Characterizing the long‐period ULF response to magnetic storms

Abstract

This study presents an analysis of long‐period ULF wave power observed at 44 ground magnetometer stations in the western hemisphere, at latitudes from the equator to the polar caps, during the magnetic storm intervals of May 1997, March 1998, May 1998, September 1998, and October 1998 identified by the GEM research community. Comparison of the long‐period pulsations (in the Pc5 frequency range) observed on the ground to the solar wind velocity and solar wind pressure observed by the WIND satellite confirms previous results that high solar wind velocity correlates well with increased Pc5 power. Although some variability was evident among the five storms, solar wind pressure and variability in velocity or pressure exhibited considerably weaker correlations. Each storm exhibited narrow‐band Pc5 wave activity during the recovery phase, but only in the dawn‐noon sector at each site. During the main phase, and at all other local times during the recovery phase, wave activity was broadband. The strongest Pc5 power was observed at frequencies above 2 mHz at stations in the auroral zone and poleward and below 2 mHz at stations at middle and low latitudes. Comparison to published time profiles of energetic electrons at geosynchronous orbit suggests that if ULF wave activity is responsible for the initial energization of these electrons, broadband activity rather than narrowband (Pc5) waves must play the dominant role. Our data cannot rule out, however, the importance of narrowband waves in providing additional energization during the recovery phase.

ULF fluctuations of the geomagnetic field and ionospheric sounding measurements at low latitudes during the first CAWSES campaign

“…ULF waves in the frequency range ∼1-100 mHz (or "magnetic pulsations", as they are usually referred to) represent an important aspect of the Sun-Earth relationships. Indeed, they play a significant role in the energy transfer from the solar wind (SW) to the magnetosphere and are an intrinsic signature of different processes taking place in the Earth's magnetosphere as, for instance, the large variety of waves typically observed during the development of geomagnetic storms and substorms (Posch et al, 2003;Olson, 1999). In addition, ULF waves recorded at a dense latitudinal array can also be used to monitor the magnetospheric plasma mass density .…”

Spatial distribution of spectral parameters of high latitude geomagnetic disturbances in the Pc5/Pi3 frequency range

“…Analysis of power spectral density was used for separation between narrow-band signals and broadband noise for auroral Pc5 (Posch et al, 2003;Baker et al, 2003), and high-latitude Pc3-4 (Ponomarenko et al, 2002;Chugunova et al, 2007). These methods enabled the authors to find a distinction in the behavior of narrowband signals and broadband noise.…”

Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

“…As Pc5 activity and auroral oval are both high-latitude phenomena, statements about Pc5 predominant occurrence/intensity at auroral latitudes are quite common [e.g., Posch et al, 2003;Pahud et al, 2009;Rae et al, 2012]. However, those statements were mainly based on expected statistical location of the auroral oval, whereas no direct comparison with a current oval location has been examined.…”

“…Broadband Pc5 disturbances are observed during the storm growth phase [Kleimenova et al, 1997] and the main phase [Schott et al, 1998] while quasi-monochromatic Pc5 waves occur during the recovery phase [Posch et al, 2003]. …”