ex09

title	author
Exercise 09 - Using Jupyter Notebooks on JASMIN	Ag Stephens

Exercise 09: Using Jupyter Notebooks on JASMIN

Scenario

I want to demonstrate how data in the CEDA Archive can be read, processed and visualised using the an interactive Jupyter Notebook. The JASMIN Notebook Service:

• provides an interactive programming interface through a web browser
• includes a set of python libraries for data analysis
• can read directly from the CEDA Archive
• can include formatted documentation and visualisations within a Notebook

Specifically, I want to:

• read some hourly temperature data from the ECMWF ERA5 dataset on a global grid
• calculate the daily maximum and minimum over the time axis (all hours)
• plot the global maps of the daily maximum and minimum variables
• write the outputs to netCDF files on JASMIN
• add some inline annotations

Objectives

After completing this exercise I will be able to:

• login to the JASMIN Notebook Service
• create a Jupyter Notebook
• import modules and run Python code interactively using a notebook
• create visualisations in a notebook
• write outputs to the JASMIN file system
• add inline annotations to a notebook

JASMIN resources

• JASMIN account with jasmin-login privilege
• JASMIN Notebook Service: https://notebooks.jasmin.ac.uk
• Help documentation at: https://help.jasmin.ac.uk/article/4851-jasmin-notebook-service

Local resources

• Web browser (such as Firefox, Chrome, Safari)

Your task

This is the outline of what you need to do. The recommended way of doing each step is covered in the "Cheat Sheet" but you may wish to try solving it for yourself first.

1. Login to the JASMIN Notebook Service in your browser
2. Create a new Notebook
3. Import the xarray module and load some surface temperature data from 01/01/2005
4. Review the content of the loaded Dataset
5. Calculate the max and min over all timesteps in the dataset
6. Plot the daily maximum and minimum
7. Write the outputs to your JASMIN $HOME directory
8. Add inline documentation

Questions to test yourself

All too easy? Here are some questions to test your knowledge an understanding. You might find the answers by exploring the JASMIN Documentation

1. How can you add extra software packages to your Notebook?
2. How can you set up and use an entirely separate conda environment in your Notebook?
3. Can you figure out how to:
   • Delete a cell from a notebook
   • Execute a cell with different outcomes

Review / alternative approaches / best practice

This exercise demonstrates how to:

1. Get started with the JASMIN Notebook Service
2. Import and use software packages in your notebooks
3. Read and write from/to the JASMIN file system
4. View the outputs inline
5. Add annotations inline

Alternative approaches could include:

1. Using other Notebooks services, for example:

   • Google Colaboratory: https://colab.research.google.com/
   • Binder: https://mybinder.org/

2. Sharing your code on github:

   • You can view notebooks directly in GitHub
   • Here is an example: https://github.com/cedadev/ceda-notebooks/blob/master/notebooks/data-notebooks/cmip6/cmip6-zarr-jasmin.ipynb

Learn more about our Notebook Service:

• Tutorial (in notebooks): https://github.com/cedadev/ceda-notebooks/blob/master/notebooks/training/intro/notebook-tour.ipynb
• Help pages: https://help.jasmin.ac.uk/article/4851-jasmin-notebook-service

Cheat Sheet

1. Login to the JASMIN Notebook Service in your browser

   Visit: https://notebooks.jasmin.ac.uk/

   It should look like this:

   

2. Create a new Notebook

   On the "Launcher" page, click the "Python 3 + Jaspy" button.

   

   Right-click on the "Untitled.ipynb" tab at the top of the notebook and rename it to: ex09_notebook.ipynb

   

3. Import the xarray module and load some surface temperature data from 01/01/2005

   This task involves two parts: (1) Finding the relevant ECMWF ERA5 file paths and (2) Reading a file path pattern into an xarray Dataset object.

   Part (1) can be done in various ways. For the sake of simplicity, we have already searched the CEDA catalogue and found this dataset record:

   https://catalogue.ceda.ac.uk/uuid/8aa70a91378d455ea63a2a1953858a7f

   Following the "Download" link (when logged in with your CEDA account) on the page reveals a browseable data path that shows the 2-metre temperature data can be found under:

   https://data.ceda.ac.uk/badc/ecmwf-era51/data/oper/an_sfc/2005/01/01 (e.g. file: ecmwf-era51_oper_an_sfc_200501010000.2t.nc)

   On the file system, this translates to this pattern:

   /badc/ecmwf-era51/data/oper/an_sfc/2005/01/01/ecmwf-era51_oper_an_sfc_20050101*.2t.nc
   

   Click in the first cell of the notebook, and type:

   import xarray as xr
   

   Click Alt+Enter to execute the contents of the cell and create a new cell underneath.

