Climate of the polar realms - The Global Climate System: Patterns, Processes, and Teleconnections - page 154

ice is present year-round, consisting typically of thick ( 3m), multi-year ice.
This sea ice is in steady movement, and through dynamical actions, pressure
ridges and leads (polynyas) are formed. Open water or thin ice that might be
present in winter is much, much warmer than the atmosphere, and the heat
transfer from the ocean to the atmosphere can be large, warming the atmo-
sphere somewhat. In contrast to this, the energy transfer from snow-covered
soil is small. Hence, it is not surprising that the lowest recorded temperature
of 67.8 8C was measured in Verkhoyansk, Eastern Siberia, where we find a
very continental climate, with very low winter temperatures and relatively
warm summer temperatures, resulting in a large annual variation in tempera-
ture. The minimum in winter is fairly flat, and any of several winter months for
a specific year might record the coldest temperature, a so-called ''coreless''
winter, which is however less pronounced than in Antarctica. Conrad (K¨ppen
1936 ) used Verkhoyansk for defining his continentality index, giving it the
value of 100%, while giving Tromsø, on the subarctic Norwegian coast, where
the annual variation in temperature is very small, the value of 0% (maritime
climate). There are large variations in mean annual temperatures of the Arctic
region (Figure 5.10a ). Murmansk (698 N) in Russia is a year-round ice-free
port with a mean temperature of 0 8C, very warm as it is still influenced by the
Gulf Stream. The mean annual temperatures are between 10 and 20 8C for
other coastal stations not influenced by the Gulf Stream as well as for the
Arctic Ocean, while the crest of Greenland records values around 27 8C; this
cold temperature is the additional effect of altitude. In Table 5.3 temperature
values for selected stations in the Arctic are presented.
Further, surface temperature inversions are frequent in the Arctic, espe-
cially in winter, at which time they are semi-permanent. They are especially
strong in sheltered valleys, as the wind aloft cannot penetrate to the surface. In
contrast to this, they are less strong over the central Arctic, where the wind
aloft may destroy them through forced mixing, especially as the surface
roughness is low and not hindered by any topography. This might be an
additional reason for the relatively benign winter temperatures at the Pole.
In general, temperatures have increased in the Arctic, and the increase has
been larger than the worldwide average, which is about 0.6 8C for the last
century (Jones 1995 ). This enhancement in temperature increase for the polar
region was expected and has also been observed for Antarctica. However, the
rate of increase is not at all uniform over the past century, a result that would
have been expected if it were solely caused by the increasing amount of CO 2
and other trace gases in the atmosphere. Further, the observed temperature
increases vary strongly not only in time, but also from place to place
(Chapman and Walsh 1993 ; Frey and Smith 2003 ; Whitfield et al. 2004 ).
Very large changes in temperature sometimes reported in the literature hold
true only for a specific place and time period, and are not valid for the Arctic