Essentials of Meteorology - Chapter 3: Air Temperature

Daytime warming

-air is a poor conductor so initial heating only effects air next to the ground
-convection begins, and rising air bubbles (thermals) help to redistribute heat.

When do the most intense solar rays occur?

The most intense solar rays are around noon

temperature lag

The delay between what the sun is doing and how the earth reacts.

How warm the air becomes depends on several factors like...

-type of soil
-moisture agent
-vegetation cover

heat capacity

The amount of heat required to raise the temperature of a specified amount of a substance by 1°C or 1 K.

Radiational cooling

occurs as the ground and air above it cool, by radiating infrared energy

Radiational inversion

increase in air temperature just above the ground

Ideal Radiational Cooling Conditions

-calm air (prevents mixing)
-long nights (winter nights)
-dry and cloud free air (outgoing LW radiation escapes to space more easily)

What protects crops from the cold night air?

-cover
-smudge pots: warm the air around trees by convection currents
-wind machines: mixing
-Irrigation: ice protects trees from sub-freezing temperatures

extreme low temperatures

the coldest area in North America are found in the Yukon and Northwest Territories of CanadaDail

Daily (diurnal) range of temperature

the difference between the daily maximum and minimum temperature

Mean(average) daily temperatures

average of the high and low temperatures in a 24 hour period

controls of temperature

-the main factors that cause variations in temperature from one place to another
-The main controls are...
-latitude
-land and water distribution
-ocean currents
-elevation

Isotherms

lines drawn on a map connecting places that have the same temperature

Applications of Air Temperature Data

-Heating degree-day: people begin using heat when temperature drops 65 degrees Fahrenheit
-Cooling degree-day: people being to cool when temperature climbs above 65 degrees Fahrenheit
-Growing degree-day: mean daily temperature is one degree above the base temperature for a crop

Sensible temperature

the human body's perception of temperature

wind-chill index

-how cold the wind makes us feel
-concerns with this- frostbite and hypothermia

Instruments

-Thermometers: liquid-in-glass, maximum, minimum, electrical resistance, and bimetallic
-Automated Surface Observing system
-Radiometers
-Thermograph: measures and records temperature
-Data loggers

Explain why the warmest time of the day is usually in the afternoon, even though the sun's rays are more direct at noon.

Earth materials retain heat so even though the sun's insolation is getting less, the earth is still warming up.

On a calm, sunny day, why is the air next to the ground normally much warmer than the air several feet above?

Air near the ground warms by conduction, so if no mixing from wind, it will warm only lower layers.

Explain how incoming energy and outgoing energy regulate the daily variation in air temperature.

When incoming energy exceeds outgoing, the air temperature rises. When outgoing exceeds incoming, the temperature falls.

Draw a vertical profile of air temperature from the
• Afternoon
• Early morning just before sunrise.
• Explain why the temperature curves are different.

The ground warms and cools faster than the air immediately above it.

Explain how radiational cooling at night produces a radiation temperature inversion

As outgoing energy exceeds incoming, ground cools. Air immediately above it cools by conduction. Hence a radiative inversion.

What weather conditions are best suited for the formation of a cold night and a strong radiation inversion?

• Clear sky
• Light winds
• Long night
• Dry air

Explain why thermal belts are found along hillsides at night.

Thermal belts exist because cold, dense air slides down mountainside into valley creating an inversion and hence a thermal belt.

List four measures farmers use to protect their crops against the cold. Explain the physical principle behind each method.

• Helicopter - mixes air
• Orchard heaters - warms air around trees by convection
• Spray blossoms - won't freeze under ice
• Flood orchard - water has high heat capacity

Why are the lower branches of trees most susceptible to damage from low temperatures?

Lowest temperatures are near the ground

Describe each of the controls of temperature.

• Latitude - colder toward poles, warmer near equator
• Land water distribution - heat capacity for each is different
• Ocean currents - warm currents (Gulf Stream) moderate temperature
• Elevation - go up in altitude, temperature drops.

Look at Fig 3.15 (temperature map for January) and explain why the isotherms dip southward (equatorward) over the Northern Hemisphere.

