## MPA: Meridian Photometer Array

### Sites

There is an eastern line close to the 335° EDFL meridian, with three instruments located at Rankin Inlet, Gillam and Pinawa and a single station to the west close to the 312° EDFL meridian at Fort Smith. The coordinates are as follows.

Location Mnemonic Lat Long Lat Long Geodetic EDFL¹ Pinawa PINA 50.15 264.12 58.48 334.19 Gillam GILL 56.37 265.40 64.54 335.14 Rankin Inlet RANK 62.82 267.92 70.94 337.80 Fort Smith FSMI 60.00 248.12 66.96 311.69

¹ EDFL - Eccentric Dipole Field Line coordinates based on the MAGSAT MGST6/80 field model for 1984.0 (?).

Platform Type and Numbers. Each message transmitted by a Canopus Platform/Instrument contains a site identification code, the Platform Type (ASCII 'P' for the MPA) and Platform Number, a single ASCII character unique to each site. These codes are as follows.

- P1...Rankin Inlet
- P2...Gillam
- P3...Pinawa
- P5...Fort Smith

### Azimuths

Selection Criteria for MPA Azimuths. 20 July, 1987 (Revised from a document dated 07/01/86 giving details on the East Line)

The azimuths for the MPA photometers are chosen as follows (MPA Science Team Meeting, 21 October 1983):

* The azimuth for the central site is taken as the mean of the azimuths which the Northern and the Southern sites subtend at the central site.

* The EDFL latitudes of the midpoints between the sites are computed by taking the mean of the latitudes of the corresponding sites. These are adjusted to the centre of the nearest latitude bin (Latitude bins are centered on the whole and half degree EDFL).

* The EDFL coordinates are then computed for points at 110 km altitude at elevation angles from 0° to 90° in 1° steps in the plane through the central site (using the azimuth determined previously), together with the lookangles for these points from the appropriate site. The azimuth of the midpoints from the the Northern and Southern site are then determined by interpolation at the midpoints. This fixes the azimuths of the other two sites and EDFL coordinates are computed in the same manner. These coordinates form the basis for the computation of the instrument step tables. A second set is generated for the red line, using an altitude of 230 km. For the East line

Geodetic Coordinates Rankin Inlet 62.82444 N, 267.88528 E, 19 m Gillam 56.37611 N, 265.35833 E 145 m Pinawa 50.19861 N, 263.95972 E 275 m Azimuth of Rankin from Gillam 10.15° Azimuth of Pinawa from Gillam 188.29° Mean Azimuth = Gillam MPA Azimuth 9.22° (Use 9.20°) EDFL Coordinates Rankin 70.38, 338.92 Gillam 63.88, 336.20 Pinawa 57.73, 335.08 Midpoints 67.17 Choose 67.00 60.85 61.00 Azimuth/Elevation of the 110 km points From Rankin 193.17°/12.66° From Pinawa 6.32°/13.56°

For the West line.

Geodetic Coordinates Contwoyto 65.75444 N, 248.74667 E, 483 m Fort Smith 60.01667 N, 248.04972 E, 201 m Meanook 54.61667 N, 246.66667 E, 610 m Azimuth of Contwoyto from Fort Smith 2.87° Azimuth of Meanook from Fort Smith 188.47° Mean Azimuth = Fort Smith MPA Azimuth 5.67° (Use 5.70°) EDFL Coordinates Contwoyto 72.40, 311.27 Fort Smith 66.55, 313.19 Meanook 60.99, 313.29 Midpoints 69.47 Choose 69.50 63.77 63.50 Azimuth/Elevation of the 110 km points From Contwoyto 180.86°/16.57° From Meanook 11.18°/21.99°

Summary of azimuths for the all sites. Also shown is the direction of the magnetic zenith, calculated as the lookangle of the 110 km point on the field line through the observer. This differs by up to about 0.25 degree from the local (110 km) inclination and declination.

Rankin Inlet 3.2° Mag Z 173.1°/84.6° Gillam 9.2° Mag Z 182.5°/80.9° Pinawa 6.3° Mag Z 185.4°/76.5° Contwoyto 0.9° Mag Z 209.0°/84.2° Fort Smith 5.7° Mag Z 202.7°/80.8° Meanook 11.2° Mag Z 200.6°/76.9°

Field models used : Canopus EDFL Model for 1985, GSFC-980 1980.0 for 1985