heat - a quantitative measure of the amount of heat energy;
                     - it is a measure of the quantity or amount of heat energy.
 
  MEASURES OF HEAT (HEAT ENERGY)
calorie (cal) - amount of heat (heat energy) required to raised 1 g of water by 1 ^oC. (calorimeter - how measure)

kilocalorie (kcal) - 1,000 calories 

British Thermal Unit (BTU) - amount of heat required to raise 1 lb. of water by 1 ^oF.

specific heat - amount of heat (# calories) needed to raise 1 g of a substance by 1 ^oC. (water = 1.0)

heat of fusion - amount of heat (# calories) needed to change 1 g of a substance from solid to
                         liquid at its melting/freezing point. (water = 80 cal/g)

heat of vaporization - amount of heat (# calories) needed to change 1 g of a substance from
                                   liquid to gas at its boiling/condensation point. (water = 540 cal/g) 
   

WAYS TO TRANSFER HEAT (HEAT ENERGY)

There are 3 ways in which heat (heat energy) can be moved.

1) conduction- flow of heat energy through a medium from molecule to molecule.

2) convection - mass movement of heat energy.

3) radiation- flow of energy as electromagnetic waves, with no transferring medium; when 
                     radiation is absorbed it may be converted to heat energy.

How the Greenhouse Effect Happens
The greenhouse effect gets its name from the  heat build-up characteristic in greenhouses during the day.  Solar radiation from the sun is composed of relatively short wavelength radiation, with about 10% being ultraviolet (UV), about 40% being visible and about 50% being short wavelength near infrared (IR).  This radiation is absorbed by the objects of the earth or inside the greenhouse and the radiant energy is converted into heat energy and the objects increase in temperature.  The objects will then begin cooling themselves by conduction, convection and radiation.  The radiation emitted (re-radiated) is long  wavelength IR.  The atmosphere and greenhouse glass are opaque to the long wavelength IR.  In the atmosphere, carbon dioxide gas and water vapor absorb the long wavelength IR, which is then radiated back down, thus trapping the long wavelength IR in the earth's atmospheric environment.  In the greenhouse, the glass bounces the long wavelength IR back down.  This trapped long wavelength IR is absorbed by objects, which causes further heating, and the cycle continues.  Thus, the earth and greenhouse act as solar collectors. 

Carbon Dioxide Emissions and Global Warming
The increased carbon dioxide emissions from burning fossil fuels (and  to a lesser degree massive forest and oil field fires) have caused the level of carbon dioxide in the atmosphere to increase from about 300 ppm to 350 ppm over the last century.  This is "fueling" speculation of global warming and climate change tipping point due to an enhanced greenhouse effect.  Is it real?  Time will tell!
 

2) heat of fusion
    - used for low intensity heat production
    Uses
    - if you freeze a 55 gal drum of water:
      55 gal x 8 lb/gal x 454 g/lb x 80 cal/g = 16 million calories or 45,000 BTU released

3) heat of vaporization
    - causes cooling of plants, animals and the environment
    Uses
    - evaporative cooling system, or fan-and-pad cooling system
    - sprinkler irrigate greenhouse or nursery crops in mid afternoon

4) infrared (IR) radiation
    - a form of radiation easily converted to heat energy when absorbed, and vice versa
    Uses
    - infrared heaters
    - radiational cooling
    - frost protection with fog, smoke and overhead coverings

5) change of state
    - constant temperature when two phases of water are present
      ice/liquid water mixture - 32 F or 0 C
      liquid water / water vapor mixture, e.g. boiling water = 212 F
    Uses
    - frost protection with overhead irrigation
    - pressure cooking

