The objective of this paper is to demonstrate that GPS signal carrier phase scintillations observed from a spaced receiver array can be used to estimate ionosphere horizontal plasma drift velocities. Due to the non-stationary nature of the carrier phase scintillations and the existence of non-scintillation related components in the carrier phase measurements, direct time domain or Fourier spectral correlation of the receiver array measurements cannot yield meaningful results. An adaptive periodagram is used to generate high-resolution time-frequency information for the scintillation signal carrier phase. The resulting timing varying spectra from the receiver array are filtered and cross-correlated to generate time delays of similar scintillation patterns across a two-dimensional array. Horizontal plasma drift velocities are estimated using the time delays, known receiver spatial separations, assumed GPS signal ionosphere piercing heights, and satellite scan velocities. Plasma drift velocities measured by the SuperDARN radar at Kodiak, Alaska are used to validate the estimation results from the GNSS receiver array.