ESCI 106 – Weather and Climate Lecture 2 8-25-2011 Jennifer D. Small Jennifer D. Small.

ESCI 106 – Weather and ESCI 106 – Weather and ClimateClimate

Lecture 2Lecture 2

8-25-20118-25-2011

Jennifer D. Small Jennifer D. Small

Weather Fact of the Day: August 25

2005: Hurricane Katrina made its first US landfall on Florida East coast between Hallandale Beach and North Miami Beach.

Sustained winds of 80 mph , gusts of 90+ mph.

Katrina killed 14 as it crossed extreme southern Florida, including several killed by falling trees/tree branches.

National Watches and Warnings

Current Hurricane Irene

D: Tropical Depression – wind speed less than 39 MPH

S: Tropical Storm – wind speed between 39 MPH and 73 MPH

H: Hurricane – wind speed between 74 MPH and 110 MPH

M: Major Hurricane – wind speed greater than 110 MPH

Current Hurricane Irene

Earth-Sun Relationships

Earth’s Motions Rotation Revolution Perihelion Aphelion

The Seasons Earth’s Orientations

Plane of the ecliptic Inclination of the axis

Solstices and Equinoxes Tropic of Cancer, summer solstice Tropic of Capricorn, winter solstice Autumnal equinox, Sprig equinox Circle of Illumination


FACT: The Earth intercepts only a tiny percentage of the energy given off by the sun!

Less than one-two billionth of the suns total output!


FACT: Solar energy is NOT distributed equally over Earth’s surface. Latitude, Time of Day, & Season


FACT: Unequal heating is responsible for winds and ocean currents (Weather).


FACT: To understand weather we need to know why different latitudes receive different amounts of energy.

Earth’s Motions

Earth’s two principle motions are: Rotation Revolution

Rotation The spinning of Earth about its axis Why we have day and night

Revolution Movement around the Sun Travels at nearly 113,000 km/hr (70,000 miles/hr) Elliptical orbit – not perfectly circular

(exaggerated!)

Earth’s Motions

Elliptical Orbit – Eccentricity is ~0.8

152.1 km Perihelion

147.3 kmAphelion

July 4th

CLOSEST from the SUN

FARTHEST from the SUN

January 3rd

The Seasons

FACT: Variations in the distance between the Sun and Earth DO NOT cause the seasonal temperature change!

Change in the length of day accounts for some.

Gradual change in the angle of the sun at noon. Affects the amount of energy

received at Earth’s surface When overhead strongest Lower angle less intense

The Seasons FACT: Variations in the distance between the Sun and

Earth DO NOT cause the seasonal temperature change! The angle of the Sun determines

the path solar rays take through the atmosphere! During summer, at 90 deg, it has

the shortest distance (one atmosphere)

The longer the path the more likely the rays will be absorbed, reflected or refracted.

On any give day only a particular latitude will receive the 90 deg rays.

At 30 deg angle, twice as much atmosphere!!

At 5 deg angle, 11 times as much atmosphere.

The Seasons SUMMARY: Most important reasons for variations in the

amount of solar energy1. Seasonal changes in the angle at which the Sun’s rays strike

the surface

2. Changes in the length of daylight

Earth’s Orientation Why does length of day and sun angle change?

Earth’s orientation to the sun constantly changes!!!

Earth’s Orientation Earth’s Axis

Imaginary lines through the poles! Inclination of the axis: 23.5 deg

from the perpendicular

Plane of the ecliptic – the plane of the orbit around the sun

WITHOUT THE TILT WE WOULD NOT HAVE SEASONS!

Earth’s Orientation Solstices

Summer Solstice Tropic of Cancer Northern limit of the Sun’s rays 23.5 N Latitude June 21-22 First day of NH summer NH tilted toward Sun

Winter Solstice Tropic of Capricorn Southern limit of the Sun’s rays 23.5 S Latitude December 21-22 First day of NH winter NH tilted away from Sun

Earth’s Orientation Equinoxes

Occur mid way between the Solstices

Vertical rays strike along the equator (0 deg latitude)

Earth not tilted toward or away

Autumnal Equinox September 22 or 23

Spring Equinox March 21 or 22 Also called Vernal Equinox

Earth’s Orientation

Length of Daylight Circle of Illumination

Boundary separating the dark and light halves of the Earth

Latitude (degrees)

Summer Solstice

Winter Solstice

Equinoxes

0 12 hr 12 hr 12 hr

10 12 hr 35 min 11 hr 25 min 12 hr

20 13 hr 12 min 10 hr 48 min 12 hr

30 13 hr 56 min 10 hr 04 min 12 hr

40 14 hr 52 min 9 hr 8 min 12 hr

50 16 hr 18 min 7 hr 42 min 12 hr

60 18 hr 27 min 5 hr 33 min 12 hr

70 2 months 0 hr 00 min 12 hr



Land of the Midnight Sun

Cerritos College~34 degrees latitude

Table 2-2 from your text!