TERMINOLOGY USED TO DESCRIBE CLIMATE OVER SMALL AREAS
1) macroclimate - the climate or weather conditions of a relatively large area, usually 24 to 50 miles.
2) local climate - the climate or weather conditions of a smaller localized area; ex. a valley,
                            stand of trees, open field, sides of a hill, etc.
3) microclimate - the climate or weather conditions of a very small area, ex. inside vs. outside
                            a canopy, upper vs. lower leaf surface, etc.
.
GLOBAL CLIMATIC ZONES (determined by position of earth relative to the sun)
1) Tropical Climatic Zone
    The area between the 23 1/2^o latitude N and S of equator.
    Between the Tropic of Cancer (off S. tip of Fla. and middle of Mexico) and the Tropic of Capricorn
    Warm, rarely if ever freezes

2) Temperate Climatic Zone
    The area between the 23 1/2^o and 66 1/2^o latitude N & S.
    Between Tropic of Cancer and Arctic Circle, and Tropic of Capricorn and Antarctic Circle.
    Has hot and cold seasons

    a) sub-tropical - often used to describe the southern most area of the Temperate Climatic Zone 
        (ex. South Florida and Rio Grande Valley), but it is not an official climatic zone.

3) Arctic Climatic Zone
   The area between the 66 1/2^o N latitude and the N. Pole and the 66 1/2^o S latitude and the S. Pole.
   North of Arctic Circle, and south of Antarctic circle.
    Always cold and frozen

• At the summer solstice

The earth's axis is orientated 23 1/2 degrees towards the sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Cancer.

• At the winter solstice

The situation is reversed, i.e. the earth's axis is orientated 23 1/2 degrees away from sun, thus the sun's rays strike the earth at a 90 degree angle at the Tropic of Capricorn.

• At the the autumnal and vernal equinox

The earth's axis is neither orientated away from nor towards the sun (I made up the term obliquely parallel to describe this, or sometimes I call it cock-eyed parallel), thus the sun's rays strike the earth at a 90 degree angle at the equator.

    Due to:  (see diagram)
    a) sun's rays spread over greater area
    b) sun's rays pass obliquely through thicker layer of atmosphere

2) Time of Year or Seasonal Variation - temperature fluctuates most in the Temperate Zone

Seasons: caused by the unique tilt of earth and orientation to sun
summer solstice - June 21 or 22, when earth's axis is tilted 23 1/2^o towards sun.
    Warmer due to:
    a) sun's rays concentrated over smaller area
    b) sun's rays travel through thinner layer of atmosphere
    c) days longer

winter solstice - Dec. 21 or 22, when earth's axis is tilted 23 1/2^o away from sun
    Colder due to:
    a) sun's rays spread over larger area
    b) sun's rays pass obliquely through thicker layer of atmosphere
    c) shorter days

vernal or spring equinox - March 20 or 21, when earth's axis is oriented oblique to,
    but neither towards nor away from, the sun

autumnal or fall equinox - Sept. 22 or 23, when earth's axis is oriented oblique to,
    but neither towards nor away from, the sun

    a) minimum average temperature: around sunrise

    b) maximum average temperature: mid to late afternoon

4)  Time of Year - hottest late summer

5) Elevation or Altitude

    a) small scale - hot air rises, cold air sinks into low areas

    b) large scale -  the temperature decreases 0.6 ^oC/100 m or 1 ^oF/330 ft increase in altitude

6) Slopes - warmest to coldest slopes of a hill or side of a building: south > west > east > north

7) Water Bodies - stabilizes temperature; warmer in winter, cooler in summer

8) Soils

    a) dark soils warm faster than light soils in spring

    b) dry soils warm faster than moist soils in spring

MINIMUM CARDINAL TEMPERATURE
a) growth: 40-50 ^oF (5-6 ^oC) for most species

b) survival

    1) tender or chilling sensitive: 32 to 45 ^oF (0 to 7 ^oC)

    2) semi-hardy plants: 15 to 29 ^oF (-9 to -2 ^oC)

    3) hardy plants: less than 0 ^oF (-18 ^oC)

OPTIMUM TEMPERATURE
a) cool-season plants: grow best at 65-75 ^oF (18-24 ^oC)

    1) in southern U.S.: grow as fall-winter crops.

