Monthly air temperature anomalies in Alaska (1951-2015)

Celem pracy jest ocena częstości występowania anomalnie ciepłych i zimnych miesięcy w stanie Alaska w latach 1951-2015, poznanie ich zasięgu przestrzennego, a także próba określenia roli Dekadowej Oscylacji Pacyficznej ( Pacific Decadal Oscillation, PDO ) w ich pojawianiu się. Opracowanie oparto na średnich miesięcznych wartościach temperatury powietrza z 15 stacji meteorologicznych. Za anomalne termicznie uznano te miesiące, w których średnia miesięczna temperatura powietrza była wyższa ( miesiąc anomalnie ciepły, ACM ) lub niższa ( miesiąc anomalnie zimny, AZM ) od średniej wieloletniej przynajmniej o dwa odchylenia standardowe. Stwierdzono 243 przypadki ACM i 298 AZM. Anomalie były największe w chłodnej połowie roku i w obszarach w zasięgu klimatu kontynentalnego, a najmniejsze w ciepłej połowie roku i w obszarach o klimacie morskim. W przebiegu wieloletnim wystąpił spadek częstości AZM i wzrost częstości ACM, co - jak wykazały badania - ma związek ze zmianą fazy PDO z ujemnej na dodatnią w 1976 r. Na szczególną uwagę zasługują ostatnie trzy lata okresu badań, charakteryzujące się dużą liczbą ACM o dużym zasięgu. Podczas ok. 80% ACM ( AZM ) wartości wskaźnika PDO były dodatnie ( ujemne ), co potwierdza, że PDO jest jednym z głównych czynników warunkujących występowanie miesięcy anomalnych pod względem termicznym na tym obszarze. Duże znaczenie mają również uwarunkowania lokalne poszczególnych stacji.The aim of this paper is to present both anomalously warm months ( AWM ) and anomalously cold months ( ACM ) in Alaska and to refine the linkage of Pacific Decadal Oscillation ( PDO ) with their occurrence. The study is based on mean monthly temperature data from 15 weather stations located in Alaska recorded during the period of 1951-2015. The anomalous months were defined as having an average temperature different from the long-term mean by at least 2 standard deviations. Temporal variability, spatial extent and temperature magnitude of AWM and ACM were characterized. In total ( considering all 15 stations ), there were 243 cases of AWM and 298 cases of ACM, which occurred during 100 and 123 months of the 65-year period respectively. AWM occurred most frequently in January and from June to August while ACM from February to April and in November and December. To some degree months with the biggest number of AWM were the same as months with the smallest number of ACM and vice versa. This indicates that during particular months synoptic and/or local conditions may be more favourable for the occurrence of positive or negative anomalies. Both AWM and ACM covered from 1 to 11 weather stations simultaneously, though the majority of the anomalous months of each type were observed at single stations or at two neighboring stations. Generally, the scale of the anomaly tended to be larger during ACM than AWM ( i.e. down to -17,0^{\circ}C compared to maximum 15,6^{\circ}C for AWM ), during winter than summer, and in the central part of Alaska than at the seaside. There is a clearly visible increase in the frequency of AWM and a decrease in the frequency of ACM after 1976 when PDO shifted from dominantly negative to positive values. Comparing two periods, 1951-1976 and 1977-2015, one can notice that in the latter the mean annual number of ACM in Alaska decreased by one-third and themean annual number of AWM doubled. The spatial extent of ACM was also considerably smaller ( on average ) and of AWM - larger. In total about 80% of AWM ( ACM ) occurred during the positive ( negative ) values of PDO index. Monthly temperature anomalies in Alaska are mainly driven by atmospheric circulation patterns. AWM coincide with advection of warm air masses from the south while ACM tend to occur in association with northern cold advections. Local effects, which include radiative cooling, temperature inversions and local winds ( i.e. chinook ), also have a great contribution to the occurrence of anomalous months in Alaska

