The Climate of (north‐central) Chile:Mean state, Variability and Trends
René
D. Garreaud
Department of GeophysicsUniversidad de Chile
www.dgf.uchile.cl/rene
Astronomical site testing data conferenceValparaiso, Chile, Dec. 1‐3, 2010
Outline
●
Climate background
●
Interannual (year‐to‐year) variability
●
Climate projection during the 21st century
●
Observed trends (last decades)
General circulation in an aqua‐planetPerpetual Equinox
0°
45°
NE trades
SE trades
ITCZ: IntertropicalConvergence Zone
Belt of higher pressure
Trop
ical
Tro
popa
use
(15
km)
Belt of lower pressure
Surface westerlies
Surface wind (arrows)Precipitation (green shadow)
30°
0°
60°
General circulation in an aqua‐planetPerpetual Equinox
Jet stream (westerly flow)aloft (10-12 km): long term mean.Boundary between subtropicaland extratropical air masses
ITCZ
Midlatitude precipitation maximum and westerly belt
120°W 90°W 60°W 30°W
60°S
30°S
0°S
S. AtlanticAnticyclone
MidlatitudeStorm track
ContinentalLow Level Jet
SE PacificAnticyclone
Midlat. Precip.
Tropical rainfall
SCu & Cold SST
Idealized (zonally symetric) circulation disturbed by continents
E
W
a. DJF
E
W
b. JJA
Zonal (east‐west) mean flow over the AndesBrown area: Terrain mean height
Dashed line: 500 hPa, half of the atmosphere below!
Latitude Latitude
Km12
5.
0.
Anual
June
January
ITCZ
SPCZ
StormTrack
OceanDesert
Precipitation and upper level winds
20 m/s
40 m/s
B
A
Frio
Cálido
500 hPa
Las perturbaciones de latitudes medias (ver clase anterior) también transportan calor hacia latitudes altas, continuando el proceso de transferencia de calor que realiza la atmósfera.
Precipitación en latitudes medias
EBUS: Subtropical anticyclones, equatorward flow and cold SST
SLP, Vsfc
SST
28°C23°C
17°C
10°C
1020 hPa1015
hPa
Persistent Stratocumulus cloud deck over the SEP
Coastline (72°W) 85°W
Persistent Stratocumulus cloud deck over the SEP
Soundings at 27°S
Warm FT
Cool MBL
Dry FT
Moist MBL
Subsidence over SEP distorted by land heating/cooling
MBL is 1 km deepat 20°S !
Garreaud & Rutllant 2005
Andes mountains disrupt mid‐level westerly flow
(a) Meridional wind at 27°S (b) Wind vectors over Santiago
Garreaud 2009
Andean slope also produces cross‐mountain circulations
Rutllant et al. 2003
South America monsoonal regime and Altiplano rainfall
Mean annual cycleColors: OLR (proxy of precipitation)Streamlines: 200 hPa (~12 km) wind
Bolivian High
South America monsoonal regime and Altiplano rainfall
VIS and IR2 GOES imagesduring an active summer afternoon
a. Zonal wind speed
W E
Pre
ssur
e [h
Pa]
b. Near surface mixing ratio and OLRW/m2
g/Kg
Summer Altiplano rainfall: Intraseasonal variability
Falvey and Garreaud 2005
Summer Altiplano rainfall: Intraseasonal variability
Falvey and Garreaud 2005
Year
b. Zonal wind (10, 20, 35 m/s)
a. Precipitable water (g/m2)
More humid than average
Less humid than average
Pres
sure
[mb]
Interannual variability of wind and moisture at 30°S‐70°W
Quadreli and Wallace, J. Climate, 2002
Interannual variability ~ changes in large‐scale circulation
Leadings modes of interannual (and longer)of atmospheric variability: ENSO – PDO(?) ‐
AAO
Leadings modes of interannual (and longer)of atmospheric variability: ENSO – PDO(?) ‐
AAO
Annual mean Precip/SAT regressed uponindex of large‐scale modes (50 years of data)
Stronger upper-Level ST Jet
Climo. Storm Track
EN years Storm Track
H
Blocking High
WeakenedST High
H
Drier/WarmerDJF
Wetter-OND
Wetter-JJA
Drier-DJF
Colder
Interannual variability -
Major ENSO
impacts
Wetter-JFMA
Warmer -
DJF
ENSO-related variability explains about 1/3 of the central Chile rainfall variability. Not quite enough for seasonal prediction…look for other forcing
+
Niño3.4 index [°C](equatorial SST anomaly)
Montecinos & Aceituno 2001
El Niño -
Wet
La Niña -
Dry
Win
ter m
ean
rain
fall
in
cent
ral C
hile
[mm
]
Who knows?Antarctic Oscillation?
