Chapter 3: Air Chapter 3: Air TemperatureTemperature

Warming and cooling the air near Warming and cooling the air near the groundthe ground

Application of temperature dataApplication of temperature data Air temperature and human comfortAir temperature and human comfort Measuring air temperatureMeasuring air temperature

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Freezing rain

Warming and Warming and Cooling Air neat Cooling Air neat

the Groundthe GroundRecord 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.noaa.gov/twc/climate/all-time.php2

Daytime WarmingDaytime Warming Solar radiation heats ground; Solar radiation heats ground; heat is transferred to the atmosphere via conduction, thermal convection (under calm heat is transferred to the atmosphere via conduction, thermal convection (under calm

wind condition), and wind-forced convectionwind condition), and wind-forced convection Clouds reduce surface Clouds reduce surface

temperature by reducing temperature by reducing

solar heatingsolar heating

Q: which surface is heated faster during the day? a) dry surface; b) wet surface; c) same

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Nighttime CoolingNighttime Cooling radiational coolingradiational cooling nocturnal inversionsnocturnal inversions

• Inversions tend to occur on Inversions tend to occur on clear, calm, dry clear, calm, dry nights:nights:

strong winds would mix air;strong winds would mix air;

clouds or water vapor would clouds or water vapor would absorb longwave radiation absorb longwave radiation and emit longwave radiation toand emit longwave radiation to heat surfaceheat surface

temperature difference between surface and 1.5m height is temperature difference between surface and 1.5m height is greater during the day than at night in magnitudegreater during the day than at night in magnitude 4

Stepped Art5

Ts reaches max at noon;

Ta reaches max at 3pm;

Both Ts and Ta reach min at sunrise;

T decreases w/ heightduring the day;

T increases w/ heightat night

At quiz, you might be asked to plot temperature profile at night and during day.

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Cold Air Near the Cold Air Near the SurfaceSurface

inversionsinversions thermal beltsthermal belts

• Drainage winds: cold air that slides downhill. Drainage winds: cold air that slides downhill.

Q: Where do you expect the minimum temperature in Tucson:

a) near river bed, b) UA campus, c) airport,

d) downtown

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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?

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Protecting Crops from Protecting Crops from the the

Cold Night AirCold Night Air To protect crops from cold surface:To protect crops from cold surface: orchard heaters for radiative heating orchard heaters for radiative heating

and convection;and convection; wind machines for mixing of colder wind machines for mixing of colder

surface with warmer air T;surface with warmer air T; flooding for slower cooling and faster flooding for slower cooling and faster

heat transfer from deeper soil;heat transfer from deeper soil; sprinkers for releasing latent heat and sprinkers for releasing latent heat and

freezing to form a thin ice on budsfreezing to form a thin ice on buds

Q: Small plants can be protected by Q: Small plants can be protected by covering them with a) straw; b) cloth; covering them with a) straw; b) cloth; c) plastic bag; d) all of themc) plastic bag; d) all of them

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The Controls of The Controls of TemperatureTemperature

Latitude:Latitude: control daylight period and sun elevation control daylight period and sun elevation land and water distribution:land and water distribution: heat capacity heat capacity ocean currents:ocean currents: moving warm/cold water around moving warm/cold water around Elevation:Elevation: T decreases with height T decreases with height

• Specific heat: energy needed to raise T of 1 kg mass by 1 K; Specific heat: energy needed to raise T of 1 kg mass by 1 K; and specific heat for water is greater than that of soiland specific heat for water is greater than that of soil

• Heat capacity: total (relevant) mass times specific heatHeat capacity: total (relevant) mass times specific heat

• Ocean has a deeper layer to absorb solar radiation; and hence Ocean has a deeper layer to absorb solar radiation; and hence has a much higher heat capacity than soil. has a much higher heat capacity than soil.

• Therefore ocean temperature changes more slowlyTherefore ocean temperature changes more slowly10

July sea level Ta

Q: why is temperature over part of the Greenland ice greater than freezing point (32oF)?

