The changing atmospheric water cycle in Polar Regions in a warmer climate

Abstract

We have examined the atmospheric water cycle of both Polar Regions, polewards of 60°N and 60°S, using the ERA‐Interim reanalysis and high‐resolution simulations with the ECHAM5 model for both the present and future climate based on the IPCC, A1B scenario. The annual precipitation in ERA‐Interim amounts to ∼17000 km3 and is more or less the same in the Arctic and the Antarctic, but it is composed differently. In the Arctic the annual evaporation is ∼8000 km3 but ∼3000 km3 less in the Antarctica where the net horizontal transport is correspondingly larger. The net water transport of the model is more intense than in ERA‐Interim, in the Arctic the difference is 2.5% and in the Antarctic it is 6.2%. Precipitation and net horizontal transport in the Arctic has a maximum in August and September. Evaporation peaks in June and July. The seasonal cycle is similar in Antarctica with the highest precipitation in the austral autumn. The largest net transport occurs at the end of the major extra‐tropical storm tracks in the Northern Hemisphere such as the eastern Pacific and eastern north Atlantic. The variability of the model is virtually identical to that of the re‐analysis and there are no changes in variability between the present climate and the climate at the end of the 21st century when normalized with the higher level of moisture. The changes from year to year are substantial with the 20‐ and 30‐year records being generally too short to identify robust trends in the hydrological cycle. In the A1B climate scenario the strength of the water cycle increases by some 25% in the Arctic and by 19% in the Antarctica, as measured by annual precipitation. The increase in the net horizontal transport is 29% and 22%, respectively, and the increase in evaporation correspondingly less. The net transport follows closely the Clausius–Clapeyron relation. There is a minor change in the annual cycle of the Arctic atmospheric water cycle with the maximum transport and precipitation occurring later in the year. There is a small imbalance of some 4–6% between the net transport and precipitation minus evaporation. We suggest that this is mainly due to the fact that the transport is calculated from instantaneous six hourly data while precipitation and evaporation is accumulated over a 6‐h period. The residual difference is proportionally similar for all experiments and hardly varies from year to year.

Physically Consistent Responses of the Global Atmospheric Hydrological Cycle in Models and Observations

“…O'Gorman et al 2012) and is central to the large-scale regional responses in precipitation. In the broadest sense, water is transported in the atmosphere by the tropical circulation from the dry, subtropical oceans (net moisture divergence) to the wet, moisture convergence zones, and also to the higher latitudes (e.g., Bengtsson et al 2011) and the continents (e.g., Trenberth et al 2011). Rising W with warming (Table 3) therefore indicates increased moisture flux (M F ).…”

Can an ensemble climate simulation be used to separate climate change signals from internal unforced variability?

“…A contributing factor is presumably the higher ocean temperatures in the northern Norwegian Sea and Barents Sea (Fig. 1a), associated with the receding sea ice, and the effect this has on the atmospheric heat transport into the Arctic (Bengtsson et al 2011).The variance in the winter Arctic circulation can be seen from the huge difference between maximum and minimum trends in the winter. (35-70)N, (10W-40E), 50-year trends (raw data) for three periods at the start, middle and end of the ensemble simulations for annual, DJF and JJA mean 2 m temperature, values in brackets indicate the ensemble member and p-value respectively.…”

The Changing Impact of Snow Conditions and Refreezing on the Mass Balance of an Idealized Svalbard Glacier

“…Additionally, precipitation in the Arctic has increased in recent decades in response to atmospheric moistening (Min et al, 2008;Zhang et al, 2012). Increases in both precipitation and temperature in the Arctic are projected to accelerate during the remainder of the twenty-first century (Bengtsson et al, 2011;Bintanja and Selten, 2014).…”