    2) in northern U.S.: grow in late spring, summer, early fall

b) warm season plants: grow best at 78-90 ^oF (24-32 ^oC)

    1) in southern U.S.: grow in late spring and summer, early fall

    2) in northern U.S.: grow in summer, but for some warm season crops the growing season
        may be too short to get good yield.

MAXIMUM CARDINAL TEMPERATURE
a) growth: 90-96 ^oF (32-36 ^oC), most species

b) survival: 130 ^oF (54 ^oC), most species.

     1) Denatures proteins (unfolding of proteins) - at 130 ^oF

B) Dies slowly or just poor growth

    1) Desiccation - causes excessive drying-out

    2) Sun scald or scorch - desiccation followed by death of tissue

    3) Respiration exceeds photosynthesis - depletes stored food
 

METHODS USED TO DECREASE HIGH TEMPERATURES
A) Soil temperatures

    1) mulch - insulates and blocks out light

B) Air temperatures

    1) Decrease light intensity (decrease both visible and infrared if possible)

        a) lath house - wooden slates covering over nursery crops

        b) shade cloth or saran over nursery crops or greenhouses

        c) shading compound or whitewash painted on greenhouse roof

        d) fluid roof greenhouse - colored solution flowing through a double-layered roof (not common)

    2) Evaporative cooling (relies on heat of vaporization)

        a) spray foliage and physical structures during mid-afternoon

        b) fine mist or fog injected into a greenhouse

        c) fan-and-pad cooling system in a greenhouse - moist pads

Chilling Injury - damage or death due to cold, yet above freezing temperatures (32 to 45 ^oF).

Freeze Injury - damage or death due to temperatures below freezing (below about 28 ^oF).

TWO TYPES OF FREEZES BASED ON HOW THEY OCCUR

1) Radiational Freeze or Frost - temperature drops due to radiational cooling which results
                                                  in a temperature inversion; occurs on calm, clear nights.
                                                  (see diagram on next page)

• radiational cooling - loss of heat by long wavelength infrared (IR) radiation.

• temperature inversion - a warm air mass above a cold air mass.

• dew point - the temperature at which air reaches 100% relative humidity. 

2 Types of Radiational Freezes

a) white frost - occurs when the temperature drops below both the current dew point (dew forms)
                       and below freezing (dew freezes).

b) black frost - occurs when the temperature drops below freezing, but remains above 
                        the current dew point.
 

2) Increased membrane leakiness

    a) membranes lose selective permeability

    b) often appears deeper green and slightly waterlogged

Sensitive Plants: usually will not kill the plant, but may stunt its growth or damage parts of the plant.

• tropical plants
• tropical fruits 
• summer annuals and bedding plants 
• chilling sensitive vegetables 

    a) Very rapid temperature drop
         - ice forms in cytoplasm and ruptures cell
         - seldom occurs, but always fatal

    b) Moderate temperature drop
         - ice forms in cell wall and cytoplasm dehydrates
         - most commonly occurs, not fatal to hardy or cold acclimated plants.

more sensitive vs. more resistant
young tissue vs. old mature tissue
growing tissue vs. dormant tissue
flower buds vs. vegetative buds
roots vs. shoots

3) Frost heaving - soil freezes and expands, thus heaving the plant out of the soil.

4) Bark splitting - cambium under bark freezes, expands, then splits the bark.

5) Physical or mechanical breakage (ice damage) - from weight of ice on plant.

6) Sun scald or Southwest injury - excessive desiccation on southwest side of tree;
                                                      sunlight is brightest on the south and west side.

2) Increase air temperature
    a) eliminate temperature inversion:
        1) wind machines 
        2) helicopters
           (A Walk in the Clouds, temperature inversion)
    b) irrigation
        1) flood irrigation; water is warmer and stabilizes temperature (due to high specific heat)
        2) overhead irrigation; constant temperature at 32 ^oF when liquid/ice present
   
 

HOW TO PREVENT ADVECTIVE FREEZE DAMAGE
1) Plant selection - the ideal method, because then no other method is needed.
    See USDA Hardiness Map
     See plant label

2) Radiational freeze methods - some are moderately effective for mild, short freezes. 
    a) Insulate: mulch, foam, hot caps (NOT fog or smoke) 
    b) Increase air temperature: irrigation, oil burners or smudge pots if mild and little wind 
    c) CANNOT USE: fog, smoke or eliminate temperature inversion

3) Site selection - avoid north side of hills, buildings, etc.; avoid frost pockets in low areas valleys  etc.

