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Article Dans Une Revue Journal of Climate Année : 1995

Space/Time structure of monsoon interannual variability

Résumé

The analysis of corrected ship reports [sea level pressure (SLP), sea surface temperature (SST), air temperature (AT)] and corrected land data (SLP, AT, rainfall) in the Indian sector reveals the existence of two low-frequency modes of monsoon variability during the 1900-1970 period. - A definite biennial (B) mode exists on the SLP fields. This B oscillation is unambiguously linked with a southwest-northeast SLP anomaly gradient. During the summer monsoon, the B SLP pattern can be interpreted as an expansion/contraction of the monsoon activity since this mode is strongly coupled with rainfall variations over peninsular India. - A strong low-frequency (LF) mode with period spanning 4-6 years is also seen on SLP fields over the Indian Ocean and subcontinent. The variance associated with this band is typically more important than the one observed for the B mode, and its spatial mark is also strikingly different since it is linked with a global pattern of variation. This mode has also a strong influence on the Indian summer rainfall fluctuations, particularly on the Ghats and in the Indo-Gangetic plains. The amplitude of these oscillations varies widely during the 1900-1970 period. The LF mode is well defined during 1900-1923 and 1947-1970. There is a tendency for the energy associated with the B mode to decrease on the land while it increases over the Indian Ocean during the whole 1900-1970 interval. Although these two timescales exist also on SST fields, cross-spectral analysis shows that ocean-atmosphere interactions are much stronger at the B timescale. This result stresses the B nature of the monsoon system. The existence of these interannual signals in the Indian areas where the annual cycle is so strong raises difficult problems : How can climatic anomalies persist for several years in spite of strong seasonality ? Or, still more intriguing, how can be explained the persistence of climatic anomalies during one year and the appearance of opposite sign climatic anomalies in the following year for the B mode ? A composite analysis has suggested an explanation for this last problem : SST anomalies produced by exceptional summer monsoons can indeed persist during the whole winter and exert an influence on the next summer monsoon.
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hal-01336304 , version 1 (04-02-2021)

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Pascal Terray. Space/Time structure of monsoon interannual variability. Journal of Climate, 1995, 8 (11), pp.2595-2619. ⟨10.1175/1520-0442(1995)008<2595:STSOMI>2.0.CO;2⟩. ⟨hal-01336304⟩
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