Alex Jovich- Atmospheric Sciences

The Perfect Ocean for Drought

On the Cause of the 1930s Dust Bowl

Martin HoerlingScience Vol 299

31 Jan. 2003

Siegfried D. Schubert et al.

Science Vol 303 19 Mar. 2004

IntroEl Nino / La NinaDust bowl- 1930s1998- 2002Drought

El Nino Warmer than

average SST in Eastern Pacific

Higher air pressure in western Pacific

Associated with wet winters in SW U.S., drought in Indonesia, Australia

Every 3-7 years

La NinaCooler than average

by SST in Eastern Pacific

Typically more precip. than average in the Midwest, mild wet summers

Typically effects are opposite from El Nino

Often preceded by an El Nino

Dust BowlDrought in the 1930s

caused major dust storms

In many places nearly ¾ of usable topsoil was blown away

2.5 million people migrated from the plains states

1998-2002 Drought- Some dry materialU.S., Mediterranean,

Southern Europe, Southwest and Central Asia

As little as 50% of the climatological annual average precip. fell during this 4 year period

WHY? WHYYY?Why was the ocean

perfect for causing droughts?

What Caused the 1930s dust bowl?

Did these regional droughts share a common influence?

Were slow external forcings responsible for prolonged drought conditions simultaneously over the mid latitudes?

The Perfect Ocean for DroughtData- observed

global surface temperature,C, anomalies which were then averaged (1971-2000 climatology)

Global precipitation anomalies mm/yr (1979-1995 climatology)

June1998-May2002 vs 4 year averaged SST variability (1948-1998)

Red is warmer than average

Blue is cooler than average

Lower chart uses a 1971-2000 climatology

Exceeds -3 std deviations in Eastern Pacific

Exceeds 4 std deviations over the warm pool

Meanwhile at Hall of Justice…Used Atmospheric

general circulation models (GCMs) to see if the ocean had anything to do with this

Comparing the observed to the ensemble mean, there is a strong implication that the drying was oceanic controlled

Mo’ Models No Problems

4 year average 200 mb height anomalies

3 more experiments, one using both warm and cool, one using just the warm, the other using just the cool

ResultsThe cool Pacific acted

synergistically with the warm tropical Indian ocean to definitively claim the ocean was “perfect” for causing drought

Suggests an increased risk for severe and synchronized drying of the mid latitudes

Wake up, wake up it’s the first of the monthOn the Cause of the

1930s Dust bowlData-precipitation

anomalies, sst anomalies

Models-used same GCMs as Hoerling, but at a coarser resolution.

Used 14 100-year (1902-2001) runs forced by observed SST

Goin’ for a long runBetween the models there

is considerable variabilityCorrelation between the

mean and observed anomalies is .57

There are periods where all of the curves tend to follow one another (ex 1930s)

Main discrepancy is over Mexico, fails to capture full extent of drought, but this is just from ensemble averaging

More stuffSST anomalies

(extrapolations)Chopped the earth

into 3 regions (Extratropics, Indian ocean, Atlantic/Pacific)

Carried out 7 more experiments

ResultsFrom the global run,

it appears that basic drought conditions are a result from

Between tropical and extratropical effects, main features reproduced by tropical run, broadened by extratropical effects

ResultsWithout the

feedback from the atmosphere and land surface, there is a 50% reduction in the deficit

Great Plains are sensitive to soil moisture feedback

More ResultsFound that most of

the deficits occurred in warm seasons

ConclusionOverall, a cool pacific and a warmer indian

working with one another have the potential to cause massive world wide droughts

The models don’t always tell the truth (1970s)

Land-Atmosphere interaction is important in how severe the drought will be

My 2 centsI agree with the findings in the papers,

however I don’t like how they use different time averages and compare them to one another.

In the future I would use a better resolution with more runs