Document Type : Original Article

Authors

• Tahmineh Chehrehara Ziabari ¹
• Somayeh hajivand paydari ²

¹ Assistant Professor, Payame Noor University (PNU), Iran

² PhD Candidate in Climatology at Kharazmi University, Tehran

Abstract

Cold waves are critical extreme phenomena that annually inflict substantial damage on human societies across various regions. This study investigates the changing trends and atmospheric mechanisms of cold waves in Isfahan city. Daily minimum temperature data from the Isfahan synoptic station were utilized over a 51‑year period (1970–2021). Temperature thresholds were derived using the 1st, 5th, and 10th percentiles, and intense, long‑lasting cold wave episodes were identified. Geopotential height data at 500 hPa and temperature advection at 1000 hPa were obtained from the NCEP/NCAR reanalysis database. Factor analysis and cluster analysis were employed to extract the contributing atmospheric factors and prevailing circulation patterns. Results indicate a mild increasing trend in minimum temperature, accompanied by a significant decrease in cold wave frequency across all selected thresholds over the past half‑century. Synoptic analysis reveals that 17 atmospheric factors account for approximately 89% of the total variance, which are categorised into four dominant circulation patterns: cut‑off lows, southward extension of the polar vortex, omega blocking, and dipole blocking. Furthermore, lower‑tropospheric temperature advection analysis demonstrates that intense cold‑air advection from high latitudes—particularly in the second and fourth patterns—combined with the persistence of blocking systems, plays the foremost role in the abrupt and sustained temperature drops over the study area.

Keywords

• Cold waves
• Atmospheric pattern
• Percentiles
• Isfahan city

Main Subjects

• Climate change