Characteristics of quarter wave standing Alfvén waves observed by the New Zealand magnetometer array
Wednesday, 3 September 2014: 11:25 AM
Regency Ballroom (Hyatt Regency)
Yuki Obana1, Colin L Waters2, Murray D Sciffer3, Gareth D Sciffer3, Frederick W Menk4 and Robert L Lysak5, (1)Osaka Electro-Communicat. Univ, Osaka, Japan, (2)University of Newcastle, Callaghan, NSW, Australia, (3)University of Newcastle, Callaghan, Australia, (4)Univ Newcastle, Callaghan, NSW, Australia, (5)University of Minnesota Twin Cities, School of Physics and Astronomy, Minneapolis, MN, United States
Abstract:
Magnetometer data from the New Zealand array (L=2.2-2.8 Re) were analyzed to investigate quarter-wave mode standing Alfven waves in mid latitudes. We used cross-phase and related methods to determine the field line resonance frequency and width of resonance region. Three typical events were observed in July 2012 which showed extraordinarily low eigenfrequencies and wide resonance width when the ionosphere above New Zealand was in darkness while its conjugate was sunlit. Later in the morning the eigenfrequency and width of resonance gradually came to the normal daytime value. The frequency change started when the terminator passed over New Zealand and finished on hour later. These observations indicate strong evidence of presence of quarter wave and mode conversion from quarter wave to more usual half wave. We also investigated the distribution of ULF wave field using a 2.5D magnetospheric model. Comparing these results, the quarter wave formation will be discussed.
