Coordinated ground and airborne measurements were conducted at three points along the Ascension Island magnetic meridian to investigate the distribution of scintillation-producing (km scale) ionospheric irregularities within an isolated equatorial plasma depletion. Airglow measurements near the northern Appleton anomaly show that irregularities are confined to the region within a 6300-¿ airglow depletion. The airglow measurements are then used to map the depletion region along magnetic field lines for comparison with scintillation measurements near the magnetic equator and near the conjugate point at Ascension Island. Results show that the irregularity region is magnetic flux tube aligned and conjugate over north-south distances of ~3000 km.