Do Changes in the Midlatitude Circulation Have Any Impact on the Arctic Surface Air Temperature Trend?

Abstract

The warming of the near-surface air in the Arctic region has been larger than the global mean surface warming. There is general agreement that the Arctic amplification of the surface air temperature (SAT) trend to a considerable extent is due to local effects such as the retreat of sea ice, especially during the summer months, and earlier melting of snow in the spring season. There is no doubt that these processes are important causes of the Arctic SAT trend. It is less clear, however, whether the trend may also be related to recent changes in the atmospheric midlatitude circulation. This question is the focus of the present paper.Model experiments have shown that in a warmer climate responding to, for example, a doubling of CO 2 , the atmospheric northward energy transport (ANET) will increase and cause polar SAT amplification. In the present study, the development of the ANET across 60°N and its linkage to the Arctic SAT have been explored using the ERA-40 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF). It is found that during 1979-2001, the ANET has experienced an overall positive but weak trend, which was largest during the period from the mid-1980s to the mid-1990s. In addition, it is found that the Arctic SAT is sensitive to variability of the ANET across 60°N and hence to variability of the midlatitude circulation: A large ANET is followed by warming of the Arctic where ANET leads by about 5 days. The warming is located primarily north of the Atlantic and Pacific sectors, indicating that baroclinic weather systems developing around the Icelandic and Aleutian lows are important for the energy transport. Furthermore, it is suggested here that a small, but statistically significant, part of the mean Arctic SAT trend is linked to the trend in the ANET.Another important indicator of the midlatitude circulation is the Arctic Oscillation (AO). Through the 1980s and early 1990s the AO index has shown a positive trend. However, even though a part of the SAT trend can be related to the AO in localized parts of the Arctic area, the mean Arctic SAT trend shows no significant linkage to the AO.

Heat Transport Pathways into the Arctic and their Connections to Surface Air Temperatures

“…• N presented by Graversen (2006, Fig.4 b). The zonal mean long-term mean transport of H amounts to 1.66 GW.…”

“…We identified a positive temperature anomaly of about 3.0 K over Svalbard, which is about 2.4 K more than explained by the total atmospheric northward energy transport. Due to finding connected temperature fields for 10 distinct transport pathways, we are able to see all influences of the atmosphere under these specific pathways and not only the specific influence of the northward energy transport, which was analyzed by Graversen (2006).…”

An Arctic CCN-limited cloud-aerosol regime

“…While the local Arctic aerosol indirect effect may well be warming, the global effect is most likely cooling. And, as the Arctic climate tends to change roughly in concert with, but twice as fast as the global mean (Serreze and Francis, 2006), partly due to advection of heat and moisture from lower latitudes (Graversen, 2006), it remains an open question whether the total impact in the Arctic is dominated by the local surface warming, or the global cooling.…”

Arctic climate change in 21st century CMIP5 simulations with EC-Earth

“…The transports are estimated with a 6-h resolution from fields at model hybrid levels. For ERA-Interim a correction is applied to take into account transports associated with erroneous mass fluxes (Trenberth 1997;Graversen 2006;). EC-Earth and ERA-Interim are in a fairly good agreement at most high, northern latitudes.…”

“…The change in the atmospheric energy transport will likely affect the Arctic climate (Graversen 2006). The energy-divergence change over the Arctic will directly cause cooling or warming.…”