Alex Jovich- Atmospheric Sciences The Perfect Ocean for Drought On the Cause of the 1930s Dust Bowl Martin Hoerling Science Vol Jan Siegfried D. Schubert et al. Science Vol Mar. 2004

Intro El Nino / La Nina Dust bowl- 1930s Drought

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 Nina Cooler 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 Bowl Drought 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

Drought- Some dry material U.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 Drought Data- observed global surface temperature,C, anomalies which were then averaged ( climatology) Global precipitation anomalies mm/yr ( climatology)

June1998-May2002 vs 4 year averaged SST variability ( ) Red is warmer than average Blue is cooler than average Lower chart uses a 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

Results The 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 month On the Cause of the 1930s Dust bowl Data-precipitation anomalies, sst anomalies Models-used same GCMs as Hoerling, but at a coarser resolution. Used year ( ) runs forced by observed SST

Goin’ for a long run Between the models there is considerable variability Correlation 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 stuff SST anomalies (extrapolations) Chopped the earth into 3 regions (Extratropics, Indian ocean, Atlantic/Pacific) Carried out 7 more experiments

Results From 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

Results Without 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 Results Found that most of the deficits occurred in warm seasons

Conclusion Overall, 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 cents I 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