Summer Solstice Review Occurs on June 21 or 22 Vertical rays of the Sun strike the

Tropic of CANCER (23.5 deg N) NH location experience their

LONGEST day (SH location experience their

SHORTEST day) NH locations experiences their

HIGHEST Sun angle (SH location experience their

LOWEST Sun angle)

Farther from the equator the longer the period of daylight (i.e. Arctic Circle has 24 hours of SUN)

Many cultures place importance on the Solstice days and mark

them with celebrations


Winter Solstice Review Occurs on December 21 or 22 Vertical rays of the Sun strike the

Tropic of CAPRICORN (23.5 deg S) SH location experience their

LONGEST day (NH location experience their

SHORTEST day) SH locations experiences their

HIGHEST Sun angle (NH location experience their

LOWEST Sun angle)

Farther from the equator the longer the period of daylight (i.e. Antarctic Circle has 24 hours of SUN)

Many cultures place importance on the Solstice days and mark

them with celebrations

Solstices and Equinoxes SUMMARY: Seasonal Fluctuations in the amount of

solar energy reaching various parts on Earth’s surface are caused by: The migrating vertical rays of the Sun The resulting variations in the Sun ANGLE and LENGTH of

daylight

What would the seasons be like if Earth was not tilted on its axis?

All locations on the globe would have 12 hrs of day and 12 hrs of night

The sun would always follow the path that it does during the current equinox

No seasonal temperature changes, temperature would be the rough “average” at that location

Energy, Heat, and Temperature

Forms of Energy Potential Energy Kinetic Energy

Temperature

Heat

Energy

Universe is made up of matter and energy Matter can be seen, smelled and touched Energy is more abstract

Energy from the Sun reaches the Earth Electromagnetic Radiation Heat and Light

Energy is the Capacity to do Work Takes many forms

Chemical energy from gas to move cars Gravitational energy to move dirt during a landslide

Energy

Potential Energy The Capability to do work.

EX: large hail stones have high potential energy because they are suspended in the cloud

Energy

Kinetic Energy Energy associated with an

object by virtue of its motion. The faster the weight is

dropped the more Kinetic Energy

The larger the weight is the more Kinetic Energy

Ex: Hurricanes have more kinetic energy than a light breeze

Heat

The TRANSFER of energy into or out of an object because of TEMPERATURE DIFFERENCES

It is the FLOW of energy!

Mechanisms of Heat Transfer

Conduction

The TRANSFER of heat through election and molecular collisions from one molecule to another.

Ability to conduct varies: Metals are better Air is poor, called an

INSULATOR

Only important for heating the air in

DIRECT contact with the surface of the Earth

Convection

Heat transfer that involves the actual movement or circulation of substance Air Water Most common form of transfer

in the atmosphere

Convective Circulation/Currents transfer the heat

Thermals

Radiation

Travels through the vacuum of space!

How solar energy reaches the planet!

CONDUCTIONCONDUCTION RADIATIONRADIATION

CONVECTIONCONVECTION RADIATIONRADIATION

Solar Radiation

Electromagnetic Radiation!

Wavelengths – the distance from one crest to the next All typesTraves at 300,000 km/sec or 186,000 miles/sec

Solar Radiation

Visible Light Often referred to as “white light” Using a Prism reveals that white light is composed of the other

colors of the rainbow Ultraviolet (UV) – Higher energy Infrared Radiation (IR) – Lower energy

Solar Radiation

Regardless of the wavelength all behave similarly When an object absorbs electromagnetic energy it

increases their molecular motion and thus temperature

Shorter wavelengths are MORE energetic (like UV) Can damage skin (i.e. cause Skin Cancer, why we wear

UV Sun block)

Longer wavelengths are LESS energetic

Solar Radiation

Sun emits all wavelengths but in varying quantities 95 % is between 0.1 and 2.5 micrometers

Visible (0.4-0.7 um) = 43% IR = 49% UV = 7% X-rays, Gamma, Radio = Less than 1%

Laws of Radiation - 1

1. ALL objects continually emit radiant energy over a range of wavelengths

Sun emits energy Earth emits energy YOU emit energy EVERYTHING emits energy...

Unless it’s at “absolute zero” when molecules stop moving


2. Hotter objects radiate more total energy per unit area than do cooler objects

Sun is 6000 K (10,000 F) Earth is 289 K (59 F) Sun 160,000 times more energy than the Earth This concept is called the Stephan-Boltzman Law


3. Hotter objects radiate more energy in the form of short wavelength radiation than do cooler objects

Hot burner on a stove glows Red Cool burner on a stove doesn’t glow at all but could still

FEEL hot Maximum radiation emitted by Earth is ~10um

This is in the INFRARED part of the spectrum


4. Objects that are good absorbers of radiation are also good emitters.

The perfect absorber (and emitter) is a “Blackbody”

Both the Earth and Sun are close to being blackbodies because they absorb and radiate with nearly 100% efficiency.

