Changes of Icing Events in China under Global Warming and Related Large-scale Atmospheric and Oceanic Conditions

Using the high-quality daily observational data at 743 stations in China from 1954 to 2009, the secular change in the number of rime and glaze days in China was analyzed. The results show a significant decreasing trend, with larger reduction of rime days than glaze days under global warming. Such decreases are closely related to the increase in temperature and the decrease in relative humidity and wind speed in China. Further, 28 extensive and persistent rime events and 19 extensive and persistent glaze events were identified by an objective method. It is also found that the extensive and persistent rime and glaze events decrease significantly after the late 1980s, with few processes observed during the period from the early 1990s to the early 21st century. Composite analyses from the perspective of internal variability of atmosphere-ocean system indicate that rime and glaze events were accompanied by low temperature and high humidity. For glaze events, extratropical circulation anomalies such as the Ural Blocking High and the southward outbreak of cold air play a dominant role. It may likely occur more under the La Niña status than under the El Niño status. For rime events, strong transport of warm-moist airflows northward plays a leading role, and the blocking high and the outbreak of extratropical cold air take a supplementary role. The occurrence probability under the La Niña and El Niño background is nearly equal. Additionally, sea surface temperatures from the Indian Ocean to the northwestern Pacific also have a contribution.