**Definitions of Units of Measure used in MMS data product files:**

Quantity | Units (original) | Notation in CDF | SI_CONVERSIONS | |
---|---|---|---|---|

markup in CDF | as rendered by plot routines | |||

Number densities | cm^-3 | cm^{-3} | cm^{-3} | 1e6>m^{-3} |

Speeds, velocities | km/s | km/s | km/s | 1.0e3>m/s |

Angles, phase shifts | deg | deg | deg | 0.0174532925>rad |

Pressures (plasma - dynamic, thermal, magnetic) | nPa | nPA | nPa | 1.0e-9>Pa |

Temperatures | eV | eV | eV | 11604.50520>K |

Heat Flux | mW/m^2 | mW/m^{2} | mW/m^{2} | 1.0e-3>W/m^{2} |

Entropy | J/K | J/K | J/K | 1.0>J/K |

Electric Field | mV/m | mV/m | mV/m | 1.0e-3>V/m |

Probe to Spacecraft Potential | V | V | V | 1.0>V |

Electric field power spectral density | (V/m)^2/Hz | (V/m)^{2}/Hz | (V/m)^{2}/Hz | 1.0>(V/m)^{2}/Hz |

ExB Velocity | km/s | km/s | km/s | 1.0e3>m/s |

Poynting Flux | mW/m^2 | mW/m^{2} | mW/m^{2} | 1.0e-3>W/m^{2} |

Magnetic Field | nT | nT | nT | 1.0e-9>T |

Magnetic Field Power Spectral Density | nT^2/Hz | nT^{2}/Hz | nT^{2}/Hz | 1.0e-18>T^{2}/Hz |

Current Density | nA/m^2 | nA/m^{2} | nA/m^{2} | 1.0e-9>A/m^{2} |

Differential Number Flux | 1/(cm^2 s sr eV) | 1/(cm^{2} s sr eV) | 1/(cm^{2} s sr eV) | |

Differential Energy Flux | eV/(cm^2 s sr eV) | eV/(cm^{2} s sr eV) | eV/(cm^{2} s sr eV) | |

Distance | km | km | km | 1.0e3>m |

- Earth radius: 6371.2 km
ASCII Date/Time: ISO8601 standard (e.g. YYYY-MM-DDTHH:MM:SS.SSS or YYYY-DDDTHH:MM:SS.SSS)

**MMS Team members are welcome to ADD ADDITIONAL QUANTITIES as they are defined.**

**The CDF Format Guide requires that UNITS and SI_CONVERSION must be specified for each parameter.**

- It is proposed that conventions should be defined, so that a standard nomenclature is used for these metadata.
- UNITS attribute
- units in Level 2 CDF files shall be taken from the list above
- The units shall be specified as a human-readable ASCII string, using the abbreviations listed above.
- guidelines for unit nomenclature are proposed, below.

- SI_CONVERSION attribute
- Gives the conversion from the MMS unit of measure to SI units
- This attribute allows for plotting/analysis tools to combine MMS data with data from other missions which use different units.
- Guidelines for SI unit nomenclature are proposed, below.
- Requires guidelines for syntax, which are also included below.

**Convention for unit nomenclature and SI conversion attribute (see table above):**

- SI unit symbols to be used for SI conversion (rather than SI unit names) without SI prefixes: e.g. T, rather than nT or Tesla; sr, rather than steradians.
The SI_CONVERSION from nT would then be "1.0e-9>T". - SI prefixes are allowed in variable units, but not in the converted SI unit (units of [km] are required for distances, but the SI conversion must be to [m]).
**Note that the SI unit for angles is radians [rad].**

The SI_CONVERSION for angles (in degrees as defined above) would be "0.0174532925>rad"- Dimensionless variables are required (by ISTP standard) to be a blank character. For consistency the conversion should also be a blank character.

The SI_CONVERSION for a dimensionless variable would be " > ". - Units that are already SI (e.g. Hz, V) will have a multiplicative factor of 1, so the SI_CONVERSION for spacecraft potential would be "1.0>V".

**Convention for compound units (see table above): **

- Only dimensional units should be used. For example, a number density would have units of [cm^{-3}] not [#/cm^{3}].
- LaTeX math notation is to be used exponents, so the units for acceleration would be [m/s^{2}]

- This is usable through IDL with the graphics routines from "Coyote's guide" (David Fanning) or the TexToIDL package.
- This is usable through MATLAB, which directly supports TeX markup in graphics by specifying an interpreter to the text object.
- This is usable in Python through the graphics package matplotlib, which can use LaTeX to render the text in graphics output for several plotting backends.
- LaTeX is directly supported by GNUplot, in case anyone still uses that!
- Where this isn't currently supported is Autoplot, though it may not be difficult for Jeremy to support basic TeX-style markup for units.
- If LaTeX markup is allowed here then there is no reason people can't use it to give equations in other attributes, which could be handy when defining calculated quantities.