Physics of Equilibration: Energy and Water

ConservationKendal McGuffie Department of Applied PhysicsUniversity of Technology Sydney

iPILPS workshop April 2005

IPILPS Phase 1 Workshop Goals

Specific Foci:1. are simulation diffs due to (i) sensitivity to

forcing; (ii) parameterisation differences; (iii) both?

2. is Craig & Gordon ‘adequate’? ( & if not what is required?)

3. on diurnal scales how large are SWI differences; what observations could illuminate ‘adequacy’?

To demonstrate that Isotopically-enabled Land Surface Schemes (ILSSs) generate plausible simulations at the diurnal scale of the exchanges of Stable Water Isotopes (SWIs) at the soil, plant, air interfaces or to identify their shortcomings and propose ways of improving the simulations.

PILPS invented some numbers

• Spin up time:– Ideally, the time till year n is identical

to year n+1– PILPS defined as <0.1Wm-2 difference

between years n and n+1for latent and sensible fluxes (Yang et al. 1995)

– Soil moisture reservoir the important control on equilibration

Yang et al (1995)

From Qu et al., 1998

Variety of methods for simulating land surface fluxes gives different net radiation and different partitioning of sensible and latent fluxes.

This portrayal of results invented for PILPS and used to classify and analyse results since mid 1990s.

Sensible latent partitioning is important performance measure for energy/moisture treatments in land surface schemes.

Results from sensitivity tests at Cabauw

PILPS invented some diagrams

Zero net radiation net radiation = observed (dot)

PILPS plots show sensible and latent fluxes wrt to net radiation. Should be on a straight line.

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Zero line

zero

Model results normalised

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iPILPS challenges: create metrics• Annual mean is likely not hard (fractionation

coefficient a weak function of temperature)– Would be similar to getting the equator-to-pole

temperature gradient correct• Focus on “…plausible simulations at the diurnal scale

of the exchanges of Stable Water Isotopes (SWIs) at the soil, plant, air interfaces…”

• Comparing isotopes is a higher order problem. Depends on nature of simulation of water fluxes. e.g. lifetime in various reservoirs.

• This ought to provide a gateway to isotopic characterization of land surface processes.

evaporate

residual

mwl

18O

D

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Meteoric water line

Yellow: evapLight blue: runoffLight green: transpired water

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Monthly means

C-evap not where expectedothers very close to mwl

Meteoric water line

trans evap

runoff

Yellow: evapLight blue: runoffLight green: transpired water

Strategy for a first look• Examine gross

fluxes and isotopic characteristics of these fluxes

• Ecanop+Esoil• Qsb+Qs• Tveg

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runoff

transp

evap

runoff

transp

evap

runoff

transp

evap

jan jul jan jul

jan julActual fluxes over diurnal cycle• some oddities• range is large for Tveg• units in evap/runoff?

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18O

Features:

• poor agreement in amplitude

• phase agreement when diurnal variation

runoff

transp

evap

runoff

transp

evap

runoff

transp

evap

Some questions

• Why the variation in amplitude of diurnal cycles in deltas?

• What mechanisms are causing isotope variations?– Water residence times?– Reservoir size?– Position in ‘PILPS’ space?– Physics differences (bucket/SVAT)

spares-follow

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Mostly D

Daily plots arranged by station

This presentation created with images taken from ipilps web on Sat 16/4/05

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Relation between fluxes and deltas

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