Disturbances in the wind speed fields due to the Crimean Mountains

Abstract

Introduction . Influence of the Crimean Mountains on the wind regime in the Crimea region for different seasons and wind directions is considered. Data and methods . Data on the monthly average temperature values on the model levels of the ERA Interim reanalysis [10] for 40 years (1979–2018) and also the results of modeling using the regional numerical model of atmospheric circulation WRF-ARW are used. Results . The fields of surface wind speeds in the Crimea region are considered at the northern and southern directions of the background wind which are close to the normal one in relation to the ridge. Annual variation of buoyancy frequency for the flat regions of the Crimea Peninsula and for its Southern Coast separated from them by the Crimean Mountains is given. The periods of the most probable disturbances in the surface wind fields induced by the Crimean Mountains are revealed. Using the regional atmospheric circulation model WRF-ARW, the wind speed fields for a few typical directions of the background undisturbed wind are simulated. Discussion and conclusions. It is shown that in a spring-summer period (April–June) in the atmosphere over the sea, the conditions required to block the air flow from the south to the Crimean Mountains ridge arise. As a result, an alongshore flow is formed, and the mesoscale zone of speed perturbations springs up. At the northern winds, stable stratification in the boundary layer over the Crimea land areas is observed, on the average, throughout the whole year, except for four summer-autumn months (June–September); significant wind speed disturbances can also develop. However, they are of local character, i.e. concentrated directly near the mountain ridge and over the leeward slope where the velocity disturbances of a bora type are formed in a narrow coastal zone. Repeatability statistics of these two cases of the wind speed field perturbation caused by the mountains is assessed and considered. WRF-ARW model. Acknowledgments: t he investigation was carried within the framework of the state tasks on theme studies of the interaction processes in ocean-atmosphere system