Quantification of the cold‐air pool in Kevo Valley, Finnish Lapland

Abstract

The ponding of cold air at low elevations is a major feature of the high-latitude climates of the Arctic, wherever low solar angles combine with incised topography. In Finnish Lapland this cold-air accumulation is critical for flora and fauna (Tenow and Nilssen, 1990; Virtanen et al., 1998) since absolute minimum temperatures control the survival of the eggs of the autumnal moth Epirrita autumnata. This moth is responsible for outbreaks of defoliation of the mountain birch Betula pubescens. Without cold-air accumulation there would be far more destructive outbreaks in the main inhabited areas. Added to the above concern is that of global warming. Warming is expected to be greater than the global average in the high latitudes (IPCC, 2007) and the temperature rise in winter in Finland over the twenty-first century is expected to be particularly large (Jylha et al., 2004). Current predictions made by the Intergovernmental Panel on Climate Change (IPCC) (2007) indicate a best estimate annual warming of around +5 degC for northern Finland by 2099 (~+7 degC in winter), as opposed to +3.2 degC for Europe as a whole (A1B scenario). If the enhancement of greenhouse gases in the atmosphere also alters the propensity for cold-pool formation, local increases in winter temperatures could be even more dramatic than the regional mean, with large consequences for forest damage, local ecology, and the formation/destruction of lake ice in autumn and spring. The cold pool is transient and its formation and destruction are controlled by synoptic conditions (atmospheric gradient winds and cloud cover/radiation balance) as well as the interaction with local topography. The research summarized in this paper comes from a pilot study which aimed to quantify the existence, temporal and spatial extent of the cold pool in Kevo Valley, northern Finland, through operation of an elevationaltransect of automatic temperature loggers.Future research is mapping the spatial extent of this cold pool in more detail, and examining the mechanisms behind its formation and destruction.