Land water distribution; water cools slower than land.

During the winter, frost can form on the ground when the minimum thermometer indicates a low temperature above freezing. Explain.

• Ground is colder than air.
• Thermometer may be at altitude of 5 feet and that air is above freezing while ground is at freezing.

Why do the first freeze in autumn and the last freeze in spring occur in bottomlands?

Cold air is more dense and sinks to low spots.

Explain why the daily range of temperature is normally greater:
• In dry regions than in humid regions
• On clear days than on cloudy days.

Atmosphere usually cools and warms at dry adiabatic lapse rate.
• Moist air retains heat
• Cloudy skies keep IR in and hence ground is warmer.

Why are the largest annual range of temperatures normally observed over continents away from large bodies of water?

Ground warms quickly in day and cools quickly at night.

Two cities have the same mean annual temperature. Explain why this fact does not mean that their air temperatures throughout the year are similar.

• First, it is an average.
• Second, one may be near the coast where the temperature range doesn't vary much and the other may be inland where the range is large, but the averages are the same.
• e.g. AVE = 65; City 1: 60-70 City 2: 35-95

What is heating degree-day?
• Cooling degree-day?
• How calculated?

• Heating degree day based on assumption folks will turn on furnaces if temperature is below 65oF.
• HDD = 65 - ave T
• Cooling degree day based on assumption folks will turn on AC if temperature is above 65oF.
• CDD = ave T - 65

During a cold, calm, sunny day, why do we usually feel warmer than a thermometer indicates?

Possibly building up layer of molecules on skin since wind is calm. Called sensible temperature. Depends if you are standing in the sun or not.

1. Assume the wind is blowing at 30 mi/hr and the air temperature is 50F. Determine the wind-chill equivalent temperature from the table.
2. Under the conditions listed above, explain why an ordinary thermometer would measure a temperature of 50F and not a much lower temperature.

1. -190F
2. A thermometer cannot measure the effect of wind. Besides, the wind chill is what you feel, not what it actually is.

What atmospheric conditions can bring on hypothermia?

cold, wet, windy day

Someone says, "Today, the air temperature measured 99oF in the sun." Why does this statement have no meaning?

Thermometer will absorb radiant energy from the sun in addition to the energy from the air molecules.

Explain why the minimum thermometer is the one with the small barbell-shaped index marker in the bore.

Barbell is indicator for minimum temperature. It is moved by the meniscus of the liquid.

Briefly describe how the following thermometers measure air temperature:
1. Liquid in glass
2. Bimetallic
3. Electrical
4. Radiometer

1. Liquid in glass - energy moves liquid up and down inside the glass tube
2. Bimetallic - two metals bonded together; one expands or contracts more than the other.
3. Electrical - a plate with electrodes on either side; change in temperature changes current across plate.
4. Radiometer - infrared sensors that measure emitted energy.

What are the three types of temperature measurements?

liquid-in-glass thermometers
thermistor
radiometers

-air temperature thermometers- use alcohol or mercury thermal expansion
-maximum/minimum thermometers

liquid in glass thermometers

electrical resistance changes with temperature
fastest way to measure temperature

thermistor

causes resistance in a circuit and measures resistance

thermistor

measures emitted radiation

radiometers

what law does the radiometer represent? why?

stefan-boultzman
high radiation= high temp

describe how minimum temperature scales work

bulb with liquid, has plastic index marker that stays at lowest temperature even as liquid rises around it

describe how maximum temperature thermometers work

stays at max temp cause of constrictor not allowing fluid to go back down

temperature changes throughout day due to relative

energy level

how does earth cool itself

by emitting radiation

true or false: when the sun rises, we immediately begin gaining energy

false, we are still losing energy

temperature generally increases when _______ solar radiation is ______ and decreases when ______ terrestrial radiation is ______

incoming, larger
outgoing, greater

maximum temperature _______maximum solar heating

lags behind

what affects the pattern of daily temperature variations

cloud cover, winds, nearby bodies of water

if there is cloud cover during the day, what happens to incoming solar radiation? what is the effect on the temperature

