EUROCS DEEP CONVECTI VE CLOUDS DI URNAL CYCLE of DEEP CONVECTI ON - - PowerPoint PPT Presentation

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EUROCS DEEP CONVECTI VE CLOUDS DI URNAL CYCLE of DEEP CONVECTI ON OVER LAND CNRM, ECMWF, LMD, Met Of f ice, NCAR & SMHI (Europe, Fr ance, Sweden, UK & US) Guichard & P et ch Beau, Belj aars, Chaboureau, Cheinet , Grabowski,

SLIDE 1

EUROCS DEEP CONVECTI VE CLOUDS DI URNAL CYCLE

DEEP CONVECTI ON OVER LAND

CNRM, ECMWF, LMD, Met Of f ice, NCAR & SMHI (Europe, Fr ance, Sweden, UK & US) Guichard & P et ch Beau, Belj aars, Chaboureau, Cheinet , Grabowski, Grandpeix, Grenier, J akob, J ones, Koehler, Laf ore, Piriou, Redelsperger, Royer, St irling, Tailleux, Tomasini EUROCS, 16 December 2002, Madrid

SLIDE 2

OBJECTI VES t o document perf ormances of GCMs t o design a f ramework t o address t he problem (a simple case study f or CRMs & SCMs) t o analyse t he case, f indings, conclusions t o improve paramet erisat ions & GCMs

SLIDE 3

Regional Climate Modelling Colin Jones most frequently occuring time of max precipitation in a diurnal cycle

(June 10-July 31 1993, from hourly accumulations)

0 2 4 6 8 10 12 14 16 18 20 22 24 hour (local time)

1 2

t he model capt ures t he broad early-lat e evening max of rainf all errors is in t he SE, could be relat ed t o t he proximit y of model boundaries

SLIDE 4

COMMON CRMs/ SCMs CASE STUDY

1 : an « observed case » to assess our models over land

Sout hern Great Plains (US)

GCSS WG4 Case3a

4-day runs wit h deep convect ion f orcings prescribed f rom observat ions

(large scale advect ion, surf ace f luxes)

2 : building an « idealized case » to address the diurnal cycle of deep convection over land and its representation in models

because most event s of t he « observed case » not linked t o our aims

(not designed f or t his purpose)

mot ivat ed by Bet t s & J akob (2002) error in t he diurnal cycle of deep convect ion: shared by short & long- t erm GCM runs reproduced in SCM runs

SLIDE 5

THE SI MULATI ONS : 6 SCMs & 4 CRMs model t ype SCM SCM SCM SCM SCM CRM CRM CRM CRM lab (model name) CNRM (ARPEGE, Clim & WF) ECMWF (I FS) LMD (LMDz) Met Of f ice (UM) SMHI (close t o HI RLAM) CNRM (mésoNH) CNRM (comeNH) Met Of f ice (UM) part icipant s Beau, Grenier, Piriou Chaboureau, J akob, Koehler, Becht old Tailleux Pet ch J ones Chaboureau & Tomasini Guichard Pet ch Grabowski NCAR (UM)

SLIDE 6

I n practice Preparat ion of t he case Def init ion of a «base list s» of relevant diagnost ics t imes series & t ime-height series of select ed f ields mean prof iles, convect ive f luxes, subgrid-scale moment s, Q1, Q2, radiat ive heat ing rat es, cloud f ract ion, cloud wat er… CRMs : Lx ~ 500 km Dx ~ 250m t o 2km Dz ~ st ret ched 70-700m or less SCMs : operat ional version Closer lab-lab CRM-SCM direct collaborat ions, e.g. CNRM-ECMWF Sharing t he work, e.g. f or CRMs, sensit ivit y st udies: UK Met Of f ice: spat ial resolut ion CNRM: sub-grid scale represent at ion

SLIDE 7

SI MULATI ON OF DEEP CONVECTI ON OVER LAND THE OBSERVED CASE broad conclusions consist ent wit h Xu et al. (2002) & Xie et al. (2002)

(new t est f or more t han 50% of models) an example : comparison wit h obs, min-max envelope f or CRMs & SCMs

min max

bet t er agreement & less scat t er among CRM result s t hat SCM ones

SLIDE 8

comparison CRMs & SCMs

(paramet ers f or which direct observat ions are not available)

bviously room f or CRMs improvement s (« cold » microphysics)

however much more consist ency among CRMs t han SCMs very weak convect ive downdraught s in several SCMs

SLIDE 9

comments

Pet ch et al. (2002) f or CRMs

import ance of t he resolut ion and of t he represent at ion of subgrid-scale processes

because the good representation

f boundary layer processes is

essential f or this issue

hour

SCMs & GCMs issues

complex int eract ions among paramet erisat ions involved

why convection occurs or not ? and how ? identif ying the major weaknesses to correct them in priority

