Statistical study of multimodal tweek-atmospherics

A new technique is used for statistical analysis of experimental records of tweek-atmospherics (tweeks). Tweeks are observed during nighttime and represent response of the Earth-ionosphere waveguide to excitation by lightning strokes. TWEEKS are formed by series of pulses consecutively reflected from the waveguide boundaries under different incident angles depending on a source-observer distance and effective ionosphere height along a propagation path. The tweek signals demonstrate the propagation of a few Earth-ionosphere waveguide modes. We determined propagation path´s parameters such as source range, ionosphere height, and azimuthal orientation of a propagation path. We used then a time-frequency representation of analyzed tweek waveforms to infer separate branches, corresponding to different waveguide modes. Obtained results show the increase of attenuation for higher modes with increase of a source distance.