Overview
MP-Maps is a browser-based tool for exploring statistical properties of Earth's magnetopause — the boundary between the solar wind and the magnetosphere. It displays maps of magnetic shear angle, reconnection rate, and current density derived from in-situ measurements, as described in Michotte de Welle et al. (2024). All computations run locally in your browser via WebAssembly (Pyodide) — no server needed after the initial load.
The plots
3D view
A three-dimensional surface mesh of the dayside magnetopause, coloured by the selected quantity. The grey wireframe shows the Shue (1998) magnetopause model for the current solar wind conditions. The arrow indicates the IMF direction. Rotate and zoom with your mouse or trackpad. When spacecraft crossings are loaded, the orbit segment is drawn in the same view and detected crossings are highlighted.
Projected map (Y–Z plane)
A cross-section of the magnetopause at the terminator (X = 0, in GSE coordinates), shown as a 2D heatmap in the Y–Z plane. The boundary of the Shue98 magnetopause appears as a white contour. The IMF clock-angle direction is shown as an arrow. This view is useful for identifying where on the magnetopause reconnection is most likely to occur.
Quantities
Shear angle (°)
The angle between the magnetospheric and magnetosheath magnetic field vectors across the magnetopause. A shear angle near 180° indicates antiparallel fields — the configuration most favourable for magnetic reconnection.
Reconnection rate (mV/m)
A proxy for the reconnection electric field, computed from the Cassak–Shay scaling law using the local field and density values on each side of the boundary.
Current density (nA/m²)
The current density computed from the orientation and amplitude of the magnetic field on both sides of the magnetopause, assuming a finite magnetopause width of 800 km.
Parameters
Manual mode
Set solar wind and IMF conditions by hand with the sliders.
| Parameter | Range | Description |
|---|---|---|
| IMF clock angle | 0°–359° | Orientation of the IMF in the Y–Z (GSE) plane. 0° is northward, 180° is southward. |
| IMF cone angle | 1°–90° | Angle between the IMF vector and the Sun–Earth line. Small values indicate a radial field. |
| Dipole tilt | −30° to +30° | Geodipole tilt angle in the GSM frame. Positive in boreal summer (northern hemisphere tilted toward the Sun). |
| IMF amplitude B | 1–20 nT | Total IMF magnitude, used to scale the reconnection rate and current density. |
| SW density n | 1–30 cm⁻³ | Solar wind proton number density. |
| Dynamic pressure Pd | 0.1–20 nPa | Solar wind dynamic pressure, which controls the magnetopause standoff distance via the Shue98 model. |
OMNI mode
Select a date and time, then click Apply. The tool fetches the corresponding 1-minute OMNI solar wind data from the NASA/GSFC OMNI database and sets all parameters automatically. The sliders become read-only while OMNI mode is active. Switch back to Manual to adjust values freely.
Spacecraft crossings
This panel lets you overlay a spacecraft orbit on the maps and detect magnetopause crossings automatically.
- Select a spacecraft from the dropdown (MMS, Cluster, THEMIS, Geotail, or Double Star TC-1).
- Set the time range using the From and To fields.
- Click Load crossings. The trajectory is fetched from NASA SSCWeb via the Speasy proxy, and crossings are detected by comparing the spacecraft position to the Shue98 magnetopause.
- Once loaded, a dropdown lists all detected crossings. Selecting one jumps to that event, draws the crossing marker on the plots, and — if OMNI data is available for that time — automatically applies the solar wind conditions at that crossing.
Export
Choose PNG or PDF from the Format selector and click Download plots. Both the 3D view and the projected map are exported together with a light background and axis labels.