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Abstract:
Periodic Density Structures (PDSs) are quasi-periodic fluctuations of solar wind density ranging from a few minutes to a few hours. Based on average velocity of the solar wind, the PDSs have radial length scales greater than or equal to the size of the Earth’s dayside magnetosphere, hence belonging to the class of “meso-scale structures”. Engulfing the dayside magnetosphere, the PDSs can lead to compressional fluctuations of the Earth’s magnetic field at similar frequency (≈0.2-4.0 mHz) in a process often referred to as “forced breathing” mode. Magnetospheric field oscillations in part of the same frequency range are also associated with Pc5 Ultra Low Frequency (ULF) waves (≈1.7-6.7 mHz). These waves can be triggered by numerous phenomena involving dayside magnetosphere interaction with the solar wind and internal instabilities and/or resonances. Differentiating the nature and source of these waves is a challenging task but necessary to improve our understating of their role in the Earth’s magnetosphere system dynamics. We have extended previous works analyzing the role of PDSs detected from Wind spacecraft observations and compressional magnetospheric field fluctuations at the Geostationary Operational Environmental Satellites (GOES) to cover measurements over two solar cycles. Using a recently developed spectral analysis approach, we have compiled a list of solar wind driven “forced breathing” modes. Here, we discuss the properties of these waves including: (i) rate of one-to-one correspondence with solar wind density fluctuations; (ii) solar cycle and/or seasonal modulation; (iii) favored Magnetic Local Time (MLT) sectors.
