a) Transverse perturbations v_z for η = 0.01, β = 0.1 plasma (ν = 0), where dashed lines represent the envelope v_z =  ± Aexp(k_Iy). b) Longitudinal perturbations v_y for same plasma, where dashed line represents y = c_st and blue horizontal line denotes v_y = 0. In both subfigures, t = 1000τ_A and dotted line represents y = v_At.