High‐latitude observations of ULF waves with large azimuthal wavenumbers

Abstract

Abstract. The Doppler Pulsation Experiment (DOPE) is an HF Doppler sounder deployed atTroms0, northern Norway, for the investigation of the ionospheric signatures of ULF wave phenomena of magnetospheric origin. This high-latitude Doppler sounder has been demonstrated to be a highly sensitive instrument for the investigation of ULF waves of large azimuthal wavenumber m. Such waves are assumed to be driven by magnetospheric waveparticle interactions and are difficult to study by other ground-based techniques owing to their strong spatial integration between the ionosphere and the ground. A new population of high-m waves has been identified in the ground-based data from DOPE, which could represent a significant new sink for ring current energy. These waves have m numbers of order 100 and are observed primarily in the morning sector. Their characteristics are described and compared to previous statistical observations from spacecraft. The DOPE sounder now offers routine measurements of the occurrence and characteristics of such high-m wave populations.

Modulation of radio frequency signals by ULF waves

“…This has important implications for the SP models when comparing theory and experimental HF and ULF wave data in the ionosphere and on the ground. Experimental studies comparing coherent scatter radar, Doppler sounder and ground magnetometer data have indicated that vertical bulk electron plasma motion driven by the electric field of the ULF wave is responsible for changes in the radio frequency (Wright et al, 1997;Yeoman et al, 2000). Parallel to these observations, the SP model has developed as the favoured theoretical description of these effects.…”

“…In this paper, we present data from the 4.16 MHz path and azimuthal wave numbers from DOPE are calculated from the 5.25 and 5.73 MHz path. Further details of the configuration are described in Yeoman et al (2000). The transmitter radiates a fixed frequency, continuous wave (CW) signal which is received ∼50 km away.…”

“…The DOPE system is located near Tromsø,Norway (geographic: 69.6 N,19.2 E) and consists of frequency stable transmitter/receivers (Yeoman et al, 2000). The system incorporates two altitude separated paths at 4.16 and 5.25 MHz (Ramfjordmoen-Seljelvnes) that are used to check phase consistency to eliminate possible infrasonic modes, and two paths that are azimuthally separated from these at 5.73 and 5.26 MHz (Ramfjordmoen-Skibotn and Ramfjordmoen-Kilpisjärvi, respectively).…”

Pc5 waves generated by substorm injection: a case study

“…Poloidal ULF waves are often observed with satellites (Eriksson et al, 2005;Schäfer et al, 2007) and radars (Yeoman et al, 2000). There are some hints that the waves are generated by substorm injected particles drifting in the magnetosphere.…”

“…Yet another mechanism was suggested by Zolotukhina (1974) and Guglielmi and Zolotukhina (1980): non-resonant generation by moving clouds of substorm injected particles (like Cerenkov emission). Klimushkin (2007, 2008) developed an analytical theory of the spatio-temporal evolution of the wave field generated by this mechanism in a curved magnetic field (a simple semi-qualitative picture of it is presented in this paper).…”