Perhaps the perfect ‘Essential Science’ feature for the winter, the formation of ice clouds. New information has allowed physicists to show how tiny particles attract water vapor and transform into ice crystals. When sufficient mass of crystals come together they form the core of the cloud. Eventually the familiar cirrus cloud forms.
Cirrus clouds appear in the sky as thin, wispy strands; white or light gray in color. The clouds are important signifiers of changing weather. When cirrus clouds arrive in advance of the frontal system, this indicates that weather conditions may soon deteriorate. While the clouds could signal the arrival of precipitation (rain), cirrus clouds only produce fall streaks (ice crystals that evaporate before landing on the ground).
The researchers successfully recreated the development of the ice cloud under laboratory conditions and used an especially equipped microscope to capture a series of images, documenting the cloud formation. In physics the process is termed “ice nucleation,” and the chemistry involved is complex.
Ice nucleation describes the phenomenon that occurs when water vapor from the air freezes and becomes ice quickly. Once formed, ice particles exert a significant effect on cloud dynamics. For instance, they can affect how some clouds can become electrified, leading to lightning; and such particles also form the seeds for rain droplets.
With clouds, the particles that form ice derive from mineral dust, volcanic ash, carbon-based material, soot, aircraft emissions and bacteria (active airborne bacteria are involved in the formation of rain and snow over several continents).
For the study, the research lab created a climate-controlled chamber, no bigger than a plant seed. This micro-device allowed the researchers to regulate climatic conditions, including temperature, pressure and relative humidity. The activities in the chamber were read using a scanning electron microscope. For the particles the researchers used the mineral kaolinite (a clay mineral, part of the group of industrial minerals. Kaolinite clay occurs in abundance in soils that have formed from the chemical weathering of rocks in hot, moist climates).
The research found that key variables were low temperatures, high altitudes and a high relative humidity. These conditions are needed for the particle to attract surrounding water vapor. A further influencing factor is the size, texture, shape of the particles. Most particles are around two micronmeters in size. The results were observed through the assembled images, with pictures being taken every three seconds.
The reason for the research was to understand more about cloud formation, given the significant influence clouds have over the Earth’s climate. Clouds, for example, help to cool the planet by reflecting away the rays of the sun; conversely, they help to warm the surface by absorbing radiation generated from the Earth’s surface.
Professor Bingbing Wang, who led the study at the Environmental Molecular Sciences Laboratory at the Department of Energy’s Pacific Northwest National Laboratory, explains to Laboratory Manager magazine: “This [ice nucleation] is one of the most critical but least understood parts of the process of how cold clouds form. The fundamental process of how ice grows is relatively well understood, but ice nucleation — that moment when the first group of molecules comes together — remains a big challenge.”
The findings are published in the journal Physical Chemistry Chemistry Physics, with the paper titled “Direct observation of ice nucleation events on individual atmospheric particles.”
This article is part of Digital Journal’s regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week we examined how nanotechnology is being used to tackle the most resistant types of breast cancer tumours. The week before we discussed the detection of a new, mysterious valley on the surface of the planet Mercury.
