On the Annual and Semi-Annual Components of Variations in Extent of Arctic and Antarctic Sea-Ice

• Published in: Geosciences
• Main Authors: Fernando Lopes, Vincent Courtillot, Dominique Gibert, Jean-Louis Le Mouël
• Format: Article in Journal/Newspaper
• Language: English
• Published: MDPI AG 2023
• Subjects: sea ice; seasonal forcing; Taylor–Couette flow; Geology; QE1-996.5; Antarctic; Arctic; Chandler; The Antarctic; Antarc*; Sea ice
• Online Access: https://doi.org/10.3390/geosciences13010021; https://doaj.org/article/d5a986a5a496498cbfa25bf5b7cf23eb

In this paper, the 1978–2022 series of northern (NHSI) and southern (SHSI) hemisphere sea ice extent are submitted to singular spectral analysis (SSA). The trends are quasi-linear, decreasing for NHSI (by 58,300 km <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>2</mn></msup></semantics></math> /yr) and increasing for SHSI (by 15,400 km <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msup><mrow></mrow><mn>2</mn></msup></semantics></math> /yr). The amplitude of annual variation in the Antarctic is double that in the Arctic. The semi-annual components are in quadrature. The first three oscillatory components of both NHSI and SHSI, at 1, 1/2, and 1/3 yr, account for more than 95% of the signal variance. The trends are respectively 21 (Antarctic) and 4 times (Arctic) less than the amplitudes of the annual components. We next analyze variations in pole position (PM for polar motion, coordinates <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>m</mi><mn>1</mn></msub></semantics></math> , <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><msub><mi>m</mi><mn>2</mn></msub></semantics></math> ) and length of day (lod). Whereas the SSA of the lod is dominated by the same first three components as sea ice, the SSA of the PM contains only the 1-yr forced annual oscillation and the Chandler 1.2-yr component. The 1-yr component of NHSI is in phase with that of the lod and in phase opposition with m 1 , while the reverse holds for the 1-yr component of SHSI. The semi-annual component appears in the lod and not in <math xmlns="http://www.w3.org/1998/Math/MathML" ...