A statistical study was made of 420 Pc 3 magnetic pulsation events observed at ATS 6 in synchronous orbit by using digital power spectral and coherency (polarization) analysis. Pc 3 are a common occurrence at ATS 6 during local morning and have a peak occurrence near 1000 LT. The dominant period is ~30 s, and the waves are linearly polarized and generally transverse to the magnetic field. Based on azimuth angle, there are two classes of waves with different characteristics: (1) azimuthal, which comprise the main portion of the dominant frequency observations, show a local time-frequency dependence (with higher frequencies occurring near noon), are linear and very transverse, and show a variation of azimuth with local times, and (2) radial, which mainly occur at frequencies higher than 0.03 Hz, show no variation of frequency with local time, are linear but often have a significant compressional component, and show a variation of azimuth with local time. These characteristics agree quite well with those predicted by models of local field line resonance excited by a surface wave generated at the magnetopause and suggest that no special feature in the density gradient is necessary for the resonance to occur.