CR 69:155-176 (2016)  -  DOI: https://doi.org/10.3354/cr01397

ABSTRACT: This study examines the climatology, inter-annual variability and long-term trends of dates of the first fall frost (FFF) and last spring frost (LSF) events, and lengths of the frost-free periods (FFP) by using daily minimum air temperature data from 80 stations in Turkey. Influences of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO) teleconnection patterns on the variability of these climatic observations are also investigated. A trend towards later FFF and earlier LSF, and a resulting lengthened FFP are detected, with some regional differences, particularly in the Black Sea Region. Linear trend analysis of nationally averaged time series showed that the LSF occurred earlier by -0.64 d per decade, while the FFP occurred later with an increase rate of +0.71 d per decade over the study period. Correlation analysis revealed that year-to-year variations in occurrence dates of FFF, and LSF events and lengths of FFP could be explained by large-scale atmospheric circulation or oscillation patterns such as NAO/AO. Negative relationships were detected between the variability of dates of FFF events over Turkey and autumn indices of the NAO and AO indices. Correlation coefficients were statistically significant at the 1% level for the majority of stations. Positive linkages between the dates of the LSF events and the NAO and AO spring indices were obtained at most of the stations in Turkey. The lengths of FFP also tended to increase during negative NAO/AO index phases, while they tended to decrease during positive phases.

KEY WORDS: Turkey · Climate variability · Frost event climatology · Frost event changes · NAO · AO