Preliminary Simulations of the CFMIP/GCSS LES ...€¦ · CFMIP LES Intercomparison (s11) vs. LTS 90-100 • Forcings for CFMIP LES intercomparison are intended to represent a particular

Preliminary Simulations of the CFMIP/GCSS LES Intercomparison andColumn Modeling of Sc Feedbacks in SP-CAM

Peter Blossey and Chris Bretherton (Univ. of Washington, USA)

with help from Matt Wyant and funding from CMMAP/NSF.Thanks to Marat Khairoutdinov for SP-CAM runs, SAM and his drizzle scheme.

Wednesday, June 10, 2009

Outline

• Column modeling of stratocumulus cloud feedbacks in SP-CAM:

• Background on column modeling approach, LTS-binning.

• Focus on stratocumulus region composite using 90-100th LTS percentiles.

• Column model results: sedimentation, diurnal cycle.

• Negative cloud feedbacks with most configurations.

• Preliminary simulations of GCSS/CFMIP LES intercomparison (s11 case):

• Temperature drift above inversion allows additional BL deepening.

• Omega feedback

• Drizzle feedback reverses sign of ΔSWCF.

• Boundary layer structure and cloud feedback are sensitive to configuration.


Column Modeling Approach

• Large-scale context for column model runs is extracted from GCM runs of control and perturbed climates. GCM is SP-CAM. CRM/LES is SAM 6.5, 6.7.

• Large-scale context: SST, soundings, omega, large-scale horizontal advection.

• Monthly SP-CAM output over tropical oceans composited based on deciles of lower tropospheric stability (LTS).

• Column LES/CRM use omega-feedback to simulate the effect of stratified adjustment in the tropics, limits T drift from composite soundings.

• Old work: Column LES/CRM simulations based on SP-CAM’s 70-80th & 80-90th percentile composites based on LTS.

• New work: LTS 90-100 from SP-CAM, CFMIP LES intercomparison Months per year in given LTS decile

Cu

Cu-Sc

Sc


Omega Feedback

• Simulates effect of stratified adjustment: local temperature anomalies are removed by large-scale vertical motion.

!

!p

!

f2 + a2m

am

!"!

!p

"

!

k2Rd

pT !

v

• Here, Tv’ and ω’ are anomalies from specified profiles.

• A lengthscale (which fixes k) and a profile of momentum damping rate (am) must be chosen.

200

400

600

800

1000Tv’

p, h

Pa

200

400

600

800

1000!’


Column Modeling of Composite SP-CAM Trade Cumulus Regimes (Blossey et al. JAMES to appear)

• Column CRM/LES simulations using composite forcings from SP-CAM’s 70-80th and 80-90th percentiles of lower tropospheric stability (LTS).

• CRM/SP-CAM: Δx=4km, Nz=30. LES: Δx=50-400m, Δz=20-160m in BL.

• Column CRM’s cloud climatology and +2K cloud response for 70-80th and 80-90th deciles of LTS is broadly similar to SP-CAM.

• Column LES has less cloud and weaker SWCF & ΔSWCF. ΔSWCF<0 for LTS 80-90, ΔSWCF~0 for LTS 70-80.

• Diurnal cycle important.

• CRM/SP-CAM: Radiatively-driven Cu increase.

• LES: more Sc under stronger inversion in +2K runs.


• Column LES has less cloud and weaker SWCF & ΔSWCF. ΔSWCF<0 for LTS 80-90, ΔSWCF~0 for LTS 70-80.

• Diurnal cycle important.

• CRM/SP-CAM: Radiatively-driven Cu increase.

• LES: more Sc under stronger inversion in +2K runs.

• Column CRM/LES simulations using composite forcings from SP-CAM’s 70-80th and 80-90th percentiles of lower tropospheric stability (LTS).

• CRM/SP-CAM: Δx=4km, Nz=30. LES: Δx=50-400m, Δz=20-160m in BL.

• Column CRM’s cloud climatology and +2K cloud response for 70-80th and 80-90th deciles of LTS is broadly similar to SP-CAM.

Column Modeling of Composite SP-CAM Trade Cumulus Regimes (Blossey et al. JAMES to appear)


SP-CAM climatology in 90-100th percentile of LTS

• Insufficient resolution leads to imperfect simulation of Sc clouds in SP-CAM.

• SP-CAM shows +2K increase in low cloud and radiative cooling in BL in LTS90-100, also across subsidence regions.

• Subsidence little changed between CTRL and +2K runs. HADVS confined largely to BL.

• Column LES run to equilibrium using steady forcings: no transient variability included in forcings.


