Тhe reliability of acoustic sounding of the atmosphere with different types of sodars by using them in a number of experimental campaigns in studying both local coastal circulation and the vertical structure of the coastal ABL is presented in a number of scientific publications describing results from different parts of the world including Antarctica. Sodar measurements have also been used in scientific studies for mesometeorological models’ data validation and performance in coastal zones.

Within this project, long-term data (August 2008 – October 2016) from a modern ground-based remote sensing instrument for acoustic sounding of the ABL (SCINTEC Flat Array Sodar MFAS) is used with a vertical range of about 1000 m. This Doppler sounding system has provided data for wind and turbulence parameters at Ahtopol with high temporal (every 10 minutes a running 20-min average value is calculated) and special resolution (data at every 10 m starting from 30 m above ground and reaching different height between 400 and 800 m depending on atmospheric conditions), thus characterizing the processes within the coastal ABL and allowing to collect unique information and new knowledge on the vertical structure and evolution of the coastal ABL. The new type of information provided by the sodar allows the realization of a number of theoretical and practical studies, such as studies of the local circulation – sea breeze, coastal area climate, assessments of wind energy potential, weather forecast improvement, etc.

Flat Array middle range instrument (MFAS) sodar: frequency range 1650 – 2750 Hz; 9 emission/reception angles (0°, ± 9.3°, ± 15.6°, ± 22.1°, ± 29°); maximum 100 vertical layers; range between 150 – 1000 m, vertical resolution of 10 m; accuracy of horizontal wind speed 0.1 – 0.3 ms-1; range of horizontal wind speed ± 50 ms-1; accuracy of vertical wind speed 0.03 – 0.1ms-1; range of vertical wind speed ± 10 ms-1; accuracy of wind direction 2 – 3 degrees.

The Bulgarian Black Sea coast is defined as a separate climatic sub-region in а detailed study of the climatic zoning of Bulgaria on the basis of climatological and synoptic data. A number of meteorological experimental campaigns related to air quality research were performed in the 70s and 80s of the XX century at the coastal towns – Varna (1973) and Burgas (1976 and 1990). Further, in the frame of collaborative international studies with several observation periods, the aerosol composition of the air at the coastal region of Ahtopol (the 90s of the XX century) was explained through reverse trajectory analysis.

Meteorological Observatory (MO) Ahtopol is located in the south-eastern part of the Bulgarian Black Sea coast region (42.084° N, 27.9513° E ), which is 60 km south-east of Burgas and at about 2 km southeast of the town of Ahtopol. It has been operational as a meteorological site since 1971. The site is about 400 m inland and 30 m height above sea level located primarily in flat grassland. The coastline is stretching out from NNW to SSE with a steep about 10 m high coast. The observatory falls into the Black Sea coastal Strandzha climate region, which is a part of the Black Sea climatic sub-region of the Continental-Mediterranean climatic zone in Bulgaria. Well expressed breeze circulation in the warm half of the year is typical for the climate in the region, whereas during the cold season a lower frequency and smaller time and spatial scales of the local circulation are registered.