ULF wave interaction with the ionosphere: radar and magnetometer observations
Abstract
Combined usage of SuperDARN/EISCAT radars and magnetometers, supported by an adequate theory of ULF wave interaction with the multi-layer system magnetosphere - ionosphere - atmosphere - ground, is an effective way to reveal a physical mechanism of ULF disturbances. Many notions derived only from satellite or ground observations may be challenged by additional information from radars (e.g., association of ULF phenomena with magnetospheric domains, ULF wave spatial structure, etc.). To identify the physical nature of global Pc5 pulsations at the recovery phase of strong magnetic storms and to determine relative contributions of different MHD modes into their structure, the method of apparent impedance can be applied. These Pc5 pulsations are considered using the IMAGE magnetometer data and EISCAT radar data from Tromso-Kiruna-Sodankyla system. An approximate analytical relationship derived from the theory of ULF wave transmission through the thin ionosphere has been compared with the measured ratio between the simultaneous ionospheric electric and ground magnetic fields. The impedances of Alfven and compressional modes are to be essentially distinct. From these observations we conclude that the global Pc5 pulsations above the ionosphere are predominantly composed from Alfven waves with a small contribution of fast compressional mode. Combined SuperDARN Hokkaido radar and magnetometer observations of mid-latitude Pi2 pulsations showed that the concept of a pure cavity mode is not sufficient to explain these observations, and that the contribution of an Alfvén waves must be taken in account. ULF waves are not just sounding signals, but an active factor of the near-Earth environment. The comparison of magnetometer data with the ionospheric parameters shows a significant modulation of the electron density, ionospheric height-integrated conductance, and ion temperature by Pc5 pulsations, even in the absence of quasi-periodic electron precipitation. The mechanisms underlying the ULF modulation effects comprise the Joule ion heating by electric field, and feeding/depleting of the ionospheric electrons by field-aligned current. Coordinated radar, magnetometer, and TEC/GPS high-sampling observations will be very promising, especially for small-scale waves not observable on the ground.
- Publication:
-
40th COSPAR Scientific Assembly
- Pub Date:
- 2014
- Bibcode:
- 2014cosp...40E2540P