290 300 310

800

850

900

950

1000

!, KPr

essu

re, h

Pa

LTS: 19.1 (19.5) K"LTS: 1.2 (1.3) K

EIS: 4.2 ( 4.8) K"EIS: 0.5 (0.6) K

CTRL+2K

0 25 50 75 100RH, %

CLDLOW: 0.25 (0.32)"CLDLOW: 0.01 (0.06)

Precip: CLB/SRFCTRL: 0.01/0.00

+2K: 0.01/0.00mm d!1

0 0.25 0.5 0.75 1Cloud Fraction

SWCF: !22.4 (!52.2)"SWCF: 3.6 (!8.0)

W m!2

Column LES Results for LTS 90-100 Bin

• LES: 2D, Lx=25.6km, Δx=25m, Δz=5-25m in BL

• Large diurnal cycle in cloud thickness related to daytime insolation leads to weak SWCF compared to SP-CAM.

• Time average too short for trustworthy ΔSWCF.

• Boundary layer shows signs of decoupling.

• Too little Sc due to LES overentrainment?

Stats: LES (SP-CAM)

LES Avg: Days 5-10


Sensitivity to Additional Sedimentation

• Many LES models are acknowledged to produce excessive entrainment at sharp inversions like those atop Sc boundary layers.

• Different effects could play a role in this over-entrainment: numerical diffusion, excessive subgrid-scale diffusivity and unmodeled physics (e.g. cloud droplet sedimentation, finite droplet evaporation timescale, partial cloudiness).

• Additional sedimentation (wsed=7.5 cm/s) is added to all cloud water to counteract this. This results in well-mixed boundary layer w/persistent cloud.

• With this amount of sedimentation, SAM simulations of DYCOMS RF01 at this vertical resolution (Δz=5m) settle into an LWP consistent with observations.


290 300 310

800

850

900

950

1000

!, KPr

essu

re, h

Pa

LTS: 19.4 (19.5) K"LTS: 1.3 (1.3) K

EIS: 4.6 ( 4.8) K"EIS: 0.6 (0.6) K

CTRL+2K

0 25 50 75 100RH, %

CLDLOW: 0.86 (0.32)"CLDLOW: 0.01 (0.06)

Precip: CLB/SRFCTRL: 0.41/0.05

+2K: 0.44/0.06mm d!1


SWCF: !99.3 (!52.2)"SWCF: !6.0 (!8.0)

W m!2

Column LES Results w/Extra Sedimentation

• Persistent cloud w/diurnal cycle in cloud thickness.

• +2K inversion shallower, has larger LWP during day.

• Negative ΔSWCF is comparable to SP-CAM, even though SWCF is about twice as strong.

Stats: LES (SP-CAM)

LES Avg: Days 10-30


Sensitivity to Diurnal Cycle of Insolation

• Perpetual (diurnally-averaged) insolation has little effect on mean LWP.

• With diurnal cycle, SWCF weaker by >30% due to daytime thinning of Sc cloud.

• Similar phenomena seen in LTS 70-80 and 80-90 bins.

Diurn Avg: Days 10-30Perpet Avg. Days 10-20

0.9

0.95

1

cld

frac

T"#$!a&'( *+,-d f0a*CTRL d"-04: 0(98

+2K d"-04: 0(98CTRL p$0p$t: 0(98

+2K p$0p$t: 0(98

0 5 10 15 200

50

100

150

200

Local Time of Day

LWP

[g m!2

]

T"#$!a&'( L?PCTRL d"-04: 113(1

+2K d"-04: 118(0CTRL p$0p$t: 108(2

+2K p$0p$t: 114(2

!300

!200

!100

0

SWC

F [W

m!2

]

T"#$!a&'( S?CECTRL d"-04: !99(3+2K d"-04: !105(3

CTRL p$0p$t: !138(0+2K p$0p$t: !139(9

0 5 10 15 200

0.1

0.2

0.3

0.4

Local Time of Day

Clo

ud A

lbed

o

T"#$!a&'( C+d A+HCTRL d"-04: 0(24

+2K d"-04: 0(25CTRL p$0p$t: 0(33

+2K p$0p$t: 0(33

CTRL diurn+2K diurnCTRL perpet+2K perpet


CFMIP LES Intercomparison (s11) vs. LTS 90-100

• Forcings for CFMIP LES intercomparison are intended to represent a particular location, while LTS90-100 forcings are a composite over 10% of tropical oceans

• Control sounding stability larger for s11 forcings in both LTS and EIS.

• CTRL→+2K increment in LTS and EIS is smaller for s11 forcings (ΔEIS = 0 K).

CFMIP s11 LTS 90-100


CFMIP LES Intercomparison (s11) vs. LTS 90-100

• CFMIP LES forcings have stronger omega than base LTS 90-100 (similar w/ω-feedback)

• Cool advection much stronger in s11 forcings for deep BL.

• Dry advection profiles similar.

