Gas pressure P_g, 0 at the inner boundary (z₀ = 1 kpc) of the flux tube for Model W (full line) and Model H (dashed line) as a function of time over 10⁸ years. After 6 × 10⁶ yr the last SN exploded and we keep the values of the boundary values fixed, except the velocity u₀. Lower panel (right): illustrates how the velocity reacts to the change of the inner boundary from increasing pressures to constant pressures after 6 × 10⁶ years. The lower panels exhibit the mass loss by the galactic wind, that is, Ṁ₀ = A₀ρ₀u₀ and the velocity at u₀. We note that Model H (dotted line) generates initially higher mass loss rates because the wind expands into a more tenuous medium than Model W (see text for more details).