Do CMIP5 emergent constraints on the large scale circulation still work in CMIP6?
In the CMIP5 archive a number of emergent constraints were proposed that linked future projected large scale circulation changes to present day climatology. If these emergent constraints are correct, then they can help us to constrain future climate projections. As advocated for by Hall et al (2019), doi.org/10.1038/s41558-019-0436-6 a primary indicator of a true emergent constraint is whether it survives an out of sample test. The CMIP6 archive provides us with a whole new set of simulations and models on which to determine whether the CMIP5 emergent constraints work to explain the distribution of in the CMIP6 models and vice-versa. An example of an emergent constraint on the large scale circulation, first proposed by Kidston and Gerber (2010) doi:10.1029/2010GL042873 and elaborated on by Simpson and Polvani (2016) doi:10.1002/2016GL067989 relates the magnitude of the poleward shift of the mid-latitude westerlies to the present day climatology during the winter (shown in the figure)
Other emergent constraints were proposed in CMIP5 for circulation change over the Pacific/North American sector with opposite conclusions. Simpson et al (2014) doi.org/10.1038/NCLIMATE2783 related the mangitude of meridional wind changes in western North America to the amplitude of climatological intermediate-scale stationary waves across the Pacific and concluded that many models are likely overestimating the amplitude of the meridional wind change over North America. This meridional wind change is connected to precipitation change over California and they concluded based on this emergent constraint that the real world is unlikely to become as wet in the winter as the CMIP5 ensemble mean suggests. In contrast Allen and Luptowitz DOI: 10.1038/ncomms16055 propose that the magnitude of circulation induced precipitation changes over California relate to a models fidelity in capturing ENSO teleconnections and that the models that have a better simulation of ENSO teleconnections exhibit more wetting over California, suggesting the precipitation increase over California may be higher than models suggest.
During the hackathon, we will devise python notebooks to calculate each of the quantities used in the above emergent constraints for present day and future simulations. We will assess whether the emergent constraints determined from CMIP5 are still present in CMIP6 and will asses whether the constraint devised from the CMIP5 spread can be used to predict CMIP6 and vice-versa.
Anticipated Data Needs
Monthly ua, va, sst, precip for historical and future scenarios for both CMIP5 and CMIP6
Anticipated Software Tools
Not sure. Maybe someone with more python expertise can suggest. But we will want to do a fourier decomposition, quadratic fits and linear fits.
People who have an interest in the large scale circulation and future hydroclimate change.