For much of the World's oceans, the stability of the water column beneath the thermocline is quite well represented byN2(z) = gρ−1 ∂zρ′ = NO2e−2z/B, where ∂zρ′ is the vertical gradient in potential density,NO≈ 3 cycles/h is the surface‐extrapolated “Brunt‐Väisälä” frequency, andB≈ 1.3 km is the stratification scale. This leads to an idealized sound channelC(z) = C1 [1 + ε(η + e−η − 1)] = C[1 + ε(1/2)η2 − (1/6)η3 + …]with a minimum velocity at the axisz = z1, η = (z − z1)/12Bbeing dimensionless depth relative toz1. The parameters ε,z1are explicitly expressed in terms of the five coefficients α, β, γ,a, b(temperature, salinity, pressure coefficients ofC; temperature and salinity coefficients of ρ′), given only the form ofN(z) and a representativeT, Srelation. The up‐down asymmetry of the channel, a consequence of the fundamental structure of the oceans, plays a first‐order role in the propagation characteristics. As an application, the ray arrivals for an axial source and receiver are computed.