Multi-decadal modulations in the Aleutian-Icelandic Low seesaw and the axial symmetry of the Arctic Oscillation signature, as revealed in the 20th century reanalysis

Abstract

Seesaw relationship in intensity between the surface Aleutian and Icelandic Lows (AIS) is a manifestation of atmospheric teleconnection that bridges the interannual variability over the Pacific and Atlantic in particular winter months. Analysis of the 20th Century Reanalysis data reveals that the strength and timing of AIS have undergone multi-decadal modulations in conjunction with those in structure of the Arctic Oscillation (AO) signature, extracted in the leading mode of interannual sea-level pressure (SLP) variability over the extratropical Northern Hemisphere. Specifically, events of what may be called ‘pure AO’, in which SLP anomalies exhibit a high degree of axial symmetry in association with in-phase SLP variability between the midlatitude Atlantic and Pacific, tended to occur during multi-decadal periods in which the inter-basin teleconnection through AIS was active under the enhanced interannual variability of the Aleutian Low. In contrast, the axial symmetry of the AO pattern was apparently reduced during a multi-decadal period in which the AIS teleconnection was inactive under the weakened interannual variability of the Aleutian Low. In this period, the leading mode of interannual SLP variability represented a meridional seesaw between the Atlantic and Arctic, which resembles SLP anomaly pattern associated with the cold-ocean/warm-land (COWL) temperature pattern. These multi-decadal modulations in interannual AIS signal and the axial symmetry of the interannual AO pattern occurred under multi-decadal changes in the background state that also represented the polarity changes of the COWL-like anomaly pattern.

• multi-decadal modulations
• AIS
• AO

5. Acknowledgements

The authors are very grateful to the two anonymous reviewers for their sound criticism and useful suggestions that have led to substantial improvement of this paper. The authors are also grateful to K. Nishii and T. Miyasaka for their helpful comments. NS is supported jointly by the Chinese Natural Science Foundation (41105042 and 41375064) and the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD). HN is supported in part by the Japanese Ministry of Environment through the Environment Research and Technology Development Fund A1201 and by the Japan Society of Promotion of Science through a Grant-in-Aid for Scientific Research in Innovative Areas 2205. The NCAR Command Language (NCL) was used for the calculation and drawing the plots.

Notes

¹It should be noted that the contour interval in Fig. 1b is three times greater than in Fig. 1a.