Outline
• Announcements
• More on thermal properties
• More on evaporation
Soil Physics 2010
Announcements
• Review session today, 11:00-1:00,
room 1581 Agronomy
• More sessions will be scheduled for
next week
• 1 more homework will be assigned
• Quiz? No, not today.
Soil Physics 2010
Measuring Thermal Properties in the Field
k
Thermal
Conductivity
q
q
Thermal
Diffusivity
Inverse methods using many
measurements at multiple
depths and times?
Soil Physics 2010
DT
cr
Volumetric
Heat Capacity
q
Measuring Thermal Diffusivity in the Field
Assumptions:
DT constant
No water movement
No latent heat movement
Sine wave
…not necessarily!
Soil Physics 2010
Measuring Thermal Diffusivity in the Field
?
The phase change method:
z1  z2 
DT 
2
21  2 
2
 z1  z2 
2
The amplitude method:
DT 
Every sensor is a temperature sensor.
But if you’re clever, you can use it to
measure something else as well.
-- Gaylon Campbell
Soil Physics 2010
 A1 
2 ln 
 A2 
2
Estimating other properties in the field
Suppose we measure T and q :
We get DT from amplitude or phase shift
We get q directly
From DT and q we calculate cr
From DT and cr we calculate k
…?
Soil Physics 2010
Evaporation
Soil Physics 2010
Evaporation
Soil Physics 2010
Lawrence et al., 2007
Evaporation from the soil
can be an important part of
the total water budget!
Evaporation
Evaporation may be limited by:
• Energy
• Water supply
e, mm/day
• Vapor transport
Soil Physics 2010
Stage
I
Stage
II
time
Stage
III
Evaporation
Water available;
(mostly) energy-limited
e, mm/day
Evaporation may be limited by:
• Energy in
• Water in
• Vapor out
Stage
I
Stage
II
time
Soil Physics 2010
Stage
III
Energy available;
Transport limiting:
water up
vapor out
Main limitations on actual evaporation from soil
• Stage I: evaporation from the surface
• Energy available at surface
• Vapor pressure deficit in air near the surface
• Transport of vapor away from the surface
• Stage II: evaporation from a retreating drying front
• Flow of liquid water to the drying front
• Stage III: evaporation from a stationary drying front
e, mm/day
• Diffusion of water vapor from the drying front to air above
the soil surface
Soil Physics 2010
Stage
I
Stage
II
time
Stage
III
Evaporation insights and innovations 1:
Maria Dragila:
Enhanced evaporation from fractures
Daytime:
Hot dry soil surface
Cooler, moister fracture face
Evaporation limited by diffusion
Nighttime:
Cool dry soil surface
Warmer, moister fracture face
Convection in the fracture
enhances evaporation
Soil Physics 2010