4) Delay development in spring - avoids damage to new spring growth and flower buds 
                                                    from late spring frost.

5) Harden-off or cold acclimation in fall: is a normal part of dormancy and preparation of 
                                                                the plant for for winter. 
    Naturally triggered by: 
    a) short days 
    b) cool temperatures 
    c) cold temperatures 

    Allow to occur naturally by observing the following:
    1) Do not encourage growth:
         a) decrease fertilization 
         b) decrease watering 
         c) avoid pruning 
    2) Avoid stress
         a) insect, disease or physical damage 
         b) poor nutrition and nutrient deficiencies 
         c) too heavy fruit load 

Purpose - to survive adverse conditions.
 

TWO TYPES OF DORMANCY
1) Quiescence - dormancy imposed by external or environmental conditions

What triggers?
a) Unfavorable environmental conditions
b) External factor, such as hard seed coat

What causes?
Unfavorable environment; too dry, cold, hot, etc.

How to overcome?
Remove unfavorable environment

What triggers?
Environment:
a) short days (SD)
b) decreasing temperatures

What causes?
Internal physiology is unfavorable:
a) low level of growth promoters (e.g. auxin or gibberellic acid), and/or
b) high level of growth inhibitors (e.g. ABA)

How to overcome?
Give period of cold between 32-45 ^oF (0-7 ^oC), which satisfies the chilling requirement.  


chilling requirement - the number of hours of cold between 32-45 ^oF (0-7 ^oC) required to satisfy rest.

VEGETATIVE AND FLOWER BUD DORMANCY

Cold is required for some trees and shrubs to flower and/or start vegetative growth in the spring, especially temperate trees, shrubs and other perennial plants that are native to the Temperate Climatic Zone.

• chilling requirement - the number of hours of cold temperatures between 32-45 ^oF 
                                   (0-7 ^oC) required to overcome rest (physiological dormancy).

• flower buds - usually have a shorter chilling requirement (that's why cherry blossom season in DC is so spectacular.
  
• vegetative buds - usually have a longer chilling requirement 

Cold is required for some bulb crops to flower; especially bulbs native to the northern part of the Temperate Climatic Zone, for example tulip.

• cold storage or bulb chilling - a period of cold to satisfy chilling requirement of bulbs to
                                                overcome flower bud rest (physiological dormancy).

• usually 6-12 weeks at 35-45 ^oC (0-7 ^oC) in a cooler or refrigerator. 

SEED REST OR EMBRYO REST

Cold is required for some seeds to germinate, especially seeds of trees and shrubs which are native to the Temperate  Climatic Zone.

• stratification - moist, cold (32-45 ^oF, 0-7 ^oC) storage  for 6-12 weeks required to 
                       overcome embryo rest (physiological dormancy).

GROWTH HABITS
rosettes - radish, carrot, turnip, mustard, kale, bluebonnet, Indian paint brush
heads - cabbage
bulbs - onion

LIFE CYCLE
1st year - germinate and grow vegetatively as rosettes or bulbs in late fall-winter
winter - are vernalized by cold of winter to trigger flower inception
2nd year - in spring the flowers forms and elongates, called bolting

Example, bluebonnet
Fall/Winter - germinate and grow as small rosette plants.
Spring - bolt and produce flower spike. 

DEFINITIONS
Vernalization - a cold treatment (32-45 ^oF for 4-12 weeks) required to trigger or initiate
                         flower formation in biennials.
 Bolting - flower formation and seed stalk elongation in biennials

De-Vernalization- exposure (1 day to 1 week) to high temperatures (90-95 ^oF) immediately 
                              after vernalization, which erases the vernalization treatment.
 
Site of Perception - growing point (apex) of stems.