Latitudinal and Seasonal Variation of Ozone

Figure 8.2 shows the latitudinal and seasonal variations of ozone content in the atmosphere (after Dobson, 1931).

Fig. 8.2 Seasonal variation of atmospheric ozone content in different latitudes Unit: 0.001 cm at S.T.P. (Reproduced from Mitra, 1952, published by the Asiatic Society of Bengal, India)

In general the ozone content in the stratosphere is much greater in high latitudes than that in low latitudes. Also, in higher latitudes, there is a large annual variation with very large values in spring as compared to those in autumn. In the equatorial stratosphere, not only is the ozone content small but it has also a small annual variation.

8.4.5 Ozone and Weather

(a) Association of ozone with high-latitude cyclonic disturbances

In middle and high latitudes, the ozone content in the stratosphere appears to vary significantly with the movement of fronts associated with tropospheric disturbances.

Fig. 8.3 Illustrating the distribution of stratospheric ozone around a typical young depression with a very marked warm sector. Note that the ozone content is low over the warm sector and high above the advancing cold airmass behind (After Dobson, 1931; Dobson et al., 1946). (Reproduced from Mitra, 1952, published by the Asiatic Society of Bengal, India)

For example, Dobson and his coworkers found that in the case of an eastward-propagating cyclone, if we take a vertical section at right angles to the fronts, there is a definite fall in ozone content ahead of an advancing warm front and a definite rise behind an advancing cold front, as shown in Fig. 8.3, reproduced from their paper (Dobson et al., 1946).

The observed variations of stratospheric ozone in the field of a midlatitude cyclone are not difficult to understand if we consider the latitudinal distribution of ozone in relation to the circulation. The southerly winds in the warm sector of the cyclone advect air from the south which has relatively less ozone content, whereas the northerly winds in the cold sector usher in airmass from high latitudes which is rich in ozone content. The effects are, however, observed only when the fronts extend well into the stratosphere. No such correlation has been found so far over the tropics or low latitudes where fronts are rare.

(b) Correlation of ozone with other meteorological parameters

Dobson (1931) found that in temperate latitudes, the ozone content varies inversely with the mean atmospheric pressure at 9-16 km level and with the mean temperature of the troposphere.

Meetham (1936) has shown that ozone has a high correlation with the potential temperature and density in the stratosphere.

(c) Variation of ozone with solar activity and terrestrial magnetic storms

Studies conducted so far seem to indicate that the average variation of the ozone content does not have any firm relationship with the eleven-year solar cycle.

A definite association has been found between the ozone content in the middle atmosphere and terrestrial magnetic storms. The ozone value always increases when there is a magnetic storm on the earth.

Fig. 8.3 Illustrating the distribution of stratospheric ozone around a typical young depression with a very marked warm sector. Note that the ozone content is low over the warm sector and high above the advancing cold airmass behind (After Dobson, 1931; Dobson et al., 1946). (Reproduced from Mitra, 1952, published by the Asiatic Society of Bengal, India)

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