http://institute.nsta.org/web_seminars.asp

NOAA/NSTA Web Seminar:

The Ocean’s Role in Weather and Climate

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The influence of the Atlantic ocean on climate, from Atlantic hurricanes to African drought

Thomas L. Delworth

Geophysical Fluid Dynamics Laboratory/NOAAPrinceton, NJ

Outline:

1. Basics of the Atlantic Ocean

2. Multidecadal changes in the Atlantic: impact on climatea. African droughtb. Conditions for tropical stormsc. Hemispheric temperature

3. Global warming and the Atlantic

from “Earth's Climate Past and Future”, Ruddiman.

Schematic of Atlantic Ocean Circulation

Ocean movesheat poleward

1.3*1015 Watts

Sinking waterat high latitudes

Question: The rate of heat (energy) transported by the Atlantic ocean is ~1.3 *1015 Watts. The amount of energy moved poleward by the Atlantic Ocean each year is the equivalent to approximately how many years of total U.S. electricity generation:

1 year

100 years

1000 years

2000 years

Observed Atlantic Sea Surface Temperature

(60oW-20

oW,6

oN-18

oN)

Tropical North Atlantic

Tem

per

atu

re (

Deg

C)

Outline:

1. Basics of the Atlantic Ocean

2. Multidecadal changes in the Atlantic: impact on climatea. African droughtb. Conditions for tropical stormsc. Hemispheric temperature

3. Global warming and the Atlantic

Atlantic Ocean Temperature

(80oW-0

oW,0

oN-60

oN)

Observed change in Sea Surface Temperature (Deg C) 1996-2005 minus 1970-1990

Data fromAug-Oct

Where did the largest

warming take

place?

Tree ring records show that AMO-like fluctuationshave existed for centuries.

Gray et al., 2004, Geophysical Research Letters

How can we better understand (and predict) the impact of the North Atlantic ocean on climate?

1. Diagnostic analyses of observational data

2. Use computer models of the climate system to better understand how the climate system works (cause and effect) and to predict its future evolution

Computer climate model is a “Virtual Earth”, in which we can perform many experiments to better understand the system.

In models, the earth’s land, ocean and atmosphere are chopped into 5 million grid cells.

Horizontal Grid (Latitude-Longitude)

Vertical Grid (Height or Pressure)

Climate models use world’s fastest supercomputers … but needcomputers that are 1000 times faster (at least!).

Where is climate modeling done?

Where is climate modeling done?

CANADA

USA

Princeton, NJ

New York, NY

Boulder, Colorado

ENGLAND GERMANY JAPAN

AUSTRALIA

ObservedPrecipitation(mm/month)100 mm/month isabout 50 inches per year

Data from Univ. ofEast Anglia, Climatic ResearchUnit (CRU)

Seasonal migration of Intertropical Convergence Zone (ITCZ)

January

July

Sahel

1950-2000 trends in observed and simulated precipitation

(JAS)

Observed Simulated

(Atmosphere model forced with observed SSTs 1950-2000)

Simulated rainfall changes Modeled AMO Index

Observed rainfall changes Observed AMO Index

Let’s do a poll question!

The rainy season in the Sahel region of Africa is:

Simulated Summer Rainfall Changes Associated with Warm North Atlantic

Units: cm/day

Blue means more rainfallwhen the North Atlanticis warm

Simulated multidecadal JJAS surface air temperature difference (K) (1931-1960) – (1961-1990)

Question: The Sahel region of Africa is particularly prone to drought because:

It is located far from the

ocean

It is located in a region of sharp transition between tropical

rainforests to the south and desert to the north

The mountainous terrain blocks moisture from

the ocean

NOAA National Hurricane Center 2005 Outlook

Reduction in Wind Shear when North Atlantic Warms relative to South Atlantic

Observations Model (GFDL CM2.1)

Red means less shear, and therefore more favorable conditions for hurricanes.

CONCLUSION: Models demonstrate that a warming North Atlantic (relative to the South Atlantic) CAUSES atmospheric circulation changes that are favorable for tropical activity.

Zhang and Delworth, 2006

Outline:

1. Basics of the Atlantic Ocean

2. Multidecadal changes in the Atlantic: impact on climatea. African droughtb. Conditions for tropical stormsc. Hemispheric temperature

3. Global warming and the Atlantic

Let’s do a poll question!

If all emissions of carbon dioxide were stopped tomorrow, how long

would the ocean continue to warm?

You are here (now)

What the Climate Models Predict:

Observed and Modeled Tropical North Atlantic SST

Modeled (GFDL CM2.1)

Observed

Steady or slightly cooling temps

RapidWarming

Key uncertainty:Role of aerosolsIn late 20th century

Looking at 21st Century SimulationsProjected Atlantic SST Change (relative to 1991-2004 mean)

Areal average70

oW-0

oW

0oN-60

oN

Results fromGFDL CM2.1Global ClimateModel(SRES A1B)

ObservedTrend from 1950-2004

Summary/Discussion

- Atlantic Ocean plays a crucial role in climate through transporting large amounts of heat from the Tropics to higher latitudes.

- Multidecadal fluctuations in ocean circulation have strong influence on climate, including African and Indian monsoon rainfall, Atlantic hurricane activity, and North American temperature.

- Increasing greenhouse gases are significantly warming

the Atlantic, and will continue to do so in the future.

National Science Teachers AssociationGerry Wheeler, Executive Director

Frank Owens, Associate Executive Director Conferences and Programs

Al Byers, Assistant Executive Director e-Learning

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NSTA Web SeminarsFlavio Mendez, Program Manager

Jeff Layman, Technical CoordinatorJudith Lopes, Administrative Assistant

Susan Hurstcalderone, Volunteer Chat Moderator