMO web page.)

• This rather simple approach is going to be implemented as a first step within the scope of “interaction with the convection scheme” (see Task 2.c).

• The implementation work is somewhat delayed, will be performed over the next COSMO year (September 2009 through August 2010)

Task 3b: Euripides Avgoustoglou (in co-operation with Matthias Raschendorfer)

Work Content

• Comprehensive testing of the existing COSMO-model sub-grid scale statistical cloud scheme with due regard for the water-ice mixed phase in order to assess whether that scheme could be used by both the turbulence scheme and the radiation scheme of the COSMO model

Expected Outcome

• A more consistent treatment of the sub-grid scale cloudiness within the COSMO model

• Eventually, an improved prediction of partial cloud cover and of the surface heat budget

Task 3b: Results

• The implementation of the sub-grid cloud scheme re-adjusts the average cloud cover relative to the default scheme regarding low, medium, and high clouds and, consequently, the total cloud cover.

• This seems to affect the average thermal radiation budget at the top of the atmosphere and at the surface, depending mainly on the season.

• Further investigation is under way in order to depict possible preponderance of any scheme, mainly with available satellite pictures. Observed temperatures and dew-point temperatures will also be compared with the forecasted values for possible trends.

Five cases were investigated, with 48 hour runs as follows:

D212+48 IFS Forecast (25Km 60 levels)Dec. 24 2007 12UTC (d071224_12)2

5

4

3

1

#

May 1 2009 12 UTC (d090501_12)

May 9 2008 12 UTC (d080509_12)

Apr. 25 2006 12 UTC (d060425_12)

Jan. 1 2005 12UTC (d050101_12)

Starting Date

D112+48hrs GME Analysis (50km 40levs)

D212+48 IFS Forecast (25Km 60 levels)

D212+48 IFS Forecast (25Km 60 levels)

12+48 IFS Forecast (25Km 60 levels)

Boundary Conditions. Domain

D2

For all cases, nested runs of 2.5 km horizontal grid were performed in addition to the main runs with horizontal grid of 7km. The domain of the nested runs is depicted in the D1 and D2 graphs with a dashed line. The vertical and horizontal lines refer to the studied cross sections.

The results will be presented for 7Km horizontal grid size and for approximate equal domains covering the wider Balkan region.D1 D2

GME IFS

ATHB_T-210

-230

TQI0.030

0.006

ATHB_S-50

-72

TQV14.1

11.7

d050101_12

CLCT

gridsubgridsubgridR

100

0

CLCH

~0

CLCM100

0

CLCL19.5

13.5

d050101_12

Task 4: Work did not start

Work Content

• Comparison of the cloud condensate diagnosed by the sub-grid scale cloud schemes (statistical and relative-humidity) and by the prognostics equations for the cloud condensate content (cloud water and cloud ice) with the grid-scale saturation adjustment procedure

Expected Outcome

• A prerequisite for improving/tuning the statistical SGS cloud scheme, for the use of the same SGS cloud scheme in both the turbulence scheme and the radiation scheme of the COSMO model, and for eventually improving the treatment of the could water and of the cloud ice with due regard for the sub-grid scale processes

Problems Encountered

• Problems of scientific character: nothing unexpected in view of the innovative nature of the project, i.e. some risk is inevitable and must be assumed

• Communication: considering high complexity of the problem, a remote mode operation is often inefficient (e.g. the project leader cannot keep an eye on the details of the implementation of all tasks)

Plan for the Next COSMO Year

Task 1. Ekaterina Machulskaya and Dmitrii Mironov

• Further comprehensive testing against observational and LES data and consolidation of a second-order closure model of a moist PBL, including transport equations for the TKE and for the scalar variances [based on the results obtained within the framework of the project by September 2009]

• Implementation of the best-compromise version of the new closure model in terms of physical realism and computational stability and efficiency into the COSMO model (the expert assistance concerning numerics is requested), testing within the single-column COSMO framework

Plan for the Next COSMO Year (cont’d)

Task 2a. Balazs Szintai

• Comprehensive component testing against LES and observational data of the existing COSMO-model one-equation turbulence scheme (the work delayed will be completed by December 2009; Balazs Szintai is no longer available for the project from December 2009)

