Amphidromic Lines in the Atmosphere: An Example of Global Pressure Field Annual Harmonic

• Main Authors: Enjin Zhao, Lin Mu, Haoyu Jiang
• Format: Article
• Language: English
• Published: American Geophysical Union (AGU) 2021-04-01
• Series: Earth and Space Science
• Online Access: https://doi.org/10.1029/2021EA001638

Abstract Amphidrome refers to an oceanic point where the amplitude of one harmonic constituent of the tidal system is zero, and the phase of the harmonic constituent is undetermined. The concept of amphidrome can also be used in climatological studies because of the existence of annual amphidromes, points of zero amplitude, and ill‐defined phase of annual cycle. This study investigated the global atmospheric geopotential height from the ERA‐interim to identify annual amphidromes at different isobaric altitudes. Many well‐defined annual amphidromes were identified. These amphidromic points appear always as twins with different rotating directions with respect to phases. This phenomenon can be explained mathematically with the basic theory of spherical algebraic topology, suggesting amphidrome twins as a common feature for periodic variables in the atmosphere. Due to the spatial continuity of atmospheric parameters, amphidromes at different isobaric altitudes can be concatenated into amphidromic lines. Amphidromic lines have a three‐dimensional structure with both clockwise and anticlockwise vertical branches connected by one or two horizontal components. Particularly, some amphidromic lines in the atmosphere can be closed loops when they are connected by two horizontal components. The rotary phases around the amphidromic loops are similar to the magnetic induction lines around a closed electromagnetic coil.