Indian Ocean Dipole - ENSO - monsoon connections and Overcoming coupled model systematic errors

Transcription

1 Indian Ocean Dipole - ENSO - monsoon connections and Overcoming coupled model systematic errors Hilary Spencer, Rowan Sutton and Julia Slingo CGAM, Reading University h.spencer@reading.ac.uk

2 Monsoon - ENSO - Indian Ocean dipole All Indian rainfall versus Niño 3.4 Slingo and Annamalai, MWR 2000 Annamalai and Liu, QJ, in press Ashok, Guan and Yamagata, GRL, 2001 Loschnigg et al, J. Clim, 2003 Meehl and Arblaster, J. Clim, 2003 All Indian rainfall from Indian Institute of tropical Meteorology HadISST (Rayner et al, 2003) overlapping years, Correlation of AIR with SST with linear regression with Niño 3.4 removed normalised JJAS AIR anomaly normalised JJAS Nino 3.4 anomaly colour: dipole index strength N 4 S 9 E 18 E 9 W El Nino weak correlation Dipole?? Weak Monsoon Strong Monsoon h.spencer@reading.ac.uk 2

3 Modelling Indian Ocean Variability and Teleconnections Challenges for coupled models: Realistic mean state and variabilty Realistic teleconnections Can coupled model biases be corrected? Heat flux correction? Wind stress correction? Does this lead to more realistic variability and teleconnections 3

4 Removing mean state biases from coupled models Heat flux correction - FC Two stage approach: 1. Haney forcing: Calculate heat flux required in order to create climate with the correct SST mean state 2. Add this (fixed, seasonally varying) heat flux correction to the surface heat flux Results of 100 years of HadCM3 with equatorial heat flux correction applied analysed (Turner, P. M. Inness and Slingo, 2004) How about wind stress correction? - τ C Two stage approach: 1. Impose the observed climatological wind stresses on the Ocean of the coupled model 2. Correct the wind stresses of the coupled model with the errors of the above model Results of 100 years of HadCM3 with tropical wind stress correction applied analysed (Spencer, Sutton and Slingo, in prep) h.spencer@reading.ac.uk 4

5 Climatological SST HadISST (Rayner et al, 2003) 3 N 3 S 6 E 12 E 18 E 12 W HadCM ocean, 20 levels (Gordon et al, 2000) 3 N 3 S 6 E 12 E 18 E 12 W Cold tongue cold bias Warm pool warm bias Strong Indian Ocean SST gradient o C HadCEM 1/3 ocean, 40 levels (Roberts et 3 N Slightly improvement al, 2004) 3 S 6 E 12 E 18 E 12 W h.spencer@reading.ac.uk 5

6 Climatological SST HadISST (Rayner et al, 2003) 3 N 3 S 6 E 12 E 18 E 12 W HadCM ocean, 20 levels (Gordon et al, 2000) 3 N 3 S 6 E 12 E 18 E 12 W Cold tongue cold bias Warm pool warm bias Strong Indian Ocean SST gradient o C HadCM3 FC (flux corrected) 3 N Massive improvements 3 S 6 E 12 E 18 E 12 W 3 N HadCM3 τ C (wind stress corrected) Smaller improvements 3 S 6 E 12 E 18 E 12 W h.spencer@reading.ac.uk 6

7 Interannual Standard Deviation of SST 3 N HadISST 3 S HadCM3 HadCM3 FC 3 N 3 S 6 E 12 E 18 E 12 W 6 E 12 E 18 E 12 W N 3 S 6 E 12 E 18 E 12 W o C ENSO variability extends across whole Pacific SE Indian Ocean too strong High sub-tropical variability ENSO variability extend slightly less Otherwise biases worse HadCM3 τ C 3 N 3 S 6 E 12 E 18 E 12 W ENSO too vigorous but mainly west of dateline SE Indian Ocean better h.spencer@reading.ac.uk 7

8 Climatological 20 C depth in the Ocean SODA data assimilation, (Carton et al, 2000) 3 N 3 S 6 E 12 E 18 E 12 W 3 N HadCM3 HadCM3 FC 3 S 6 E 12 E 18 E 12 W N m Cold tongue cold bias SW Indian Ocean dome too deep and too far east No improvements 3 S HadCM3 τ C 3 S 6 E 12 E 18 E 12 W 3 N SW Indian Ocean dome shallower and further east 6 E 12 E 18 E 12 W Cold tongue warmer BUT Arabian Gulf deep error worse h.spencer@reading.ac.uk 8

9 use wind stress corrected HadCM3 τ C for study of Indo-Pacific coupled variability Composite El Niño and Indian Ocean dipole Use October Niño 3.4 index and dipole index (DI) Monthly means 121 smoothed and linearly detrended Strong El Niño, strong dipole, Niño 3.4 > σ, DI > σ, 1972, 1982, 1997 Strong El Niño weak dipole, Niño 3.4 > σ, DI < σ, 1951, 1957, 1965, 1987 Strong dipole, weak El Niño Niño 3.4 < σ, DI > σ, 1961, 1963, 1967, 1994 h.spencer@reading.ac.uk 9

