Rare phenomenon: Antarctica persists drizzle at temperatures below 0

Usually when the temperature drops below freezing, instead of rain, it will snow. However, for the first time in Antarctica, scientists have recorded persistent drizzle at temperatures below freezing.

Using both ground and satellite measurements, the researchers recorded drizzle below minus 13 degrees Fahrenheit (minus 25 degrees Celsius) lasting more than 7.5 hours at McMurdo Station, South Pole.

Mobile device for measuring atmospheric radiation (ARM) is deployed at McMurdo Station, Antarctica.

The researchers have published their findings in the Journal of Geophysical Research: Atmosphere. Previous reports have noted supercooling drizzle at these temperatures, but only for a short time. Drizzling for a few hours in Antarctica may have some impact on climate model predictions.

"Drizzle often happens in warm temperatures. At lower temperatures, drizzle occurs more often in warm temperatures," said Israel Silber, assistant professor of research at the Department of Meteorology and Atmosphere, Pennsylvania, USA . , ice formation and growth processes make the probability of drizzle production significantly lower. "

Data collected from laser measurements showed the presence of spherical water droplets, which could indicate they were drizzle drops. Analysis of this data combined with other ground and satellite measurements has confirmed that these particles are indeed drizzle drops.

Meteorologists define drizzle as droplets of water with a diameter of less than 0.5 mm, or about 1/5 inch . According to assistant professor Silber, drizzle and rain are interchangeable in climate models because both are in the liquid phase, compared to other forms of rain, such as snow and hail. The presence of prolonged drizzle in a very cold region like Antarctica is meant to improve the accuracy of climate models in the polar regions.

The laser resolution meter measures rainfall as it passes through to collect data at McMurdo Station.(Photo: Atmospheric radiation measurement unit (ARM) of the US Department of Energy).

"Drizzle removes water from the cloud when water droplets combine and eventually fall , " Silber said. "That means drizzle will affect the life of the cloud and affect the amount of heat reaching the Earth's surface."

The data collected in these observations is used in high-resolution model simulations of polar atmospheres. By simulating virtually all conditions that allow the cloud to form, the researchers were able to determine the parameters affecting drizzling production by adjusting other variables in the simulation.

Using the simulations, the researchers found that low concentrations of certain types of particles suspended in the earth's atmosphere, such as sea salt and dust, were very beneficial to the formation of drizzle.

"In Antarctica, the air is very clean," Silber said. "There are fewer pollutants and therefore fewer particles in the air."

The low concentration of these particles allows drizzle to be liquid, although the air temperature is below freezing, the scientist explained.