# CVA-CTA-Calculator

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### Contents:

- Overview
- Inputs
- Outputs
- Bugs/Caveats
- Other MPE/ISSI PlugIns

### Overview

This PlugIn calculates a boundary norma and boundary normal velocity according to the CTA (Constant Thickness Approach) and CVA (Constant Velocity Approach) methods listed in Haaland et al, Annales Geophysicae, No 2, 2004.

### Input data

Required inputs are the four spacecraft positions, the center time and the relative crossing times for the four spacecrafts. An optional array with crossing half durations may suypplied - CTA outputs (normal, velocity and thickness) are then returned.

### Outputs

Output quantities are:
- CVA_Normal - vector with the boundary unit normal from CVA
- CTA_Normal - vector with the boundary unit normal from CTA (if half thicknesses supplied)
- Vn_Cva - boundary velocity along the CTA_normal

In addition, the normals and velocities (and CTA thickness) is printed to the standard output window.

### Bugs/Caveats

Important: Note that the crossing durations are characteristic half time thicknesses; i.i., the time [in seconds] it takes for a SC to transverse from the outher edge of the boundary to the centre of the boundary.

### Other MPE/ISSI PlugIns

- Generic residue analysis of conservation laws
- Vector calculator/ Curlometer
- DeHoffmann-Teller analysis
- Solar wind utility. Calculates IMF clock angle, energy input, dynamic pressure etc.
- EDI filter utility
- Separate plasma velocity into paralell and perpendicular components
- Plasma calculator. Calculates plasma beta, magnetic pressure, resistivity inertial lengths etc.
- Modify, mask and manipulate components of a vector
- Construct a matrix time series from scalar time series
- Four Spacecraft boundary normal, thickness and velocity

SEH, 13 Jan, 2004