AMO modulates ENSO variability

36 Pages·2012·7.13 MB·English

Atlantic Ocean influence on the interdecadal
Asian Summer Monsoon and its interaction
with the El Niño-Southern Oscillation
Buwen Dong1, Rowan Sutton1, Riyu Lu2, and Wei Chen2

1.National Centre for Atmospheric Science-Climate, University of
Reading, UK
2. Institute of atmospheric Physics, Chinese Academy of Sciences,
China
 Atlantic Multidecadal Oscillation (AMO)
 AMO modulates Asian summer monsoon
 Atlantic-Pacific teleconnection: AMO modulates
ENSO variability
 AMO modulates ENSO-South Asian summer
monsoon relationship
 Recent AMO changes, possible role on PDO phase
change in the late 1990s
 Conclusions
Atlantic Multidecadal Oscillation (AMO)
Sutton and
Hodson, 2005
The AMO is characterized by opposite signs of SST anomalies in the North
and South Atlantic and is thought to be related in part to multidecadal
fluctuations of the Atlantic Thermohaline Circulation (THC).
The climatic impacts of AMO
Contributes to fluctuation in global mean surface temperature in
the 20th century (Schlesinger and Ramankutty 1994, Zhang et
al. 2007)
Affects North American and European climate (Enfield et al. 2001;
Sutton and Hodson 2005)
Affects rainfall in the Sahel and North-East Brazil (Folland et al.
2001, Knight et al. 2006)
Affects Atlantic hurricane activity (e.g., Goldenberg et al. 2001,
Knight et al. 2006).
Affects the indian and East Asian summer monsoons
(Goswami et al. 2006. Lu et al. 2006, Zhang and Delworth
2007, Li et al. 2008, Song and Hu 2008)
Modulates the ENSO variability (Dong et al. 2006, Dong and
Sutton 2007, Timmermann et al. 2007).
Modulates the ENSO-Monsoon interaction (Chen et al 2010).
 Atlantic Multidecadal Oscillation (AMO)
 AMO modulates Asian summer monsoon
 Atlantic-Pacific teleconnection: AMO modulates
ENSO variability
 AMO modulates ENSO-South Asian summer
monsoon relationship
 Recent AMO changes, possible role on PDO phase
change in the late 1990s
 Summary
Obser vation evidences on the link between
AMO and monsoon pr ecipitations (J J A)
Correspondence between AMO and AIR. Positive AMO phase with strong AIR
and negative AMO phase with weak AIR. Both AIR and rainfall based on CRU
data shows similar relationship to AMO. (mean=7-9.0mm day-1, sdv=0.15-0.16
mm day-1)
Obser vation evidences on the link between
AMO and monsoon pr ecipitations (J J A)
Correspondence between AMO, rainfall over East Asia, and EASM index
on the multi-decadal time scale. Positive AMO phase are associated with
above rainfall and positive EASM index and negative AMO phase with
below rainfall and negative EASM index. Strong correspondence in the
last 60-70 years. (mean=4.8-5.0mm day-1, sdv=0.11-0.12 mm day-1)
Obser vation evidences on the link between
AMO and China climate (J J A)
JJA precipitation
JJA air temperature
Positive AMO phase: 1951-1965 and 1996-2000
Lu et al. 2006
Negative AMO phase: 1966-1995
Relative to the AMO negative phase, summer surface air temperature over east
Asia is warmer and precipitation is stronger during the positive phase of AMO.
The above observational evidences suggest a possible link
between the North Atlantic ocean state and Asian summer
monsoon intensity on multidecadal and millennial time scales.
When the North Atlantic was anomalous warmer, the main
remote features are:

(2) Enhanced Indian summer monsoon

(3) Enhanced east Asian summer monsoon

Now we use a coupled atmosphere-ocean GCM with specially
designed experiments to investigate this possible link and to try
to elucidate possible mechanisms behind this link.
Regional Coupled Model Experiments

•
2x150 year experiments with HadCM3 coupled model
(Atm: 2.5oX3.75o with 19 levels. Ocean: 1.25oX1.25o
with 20 levels)

•
+/- AMO: Atlantic SSTs relaxed to seasonally varying
climatology from the coupled model
+/- 3 x EOF pattern in Atlantic. 150 years.

•
Relaxation timescale = 2.5 days
(Lu et al 2006).