Alex Jovich - Atmospheric Sciences
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Transcript of Alex Jovich - Atmospheric Sciences
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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
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IntroEl Nino / La NinaDust bowl- 1930s1998- 2002Drought
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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
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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
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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
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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
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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?
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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)
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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
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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
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Mo’ Models No Problems4 year average 200
mb height anomalies3 more experiments,
one using both warm and cool, one using just the warm, the other using just the cool
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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
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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
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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
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More stuffSST anomalies
(extrapolations)Chopped the earth
into 3 regions (Extratropics, Indian ocean, Atlantic/Pacific)
Carried out 7 more experiments
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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
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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
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More ResultsFound that most of
the deficits occurred in warm seasons
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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
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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