Global Positioning System phase fluctuations and ultraviolet images from the Polar satellite

In a study designed to determine the temporal development of ionospheric ir regularities in the auroral region in magnetic storm periods, different typ es of simultaneous observations were compared for the storms of January 10, April 10-11, and May 15, 1997. The data sets consisted of ultraviolet imag es (UVI) from the Polar satellite, phase :fluctuations and total electron c ontent (TEC) from Global Positioning System (GPS) recordings at a large num ber of sites, magnetometer observations and hemispheric power precipitation . The large-scale global or macroscale picture of the magnetic storm showed the importance of universal time in the development of irregularities. The hemispheric total power picture and the global Indices such as Kp show thi s macroscale picture of the entire storm period. However, individual sites show differences in localized magnetic field variations and the development of irregularities; this we term the microscale. The storms of January 10 a nd May 15 show the importance of local magnetic time and local magnetic var iations at the sites, while the storm of April 10-11 was dominated by the U T storm development. During the intense activity of the storms, total elect ron content shows minute-by-minute increases with the satellite moving to p ositions 6 km apart in the minute. The structured precipitation either dire ctly produces irregularities or indirectly sets instability conditions for irregularity development in the auroral region. Good correlation was establ ished for the three storms between VVI intensity and phase fluctuation deve lopment. The UVI Lyman-Birge-Hopfield-long (170 nm) emission is sensitive t o 100-200 km precipitation. Phase fluctuation development undoubtedly arise s from perturbations in the F region as well. Topside and bottomside soundi ngs have shown the high occurrence of spread-F in the auroral region. The c omparison of the data sets from these storms and from other studies indicat es that the creation of irregularities develops from conditions existing ov er a large range of bottomside heights, i.e., at altitudes from 100 km to t he F layer.