An analysis of static stability in the Arctic atmosphere

A general indication of atmospheric instability is the observation of air-mass thunderstorms. In the Arctic, interest in changes to atmospheric stability is motivated in part by a large number of studies using indigenous or traditional knowledge which indicate an increase in the frequency and/or severity of thunderstorms and lightning. In many cases, interviews with native elders indicate the recent occurrence of thunderstorms in locations where few or none had been observed previously. Additional motivation is drawn from the study of the interannual variability of wintertime atmospheric phenomena. By definition, the quantity of energy preventing convection, or energy of inhibition (CINE), is a proxy for the pervasive near-surface polar temperature inversion. Recent studies have shown trends towards warmer wintertime near-surface temperatures over Northern Hemisphere high latitude land surfaces over the last 35 years. The implications of these near-surface trends on the total atmospheric column are not clear, however. Prior studies of the Arctic atmosphere from a classical stability analysis perspective are rare. In this study, estimates of convective available potential energy (CAPE) and the energy of convective inhibition are made for available Arctic sounding data. On interannual time scales, computations suggest the atmosphere over the Siberian Arctic has become more stable in winter and less stable in summer. The wintertime increase in CINE is manifest as a step change occurring in the early 1970s that is concurrent with atmospheric circulation changes in the location and intensity of the Siberian high. In the summer, sounding locations experiencing critical values of CAPE suggesting thunderstorm activity are preferentially located along the Arctic front zone. There are no discernible trends in the frequency of large CAPE, however the frequency of small CAPE values in July increases steadily from the 1960s until the present. Layer stability analysis is used to further illuminate the mechanisms involved in these changes.