engleski

Is severe Adriatic bora associated with tropopause fold?

Bora (bura locally), a dry, cold, gusty, downslope wind, is well known among inhabitants of the eastern Adriatic coast and the inland adjacent regions. Bora is always accompanied with the high N-S synoptic-scale pressure gradients and cold air outbreaks from the north. Bora-like flows also occur in other parts of the world, such as in Novorossiysk and Caucasus coast of the Black Sea, in the Gulf of Tehuantepec at the Pacific Coast of Mexico (known as papagayos or tehuantepecers), in the Kanto Plain, Japan (where it is called oroshi or karakkaze), and, at the foothills of Rocky Mountains (Boulder windstorm). Since the bora layer usually occupies a few lowermost kilometers of the atmosphere, synoptic conditions within the lower troposphere prior and during bora are well examined and documented. However, to our knowledge, there are no studies addressing to atmospheric conditions within the upper troposphere. Therefore, in this study we analyzed both measured and modeled upper tropospheric meteorological fields established during several severe bora episodes. For this purpose, we utilized ECMWF analyses database and the nonhydrostatic Fifth-Generation Pennsylvania State University - National Center for Atmospheric Research (PSU-NCAR) Mesoscale Model (MM5) version 3.6.3. Numerical simulations were performed at horizontal resolution of 27 km. According to obtained results, it seems that severe bora episodes may be related to tropopause fold events, where tropopause fold, i.e., upper-tropospheric potential vorticity anomaly accompanied with minimum relative humidity, tends to be west of Adriatic.

Adriatic; cut-off low; Dinaric Alps; MM5; potential vorticity anomaly; stratospheric intrusion

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