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Although the enhancements in the alpha-proton ratio in the solar wind(expressed as $A_{He} = N_a/N_p*100$) in the Interplanetary Coronal MassEjections (ICMEs) have been studied in the past, $A_{He}$ enhancements at thestream interface region received very little attention so far. In this letter,by extensively analyzing the stream interaction region (SIR) events observed insolar cycle 23 and 24, we show that the stream interface of alphas startsseparating out from that of protons from the minimum of solar cycle 23. Thepopulation of alpha particles are enhanced compared to protons at higher anglesbetween bulk velocity and local magnetic field (henceforth, bulk velocityangle) in the fast wind region of SIRs if the background solar wind is taken asreference. The analysis of differential velocities between alphas and protonsalso reveals that the faster alpha particles accumulate near the fast wind sideof the stream interface region leading to enhancement of $A_{He}$. Theinvestigation brings out, for the first time, the salient changes in $A_{He}$in SIRs for the two solar cycles and highlight the importances of bulk velocityangle and differential velocity in the fast wind region for the changes in$A_{He}$ in SIRs.

New insights on the behaviour of solar wind protons and alphas in the Stream Interaction Region in solar cycle 23 and 24