Calculate and plot maps of the model Average Magnetic field and Polar current System (AMPS)

## Overview

Python interface for the Average Magnetic field and Polar current System (AMPS) model.

The AMPS model is an empirical model of the ionospheric current system and associated magnetic field. The model magnetic field and currents are continuous functions of solar wind velocity, the interplanetary magnetic field, the tilt of the Earth’s dipole magnetic field with respect to the Sun, and the 10.7 cm solar radio flux index F10.7. Given these parameters, model values of the ionospheric magnetic field can be calculated anywhere in space, and, with certain assumptions, on ground. The full current system, horizontal + field-aligned, are defined everywhere in the polar regions. The model is based on magnetic field measurements from the low Earth orbiting Swarm and CHAMP satellites.

pyAMPS can be used to calculate and plot average magnetic field and current parameters on a grid. The parameters that are available for calculation/plotting are:

• field aligned current (scalar)
• divergence-free current function (scalar)
• divergence-free part of horizontal current (vector)
• curl-free part of horizontal current (vector)
• total horizontal current (vector)
• eastward or northward ground perturbation corresponding to equivalent current (scalars)

### Installation

Using pip:

```pip install pyamps
```

Dependencies:

### Quick Start

```>>> # initialize by supplying a set of external conditions:
>>> from pyamps import AMPS
>>> m = AMPS(350, # Solar wind velocity in km/s
-4, # IMF By (GSM) in nT
-3, # IMF Bz (GSM) in nT,
20, # dipole tilt angle in degrees
80) # F107_index
>>> # make summary plot:
>>> m.plot_currents()
```
```>>> # All the different current functions can be calculated on
>>> # a pre-defined or user-specified grid.
>>> import numpy as np
>>> mlat, mlt = np.array([75, -75]), np.array([12, 12])
>>> Ju = m.get_upward_current(mlat, mlt)
>>> Ju
array([ 0.23323377, -0.05599236])
```

### References

Laundal, K. M., Finlay, C. C., Olsen, N. & Reistad, J. P. (2018), Solar wind and seasonal influence on ionospheric currents from Swarm and CHAMP measurements, Journal of Geophysical Research - Space Physics. doi:10.1029/2018JA025387

Since April 2019, pyAMPS uses an updated set of model coefficients compared to the model discussed in the paper. The only difference is that the updated set of model coefficients were calculated using a larger Swarm dataset.

See also: Laundal, K. M., Finlay, C. C. & Olsen, N. (2016), Sunlight effects on the 3D polar current system determined from low Earth orbit measurements. Earth Planets Space. doi:10.1186/s40623-016-0518-x

### Acknowledgments

The code is produced with support from ESA through the Swarm Data Innovation and Science Cluster (Swarm DISC). For more information on Swarm DISC, please visit https://earth.esa.int/web/guest/missions/esa-eo-missions/swarm/disc

## Changelog

Version 1.1: Added support for calculations on regular mlat/mlt grids with less memory use Version 1.4: Updated model vectors and fixed a bug which affected toroidal field

## Project details

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