Task 2a. Matthias Raschendorfer

• Introduction of a parameter tuning option into COSMO-SC

• Performing detailed component testing with the COSMO-SC using measurement data (for forcing and verification), 3D-model results (for 3D corrections), or LES results (for forcing, 3D corrections and verification) in order to fix weaknesses

Plan for the Next COSMO Year (cont’d)

Task 2b. Veniamin Perov

• Testing of the new formulation of the turbulence length against observational and LES data through single-column numerical experiments

• Testing of the new length-scale formulation within full 3D COSMO model

• Verification of results for different weather situation situations

Plan for the Next COSMO Year (cont’d)

Task 2c. Matthias Raschendorfer

• Detailed testing the omission of numerical restrictions for stable stratification including a possible stability restriction of turbulent MLS

• Testing the statistical condensation scheme as input for the radiation scheme and as a substitute of grid-scale saturation adjustment in order to have the full thermodynamic effect of sub grid scale condensation (see Tasks 2.a,b)

• Vertically-resolved roughness layer with further modifications due to the sub-grid scale structure of the surface (generalized BL approximation, adopted profile of turbulent MLS)

• Verification of the “interactions with horizontal shear modes and the SSO scheme”

• Full implementation and verification of a reformulated circulation term

• Full implementation and verification of the “interaction with the convection scheme” into the turbulence scheme; attempt to describe entrainment and detrainment within the convection scheme using turbulence parameters

• Completing full re-organisation of the turbulence scheme together with the reformulated surface scheme and detailed documentation

Plan for the Next COSMO Year (cont’d)

Task 3a. Matthias Raschendorfer

• Implementation into the COSMO-model code and testing of an advanced SGS statistical cloud scheme that appropriately accounts for the non-symmetric (skewed) PDF of the SGS temperature and humidity fluctuations and for the enhancement of mixing due to shallow cumuli (see 2008-2009 plan)

• Full implementation of the superimposed convective modulation for the statistical condensation scheme into the current COSMO framework (using the mixed-phase approach scaled by the current values of prognostic cloud water and cloud ice) and performing first tests

• Combination of the ”interaction with convection” in the turbulence scheme

• Tuning and verification of the new approach

- only within the moist turbulence scheme,

- also as an input to the radiation scheme (see Task 3.b)

- also as a substitute for the grid-scale saturation adjustment scheme in order to have the full thermodynamic effect of sub grid scale condensation (see Task 2.c)

Plan for the Next COSMO Year (cont’d)

Task 3b. Euripides Avgoustoglou

• Systematic evaluation of SGS cloud schemes (incl. water-ice mixed phase) in terms of cloud cover, T2m, Td2m, radiation budget at the surface

Summary

• The project results obtained so far do not look too discouraging

• The project will (hopefully) proceed according to the plan

Thank you for your kind attention!

Stuff Unused

• ...

Plan for the Next COSMO Year

Task (i). NN

• Later: examination of critical (and possibly dangerous) issues related to the simultaneous use of an SGS statistical cloud scheme and of prognostic equations for the grid-scale cloud water and cloud ice (Tompkins 2002, 2005)

TKE and Potential-Temperature Variance in Convective PBL One-Equation and Two-Equation Models vs. LES Data

TKE (left panel) and <’2> (right panel) made dimensionless with w*2 and *

2, respectively Black dotted curves show LES data, red – one-equation model, blue – two-equation model.

Mean Temperature in Shear-Free Convective PBL One-Equation and Two-Equation Models

Red – one-equation model, green – two-equation model, blue – one-equation model with the Blackadar (1962) formulation for the turbulence length scale. Black curve shows the initial temperature profile.

Potential temperature minus its minimum value within the PBL. Black dashed curve shows LES data (Mironov et al. 2000), red – one-equation model, green – two-equation model, blue – one-equation model with the Blackadar (1962) formulation for the turbulence length scale.

Component Testing Results

• Turbulent transport of TKE is too weak

• Negative buoyancy flux at PBL top is practically missing

• Horizontal velocity variances are poorly described at the PBL top and near the surface

Shear-free convective PBL (LES of Mironov et al. 2000)

COSMO

LES

Budget terms are estimated from tower turbulence measurements (mean of measurements taken at 50 m and at 90 m above the ground) and compared to COSMO time series

Time Series of TKE Budget Terms