Chapter%203:%20Air%20Temperature - PowerPoint PPT Presentation

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Chapter%203:%20Air%20Temperature

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Chapter 3: Air Temperature Warming and cooling the air near the ground Application of temperature data Air temperature and human comfort Measuring air temperature – PowerPoint PPT presentation

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Title: Chapter%203:%20Air%20Temperature


1
Chapter 3 Air Temperature
  • Warming and cooling the air near the ground
  • Application of temperature data
  • Air temperature and human comfort
  • Measuring air temperature

Freezing rain
2
Warming and Cooling Air neat the Ground
Record high T 58oC or 136oF (Libya) Record
low T -89oC or -129oF (Antarctic) Q What is
the record high temperature in Tucson a)
105oF b) 111oF c) 117oF d) 123oF Q What is
the record low temperature in Tucson a)
0oF b) 6oF c) 12oF d) 18oF http//www.wrh.noa
a.gov/twc/climate/all-time.php
3
Daytime Warming
  • Solar radiation heats ground
  • heat is transferred to the atmosphere via
    conduction, thermal convection (under calm wind
    condition), and wind-forced convection
  • Clouds reduce surface
  • temperature by reducing
  • solar heating

Q which surface is heated faster during the
day? a) dry surface b) wet surface
c) same
4
Nighttime Cooling
  • radiational cooling
  • nocturnal inversions
  • Inversions tend to occur on
  • clear, calm, dry nights
  • strong winds would mix air
  • clouds or water vapor would
  • absorb longwave radiation
  • and emit longwave radiation to
  • heat surface
  • temperature difference between surface and
    1.5m height is
  • greater during the day than at night in
    magnitude

5

Stepped Art
6

Ts reaches max at noon Ta reaches max at
3pm Both Ts and Ta reach min at sunrise T
decreases w/ height during the day T increases
w/ height at night At quiz, you might be asked
to plot temperature profile at night and during
day.
7
Cold Air Near the Surface
  • inversions
  • thermal belts
  • Drainage winds cold air that slides downhill.
  • Q Where do you expect the minimum temperature in
    Tucson
  • near river bed,
  • b) UA campus,
  • airport,
  • downtown

8
Q Surface air temperature would keep increasing
as long as the sun heats the surface. a)
true b) false Q Surface air temperature
reaches its maximum when a) the solar
radiation is maximum b) the difference of
solar radiation minus longwave radiation
becomes zero (from positive) Q At night,
compared with min Tair, the min Tsfc is a)
higher, b) lower, c) the same Q What weather
conditions are most favorable for cold
night and a strong inversion? Q Why does a
heavy jacket keep you warm in cold winter?
9
Protecting Crops from the Cold Night Air
  • To protect crops from cold surface
  • orchard heaters for radiative heating and
    convection
  • wind machines for mixing of colder surface
    with warmer air T
  • flooding for slower cooling and faster heat
    transfer from deeper soil
  • sprinkers for releasing latent heat and
    freezing to form a thin ice on buds
  • Q Small plants can be protected by covering them
    with a) straw b) cloth c) plastic bag d) all
    of them

10
The Controls of Temperature
  • Latitude control daylight period and sun
    elevation
  • land and water distribution heat capacity
  • ocean currents moving warm/cold water around
  • Elevation T decreases with height
  • Specific heat energy needed to raise T of 1 kg
    mass by 1 K and specific heat for water is
    greater than that of soil
  • Heat capacity total (relevant) mass times
    specific heat
  • Ocean has a deeper layer to absorb solar
    radiation and hence has a much higher heat
    capacity than soil.
  • Therefore ocean temperature changes more slowly

11

Q why is temperature over part of the Greenland
ice greater than freezing point (32oF) in this
figure?
July sea level Ta
12

Q Winter T in UK is warmer than Russia over the
same latitude, because of a) warm ocean
current, b) land-sea contrast,
c) elevation difference
January sea level Ta
13

Using the January sea level Ta data below Q
which has a higher temperature over the same
midlatitude in northern hemisphere a)
land b) ocean c) same Q which has a higher
temperature over the same midlatitude in
southern hemisphere a) land b) ocean c)
same Q which hemisphere has a greater
temperature change with latitude a)
northern hemisphere b) southern hemisphere
c) same
14
Daily Temperature Data
  • diurnal temperatur range Tmax Tmin
  • large range occurs for dry, clear sky
    over desert (dry soil)
  • clouds and humidity effects reduce daytime T but
    increase nighttime T
  • dry soil has a smaller specific heat and lower
    evaporation
  • Q why does water surface have a smaller diurnal
    range?

