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Resonance features of the Ionospheric Alfvén Resonator (IAR) can beobserved in pulsation magnetometer data from Sodankylä, Finland usingdynamic spectra visualizations. IAR resonance features were identified on 13of 30 days in October 1998, with resonance structures lasting for 3 or morehours over 10 intervals. The diurnal evolution of the harmonic features wasquantified for these 10 intervals using a manual cursor-clicking technique.The resonance features displayed strong linear relationships betweenharmonic frequency and harmonic number for all of the time intervalsstudied, enabling a homogeneous cavity model for the IAR to be adopted tointerpret the data. This enabled the diurnal variation of the effective sizeof the IAR to be obtained for each of the 10 time intervals. The averageeffective size was found to be 530 km, and to have an average variation of32% over each time interval: small compared to the average variation inAlfvén velocity of 61%. Thus the diurnal variation of the harmonicsis chiefly caused by the changing plasma density within the IAR due tochanging insolation. This study confirms Odzimek (2004) that the dominatingfactor affecting the IAR eigenfrequencies is the variation in the Alfvénvelocity at the F-layer ion-density peak, with the changing IAR sizeaffecting the IAR eigenfrequencies to a smaller extent. Another IARparameter was derived from the analysis of the IAR resonance featuresassociated with the phase matching structure of the standing waves in theIAR. This parameter varied over the time intervals studied by 20% onaverage, possibly due to changing ionospheric conductivity.<p><b>Keywords.</b> Ionosphere (Auroral ionosphere;Wave propagation)– Radio science (Electromagnetic noise and interference

annales geophysicae

A quantitative analysis of the diurnal evolution of Ionospheric Alfvén resonator magnetic resonance features and calculation of changing IAR parameters