Climate Data

Using NetCDF in Python

Overview

Teaching: 20 min
Exercises: 10 min
Questions

  • How can I look at datasets using Python?

  • What operations are available?

Objectives

  • Use the Xarray library to read a file

  • Explain dimensions, variables and attributes

  • Perform simple numpy operations on datasets

There are quite a few libraries for working with climate data files in Python, here are a few:

Most are equally happy to open a file either on disk or over OPENDAP

We’ll mostly look at xarray here, a ‘higher-level’ library for working with gridded data

Example: Inspecting a file with xarray

Notebook

Behind the scenes Xarray stores data using an optimised library called numpy, with Xarray adding coordinates and metadata.

A lot of the time you don’t want to work with the whole dataset, you need to reduce it somehow. Perhaps you’re only interested in a specific region, or want to work with seasonal instead of monthly data

Example: Slicing and dicing datasets

Notebook

According to model data, what temperature was it in Melbourne today?

The OPENDAP link to ACCESS1.3 RCP45 surface temperature is ~~~ http://dapds00.nci.org.au/thredds/dodsC/ua6/authoritative/CMIP5/CSIRO-BOM/ACCESS1-3/rcp45/day/atmos/day/r1i1p1/latest/tas/tas_day_ACCESS1-3_rcp45_r1i1p1_20060101-20301231.nc ~~~

Example: Calculating the NINO 3.4 index

The NINO 3.4 index is defined as the anomaly over the region (5N - 5S, 170W - 120W) compared to the historical average between 1961 and 1990

Notebook

How do the RCP45 and RCP85 scenarios’s NINO 3.5 index compare?

OPENDAP links

http://dapds00.nci.org.au/thredds/dodsC/ua6/authoritative/CMIP5/CSIRO-BOM/ACCESS1-3/historical/mon/atmos/Amon/r1i1p1/latest/ts/ts_Amon_ACCESS1-3_historical_r1i1p1_185001-200512.nc
http://dapds00.nci.org.au/thredds/dodsC/ua6/authoritative/CMIP5/CSIRO-BOM/ACCESS1-3/rcp45/mon/atmos/Amon/r1i1p1/latest/ts/ts_Amon_ACCESS1-3_rcp45_r1i1p1_200601-210012.nc
http://dapds00.nci.org.au/thredds/dodsC/ua6/authoritative/CMIP5/CSIRO-BOM/ACCESS1-3/rcp85/mon/atmos/Amon/r1i1p1/latest/ts/ts_Amon_ACCESS1-3_rcp85_r1i1p1_200601-210012.nc

Key Points