Effects of the interplanetary magnetic field on the characteristics of Pc 3-4 pulsations at globally coordinated stations

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Daytime Pc 3-4 pulsation activities observed at globally coordinated low-latitude stations [SGC (L=1.8,λ=118.0°W), EWA (1.15,158.1°W), ONW (1.3,141.5°E)] are evidently controlled by the cone angle θ_<XB> of the IMF observed at ISEE 3. Moreover, the Pc 3-4 frequencies (ƒ) at the low latitudes and high latitude (COL; L=5.6 and λ=147.9°W) on the ground and that of compressional waves at geosynchronous orbit (GOES 2; L=6.67 and λ=106.7°W) are simultaneously correlated with the IMF magnitude (B_<IMF>). The correlation of ƒ of the compressional Pc 3-4 waves at GOES 2 against B_<IMF> is higher than those of the Pc 3-4 pulsations at the globally coordinated ground stations, i. e., γ=0.70 at GOES 2,and (0.36,0.60,0.66,0.54) at (COL, SGC, EWA, ONW), respectively. The standard deviation (σ_n=±ΔƒmHz) of the observed frequencies from the form ƒ (mHz)=6.0×B_<IMF>(nT) is larger at the ground stations than at GOES 2,i. e., Δƒ=±6.6mHz at GOES 2,and ±(13.9,9.1,10.7,12.1) mHz at (COL, SGC, EWA, ONW), respectively. The correlations between the IMF magnitude B_<IMF> and Pc 3-4 frequencies at the low latitudes are higher than that at the high latitude on the ground, which can be interpreted as a "filtering action" of the magnetosphere for daytime Pc 3-4 magnetic pulsations. The scatter plots of pulsation frequencies observed in the magnetosphere versus the IMF magnitude show a remarkable distribution restricted within the forms of ƒ=4.5×B_<IMF> and ƒ=7.5×B_<IMF>. The observed frequency range is theoretically confirmed to be consistent with the inferred frequency range (ω_<sc>/Ω_i=0.3-0.5) in the spacecraft frame of the magnetosonic upstream waves excited by the anomalous ion cyclotron resonance with reflected ion beams, which is observed to be V_‖=650-1150km/s in the solar wind frame by the ISEE satellite in the earth's foreshock. It is concluded that the magnetosonic right-handed waves excited by the reflected ion beams in the earth's foreshock are convected through the magnetosheath to the magnetopause, being transmitted into the magnetosphere without significant changes in spectra, and then couple with various HM waves in the Pc 3-4 frequency range at various locations in the magnetosphere.

Effects of the interplanetary magnetic field on the characteristics of Pc 3-4 pulsations at globally coordinated stations

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