Isotopic constraints on moist processes over the tropics in NASA GISS ModelE2

Robert Field, Daehyun Kim, Gavin Schmidt, John Worden, Allegra LeGrande, Max Kelley

JPL

Motivation

Climate projections with ModelE form a major part of the GISS contribution to IPCC.

Are measurements of the isotopic composition of water vapor useful for model evaluation? Can we use them to identify compensation errors in the parameterizations?

What physical processes might they be constraining, especially those that are hard to measure?

Moisture in lower free troposphere

ERA-I

ModelE

Model performance across different metrics

Pattern correlation

Ocean Land

Aura TES HDO/H2O Simulator

Varying TES retrieval quality and vertical sensitivity must be taken into account.

See: Field, R.D., C. Risi, G.A. Schmidt, J. Worden, A. Voulgarakis, A.N. LeGrande, A.H. Sobel, R.J. Healy, A Tropospheric Emission Spectrometer HDO/H2O retrieval simulator for climate models, Atmospheric Chemistry and Physics, 12, doi:10.5194/acp-12-10485-2012, 10485-10504, 2012.

Retrieval quality (%)

Height of peak HDO retrieval sensitivity (hPa)

Effects of TES operator on modeled δD fieldsRaw model δD (‰)

Change to raw model δD after applying ‘standard’ TES operator.Only works for prescribed meteorology.

Change to raw model δD after applying new TES operator.Works for arbitrary, free-running model configurations.

δD over lower free troposphere

TES

ModelE with operator

Pattern correlation

Model performance across different metrics

Ocean Land

Model performance across different metrics

Pattern correlation

Ocean Land

q as a constraint on convective recycling

Pattern correlation

Convective recycling ratio

Ocean Land

δD as a constraint on convective recycling

Pattern correlation

Convective recycling ratio

Ocean Land

Key points• Isotopic measurements provide a stronger

constraint than moisture amount or precipitation, especially over the ocean.

• They can provide guidance on the fidelity of hard-to-measure processes within the model.

• Next up:– Mechanistic constraints on model variability: MJO & ENSO– Land surface fluxes: evaporation / transpiration

partitioning– Observational error

Convective moisture recycling• Ratio of re-evaporated to total convective

condensate• Not well constrained

q and δD over lower free troposphere

HDO concentrations are expressed relative to an ocean water standard, in units of permil (‰).

qERA-I

δDTES

Capturing variation in vertical sensitivity

More com

plicated categorizationsObs.

GPCP

ModelE

Precipitation

TES vs. ModelE δD

δDRaw - δDTES

δDTES

δDRetrAK - δDTES

δDCatAK - δDTES

Stable isotopes (isotopologues) of water

16O

1H 1H

99.73%

18O

1H 1H

0.20%

16O

2H 1H

0.03%

The heavy isotopes of water evaporate less readily and condense preferentially.

There are now sufficient HDO measurements in the troposphere against which to evaluate models. We are currently working with HDO/H2O retrievals from the Tropospheric Emission Spectrometer (TES).