Monsoon, Floods and Droughts

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Monsoon, Floods and Droughts
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Review of last lecture

• Primary high and lows
• Three-cell model. Mechanism for each cell
• Two characteristics of temperature structure
• Two characteristics of wind structure. Why does
  westerly winds prevail in the extratropical
  troposphere? What cause the jet streams?
• What drives the ocean surface currents? In the
  case of Ekman spiral, what is the direction of
  surface current relative to surface wind? Two
  types of ocean upwelling

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Seasonal Monsoon
Seasonal temperature distributions

• T decreases poleward
• Isotherms shift seasonally
• T over land gt water in summer

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Temperature Ranges (Summer minus Winter) Large
over land, small over ocean
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The Seasonal Monsoon

• A seasonal reversal of wind due to seasonal
  thermal differences between landmasses and large
  water bodies
• Orographic lifting often enhances precipitation
  totals

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Orographic effect and rain shadow
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Worlds major monsoon systems
NH summer
NH winter
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Australian monsoon
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North American monsoon
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Effect of monsoon rainfall
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Interannual variation of monsoon Floods and
droughts
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Monsoon floods
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Monsoon droughts
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Causes of floods and droughts
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Mini monsoon Diurnal Sea/Land Breeze

• Daily reversal of winds resulting from
  differences in thermal properties of land and sea
• During the day (night) land (water) surfaces
  are hotter (cooler) than large water (land)
  surfaces
• Thermal low develops over warmer region - air
  converges into the low, ascends, and produces
  clouds

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Summary

• Tropical climate
• Mean state The two basic regions of SST? Which
  region has stronger rainfall? What is the Walker
  circulation?
• El Nino and La Nina Which region has warm SST
  anomaly during El Nino? 4-year period.
• Land-sea contrasts seasonal monsoon, diurnal
  sea and land breeze
• Extratropical climate
• Mean state westerly winds, polar vortex
• What is the primary way El Nino affect
  extratropics? (PNA)
• The oscillations associated with
  strengthening/weakening of polar vortex AO, AAO