Verkley (1987, 1990) constructed modons as a model of the atmospheric blocking phenomenon. They are exact solutions of the barotropic potential vorticity equation on a sphere. In this note, it is shown that the 1987 modon changes continuously into the 1990 modon as the value of -dQ/dΨ within the modon goes to zero, where Q and Ψ are potential vorticity and streamfunction of the 1987 modon, respectively. Thereby it is revealed that the stability properties of the 1990 modon can be studied by means of Arnol'd's invariant of the 1987 modon though Arnol'd's invariant can not be defined for the 1990 modon.
Total ozone data (from ground-based measurements) for 3 zones (north polar, north temperate, tropics) and for the world as a whole, as well as the ozone content in troposphere and stratosphere layers over the north polar and north temperate regions have been analyzed to detect long-term variations (trends) and short-term variations (related to the QBO, ENSO, and the 11-year solar cycle). Various multiple regression models (adjusted for the trends, interannual quasi-periodical variations, and the serial correlations) have been used to delineate the anthropogenic effects in the atmospheric ozone. An apparent downward trend in the total column amount of ozone over mid and high latitude areas of the northern hemisphere, as well as over the tropic region, and the globe as a whole has been found during the period 1970-1990 in all seasons. The rate of ozone loss depends on the season (in the extratropical zones) and shows an increase with latitude. The trends in the layer-mean ozone at mid and high latitudes vary with altitude, i.e., tropospheric ozone increases whereas stratospheric ozone decreases. The negative trends in total ozone over the northern extratropical regions are caused by the ozone depletion in the lower stratosphere (16-24 km layer). Latitudinal changes in the ‘natural’ interannual variations in ozone, related to the QBO, ENSO, and the long-term solar forcing, have been discussed. We have found that the magnitude of the ‘natural’ variations in total ozone may depend both on the phase of the QBO (east, west), ENSO (warm, cold) and on the strength of the QBO, ENSO, and the long-term solar activity. The long-term changes in the atmospheric dynamics seem to influence the observed trends in the atmospheric ozone only slightly.