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Two-year oscillation of monsoon rainfall and global climate in the present decade

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 0.25 ⁰ rainfall 1998-2006 TRMM TMI daily 0.25 ⁰ SST 1998-2006

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Two-year oscillation of monsoon rainfall and global climate in the present decade

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  1. Two-year oscillation of monsoon rainfall and global climate in the present decade Debasis Sengupta, Arathy Menon CAOS, Indian Institute of Science, Bangalore

  2. 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

  3. TBO in Rainfall

  4. Wet: 1999, 2001, 2003, 2005 Dry: 2000, 2002, 2004 Central India-Bay of Bengal (CI-BoB)

  5. Are the recent biennial oscillations significant? D(i)= R(i+1) – R(i) MD=1/N ∑ |D(i)|

  6. TBO in SST

  7. East Pacific SST does not have biennial oscillation.

  8. Pacific SST: El Nino years with Indian monsoon drought minus El Nino years without drought (Krishnakumar et al., 2006, Science)

  9. 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

  10. Arctic Oscillation Thompson and Wallace (1998) GRL

  11. http://www.jisao.washington.edu/wallace/

  12. Northward shift of Atlantic ITCZ

  13. Atlantic ITCZ shifted north ITCZ shift towards warmer hemisphere Kushnir et al. (2006) J. Clim. Broccoli et al. (2006) GRL Wang et al., Chiang and Koutavas (2004) Nature AMO: Warm North Atlantic, stronger Asian monsoon Goswami et al. (2006) GRL Zhang and Delworth (2006) GRL

  14. Atlantic Meridional Mode (AMM) No previous report of biennial Variability in AMM From Kushnir et al., 2006

  15. Tropical N. Atlantic winter SST: Evaporation changes in autumn (~10-15 W/m2). Insolation changes are ~3-5 W/m2.

  16. Conclusions • Modern 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).

  17. Models suggest that biennial variance of tropical climate increases as the earth warms (Nanjundiah et al. 2005 ASL) – are we seeing the first signs ?

  18. TBO in Wind speed

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