15
Diurnal temperature range decreases with
height Q where is the diurnal temperature range
higher a) urban area b) rural c) same
16
Monthly and Yearly Temperature Data
  • annual temperature range
  • max monthly T - min monthly T
  • Q Why does Richmond have a much larger annual
    range?
  • because Richmond is primarily affected by the
    ocean
  • because Richmond is primarily affected by the
    American continent

17
Normal T refers to the 30-year average T for
that day Q What is the normal temperature for
a particular day (March 15 over southwestern
U.S.) in the figure? A not a single value but a
range of values (computed using statistical
method)
Q Is 85oF abnormal based on this figure a) yes
b) no
18
The Use of Temperature Data
  • heating degree-days daily mean T lt 64oF (left
    panel)
  • cooling degree-days daily mean T gt 65oF (right
    panel)

Q Todays average temperature is 85oF. What is
the cooling degree days? a) 5 b) 10 c)
20 d) 30
19
The Use of Temperature Data
  • growing degree-days daily mean T gt base T

Q For an idealized situation base T of 50oF,
daily average T of 60oF, and GDD to maturity of
1200, how many months are needed (after planting)
for harvest a) 1 months b) 2 months c) 3
months d) 4 months
20
Air Temperature and Human Comfort
  • Human body stabilizes its T (i.e., prevents its
    T decrease)
  • primarily by converting food into heat
    (metabolism)
  • The stronger the wind, the faster the bodys
    heat loss
  • High winds in below-freezing air can remove heat
    from exposed
  • skin so quickly that the skin may actually
    freeze (called frostbite)
  • Dry heat perspire to feel cool
  • Heat and humidity feel hotter

21
Air Temperature and Human Comfort
  • wind chill index frostbite could occur in 30 min
    or less in
  • shaded areas

Q For the same wind speed of 5 mile/hr, the wind
chill effect is stronger at a) lower T,
b) higher T, c) same
22
  • Hypothermia the rapid, progressive mental and
    physical collapse that accompanies the lowering
    of human body temperature. Favorable condition
    for hypothermia cold, windy, and wet
  • Q For temperature of 0oF and wind speed of 20
    mile/hr, the wind-chill temperature is a) 0oF
    b) -20oF c) -22oF

23
Measuring Air Temperature
  • Q T is as high as 500oC
  • in the upper atmosphere of
  • 300 km. Without protection suit,
  • astronauts would be dead due to
  • too high T,
  • too cold T
  • strong solar UV radiation
  • Q how do you measure T in such
  • an environment?
  • a) using a special thermometer
  • b) using a special radiometer

24
Measuring Air Temperature
  • liquid-in-glass thermometers mercury or alcohol
  • maximum and minimum thermometers
  • Electrical thermometers
  • instrument shelters
  • Infrared sensor or radiometer (for surface T)

25
  • Q Even when Tair is 90F in Tucson, you would
    feel hot as you go under the sun, because
  • Tair refers to T under the shade
  • solar heating is too strong in Tucson
  • both

Q what is the measurement height of surface air
temperature? a) 0.5m b) 1.5m c) 2.5m
26

Over 900 Automated Surface Observing System
(ASOS)
Precip, wind, T/Td, rain type, lightning,
cloud base, freezing rain, visibility
Where to get T data?
UA http//www.atmo.arizona.edu/index.php?section
weather Tucson NWS http//www.wrh.noaa.gov/twc
/ US http//www.ncdc.noaa.gov/
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