   In the second cell, define the file pattern and open the netCDF files as an xarray Dataset with:

   file_pattern = "/badc/ecmwf-era51/data/oper/an_sfc/2005/01/01/ecmwf-era51_oper_an_sfc_20050101*.2t.nc"
   ds = xr.open_mfdataset(file_pattern)
   

   Click Alt+Enter to execute the contents of the cell and create a new cell underneath. From now on, remember that you need to click Alt+Enter to execute each cell.

4. Review the content of the loaded Dataset

   Notebooks are interactive, so you can look at the structure, attributes and time values of the Dataset, by typing each of these in a separate cell and executing them:

   # view the dataset structure
   ds
   
   # `ds.t2m` accesses the 2-metre temperature variable, `attrs` gives its attributes
   ds.t2m.attrs
   
   # view the time values
   ds.time.values
   

   The latter should look like:

   

5. Calculate the max and min over all timesteps in the dataset

   You can access the 2-metre temperature variable using: ds.t2m

   The ds.t2m Dataset has its own methods: max() and min(). They require the argument axis=0 in order to specify calculating the max and min only over the time axis. Calculate two new variables:

   daily_max = ds.t2m.max(axis=0)
   daily_min = ds.t2m.min(axis=0)
   

   Check the shape attribute of the daily_max and daily_min variables to ensure they are 2D (i.e. time has been removed).

   daily_max.shape, daily_min.shape
   

6. Plot the daily maximum and minimum

   Typically, in a Notebook environment, you need this line before trying to view plots inline.

   %matplotlib inline
   

   The daily_max and daily_min variables now both have a plot() method. You can plot each of them individually.

   daily_max.plot()
   

   ...and...

   daily_min.plot()
   

   You can even plot a map of the difference between them with:

   diff = daily_max - daily_min
   diff.plot()
   

   This should look like:

   

7. Write the outputs to your JASMIN $HOME directory

   The JASMIN Notebook Service can also see your JASMIN $HOME directory. You can write your outputs there (as long as they are not too big!).

   Create an outputs directory in your $HOME directory

   import os
   output_dir = f"{os.environ['HOME']}/outputs"
   
   if not os.path.isdir(output_dir):
       os.makedirs(output_dir)
   

   Write the daily_max and daily_min variables to NetCDF files, using the to_netcdf() method on each variable. The method requires the output file path as the argument.

   daily_max.to_netcdf(f"{output_dir}/max_t2m.nc")
   daily_min.to_netcdf(f"{output_dir}/min_t2m.nc")
   

8. Add inline documentation

   One of the most powerful features of Jupyter Notebooks is that you can explain your working. That is, you can include documentation cells along with the code and the results.

   For each cell, you can select either "Code", "Markdown" or "Raw" in the toolbar at the top of the notebook. If you select "Markdown", then the cell is no longer interpreted as Python code. Instead, it is interpreted as a mark-up language called markdown. This allows sophisticated formatting of text, images, code blocks etc., as described here:

   https://guides.github.com/features/mastering-markdown/

   In order to add Markdown cells to an existing notebook, click on the cell above the one you wish to annotate, then click the + button on the toolbar. Then change the cell format to "Markdown" in the drop-down menu.

   

   Once you have completed the content, press Shift+Enter to see the formatted version. If you need to edit a formatted cell, just double-click into it.

   Here is an example cell shown first in markdown format...

   

   ...and now formatted (after execution)...

   

Answers to questions

1. How can you add extra software packages to your Notebook?

See this example notebook to create your own virtual environment to install extra packages into your $HOME directory for use in a notebook:

https://github.com/cedadev/ceda-notebooks/blob/master/notebooks/training/virtualenvs-on-jasmin.ipynb

2. How can you set up and use an entirely separate conda environment in your Notebook?

See this example notebook to create new conda environments and make them visible to the JASMIN Notebook Service when you select a kernel:

https://github.com/cedadev/ceda-notebooks/blob/master/notebooks/docs/add_conda_envs.ipynb

3. Can you figure out how to:

• Delete a cell from a notebook

To delete a cell, select the cell by clicking to the left of it (i.e. by [2] in the image below)

Once the cell is selected, press "dd" on the keyboard and the cell will disappear.

• Execute a cell with different outcomes

You can control what happens when you execute a cell, as follows:

• Shift+Enter - which executes the cell and moves to the next one. If there isn't one below, it creates a new one for you.
• Ctrl+Enter - which executes the cell (and stays focussed on the current cell).
• Alt+Enter - which executes the cell and creates a new one for you.

Clicking the + button in the toolbar will insert an empty cell below the currently selected cell.