Variabilidad interanual de la precipitaciónde invierno en Chile central
Summer Altiplano rainfall: Interannual variability
Summer Altiplano rainfall: Interannual variability
Correlation between DJF precipitation and U200 (17S-70W)
Observed trends (last 3 decades): Air temperature
offshore
coast
inland
WestAndes
East Andes
Observed trends (last 5
0 years): SAT
Falvey & Garreaud 2008
Ocean cooling –
land warming along north‐central Chile.Pattern reverses farther south
Falvey & Garreaud 2008
Cooling MBL / warming lower free troposphere increased lower tropospheric stability …. Sc?
Falvey & Garreaud 2008
• Semiarid climate• MAP
30-500 mm
• (IA)/MAP
0.3 –
0.5• Strong ENSO Impact• No significant trend
• Rainy climate• MAP
1000-3000 mm
• (IA)/MAP
0.1• Weak ENSO Impact• Significant drying trend
Observed trends: Precipitation 1970‐2000
Future Climate Scenarios GHG (CO2,…) emissions projections + GCMs
20+ GCMsCMIP3/IPCC AR4
Multimodel average of difference in zonal mean air temperature between A2 and BL
Warming of the tropical upper troposphere ►Increased static stability at subtropics and midlatitudes ► polerward expansion of the Hadley cell
Pres
sure
Lu et al. 2007
Multimodel average SLP difference between A2 (2070‐2100) and BL (1970‐2000)
Strengthening of the poleward flank of subtropical anticyclones and poleward shift of the midlatitude storm track is very consistent among GCMs
Annual mean
Garreaud & Falvey 2007
©
IPCC 2007: WG1-AR4 (2007)
Multimodel precipitation and surface temperature Changes (A2‐BL)
Multimodel mean diff. A2-BLin 200 hPa wind, summer
Multimodel mean diff. A2-BLin zonal wind along 70°W
summer
Futu
re C
limat
e Sc
enar
ios
-1° 0° 1° 2° 3° 4° 5° C
Differences A2(2100‐2070) –
BL(1960‐1990)Obtained with a regional climate model (PRECIS) forced by HadCM3
/ A2
-50 0 +50 mm/mes
Temperatura Superficial (SAT) Precipitación (P)
PRECIS-DGF-UCH
21-23°S 36-39°S
T (A2-BL) versus Height
SAT over Western Slope (Chile)
SAT over Eastern Slope (Argentina)
Free Tropos. Temp. at 76°W (Off Chile)
Free Tropos. Temp. at 66°W (Over Argentina)
Extra surface warming
°C °C
T (A2‐BL) versus Height
Precipitation Changes over the Altiplano: ¿?
Precipitation Changes over the Altiplano: Drier and warmer
Material Adicional….
gFpVkfdtVd
R
1ˆ
SfcConvRADP QQQSTVt
)(
0
pV
pRT
pgz
)(
Momentum eqn.
Energy eqn.
Mass eqn.
Idea gas law
Atmospheric circulation is governed by fluid dynamics equation + ideal gas thermodynamics
ECdt
dqv
rr SEC
dtdq
Water substance eqns.
lat
lon
z
lat ~
lon ~ 1
- 3 z ~ 1 km t ~ minutes-hoursTop of atmosphere: 15-50 km
Global Models (GCM)
Seasonal correlation between Precip/SAT andMultivariate ENSO Index (50 years of data)
Projected Changes PRECIS-DGF
Futuro: 2071-2100 / Presente: 1960-1990
>+5
+4 +5
+3 +4
+2 +3
+1 +2
-1 -2
-2 -3
-3 -4
-4 -5
< -5
0 -
25
25 -
50
50 -
70
70 -
80
80 -
90
110 -
120
120 -
130
130 -
150
150 -
200
> 200
TA2
-TBL PA2
/PBL
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