Temperature and Energy
Energy is the ability to do work, it is never gained or lost but changes form.
Kinetic Energy is energy of movement, includes radiation.
Potential Energy sources include gravitation, magnetism, bonds, elastic bands, and electrostatic energy.
Temperature was defined by Clark as “that property of a body that determines whether it will gain or lose energy in particular circumstances”.
Temperature is not heat. Heat is the total energy within a system, whereas temperature is an average over the system. This is why an elephant and mouse can have the same temperature but contain radically different amounts of heat.
What is Winter?
Isotherms are lines on a map of (on average) constant temperature. Isotherms during winter in half the US are below freezing.
- Winter involves low pressure systems that generate wind.
- Wind is drying and cooling.
Winter is Snowy
- Mean snowfall in North America ranges from 3 cm to 800 cm.
Snow is important ecologically due to:
Cooling - reflectance, or albedo of snow cools an area.
White coloration (reflectance, blending)
Snow is opaque (hiding, conductivity).
Duration of snow cover is critical. In the south, it ends as early as february. In the north, can take until July.
Winter is dark.
Winter is dark because the north pole tilts away from the sun.
At low latitudes, darkness lasts less than at higher latitudes.
Where is Winter?
Stoats (short-tailed weasels) change form from brown to completely white (ermine) form in winter.
- This transition parallels the -1.1 degree C january isotherm in the US.
Can also dilineate where winter is via spruce trees.
Some abiotic winter borders include:
Mean jan temp of 1.1 degrees C
Max wind speed of 37 m/s
Mean annual snowfall of 40 cm
Mean annual insulation of 375 cal/cm
Continuous snow cover by Dec 12.
SNow cover dissappears by February 15th.
Responses to Winter
two-way seasonal movement.
Specialized food and physiology.
Integrates multiple locations and climate change.
Can be from warmer to colder places.
True hibernation is rare as organisms must expend huge amounts of energy to keep from freezing by warming back up constantly.
Regulates temperature at low levels.
Warming is easier with small bodies.
Body size mediates storage inside or outside body.
- Suspended development in insects. Can occur in immobile or active stage.
Seeds - Coldest winters favor annual plants. Seeds are cold tolerant.
This is maintenance of a high metabolism in endotherms. Energetic requirements of resisting are high.
Adaptations to reduce heat loss include:
timing of activity
Ectotherms can’t regulate temperature. Use two strategies to cope:
Freeze-avoidance: antifreeze in body liquids lowers freezing point, elimination of ice nucleators, supercooling (going below freezing without freezing, very dangerous).
Freeze-tolerance: freezing is kept in extracellular space, drawing water out to avoid ice damage. More common in southern hemisphere.
Energy and Snow
Light and Heat
Light is electromagnetic radiation. One form of lost heat.
Heat is lost by:
Radiation: Movement of energy through a medium without modifying the medium.
Conduction - transfer of energy by molecular contact.
Convection - transfer of energy by movement of a medium surrounding an object.
Evaporation - transfer of energy due to phase change of liquid to vapor.
Latent Heat of Vaporization
Hydrogen bonds are collectively strong. More energy is used in boiling water than raising its temperature from 0 - 100 degrees C.
533 Cal/gram of water is latent heat of vaporization. Latent heat is the hidden heat involved in a phase change. This heat is absorbed into water during vaporization.
Latent heat of fusion (melting) is 79.7 Cal/gram
Lots of different kinds of snow.
Diversity is caused by temp and moisture during formation as well as metamorphosis once snow touches ground.
Crystals form when vapor freezes around nucleus.
Snowflakes can be:
Hollow columns and solid needles.
Spatial dendrites (kind of like pine needles)
Rimming - supercooled water droplets freeze on impact with a crystal - Graupel, ice pellets, hail.
Structure of snow crystals changes function.
- Needles are associated with avalanches.
Snow crystal type is determined by temp and vapor supply.
International classification scheme goes from F0 to F8
Metamorphism - Snow changes form when it touches the ground.
Desctructive Metamorphism - Mostly physical wear, changes crystals from spiky to round cores, packing in of wind, breakage and fusion of crystals, making for tighter packing.
Constructive metamorphism - Results from warmer vapor going up the concentration gradient in the snowpack from warmer bottom snow to cold top snow. Vapor sublimates and pulls water away from bottom condensing on the top of snowpack (depth hoar)
Melt Metamorphism - Melting at surface of snow accumulates heat into water, which is released deeper in the snow as water refreezes after pouring down. Heat transfer from top to interior, equilibrating snowpack despite lower conductivity meaning top and bottom were different before.
Insulative value of snow
- The lower the density of the snow, the better an insulator it is (the worse at conduction it is).
Snow reflects light and absorbs/emits heat
Reflected light cools climate in late winter.
Emitted heat at surface and absorbed heat from ground lead to temp inversion (warm air below and cold air above due to lack of convection)
Snow in evergreen forest emits heat but is shaded from light so it takes long to melt.
Arctic radiation energy balance is negative most of the year. Heat emitted by snow is greater than heat absorbed from sunlight (reflectivity).
Light transmission is highly reduced in snowpack, but this depends on the density of it.
Heat and Temperature
Something with a higher temperature can feel colder because it conducts heat away from your hand faster than something else.
Heat is a function of the total kinetic energy of the system. Is measured in joules.
Temperature is function of the average kinetic energy, units are C or K.
Potential energy is converted to work. No perfectly efficient conversion, heat is lost.
Heat content is proportional to thermodynamic temperature (don’t need to worry about this).
Anders Celsius found that When you add heat you can cause temp to rise or power a phase change, but not both.
Heating up objects
Specific heat is a property of a material.
Heat needed to raise an object one unit of temperature.
\(C_p = J / g \cdot K\)
Water has a specific heat of 4.2 \(J/g \cdot K\)
Thermal capacitance is how much heat is required to raise temperature of a body by 1K.
- \(mass \times C_p\)
Latent heat is heat associated with phase change, can be lost or gained.
- Hydrogen bonds are collectively strong. More energy used in transfer from liquid water to gas than in raising temp from 0 to 100 C, 533 Cal/gram.
Ice is arrangement of molecules with very little kinetic energy.
When water freezes, releases latent heat of fusion 79.7 Cal/gram.