landscapes and climate

Landscapes and Climate

David S. BattistiUniversity of Washington

• The Annual Mean Precipitation• Storminess and Climate• Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate:

Can we know about them using climate models?


• The Annual Mean Precipitation– Today: observed vs. simulated– Precipitation in warmer climates– Precipitation: controlled by large-scale circulation

or weather?

• Storminess and Climate• Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate:


How well do Atmospheric General Circulation Models work?

Typical biases in Seasonal Average Temperature (AGCMs circa 2003)


Typical biases in Seasonal Averaged Precipitation (circa 2003)


Covey et al 2000

TemperatureSea Level PressurePrecipitation

Projected Annual Average Precipitation due to increased CO2 (“2080-2099” minus “1980-1999”)

Scenario A1B

Stippling is where the multimodel average change exceeds the standard deviation of the models

Warmer climates should have less subtropical precipitation (20-35 latitude) and more tropical and high

latitude precipitation, for sound dynamical reasons.

Warmer Climates and Precipitation Patterns

Large-scale Circulation vs. Storm Dynamics• Cases where the large-scale circulation/forcing (e.g.,

Himalaya orography; land-ocean temperature contrast) drives weather?

SE Asian Monsoon, Indonesian Monsoon, ITCZ … South-Central US Monsoon

• Cases where the large-scale circulation inextricably tied to the weather (and not directly to topography)?

– Europe winter precipitation (NAO <--> storminess)– Pacific Northwest winter precipitation

(midlatitude Pacific storm track re-birth; ENSO)

• Don’t know:– Eastern Mediterranean and Middle East: are seasonal precip

changes due to changes in storm track dynamics or to changes in the frequency of lee cyclogenesis?

Climate and Landscapes

• The Annual Mean Precipitation• Storm Tracks and Climate

– Modern day– Glacial times

• Mountains -> Circulation -> Weather • Extreme Precipitation Events and Climate:


• Dogma says as the equator-to-pole temperature gradient (dT/dy) increases, so should storminess increase. There is more to the story.

• Counter examples abound (linked to mountains)• A modern day example: midwinter suppression of the Pacific storm track

… the Jet increases by ~20 m/s, … but storminess decreases by ~25% and the atmospheric heat transport goes down.

Going from November to January (increases dT/dy) and…

Yin and Battisti (2005), Li et al (2005)

Storminess and Climate

Storminess and Climate

Another counter example: In the LGM, the meridional temperature gradient increased and storminess decreased compared to today

poleward heat flux 850mb (Km/s)

Modern

Amplitude of Storms(e.g., eddy heat transport)

250 hPa Zonal Wind (contour in 10 m/s, starting at 30)

Li and Battisti 2007

Contours are west-to-east (zonal) wind speedTemperature is colored

Atlantic Jet Cross Section

Height

20N 60N 20N 60N


• The Annual Mean Precipitation• Storminess and Climate

• Mountains -> Circulation -> Weather– Major forcing of the global (NH) circulation by the:

• The Andes (Location of the Pacific ITCZ)

• The Rockies (Warm Europe vs. Cold NE US)

• Tibetan Plateau (SE Asian Monsoon)

– Mountains and storm tracks: seeding of midlatitude storms

• Extreme Precipitation Events and Climate: Can we know about them using climate models?

Observed annual mean stateRainfall (colors), SST (contours) and surface streamlines

Subtropical anticyclones

Cool

ITCZ

SPCZ

Data: GPCP, NCEP OI SST, QSCAT

Why is the ITCZ in the northern hemisphere, and why is the SE Pacific cold?

Note: this asymmetry is fundamental to El Nino physics, and the global climate anomalies that caused by it.

1. The Andes and the Observed Annual Mean State in the Tropical Pacific

Summary of main mechanisms

There is only one ITCZ in the eastern-central Pacific and it is north of the equator …

Precipitation & SST

… because of the mechanical affect of the Andes on the atmosphere and the resulting thermodynamic feedbacks with the ocean.

Observed Climatology

Simulated Climatology: an atmospheric GCM coupled to a slab ocean. Only Andes orography is included; there is no land.

Takahashi and Battisti 2006

2. The importance of mountains in wintertime

Mountains No Mountains

Winds, SLP and Eddy Temperature in January

Seager et al 2000

The importance of mountains in wintertime

Change in surface air temperature due to mountains is about ~25% of the annual cycle in some places

(e.g., Northeast China would be ~ 8C warmer in winter w/o the Tibetan Plateau)

Seager et al 2000

3. The Asian Winter MonsoonNovember - March

850 hPa Wind & Wind Speed Precipitation(cm/month)

3. The Asian Winter Monsoon

• Case 1: No topography

– The result: two zonal bands of rainfall near the equator (ITCZs), Trade winds, subtropical Highs at 30˚ latitude, and midlatitude jets and storm tracts at about 35˚latitude.