10 3 N El Niño and Dipole Composite SST and 10m wind Anomalies HadISST and NCEP, SON HadCM3, SON - τ C El Niño and dipole 3 N 3 S 6 E 12 E 18 E 12 W 6 W 3 S El Niño, no dipole 6 E 12 E 18 E 12 W 6 W 3 N 3 N 3 S 6 E 12 E 18 E 12 W 6 W 3 S dipole, El Niño weak 6 E 12 E 18 E 12 W 6 W 3 N 3 N 3 S 6 12 E 18 E 12 W 6 3 S E W 6 E 12 E 18 E 12 W 6 W 2 m/s o C h.spencer@reading.ac.uk 10

11 What are the pre-cursers to El Niño and the dipole in the ocean? 11

12 El Niño and Dipole Composite 20 C depth anomalies, equator and 10 S SODA HadCM3, - τ C El Niño and dipole equator equator 8 o S-12 o S 5 o S-10 o S 40E 60E 90E 120E 150E W 120W 90W 40E 60E 90E 120E 150E W 120W 90W m La Niña El Niño following year La Niña dipole following year h.spencer@reading.ac.uk 12

13 El Niño only Composite 20 C depth anomalies, equator and 10 S SODA HadCM3, - τ C El Niño, no dipole equator equator 8 o S-12 o S 5 o S-10 o S 40E 60E 90E 120E 150E W 120W 90W 40E 60E 90E 120E 150E W 120W 90W m spontaneous weak El Niño no dipole but weak negative dipole the year after h.spencer@reading.ac.uk 13

14 Dipole only Composite 20 C depth anomalies, equator and 10 S SODA HadCM3, - τ C dipole, El Niño weak equator equator 8 o S-12 o S 5 o S-10 o S 40E 60E 90E 120E 150E W 120W 90W 40E 60E 90E 120E 150E W 120W 90W m heat build up in W. Pacific dipole the following year but no El Niño h.spencer@reading.ac.uk 14

15 Equatorial Kelvin waves following year La Nina El Nino Rossby waves south of equator following year atmospheric teleconnection same year Dipole 15

16 How do surface heat fluxes influence the dipole? 16

17 3 N Dipole Only Composite Surface Heat Flux Anomalies NCEP, SON HadCM3, SON - τ C dipole, El Niño weak 3 N 3 S 3 E 6 E 9 E 12 E 15 E 3 S 3 E 6 E 9 E 12 E 15 E W/m 2 Surface fluxes provide a negative feedback on dipole SSTs Confirms the importance of the ocean dynamics in the Indian Ocean h.spencer@reading.ac.uk 17

18 Dipole - ENSO - monsoon connections h.spencer@reading.ac.uk 18

19 3 N El Niño and Dipole Composite Precipitation Anomalies CMAP, JJA HadCM3, JJA - τ C El Niño and dipole (CMAP, 1982 and 1997) 3 N 3 S 3 N 9 E 18 E 9 W 3 S El Niño, no dipole (CMAP, 1987) 3 N 6 E 12 E 18 E 12 W 6 W 3 S 3 N 9 E 18 E 9 W 3 S dipole, El Niño weak (CMAP, 1994) 3 N 6 E 12 E 18 E 12 W 6 W 3 S 9 E 18 E 9 W mm/day S 6 E 12 E 18 E 12 W 6 W mm/day El Niño weak Indian monsoon dipole strong Indian monsoon h.spencer@reading.ac.uk 19

20 But how do the Indian Ocean and the monsoon interact? The Pacific may still be domminant 20

21 Suppress El Niño in the Pacific Wind stress fixed to seasonally varying climatology in the tropical Pacific Wind stress corrected in the rest of the tropics Similar to Fischer et al but observed wind stress used rather than model climatology 3 N Interannual standard deviation of SST 3 S 6 E 12 E 18 E 12 W o C SST variability removed from equatorial Pacific SST variability remains in SE Indian Ocean h.spencer@reading.ac.uk 21

22 El Niño suppressed, Indian Ocean Dipole Composite Anomalies 3 N SON SST and 10m wind anomalies 20 C depth anomalies 3 S 6 E 12 E 18 E 12 W 6 W 2 m/s N JJA precipitation anomalies 3 S 6 E 12 E 18 E 12 W 6 W mm/day o C 5 o S-10 o S equator 40E 60E 90E 120E 150E W 120W 90W m Same pattern of ocean-atmosphere variability without interaction with the Pacific Dipole and strong monsoon - almost linked! h.spencer@reading.ac.uk 22

23 Conclusions Wind stress correction > heat flux correction for correcting Indian and Pacific basic state and variability Heat flux provides negative feedback on weak El Niño dipoles importance of ocean dynamics confirmed & explains weakness and rarity of non-el Niño dipoles ocean dynamics Equatorial Kelvin waves following year La Nina El Nino Rossby waves south of equator following year atmospheric teleconnection same year Dipole Indian Ocean dipole possibly associated with strong Indian summer monsoon 23