119 week 8 Flashcards
ways that humans modify small scale climate through surface conditions
albedo
altering geometry
mulching
moisture control
ways to alter near surface atmospheric conditions to control frost
preventing heat loss
adding heat
redistributing heat within the system
ways that humans modify small scale climate
change surface conditions
control for frost (near surface)
control fog conditions by adding and redistributing heat
control wind with barriers
Human modifications change what properties?
Radiative properties (K,L)
moisture properties (water, QE)
thermal properties (conductivity, QH)
Momentum (wind)
what does albedo regulate?
K (important for radiation and heat)
what does high albedo mean?
high perfection of K is reflected back
how can you change geometry to control radiation? what are some examples/
affects shortwave radiation absorption and long wave emission
- ridge and furrow induces multiple reflection, long wave emission reduced because sky view factor is lower (reduces cooling)
- receives energy at a more perpendicular angle
Ways that surface geometry affect radiative exchanges
- insolation of a flat surface
- insolation on a sloped surface, angle of incidence and multiple reflection (effective albedo)
- long wave emission from a sloped surface, sky view factor influences total emission
how can solar collector be altered to maximize solar energy depending on the season?
in the winter when the sun is low, a more upright solar collector will have a more perpendicular angle of incidence with the solar beam
In the summer when the sun is high, a more horizontally positioned solar collector is best
what is aerating?
covering the surface layer with hay, woodchips, gravel, or other material with relatively large amounts of airspace. Air has a lower energy conductivity than bare soil, so air passes less energy to other objects.
what are the three ways that mulching controls evapotranspiration and soil warming
aerating
lowering albedo
conductivity
how does mulching change the conductivity of soil?
Covering the surface with material that has lower conductivity than the soil (i.e.,
paper). Even paper with similar albedo as bare soil can mediate temperature
fluctuations because it inherently has a lower conductivity than the soil
when is mulch laid down? why?
To prevent soil freeze, mulch is laid down in autumn to trap in subsurface heat (QG) throughout the winter. However, it must be removed in spring to allow input of
insolation during the warm season.
when does frost occur?
Frost occurs when surface temperature of the ground or plant falls below 0oC. Frost
control aims to keep temperatures at or above freezing
two types of frost
Radiative frost – due to radiative divergence.
Advective frost – due to a cold airmass horizontally transporting cold air into
the environment.
two ways to control frost
avoidance - do not put cold sensitive plants in cold places (regions where the air stagnates)
modification of the radiation and thermal energy balances
When does frost tend to occur?
at night under cold clear conditions (stable)
how do you control fog by altering energy conditions?
increasing turbidity
- to slow down energy loss from the system. This includes
Intentionally creating fog, smoke, or mist layers that increase atmospheric
absorptivity and sensible heat released toward the ground
increasing QH
- increasing QH with heat lamps. This is most effective when there is an inversion
layer that keeps warm air from rising and being replaced by sinking cooler air
redistributing QH
- Redistributing QH to the surface with fans. This method creates a vertically
mixed layer of moderate temperature. The rising hot air is brought back down
what does creating clouds of fog do?
creating clouds of fog or mist, or smoke reduces nocturnal loss of Lup, especially when the
atmospheric window is wide open. This reduces the sky view factor by placing a “radiative screen”
above the surface that closes the window. This is done using smudge pots, as well as cheesecloth
and glass pots.
why do they use heaters on orchards?
Orchards may use heaters to increase QH content. The impact of heating is restricted to the foliage
and fruit due to upward convection of the heated air. To bring QH back down, the use of heaters
may be combined with fans