The daily minimum and maximum temperatures at seven Polish stations were used in an analysis of the occurrence of heatwaves in the years 1951-2006. Heatwaves were defi ned as days with temperatures exceeding selected thresholds (t max ≥25°C, t max ≥30°C, t min ≥18°C). The mean length of a wave of very warm days lasts from 2-4 days, the longest no fewer than 23 days. Waves comprising hot days and nights are shorter. The frequencies of very warm and hot days and hot nights increased in the analyzed period, especially its second half (1979-2006). The occurrence of heatwaves characteristically links up with high-pressure systems over Central Europe, along with associated blocking episodes.

ABSTRACT:With the overall aim of quantifying urban atmospheric effects on different parts of the solar spectrum, a multi year analysis of data collected at Łódź was undertaken. UV (290-400 nm) and global solar radiation measured by means of a Kipp and Zonen CUV3 radiometer and a Kipp and Zonen CM11 pyranometer

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Four years of summertime paired urban‐rural meteorological and radon observations in central Poland are used to assess the relationship between atmospheric stability and urban‐induced changes to the radiation balance and surface energy budget. An existing radon‐based technique for nocturnal stability classification is improved and extended to also infer daytime mixing conditions. The radon‐based scheme is shown to provide a simple, effective, objective means of investigating urban energy budget closure over a range of meteorological conditions, which promises to improve estimates of energy storage and loss terms associated with urban canopies. Special attention is paid to quantifying atmospheric characteristics associated with the arbitrarily assigned radon‐derived stability categories in terms of the more conventional measures: bulk Richardson number and the Monin‐Obukhov stability parameter (z/L). The bulk Richardson number approach is demonstrated to be less effective at grouping periods of similar mean stability, and less selective of extremely stable conditions, than the radon‐based technique. A simple box model is used in conjunction with radon observations and an assumed source function of 15 mBq·m−2·s−1, to show that nocturnal effective mixing heights were deeper and less variable over the urban region. On stable nights hourly median effective mixing heights were 15–20 m over the rural region compared to 40–45 m over the urban region.

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