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January sea level Ta

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

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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

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Daily Temperature DataDaily Temperature Data diurnal temperatur range: Tdiurnal temperatur range: Tmaxmax – T – Tmin min

large range occurs for dry, clear sky over desert (dry soil)large range occurs for dry, clear sky over desert (dry soil) clouds and humidity effects: reduce daytime T but increase nighttime T clouds and humidity effects: reduce daytime T but increase nighttime T dry soil has a smaller specific heat and lower evaporation dry soil has a smaller specific heat and lower evaporation

Q: why does water surface have a smaller diurnal range? Q: why does water surface have a smaller diurnal range?

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Diurnal temperature range decreases with height

Q: where is the diurnal temperature range higher:a) urban area; b) rural; c) same

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Monthly and Yearly Temperature Monthly and Yearly Temperature DataData

annual temperature range: annual temperature range: max monthly T - min monthly Tmax monthly T - min monthly T

Q: Why does Richmond have a much larger annual range?

a) because Richmond is primarily affected by the ocean;

b) because Richmond is primarily affected by the American continent

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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 abnormalbased on this figure: a) yes; b) no

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The Use of Temperature The Use of Temperature DataData

heating degree-days: daily mean T < 64heating degree-days: daily mean T < 64ooF (left panel)F (left panel) cooling degree-days: daily mean T > 65cooling degree-days: daily mean T > 65ooF (right panel)F (right panel)

Q: Today’s average temperature is 85oF. What is the cooling degree days? a) 5; b) 10; c) 20; d) 30

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The Use of Temperature The Use of Temperature DataData

growing degree-days: daily mean T > base T growing degree-days: daily mean T > 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

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Air Temperature and Air Temperature and Human ComfortHuman 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 body’s 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

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Air Temperature and Human ComfortAir Temperature and Human Comfort wind chill index: frostbite could occur in 30 min or less in wind chill index: frostbite could occur in 30 min or less in

shaded areasshaded 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 21

Hypothermia: the rapid, progressive mental and physical collapse Hypothermia: the rapid, progressive mental and physical collapse that accompanies the lowering of human body temperature. that accompanies the lowering of human body temperature. Favorable condition for hypothermia: cold, windy, and wetFavorable condition for hypothermia: cold, windy, and wet

Q: For temperature of 0Q: For temperature of 0ooF and wind speed of 20 mile/hr, the F and wind speed of 20 mile/hr, the wind-chill temperature is: a) 0wind-chill temperature is: a) 0ooF; b) -20F; b) -20ooF; c) -22F; c) -22ooFF

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Measuring Air Measuring Air TemperatureTemperature

Q: T is as high as 500oCin the upper atmosphere of300 km. Without protection suit,astronauts would be dead due toa) too high T,b) too cold Tc) strong solar UV radiation

Q: how do you measure T in such an environment? a) using a special thermometer; b) using a special radiometer

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Measuring Air Measuring Air TemperatureTemperature

liquid-in-glass liquid-in-glass thermometers: thermometers: mercury mercury or alcohol or alcohol

maximum and minimum maximum and minimum thermometersthermometers

Electrical Electrical thermometersthermometers

instrument sheltersinstrument shelters Infrared sensor or Infrared sensor or

radiometer (for radiometer (for surface T)surface T)

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Q: Even when Tair is 90F in Tucson, you would feel hot as you go under the sun, because

a) Tair refers to T under the shade;

b) solar heating is too strong in Tucson

c) both

Q: what is the measurementheight of surface air temperature? a) 0.5m; b) 1.5m; c) 2.5m

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Precip, wind, T/Td, rain type,lightning, cloud base, freezing rain, visibility

UA: http://www.atmo.arizona.edu/index.php?section =weatherTucson NWS: http://www.wrh.noaa.gov/twc/US: http://www.ncdc.noaa.gov/

Where to get T data?

Over 900 Automated Surface Observing System (ASOS)

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