Contents lists available at ScienceDirect Dynamics of Atmospheres and Oceans journal homepage: www.elsevier.com/locate/dynatmoce Study of the climatological behaviors of Euro-Atlantic and West Asia blockings in the period of 1959–2018 Sara Fahimi a , Farhang Ahmadi-Givi b, *, Amir Hussain Meshkatee a , Majid Mazraeh Farahani b a Department of Earth Sciences, Science and Research Branch, Islamic Azad University, Tehran, Iran b Department of Space Physics, Institute of Geophysics, University of Tehran, Iran ARTICLE INFO Keywords: Climatology Atmospheric blocking Seasonality Atlantic-European Asia ABSTRACT In this study, comparison of blocking climatological behaviors is presented for the two periods of 1959–1988 and 1989–2018 in a part of the Northern Hemisphere including the Atlantic Ocean, Europe and West Asia regions. Blocking events were detected using a modified blocking index that is based on vertically integrated potential vorticity. By applying this index, the character- istics of detected blocking events such as frequency, duration, intensity and area were de- termined and compared for both the periods. According to the results, on average, 16 and 15 blocking events per year were identified in the first and second periods, respectively. The trend analysis shows that the number of blocking events in the period 1959–1988 was significantly decreased, while it was slightly increased in the period 1989–2018. Blocking activity was most prevalent from the eastern Atlantic through Europe to West Asia, but this longitude band exhibits a relatively eastward shift in the second period. In addition, the seasonal distributions are similar to those found in previous studies with the higher occurrence of blocking events during winter and autumn seasons and the lowest frequency in summer, as well as long-lasting events and greater intensity and extension in winter than the summer time, especially in the second period. These seasonal variations of blocking frequency may be due to synoptic scale eddies and planetary waves which are more active and stronger in the colder seasons than the other seasons. On the other hand, a comparison between the two periods shows that the blocking events tend to be more frequent over West Asia espe- cially during summer in recent years. Although discrepancies between the two periods are not significant, they could be partly due to the impacts of climate change in recent decades. 1. Introduction Atmospheric blocking is a large-scale phenomenon in the middle latitudes, which is in the category of phenomena with low frequency variability (Rex, 1950a, b; Barriopedro et al., 2006). The occurrence of this phenomenon is accompanied by the estab- lishment of a strong anticyclone in the middle and high latitudes, which is located in the polar-ward of anomalous easterly winds (Pelly and Hoskins, 2003; Schwierz et al., 2004). In addition, blocking has also two important characteristics. The first feature is being quasi-stationary and the second is its localized characteristic (Rex, 1950a, b; Wiedenmann et al., 2002; Pelly and Hoskins, 2003). https://doi.org/10.1016/j.dynatmoce.2020.101130 Received 11 September 2019; Received in revised form 8 January 2020; Accepted 8 January 2020 ⁎ Corresponding author at: Institute of Geophysics, University of Tehran, P. O. Box 14155-6466, Tehran, Iran. E-mail address: ahmadig@ut.ac.ir (F. Ahmadi-Givi). Dynamics of Atmospheres and Oceans 89 (2020) 101130 Available online 01 February 2020 0377-0265/ © 2020 Published by Elsevier B.V. T