EGU2020-1796, updated on 12 Jun 2020
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Mode-Decomposed Equation Diagnosis for Atmospheric Blocking Development

Masaru Inatsu1, Takuya Aikawa2, and Naoto Nakano3
Masaru Inatsu et al.
  • 1Hokkaido University, Faculty of Science, Department of Earth and Planetary Science, Japan (
  • 2Japan Meteorological Agency
  • 3Institute for Liberal Arts and Sciences, Kyoto University

This paper proposes a new method to identify atmospheric blocking development without the time filtering used in previous studies. A mode-decomposed vorticity equation is formulated from the principal components (PCs) of 500-hPa geopotential height by applying a new idea; the orthonormality of PCs allows any variable to be decomposed into a projection corresponding to the PCs. To test this, sectorial blocking episodes in Northern Hemisphere winter were identified by Barriopedro’s method. A blocking index was defined for each longitudinal range as the linear combination of the 10 largest PCs by means of the composite for the blocking episodes. Blocking development was diagnosed, in terms of the low modes of PC1–PC10 and the high modes of PC11–PC50. The results suggest that the intensification of blocking over the North Pacific and Eurasia is associated with nonlinear interaction among high modes, whereas the intensification (decay) of North Atlantic blocks is related mainly to enhanced nonlinear interaction among low-frequency (high-frequency) eddies. This main result is insensitive to the choice of definition for blocks and the choice of the mode separation boundary.

How to cite: Inatsu, M., Aikawa, T., and Nakano, N.: Mode-Decomposed Equation Diagnosis for Atmospheric Blocking Development, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1796,, 2019

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