High‐latitude observations of ULF waves with large azimuthal wavenumbers

The Doppler Pulsation Experiment (DOPE) is an HF Doppler sounder deployed at Tromsø, 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 wave‐particle 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.