| Popis: |
For more than one century, the penetration of the Mediterranean Sea Breeze into the Jordan Valley has been studied. At times, the associated downslope westerlies in the Dead Sea area exhibit foehn characteristics, leading to a warming and drying upon arrival and therefore contradicting the typical characteristics of a sea breeze. In this paper, a particular summer day (16 August 2014) is analyzed using a kilometre-scale model simulation. For the first time, the Mediterranean Sea Breeze penetration is investigated with Lagrangian backward trajectories and its characterization is extended to the entire Jordan Valley. Along the western slopes of the valley, two well-distinguishable layers are detected in the afternoon: a moist and cold sea breeze layer, and a dry and warm foehn layer above. While the air parcels of both layers cover similar pathways in the hours before reaching the Jordan Valley, they originate from strikingly different altitudes. For this reason, significant differences in their temperature evolution and humidity content are detected. In the evening, the Mediterranean Sea Breeze layer is eroded, enabling the foehn layer to reach the surface. The arrival of foehn retards the afternoon cooling and leads to a decrease in relative humidity. This unique imprint of foehn breakthrough is confirmed by in situ measurements. Therefore, the two-layered flow pattern is found to be a key element in understanding the mesoscale wind system and the surface signals in the Dead Sea area. The foehn layer is spatially confined to the Dead Sea area since the locally elevated upstream Judean Mountains cause a major disturbance of the westerly flow. This work extends the knowledge on summer mesoscale flows in the Jordan Valley and on different types of foehn-breeze interactions. |