3. The Asian Winter Monsoon• Case 2:

– As in case 1, but add the Tibetan Plateau. Land temperature is fixed and adjusted at the surface lapse rate.

• Hence, there is no land heating in this experiment – Orography forces a stationary wave that cools the northeastern half of China by advection of cold

air from the northeast– Eg., cooling of Beijing of 8C– The Rockies have a similar affect on northeastern North America: cooling NE North America by

~9C & warming Europe by +3C (Seager et al 2000)

HJet

HH HH

LLLL

L Cold Air Advection


• Case 2: with Tibetan Plateau– Results: enhanced downstream jet stream & accompanying

circulation that • drives enhanced trades north of the equator, pushing the ITCZ

south of the equator through atmosphere-ocean feedbacks;• causes southerly winds in southern China, enhancing winter

rainfall (with local orographic amplification).

H

L

H

Jet

Trades

HH HH

LL LL

Surface Flow Upper Level Flow

L

H

3. The Asian Winter Monsoon… is forced mechanically by orography

Precipitation & Surface Streamlines

mm/day

Takahashi & Battisti 2007

3. The Asian Winter MonsoonNovember - March

850 hPa Wind & Wind Speed Precipitation(cm/month)

Convergence

… is forced mechanically by orography

Mountains and the seeding of midlatitude storms

Mountains are a primary cause of the birth of storms in the midlatitudes

Frequency of cyclogenesis as diagnosed from 850mb vorticity field.

Gray areas are above 1500m

S. Penny, pers. comm. 2007


Tracks of all storms that formed in the lee of mountains

…with upper level forcing: 935 … without upper level forcing: 696

Genesis Location


Mountains (ice sheets) and the seeding of midlatitude storms

LGMModern

A. Donohoe 2007

Amplitude of disturbances seeding the Atlantic storm

track are weaker in the LGM

Contours are west-to-east (zonal) wind speedTemperature is colored

Atlantic Jet Cross Section

Height

20N 60N 20N 60N

Li and Battisti 2007



Can we know about them using climate models?– Yes– Maybe

… but not yet.

Extreme Precipitation Events and Climate: Can we know about them using climate models?

• Yes, when changes in extreme events are due to weather that is controlled by large-scale circulation

• Examples: SE Asian Monsoon, Indonesian Monsoon, The Pacific ITCZ, Hurricanes (likely intensity, not likely tracks),

• At present GCM resolution, complementary downscaling (empirical/numerical) models are useful/necessary to assess changes in extreme events.

• Maybe, where weather and large-scale circulation are inextricably linked

… but not yet. Efforts are ongoing, but it will take time.




Mountains

Circulation

Weather?

Observed annual mean state

Rainfall (mm/day)

and 925 mb streamlines

Subtropical anticyclones

ITCZSPCZ

Data: GPCP, NCEP/NCAR Reanalysis, NCEP OI SST.

Sea surface temperature (SST, °C)

Cool

Andes and ML

Rainfall (mm/day, shaded)

SST (C, contours)

Mean sea level pressure (mb, shaded)

925 mb streamlines

Andes, Himalayas and Rockies


SST (C, contours)


925 mb streamlines

Double Andes (2)


SST (C, contours)


925 mb streamlines

Thermocline tilt


SST (C, contours)


925 mb streamlines

Thermocline tilt + Seasonality


SST (C, contours)


925 mb streamlines

Storm Tracks and ClimateAnother counter example: storminess and eddy heat transport are reduced in the LGM compared to today

The Indian Monsoon… is mainly thermally driven

Heating of continental India and SE Asia is key to the “Indian monsoon”

Pot. Temp. 850hPa Pot. Temp. 300hPa

The Indian Monsoon… is mainly thermally driven

May PrecipitationMay Wind 1000hPa

mm/daym/sec

The Indian Monsoon

June Precipitation

Precipitation, circulation and diabatic heating are grossly similar from month-to-month (once the Indian monsoon gets going) from June to September.

June Pot. Temp. 300hPa

The Indian Monsoon

Land-Sea thermal contrast is the major driver. But is it the “hot Tibetan Plateau” or is it “the hot India/Southeast Asia plus the Himalaya wall”?

The atmosphere is heated south of the Tibetan Plateau

The observed column averaged diabatic heating (JJA)

Rodwell and Hoskins 2001

The Indian MonsoonDoes the orography drive the low level flow that fuels

the monsoon heating?

