Abstract
Fifteen temperature indices recommended by the ETCCDI (Expert Team on Climate Change Detection and Indices) were applied to evaluate spatiotemporal variability and trends in annual intensity, frequency, and duration of extreme temperature statistics in Finland during 1961–2011. Statistically significant relationships between these high-resolution (10 km) temperature indices and seven influential Northern Hemisphere teleconnection patterns (NHTPs) for the interannual climate variability were also identified. During the study period (1961–2011), warming trends in extreme temperatures were generally manifested by statistically significant increases in cold temperature extremes rather than in the warm temperature extremes. As expected, warm days and nights became more frequent, while fewer cold days and nights occurred. The frequency of frost and icing days also decreased. Finland experienced more (less) frequent warm (cold) temperature extremes over the past few decades. Interestingly, significant lengthening in cold spells was observed over the upper part of northern Finland, while no clear changes are found in warm spells. Interannual variations in the temperature indices were significantly associated with a number of NHTPs. In general, warm temperature extremes show significant correlations with the East Atlantic and the Scandinavia patterns and cold temperature extremes with the Arctic Oscillation and the North Atlantic Oscillation patterns.
Highlights
In recent decades, changes in climatic extremes have received considerable attention in international communities due to potential effects of floods, droughts, hurricanes, severe cyclonic storms, heat waves, and cold spells (e.g., [1,2,3,4,5])
Daily minimum and maximum surface air temperature (SAT) time series spatially interpolated onto 3322 regular grid (10∗10 km2) points across Finland for the years 1961–2011 (Figure 1(c)) were obtained from PaITuli-Spatial Data for Research and Teaching at the CS-IT centre for Science Ltd. website: http:// www.csc.fi/english. e Finnish Meteorological Institute (FMI) used daily minimum and maximum SAT measurements at 100–200 meteorological stations properly uniformly scattered throughout Finland (Figure 1(d)) as input to a spatial model [28] developed based on the kriging approach [29] to generate the Finnish daily gridded SAT datasets
Interannual variations in the number of SAT measurement stations used by the FMI for creating the gridded minimum and maximum daily SAT time series for the period 1961–2011 are shown in Figure 1(e). e accuracy and homogeneity of the gridded daily minimum and maximum SAT data generated were qualified during the establishment of the PaITuli database
Summary
Changes in climatic extremes have received considerable attention in international communities due to potential effects of floods, droughts, hurricanes, severe cyclonic storms, heat waves, and cold spells (e.g., [1,2,3,4,5]). E most recent global analysis of trends in extreme temperatures shows decreases (increases) in cold (warm) extreme indices over majority of regions since 1900. Atmospheric circulation is one of the key physical processes causing the variability and changes in extreme temperatures [16] and mainly follows a number of preferred modes [17] Such atmospheric circulation modes are generally described by teleconnection patterns (e.g., Arctic Oscillation, AO), which are defined as persistent, recurrent, and large-scale modes of atmospheric pressure anomalies. Irannezhad et al [25] focused only on long-term variations and trends in annual, seasonal, and monthly mean temperatures in Finland and their connections to different Northern Hemisphere teleconnection patterns (NHTPs). Specific objectives of the present study are to (1) determine trends in a set of extreme temperature indices; (2) evaluate spatial variations and changes in these indices throughout the country; and (3) explore relationships between the temperature indices and a number of well-established NHTPs
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