Huan Guo (GFDL/UCAR)

double-Gaussian distribution

Sub-grid Parameterization Based on Probability Density Functions in GFDL Atmospheric General Circulation

Model: Global Tests

Guo H., J.-C. Golaz, L. J. Donner, P. Ginoux, and R. S. Hemler, 2014: Multi-variate probability functions with dynamics in the GFDL atmospheric general circulation model: Global Tests. J. Climate, 27(5), 2087-2108, doi: 10.1175/JCLI-D-13-00347.1.

2/16

outline

CLUBB: cloud layer unified by bi-normal

Motivation: strato-cumulus, aerosol effect

AM3-CLUBB: better strato-cu and aerosol

Summary: pros and cons of AM3-CLUBB

3/16

negative strato-cumulus cloud forcing

Wood (MWR, 2012), Hahn &Warren (2007)

high cover & albedo strong negative cloud forcing

Hwang & Frierson (PNAS, 2013)

shortwave cloud forcingcloud cover

Insufficient data

(%)

4/16

positive shortwave cloud forcing bias

low-bias in strato-cumulus

deficient strato-cumulus in GCMs(Hwang & Frierson, PNAS, 2013) CMIP5

GFDL AM2 GFDL AM3

(W/m2)

5/16

outline

CLUBB (cloud layer unified by bi-normal): unified cloud and turbulence parameterization based on assumed sub-grid probability density function

Motivation

AM3-CLUBB global results

Summary

6/16

why choose double-Gaussian

Variable skewness

Reasonable tails

Multi-dimensional

Analytical cloud properties

Agreement with observations

Golaz et al. (JAS, 2002)

Double-Gaussian is a linear combination of two Gaussians, and offers unified treatment for various cloud regimes:

7/16

implementation of AM3-CLUBB

Donner et al. (J. Climate, 2011); Guo et al. (J. Climate, 2014)

AM3 AM3-CLUBB

Deep conv. Donner

Shallow conv. UW shallow

PBL Lock

Macro-physics Tiedtke

Micro-physics 1-moment Rotstayn-Klein

Donner

CLUBB

2-momentMorrison-Gettelman

8/16

outline

CLUBB

Motivation

AM3-CLUBB global results: better strato-cu and aerosol simulation Summary

9/16

Observation (CERES-EBAF)

AM3-CLUBB minus Obs. AM3 minus Obs.

1-degree AMIP simulations (1981-2000) shortwave

cloud forcing

(W/m2)

(W/m2)

10/16

better strato-cumulus simulation

(W/m2)

AM3-CLUBB has smaller shortwave cloud forcing bias in strato-cumulus regions studied by Klein & Hartmann (J. Climate, 1993)

11/16

better SW cloud forcing seasonal cycleS

WC

F (

W m

-2)

more realistic phase and amplitude in AM3-CLUBB

Obs. (CERES-EBAF)

12/16

sharper inversion in AM3-CLUBB

13/16

Longwave cloud forcing

AM3 minus Obs.

AM3-CLUBB minus Obs.

Observation

ice clouds underestimate

(W/m2)

(W/m2)

14/16

precipitation AM3 AM3-CLUBB

excessive precipitation

surface precip. from deep convection (mm/day)60S 30S EQ 30N 60N

1234567 AM3-CLUBB

AM3

more deep convection in AM3-CLUBB

(mm/day)

15/16

smaller bias in aerosol optical depth (AOD)

AM3 minus MISR Obs. AM3-CLUBB minus MISR Obs.

AM3-CLUBB

AM3

Observation (AERONET)

annual mean and seasonal cycles agree better with observations in AM3-CLUBB

monthly AOD (BeiJing)

16/16

higher correlation with observation

aerosol optical depth (AOD) correlations with Aerosol Robotic Network (AERONET) are 0.8 in CLUBB, and only 0.56 in non-CLUBB.

relative difference: (model/AERONET-1)

Figure courtesy Paul Ginoux

CLUBB

non-CLUBB

17/16

take-home message

deficient strato-cumulus (e.g, in GFDL AM2, AM3) longstanding issue in many GCMs:

AM3-CLUBB improves coastal strato-cumulus simulations, especially at 1-degree resolution or higher.

AM3-CLUBB issues and future work: more expensive computationally insufficient ice-phase cloud representations prognostic precipitation in microphysics

. . .

18/16

Wood (MWR, 2012)

Strato-cumulus simulation is challenging

subtle balance among radiative cooling/heating, microphysics, entrainment, turbulence mixing, surface fluxes …

19/16

AM3-CLUBB coupled run drifts

20/16

Strato-Cu cloud thickness

Shallower strato-cu near California

21/16

CLUBB in AM3: AM3-CLUBB flowchart

Close higher-order moments

buoyancy

Prognose u, v, qt,θl, u’2, v’2, w’2, qt’2, θl’2, qt’θl’, w’qt’, w’θl’, w’3

Select PDF

Diagnose CF, qc

from PDF

Input 2-moment

MG microphys.Δt

Golaz et al. (JAS, 2002a, 2002b); Guo et al. (J. Climate, 2014)

Activateaerosols

w’2