NATS 101

Lecture 6 TRTemperature Variations

Term Project

Term Project Description• One of Two Options

1. Scientific analysis of one of two films on climate change.2. Analysis of the daily afternoon weather for Tucson over a three-week period.

Term Project

• Recommendations1.Start project very soon. Preferably now.2.Scientific exchange with other students is OK,

but the paper that you submit must be your own and reflect your final thoughts.

3.Turnitin software will be used to identify possible cases of plagiarism.

Temperature Questions

• What causes diurnal temperature variations?

• What physical processes can influence daily temperature variations?

• Why is MAX temperature after solar noon?• Why is MIN temperature just after sunrise?• What is Wind Chill Factor? (if time allows)

MAX Temperature near Surface

2) Conduction2) Conduction

1) Solar SW1) Solar SW

Ahrens, Fig 3.1

3) Convection3) Convection

4) Air near ground is heated the most

MIN Temperature near SurfaceAhrens, Fig 3.31) Outgoing 1) Outgoing

InfraredInfrared

3) Absorbed 3) Absorbed & Re-emitted & Re-emitted

InfraredInfrared

2) Conduction2) Conduction

INVERSION – Temp increases w/height

4) Air near ground is cooled the most

Daily Range of TemperaturesAhrens, Fig 3.10

MAX-MIN difference decreases with height above ground

12 and 00 UTC TUS Sounding

MAX-MIN Range 0oC at 700 mb-2400 m

2oC at 850 mb-800 m

6oC at 910 mb-150 m

12oC at 925 mb-ground

Range decreases with height

isotherm

sisobars

Inversion-Warmer with Height

Rapid Cooling with Height

Diurnal Range

Growth and Decay of Inversion Evening Morning

Temperature

Hei

ght

t1

t2

t3

Temperature

Hei

ght

t2

t3

t1

t4t4

Cooled the most at the ground level Warmed the most at the ground level

What Affects Inversion Strength?

Cloud CoverClear skies-strong inversionCloudy skies-weak inversionLand CharacteristicsSnow cover-strong inversionBare ground-weaker inversionWind SpeedCalm winds-strong inversionStrong winds-weak inversion

Weak IR Strong IR

Absorption Re-Emission

Warm

Cold

Mixing with Fast Winds

When Does MAX-MIN Occur?

Ahrens, Fig 3.2

Ahrens, Figs. 3.8, 3.9Ahrens, Figs. 3.8, 3.9

100100ooFF 1010ooFF

DJFDJF

JJAJJA

Winter-Summer Temperature Variations at

Sea LevelContinents undergo

larger changes than oceans

High latitudes undergo larger changes than low latitudes

Controls of Temperature

• LatitudeAverage temperatures in middle latitudes change by 5-10oC every 10o latitude change

• ElevationLapse rate in troposphere is 6.5oC/kmTucson (2,500 ft) July Max - 100oFMt. Lemmon (8,500 ft) July Max - 76oF

Controls of Temperature

• Ocean Currents and Prevailing WindsWarm-Gulf StreamCold-California Current

• Land versus WaterHeat capacity of water is 5X that of landAbsorbed solar energy is distributed a greater depth in water than in land

Specific Heat CapacityHeat required to raise the temperature of

1 gm of mass 1oC.Water has higher heat capacity than rock.

Material Specific Heat Capacity (Cal gm-1 oC-1)

Still Water 1.00 Dry Air 0.24 Granite (Rock) 0.19

Still water warms or cools very slowly compared to air and land

Water-Soil Heating Depth

Deep Penetration

Shallow Penetration

Consider the Fate of Incoming Solar Radiation Penetrating Water vs. Soil

Convective Mixing

Small warming over great depth Large warming in shallow layer

Conduction No mixing

Large Heat Capacity Small Heat Capacity

Soil Temperature

Wallace and Hobbs

Wallace and Hobbs

Ocean Temperature

Wind Chill

Still air is poor conductor; lack of wind allows insulating layer of still air to form next to skin

Wind blows insulating layer of air from skin Forced convection or heat transport by advection

The main reason for seasons is?

1. Eccentricity of the earth’s orbit2. Tilt of the earth’s axis (obliquity of the

ecliptic)3. Precession of the equinox4. Millennium variations in earth-to-sun

distances at aphelion and perihelion

Which statement is not a reason that coastal sites experience less extreme

seasons than inland sites?1. Water has a higher heat capacity than soil2. Convective heat transfer is far more

efficient in water than soil3. Water has a higher thermal conductivity

than soil4. Sunlight penetrates deeper into water than

soil

Summary • Balance between incoming and outgoing energy

controls temperature rises and fallsMAX late afternoon, MIN just after sunrise

• Diurnal temp. changes are largest at groundAffected by wind, cloud cover, land type

• Winter-Summer differencesLargest over land, high latitudes

• Temperature controlsLatitude, Altitude, Land-Sea, Ocean Currents

Next Class AssignmentAtmospheric Moisture

• Reading - Ahrens3rd-Pg: 75-86, B: 426, D: 429-4324th-Pg: 77-89, B: 430, D: 433-4365th-Pg: 79-91, B: 440, D: 443-446

• Homework03 - D2L (Due Monday Feb 8th)3rd-Pg 106: 4.1, 4.2, 4.5, 4.6, 4.9, 4.104th-Pg 108: 4.1, 4.2, 4.5, 4.6, 4.9, 4.105th-Pg 108: 4.1, 4.2, 4.5, 4.6, 4.9, 4.10