Evidence of very-large-amplitude solitary waves in the atmosphere

ATMOSPHERIC solitary waves are gravity waves that retain their integrity over long periods because of a near balance between nonlinearity and dispersion. They have been observed on various scales in many regions of the world^1-3, but we present here detailed measurements of solitary waves with amplitudes comparable to the scale height of the lower troposphere. Two such waves were generated downstream of intense mid-tropospheric pressure troughs over the central United States. They propagated over 1,000km (several times their wavelength) with no appreciable change in structure within a 'waveguide' formed by surface inversion and a middle tropospheric critical level. Fluctuations in surface pressure associated with the two waves exceeded 6 mbar and 10 mbar. The waves caused banded patterns of precipitation and significantly influenced other meteorological phenomena. The restoration of balance between pressure-driven air flow and the Coriolis force ('geostrophic adjustment') seems to have a prominent role in the formation of these solitary waves.