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![Page 1: Two-year oscillation of monsoon rainfall and global climate in the present decade Debasis Sengupta, Arathy Menon CAOS, Indian Institute of Science, Bangalore.](https://reader030.fdocuments.net/reader030/viewer/2022020417/56649f395503460f94c55cf9/html5/thumbnails/1.jpg)
Two-year oscillation of monsoon rainfall and global climate in the present decade
Debasis Sengupta, Arathy Menon
CAOS, Indian Institute of Science, Bangalore
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Data
TRMM 3B42 V6 daily 0.25⁰ rainfall 1998-2006
TRMM TMI daily 0.25⁰ SST 1998-2006
QuikSCAT/FSU daily 0.5 ⁰ wind 1999-2005
CPC monthly 0.5 ⁰ air temperature 1998-2006
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TBO in Rainfall
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Central India-Bay of Bengal (CI-BoB)
Wet: 1999, 2001, 2003, 2005
Dry: 2000, 2002, 2004
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Are the recent biennial oscillations significant?
D(i)= R(i+1) – R(i) MD=1/N ∑ |D(i)|
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TBO in SST
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East Pacific SST does not have biennial oscillation.
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Pacific SST: El Nino years with Indian monsoon drought minus El Ninoyears without drought (Krishnakumar et al., 2006, Science)
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Central Pacific SST (“El Nino Modoki” Ashok et al., 2007); Trans Nino Index (Krishnakumar et al., 2006) do not have significant biennial oscillation.
SOI does, but only in 2001-2006
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Arctic Oscillation
Thompson and Wallace (1998) GRL
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http://www.jisao.washington.edu/wallace/
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Northward shift of Atlantic ITCZ
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Atlantic ITCZ shifted north
ITCZ shift towards warmer hemisphere Kushnir et al. (2006) J. Clim.Broccoli et al. (2006) GRLWang et al., Chiang and Koutavas (2004) Nature
AMO: Warm North Atlantic, stronger Asian monsoon Goswami et al. (2006) GRLZhang and Delworth (2006) GRL
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Atlantic Meridional Mode (AMM)
No previous report of biennial Variability in AMM
From Kushnir et al., 2006
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Tropical N. Atlantic winter SST: Evaporation changes in autumn (~10-15 W/m2). Insolation changes are ~3-5 W/m2.
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ConclusionsModern observations show clear two-year oscillation in CI-BoB
and far West Pacific summer monsoon rain in 1999- 2005.2002 is a weak ENSO year, but East Pacific SST does not have a
two-year oscillation. Biennial oscillation (TBO) of monsoon is part of pervasive TBO
of global surface climate, including west Indian, west Pacific and tropical north Atlantic SST; the Arctic Oscillation; north Asia and north America surface air temperature.
Summer ITCZ over Bay of Bengal/India is intensified in the north. Atlantic and central Pacific winter ITCZ shifts north by ~2⁰ in years of warm northern hemisphere (tropical north Atlantic, north Eurasia and north America).
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Models suggest that biennial variance of tropical climate increases as the earth warms (Nanjundiah et al. 2005 ASL) – are we seeing the first signs ?
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TBO in Wind speed
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