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Freezing Precipitation and Freezing Events over Northern Eurasia and North America

Name
Pavel
Surname
Groisman
Scientific organization
P.P. Shirshov Institute of Oceanology, RAS
Academic degree
Ph.D.
Position
Lead Scientist
Scientific discipline
Earth Sciences, Ecology & Environmental Management
Topic
Freezing Precipitation and Freezing Events over Northern Eurasia and North America
Abstract
The issue of near 0°C precipitation is linked with several hazardous phenomena including heavy snowfall/rainfall transition around °C; strong blizzards; rain-on-snow events causing floods; freezing rain and freezing drizzle; and ice load on infrastructure.
In our presentation using more than 1,500 long-term time series of synoptic observations for the past four decades, we present climatology and the empirical evidence about changes in occurrence, timing, and intensity of freezing events over most of the extratropics.
Keywords
freezing rain, freezing drizzle, precipitation
Summary

Near 0°C precipitation events are widespread and may represent/create natural hazards; their frequency and intensity are changing in contemporary climatic changes, and  these changes are not yet well understood and/or documented

Automation (where it was introduced) and temporal paucity (e.g., 3-h. versus 1-h. reports) affect the homogeneity of reporting of freezing events (especially, for freezing drizzle and intense freezing events).  Three-hourly reporting (e.g., in the Russian Federation) seriously underestimates the daily frequency of freezing events.

Using more than 1,500 long-term time series of synoptic observations for the past four decades, we present climatology and the empirical evidence about changes in occurrence, timing, and intensity of freezing rains and freezing drizzles America, most of Europe, Russia, Belarus, and Kyrgyzstan and their changes in the past decade.

The regions with the highest frequency of freezing rains (from 3 to 10 days per year) reside in the northeastern quadrant of the conterminous United States and adjacent areas of southeastern Canada south of 50°N, over the south and southwest parts of the Great East European Plain, and Central Europe. The frequency of freezing drizzle exceeds the frequency of freezing rain occurrence in all areas.  

During the last decade,  substantial changes in the annual freezing rain occurrence  were found:

– On the southern edge of our study domain (southeastern U.S., Central Europe, southern Russia) the frequencies of freezing events decreased along with the duration of the cold season;

–  In the Arctic (Norway, north of North America, some taiga areas in Russia) and at high elevations (The Tian Shan Mountains), they “followed” the expansion of the short warm season;

–  Changes in the occurrence of freezing drizzle were estimated only for Russia. We found a statistically significant nationwide decrease in this element.