The relationship between atmospheric blocking and precipitation changes in Turkey between 1977 and 2016

The relationship between blocking events and mean precipitation frequency (MPF) was investigated in this work for Turkey during 1977-2016. The overall MPF for the examined stations during blocked days (nonblocked days) fluctuated between 0.15 and 0.43 (0.12 and 0.38). The ratio of MPF during the blocked days to nonblocked days ranges between 12 and 38%. During the winter season, the country has higher MPF values during blocked days. The greatest ratio of MPF values during blocked days to nonblocked days is observed in summer due to smaller values of MPF occurring during this season overall. Higher MPF occurs when the event center was located between 0(o) and 30(o) E (mean 0.27, range 0.17-0.51). There is no relationship between blocking duration and MPF for all seasons. There is a positive relationship between blocking intensity and MPF during summer (CC=0.35, significant at the 95% level) and fall (CC=0.43, significant at the 95% level). The relationship between blocking longitudinal extent and MPF is significant at the 95% confidence level during the summer and fall seasons with correlation coefficients of 0.29 and 0.25, respectively. A composite of the 10 blocking events associated with the largest MPF demonstrated that there is moist advection via westerly flow into Turkey in all seasons. During winter, a greater proportion of these events is observed during the La Nina phase of El Nino Southern Oscillation, but during El Nino in spring and summer. For the blocking case study (31 October to 5 November 2009) associated with the largest MPF, the mean value across the country was 0.73. The mean total precipitation during this period was 63.4 mm.