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Two-year oscillation of monsoon rainfall and global climate in the present decade
Debasis Sengupta, Arathy Menon
CAOS, Indian Institute of Science, Bangalore
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
TBO in Rainfall
Central India-Bay of Bengal (CI-BoB)
Wet: 1999, 2001, 2003, 2005
Dry: 2000, 2002, 2004
Are the recent biennial oscillations significant?
D(i)= R(i+1) – R(i) MD=1/N ∑ |D(i)|
TBO in SST
East Pacific SST does not have biennial oscillation.
Pacific SST: El Nino years with Indian monsoon drought minus El Ninoyears without drought (Krishnakumar et al., 2006, Science)
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
Arctic Oscillation
Thompson and Wallace (1998) GRL
http://www.jisao.washington.edu/wallace/
Northward shift of Atlantic ITCZ
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
Atlantic Meridional Mode (AMM)
No previous report of biennial Variability in AMM
From Kushnir et al., 2006
Tropical N. Atlantic winter SST: Evaporation changes in autumn (~10-15 W/m2). Insolation changes are ~3-5 W/m2.
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).
Models suggest that biennial variance of tropical climate increases as the earth warms (Nanjundiah et al. 2005 ASL) – are we seeing the first signs ?
TBO in Wind speed
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