Thermal Stratification and the Heat Budget - PowerPoint by icecube

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									• thermal properties of water and lakes
• annual stratification
• lake classification based on thermal
  stratification patterns
     Thermal Properties of Lakes
             Sources of heat:
•   Solar radiation
•   Sensible heat conduction
•   Stream Input
•   Sediment absorption of sunlight
•   Geothermal
•   Biogenic
     Thermal Properties of Lakes
               Sinks of heat:
•   Evaporation
•   Sensible heat conduction
•   Back radiation from lake surface
•   Stream inputs (snow melt)
•   Surface outflow
Lake Tahoe, CA-NV
Lake Mendota, WI
   Annual Lake Heat Budget
           S = Rn – E – H – Q

where S = storage rate of heat in the lake
      Rn = net radiation
      E = evaporation
      H = sensible heat transfer, conduction
      Q = advective heat transfers due to water
           inflows and outflows
 Lakes stratify because water
density varies with temperature




                      Figure 3-4 in
                      Horne and Goldman
          Thermal Stratification
          for a typical temperate lake
1. Spring Circulation




2. Summer Stratification
Castle Lake
Stratification
3. Fall Circulation




4. Winter Stratification (inverse stratification)
     Lake Classification Based on
    Thermal Stratification Patterns
1. Holomixis
  a. monomictic – mixes once per year
      • warm monomictic – never below 4°C
      • cold monomictic – never above 4°C
      • ex: Lake Tahoe
             - large volume and large depth
             - no winter ice cover
b. dimictic – mixes twice per year
   • ex: Castle Lake and Lake Mendota
              small temperate lake
              freezes over during winter

c. amictic – does not mix, permanently ice-covered
   • ex: Lake Vanda, Antarctic
              high latitude lake
Lake Vanda, Antarctica
d. oligomictic – mixes rarely, thaws rarely
    • ex: small lakes at high altitude or latitude


e. polymictic – mixes many times per year
    • warm polymictic
    • cold polymictic
    • ex: Clear Lake
        shallow lake

        exposed to strong winds
2. Meromixis
  a. structure of a meromictic lake
        • mixolimnion
        • chemocline
        • monimolimnion

								
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