Name
Camille Risi
LMD (Laboratoire de Météorologie Dynamique), Paris, France

Title
The added value of tropospheric water vapor isotopic measurements for process-oriented evaluation of convective, cloud and transport processes in climate models

Time and place
Thu 2 Oct 2012, 11.15
Room C609, Arrhenius Laboratory, 6th floor

(this event has taken place)

 

Abstract
Differences between model representations of convective and cloud processes remain the dominant source of inter-model dispersion in climate change projections for a given grenhouse gas scenario. Evaluating the representation of the water cycle in climate models remain a challenge. Because of fractionation during phase changes, the water vapor isotopic composition reflects the history of phase changes during the water cycle. The development and availability of a growing number of remote sensing retrievals of isotopic composition (e.g. SCIAMACHY, GOSAT, TES, ACE-FTS, MIPAS, IASI, ground-based FTIR) provides an opportunity to explore the added value of tropospheric water vapor isotopic measurements for process oriented evaluation of convective, cloud and transport processes in climate models.

The first step in this direction is to learn to make the link between model-data isotopic differences and model biases in their representation of physical processes. To understand how different representations of physical processes are imprinted in the simulated isotopic composition, we use the isotope-enabled atmospheric general circulation model (GCM) LMDZ and we perform sensitivity tests to the physical representation of convective, cloud and transport processes. Once we gain this understanding, we can use isotopic data to evaluate the representation of physical processes in GCMs and to identify and interpret model biases.

In this seminar I'll give an example of this approach for the evaluation of subtropical tropospheric humidity. Comparison between LMDZ sensitivity tests, 7 isotope-enabled GCMs and various isotopic datasets suggests that most GCMs suffer from excessive vertical diffusion, and that this problem explains the upper-tropospheric moist bias that has long been noticed in GCMs. Then, I'll present work in progress on how isotopic observations could be used to better evaluate and constrain the representation of convective and cloud processes.

(this event has taken place)