Heat transport during the Last Glacial Maximum in PMIP2 models

January 2012

With Shih-Yu Lee

PMIP2 Models

• CNRM T63 L45• IAP FGOALS T42 L26• HadCM3 2.5%3.8 L19• IPSL 2.5X3.75 L19• Micro3.2 (medres) T42 L20• CCSM T42 – lower resolution than the CMIP3

(I’m missing E and P fields)• MPI ECHAM 5 (lower resolution– I don’t have a

PI run at the same resolution – Don’t use here)

Planetary albedo change and partition

Planetary albedo partitioning?

Earth’s Surface

Atmosphere

Solar Incident

Reflected by Atmosphere

Reflected by Surface

Surface albedo and planetary

Calculating MHT (annual average)• Total MHT is (ASR-OLR) integrated over the polar cap

to the latitude where the flux is calculated (the global mean of ASR-OLR is removed so that there is no heat transport through the poles)

• The ocean heat transport (OHT) is the surface heat flux integrated over the polar cap (global average removed)

• Atmospheric heat transport (AHT) is the residual: AHT = MHT –OHT

• Atmos. Moist heat transport is L(P-E) integrated over the polar cap (with a global average adjustment)

• Atmos. Dry heat transport is the residual: Atmos. Dry=AHT –Atmos. Moist

• We’d like to do the stationary, mean overturning and, transient decomposition as well

The LGM-PI difference in total (Ocean + Atmos) meridional heat transport is smaller than the inter-model spread

Ensemble average MHT change

Solid line is the ensemble average. Shading is 1 sigma. The change in heat transports are not significantly different from 0 (the cross-equatorial change is)

Understanding MHT change

5.8 PW

Heat Transport = -

8.2 PW 2.4 PW

ASR* OLR*

ΔMHT = ΔASR* - ΔOLR*

ΔMHT = ΔASR* - ΔOLR*

meansNH

SH

ΔASR* = ΔMHT + ΔOLR* (regress against Δ ASR* spread)

slopesNH

SH

+0.1 PW = +0.8 PW - 0.7PW

-0.05 PW = -0.04 PW - 0.01 PW

1 = 0.44 + 0.56

1 = 0.45 + 0.55

Dominant balance is between ASR* and OLR* !

The surface and atmospheric reflection contributions to ASR*

What determines ΔASR*?Reminder: partitioning in modern climate.

ASR* change (surface and atmos. Components)

ΔASR* = ΔASR*SURF + ΔASR*CLOUD + incident

meansNH

SH

slopesNH

SH

+0.8 PW = +1.12 PW - 0.37PW + 0.05PW

-0.04 PW = +0.15 PW - 0.18 PW - 0.01 PW

1 = 0.22 + 0.77 + 0.01

1 = 0.66 + 0.38 -0.04

ΔASR* = ΔASR*SURF + ΔASR*CLOUD + incident

Ensemble mean ΔASR* is due to surface albedo change. Spread in the NH is due to cloud response differences.

Ensemble average MHT change

Solid line is the ensemble average. Shading is 1 sigma. The change in heat transports are not significantly different from 0 (the cross-equatorial change is)

ΔMHT = ΔAHT + ΔOHT

meansNH

SH

slopesNH

SH

+0.1 PW = +0.24 PW - 0.14PW

-0.04 PW = 0.0 PW - 0.04 PW

1 = 0.20 + 0.80

1 = 0.75 + 0.25

ΔMHT = ΔAHT + ΔOHT (regress vs. MHT)

Ocean atmos. Compensation R^2 is 0.40 in the NH and 0.70 in SH

MHT change and ocean/atmos contributions

Ensemble average AHT change

Solid line is the ensemble average. Shading is 1 sigma. The trade off between moist and dry AHT is robust across models (moisture transport goes down in the LGM). At the equator the changes are consistent with Northward cross equatorial heat transport by the Hadley cell (with the moisture transport opposing the net heat transport)

ΔAHT = Δdry + Δmoist

meansNH

SH

slopesNH

SH

+0.1 PW = +0.27 PW - 0.17PW

-0.1 PW = 0.14 PW - 0.24 PW

1 = 1.16 - 0.16

1 = 0.60 + 0.40

ΔMHT = Δdry + Δmoist (regress vs. AHT)

AHT change and moist/dry contributions

AHT #s are different cause CCSM is excluded here

Cross equatorial heat transport• Cross equatorial MHT (atmos + ocean) is half the

hemispheric difference in ASR (SH – NH) – the hemispheric difference in OLR (SH-NH)

• MHTEQ= (ASRSH - ASRNH )/2 - (OLRSH - OLRNH )/2 • MHTEQ = <ASR> - <OLR>

<OLR> <OLR>

<ASR>

<ASR>

MHTEQSH NH

ΔMHTeq , Δ<ASR> and, Δ<OLR>

Robust increase in cross equatorial total heat transport due to <ASR> change

MHTEQ, AHTEQ and OHTEQ

ITCZ change

ITCZ intensity change and AHTEQ

Change in Annual mean surface temp

Colors are the ensemble mean changeContours are the inter-model spread with contour interval 2k

Precipitation change

Contours are precipitation in the PI climatology

Seasonal precipitation changes

Seasonal Cycle of Surface Temp.

Contours are inter-model spread with contour interval 2K

Seasonal Heating

Seasonal Heating Climatology

LGM change in seasonal heating

Less water vapor and more topography (thinner atmosphere) leads to lessShortwave atmospheric absorption

Change in seasonal surface fluxes

More sea ice insulates the system from the heat capacity of the ocean leadingTo larger seasonal energy fluxes to the atmosphereLand ice has high albedo -> less seasonal energy input to the atmosphere

Seasonal surface flux changeand ice change

Zonal average change in seasonal heating

Change in seasonal amplitude of temperature

EXTRAS

MHT and partition change in each model

Same data- grouped by circulation classes

The only robust changes across the models is the decreased moist transport and increased dry transport

Does the change in ocean heat transport predict the change in AHT?

Climatological seasonal amplitude of temperature