A ONCE-CONTROVERSIAL THEORY

While the prevailing view is that winds are determined by temperature gradients, Anastassia, Victor and others, including myself, have advanced a theory describing how evaporation and condensation influence atmospheric dynamics.

While this theory was once viewed as controversial, accumulating understanding and evidence mean that it is gaining acceptance.

One important insight from this theory is that areas that sustain high rates of rainfall, such as forests and cyclones, also generate low surface-level atmospheric pressure that draws in surrounding low-level air and any water vapor it contains, which converges and rises, leading to condensation of any moisture it contains, feeding further pressure drops and resulting in a positive feedback that can be sustained as long as moist air is available. This mechanism explains how both forests and cyclones capture and concentrate such high levels of rain.

A growing body of evidence

Conventional atmospheric science assumes that the change in particle densities that occurs as water evaporates and condenses is largely irrelevant to understanding winds, as the key large-scale pressure differences are dominated by temperature. Our work indicates that this neglect is unjustified and that the change in molecule numbers during evaporation and condensation is a major mechanism shaping wind patterns and atmospheric moisture transport.The physical details of the theory and its implications have been published in peer-reviewed physics journals (1,2,3) and atmospheric science journals (4,5,6,7) and a compilation of relevant publications can be found (8,9,10). In advancing these ideas we have described failings in the temperature-driven theory of winds (11) and revised the fundamental equations governing atmospheric dynamics (12). Conventional atmospheric science assumes that the change in particle densities that occurs as water evaporates and condenses is largely irrelevant to understanding winds, as the key large-scale pressure differences are dominated by temperature. Our work indicates that this neglect is unjustified and that the change in molecule numbers during evaporation and condensation is a major mechanism shaping wind patterns and atmospheric moisture transport.The physical details of the theory and its implications have been published in peer-reviewed physics journalsand atmospheric science journalsand a compilation of relevant publications can be found here . We have developed introductions and summaries for non-specialists too. In advancing these ideas we have described failings in the temperature-driven theory of windsand revised the fundamental equations governing atmospheric dynamics

The proposed physical mechanisms are consistent with energetic and thermodynamic laws. Water vapor provides a source of energy, a substantial fraction of which can accelerate air when the vapor condenses, thus causing winds (this process can be further encouraged by aerosols—that is, by particles and compounds released from the forest into the atmosphere). This theory explains how high rainfall can be maintained within continental interiors and how cyclones, by concentrating so much available energy, can be so powerful.

Is there evidence for these ideas? Yes. For example, the theory predicts that rainfall over actively transpiring forests will be more likely when more moisture has locally accumulated, suggesting that there will be a positive difference in local atmospheric pressure prior to rain (when the difference switches to negative). This has been observed in long-term data from many sites in the Amazon, and is absent from neighboring, less forested regions.

Furthermore, if the maintenance of high rainfall in continental interiors is dependent on actively transpiring forests, it should disappear each winter over Siberia. Again, this prediction matches observations.

We can claim various other achievements, too. For example, if we estimate the global rate at which the kinetic energy of winds is generated (atmospheric power) we find that this also matches our theoretical predictions.