Thermo Design Document

Introduction

People need to use equations to calculate thermodynamic quantities all the time. There should be a nice interface to do this.

Requirements

• Easy to use interface that minimizes how much you need to memorizes
• Works on xarray dataarrays
  • Takes full advantage of labeled data and automated broadcasting (e.g. for latitude-dependent calculation of absolute salinity)
• Handles units – where present in metadata or passed in by user as keyword
• Can work for atmosphere or ocean (or arbitrary set of equations)
• Scales to big data
• Can take advantage of metadata stored in DataArrays
• Clear in documentation which form of equations are being solved
• Support for custom equation of state (particularly for ocean)
• What does it calculate?
  • Atmosphere
    • Potential temperature
    • saturation vapor pressure
    • Slope of adiabats in T-P space etc
    • etc
  • Ocean
    • Density
    • Slope of isopycnals in T-S space
    • etc
  • All functions of thermodynamic state variables

Design

• Isolate solving code into a new package, that gets used by the atmos package
• Someone can make an ocean package that does something similar to the atmos package, containing equations for ocean thermodynamics
• Have saturation vapor pressure assumption treated specially as keyword argument
• Chain numba calls when doing ocean eqns, they’re huge!
• Aim for pure Python / numba implementation

What are people doing now?

• Ocean
  • GSW
  • Seawater toolkit (depractated but still widely used)
  • Or using routines extraced from models
  • No one rolls their own (formulas too clunky)
• Atmosphere
  • aoslib (python wrappers of fortran-based)
  • cf-python (link broken)
  • atmos
  • climt
  • climlab
  • metpy
  • pyCESM
  • etc
  • Formulas are simple, so most people just roll their own
• Don’t have a package that can use labeled xarray data effectively

link to hackpad