Search

Ozone enhanced layers observed inside the Antarctic ozone hole were investigated using ozonesonde data at Syowa and Neumayer Stations during the dissipation period of the ozone hole in 2003. In 22 ozonesonde observations performed at Syowa and Neumayer Stations during one month after the maximum of ozone hole area, 17 ozone enhanced layers (i.e., up to three layers per one observation) were detected between 14 and 21 km in the lower stratosphere. They always had a thickness thinner than 2.1 km. Maximum ozone mixing ratios in the ozone enhanced layers suggested that most of the layers had their origin in the vortex boundary region. A reverse domain filling analysis indicated that air parcels originating in the vortex boundary region reached Syowa and Neumayer Stations in a form of horizontally-thin filaments. These filamentary structures were generated through chaotic advection due to transient planetary-scale Rossby waves, and became thin also in the vertical because of the vertical shear of horizontal wind. This study suggests that the ozone enhanced layers inside the ozone hole could be a useful measure to identify the poleward Rossby wave breaking and the origin of transported air parcels. A contribution of the ozone enhanced layers to an increase of total ozone was estimated at about 2.1 DU for the analysis period of one month, which is less than one tenth of the increase of vortex average total ozone during the same period. On the other hand, it is corresponding to about a half of the background ozone column in the height region of 14-21 km at the time of the ozone hole area maximum.

The transformed Eulerian-mean (TEM) equations are useful in examining how the generation and/or dissipation of atmospheric waves drives the mean meridional circulation. However, the TEM equations do not provide a three-dimensional view of the transport. Several previous studies extended the TEM equation system to three dimensions but usually under the quasi-geostrophic assumption, which excludes small-scale phenomena such as gravity waves. Miyahara recently derived three-dimensional wave activity flux and the corresponding residual circulation applicable to gravity waves. However, his formulation has two flaws. First, the three-dimensional residual mean circulation does not satisfy the continuity equation. Second, the Eulerian-mean flow appears in the advection terms and the residual circulation appears in the Coriolis force term of the zonal momentum equation, unlike in the TEM one. The present study developed theoretical formulae of a three-dimensional residual mean circulation and wave activity flux on the basis of primitive equations that overcome these flaws. It is confirmed that the three-dimensional residual mean circulation accords with the sum of the Eulerian time-mean flow and the Stokes drift and that the three-dimensional wave activity flux accords with the mean tangential forces across material surfaces corrugated by the waves under an assumption similar to the TEM equations. A simple physical meaning is given for the terms including the shear of time-mean flow in the three-dimensional wave activity flux. Moreover, the time mean tracer transport equation is derived using the three-dimensional residual mean circulation. A simple case study using the new formulae was made on the three-dimensional transport of stratospheric ozone in the Southern Hemisphere. It is shown that the product of the Coriolis parameter and the strong poleward/equatorward Stokes drifts also balances the divergence/convergence of the three-dimensional wave-activity flux.

An intensive radiosonde observation with time intervals of 3 h was performed in June 2002 at Syowa Station (39.6°E, 69°S) in the Antarctic. A wavelike disturbance with a wave period of 12-15 h, having a nearly barotropic structure was observed above a height of 22 km in the time period of 27-28 June 2002. A result of the hodograph analysis suggests that the short-period disturbance is not due to an inertiagravity wave. A similar short-period disturbance is observed in the European Centre for Medium-Range Weather Forecasts (ECMWF) operational analysis data. Results of detailed analysis using the ECMWF data show that the short-period disturbance has a horizontal wavelength of about 2000 km, and propagates along a potential vorticity minimum region with a horizontal phase velocity of about 40 m s−1. This phase velocity is equal to the background horizontal wind velocity at the potential vorticity minimum. A necessary condition for the barotropic instability is locally satisfied at the potential vorticity minimum. However, it is rather appropriate that the short-period disturbance is interpreted as a neutral wave than as an unstable wave in the barotropically unstable background flow. This result implies any unknown mechanism of the suppression of barotropic instability in the locally unstable background flow associated with a disturbed polar vortex.