Abstract
Daily precipitation data from the European Centre for Medium-Range Weather Forecasts (ERA-Interim) from 1979 to 2016 are analyzed to determine the trends in seasonal and extreme precipitation across the pan-Arctic and estimate the contributions to the trends from the dynamic (e.g., changes in circulation patterns) and thermodynamic processes (e.g., sea ice melt–water vapor feedback) and their interactions. The trends in the seasonal total precipitation are generally consistent with the trends in the occurrence of seasonal extreme precipitation. Although the trends vary considerably in direction and magnitude across the pan-Arctic and the seasons, more regions experience a statistically significant positive trend than negative trend, particularly in autumn and winter seasons and over areas of the Arctic Ocean and the northern North Atlantic. Statistically significant negative trends are mostly found in areas of northern Eurasian and North America. The thermodynamic processes account for more than 85% of the total trends, with the rest of the trends explained by the dynamic processes (e.g., changes in circulation patterns) and the interaction between dynamic and thermodynamic processes.
Highlights
Precipitation is a crucial component of the Arctic freshwater budget that influences, among other things, North Atlantic deep-water formation and global thermohaline circulation (Walsh et al 1998)
The increase in local evaporation associated with sea ice loss in the past two decades has contributed to an increase in Arctic sourced moisture at a rate of 18.2±4.6% and 10.8±3.6% per 100,000 km2 sea ice loss in the Canadian Arctic and Greenland Sea regions, respectively (Kopec et al 2016), and more moisture in the atmosphere has contributed to enhanced precipitation and to amplification of water vapor-cloud-radiation feedback that has in term reinforced Arctic warming (Cai 2005)
4 Conclusions and discussions In this study, daily precipitation data from 1979 through 2016 are utilized to examine Arctic precipitation, focusing on the trends in the seasonal precipitation and the number of days of extreme precipitation defined as daily precipitation amount exceeding the 95th percentile of the daily precipitation in a season over the study period
Summary
Precipitation is a crucial component of the Arctic freshwater budget that influences, among other things, North Atlantic deep-water formation and global thermohaline circulation (Walsh et al 1998). Over most of the Arctic land, both observations (Hanssen-Bauer and Førland 1998; Berner et al 2005; Khon et al 2007) and climate model simulations (Kattsov and Walsh 2000; Kattsov et al 2007) revealed an increasing trend in precipitation, in winter season, in the later part of the 20th century, but an opposite trend was found for the annual snow amount and total number of snow days for the 1979-2009 period (Liston and Hiemstra 2011) These trends have been attributed to anthropogenic influences (Min et al 2008) and an increase in local moisture source from evaporations of ice-free ocean surfaces as well as moisture transport by atmospheric circulations (Ghatak et al 2012; Park et al 2013; Kopec et al 2016). We apply the Self-Organizing Map (SOM) method (Kohonen 2001) to explain the trends by means of dynamic and thermodynamic contributions and the contribution from their interactions
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