SLIDE 10

THE I DEALI ZED CASE

similar t ype of f ramework as t he 1st one: 27 Mai 1997 of GCSS case 3a repeat ed t wice

(prescribed large-scale adv. & surf ace heat f luxes)

st art ing in t he morning inst ead of t he evening

night time local solar time (hour)

rainf all event s t end t o occurs earlier in SCMs t han in CRMs

SLIDE 11

precipitation CAPE CIN precipitation

20 days

julian day (1997)

values derived f rom observat ions (Xie et al. 2001)

f ree convection level température ~ 10 km ~ 1 km heigth f ree convection level

CI N CAPE

adapt ed f r om Roux (1991) dry adiabat atmospheric prof ile pseudo- adiabat Particule P condensation level thermal equilibrium level

What are the main reasons accounting f or these dif f erences ? (beginning)

development of large CAPE during dayt ime associat ed wit h boundary layer evolut ion by design, st rong link wit h CAPE in many paramet erizat ions (CAPE closure) Not much account of CI N in exist ing f ormulat ions

SLIDE 12

Convective I nhibition (CI N)

large f luct uat ions linked t o t he surf ace but

in SCMs in CRMs

I n CRMs, signif icant increase of CI N associat ed wit h deep convect ion in SCMs, more largely cont rolled by t he diurnal cycle of t he surf ace t he impact of convect ion on CI N is t oo weak

SLIDE 13

What are the main reasons accounting f or these dif f erences ? (cont inue)

SLIDE 14

What are the main reasons accounting f or these dif f erences ? (cont inue)

…before the development of deep convection a « shallow » non-precipitating transition period which last one to a few hours in CRMs …

Lx: 300 km 15 km

transition regime in CRMs, corresponding t o t he build up

f convect ion: a f eat ure

« broadly coherent » wit h several previous observed st udies

Wylie & Woolf (2002)

total clouds

cold clouds

which f actors control the lenght of this phase? role of buoyancy, wind shear, moist ure…

snapshots of cloud + rain water content in CRM run (UK UM CRM, Petch)

SLIDE 15

in CRMs

saturation def icit

cloud f raction rain mixing ratio

SLIDE 16

SCMs: saturation def icit SCMs: upward convective mass f lux

SLIDE 17

Chaboureau, Becht old, Köhler, Belj aars, et al.

ECMWF GCM

f ormulat ion of t he trigger f unction adding a represent at ion of local subgrid-scale f orcing (correct represent at ion of shallow convect ion required) 1D column mode

idealized EUROCS case (4-day composit e)

3D mode (i.e. ; f ull GCM)

Rhodonia, Amazonia (1-mont h composit e)

SLIDE 18

Chaboureau, Becht old, Köhler, Belj aars et al.

diurnal cycle of rainf all in the Tropics

diurnal composit e, Hovmüller diagram (20S-20N avg)

Africa Amazonia OBS Feb 1999 (TRMM data) ECMWF GCM Standard Feb 1999 ECMWF GCM Modif ied Feb 1999

SLIDE 19

CONCLUSI ON, PERSPECTI VES

document at ion of GCMs & RCMs weaknesses/ diurnal cycle of deep convect ion assess CRMs/ SCMs over land wit h GCSS/ ARM case design an idealized case t o address t he problem

and it worked! i.e., deep convect ion occurs ear lier t han observed in many SCMs runs (consist ent wit h result s of GCMs)

bet t er result s/ consist ency among CRMs t han SCMs

(T & q, cloud paramet ers: agreement wit h previous st udies)

CRM runs : t he t reat ment of t he BL is crucial

increased horizont al resolut ion &/ or subgr id-scale processes raising issues concerning t he gap bet ween shallow and deep convect ion (numer ical invest igat ion)

EUROCS DEEP CONVECTI VE CLOUDS DI URNAL CYCLE

DEEP CONVECTI ON OVER LAND

CNRM, ECMWF, LMD, Met Of f ice, NCAR & SMHI (Europe, Fr ance, Sweden, UK & US) Guichard & P et ch Beau, Belj aars, Chaboureau, Cheinet , Grabowski, Grandpeix, Grenier, J akob, J ones, Koehler, Laf ore, Piriou, Redelsperger, Royer, St irling, Tailleux, Tomasini EUROCS, 16 December 2002, Madrid

OBJECTI VES t o document perf ormances of GCMs t o design a f ramework t o address t he problem (a simple case study f or CRMs & SCMs) t o analyse t he case, f indings, conclusions t o improve paramet erisat ions & GCMs

Regional Climate Modelling Colin Jones most frequently occuring time of max precipitation in a diurnal cycle

(June 10-July 31 1993, from hourly accumulations)

0 2 4 6 8 10 12 14 16 18 20 22 24 hour (local time)

1 2

t he model capt ures t he broad early-lat e evening max of rainf all errors is in t he SE, could be relat ed t o t he proximit y of model boundaries

