Title: Chapter%203:%20Air%20Temperature
1Chapter 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
2Warming 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
3Daytime 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
4Nighttime 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.
7Cold Air Near the Surface
- 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
8Q 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?
9Protecting 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
10The 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
14Daily 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?
15Diurnal temperature range decreases with
height Q where is the diurnal temperature range
higher a) urban area b) rural c) same
16Monthly 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
18The 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
19The 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
20Air 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
21Air 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
23Measuring 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
24Measuring 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/