Abstract. Whistler waves which are termed "lion roars" in the magnetosheath are studied using data obtained by the Spectrum Analyser (SA) of the Spatio-Temporal Analysis of Field Fluctuations (STAFF) experiment aboard Cluster. Kinetic theory is then employed to obtain the theoretical expression for the whistler wave with electron temperature anisotropy which is believed to trigger lion roars in the magnetosheath. This allows us to compare theory and data. This paper for the first time studies the details of the electron velocity distribution function as measured by the Plasma Electron And Current Experiment (PEACE) in order to investigate the underlying causes for the different types of lion roars found in the data. Our results show that while some instances of lion roars could be locally generated, the source of others must be more remote regions of the magnetosheath.

Key Points:• Lion roar emission is explained by (r, q) distribution• Bi-Maxwellian model cannot always explain observation• The (r, q) model satisfactorily resolves observational uncertainties (2006) investigated the underlying cause of the lion roar generation. However, the analysis based upon the bi-Maxwellian distribution function did not adequately explain the observations qualitatively as well as quantitatively. This outstanding problem is revisited in the present paper, and a resolution is put forth in which, the flat-top non-Maxwellian distribution function with a velocity power law energetic tail, known as the (r, q) distribution, or the generalized kappa distribution is employed. Upon carrying out the linear stability analysis of the (r, q) distribution against the whistler wave perturbation, and upon comparison with the Cluster data, good qualitative and quantitative agreements are found between theory and data.