soil temperature. energy balance incoming shortwave from sun incoming shortwave from sun outgoing...
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Soil TemperatureSoil Temperature
Energy balanceEnergy balance
Incoming shortwave from sunIncoming shortwave from sun Outgoing longwave from earth-Outgoing longwave from earth-
atmosphereatmosphere
Overall balance in soil:Overall balance in soil:
Daily Daily (diurnal):(diurnal):– Net gain in day Net gain in day – Net loss at night Net loss at night
AnnualAnnual::– Net gain in summerNet gain in summer– Net loss in winterNet loss in winter
Soil heat fluxSoil heat flux
amount of thermal energy that amount of thermal energy that moves through an area of soil in a moves through an area of soil in a unit of time.unit of time.
Heat flux diagram handoutHeat flux diagram handout
AnnualAnnual::– Winter heat fluxWinter heat flux– Summer heat fluxSummer heat flux
Re: heat flux diagram:Re: heat flux diagram: Notice: Notice:
– Crossover at ~ 4 m.Crossover at ~ 4 m. penetration lag of cold and warm transmitted to penetration lag of cold and warm transmitted to
depthdepth
– Spring, fall: transitionalSpring, fall: transitional Turnovers are important triggers for soil animalsTurnovers are important triggers for soil animals
– Constant temp. at depthConstant temp. at depth ““depth of zero annual range”depth of zero annual range” MAST (mean annual soil temp.)MAST (mean annual soil temp.)
– About 1About 1°C warmer than mean annual air temp (39.1°C warmer than mean annual air temp (39.1⁰ Duluth)⁰ Duluth) high lat :20 m high lat :20 m midlat: 15 m midlat: 15 m Tropics: 10 mTropics: 10 m
MAST corresponds roughly to the water MAST corresponds roughly to the water temperature measured in groundwater wells 30 – temperature measured in groundwater wells 30 – 50’ deep50’ deep
MAST observations at individual stations, superimposed on well-water temperature contours.
Geothermal heatGeothermal heat(not volcanic type)(not volcanic type)
Transfers heat to building from soilTransfers heat to building from soil– In summer, soil can remove heat from In summer, soil can remove heat from
buildingbuilding– In winter, can transfer heat from soil to In winter, can transfer heat from soil to
buildingbuilding– Horizontal tubing in trenches within Horizontal tubing in trenches within
zone of MASTzone of MAST
Soil temp cyclesSoil temp cycles
Diurnal pattern
Annual pattern
Soil temperatures cycles Soil temperatures cycles handouthandout
Notice:Notice:1. Decreased amplitude and increased lag 1. Decreased amplitude and increased lag
time with depthtime with depth Changes in conductivity with depthChanges in conductivity with depth
2. Diurnal temp wave discernible to about 2. Diurnal temp wave discernible to about 0.8 m0.8 m
3. Annual temp wave to 14 m 3. Annual temp wave to 14 m
Thermal propertiesThermal properties
Specific heat/heat capacitySpecific heat/heat capacity
Thermal conductivityThermal conductivity
Specific heat/heat capacitySpecific heat/heat capacity
Ability to store heatAbility to store heat– Amount of heat required to raise Amount of heat required to raise
temperature of 1 g of substance by 1 degree temperature of 1 g of substance by 1 degree CC
greater the heat capacity of a greater the heat capacity of a substance, the more heat it can gain (or substance, the more heat it can gain (or lose) per unit rise (or fall) in temperaturelose) per unit rise (or fall) in temperature
Soil: 0.2 cal/g Soil: 0.2 cal/g Water: 1.0 cal/gWater: 1.0 cal/g
..
light dry soils experience greater light dry soils experience greater seasonal temperature swings at a seasonal temperature swings at a
given depth than wet soils.given depth than wet soils.
Thermal conductivityThermal conductivity
Ability to conduct heatAbility to conduct heat– Affected by:Affected by:
moisturemoisture texturetexture
1. moisture1. moisture
thermal conductivity of water is thermal conductivity of water is about two to three times about two to three times greatergreater than that of soil.than that of soil.
– In saturated soils, pore spaces filled with In saturated soils, pore spaces filled with water rather than airwater rather than air
Wet soils have higher conductivity than dryWet soils have higher conductivity than dry
2. texture:2. texture:
thermal conductivity of air is about thermal conductivity of air is about one hundred times one hundred times lessless than that of than that of soil . soil .
– Finer soils have more particle-to-particle Finer soils have more particle-to-particle contact and smaller pore spaces, contact and smaller pore spaces, therefore increased conductivitytherefore increased conductivity. .
Conductivity increases as texture becomes Conductivity increases as texture becomes increasingly fine.increasingly fine.
Notice that adding water makes Notice that adding water makes texture have opposite effect (wet sand texture have opposite effect (wet sand
higher cond. than wet clay)higher cond. than wet clay)
Texture determines how quickly soil Texture determines how quickly soil will heat (in spring) or cool (in fall).will heat (in spring) or cool (in fall).
Sandy soils contain less water (lower Sandy soils contain less water (lower porosity) and therefore heat more porosity) and therefore heat more quickly than clay.quickly than clay.