Stratospheric Dynamics

Vertical profiles of long lived trace gases can be used as a basis for the analysis of stratospheric dynamics. The structure of these profiles gives indications for vertical and horizontal transport processes, i.e. descent inside and filamentation of the vortex. An attempt of a vortex climatology describing seasonal subsidence and the position of the measured air parcels relative to the vortex centre is made by comparing the correlation of N20 mixing ratios versus PV values for different years. 

Kodera, K., 1994. Influence of volcanic eruptions on the troposphere through stratospheric dynamical processes in the Northern Hemisphere winter. Journal of Geophysical Research, 99, 1273-1282. 

The distribution patterns shown in Fig. 11 can briefly be explained as follows. Stratospheric ozone formed by photochemical processes is transported in poleward direction by atmospheric motions. This circulation is particularly strong in winter and spring months when stratospheric air moves downward over polar regions. At the same time the lower stratosphere over the tropics is characterized by a slow updraft (Brewer, 1949). Thus, stratospheric dynamics lead to the accumulation of ozone rich air in the lower polar stratosphere. It should be recalled here that at this altitude 03 is a conservative property of the air. During the late spring and summer, especially, the stratospheric 03 reaches the troposphere first of all through the tropopause gaps. In the troposphere this species is removed from the air by various sinks, as this will be shown in the next section. 

Hood, L.L., and J.L. Jirikowic, Stratospheric dynamical effects on solar ultraviolet variations Evidence from zonal mean ozone and temperature data. J Geophys Res 96, 7565, 1991. 

Some authors have argued that changes in stratospheric dynamics could have contributed to the observed mid-latitude ozone trends. A review is provided in Ravishankara et al. (1999 see references therein). In brief, some studies (e.g., Hood and Zaff, 1995 McCormack and Hood, 1997 Hood et al., 1997 Fusco and Salby, 1999) have argued for a component of purely dynamical change in mid-latitude ozone relating, for example, to changes in the meridional transport of ozone. It is well known that dynamical processes strongly influence ozone variability... 

Grewe, V., M. Dameris, and R. Sausen, Impact of stratospheric dynamics and chemistry on northern hemisphere midlatitude ozone loss. J Geophys Res 103, 25,417, 1998. 

Much of the observed structure of the stratosphere can be understood in terms of elementary wave propagation, momentum and heat transport by waves, and in situ forcing by radiatively active trace gases. The dynamical aspects of these interactions can often be described satisfactorily in analytical terms, although detailed calculations of the stratospheric circulation require the use of numerical (computer) methods. In what follows, a brief introduction to stratospheric dynamic meteorology is presented. The conceptual development will be oriented toward the interpretation of the stratospheric observations discussed in the previous sections. 

Because wave propagation and dissipation is a crucial feature of stratospheric dynamics, it is also convenient to distinguish between zonal-mean fields and perturbations thereto ... 

Nonetheless, several areas of stratospheric dynamics pose problems that are incompletely understood at present. The nature of the waves that drive the quasibiennial oscillation is one of them. Although the basic mechanism of the QBO (wave-mean flow interaction in a region of weak Coriolis force see Section III.B) is undoubtedly correct, the oscillation has not been simulated satisfactorily with current computer models. The results of partially successful simulations suggests that the QBO is probably driven by gravity waves of scales small enough that they are not represented properly in existing models. 

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