FaradayInternationalReferenceIonosphere.jl

Julia tools for working with FIRI ionosphere profiles.

The Faraday-International Reference Ionosphere (FIRI) is a semiempirical model of the nonauroral ionosphere that enhances and extends the IRI model down to 60 km and densities above 10⁶ e-/m³. FIRI blends results from a simple ion-chemical model with sounding rocket profiles made by Langmuir probe and HF Faraday rotation measurements. FIRI-2018 is the most recent version of the model by M. Friedrich, C. Pock, and K. Torkar, but it was originally published in 2001 by Friedrich and Torkar. See the Citations section below.

Only one function is exported from FaradayInternationalReferenceIonosphere: firi. firi returns the average profile after filtering the model by the keyword arguments to the function.

profile = firi(; chi=(0, 130), lat=(0, 60), f10_7=(75, 200), month=(1, 12))

Each of the keyword arguments can either be a Tuple that inclusively brackets the range of values to be included in the average profile or can be a single value. Note that no interpolation occurs! If the value specified for f10_7 is 100 (which is not one of the values in the model output) then a warning will be printed and an empty profile will be returned.

⭐ Tip:

For convenience, load the package into your environment like

using FaradayInternationalReferenceIonosphere
import FaradayInternationalReferenceIonosphere as FIRI

The first line brings firi into scope. If that's all you need, then you can stop there. However, the second line lets you reference the package using the shorthand FIRI. I assume the package has been loaded this way in the examples below.

The raw model data can be accessed as FIRI.ALTITUDE for a Vector of the altitude in meters, FIRI.DATA for a Matrix of each electron density profile in electrons per cubic meter, and FIRI.HEADER for a Table with each combination of FIRI model parameters. To find the acceptable values of the f10_7 field, for example, you can use

unique(FIRI.HEADER.f10_7)

Although day of year ("DOY") appears as an independent field in the original published FIRI model file, this is entirely redundant with the month number. Each day of year simply corresponds to the day number in the middle of each month. Therefore, we use only the month field.

The keyword defaults bracket the full range of each field so that no filtering occurs.

The latitude and solar zenith angle (chi) fields can be interpolated with the function form

profile = firi(chi, lat; f10_7=(75, 200), month=(1, 12))

This performs a simple linear interpolation at each altitude of the profile for the specified chi and lat. The latitude can also be linearly extrapolated beyond 60°. If a chi or lat less than 0° is provided, a warning is thrown. According to Friedrich et al., 2018, although FIRI is only valid for the Northern Hemisphere, it can be used to predict values for the Southern Hemisphere by adding 6 months. Any chi greater than 130° (night) returns the profiles for exactly 130°.

The average profile returned by firi is skewed towards higher electron densities. If preferred, profile quantiles can be returned with the function FIRI.quantile. The quantile function is not exported to avoid collisions with Statistics.quantile. The usage of FIRI.quantile is similar to firi, except the quantile(s) are specified by p on the interval [0, 1].

profile = FIRI.quantile(p; chi=(0, 130), lat=(0, 60), f10_7=(75, 200), month=(1, 12))

There is also an interpolating form

profile = FIRI.quantile(chi, lat, p; f10_7=(75, 200), month=(1, 12))

To extrapolate the bottom of a profile to lower altitudes, use FIRI.extrapolate. This function will also interpolate to new (finer or coarser) altitudes in newz.

The function call is

newprofile = FIRI.extrapolate([z,] profile, newz)

Friedrich, M., and Torkar, K. M. (2001). FIRI: A semiempirical model of the lower ionosphere. Journal of Geophysical Research: Space Physics, 106, 21409-21418. doi: 10.1029/2001JA900070

Friedrich, M., Pock, C., & Torkar, K. (2018). FIRI-2018, an updated empirical model of the lower ionosphere. Journal of Geophysical Research: Space Physics, 123, 6737-6751. doi: 10.1029/2018JA025437