Chinese Academy of Sciences
During March 13-16, 2021, an extremely strong dust storm struck Mongolia and northern China successively. When the dust storm reached central Inner Mongolia in the early morning of March 15, the gust speed reached up to 40 m s-1, which is equivalent to the intensity of a grade 12 typhoon.
This extreme dust-storm weather is caused by the rapid intensification and eastward movement of a Mongolian cyclone. Recently, a research team from the Institute of Atmospheric Physics, Chinese Academy of Sciences, revealed the development process and contributing factors of this powerful Mongolian cyclone from the perspective of high-frequency eddy energetics.
The results were published in Atmospheric and Oceanic Science Letters.
The Mongolian cyclone is often generated over the Mongolian Plateau in spring, but it is extremely rare for it to develop into a super-strong cyclone with typhoon intensity. The topography of the Mongolian Plateau alone is not the key reason for a Mongolian cyclone developing into a super cyclone, because the terrain remains unchanged, but the intensity of Mongolian cyclones varies from case to case.
"If the upstream upper-tropospheric disturbance that triggered the Mongolian cyclone had already been sufficiently strong when it approached the Mongolian Plateau, the combined effect of the Mongolian Plateau's topography and the downward transfer of eddy kinetic energy would have been favorable for the occurrence of a strong Mongolian cyclone in the lower troposphere," said Prof. Cholaw Bueh, first and corresponding author of the study.
If the anomalous state of the circulation at the interannual scale can also provide a more favorable background at this time in terms of available potential energy, the high-frequency disturbance will obtain more eddy available potential energy from the time-mean available potential energy such that the Mongolian cyclone will develop into an even stronger cyclone.
Becoming a super-strong Mongolian cyclone needs a favorable low-frequency background circulation condition as well. "During an intense development of the Mongolian cyclone, the high-frequency eddy also draws energy from the low-frequency available potential energy and strengthens further. The interaction between high- and low-frequency waves is also very important for the intensification of the Mongolian cyclone," said Dr. XIE Zuowei, a coauthor of the paper.
As has been noted, the development of the Mongolian cyclone into a super-strong cyclone requires various favorable conditions, including the intensity of the weather disturbance itself over the Mongolian Plateau, the interaction between the disturbance and the topography, the low-frequency background circulation, and the interannual anomalous circulation background.
"The subtle role of the Mongolian Plateau's topography has not yet been clearly revealed. The contributions of the topography to the downward transfer process of eddy kinetic energy and to the amplification of eddy available potential energy conversion from its background counterpart still need to be further revealed," said Dr. ZHUGE Anran, another coauthor of the paper.
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