Abstract
Abstract. The behaviour and characteristics of the marine component of sea breeze cells have received little attention relative to their onshore counterparts. Yet there is a growing interest and dependence on the offshore wind climate from, for example, a wind energy perspective. Using idealized model experiments, we investigate the sea breeze circulation at scales which approximate to those of the southern North Sea, a region of major ongoing offshore wind farm development. We also contrast the scales and characteristics of the pure and the little known corkscrew and backdoor sea breeze types, where the type is pre-defined by the orientation of the synoptic scale flow relative to the shoreline. We find, crucially, that pure sea breezes, in contrast to corkscrew and backdoor types, can lead to substantial wind speed reductions offshore and that the addition of a second eastern coastline emphasises this effect through generation of offshore "calm zones". The offshore extent of all sea breeze types is found to be sensitive to both the influence of Coriolis acceleration and to the boundary layer scheme selected. These extents range, for example for a pure sea breeze produced in a 2 m s−1 offshore gradient wind, from 0 km to 21 km between the Mellor-Yamada-Nakanishi-Niino and the Yonsei State University schemes respectively. The corkscrew type restricts the development of a backdoor sea breeze on the opposite coast and is also capable of traversing a 100 km offshore domain even under high along-shore gradient wind speed (>15 m s−1) conditions. Realistic variations in sea surface skin temperature and initializing vertical thermodynamic profile do not significantly alter the resulting circulation, though the strengths of the simulated sea breezes are modulated if the effective land-sea thermal contrast is altered. We highlight how sea breeze impacts on circulation need to be considered in order to improve the accuracy of both assessments of the offshore wind energy climate and forecasts of wind energy output.
Highlights
The sea breeze has been documented in historical texts as early as ancient Greece and to date there have been as many as 1300 articles on the subject, making the sea breeze one of the most intensely studied meso-scale meteorological phenomena
Corkscrew sea breezes are stronger circulations than pure types and can be produced under gradient wind speeds which are too high for a pure type to establish (Table 3)
The combination of the offshore calm zone (10 m wind speed < 1 m s−1) and the offshore extent of the sea breeze extends to a greater distance with the Yonsei State University (YSU) PBL, reaching 90 km offshore from the western coast compared with maxima of 72 km for both the MYJ and MYNN schemes without Coriolis acceleration
Summary
The sea breeze has been documented in historical texts as early as ancient Greece and to date there have been as many as 1300 articles on the subject, making the sea breeze one of the most intensely studied meso-scale meteorological phenomena. The effect of a second coastline is an important detail that is under-studied; Savijarvi and Alestalo (1988) addressed this point but, even so, their primary focus remained on the inland component Their approach was to use a 2-dimensional mesoscale model to simulate sea breezes across a channel 80 km wide with SST, land surface temperature and roughness length variations representative of the Gulf of Finland. Both wind speed and direction were varied to examine the behaviour of the sea breeze in this situation. Three different boundary layer physics schemes are tested in order to assess the consistency of results in terms of timing, extent, duration and strength of the sea breeze
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