Duct occurrence and characteristics for Bulgarian Black sea shore derived from ECMWF data

•Tropospheric ducts' occurrence and parameters are studied in Varna and Burgas bays.•Mean and median M-deficits are commonly higher for Varna bay than for Burgas bay.•When ducting is assessed one can not rely on the geographic proximity of two points.•Along Bulgarian shore spring season may be rich in trapping layers.

Non-standard propagation due to sharp gradients in tropospheric refraction is known to have significant impact on radar and communication systems working in microwave range. The formation of tropospheric ducts is the most severe deviation from the standard propagation conditions. The presented study reports results on the tropospheric ducts' occurrence and properties along the Bulgarian Black sea shore. The meteorology needed to reconstruct the refractivity profiles is derived from ECMWF current operational model, TL799L91, and refers to two-year period. Statistics of essential duct parameters for surface, surface-based and elevated ducts are reported for the summer months and overall duct statistics are given for the other seasons.