A dual mass flux framework A dual mass flux framework for boundary layer convectionfor boundary layer convection

Explicit representation of cloud base Explicit representation of cloud base coupling mechanismscoupling mechanisms

Roel Neggers, Martin Köhler, Anton Beljaars

Contents

The coupling between cumulus clouds and the mixed layer

Mass flux feedbacks

The dual mass flux scheme

The eddy diffusivity mass flux (EDMF) approach

An extension for shallow cumulus

Introducing more complexity

New parameterizations

SCM evaluation

Idealized prototype cases

Daily evaluation against ARM and CloudNet data

Interactive with the larger scale dynamics

II. Retaining the area fraction in the cumulus mass flux

waM

Neggers,Siebesma, Lenderink and Holtslag, 2004: “An Evaluation of Mass Flux Closures for Diurnal Cycles of Shallow Cumulus”. MWR, 132, 2525-2538.

I. Using a constant pre-factor

* 03.0 wM Grant, 2001: “Cloud-base fluxes in the cumulus-capped boundary layer”. Quart. J. Roy. Met. Soc., 127, 407-422.

Closures staying close to thís structure:

* waM cloud

* (CIN) wfM

Cumulus mass flux at cloud base

Definition

Bretherton, McCaa and Grenier, 2004: “A new parameterization for shallow cumulus convection and its application to marine subtropical cloud-topped boundary layers. Part I: Description and 1D results”. Mon. Wea. Rev., 132, 864-882.

A *SIMPLE* equilibrium model including a mass flux closure with flexible fraction

Neggers, Stevens and Neelin, 2006: “A Simple Equilibrium Model for Shallow Cumulus Topped Mixed Layers”. Special Issue of the Theor. Comp. Fluid-Dynamics, in press, September 2006.

humidity

heat

mass

Variance scaling at mixed layer topNeggers, Stevens and Neelin, 2006: “Variance Scaling in Shallow Cumulus Topped Mixed Layers”. Submitted to QJRMS, August 2006.

Equilibrium model solution

BOMEX forcings and boundary conditions

MwEt

h

Feedbacks between cumulus mass flux and humidity at mixed-layer top

Equilibrium model solution on ERA40 forcings and boundary conditions

50 years of ship based synops observations (Norris, J.Clim. 1998)

The dual mass flux scheme – main EDMF upgrades

Moist updrafts

Flexible area partitioning

aup

Dry updrafts

K diffusion

a1up a2

up

h

z0

1 - aup

I. Multiple updrafts

N

i

upi

upi

upi

upup wawa1

)(´´

II. Flexible updraft area fractions – LCL coupling

VII. Extension of EDMF into statistical cloud modelling (a bimodal PDF)

III. Updraft initialization

upupK waz

Kaw ´´´´

},{ tl q

Eddy diffusivity - mass flux (EDMF) approach

IV. Updraft budgets

V. Mass transport

VI. Diffusion – an entrainment efficiency closure for cumulus

Flexible updraft area fractions facilitate representation of gradual regime transitions

E

LCL

h

LCL

h

LCL E E

M2 M1

Stratocumulus Transition Shallow cumulus Dry convection

M1

M2

a2

a1

Moist and dry updrafts can coexist at any time

I. Multiple updrafts with flexible area fractions

II. Closure of the flexible updraft area fractions

Explicit representation of the coupling between cumulus updrafts and mixed-layer

III. Vertical integration of updraft budgets then reconstructs the joint-PDF

I. First guess of cloud core fraction at cloud base, using local variance scaling

II. These fractions are subsequently used in surface initialization of updrafts

Knowledge of how many updrafts manage to reach LFC is `back-stitched` into the partitioning and initialization of the updrafts

Variance scaling at mixed layer top

This gives an implicit solution for the area fraction that carries mass flux:

Neggers, Stevens and Neelin, 2006: “Variance Scaling in Shallow Cumulus Topped Mixed Layers”. Submitted to QJRMS, August 2006.

shape parameter of Beta function

h

LES

SCM evaluation

I. For idealized prototype cases (LES)

II. Daily evaluation against ARM and CloudNet data

III. Interactive with the large scale dynamics

SCM results for prototype cases

qt and qs

l

cloud fraction

condensate

marine steady state shallow cumulus

RICO

BOMEX – interactive radiation

ARM SGP transient continental shallow cumulus 21 June 1997

DualMcy30r1

cy30r1DualM

2

[hr]

cy30r1

Developing suppressed cumulus… the mass flux valve mechanism at work

Moist updraft mass flux [m/s]

Daily evaluation against ARM and CloudNet data

Setup:

- initialize with ECMWF analysis state at midnight (local time)

- 2 day time integration

- relaxation towards forecast state (on a 6 hour timescale)

- LS advective forcings are also applied

At multiple sites around the world where relevant observational data is available

cy30r1 DualM

Chilbolton June 7, 2006 A diurnal cycle of shallow cumulusResults

Cabauw 24 July 2006 Shallow cumulus

DualMcy30r1

cy30r1DualM

A too fast hydrological cycle

ARM SGP transient continental shallow and deep cumulus July 1999

comparison to ARSCL (radar,lidar)

Preliminary IFS results

Shallow cu mass flux [m s-1]

Climate run

Summary

An extension for EDMF is formulated that allows representation of shallow cumulusAn extension for EDMF is formulated that allows representation of shallow cumulus convection convection

Key component is the explicit representation of the coupling of shallow cumulusKey component is the explicit representation of the coupling of shallow cumulus clouds to the mixed layer clouds to the mixed layer

This is done through flexible mass flux area fractions, which introduces cloudThis is done through flexible mass flux area fractions, which introduces cloud base valve-mechanisms base valve-mechanisms

The DualM scheme brings significant improvements for shallow cumulus concerning The DualM scheme brings significant improvements for shallow cumulus concerning i) mixed layer stability i) mixed layer stability ii) structure of mean, turbulent and cloudy state ii) structure of mean, turbulent and cloudy state iii) mixed layer depth and 2m humidity iii) mixed layer depth and 2m humidity

Further evaluation against ARM and CloudNet data illustrates that these Further evaluation against ARM and CloudNet data illustrates that these results are representative of nature and robust for different large-scale scenarios. results are representative of nature and robust for different large-scale scenarios.

Outlook: Implementation and testing in IFSOutlook: Implementation and testing in IFS

Implementation completed Implementation completed Evaluation in full progress Evaluation in full progress