Observations of ULF space plasma waves in Antarctica

Brief description

This project records ultra-low frequency (ULF) waves in the 1mHz - 3Hz band at the Antarctic stations Davis, Casey, Mawson, and Macquarie Island and Zhongshan (PRC station). Search coil magnetometers are employed with identical instrumentation at all stations. Over the southern summers of 2002-2005 two additional remote magnetometers were deployed poleward of Davis and Zhongshan, forming a square network.

This work is included in the ongoing ASAC project ASAC_606.

These data are stored on the Australian Antarctic Divisions servers in the Space and Atmospherics Sciences section, and also on DVD in the Australian Antarctic Data Centre.

Project objectives:
The Earth's near-space environment is dominated by a complex dynamic interaction between the solar wind, the interplanetary magnetic field and the geomagnetic field. In the high latitude regions there is a transfer of energy from the solar wind to the magnetosphere, then through to the ionosphere, the atmosphere, to the ground. Of interest is the effect of solar variability on the energy input into the magnetosphere-ionosphere-atmosphere system; the so-called "space weather" phenomenon (e.g. Maynard and Siscoe, 1998). In the dayside high latitude cusp regions, field lines from the magnetopause map down to a limited region in the ionosphere and small-scale phenomena such as ultra-low frequency (ULF) (1 mHz-1 Hz) waves play an important role in understanding the variability of the cusp and boundary regions which encompass the polar cap, a largely unexplored region.

The primary aim of this project is to study magnetosphere-ionosphere coupling at high latitudes in Antarctica using multi-instrumented arrays of ground-based observatories in conjunction with in situ satellite data with an emphasis on ULF waves which can be an indication of boundary region instability. Regions of study include:

(i) the outer magnetosphere and its projection via closed geomagnetic field lines to the ionosphere,

(ii) the polar cap, where the IMF connects directly to the ionosphere, and

(iii) the boundary region where closed field lines become open.

This project is unique in that it will use new ULF wave techniques concentrating on wave phase, a very stable parameter, to study the dynamics of small scale phenomena in relation to large scale polar cap convection which is under the control of time varying reconnection processes (Dungey, 1961). Scientific objectives are to:

A. Study the response of the open/closed field line boundary region (OCB)and polar cap dynamics to solar wind and IMF variability.

B. Characterise ultra-low frequency (ULF) waves and transient phenomena in the boundary layer and relate these micro-scale processes to convection processes in the cusp and polar cap.

C. Study the morphological and dynamical aspects of the coupling between the dayside cusp/cleft and nightside substorm phenomena.

Taken from the 2008-2009 Progress Report:
Progress against objectives:
Significant progress has been made on Objective A - study of the response of the open/closed field line boundary region (OCB) to solar wind and IMF variability, in association with Objective B, the characteristics of ULF waves in the boundary layer. In particular we have used Davis-Zhong Shan two station and the four station square array data from 200 to study the diurnal variations in Pc5 (1-7 mHz) ULF waves. Earlier work by Ables et al., (1998) identified a dip in frequency at Davis near local noon. Using inter-station Pc5 phase data related to field line resonances and supported by rigorous 3-D modelling involving eigen functions solutions of shear Alfven waves we have shown the noon dip or "saddle" is due to field line curvature and twisting. A paper (Ables et al., 2009) describing this work has been submitted to Geophysical Research Letters (Impact factor 2.744).
Work on Objective C relates to cross-polar cap coupling of ULF waves has commenced. In a conference paper Ponomarenko and Fraser (Western Pacific Geophysics Meeting, 2009) showed, using 2 years of Scott Base (NZ) and Casey Pc3-4 (10-100 mHz) that 20-50 mHz waves may propagate across the polar cap. Studying the phase relationship between the two stations in order to establish propagation directions is complicated and varies with time of day, and related to solar wind and interplanetary conditions. There are also marked seasonal variations.

Taken from the 2009-2010 Progress Report:
Progress against objectives:
Significant progress has been made on Objective A - study of the response of the open/closed field line boundary region (OCB) to solar wind and IMF variability, in association with Objective B, the characteristics of ULF waves in the boundary layer. In particular we have used Davis-Zhong Shan two station and four station square array data from 2008 to study the diurnal variations in Pc5 (1-7 mHz) ULF waves. Earlier work by Ables et al., (1998) identified a dip in frequency at Davis near local noon. Using inter-station Pc5 phase data related to field line resonances and supported by rigorous 3-D modelling involving eigen functions solutions of shear Alfven waves we have shown the noon dip or "saddle" is due to field line curvature and twisting. Following comments a paper (Ables et al., 2010b) describing this work has been re-submitted to Geophysical Research Letters (Impact factor 2.744).

Work on Objective C relates to cross-polar cap coupling of ULF waves has commenced. In a conference paper Ponomarenko and Fraser (Western Pacific Geophysics Meeting, 2009) showed, using 2 years of Scott Base (NZ) and Casey Pc3-4 (10-100 mHz) that 20-50 mHz waves may propagate across the polar cap. Studying the phase relationship between the two stations in order to establish propagation directions is complicated and varies with time of day, and is related to solar wind and interplanetary conditions. Cross-polar cap studies using Scott Base and Casey have been undertaken on Pc1-2 (0.1-5 Hz) waves. This work explores the wave source and propagation characteristics and whether the waves on open field lines can convect over the polar cap (Ables et al., 2010a).

Considerable effort has been directed towards the response of Pc1-2 electromagnetic ion cyclotron (EMIC) waves to geomagnetic storm activity. This includes a statistical study at geosynchronous orbit (Fraser et al., 2010) and a radial (latitudinal) study using CRRES elliptically orbiting satellite data (Halford et al., 2010). A multipoint (ground-ionosphere-satellite) study of Pc1-2 wave event by Morley et al. (2009) showed that Earthward propagating EMIC waves preferentially follow the high density dege of magnetospheric plasma drainage plumes (Morley et al., 2009).

Following last years study measuring the Pc3 wave vectors in space we have now determined the transverse scale size of the wave spatial resonance structure (Liu et al., 2009). Using ground data it has also been shown that Pc3 waves, showing resonance properties at high latitudes also propagate to lower latitudes as travelling waves (Menk and Howard, Fall AGU Meeting, 2009).