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