Positive low cloud feedback primarily caused
by increasing longwave radiation from the sea surface
in a climate model MIROC6
Tomoo Ogura1 and Mark J. Webb2
1.National Institute for Environmental Studies
2.Met Office Hadley Centre

26th July 2022, 3rd Pan-GASS Meeting, Understanding and Modeling Atmospheric Processes @Monterey

1Motivation：positive low cloud feedback in CMIP5 & 6
Global-Mean Cloud Feedbacks(abrupt-4xCO2 runs)

CMIP5CMIP6

Adapted from Zelinka et al. (2020)

Low cloud feedback mostly positive in CMIP5 & CMIP6 GCMs. Why are they positive?

Why low cloud feedback positive in low latitudes ?
AMIP experiment

LW

Ts_radAMIP-p4K experiment

LH

SH

Ts_turb

LW

Ts_rad+4K

LH

SH

Ts_turb+4K

Why low cloud feedback positive in low latitudes ?
AMIP experiment

LW

Ts_radAMIP-p4K experiment

LH

SH

Ts_turb

LW

Ts_rad+4K

LH

SH

Ts_turb+4K

Latent heat flux increases.
Warmer & moister atmosphereWhy low cloud feedback positive in low latitudes ?
Negative feedback (cloud increase)
AMIP experiment

Subsidence weakens

AMIP-p4K experiment

Myers and Norris (2013)

Inversion strengthens

Miller (1997)

LW

LHSH

LW

LHSH

LW cooling increases in B-Layer

Wyant et al. (2009)

Moisture convergence increases

Zhang et al. (2013)

Ts_radTs_turb

Ts_rad+4K

Ts_turb+4K

Positive feedback (cloud decrease)
Cloud-top LW cooling weakens

Bretherton et al. (2013)

MSE/moisture contrast increases

Brient and Bony (2013)

Penetrative entrainment increases
Rieck et al. (2012)

Wind speed & static stability reduces
Webb and Lock (2012)

Latent heat flux increases.
Warmer & moister atmosphereWhy low cloud feedback positive in low latitudes ?
Negative feedback (cloud increase)
AMIP experiment

Subsidence weakens

AMIP-p4K experiment

Myers and Norris (2013)

Inversion strengthens

Miller (1997)

LW

LH

SH

LW

LH

SH

LW cooling increases in B-Layer

Wyant et al. (2009)

Moisture convergence increases

Zhang et al. (2013)

Ts_radTs_turb

Ts_rad+4K

Ts_turb+4K

Positive feedback (cloud decrease)
Cloud-top LW cooling weakens

Bretherton et al. (2013)

MSE/moisture contrast increases

Brient and Bony (2013)

Positive > Negative in LES.
Does this explain
positive sign in GCMs?

Penetrative entrainment increases
Rieck et al. (2012)

Wind speed & static stability reduces
Webb and Lock (2012)

Latent heat flux increases.
Warmer & moister atmosphereWhy low cloud feedback positive in low latitudes ?
Negative feedback (cloud increase)
AMIP experiment

Subsidence weakens

AMIP-p4K experiment

Myers and Norris (2013)

Inversion strengthens

Miller (1997)

LH

LW

SH

LW

LH

SH

LW cooling increases in B-Layer

Wyant et al. (2009)

Moisture convergence increases

Zhang et al. (2013)

Ts_radTs_turb

Ts_rad+4K

Ts_turb+4K

Positive feedback (cloud decrease)
Cloud-top LW cooling weakens

Bretherton et al. (2013)

MSE/moisture contrast increases??

Here we have a gap in knowledge.

Brient and Bony (2013)

Positive > Negative in LES.
Does this explain
positive sign in GCMs?

Penetrative entrainment increases
Rieck et al. (2012)

Wind speed & static stability reduces
Webb and Lock (2012)

Latent heat flux increases.
Warmer & moister atmosphereNumerical experiments with MIROC6
AMIP experiment

LW

Ts_radAMIP-p4K experiment

LH

SH

Ts_turb

LW

Ts_rad+4K

LHSH

Ts_turb+4K

Numerical experiments with MIROC6
AMIP experiment

AMIP-p4Krad experiment

AMIP-p4K experiment?
LW

Ts_radLH

SH

Ts_turb

LW

Ts_rad+4K

LH

SH

Ts_turb+4K

LW

Ts_rad+4K

LH

SH

Ts_turb

Numerical experiments with MIROC6
AMIP experiment

LW

Ts_radAMIP-p4K experiment

LH

SH

Ts_turb

LW

Ts_rad+4K

LH

SH

Ts_turb+4K

AMIP-p4Krad experiment

AMIP-p4Kturb experiment

?

?

LW

Ts_rad+4K

LH

SH

Ts_turb

LW

Ts_radLH

SH

Ts_turb+4K

Numerical experiments with MIROC6
AMIP experiment

LW

Ts_radAMIP-p4K experiment

LH

SH

Ts_turb

LH

LW

Ts_rad+4K

Total response

Total response(e.g., low cloud feedback)SH

Ts_turb+4K

AMIP-p4Krad experiment

AMIP-p4Kturb experiment

?

?

LW

Ts_rad+4K

Radiative component

LH

SH

Ts_turb

LW

Ts_radTurbulent component= Radiative component + Turbulent component + Residual

Which term makes the low cloud feedback positive ?

