Structure of temperature variability in the high latitudes of the Northern hemisphere

• Published in: Izvestiya, Atmospheric and Oceanic Physics
• Main Author: Semenov, Vladimir
• Format: Article in Journal/Newspaper
• Language: English
• Published: MAIK Nauka/Interperiodica 2007
• Subjects: Arctic; Global warming; North Atlantic; North Atlantic oscillation
• Online Access: https://oceanrep.geomar.de/id/eprint/7463/; https://oceanrep.geomar.de/id/eprint/7463/1/Semenov2007.pdf; https://doi.org/10.1134/S0001433807060023

The spatial structure of surface air temperature (SAT) anomalies in the extratropical latitudes of the Northern Hemisphere (NH) during the 20th century is studied from the data obtained over the period 1892–1999. The expansion of the mean (over the winter and summer periods) SAT anomalies into empirical orthogonal functions (EOFs) is used for analysis. It is shown that variations in the mean air temperature in the Arctic region (within the latitudes 60°–90°N) during both the winter and summer periods can be described with a high accuracy by two spatial orthogonal modes of variability. For the winter period, these are the EOF related to the leading mode of variability of large-scale atmospheric circulation in the NH, the North Atlantic Oscillation, and the spatially localized (in the Arctic) EOF, which describes the Arctic warming of the mid-20th century. The expansion coefficient of this EOF does not correlate with the indices of atmospheric circulation and is hypothetically related to variations in the area of the Arctic ice cover that are due to long-period variations in the influx of oceanic heat from the Atlantic. On the whole, a significantly weaker relation to the atmospheric circulation is characteristic of the summer period. The first leading variability mode describes a positive temperature trend of the past decades, which is hypothetically related to global warming, while the second leading EOF describes a long-period oscillation. On the whole, the results of analysis suggest a significant effect of natural climatic variability on air-temperature anomalies in the NH high latitudes and possible difficulties in isolating an anthropogenic component of climate changes.