Preceding features and relationship with possible affecting factors of persistent and extensive icing events in China

As two major types of icing, rime and glaze, especially those with long persistency and extensive coverage, cause great economic and social damages for China. Based on 28 persistent and extensive rime events and 19 glaze events in China, this article examined their preceding features and relationship with large-scale climate factors. The results show that the pronounced preceding signals for these events include the Ural and Okhotsk blocking highs, major East Asian trough, cold air actives, southwesterly moisture transportation and upper-level jet stream. They intensify greatly 5-7 days ahead, indicating the forthcoming icing events and weaken significantly foretelling the ending of the events. Large-scale climate factors such as negative phase of the Arctic Oscillation, strong Siberian high, La Nina background and low sea surface temperature from the tropical Indian Ocean to the tropical western Pacific favour the occurrence of glaze events in China by intensifying the East Asian winter monsoon and exciting the southward outbreak of cold airs. In the meantime, deep wintertime semi-permanent trough in the southern branch of westerlies is crucial for the northward moisture transportation. However, only the low sea surface temperature from the tropical Indian Ocean to the tropical western Pacific and the deep wintertime semi-permanent trough in the southern branch of westerlies are significantly related to the occurrence of rime events in China. Although weak Australian low and strong western Pacific subtropical high also favour water vapour transportation, they are observed only during a small portion of icing events.