LHSH

Ts_turb+4K

Which term makes the low cloud feedback positive?
Low cloud feedback induced by 4K increase in SST
Total response

Radiative component=

Synergy (residual)

Turbulent component++Radiative + Turbulent
Pattern correlation
0.81

Radiative component makes the feedback positive. But how?

Which term makes the low cloud feedback positive?
Low cloud feedback induced by 4K increase in SST
Total response

Radiative component=

Synergy (residual)

Turbulent component++

Radiative + Turbulent
Pattern correlation
0.81

Radiative component makes the feedback positive. But how?

Which term makes the low cloud feedback positive?
Total responseWhich term makes the low cloud feedback positive?
Total responseWhich term makes the low cloud feedback positive?
AMIP & AMIP-p4K experiments

Hybrid sigma-p

Cloud fraction [%]0.6T [℃]

Qv [g/kg]

RH [%]
0.6

0.6

0.6

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9

AMIP
AMIP-p4K

0.7

0510152030

405060

7080

90

24680

10 12 14 16510152025 30

Total response (AMIP-p4K minus AMIP)
Δ Cloud fraction [%]Hybrid sigma-p

Total response

Δ Qv [g/kg]

Δ RH [%]0.6

0.6

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9-9-6-30369-6 -4-202468

0.6

0.6-0.5 012340Δ T [℃]123456

Which term makes the low cloud feedback positive?
AMIP & AMIP-p4K experiments

Hybrid sigma-p

Cloud fraction [%]
0.6

T [℃]

Qv [g/kg]

RH [%]
0.6

0.6

0.6

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9AMIPAMIP-p4K

0.7

05101520304050607080902468010 12 14 16510152025 30

Total response (AMIP-p4K minus AMIP)
Δ Cloud fraction [%]Hybrid sigma-p

Total response

Δ Qv [g/kg]

Δ RH [%]

0.6

0.6

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9

-9-6-30369-6 -4-2

0Turbulent

24

68

0.6

0.6

-0.5 012340

Δ T [℃]

123456

Which term makes the low cloud feedback positive?
AMIP & AMIP-p4K experiments

Hybrid sigma-pCloud fraction [%]0.6T [℃]

Qv [g/kg]

RH [%]
0.6

0.6

0.6

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.90.9AMIPAMIP-p4K

0.7

0510152030405060708090

2468010 12 14 16510152025 30

Total response (AMIP-p4K minus AMIP)
Δ Cloud fraction [%]Hybrid sigma-p

Total response

0.6

0.6

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9-9Radiative

Δ Qv [g/kg]

Δ RH [%]-6-30369-6 -4-20Turbulent

24680.6

0.6-0.5 012340Δ T [℃]123456

Which term makes the low cloud feedback positive?
AMIP & AMIP-p4K experiments

Hybrid sigma-p

Cloud fraction [%]
0.6

T [℃]

Qv [g/kg]

RH [%]
0.6

0.6

0.6

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9

AMIP
AMIP-p4K

0.70510152030

405060708090

2468010 12 14 16510152025 30

Total response (AMIP-p4K minus AMIP)
Δ Cloud fraction [%]Hybrid sigma-p

Total response

0.6

0.6

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.9

0.9

0.9

0.9-9Radiative

Δ Qv [g/kg]

Δ RH [%]-6-30369Turbulent+Radiative-6 -4-20Turbulent

24

68

0.6

0.6-0.5 012340Δ T [℃]123456

Latent heat flux decreases in radiative component
Δ Latent heat flux
(AMIP-p4Krad minus AMIP)
AMIP-p4Krad experiment

LWLHSH
Surface air T warms up

Ts_rad+4K-20 -16 -12 -8-4048

12 16 20 [W/m2]

Ts_turb

Ts_turb stays the same

Static stability increases at air-sea interface

Bulk coefficient decreases, LH decreases

Why low cloud feedback positive in low latitudes ?
Negative feedback (cloud increase)
AMIP experiment

Subsidence weakens

AMIP-p4K experiment

Myers and Norris (2013)

Inversion strengthens

Miller (1997)

LWLH

SH

LW

LHSH

LW cooling increases in B-Layer

Wyant et al. (2009)

Moisture convergence increases

Zhang et al. (2013)

Ts_radTs_turb

Ts_rad+4K

Ts_turb+4KPositive feedback (cloud decrease)
Cloud-top LW cooling weakens

Bretherton et al. (2013)

MSE/moisture contrast increases
Positive feedback (cloud decrease)
Increase in LW from sea surface
Warming & drying (ΔQv < 0) in B-Layer
Decrease in low cloud

Brient and Bony (2013)

Positive > Negative in LES.
Does this explain
positive sign in GCMs?
Negative > Positive in MIROC6

Penetrative entrainment increases
Rieck et al. (2012)

Wind speed & static stability reduces
Webb and Lock (2012)

Latent heat flux increases.
Warmer & moister atmosphereDiscussion & Summary
Positive feedback from LW heating work in other GCMs?

Yes & No.
Mark Webb is presenting multi-GCMs analysis (next talk).
Results of some GCMs consistent with the present study.

Positive feedback from LW heating work in LES?
Yes.
Adrian Lock presented LES experiments in CFMIP.
Radiative component consistent with MIROC6.
Turbulent component more complicated than MIROC6.

 Positive low cloud feedback primarily caused by increasing LW radiation from the sea surface in MIROC6.