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İstanbul Teknik Üniversitesi (2019)

Influences of atmospheric blocking over Turkey : climatological analysis

EFE Bahtiyar

Titre : Influences of atmospheric blocking over Turkey : climatological analysis

Atmosferik engellemenin Türkiye üzerine etkileri : klimatolojik analiz

Auteur : EFE Bahtiyar

Université de soutenance : İstanbul Teknik Üniversitesi

Grade : Doctor of Philosophy (PhD) 2019

Résumé
The relationship between atmospheric blocking and meteorological parameters has not been studied in depth for Turkey. The scope of this dissertation is to put forth the relationship between atmospheric blocking and temperature anomalies, mean precipitation frequency and extreme temperatures for Turkey. In this dissertation, these relationships are investigated for the period 1977 – 2016 using 77 stations that have complete meteorological data for the aforementioned period from Turkish State Meteorological Service. The 500 hPa geopotential height data from National Center for Environmental Protection (NCEP) – National Center for Atmospheric Research (NCAR) Reanalysis 1 data set was used in order to detect blocking and compute blocking characteristics. The statistical characteristics of atmospheric blocking events with respect to seasons in the study domain are calculated. The maximum value for mean block duration occurs during the winter and spring seasons at 9.2 days. The fall season has the minimum block duration at 8.1 days, while the overall value for the mean duration is 8.8 days. The mean occurrence for atmospheric blocking events is nearly the same during winter, summer and fall at 2.7, 2.5 and 2.6 events, respectively. In contrast, spring has more blocking occurrences than any other season (3.9 events). The mean seasonal values for blocking intensity (BI) range between 1.91 and 2.65 in the study area. The most intense blocking events are observed in winter (2.65), while the weakest blocking events are observed in summer (1.91). Spring and fall have nearly the same values for BI, 2.31 and 2.36, respectively. The overall mean BI is 2.41 in the study domain. The last blocking characteristic examined here is the longitudinal extent as measured by degrees longitude. The seasonal longitudinal extent fluctuates between 25 and 29 degrees longitude. The longitudinal extent of atmospheric blocking is the largest in winter (29 degrees longitude), while spring (27 degrees longitude) had the second largest extent, and summer and fall had a nearly the same longitudinal extent (25 degrees longitude). The first meteorological parameter, the temperature is investigated according to its relationship with atmospheric blocking in terms of anomalies. The temperature anomalies of any station were calculated by using the seasonal mean temperature observations. The seasonal mean temperature anomalies at all stations during blocked days varies between -2.1o C and 0.8o C. There are four main patterns representing the mean seasonal anomaly curve of all stations

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