Basic conversion operators for humidity, temperature and pressure

[daflack]

Creates a series of basic conversion operators, not worrying about grid staggering or vertical levels at this point. The humidity, pressure, and temperature are all treated together due to the fact that they are strongly linked to each other and require the mix of code to be calculated.

Fixes #1852.

Contribution checklist

Aim to have all relevant checks ticked off before merging. See the developer's guide for more detail.

• Documentation has been updated to reflect change.
• New code has tests, and affected old tests have been updated.
• All tests and CI checks pass.
• Ensured the pull request title is descriptive.
• Conda lock files have been updated if dependencies have changed.
• Attributed any Generative AI, such as GitHub Copilot, used in this PR.
• Marked the PR as ready to review.

[github-actions]

[daflack]

Conversions required, once basic code is done (excluding tests and full documentation will tick off)

A set of conversion operators for different humidity variables to be stored under humidity.py:

• specific humidity to mixing ratio
• mixing ratio to specific humidity
• specific humidity to relative humidity
• mixing ratio to relative humidity
• relative humidity to specific humidity
• relative humidity to mixing ratio

A set of derived temperature operators in 'temperature.py':

• Virtual temperature
• Dewpoint temperature
• Wet-bulb temperature
• Potential temperature
• Equivalent potential temperature
• Virtual potential temperature
• Saturation potential temperature
• Wet-bulb potential temperature

A set of derived pressure operators in 'pressure.py':

• Vapour pressure
• Vapour pressure from RH
• Exner pressure

[daflack]

Once full documentation done, will tick off.

A set of conversion operators for different humidity variables to be stored under humidity.py:

• specific humidity to mixing ratio
• mixing ratio to specific humidity
• specific humidity to relative humidity
• mixing ratio to relative humidity
• relative humidity to specific humidity
• relative humidity to mixing ratio

A set of derived temperature operators in 'temperature.py':

• Virtual temperature
• Dewpoint temperature
• Wet-bulb temperature
• Potential temperature
• Equivalent potential temperature
• Virtual potential temperature
• Saturation potential temperature
• Wet-bulb potential temperature

A set of derived pressure operators in 'pressure.py':

• Vapour pressure
• Vapour pressure from RH
• Exner pressure

[daflack]

Once tests done, will tick off.

A set of conversion operators for different humidity variables to be stored under humidity.py:

• specific humidity to mixing ratio
• mixing ratio to specific humidity
• specific humidity to relative humidity
• mixing ratio to relative humidity
• relative humidity to specific humidity
• relative humidity to mixing ratio

A set of derived temperature operators in 'temperature.py':

• Virtual temperature
• Dewpoint temperature
• Wet-bulb temperature
• Potential temperature
• Equivalent potential temperature
• Virtual potential temperature
• Saturation potential temperature
• Wet-bulb potential temperature

A set of derived pressure operators in 'pressure.py':

• Vapour pressure
• Vapour pressure from RH
• Exner pressure

[daflack]

Recommendation is for a technical review and a science review. Suggested approach is to either review by commits or do each operator in turn as you see fit/as is easiest for you.

[Sylviabohnenstengel]

Thank you for coding up this long list of conversions. I only have made few changes and happy to approve once a technical review has been conducted. I have put the emphasis of the review on the operators incl unit checks, equation checks etc. The tests look sensible to me i.e. checking metadata and physics, but i have not checked them in detail.

[Sylviabohnenstengel]

@daflack @jfrost-mo I have done the review and included a number of minor commits. Over to you @jfrost-mo for science and technical review and then happy to approve. Thank @daflack for coding up the long list of conversions!