At first glance it may seem that a desert has no life, beyond the fact that the dunes grow and move. However, the results of decades-long research show how water vapor penetrates the dust and grains of desert sand .
“The wind flows over the dune and as a result creates local pressure imbalances, which literally forces air into and out of the sand. So the sand breathes, like an organism does,” explains Michel Louge, lead author of the study and professor of mechanical and aerospace engineering at Cornell University in the United States.
This kind of respiration is what allows microbes to exist in the depths of the hyper-arid dunes, despite the high temperatures. For much of the last decade, Professor Louge has collaborated with Anthony Hay, associate professor of microbiology at Cornell, to study how microbes can help stabilize dunes and prevent them from reaching roads and invading infrastructure.
Louge and his team also determined that desert surfaces exchange less moisture with the atmosphere than expected, and that the evaporation of water from individual sand grains behaves like a slow chemical reaction.
The study that has been recently published in the Journal of Geophysical Research-Earth Surface is the result of work that has lasted decades. It all begins when Michael Louge seeks to better understand the process by which farmland turns into desert , an interest that has become more urgent with the rise of global climate change. To understand the process, Louge had to be able to measure the moisture content of the sand dunes.
With the idea of measuring matter with greater sensitivity, the professor developed a new instrument called capacitance probes , which use multiple sensors to record everything from solids concentration to velocity and water content, all with fine resolution. unprecedented space. The probe ended up revealing how porous the sand is, through which a small amount of air seeps. Other previous investigations had suggested that this type of filtration occurred in the dunes, but such a thing had not been proven. Until now.
According to Louge, the wind that blows through the dune generates imbalances in the local pressure that causes the air to enter the sand and then leave, producing a kind of respiration.
The bulk of the data used in the research was collected in 2011, but it took Louge and his collaborators another decade to make sense of some of the findings, such as the identification of surface-level disturbances that force evanescent waves , or non-linear, moisture to spread down very quickly through the dunes.
The researchers anticipate that their probe will have various applications , from studying how soils absorb or drain water in agriculture, to calibrating satellite observations over deserts, to exploring extraterrestrial environments that may contain traces of water. It would not be the first time that Louge’s research reaches space.
But perhaps the most immediate application is the detection of moisture contamination in pharmaceutical products. Since 2018, Louge has been collaborating with a pharmaceutical company to use the probes in continuous manufacturing, which is seen as faster, more efficient, and less expensive than batch manufacturing.
The research was supported by the Qatar Foundation.
Louge et. al. 2022. Water vapor transport across an arid sand surface – non-linear thermal coupling, wind-driven pore advection, subsurface waves, and exchange with the atmospheric boundary layer. Journal of Geophysical Research-Earth Surface. DOI: 10.1029/2021JF006490