Variability of growing degree days in Poland in response to ongoing climate changes in Europe

An observed increase in air temperature can lead to significant changes in the phenology of plants and, consequently, changes in agricultural production. The aim of the study was to evaluate the spatial differentiation of thermal resources in Poland and their variability during a period of changing thermal conditions in Europe. Since the variability of thermal conditions is of paramount importance for perennial crops, the study focused on apple, plum, and cherry orchard regions in Poland. The analysis was conducted for the period of 1951–2010 using air temperature daily data. Thermal resources have been defined using the growing degree days (GDD) index calculated independently for the whole year and during in frost-free season for three air temperature thresholds: 0, 5, and 10 °C, which determine the non-winter period, growing season, and the period of full plant growth, respectively. In addition, due to the high significance for perennials in particular, the incidence and intensity of frost during flowering were calculated. In this study, a detailed analysis of the spatial differentiation of thermal resources was first performed, followed by an evaluation of long-term variability and associated change patterns. The obtained results confirmed an increase in thermal resources in Poland as a consequence of the lengthening of the growing season. However, the frequency and intensity of spring frost, especially during flowering or even during ripening of plants, remain a threat to harvests in both the eastern and western parts of the country

Temporal variability of summer temperature extremes in Poland

The aim of the study is to estimate the trend in summer maximum air temperature extremes in Poland during the period 1951–2015 by demonstrating the changes in the magnitude of temperature anomalies, temperature “surplus”, as well as the area influenced by extreme temperature occurrence. To express the latter two variables, daily maps of maximum air temperature were created to calculate the total area affected by temperature extremes. To combine the effect of spatial extent and temperature anomaly, an Extremity Index was introduced. The results confirmed an increase in summer maximum air temperature of about 0.4 °C per 10 years, evidenced also in the increase of summer extremeness. Positive anomalies have dominated since the 1990s, with the largest anomalies occurring during the summers of 1992, 1994, 2010 and finally 2015, the most exceptional summer during the analyzed period

Fale upałów latem 2015 roku i ich uwarunkowania cyrkulacyjne

The main goal of the study was to characterize the thermal conditions during the hot summer of 2015 and to determine the circulation types with respect to the occurrence of extremely high air temperature and heat waves in Poland. The daily maximum (TMAX) and minimum (TMIN) air temperatures from 7 stations in Poland in 1951–2015 were used, as well as the Grosswetterlagen and Niedzwiedź circulation type classifications. A day with an extremely high air temperature (DTE) was defined as having TMAX above the 95th percentile and a heat wave as a sequence of at least 3 such days. The results prove that the summer of 2015 in Poland was unusually hot, especially in the south-western part of the country. The circulation types accompanying DTE and the heat waves were mainly anticyclonic with an advection of tropical air masses from the southern sector.720522316Badania Fizjograficzn

Atmospheric circulation conditions during winter warm spells in Central Europe

The objective of the paper was to characterise the temporal and spatial variability of winter warm spells in Central Europe in the years 1966/1967-2015/2016 and to determine the circulation conditions of their occurrence. The applied data were obtained from the Polish Institute of Meteorology and Water Management, Deutscher Wetterdienst and the National Centre for Environmental Prediction/National Centre for Atmospheric Research. A warm spell was defined as a sequence of at least three warm days, i.e. when the maximum air temperature is higher than the 95th percentile of the probability density function designated from observation. The research has proven that over the study period the air temperature increased in the winter season in Central Europe and this translated into an increase in the number of warm days. An average of 3-5 warm spells was recorded per 10 years. The most numerous warm spells occurred during three winter seasons, i.e. 1989/1990, 2006/2007 and 2015/2016. The occurrence of warm spells was related to positive anomalies of geopotential heights over the study area in the cross section of the entire troposphere. Maximum anomalies appeared at 250 hPa geopotential height, and they developed on average 9 days before the commencement of warm spells over the study area