Influence of atmospheric systems on dry conditions in Serbia

Daily weather types over Serbia were obtained using the objective weather typing system of Jenkinson and Collison (1977), which is based on the Lamb weather types (Lamb 1972). The daily atmospheric circulation that affects Serbia was characterized using a set of indices associated with the direction and vorticity of the geostrophic flow over an area that covers the majority of Europe and the Mediterranean Sea. To obtain the circulation types, the daily values of the sea level pressure (SLP) and the geopotential height at 500 hPa for the period 1961-2020 were retrieved from the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis (Kalnay et al. 1996) on a 2.5° × 2.5° longitude-latitude grid.

Composite maps of ten circulation weather types (CWT): northerly (N), northeasterly (NE), easterly (E), southeasterly (SE), southerly (S), southwesterly (SW), westerly (W), northwesterly (NW), cyclonic (C) and anticyclonic (A), were constructed for the period 1961-2020 for all seasons. The C and AC weather types are based on the severity of the geostrophic vorticity. Each of the CWT has a distinct underlying synoptic pattern that produces the expected type and direction of flow over the study area. The relative frequencies of the circulation types were computed. It was found that the AC type with 25.2% was the most common type, followed by the C type with a frequency of 14.6%.

Multiple Linear Regression (MLR) models were used to establish the relationship between atmospheric circulation and number of days without precipitation. The models were calibrated for the first 40 years and validated for the remaining 20 years. Using ten circulation weather patterns (eight pure directional, cyclonic, and anticyclonic) as predictor variables, good results were obtained for modelling of number of days without precipitation in Serbia. Almost 52% of the variability could be explained by ten circulation types in Belgrade.

References

Jenkinson AF, Collison FP (1977) An initial climatology of gales over the North Sea. Synoptic Climatology Branch Memorandum 62, Meteorological Office, Bracknell, UK

Kalnay E, Kanamitsu M, Collins W, Deaven D, Gandin L, Iredell M, et al (1996) The NCEP/NCAR 40-year reanalysis project. Bull Am Meteorol Soc 77:437–470

Lamb HH (1972) British Isles Weather Types and a Register of Daily Sequence of Circulation Patterns, 1861–1971. Geophysical Memoir 116, HMSO, London (UK), 85 pp