Monitoring of actinometric parameters over Poland in may 2024

May 2024 became 12th month in a row with record high temperatures, if we count from June 2023. «Copernicus» (https://www.copernicus.eu/en): «2024 was by far the hottest year on Earth, as confirmed by all five global temperature datasets». May 2024 was warmer than the global average temperature for May: by 1.52⁰С relative to the pre-industrial period 1850-1900 and by 0.65⁰С relative to the period 1991-2020. According to experts, the global warming is caused by greenhouse gas emissions.

In 2024, temperatures exceeding monthly norms were observed throughout Poland. According to the quantile classification, thermal conditions in May this year, determined by the average temperature in Poland, were assessed as “extremely warm”. At the same time, for the European part of Russia, the first 10 days in May 2024 turned out to be the coldest in the entire history of observations. The Hydrometeorological Center named several reasons for the extremely low temperatures.

The purpose of the article is to draw attention to the phenomenon described. The study traces the influence of physical and geographical conditions on the indicators of weather anomalies. Weather data for May 2024 is provided. Observations at four Polish stations located in different places were studied: on the shores of the Baltic Sea, in the mountains, in the continental part of the country in urban and rural conditions (in the east-central part of the country). It turned out that in May 2024, at all stations, the monthly means values of global solar radiation (GSR) exceeded similar values in the summer months of this year.

As a result, periods in May with anomalous daily actinometric indicators were identified, correlating with meteorological parameters.  A three-dimensional climatological complex was used for the analysis: atmospheric radiation, relative humidity and temperature. The author examines the relationship between GSR and sunshine duration (SS). The base period is a 10-year interval for May conditions.  Statistical processing of observations was carried out using the method of normalized deviations (t), calculated for GSR and SS. Graphic material illustrating statistical indicators is presented in the work. Polish stations are ranked by t. The maximum value of the normalized deviation  was obtained for the Warsaw st., the minimum – for the station located on the sea coast. It is noteworthy that at the Koszalin station in May the maximum number of days (61%) with atmospheric radiation values higher than in June were observed.  For the same location, the proportion of diffuse radiation in the monthly average of GSR was the lowest of the three stations: 26%. Typically, during the last month of spring, cloudiness and precipitation decrease, allowing more sunlight to reach the Earth's surface. It has been suggested that due to positive feedbacks arising from the tendency for air temperature to increase, the moisture content of the atmosphere decreases, and this entails a decrease in the diffuse radiation component, the amount of cloudiness and precipitation. Perhaps, the main reason for the extreme values of atmospheric radiation and temperature this month was the unusual synoptic situation that developed over Central Europe.

The source of data on solar radiation was WRDC (FGBU "MGO", St. Petersburg), which has been collecting and publishing them for over 60 years. Meteorological conditions are taken from the bulletin IMGWP of the Republic of Poland for 2024, May 2024.