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Alex Jovich - Atmospheric Sciences

Alex Jovich - Atmospheric Sciences. The Perfect Ocean for Drought. On the Cause of the 1930s Dust Bowl. Martin Hoerling Science Vol 299 31 Jan. 2003. Siegfried D. Schubert et al. Science Vol 303 19 Mar. 2004. Intro. El Nino / La Nina Dust bowl- 1930s

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Alex Jovich - Atmospheric Sciences

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  1. Alex Jovich- Atmospheric Sciences The Perfect Ocean for Drought On the Cause of the 1930s Dust Bowl Martin Hoerling Science Vol 299 31 Jan. 2003 Siegfried D. Schubert et al. Science Vol 303 19 Mar. 2004

  2. Intro • El Nino / La Nina • Dust bowl- 1930s • 1998- 2002Drought

  3. 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

  4. 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

  5. Dust Bowl Drought in the 1930scaused major dust storms In many places nearly ¾ of usable topsoil was blown away 2.5 million people migrated from the plains states

  6. 1998-2002 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

  7. 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?

  8. The Perfect Ocean for Drought • Data- observed global surface temperature,C, anomalies which were then averaged (1971-2000 climatology) • Global precipitation anomalies mm/yr (1979-1995 climatology)

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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 14 100-year (1902-2001) runs forced by observed SST

  14. 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

  15. More stuff • SST anomalies (extrapolations) • Chopped the earth into 3 regions (Extratropics, Indian ocean, Atlantic/Pacific) • Carried out 7 more experiments

  16. 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

  17. 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

  18. More Results • Found that most of the deficits occurred in warm seasons

  19. 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

  20. 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

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