Potential-Vorticity Regimes Over the Eastern Mediterranean and Their Relation to Local Boundary Layer Profiles

Abstract

The relation between the variability of the mid and upper tropospheric levels and the boundary layer profile is investigated by the aid of self-organising maps (SOM) clustering. For this purpose, two separate analyses of synoptic parameters and boundary layer profile are devised. This is the first comprehensive study to reveal this relation over the eastern Mediterranean region. The variability of the synoptic regimes is first analysed by the aid of potential vorticity (PV) at 320 K isentropic level and geopotential height at 1000 hPa (GPH1000). Projection against previous boundary layer profile SOM clustering shows the ability to infer the boundary layer profile from synoptic data according to the vertical coupling along the troposphere. Multi-variable SOM clustering of PV and GPH1000 presents 20 clusters which follow the variability of surface winter lows, highs, and Red Sea troughs. The active Red Sea trough relates to the north easterly and relatively narrow PV stream. Clusters presenting strong winter highs or lows with strong PV gradients have the highest persistence and directly indicate specific boundary layer profile patterns due to strong coupling along the troposphere. Under shallow GPH1000 gradients, when the dominating processes in the BL are local and the synoptic contribution is minimal and/or rapidly changing, indication of the boundary layer profile pattern is less predictable. This clustering framework offers further studies of the synoptic regimes dynamics, particularly the vertical interactions between the boundary layer and the free troposphere under pronounced surface pressure and PV gradients. Moreover, understanding these interactions has implications for the dispersion of anthropogenic pollutants across the eastern Mediterranean region.