In order to understand propagation mechanisms of daytime Pc 3--4 magnetic pulsations with 10-70 s periods in the magnetosphere, we studied relationships among the interplanetary magnetic field (IMF) observed at ISEE 3, Pc 3--4 pulsations detected at the GOES 2 geostationary satellite (L=6.67,&lgr;=106.7¿W), and those observed at the ground stations at College (5.6, 147.9¿W), San Gabriel Canyon (1.8, 118.0¿W), Ewa Beach (1.15, 158.1¿W), and Onagawa (1.3, 141.5¿E). Activities of low-latitude PC 3--4 pulsations at the ground stations and compressional Pc 3--4 waves at GOES 2 are found to be weakly correlated with the cone angle of the IMF [&thgr;XB=cos-1(BX/BIMF)>. The frequency of both the daytime Pc 3--4 pulsations at the three low-latitude stations and the compressional Pc 3--4 waves in the magnetosphere are functions of the IMF magnitude, i.e., f(mHz)~5.5¿BIMF)nT). High-latitude Pc 3--4 pulsations detected at College are interpreted as consisting of various pulsations which are sometimes associated with the compressional Pc 3--4 waves in the magnetosphere and upstream waves in the earth's foreshock. It is also found that although there are latitudinal and longitudinal dependences of the above relationships, the compressional Pc 3--4 waves in space are well correlated with the low-latitude Pc 3--4 pulsations recorded at the ground near the satellite's meridian. From these correlation analyses, we infer that there are two different external sources for the daytime Pc 3--4 pulsations.

One is surface waves (i.e., evanescent modes) in the Pc 3--4 frequency range excited near the magnetopause, and the other source is the upstream wave in the earth's foreshock. The surface waves are the major source of pulsations in the outer magnetosphere (L>10), whereas the upstream wave transmitted through the magnetosheath and the magnetopause is the major source of the compressional Pc 3--4 waves at synchronous orbit (L=6.67). The compressional Pc 3--4 waves, which can propagate farther into the inner magnetosphere (L<6.6), can couple with various hydromagnetic oscillations in the plasmasphere and, finally, can be observed as the low-latitude Pc 3--4 pulsations on the ground.