[1] We present an interval of extremely long-lasting narrow-band Pc5 pulsations during the recovery phase of a large geomagnetic storm. These pulsations occurred continuously for many hours and were observed throughout the magnetosphere and in the dusk-sector ionosphere. The subject of this paper is the favorable radial alignment of the Cluster, Polar, and geosynchronous satellites in the dusk sector during a 3-hour subset of this interval that allows extensive analysis of the global nature of the pulsations and the tracing of their energy transfer from the solar wind to the ground. Virtually monochromatic large-amplitude pulsations were observed by the CANOPUS magnetometer chain at dusk for several hours, during which the Cluster spacecraft constellation traversed the dusk magnetopause. The solar wind conditions were very steady, the solar wind speed was fast, and time series analysis of the solar wind dynamic pressure shows no significant power concentrated in the Pc5 band. The pulsations are observed in both geosynchronous electron and magnetic field data over a wide range of local times while Cluster is in the vicinity of the magnetopause providing clear evidence of boundary oscillations with the same periodicity as the ground and geosynchronous pulsations. Furthermore, the Polar spacecraft crossed the equatorial dusk magnetosphere outside of geosynchronous orbit (L $ 6-9) and observed significant electric and magnetic perturbations around the same quasi-stable central frequency (1.4-1.6 mHz). The Poynting vector observed by the Polar spacecraft associated with these pulsations has strong field-aligned oscillations, as expected for standing Alfvén waves, as well as a nonzero azimuthal component, indicating a downtail component to the energy propagation. In the ionosphere, ground-based magnetometers observed signatures characteristic of a field-line resonance, and HF radars observed flows as a direct consequence of the energy input. We conclude that the most likely explanations is that magnetopause oscillations couple energy to field lines close to the location of Polar, setting up standing Alfvén waves along the resonant field lines which are then also observed in the ionosphere. In the absence of monochromatic dynamic pressure variations in the solar wind, this event is a potential example where discrete frequency pulsations in the magnetosphere result from the excitation of a magnetospheric waveguide mode, perhaps excited via the Kelvin-Helmoltz instability or via overreflection at the duskside magnetopause.Citation: Rae, I. J., et al. (2005), Evolution and characteristics of global Pc5 ULF waves during a high solar wind speed interval,

Numerous field line resonance events have been observed with three HF radars (Saskatoon, Kapuskasing, and Goose Bay) of the Super Dual Auroral Radar Network (SuperDARN). The field line resonances cause oscillations in the F region plasma flows which are detected in the measured line of sight Doppler velocities.After analysis, it was found that the resonances were of two types: those with low azimuthal wave number, low-m, and those with high azimuthal wave number, high-m. The high-m events showed many similarities with high-m pulsations of previous reports including local time of most occurrences (noon-dusk), pulsation frequencies, westward propagation, increase in phase with latitude, and north-south polarization. The low-m events exhibited typical field line resonance characteristics and were found near dusk and dawn with anti-Sunward propagation. The most notable result was the fact that the high-and low-m events shared many common features. They both were found to occur at the same discrete and stable frequencies.The most common frequencies were 1.3, 1.9, and 2.5-2.6 mHz, which have previously been associated with magnetospheric waveguide modes. They also occurred at other less common frequencies, such as 1.5-1.6 mHz. Both types of events were localized in latitude with an inverse relation between frequency and latitude. Both were characterized by a wave packet structure with a duration of approximately I hour. The numerous features shared by the high-and low-m resonances strongly suggest that they are caused by the same source mechanism. A dispersive waveguide model as a source for the field line resonances is discussed. tering a positive gradient in the Aifv•n velocity. Eventually, it reaches a turning point where it is partially reflected and partially transmitted. Beyond the turning point the wave evanescently decays until it reaches a singularity at the resonance point where the local shear Copyright 1995 by the American Geophysical Union. Paper number 95JA02024. 0148-0227/95/95JA-02024505.00. Alfv•n resonance frequency equals that of the incident compressional wave. The large wave field corresponding to the singularity at the resonance excites the shear Alfv•n wave which then reflects from the ionospheres setting up a standing wave mode. The distinguishing characteristics of a field line resonance are discussed in detail by Walker et al. [1979] and include the following. They are very localized in the radial direction with finite azimuthal extent. The electric, magnetic, and velocity wave fields all exhibit a 180 degree phase shift across the localized position of the resonance. Resonances measured at the ionosphere exhibit an inverse relation between frequency and latitude, i.e., higher frequencies at lower latitudes, due to the radially inward gradient in the local shear Alfv6n resonance frequency. ULF pulsations exhibiting FLR characteristics have been observed in HF coherent scatter radar data [e.g., Ruohoniemi et al., 1991; Walker et al., 1992; Samson et al., 19924], ground-based magnetometer data [...

Abstract.The polarity of a magnetic cloud refers to its changing magnetic field direction. It is classified as S-N polarity when the magnetic field rotates from southward to northward and N-S polarity when the field is initially northward and rotates southward. A study of 29 magnetic cloud events has found that 40-45% of magnetic clouds, independent of polarity, are followed by a fast solar wind stream which compresses the tail end of the cloud. The compression results in an increase in the solar wind plasma density and in 64% of the cases an increase in the magnetic field strength towards the latter part of the cloud. Such tail end compression can have a significant effect upon geomagnetic storm intensity if the magnetic cloud is of N-S polarity. This is because only in the N-S polarity case does the compression coincide with the southward IMF portion of the cloud. To test the "geoeffectiveness" of N-S versus S-N magnetic clouds three selected magnetic cloud events, two of S-N polarity and one of N-S polarity, are investigated in terms of their geomagnetic response through measured and estimated Dst values. It is found that there is an increased geoeffectiveness of N-S polarity clouds due to both an increased solar wind dynamic pressure and a compressed southward field associated with a following fast solar wind stream.

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A discussion is presented of the evaluation of multiple relaxation components from water protons in biological tissue. The principal focus is to draw attention to the way in which limitations in the raw NMR data, such as signal-to-noise ratio, data sampling density and acquisition window width, affect the precision and resolution in the processed multiple component solution of the return to thermal equilibrium. The second issue discussed is the interpretation of these multiple components in terms of microstructural compartments of the biological sample and, thirdly, we outline some of the successes in determining regional and pathological variations in microstructure in the human body in-vivo, using the technique of multiple relaxation components.