Low level streamfunction in summer (JJA)

Mountains only

Mountains plus heating

The summer monsoon doesn’t seem to be driven by topography

Rodwell and Hoskins 2001

The Indian Monsoon

• The onset of the Indian Monsoon appears to be driven by heating over India and SE Asia– Modeling (not shown) and observations suggest the

Indian monsoon is not driven by heating over the Tibetan Plateau

• The Himalaya and the orography of SE Asia are important for localizing the precipitation and diabatic heating– This geometry ensures a gross similarity in monthly

circulation, precipitation, etc during the monsoon season.

The Asian Spring-Summer Monsoon

The jet transitions from south of the plateau in April to north in July. Until the transition takes place, the downstream flow will still favor low-level convergence over south-central China.

May

June

Apr

il

July

Zonal Wind Averaged 70-100E

The Asian Spring-Summer MonsoonMay wind and wind speed climatology

850 hPa

The deep west-northwesterly flow into central China brings dry air that converges with moist air at lower levels arriving from the south.

500 hPa


Wind velocity/speed at 500 hPa Zonal wind (color) and specific humidity along 95-100E

Eq 50N

May

May


So, we expect the same (dynamically) driven monsoon but with more rainfall in spring/summer than in winter:

•Higher SST -> more evaporation -> more moisture convergence -> more precipitation

•More precipitation -> more land evaporation -> more precipitation (local feedback)

•More precipitation -> more convergence

Jan June

The Meiyu Front: the summer Monsoon in south central China & Japan

Precipitation maximizes in central China in June/July -- when the dynamics can maintain the humidity front and moisture is streaming along the front from the WSW (Indian Ocean) at 700-500 hPa. Hence, there is strong sheer and low vertical stability.

Zhou et al 2004

Theta_e & moisture flux 700 hPa

H

Dynamically induced humidity Front (surface - 500mb)

Subtropical High

Vector wind and speed at 700 hPa

Moisture flux

Demise of the Asian Summer Monsoon

•At the end of July, the jet transitions north of the Tibetan plateau, decreasing the stationary wave downstream and hence weakening the dynamical support for the moisture front and reducing the horizontal sheer.

•Hence, the monsoon declines - first in the south, then north central China - prior to the maximum land-sea temperature contrast.

July

Zonal Wind Averaged 70-100E

Jan Apr July Oct Dec

D

H

Variability in the Indian Monsoon

• All months contribute to the variability in the net summer precipitation over India– June (onset month) has the least impact– September anomalies have the greatest impact– A suggestion of important land-atmosphere

feedbacks (memory) in Aug-Sept

• ENSO has a very week impact on the Indian monsoon (r ~ 0.3)

Variability in the Asian Monsoon

• ENSO has a moderate impact on the Winter monsoon rainfall (Nov-April) in southeastern China (r ~ 0.6)

January - March

Correlation of Nino3.4 with precipitation

• An unusually early poleward displacement of the jet in late spring - early summer brings earlier rains into east-central China

– Sometimes linked to unusually heavy precipitation in India (r ~0.4 in May-June at Hulu, which moves the jet poleward via a localized diabatic heating).

Variability in the Asian Monsoon

June India precip w/ U 70-100E June India precip w/ precip

• Otherwise, the interannual variability in the Asian monsoon is unrelated to that in the Indian monsoon (r ~ 0.1 monthly and seasonally)

The modern day Indian and Asian monsoons & millennial scale variability

in the proxy records

• The Indian and Asian monsoons in the modern climate

• Implications for interpreting the proxy records

Error depends on spatial and temporal scale and on the climate variable

Surface Air Temperature

Errors of surface air temperature (climatological annual cycle) simulated by CMIP2 model control runs. Shown are the total errors, the global and annual mean error (“bias”), the total r.m.s (“pattern”) error, and the following components of the climatological r.m.s. error:zonal and annual mean (“clim.zm.am”); annual mean deviations from the zonal mean (“clim.zm.am.dv”), seasonal cycle of the zonal mean (“clim.zm.sc”); and seasonal cycle of deviations from the zonal mean (“clim.zm.sc.dv”).

Precipitation

The Andes and the South Pacific Anticyclone

Rodwell and Hoskins, 2001

-

-

-

+

+

++

Run with zonally symmetric SST: 850 mb winds (m/s) and omega (Pa/s)

Andes

And

es


Wind Direction (vector) and wind speed (color)

November - March

850 hPa (~1500m)


Tracks of all storms that formed in the lee of mountains

Genesis Location


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