Impacts of Recirculation on Biosphere-Atmosphere Interactions over Complex Terrain

In conditions of low or moderate wind speed, large eddy structures – or recirculation bubbles – may form in the atmosphere over complex terrain. Recirculation bubbles were recently predicted by an analytical model (Wang and Yi, 2012), and a numerical model (Xu and Yi, 2012). We conducted an experiment using two nearby towers in Black Rock Forest, New York, to investigate the predicted phenomenon. Sensors were installed at five different levels on a tower at the top of a forested hill, and at five different levels at the middle of the eastern slope of the same hill. Each tower contained sensors both above and within the canopy measuring wind speed and direction, temperature, carbon dioxide, water vapor, atmospheric pressure, net radiation, ground heat flux and other key parameters. Sensors collected data from 20 April to 9 June, 2013. The energy flux balances at the tops of the hilltop and midslope towers were approximately 75% and 85% of closure, respectively, over the entire collection period. The formation of recirculation bubbles was observed to be dependent on wind speed and direction, terrain features, temperature gradients and prevailing synoptic conditions. We examine the contrast between biosphere-atmosphere interactions during typical, non-recirculating conditions and recirculation conditions.

Acknowledgement: This research was supported by NSF Grants ATM-0930015 and PSC-CUNY ENHC-44-83.