Trends of Vertically Integrated Water Vapor over the Arctic during 1979–2016: Consistent Moistening All Over?

Abstract

Arctic trends of integrated water vapor were analyzed based on four reanalyses and radiosonde data over 1979–2016. Averaged over the region north of 70°N, the Arctic experiences a robust moistening trend that is smallest in March (0.07 ± 0.06 mm decade−1) and largest in August (0.33 ± 0.18 mm decade−1), according to the reanalyses’ median and over the 38 years. While the absolute trends are largest in summer, the relative ones are largest in winter. Superimposed on the trend is a pronounced interannual variability. Analyzing overlapping 30-yr subsets of the entire period, the maximum trend has shifted toward autumn (September–October), which is related to an accelerated trend over the Barents and Kara Seas. The spatial trend patterns suggest that the Arctic has become wetter overall, but the trends and their statistical significance vary depending on the region and season, and drying even occurs over a few regions. Although the reanalyses are consistent in their spatiotemporal trend patterns, they substantially disagree on the trend magnitudes. The summer and the Nordic and Barents Seas, the central Arctic Ocean, and north-central Siberia are the season and regions of greatest differences among the reanalyses. We discussed various factors that contribute to the differences, in particular, varying sea level pressure trends, which lead to regional differences in moisture transport, evaporation trends, and differences in data assimilation. The trends from the reanalyses show a close agreement with the radiosonde data in terms of spatiotemporal patterns. However, the scarce and nonuniform distribution of the stations hampers the assessment of central Arctic trends.

A systematic assessment of water vapor products in the Arctic: from instantaneous measurements to monthly means

“…Radiosondes launched at only few stations are still considered as the best climatological record to assess trends although depending on the used radiosonde type at each station issues about their uncertainty exist. From their limited data record as well as from global reanalyses only few regions and seasons with robust IWV trends can be derived (Rinke et al, 2019). With the emergence of new satellite series providing already decade long data as well as high resolved reanalysis (ERA5) there is hope for a better assessment of Arctic IWV changes.…”

“…The same four modern global atmospheric reanalyses as in Rinke et al (2019) 2017). Due to the lack of any reference data and in order to compare with Rinke et al (2009), the median of the four reanalyses is taken as reference.…”

“…Despite its importance, the Arctic suffers from a lack of reliable water vapor measurements due to the limited amount of surface stations. Thus, studies aiming at the detection of changes in the water vapor distribution mainly make use of reanalyses and radiosondes (e.g., Serreze et al, 2012;Dufour et al, 2016;Rinke et al, 2019). The latter are limited to land areas and concentrated in northern America and Europe.…”

“…When looking at IWV variability around the globe, Schröder et al (2016) found the highest relative standard deviation (STD) between long-term data sets in the polar regions. Thus, it is no surprise that still strong discrepancies about pattern and magnitude of water vapor trends in the Arctic exist (Rinke et al, 2019).…”

Diurnal variability of the planetary boundary layer height estimated from radiosonde data

“…The increases of daytime PBLH may be associated with the increases of near‐surface temperature and decreases of near‐surface relative humidity. However, according to the previous literatures (Bates and Jackson, 2001; Santer et al, 2014; Rinke et al, 2019), the trends in the tropospheric temperature and humidity might be different at regional scale. In addition, the increase of greenhouse gases and soil moisture heterogeneity might also be contributing to the observed increasing trend.…”