THE ENERGY BALANCE AT SURFACE
1st LAW OF THERMODYNAMICS (CONSERVATION OF ENERGY):
Energy only changes from one form to another. It cannot be created or
destroyed.
Net Radiation + Sensible Heat + Latent Heat +
Ground Heating = 0
Read pages 49, 56-57 Book
SENSIBLE AND LATENT HEAT
STATES OF MATTER
Gas: The particles move rapidly; there are larger spaces between them
Liquid: The particles move less rapidly; they are closer
Solid: The particles move very little and are arranged in a tight pattern
Gas
Liquid
Solid
SENSIBLE AND LATENT HEAT
HEAT TRANSFER:
•Radiation: electromagnetic waves transport energy trough space (e.g. sun
radiation)
•Conduction: the transfer of energy trough matter from particle to particle.
•Convection: the transfer of heat by mass motion of a fluid (water, air) when the
heated fluid is caused to move away from the source of heat (the heated fluid is
less dense and rises)
SENSIBLE HEAT:
•Heat sensed by touching or feeling (measured by a
thermometer)
•Sensible heat transfer (Ex: conduction, convection)
LATENT HEAT:
•Hidden heat. It’s stored in the form of a molecular motion when
a substance change from solid to liquid, liquid to gas, or solid to
gas
•Latent heat transfer: when water evaporates from a moist
surface or water surface it removes the heat stored in the
change of state (transference of heat from surface to
atmosphere)
cooling surface
SENSIBLE HEAT
LATENT HEAT
SURFACE AND AIR TEMPERATURE
TEMPERATURE:
Temperature is the measure of level of sensible heat of matter
(gaseous, liquid, solid)
SURFACE TEMPERATURE:
Temperature in a surface is determined by the balance among
various energy flows:
• Net radiation (positive at day, negative at night)
•Sensible heat transfer
Conduction: from warm to cold trough direct contact
(ex: heat into soils)
Convection: fluid is heated by warm surface, expand, rises
(upward flow)
•Latent heat transfer:when water evaporates at a surface, it
removes heat stored (cooling surface). When condenses at
surface, latent heat is released (warming surface)
THE AIR TEMPERATURE (CHAPTER 3 BOOK)
•Temperature observed at short distance above surface
(1.2m or 4 feet)
•Air temperature and surface temperature can be
different, but air temperatures tend to follow surface
temperatures (because of heat flows)
•Weather information uses air temperature
AIR TEMPERATURE MEASUREMENT
•In US is widely measured using Farenheit
•The Celsius scale is the international standard
•The World Meteorological Organization (WMO) is a specialized agency of
United Nations. One of its purposes is to promote standardization of
meteorological observations
http://www.worldweather.org/
•Instrument used:
Thermometer
• liquid-filled (expands when liquid is heated, contracts when is cooled)
• thermistor (change of electrical resistance with temperature)
Not always temperature at same latitudes are similar, for
example:
Mongolia (Midlatitude)
Min: 6.0 F
Max: 60.0 F
Baltimore (Midlatitude)
Min: 45.0 F
Max: 65.0 F
TEMPERATURE RANGE
Daily: Tmax- Tmin
Annual: Difference between the lowest and
highest monthly mean temperatures
THE AIR TEMPERATURE
The factors that influence air temperature are:
1.
Insolation
2. Latitude
3. Surface type (urban, moist soil, forest, deserts)
4. Coastal vs interior location:
•
Narrower range of air temperatures in coast (water
heats and cools more slowly than land)
5. Elevation
ANNUAL CYCLE OF MAXIMUM AIR TEMPERATURE
(SOUTHERN HEMISPHERE)
40
Max Temp (°C)
S
E
35
S
E
30
25
20
15
10
Nairobi
Asuncion
5
Bariloche
0
J
F
In-class Exercise
M
A
M
J
J
A
S
O
N
D
URBAN-RURAL DIFFERENCES
RURAL:
moist soil
vegetation
evaporation
transpiration
cooler surface
URBAN:
dry surface
asphalt and roofing
(dark surfaces)
insolation
warmer surface
more absorption
(twice the
vegetation)
warmer surface
LAND AND WATER
CONTRASTS
• The range of temperature is lower in water
• Continental air temperature isotherms shift over a much wider latitude range
from summer to winter than oceanic air temperature isotherms.
LAND AND WATER
CONTRASTS
•Reasons:
1. Penetration vs no penetration of radiation
2. Water heats and cools slowly than land
3. Mixing (warm and cool water) vs no mixing
4. More evaporation vs less evaporation
4. More evaporation
1. penetration
4. Less evaporation
1.
No penetration
2.
Land heats quickly
3. No mixing
3.mixing
2. Water heats slowly
HIGH-MOUNTAIN ENVIRONMENTS
DAILY CYCLE OF AIR TEMPERATURE
•Factors: Earth’s rotation on its axis, latitude, urban/rural,
elevation
•During day: net radiation is positive
surface gains heat
•During night: is negative
surface loses heat
Location at 45°N
Why minimum temperature takes place in early morning and not during the night?
In-class Exercise
During night: NEGATIVE net radiation
heat flows from ground surface
surface air layer warms a little bit, but
remains with low temperatures
Surface air layer is cooled
Lower temp
Lower temp…
Until net radiation is
POSITIVE
Ground surface is cooled