COMMON CRMs/ SCMs CASE STUDY

1 : an « observed case » to assess our models over land

Sout hern Great Plains (US)

GCSS WG4 Case3a

4-day runs wit h deep convect ion f orcings prescribed f rom observat ions

(large scale advect ion, surf ace f luxes)

2 : building an « idealized case » to address the diurnal cycle of deep convection over land and its representation in models

because most event s of t he « observed case » not linked t o our aims

(not designed f or t his purpose)

mot ivat ed by Bet t s & J akob (2002) error in t he diurnal cycle of deep convect ion: shared by short & long- t erm GCM runs reproduced in SCM runs

SI MULATI ON OF DEEP CONVECTI ON OVER LAND THE OBSERVED CASE broad conclusions consist ent wit h Xu et al. (2002) & Xie et al. (2002)

(new t est f or more t han 50% of models) an example : comparison wit h obs, min-max envelope f or CRMs & SCMs

min max

bet t er agreement & less scat t er among CRM result s t hat SCM ones

comparison CRMs & SCMs

(paramet ers f or which direct observat ions are not available)

however much more consist ency among CRMs t han SCMs very weak convect ive downdraught s in several SCMs

comments

Pet ch et al. (2002) f or CRMs

import ance of t he resolut ion and of t he represent at ion of subgrid-scale processes

because the good representation

essential f or this issue

SCMs & GCMs issues

complex int eract ions among paramet erisat ions involved

why convection occurs or not ? and how ? identif ying the major weaknesses to correct them in priority

THE I DEALI ZED CASE

similar t ype of f ramework as t he 1st one: 27 Mai 1997 of GCSS case 3a repeat ed t wice

(prescribed large-scale adv. & surf ace heat f luxes)

st art ing in t he morning inst ead of t he evening

night time local solar time (hour)

rainf all event s t end t o occurs earlier in SCMs t han in CRMs

20 days

values derived f rom observat ions (Xie et al. 2001)

What are the main reasons accounting f or these dif f erences ? (beginning)

development of large CAPE during dayt ime associat ed wit h boundary layer evolut ion by design, st rong link wit h CAPE in many paramet erizat ions (CAPE closure) Not much account of CI N in exist ing f ormulat ions

Convective I nhibition (CI N)

large f luct uat ions linked t o t he surf ace but

in SCMs in CRMs

I n CRMs, signif icant increase of CI N associat ed wit h deep convect ion in SCMs, more largely cont rolled by t he diurnal cycle of t he surf ace t he impact of convect ion on CI N is t oo weak

What are the main reasons accounting f or these dif f erences ? (cont inue)

What are the main reasons accounting f or these dif f erences ? (cont inue)

…before the development of deep convection a « shallow » non-precipitating transition period which last one to a few hours in CRMs …

Lx: 300 km 15 km

transition regime in CRMs, corresponding t o t he build up

« broadly coherent » wit h several previous observed st udies

Wylie & Woolf (2002)

cold clouds

which f actors control the lenght of this phase? role of buoyancy, wind shear, moist ure…

snapshots of cloud + rain water content in CRM run (UK UM CRM, Petch)

in CRMs

saturation def icit

cloud f raction rain mixing ratio

SCMs: saturation def icit SCMs: upward convective mass f lux

Chaboureau, Becht old, Köhler, Belj aars, et al.

ECMWF GCM

f ormulat ion of t he trigger f unction adding a represent at ion of local subgrid-scale f orcing (correct represent at ion of shallow convect ion required) 1D column mode

idealized EUROCS case (4-day composit e)

3D mode (i.e. ; f ull GCM)

Rhodonia, Amazonia (1-mont h composit e)

Chaboureau, Becht old, Köhler, Belj aars et al.

diurnal cycle of rainf all in the Tropics

diurnal composit e, Hovmüller diagram (20S-20N avg)

Africa Amazonia OBS Feb 1999 (TRMM data) ECMWF GCM Standard Feb 1999 ECMWF GCM Modif ied Feb 1999

CONCLUSI ON, PERSPECTI VES

document at ion of GCMs & RCMs weaknesses/ diurnal cycle of deep convect ion assess CRMs/ SCMs over land wit h GCSS/ ARM case design an idealized case t o address t he problem

and it worked! i.e., deep convect ion occurs ear lier t han observed in many SCMs runs (consist ent wit h result s of GCMs)

bet t er result s/ consist ency among CRMs t han SCMs

(T & q, cloud paramet ers: agreement wit h previous st udies)

CRM runs : t he t reat ment of t he BL is crucial

increased horizont al resolut ion &/ or subgr id-scale processes raising issues concerning t he gap bet ween shallow and deep convect ion (numer ical invest igat ion)

SCM runs: ident if ying t he maj or weknesses & t est ing modif icat ions no succession of dry-shallow-deep regimes in SCMs, dry t o deep direct ly