• LES setup same as LTS 90-100: 2D, Lx=25.6km, Δx=25m, Δz=5-25m in BL.

CFMIP s11

LTS 90-100


Temperature Drift Above Inversion

• Temperature drifts cold above inversion, allows boundary layer to deepen substantially. (TH BIAS plotted starting 200m above cloud.)

• Sc layer persists with additional sedimentation, decouples without.

• Drift more prominent in +2K runs.

Diurnal Cycle

Diurnally-Averaged Insolation


290 300 310

800

850

900

950

1000

!, K

Pres

sure

, hPa

LTS: 22.9 (23.0) K"LTS: 0.1 (0.7) K

EIS: 8.5 ( 8.6) K"EIS: !0.5 (0.0) K

CTRL+2K

0 25 50 75 100RH, %

CLDLOW: 0.82"CLDLOW: !0.05

Precip: CLB/SRFCTL: 1.05/0.38+2K: 1.14/0.53

mm d!1


SWCF: !151.4 W m!2

"SWCF: 13.8 W m!2

Asymmetric Temperature DriftAbove Inversion

• Simulations without omega feedback, with additional sedimentation.

• +2K run drifts cold above inversion, leads to smaller ΔLTS than base state.

• +2K run slightly decoupled.

• Strong SWCF, strong positive ΔSWCF.

Time Avg: Days 5-20

290 300 310

800

850

900

950

1000

THETA [K]

p [h

Pa]

LES: THETA(p,t=tf)

LES CTRLLES +2Ks11 CTRLs11 +2K

0 20 40

LES: !0

hPa d-1


290 300 310

800

850

900

950

1000

THETA [K]

p [h

Pa]

LES: THETA(p,t=tf)


0 20 40 60OMEGA [hPa d!1]

LES: !0 + !’

290 300 310

800

850

900

950

1000

THETA [K]

p [h

Pa]

LES: THETA(p,t=tf)


0 20 40

LES: !0Effect of omega feedback

• Omega feedback eliminates drift above inversion. LTS, EIS, Δ’s consistent w/specs

• Results in more cloud, stronger SWCF than without omega feedback.

• ΔSWCF still positive.

Time Avg: Days 5-15

No ωFeedback

With ωFeedback

290 300 310

800

850

900

950

1000

!, K

Pres

sure

, hPa

LTS: 23.0 (23.0) K"LTS: 0.8 (0.7) K

EIS: 8.6 ( 8.6) K"EIS: 0.1 (0.0) K

CTL 100+2K 100

0 25 50 75 100RH, %



mm d!1


SWCF: !179.9 W m!2

"SWCF: 14.9 W m!2


290 300 310

800

850

900

950

1000

!, K

Pres

sure

, hPa

LTS: 22.8 (23.0) K"LTS: 0.8 (0.7) K

EIS: 8.3 ( 8.6) K"EIS: 0.1 (0.0) K

CTL 200+2K 200

0 25 50 75 100RH, %



mm d!1


SWCF: !197.8 W m!2

"SWCF: !5.6 W m!2

290 300 310

800

850

900

950

1000

!, K

Pres

sure

, hPa

LTS: 23.0 (23.0) K"LTS: 0.8 (0.7) K

EIS: 8.6 ( 8.6) K"EIS: 0.1 (0.0) K

CTL 100+2K 100

0 25 50 75 100RH, %



mm d!1


SWCF: !179.9 W m!2

"SWCF: 14.9 W m!2

Drizzle Feedback Changes Sign of ΔSWCF

• Sensitivity to cloud droplet number concentration Nc0.

• Drizzle-free, Nc0=200 simulations have thicker, deeper cloud.

• SWCF sensitivity to +2K change reverses sign with Nc0 change.

• Diurnal cycle might make drizzle feedback less prominent...

N100 Avg: Days 5-15N200 Avg: Days 5-15

Nc0=100

Nc0=200


Summary

• Column modeling of stratocumulus cloud feedbacks in SP-CAM:

• Additional sedimentation required for cloud to persist through daytime.

• Negative cloud feedbacks with most configurations (ΔEIS>0?).

• Diurnal cycle of insolation has strong impact on time-mean SWCF.

• Preliminary simulations of GCSS/CFMIP LES intercomparison (s11 case):

• Temperature drift above inversion allows additional BL deepening.

• Omega feedback provides consistent environment for evaluating cloud changes.

• Drizzle feedback reverses sign of ΔSWCF.

• Boundary layer structure and cloud feedback is sensitive to configuration.


Documents

Preliminary Simulations of the CFMIP/GCSS LES ...€¦ · CFMIP LES Intercomparison (s11) vs. LTS 90-100 • Forcings for CFMIP LES intercomparison are intended to represent a particular