Whistler wave instability and plasma sheet ALC distribution at substorm onsets

318-324Whistler waves interacting with an assumed anti-loss cone (ALC) distribution is shown to become highly unstable at times of substorm onsets. This establishes the presence of ALC electrons at onset-time geomagnetosphere plasma sheet (PS). The stability analysis proves that the whistler instability resulting from ALC interactions arises at frequencies greater than the electron cyclotron frequency. The study establishes the role of plasma β as a factor determining the extent of whistler instability even at times of highly disturbed conditions. The major part of free energy available at PS during substorm onsets is proved to be the contribution due to the anisotropy of the ALC distribution function. Presence of a few cold electrons along with hot ALC plasma is shown to cause wave decay