The near-surface evening transition

摘要: Understanding of the evening boundary-layer transition has increased substantially in past few years although such progress led to new questions particularly regarding evolution wind field. Results from literature and analyses measurements three contrasting sites our study suggest that near-surface temperature begins with a late afternoon period slow cooling. Subsequent reversal upward heat flux downward is followed by rapid-cooling. This rapid cooling typically occurs over 60-90 min period, mostly before sunset, accounts for much total “nocturnal cooling”. The subsequently transitions into can last rest night. details varies between nights at given site. The fields during are coupled, but both characterized unique features. usually decelerates sometimes reaching temporary near-calm conditions. wind-directional shear close surface account most vector part transition. Even weak slopes generate local drainage flows eliminated formation regional flows. Our also examines other aspects do not necessarily fit this simple framework. For example, one site, an intermediate flow develops elimination larger-scale upslope cold air drainage.