Arctic dust determines ice formation in low clouds

July 7 () –

Dust from land without snow cover in the Arctic has been identified as a major source of particles that form ice crystals in low-lying clouds. during the summer and fall.

The formation of ice crystals in low clouds is considered to affect the weather because it can cause ice particles to grow at the expense of liquid droplets and then fall as precipitation, resulting in lower reflectance of sunlight and a shorter lifetime for clouds.

“The Arctic is said to be warming two to four times faster than the rate of global warming,” said Dr. Kei Kawai of Nagoya University, the study’s first author. “Given that the distribution and lifetime of low clouds affect climate, our finding could help improve predictions of climate change in the Arctic.” The researchers published their findings in Geophysical Research Letters.

Dust is made up of very small mineral particles of earth or sand. It acts as a nucleus for the formation of ice crystals in clouds. Although it is emitted primarily from arid regions at low or mid-latitudes, recent studies have shown that dust is also emitted from areas where there is no snow, ice, or vegetation in the Arctic. An earlier study suggested that arctic dust serves as an efficient nucleus for forming ice crystals. because it contains a small amount of organic matter that has a high ice nucleation capacity.

“In the Arctic, dust is mostly emitted from summer to early fall, when surface temperatures are high and snow cover is low,” Kawai said. “In this season, Arctic dust is distributed in the lower troposphere of the Arctic (below an altitude of about 3 km), where temperatures exceed -15 °C. In general, dust particles from a desert in Low or mid-latitudes cannot function efficiently as nuclei to form ice crystals at temperatures above -15°C. In contrast, Arctic dust particles can function as such nuclei between -20°C and -5°C due to their high ice nucleation capacity.”

However, until now, the significance of the high ice nucleation capacity of Arctic dust was unclear because it was not considered in any modeling studies.

To address this shortcoming, Associate Professor Hitoshi Matsui and Dr. Kawai of Nagoya University, in collaboration with Associate Professor Yutaka Tobo of the National Institute of Polar Research, conducted a study using the CAM-ATRAS global aerosol climate model. .

First, they incorporated into their model the recently observed high ice nucleation capacity of Arctic dust. They then compared simulations that considered this ability with simulations that did not.

The results showed that in simulations that considered this ability, Arctic dust efficiently acted as ice nucleators in the Arctic region. The simulations also closely replicated observations of nucleated ice particles at various locations in the Arctic. In contrast, in simulations that did not consider it, the Arctic dust hardly acted as ice nucleating particles.

The results also showed that the amount of dust ice nucleation particles from around the world in the Arctic lower troposphere during summer and autumn increased more than 100-fold considering the high dust ice nucleation capacity. of the arctic. Furthermore, almost all of the ice nucleation particles were found to be derived from Arctic dust.