The longitudinal dielectric function is used to study purely electrostatic plasma waves. The present paper is concerned with linear waves in a spatially homogeneous, collisionless, uniformly magnetized plasma. The plasma is described by a two temperature, streaming Maxwellian distribution. Sample plasma parameters are selected to model the auroral ionosphere at rocket altitudes, and wave numbers are selected to produce resonance with energetic auroral electrons. The longitudinal dielectric function is investigated in detail as the plasma density is varied to produce an interaction between upper hybrid and electron cyclotron waves. The strongest wave growth we have found to date in the auroral ionosphere is associated with this interaction.