Bunyard, Peter Paul; Hodnett, Martin; Poveda, Germán; Burgos Salcedo, Javier D; Peña, Carlos (2016): Condensation versus air density change as a major cause of airflow: experimental evidence, link to data files and videos [dataset]. PANGAEA, https://doi.org/10.1594/PANGAEA.863123,

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Supplement to: Bunyard, PP et al. (2015): Experimental evidence of condensation-driven airflow. Hydrology and Earth System Sciences Discussions, 12(10), 10921-10974, https://doi.org/10.5194/hessd-12-10921-2015

The dominant model of atmospheric circulation posits that hot air rises, creating horizontal winds. A second major driver has recently been proposed by Makarieva and Gorshkov in their biotic pump theory (BPT), which suggests that evapotranspiration from natural closed-canopy forests causes intense condensation, and hence winds from ocean to land. Critics of the BPT argue that air movement to fill the partial vacuum caused by condensation is always isotropic, and therefore causes no net air movement (Bunyard, 2015, hdl:11232/397).

This paper explores the physics of water condensation under mild atmospheric conditions, within a purpose-designed square-section 4.8 m-tall closed-system structure. Two enclosed vertical columns are connected at top and bottom by two horizontal tunnels, around which 19.5 m**3 of atmospheric air can circulate freely, allowing rotary airflows in either direction. This air can be cooled and/or warmed by refrigeration pipes and a heating mat, and changes in airflow, temperature, humidity and barometric pressure measured in real time.

The study investigates whether the "hot-air-rises" or an implosive condensation model can better explain the results of more than 100 experiments. The data show a highly significant correlation (R2 >0.96, p value <0.001) between observed airflows and partial pressure changes from condensation. While the kinetic energy of the refrigerated air falls short of that required in bringing about observed airflows by a factor of at least 30, less than a tenth of the potential kinetic energy from condensation is shown to be sufficient.

The assumption that condensation of water vapour is always isotropic is therefore incorrect. Condensation can be anisotropic, and in the laboratory does cause sustained airflow.