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Which external boundary conditions are specified in the GENESIS model?
solar luminosity
land/sea distributions
topography: mtn. range location estimated more accurately than their elevations
land surface: unrealistic uniform vegetation (savannah) imposed throughout
atmospheric CO2: levels of 1, 4 and 8x present-day concentrations
orbital parameters: eccentricity of 0 and modern obliquity (23.5 degrees) for Sakmarian; for Wordian extreme values were imposed
What factors cause the model to predict weakening of the Northern Hemisphere summer monsoon between the Sakmarian and Wordian stages?
- more land in the northern subtropics during the Sakmarian
- northern subtropics topography is lower by the Wordian because the Hercynian orogeny has waned
- N-S temp gradient increase from Sakmarian to Wordian because of poleward shift and cooling of high lat land
- strengthens NH westerlies (especially in the winter)
- shifts max storm-track precip slightly to south in boreal winter (DJF)
- SH westerlies band and storm track band both narrow from Sak to Wor
What is some of the geological evidence (at least two proxies) for the weakening of the Northern Hemisphere summer monsoon?
- model precip/evap vs. coal/evaporite patterns:
- both Sak and Wor: wet high latitudes, arid cont. interiors and west coasts, wet tropical east-facing (monsoon dom) coasts and wet western equatorial coasts
- good match between model results and data
- coals align along positive P-E balance areas
- evaporites/sands along negative P-E balance areas
- magnitude of positive P-E decr between Sak and Wor
- model precip vs brackish water deposits:
- organic-rich shales found in upwelling zones and where P-E balance is positive in estuarine circ areas where run-off brings in terr nutrients and stratification lowers oxygen levels at sed/water interface
- model wind directions vs. eolianite transport patterns:
- model simulations generally confirm wind directions inferred from data
- model wind directions vs. upwelling deposits
- most upwelling zones are related to predictably strong and consistent trade winds within the subtropics
What factors cause the model to predict the strengthening of the Southern Hemisphere summer monsoon between the Sakmarian and Wordian stages?
- low pressure area (less than 1010 mb) during SH summer monsoon is larger in the Wordian than in the Sakmarian b/c more land area in the southern subtropics
- NH monsoon winds are weaker in the Wordian compared to the Sakmarian leading to decr. precipitation
- an E-W mountain range shifts from the SH to the equator between the sak and Wor and increases in elevation; enhances advection of moisture from the west
What is some of the geological evidence (at least two proxies) for the strengthening of the Southern Hemisphere summer monsoon?
- Similar to evidence for Northern Hemisphere.
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