Eastern Pacific SST Biases and Trends in CMIP6 vs. Observations
The Eastern Tropical Pacific is one of the most important regions in the world in terms of climate variability and teleconnections. What happens here affects the entire globe. Some recent papers have noted how trends in this region are quite distinct in CMIP5 models vs. observations.
Coats, S., & Karnauskas, K. B. ( 2017). Are simulated and observed twentieth century tropical Pacific sea surface temperature trends significant relative to internal variability? Geophysical Research Letters, 44, 9928–9937. https://doi.org/10.1002/2017GL074622
This paper showed that, over the past century, the SST gradient is strengthening in observations, but this strengthening trend is not reproduced in models. In the obs, the eastern tropical pacific is warming more slowly than the western, enhancing the meridional gradient.
In a more recent paper, Seager et al. (including myself and @naomi-henderson), examined the trends across a very wide range of CMIP5 models and reanalysis products.
Seager, R., Cane, M., Henderson, N., Lee, D. E., Abernathey, R., & Zhang, H. (2019). Strengthening tropical Pacific zonal sea surface temperature gradient consistent with rising greenhouse gases. Nature Climate Change, 9(7), 517. https://doi.org/10.1038/s41558-019-0505-x
We argued that this different trends in models was a consequence of the cold bias of their equatorial cold tongues. So understanding and eliminating this bias is a key challenge for climate modeling.
@naomi-henderson has apparently done some digging into CMIP6 and confirmed that the bias is still there.
- Examine the tropical pacific SST trends in the CMIP6 models
- Examine biases in SST climatology and thermocline structure compared with obs
- Look for quantitative relationships between winds, equatorial currents (incl. the undercurrent), and cold tongue bias
- See if this can explain the spread in SST trends under global warming
Anticipated Data Needs
Monthly-average ocean fields of
- 3D ocean temperature, salinity, and velocity
- Surface heat flux and wind stress
For preindustrial, historical, and future warming scenarios. Ideally we would do the full ocean heat budget, but I think this is not feasible with CMIP data.
For observations, we will need some reanalysis and climatologies (i.e. WOA). Kris also mentioned a new high-resolution glider-based climatology of the equatorial region that could be ideal model validation.
Anticipated Software Tools
This is mostly all doable in standard xarray.
People who actually understand tropical dynamics! (Not me unfortunately )