A new perspective on surface wind speed variation with respect to the contribution of sea-land breezes

Wind is crucial to human society because it is closely related to energy supply, agricultural production and pollution dispersion. The surface wind speed (SWS) is dependent on the natural variability and the impact of urbanization. Over the coastal areas where nearly half of the world population live, sea land breezes (SLBs) are a common thermodynamic circulation that can affect SWS variation. However, few have distinguished coastal areas from inland areas to particularly investigate the SLB's contribution to SWS variation. This study investigates quantified contributions of both sea-breezing wind (SBW) and land-breezing wind (LBW) to SWS variation by extracting the SLB and the wind from synoptic-scale systems (synoptic wind) from the original long-term wind observation. The results show that there were no unified increasing or decreasing trends of SWS at coastal sites. Both synoptic wind and SLB contributed significantly to SWS variation at sites where both served as major components of local wind fields. However, among typical monsoon areas, synoptic wind remained mainly responsible for SWS variation. SLB contributed more than 82% to SWS variation among areas where SLB solely served as the major component of local wind fields. In contrast, the contribution of synoptic wind ranged from 2.7% to 17.2% for regions dominated by SLB, which was quadratically proportional to the local cloud fraction.