Irreversible transport in the stratosphere by internal waves of short vertical wavelength

Abstract

The U‐2 aircraft was instrumented and flown in the stratosphere during the Stratosphere‐Troposphere Exchange Project's experiments of April 1984 to provide a set of simultaneous measurements by fast responding sensors that would aid in the identification of the modes of cross‐jet transport. The measurements confirm the preexperimental deductions that transport is dominated by waves, not by large‐scale circulations. Monotonic gradients of trace constituents normal to the jet axis, with upper stratospheric tracers increasing poleward and tropospheric tracers increasing equatorward, are augmented by large‐scale confluence as the jet intensifies during cyclogenesis. These gradients are rotated, intensified, and significantly increased in area as their mixing ratio surfaces are folded by the differential transport of a very low frequency, transverse wave. The quasi‐horizontal transport produces a laminar structure with stable layers rich in upper stratospheric tracers alternating vertically with less stable layers rich in tropospheric tracers. The transport proceeds toward irreversibility as higher frequency, shear‐gravity waves extend the folding to smaller horizontal scales. It becomes irreversible when these short waves actually fold the isentropic surfaces and small‐scale mixing develops. The progression to higher wave numbers is a discrete, not a continuous, cascade with major gaps in the observed horizontal wavelengths. The wave modes are identified by matching the observed amplitudes and phases against those obtained by linear perturbation theory. Prior to mixing, the wave‐generated perturbations maintain the correlations produced by advecting the larger‐scale mean gradients; thus the high resolution measurements support the linear turbulence closure assumption.

Secondary maxima in ozone profiles

“…For the origin of laminae, they suggested that a mechanism operates at the lower edge of the polar vortex (where ozone mixing ratio increases sharply on isentropic surfaces) which transports ozone to middle latitude in the form of laminae, particularly during spring when the polar vortex dissipates. Possible candidates for this mechanism are inertia-gravity waves associated with the subtropical jet stream as proposed by Danielsen et al (1991) or distortions of the polar vortex boundary by synoptic scale motions as proposed by Tuck et al (1992). Reid et al (1994), using the EASOE ozonesonde archive, analyzed the occurrence of laminae in the course of the 1992 winter confirming the findings of Reid and Vaughan (1991) and Reid and Vaughan (1993).…”

Seasonal evolution of Rossby and gravity wave induced laminae in ozonesonde data obtained from Wallops Island, Virginia

“…Studies using data obtained from ozonesonde ascents show that these laminae are most often encountered during the winter and spring, and that the frequency of ozone laminae tends to increase from subtropical to polar latitudes [Dobson, 1973]. Attempts to understand the processes which give rise to these laminae have focused on the statistical relationship between the frequency of larninae and seasonal changes in the stratospheric circulation [Reid and Vaughan, 1991 herea/•er RV91] and analysis of individual soundings for signatures of wave induced transport [Danielsen et al, 1991]. Quasi-horizontal, meridional transport by planetary and synoptic scale Rossby waves, and vertical transport by gravity waves, are believed to be the primary mechanisms by which the ozone laminae form.…”

Mountain waves modulate the water vapor distribution in the UTLS

“…Irreversible mixing is promoted by turbulence induced, for example, by nonlinear wave interaction, wave breaking, or dissipation Whiteway et al, 2003;Koch et al, 2005;Lane and Sharman, 2006). Danielsen et al (1991) showed that waves with large horizontal wavelengths (∼ 36-270 km) and enhanced vertical amplitudes are significant carriers of energy, momentum and trace species. Small-scale waves (horizontal wavelength smaller than 30 km) may cause mixing and thus enable the irreversibility of the transport induced by large-scale waves.…”

“…There are a few studies that refer to trace gas transport induced by gravity waves (e.g., Danielsen et al, 1991;Langford et al, 1996;Schilling et al, 1999;Moustaoui et al, 2010). Gravity waves are known to play an important role in the circulation, structure and variability of the atmosphere (Fritts and Alexander, 2003).…”