Marine Heat Wave (MHW) analysis with xarray (ohw20-proj-marine-heat-waves)

This project aims to apply the MHW definition of Hobday et al. (2016) using the capabilities of xarray and dask. The project was started as an Ocean Hack Week 2020 project with the following objectives:

This project objectives are to:

• update E. Oliver's Marine Heat Waves (MHW) python code to take advantage of xarray, datetime, and dask
• adapt to use AWS MUR SST data
• expand to regions (2D) analysis, as well as time series

First steps are to update/rewrite the MHW code using xarray with testing to verify the code produces the same results as the marineHeatWaves python package. This version of the python code does the analysis of a single point time series. Here we want to expand to the spatial data available from satellite sea surface temperature (SST) data products, and so changing from the data format in the previous code to one using xarray is the logical step.

Other MHW codes

In addition to the python MHW code, an R MHW code and Matlab MHW toolbox exist.

How to contribute?

Current issues can be found or created here.

Current status

The Jupyter notebook Test_Run_Timeseries.ipynb integrates our efforts at the end of Ocean Hack Week 2020. See issues above for more updated status.

Cloud computing for this project:

To use GCP cloud 'Pangeo Binder GCE us-central1'.

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To use AWS cloud 'Pangeo Binder AWS us-west-2'

Definitions

The definitions of Hobday et al. (2016) are given below (or refer to Table 2 of the paper).

Climatology T_m (deg C) is the climatological mean, defined with the following equation . Subscripts s and e are start and end of the climatological record, T is the temperature (defined as daily temperature), j the day of the year index. T(d,y) indicates the SST on the d:day and y:year.

Threshold The threshold temperature, T_% (deg C), is determined by the percentile value desired (i.e. T₉₀ is 90% threshold, T₉₅ is a 95% threshold, etc.). The equation is given by where P₉₀ is the 90% and . Hobday et al. (2016) use the 90th percentile as the threshold to define an MHW.

MHW Start and End The start time t_s (days) and end time t_e (days) of the MHW are defined when (start): T(t)>T₉₀(j) and T(t-1)<T₉₀(j) and (end): t_e>t_s and T(t)<T₉₀(j) and T(t-1)>T₉₀(j)

References

Hobday, A.J., Alexander, L.V., Perkins, S.E., Smale, D.A., Straub, S.C., Oliver, E.C., Benthuysen, J.A., Burrows, M.T., Donat, M.G., Feng, M. and Holbrook, N.J., 2016. A hierarchical approach to defining marine heatwaves. Progress in Oceanography, 141, pp.227-238. https://doi.org/10.1016/j.pocean.2015.12.014