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The evolution of the Planetary Boundary Layer Height (PBLH) is a very important meteorological parameter because most of the population carries out their socio-economic activities inside this layer and because it has a significant impact on weather events and air quality. This parameter is influenced by energy and mass exchanges between the land surface and the atmosphere. In our study, hourly PBLH data were used over a period of 30 years (1989-2018), for the warm season (May, June, July, August and September). The data we used comes from the ECMWF (European Centre for Medium-Range Weather Forecasts) database, ERA5. By means of Open GrADS (The Grid Analysis and Display System), the PBLH deviations were graphically represented and interpreted. On the other hand, the NAO (The North Atlantic Oscillation) has influences over the climate variability and weather worldwide. It is well known that NAO exhibits considerable variability throughout a season and during a year, as well, and prolonged periods (for a few months) of both positive and negative phases of the pattern are ordinary. Both the PBLH variations and the NAO index can have an impact on the weather and climate conditions. In this study we will present the patterns of PBLH during 1989-2019 and correlations between the NAO index and the variability of the monthly summer PBLH in Moldavia Region, Romania.

On June 30th, 2021, a low-pressure formed in the center of Europe, causing the advection of warm air and the infiltration of cold air from the rear sector of the low-pressure field. This resulted in the formation of a strong convergence line in the Moldavia region, which generated a multicellular system. We analyzed the forecast atmospheric sounding for this date at 12 UTC in various locations in Moldavia, using the European Centre for Medium-Range Weather Forecasts (ECMWF) to identify areas with high convective potential. The planetary boundary layer (PBL) was determined through the analysis of selected atmospheric sounding, and a well-mixed PBL was observed. As the air particle rises, it cools adiabatically, carrying moisture with it. However, slight variations in the height of PBL were noted at different locations, with the northern-central part of Moldavia experiencing more convection than the southern part, which was less affected by severe weather. The region of the atmosphere closest to the ground surface that is directly influenced by it in terms of turbulence, wind direction and speed, moisture, heat, and convective activity is known as PBL. Most of the water vapor and aerosols in the atmosphere are concentrated in this layer, where turbulent mixing occurs and atmospheric fronts and their associated phenomena are manifested. It is important to analyze the height of PBL and how it varies, as it does not have the same height everywhere and changes over time and space. In our work we determined the height of PBL through the use of atmospheric sounding. Keywords: forecast, convection, PBL, atmospheric sounding