Variations In Stratospheric Circulation Research Articles

Seasonal Variations in Stratospheric Circulation and Interactions between the Troposphere and the Stratosphere

Based on the data of the ERA5 reanalysis, the dates of spring and autumn rearrangements of the stratospheric circulation on isobaric surfaces of 30, 20 and 10 gPa in the latitude zone of 30–90° C. in the period 1979–2020 were obtained. Of the 42 cases of spring restructuring, 10 belong to the early, 15 to the middle and 17 to the late. The spread in the dates of spring rearrangements on the surface of 10 hPa is 69 days. Most often, the spring restructuring of the circulation occurs from top to bottom, in some years, the delay of spring restructuring on the surface of 30 gPa relative to the surface of 10 gPa reaches 22–25 days. Autumn perestroika takes place from the bottom up and their terms at the 3 levels under consideration are close to each other. The relationship between the timing of the spring restructuring of the stratospheric circulation with solar activity and large sudden winter stratospheric warming is shown. Analysis of the fields of anomalies of daily temperature values and zonal wind velocity in the 1000-1 hPa layer in the period January-May showed their significant spatio-temporal difference in the case of early and late spring perestroika. Thus, foci of positive anomalies of temperature and wind speed are formed initially in the upper stratosphere, and then shifted from top to bottom. The interrelations between the layers of the atmosphere in different seasons are considered.

Tropospheric ozone variations governed by changes in stratospheric circulation

The downward transport of stratospheric air can deliver significant quantities of ozone to the upper troposphere. An analysis of satellite data suggests that year-to-year variations in stratospheric circulation can account for around half of the interannual variability in tropospheric ozone levels in the northern mid-latitudes. The downward transport of stratospheric ozone is an important natural source of tropospheric ozone, particularly in the upper troposphere, where changes in ozone have their largest radiative effect1. Stratospheric circulation is projected to intensify over the coming century, which could lead to an increase in the flux of ozone from the stratosphere to the troposphere2,3,4. However, large uncertainties in the stratospheric contribution to trends and variability in tropospheric ozone levels5,6,7 make it difficult to reliably project future changes in tropospheric ozone8. Here, we use satellite measurements of stratospheric water vapour and tropospheric ozone levels collected between 2005 and 2010 to assess the effect of changes in stratospheric circulation, driven by El Nino/Southern Oscillation and the stratospheric Quasi-Biennial Oscillation, on tropospheric ozone levels. We find that interannual variations in the strength of the stratospheric circulation of around 40%—comparable to the mean change in stratospheric circulation projected this century2—lead to changes in tropospheric ozone levels in the northern mid-latitudes of around 2%, approximately half of the interannual variability. Assuming that the observed response of tropospheric ozone levels to interannual variations in circulation is a good predictor of its equilibrium response, we suggest that the projected intensification of the stratospheric circulation over the coming century could lead to small but important increases in tropospheric ozone levels.

The changing stratosphere

Large reductions in O 3 observed in recent years over Antarctica in spring are the consequence of catalytic reactions involving industrially related radicals of chlorine and bromine. About 75% of the loss observed in 1987 was due to the CIO dimer scheme proposed by Molina and Molina (1987, J. phys. Chem. 91, 433) with the balance associated with the ClO-BrO mechanism introduced by McElroy et al. (1986, Nature 321, 759). The magnitude of O 3 loss is sensitive to the extent of denitriflcation, the efficiency with which HNO 3 is removed from the stratosphere by precipitation in paniculate form. It depends also, according to present understanding, on the relative abundances of CINO 3 and HCl in air trapped originally in the polar vortex in late fall or early winter. High concentrations of ClO and BrO were observed also in the Arctic stratosphere during January and early February of 1989. It is estimated that about 10% of O 3 contained in the Arctic stratosphere between about 16 and 20 km was lost during the winter of 1989. The extent of dcnitriflcation and the persistence of the vortex are the key factors influencing the magnitude of O 3 loss in the north. It is shown, based on analysis of data from the Atmospheric Trace Molecule Spectroscopy experiment for early May 1985 at 47°S (Farmer et al., 1987, JPL Publication 87-32, JPL. Pasadena, CA), that heterogeneous chemistry (specifically the reaction of N 2O 5 with H 2O on sulfuric acid droplets) can have an influence also on the composition of the mid-latitude stratosphere. Implications for midlatitude O 3 of consequent changes in the concentrations of nitrogen, hydrogen and halogen radicals are discussed. It is suggested that changes in the abundance of O 3 in the lower stratosphere in the tropics can have implications also for climate. The relatively warm climates of the Eocene and Cretaceous and the cold climates of recent glacial epochs may be associated with shallower and deeper stratospheres, respectively, with related expansion and contraction of the symmetric (Hadley) circulation. Changes in lower stratospheric O 3 may be related to variations in stratospheric circulation corresponding to differing levels of CO 2, with additional contributions for the contemporary environment due to elevated levels of industrial chlorine and bromine.