The ozone layer has never been so thin over Hungary as it was on the 21st of July last week. According to, the phenomenon was probably caused by a western stream. Besides the thin ozone layer, the UV radiation rates increased quite a lot, so it’s fortunate that the sky became cloudy in most places.

Record breakingly low ozone content rates were measured by the Hungarian Meteorological Service’s Marczell György Main Observatory last Thursday. The continuous measurement of the ozone content has been done since 1969 in the observatory. The measured 298 and 294 DU rates are 12% lower than the average rate operative for that day. The lower boundary of natural versatility (in other words, the rate difference compared to the average of many years, which is still normal according to the data of long years) was 11% on the 21st of July, meaning that this rate is abnormally low.

The DU (Dobson Unit) rate is used to characterise the ozone layer. Similar rates were measured at the Antarctic when the world actually realised that the ozone layer is dangerously thinning there: the thickness of the ozone layer dropped from 320 to 280 DU between 1955 and 1975.

So the 294 DU counts as record setting since the lowest rate ever measured on this day of the year was 293 DU (in 1972, 2007 and 2011), also considering that the uncertainty of measurements can reach 2-3 DU.

The reason behind the outstanding lack of ozone is not totally clear yet, but the current stream conditions, high above Hungary, could have contributed to the phenomenon. Such a stream came to Hungary from the West last Thursday, from Mediterranean regions, and the ozone content is always lower in the Mediterranean regions.

The Hungarian Meteorological Service measured very high UV radiation rates at four stations: in Budapest, Kecskemét, Keszthely and Siófok. The UV index already reached rate 8 at noon last Thursday. In those places where the sky kept clear in the afternoon hours as well, UV radiation could have reached the extremely high rate of 8.5.

Copy editor: bm


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