A ‘low‐level’ explanation for the recent large warming trend over the western Antarctic Peninsula involving blocked winds and changes in zonal circulation

Abstract

We demonstrate a mechanism whereby the impact of stronger circumpolar westerly winds on the mountains of the Antarctic Peninsula contributes significantly to the enhanced warming trend observed over its western side in the last 50 years. Numerical and laboratory meteorological modelling demonstrate how, when westerly winds impinge on this side, warm air below the height (1.5–2.0 km) of the Peninsula is advected in a southerly direction. The strength of the annual mean westerly winds has increased by about 15–20% since the 1960s, while the modelling results indicate that contemporaneously the air advected to its western side originates from an increasingly northerly (and warmer) location. This gives rise to increased northerlies and a greater transport of warm air into this region. Consequently there is a reduction in the sea‐ice extent, further amplifying the local warming. This ‘low‐level’, orographic mechanism for the local climate trend is supported by observational evidence.