Mode-Decomposed Equation Diagnosis for Atmospheric Blocking Development

Author:

Aikawa Takuya1,Inatsu Masaru2,Nakano Naoto3,Iwano Tetsuya4

Affiliation:

1. Japan Meteorological Agency, Tokyo, Japan

2. Faculty of Science, and Research Institute for Electronic Science, and Center for Natural Hazards Research, Hokkaido University, Sapporo, Japan

3. Institute for Liberal Arts and Sciences, Kyoto University, Kyoto, Japan

4. Graduate School of Science, Hokkaido University, Sapporo, Japan

Abstract

Abstract 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.

Funder

Japan Society for the Promotion of Science

Precursory Research for Embryonic Science and Technology

Japan Society for the Promotion of Science London

Environment Research and Technology Development Fund

Publisher

American Meteorological Society

Subject

Atmospheric Science

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