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    Analysis of observed variability and trends in numbers of frost days in Turkey for the period 1950-2010
    (Wiley, 2012) Erlat, Ecmel; Turkes, Murat
    This study examines the climatology of annual frost days, and analyses the size and behaviour of the long-term variability and trends in annual numbers of frost day at the 72 stations over Turkey from 1950 to 2010. The main results are summarized as follows: (1) The annual number of frost days has evidently decreased at most of the stations with some observed regional differences, (2) The decreasing trends are largest over the Eastern Anatolia, the Marmara regions and along the Mediterranean coastline. The meteorological stations located in the continental northeast and the easternmost parts of the Anatolian Peninsula, including Ardahan, Igdir and Van, show a negative linear trend with a rate of four days per decade, (3) As in other regions of the Earth, changes in number of frost days are very likely associated with changes in minimum air temperatures and increasing growing season lengths in Turkey, (4) The decreasing trends in number of frost days also indicated considerable decadal-scale variability. This variability is very likely attributable to the large-scale atmospheric circulation and atmospheric oscillations such as the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO) and the North Sea-Caspian Pattern, (5) Consequently, the long-winter (DJFM) composites of number of frost days were examined for extreme phases of the AO index during the period 19502010 in order to assess the influence of atmospheric oscillations on year-to-year variability in number of frost days. According to the Cramer's tk test, winter number of frost days tended to increase significantly during the high (positive) index AO phase, while they tended to decrease significantly during the low (negative) index AO phase. These relationships are statistically significant at the 1% level at the majority of stations. Copyright (c) 2011 Royal Meteorological Society
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    Öğe
    Observed changes and trends in numbers of summer and tropical days, and the 2010 hot summer in Turkey
    (Wiley, 2013) Erlat, Ecmel; Turkes, Murat
    Long-term variability and trends of the annual numbers of summer and tropical days were investigated by using nonlinear (monotonic) and linear trend detection tests for the period 1950-2010 for 97 meteorological stations of Turkey. The results suggest that the numbers of both summer and tropical days indicate a general increasing tendency in Turkey. For the study period, statistically significant increasing trends for summer (tropical) days are detected at 64 (71) stations, of which 51 (58) of these positive trends are significant at the 0.01 significance level. Two periods of changes in summer and tropical days are identified: in the 1950-1975 sub-period with an episode of slight cooling, the annual number of summer and tropical days decreases, whereas in the sub-period of 1976-2010 with an episode of significant increasing trend, the annual number of summer and tropical days increases. The summer of 2010 was exceptional for the number of summer and tropical days at most of the stations in Turkey. Normalized anomalies of summer (tropical) days at 2010 were larger than three standard deviations with respect to 1961-1990 normal at 27 (43) stations. The largest positive anomalies are observed in the northeastern Anatolia sub-region. This increasing trend has significant impacts on agriculture, energy, tourism and natural ecosystems (e.g., forest fires) in Turkey. Copyright (c) 2012 Royal Meteorological Society
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    Öğe
    Winter mean temperature variability in Turkey associated with the North Atlantic Oscillation
    (Springer Wien, 2009) Tuerkes, Murat; Erlat, Ecmel
    Changes and variability in seasonal average mean and monthly mean winter (DJF) air temperature series at 70 stations of Turkey and the circulation types at 500-hPa geopotential height level were investigated to explain atmospheric controls of temperature variations during the extreme (weak and strong) phases and normal (negative and positive) phases of the North Atlantic Oscillation (i.e., Ponta Delgada-Reykjavik and the Gibraltar-Reykjavik) indices. During the positive phases of the North Atlantic Oscillation indices (NAOIs), northeasterly circulation increased, and thus spatially coherent and significant cold signals dominate over the majority of Turkey. This pattern is closely linked to anomalously low 500-hPa heights over the region of the Icelandic Low, and anomalously high geopotential heights over the regions of the Azores High, the western Mediterranean basin and the Europe, in general including the Balkans and northwest Turkey. Contrarily, during the negative phases of the NAOIs, prevailing westerly winds that originate from the subtropical northeast Atlantic increase, and thus spatially coherent and significant warm signals over the Anatolian peninsula appear. This pattern is closely linked to the increased cyclonic activity and associated increased westerly and southwesterly circulation causing warm maritime air advection over the Mediterranean basin toward Turkey.