Stratospheric ozone

Special attention has been paid to the study of the stratospheric ozone since the discovery of the Antartic ozone hole in the early 1980s. The direct cause-effect relationship between the chlorated compounds of anthropogenic origins (CFC) and the ozone destruction was first experimentally proved in  1985, when the NASA organized an aerial measurement campaign. At present it is a scientifically accepted fact that the massive destruction of Antartic ozone in the spring is related to the particularly cold metheorological conditions of the Polar stratosphere in the winter and to the increase in halogenated constituents (chlorated and bromated) caused by human activities.

The significant cooling of the stratosphere in the winter leads to the formation of polar stratospheric clouds. The chemical reactions take place on the suface of these clouds transforming most of the halogenated components into active components capable of destroying the ozone through very quick catalytic cycles, from the sun’s reappearance over the pole. In the Antarctic, these chemical processes lead to a decrease of about 60% of the total ozone content each October, with an almost complete disappearance between 12 and 20km. The area of the Antarctic ozone hole has increased regularly along the 1990s, reaching an extent of 29,7 x 10⁶ km² in 2000. In addition, satellite measurements have shown that, during the polar spring, the action of the planetary waves moves the ozone hole towards the peopled regions of the southern hemisphere (South America, New Zealand) producing an increase in the UV solar radiation during these episodes in the area.

On the other hand, the hypothesis to explain the observed decrease in the stratospheric ozone in the middle latitude regions are the following:

a)     the hemisphere-scale dilution of the masses of polar air affected by the

ozone destruction after the rupture of the Antarctic polar vortex.

b) the intensification of the heterogeneous chemistry processes on the in situ  stratospheric aerosols connected to the increase in halogenated components.

c) a change in the stratosphere’s atmospheric circulation related to the evolution of the global climate.

As a result of the ban on the CFCs, the halogenated components in the stratosphere will tend to go down in the next years, which should produce an increase in the global ozone. At the same time, however, the growth of the greenhouse effect gases results in a cooling of the stratosphere which favours the PSC formation and the ozone destruction processes. A recent study has proved the existing correlation between the interannual variation in the solar erythemal irradiance and the quasi-biennial oscillation of the stratospheric winds in the tropical region, which has an influence on the hemisphere’s ozone content.

One of our goals is to study the ozone balance in the southern hemisphere and to quantify, on an interannual base, the impact of the Antarctic ozone destruction on the ozone content and the UV radiation over Argentina. The proposed methodology relies on the constant comparison between models and measurements.

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Water vapor

The study of the evolution of water vapor is particularly important within the greenhouse effect problem and the study of atmospheric ozone, taking into account the role it plays in the atmosphere’s radiative processes, in the physichemical processes present between the ozone and the HOx radicals and in the formation of polar stratospheric clouds. The measurements made on this ground and from balloons, airplanes and satellites, taken as a whole, have revealed a global increase in water vapor, in the low stratosphere and the high troposphere, of about 2 parts in a million [ppmv] in the last 45 years, that is, 0,05 ppmv per year. The reasons for this growth, however, remain uncertain, and the database which allows to determine the water vapor’s evolutive tendency in this region is incomplete.

This is why the adjusting of lidar measurement instruments for the vigilance of the water vapor is considered among the priorities of the NDSC (Network for the Detection of Stratospheric Changes). The development of such system in Argentina will allow to efficiently complete the present network of measurements, which in the southern hemisphere is very limited.

One of the research lines of the LIDAR group has as its main goal the capture of vertical profiles of water vapor in the high troposphere (HT) and the low stratosphere (LS) to properly characterize the transport processes and the HT-LS exchanges and understand the water vapor’s global balance.

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Aerosols

Radiation

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