LGM Seasonal Energetics

LGM Seasonal Energetics

October, 2009

Annual mean insolation

Reflects Obliquity Change Only (Modern = 23.45 LGM = 22.95)

TOA seasonal incoming Insolation

Primarily reflects obliquity (precession change from 102 in modern to 114 in LGM), biggest high latitude effect in summer

Insolation Changes

Solid = Land average, Dotted = Ocean Average

Absorbed Solar Radiation

High Latitude summer changes dominate

ASR by components

• Delta_ASR = delta_Incoming + delta_surface_net + delta_atmosphere_net

• we have delta_surface_sw– presumably this associated with a surface albedo change

• We also have delta incomin• Therefore delta_atmosphere =

delta_SW_net_TOA – delta_incoming –delta_surface_sw_net

• Can’t say if this is due to a change in atmospheric albedo or atmospheric absorption of SW

ASR by components

Solid = incoming / Dashed = surface / dotted = atmosphere

Surface albedo chnages in the mid-latitude summer dominate

Surface Changes- Land Ocean

Solid = Land Domain / Dotted = Ocean Domain

Atmospheric ASR changes/ Land-Sea

Solid = Land /Dotted = OceanNote; this is atmos contribution to total ASR, not ASR in the atmosNecessarily (could be atmos albedo change)

SURFACE HEAT BUDGET annual mean

LGM surface LW goes up despite lower temperature- mustBe because atmos has more vapor

SURFACE HEAT FLUX – OCEAN Domain

Positive = to the atmosphere- LGM has smaller seasonal heat fluxIn both hemisphere’s because of more extensive sea-ice- NA is weird

Bottom Plot TakesInto AccountChange inLand FracIn LGM

SURFACE HEAT FLUX – LAND Domain

Positive = to the atmosphere Bottom is an order of magnitude smaller than ocean

FS Change

LGM gets more heat from ocean in NH winterNOT sure abour SH Land changes

Where does the LGM atmosphere get additional winter heat from?

JFM FS (colors inW/m^2) and sea Ice concentration

MODERN

LGM

JFM FS change (LGM-MOD)

SEA ICE is from LGM

JFM FS change- define regionsof interest

Composite around regions of large FS changeWhere does the energy come from

Composite FS seasonal cyclesNorth Atlantic Regions

Each region changes its annual mean FS- consequence of uncoupledRun? Are there really large ocean heat transport changes

North Atlantic Feb. FS and TS

Solid = Modern, Dashed = LGMSea ice edge has large FS gradient, leads to large temp. gradTemp. grad reverses north of Ice edge

Global Mean Energetics

Solid = PI (CAM)/ Dashed = LGM / Dotted = Observations

Should we be worried about model-observation difference?

3 Box Surface Temp.

Elevation change in LGM is a potential issueLarger LGM high latitude seasonal cycle

3 Box Atmos Temp.

Elevation change in LGM is a potential issueSlightly Larger LGM high latitude seasonal cycle

3-BOX_Energies

SOLID = MODERN / DASHED = LGMLGM polar region has less seasonality in ASR (albedo is higher) but Equally large changes in FS

3 BOX energy changes (LGM-MOD)

SH has smaller ASR amplitude but even smaller MHT variability, so the OLR and MHT amplitude upNH Summer changes dominate

(ASR-FS) is the energy fluxed to the atmosphere. Seasonal cycle ASR goes down in the LGM(enhanced albedo) but so does FS, so the energy fluxed to the atmosphere is unchanged. The partitioning of that energy between OLR and MHT is interesting.

6 box energies- PI (cam) and obs

Solid = observations / dashed = modeled

6-box temperatures- TS

6-box temperatures- TV

6-box energies- **SAME LAND MASK** (modern grid boxes with >95% LFRAC)

LGM = dashed/ MOD =SolidLess energy into LGM Ocean = more energy into LGM atmos over ocean =

larger temp variability over ocean -> less zonal heat transport to the land -> larger seasonal cycle over land

6-box energies- LGM-MOD

Land Domain Seasonal Amplitudes

Less LGM ASR cycle- but less energy is exported zonally because ocean temps. Have a larger seasonal cycle. The energy accumulated over land doesn’t change muchTotal energy accumulated = MHT, OLR, and CTEN (quadrature) variability

ZHTTo landIs outOf phaseWith ASR

Ocean Domain Seasonal Amplitudes

Note- ASR and ZHT are in phase over ocean

Change in non-open ocean

Diffusive heat transportStart with zonal mean vertically averaged temp

MOD = RED / LGM =BLUE– solid=raw / dashed = trunc. Legendre exp.Not many zonal mean differences beyond the global mean

I interpolateBelow the TopographyTo makeA verticallyIntegratedTemp record That isn’t biasedBy topography(I think)

Heat transport divergence

MOD = RED / LGM =BLUE– solid=raw / dashed = trunc. Legendre exp.

Not many zonal mean differences

Legendre Fourier expand temp and MHT_div

LGM –MOD legendre four. Coef.s

Stronger annual mean temp. grad. In LGM. Seasonal changes are moreComplex; Annual mean heat flux changes also up in LGM

Back out D

Not all wavenumbers fall on a line of constant D- BUT the #2 in the LGM and MOD do- D/a^2 = .98

Reconstruct HT, from T and D

D is held constant, from the mod Wave#2 fit- SH placement is off

T isTruncatedAt wave#6

Reconstruct HT from T and D

MAX HT reconstruct