the incoming solar radiation reflects back off of the clouds and into the sky above
results in a cooler day

if there is cloud cover at night, what happens to outgoing terrestrial radiation? what is the effect on the temperature

the outgoing radiation reflects off the clouds and comes back down to earth resulting in a warmer night

when does the minimum daily temperature occur

a few minutes to half hour after sunrise

when does the maximum daily temperature occur

when incoming energy equals outgoing energy, after maximum incoming solar radiation

do we have more direct radiation in june or december

june

how do clouds affect temperature

reflected sun and radiation cant get through to warm surface so cooling during the day, greenhouse effect at night warms the surface

air temperature data
maximum, minimum, mean, range

daily (diurnal)

average of diurnal mean

monthly mean

average of monthly mean temperatures for a year

annual mean

what are cooling degree days

daily mean to 65 F

what are heating degree days

65 F to daily mean

During the day the Earth _____ more radiation than it _____ and the ground warms

absorbs
emits

how does the ground warm the air

by conduction convection annd latent heating

During the night the Earth _______more radiation than it ______ and the ground cools

emits
absorbs

what is an inversion

The increase of air temperature with height is called an inversion

true or false: the temp at the ground is erratic

true!

what is the standard height to measure temp

1 1/2 m up

generally, temperature ______ as you go up in the troposphere

decrease

at night, Earth emits _____ radiation causing ground and surrounding air to _____

infrared
cool causing inversion

Factors that will cause strong inversions

Long nights
Calm winds keeping warm air from mixing down
Clear sky allowing ground to radiate to space
Cold air, being more dense, often drains into valleys

what do long nights that cause inversions depend on

winter and latitude

what effect do cloudy nights have on inversions

prevent inversions from occurring due to the greenhouse effect they produce by absorbing the radiation and sending it back to ground surface warming it

true or false: inversions only effect the surface

false
inversions have effects throughout the atmosphere, can affect smells

the increase of air temperature with height caused by the ground cooling the air near the earth's surface

inversion

why does ann arbor often have the coldest temperature

the temperature station is in a valley, where an inversion occurs at night

true or false: annual and daily cycles of temperatures usually have a larger range for locations near water

false, usually have a smaller range

what do the following reasons support:
Solar radiation heats a thin layer of soil versus a deep layer of water
Water evaporates countering the solar radiation heating
Water has a much higher specific heat

why locations near water have smaller range for annual and daily cycles of temperatures

what is specific heat

the amount of energy needed to raise the temperature of 1 g of a substance to 1 K

for the month of january, a land-water distribution map shows the temp line staying _____. why?

southward
water is warmer, land is colder

why are the lines not straight in a land-distribution map

land and water heat differently

which reasoning for why locations near water have smaller range for annual and daily cycles of temperatures does the following support:
when you bury yourself in the sand, it is dark and no light penetrates
when you swim 5ft down in the water at the beach, sun still penetrates

solar radiation heats a thin layer of soil vs a deep layer of water

which reasoning for why locations near water have smaller range for annual and daily cycles of temperatures does the following support:
evaporation causes water to lose energy

water evaporates countering the solar radiation heating

land masses have greater _________ than water

seasonality

land masses are _____ in the summer and _____ in the winter compared to water

warmer
cooler

Radiational Cooling

both the ground and air above cool by radiating infrared energy

Radiation Inversion

a measured increase in air temperature just above the gound

Nocturnal Inversion

radiation inversions that occur on most clear, calm nights

Freeze

extreme cold

Thermal Belts

middle latitudes that are less likely to experience freezing temperatures

Orchard Heaters (Smudge Pots)

machines used to warm the air around the trees by setting up a convection current close to the ground

Wind Machines

power-driven fans that resemble airplane propellers

Daily Range of Temperature

the difference between the daily maximum and minimum temperature

Mean Daily Temperature

the average of the highest and lowest temperature observed in a given 24-hour period

Controls of Temperature

the main factors that cause variations in temperature from one place to another

Isotherms

lines connecting places that have the same temperature