SPEEDY‐IER: A fast atmospheric GCM with water isotope physics

Abstract

The interpretation of variations in the global isotopic composition of precipitation and water vapor can be strengthened using an isotope‐enabled atmospheric general circulation model (AGCM). Here we present a fast‐physics atmospheric circulation model suitable for long ensemble integrations: the efficient AGCM Simplified Parameterizations, Primitive Equation Dynamics (SPEEDY), with newly added water isotope physics. The model (SPEEDY‐isotope‐enabled reconstructions (IER)) simulates the hydrological cycle and isotope ratios in atmospheric water at a fraction of the computational cost of Intergovernmental Panel on Climate Change (IPCC)‐class GCMs. Despite its simplified physics, SPEEDY‐IER captures many key features of the observed range of tropical, subtropical, and midlatitude isotope variability when compared to the Global Network of Isotopes in Precipitation, Stable Water Isotope Intercomparison Group (SWING2) simulations, and satellite observations of isotopes in vapor. The incorporation of water isotopes in SPEEDY required two updates to the model's physics: postcondensational exchange associated with falling rain and soil hydrology. It is evident that these physical processes are essential for a skillful simulation of isotopes in precipitation and vapor. We conduct a suite of sensitivity tests to constrain effective parameters in the rain exchange and land models and assess the impact of the new physics to isotope simulations. The strong sensitivity to parameter choice in these components reaffirms the importance of land‐atmosphere interactions and rain‐vapor exchange on stable water isotope ratios in the atmosphere and thus on the interpretation of paleoclimate records. The utility of SPEEDY‐IER for climate applications is discussed.

Stable isotopes in atmospheric water vapor and applications to the hydrologic cycle

“…Roche et al [] equipped the CLIMBER model with isotopic tracers in a coupled model with simplified ocean and atmosphere components. Other intermediate‐complexity models equipped with isotope tracers are the University of Victoria Earth System Climate Model [ Brennan et al , ], the iLOVECLIM model [ Roche , ], and the Simplified Parameterizations, Primitive Equation Dynamics Isotope‐Enabled Reconstructions Model (SPEEDY‐IER) [ Dee et al , ].…”

“…Other intermediate-complexity models equipped with isotope tracers are the University of Victoria Earth System Climate Model [Brennan et al, 2012], the iLOVECLIM model [Roche, 2013], and the Simplified Parameterizations, Primitive Equation Dynamics Isotope-Enabled Reconstructions Model (SPEEDY-IER) [Dee et al, 2015].…”

On the utility of proxy system models for estimating climate states over the common era

“…To provide climate state vectors for the DA prior (see equation (1)), and to provide climate fields for the PSM-generated network, we primarily use the isotope-enabled GCM SPEEDY-IER [Dee et al, 2014]. SPEEDY-IER is an intermediate complexity atmospheric GCM (IC-AGCM), and constitutes an efficient option for long paleoclimate integrations.…”

Groundwater isotopic data as potential proxy for Holocene paleohydroclimatic and paleoecological models in NE Brazil

“…The use of d-excess is already largely implemented in dated ice cores to evaluate past moisture source relative humidity conditions (e.g., Steffensen et al, 2008) Dee et al, 2015) and highlight the importance of the knowledge of the ecosystem type to better constrain proportion of evaporation versus transpiration recycling processes through d-excess (Jaseckco et al, 2013;Dee et al, 2015). This is yet challenging for present day modeling but can be constrained thanks to observational network H data, is only sparsely available over glacial-interglacial time scales, and mainly in ice cores (Werner et al, 2016).…”