Abstract
abstractWintertime cold outbreaks were studied via a 2-D numerical model set across an 80 km wide non-frozen sea gulf along 60°N (‘Gulf of Finland’). In calm conditions, land breezes develop over both coasts with relatively large along-shore wind components. The mid-gulf convergence of the colliding land breezes leads to a moderate rising motion at about 600 m height, forcing bands of low cloud and snowfall along the gulf, whereas the near-surface horizontal wind shear may induce ‘mini-hurricanes’. A weak large-scale cold outbreak across the gulf distorts the land breeze cells, damping the rising motion, whereas a moderate cross-coast outbreak modifies them into a typical heat island circulation pattern with only a modest rising motion over a flat windward shore. A cold outbreak along the non-frozen gulf leads to strong heat transfer from the sea. This maintains the embedded coastal land breeze circulations that contribute to a double low-level jet structure. The strongest rising motion was obtained for surface winds blowing along the gulf. It is suggested that the Swedish Gävle snowstorm of December 1998 was such a case.
Highlights
Cold air outbreaks are quite common over the Baltic Sea area in the autumn and in winter
Once over the cold windward coast, the winds quickly return to the quasi-Ekman profile of a very stable and shallow boundary layer (BL), indicating weak surface winds and large cross-isobar angles and displaying no signs of the onshore coast land breeze cell, which is still recognizable from Fig. 2
Figs. 1Á3 nicely demonstrate the transition from a pure land breeze circulation (Fig. 1) to the steady heat island circulation induced by a weak (Fig. 2) and a moderate (Fig. 3) constant basic flow across a warm zone
Summary
Cold air outbreaks are quite common over the Baltic Sea area in the autumn and in winter. In the relatively narrow Gulf of Finland, cold outbreaks are associated with large coastal gradients in the wind speed and air temperature, and bands of intense snowfall are common. Their prediction and understanding is important as these showers may cause serious problems, for example for the coastal road, train and aircraft traffic. A more general treatise of cold outbreaks over a high-latitude non-frozen sea gulf has been lacking. It is the subject of this article.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
