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Recent Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, J. Han, R. Sun, S. Moorthi UCLA: C. R. Mechoso, H. Xiao
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Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Apr 27, 2018

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Page 1: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Recent Developments in PBL and ShallowConvection Parameterization at

NCEP/EMC NCEP: H. Pan, J. Han, R. Sun, S. Moorthi

UCLA: C. R. Mechoso, H. Xiao

Page 2: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Annual cycle ofprecipitation inthe East Pacific

CMAP

NCEP

CFS

30S 30N

In the southeasternPacific, most CGCMshave difficulties withthe simulation of theITCZ and SPCZ southof the equator, and/or the SST under thestratocumulus decks.

The Double ITCZ Syndrome of CGCMs

Page 3: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Obs

CFSOBS

NCEP Coupled GCM Errors in the Southern Spring

CFS

During the southernspring, NCEP’s ClimateForecast System (CFS)predicts for the easternTropical Pacific notenough stratocumulusand too warm SSTs.

PREC

SST

Page 4: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

1/3x1 - 1x146MIT OGCM

1/3x1 - 1x140MOM3

T126 ~100km64NCEP GFS

OPS: current operational version (*)

CTL: experimental version of GFS

EXP1a: Simple Modifications 1

EXP1b: Simple Modifications 2

EXP2: New parameterizations

2x2.5, ~250km29UCLA AGCM v7.3

ResolutionLevelsModel

(*) 2009

Page 5: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

In the current (*) operational GFS:

• The shallow convection parameterization is applied whereverthe deep convective parameterization is not active.

• It is applied via enhanced vertical diffusion in the cloud layersbelow pT = 0.7ps, where ps is surface pressure.

• Cloud top is defined as the layer above the highest positivelybuoyant layer below pT.

• The shallow convection parameterization erroneouslycontributes to the lack of the stratocumulus.

(*) Moorthi

Page 6: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Exp1a: Simple modifications to improve stratussimulation in OPS GFS (*)

• Condition for CTEI is

where and are the equivalent potentialtemperature and total moisture jumps across the inversion;

If the condition for CTEI is not satisfied, then the top ofshallow convection is set to be just below the inversion.

• The background vertical diffusion coefficient is set to zeroabove inversion

tep qLC !<! 7.0"

e!" t

q!

An additional set with modification of the original shallowconvection (by limiting the cloud top to below the region ofnegative buoyancy) and adding an additional layer when conditionfor CTEI is satisfied. (*)

Exp1b: Additional modifications

Page 7: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Methodology

• Ensembles of four control and sensitivity experiments (with themodifications) are performed

• Simulations are 48-day long and use observed SSTs. Initialconditions correspond to Dec 15, 00Z 2008 and June 15 00Z,2008.

• RAS version 2 (updated version of Moorthi and Suarez, 1999)is used for convective parameterization.

• A critical relative humidity of 90% is used with Zhaomicrophysics

• Resolution: T126, 64 levels

Page 8: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Total Clouds in Southeast Pacific

JAN GFS* EXP1aJAN GFS* OPS JAN GFS* EXP1b

JUL GFS* OPS JUL GFS* EXP1a JUL GFS* EXP1b

Page 9: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Net Short Wave Radiation at the Surface

JAN GFS* Exp1aJAN GFS OPS

JUL GFS CTL JUL GFS* EXP1a

JAN GFS* EXP1b

JUL GFS* EXP1b

Page 10: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Impact of Resolution (in EXP1)

Page 11: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

New parameterization for moistturbulence processes (*)

• Include stratocumulus-top driven turbulencemixing in the lower troposphere

• Enhance local diffusion in cloudy air

• Specify explicit entrainment at PBL top

• Use local diffusion for the nighttime stable PBL

• Include non-local mixing for momentum

(*) Han and Pan

Page 12: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

New shallow cumulus convectionparameterization (*)

• Use a bulk mass-flux parameterization

• Based on the simplified Arakawa-Shubert (SAS) deepconvection scheme, which is being operationally usedin the NCEP GFS model

• Separation of deep and shallow convection isdetermined by cloud depth (currently 150 mb)

• Main difference between deep and shallow convectionis specification of entrainment and detrainment rates

• Only precipitating updraft is considered; downdraft isignored

(*) Han and Pan

Page 13: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Opr

New shallowconvectionscheme

Page 14: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Deep andshallow

Shallow only(<150mb)

Cloud Depth (mb) January

Page 15: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

CFS PBL and Low Clouds(combined)

ISCCP

OPS

New PBL andshallow convection

Page 16: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

prate_gfs_ccnorm

Precipitation

Oct 06 UCLA AGCMOct CMAP

Oct06 GFS CTL Oct06 GFS EXP2

Page 17: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

totcld_gfs_ccnorm

Total Clouds in Southeast Pacific

Oct06 GFS CTL Oct06 GFS EXP2

Oct06 UCLA AGCMOct MODIS

Page 18: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

ntswradsfc.gfs.ccnorm

Net Short Wave Radiation

Oct06 GFS CTL

Oct ISCCP Oct06 UCLA AGCM

Oct06 GFS EXP2

Page 19: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

prate_cfs_ccnorm

Precipitation

Oct CFS EXP2Oct CFS CTL

Oct UCLA CGCMOct CMAP

Page 20: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

totcld_cfs_ccnorm

Oct CFS CTL Oct CFS EXP 2

Oct UCLA CGCM

Total Clouds in Southeast Pacific

Oct MODIS

Page 21: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

ntswradsfc_cfs_ccnorm

Net Short Wave Radiation

Oct UCLA CGCM

Oct CFS CTL Oct CFS EXP2

Oct ISCCP

Page 22: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Cloud Liquid Water and SST Errors

Oct CFS CTL Oct CFS EXP2

Page 23: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

SST Errors in the Southeastern Pacific

Oct CFS CTL Oct CFS EXP2 Oct UCLA CGCM

Page 24: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Profiles at (85W, 20S)

Page 25: Recent Developments in PBL and Shallow Convection ... Developments in PBL and Shallow Convection Parameterization at NCEP/EMC NCEP: H. Pan, ... operational GFS: ... in the NCEP GFS

Summary

• Intense work has been made to improve PBL and

Low Clouds in NCEP/EMC models

• Simple modifications to the code based on inversion

height were tested (Exps 1a and 1b).

• New parameterizations of moist turbulence processes

and Shallow Convection were incorporated (Exp. 2)

• Significant improvements have been achieved

• Flow near high orography shows errors. These

decrease with increased resolution