Atmosphere is transparent (radiation passes through) and opaque (radiation is absorbed) to different wavelengths.

What Happens to Incoming Solar Radiation?

Absorbed Transmit Reflection Scattering

DEPENDS ON THE WAVELENGTH OF THE ENERGY

Reflection and Scattering

Reflection Bounces off at the

same angle

Scattering Produces a larger

number of weaker rays

More is scattered forward

Less is “Backscattered” And at

the same intensity

Reflection and the Earth’s Albedo

Energy is returned to space via reflection and emission ALBEDO - The percentage

reflected About 30% is reflected for

Earth 5% from land and ocean 25% from clouds and ice


Diffused Light Dust particles an gas

molecules scatter energy in different directions

Explains how light reaches beneath the shade of a tree

Moon have Black shadows and Pitch Black skies


Blue Skies and Red Sunsets Gas molecules more

effectively scatter the shorter wavelengths (blue and violet) than the longer wavelengths (red and orange)

At sunset light has to pass through MORE atmosphere


Most spectacular Sunsets occur when lots of fine particles in the atmosphere… Dust Volcanic Ash

Spectacular sunsets from the Sarychev volcanic eruption earlier in June.

Volcanic sunsets depicted in Munch's The Scream

1883 eruption of Krakatoa


Fog, haze or smog scatter light more equally in all wavelengths


Color of the sky gives an indication of the number of large or small particles present Numerous small particles produce RED SUNSETS Numerous large particles produce WHITE GREY skies The BLUER the sky the CLEANER the air!

Radiation emitted by the Earth

Earth emits radiation at longer wavelengths than the sun. Emits considerably less radiant energy than the sun Over 95% of the Earth’s radiation has wavelengths

between 2.5 and 30 micrometers (Infrared)

Heating the Atmosphere Gases are the most effective

absorbers of radiation and play the primary role in heating the atmosphere

Nitrogen is transparent

Water vapor and oxygen and ozone absorbed most of the energy in the atmosphere

CO2 is important at long wavelengths

Atmospheric windows

Heating the Atmosphere Clouds are made of tiny

water droplets and are excelled absorbers of energy in the range of 8-12 um. Clouds absorb the Longwave

infrared radiaiton emitted by the Earth

Why nights feel warmer when they are cloudy

Lower the rate at which the surface cools

Heating the Atmosphere - Summary The atmosphere is largely

transparent to incoming shortwave (high energy) radiation

The atmosphere is more absorptive of the longwave (lower energy) emitted by the Earth

The atmosphere is HEATED from the GROUND UP Explains why temperature

decreases in the troposphere

Greenhouse Effect Without an atmosphere the

Earth’s temperature would be below zero. BRRRRR!

The atmosphere warms the planet

Water Vapor, CO2 and other trace gases absorb the outgoing IR radiation

The absorbed energy heats the air.

The average temperature of the earth is 59 F (33C)

Greenhouse Effect Why is it called the Greenhouse

effect? Originally though that

greenhouses (for plants) worked the same way:

Let in shortwave radiation Objects in house get warmer They radiate longwave energy Glass is nearly opaque to

longwave so they’d be “trapped” in side.

Greenhouses actually are warmer because the air flow is restricted.

The name stuck, even if it isn’t perfect.

Greenhouse Effect Greenhouse Gases (GHGs) are

the “villian” in the Global Warming Debate.

The Greenhouse Effect and Global Warming are NOT the same thing

Without the Greenhouse Effect Earth would be uninhabitable!!!!!

Human activity may be making the atmosphere more efficient at retaining long wave emissions from the Earth.

Venus – why is it hot? Venus has a surface temperature

of close to 941 F (523 C)!!!!! Way hotter than our 59 F!

GHGs on Earth only account for 1% of the atmosphere

GHGs (mostly CO2) on Venus account for 97% of the atmosphere

Venus simply has a a supercharged GH Effect!!

The high temperature is not caused simply by its closer location to the Sun.

Role of Clouds in Heating the Earth FACT: Clouds are good

absorbers of IR radiation emitted from the Earth

Thick cloud cover absorbs most outgoing IR radiation, re-radiating it back to the surface Warm cloudy nights, again

The effect of heating really depends on the type of cloud…

Role of Clouds in Heating the Earth

High Thin Clouds transmit incoming SW solar radiation

Absorb some of the outgoing LW radiation, and re-emit back down

Tend to WARM the surface

Role of Clouds in Heating the Earth

Low Thick Clouds block incoming SW solar radiation

They have a high albedo and reflect most of the energy back to space..

Tend to COOL the surface

Role of Clouds in Heating the Earth Whether a specific cloud

will warm or cool the surface depends on:

The time of day Cloud’s thickness Cloud’s height above the

surface Liquid, ice or both

On average clouds Cool the Earth

Heat Budget

Earth’s average temperature remains fairly constant

There is a balance of incoming and outgoing radiation Otherwise we’d keep

heating up or keep getting colder.

Heat Budget

We care about the GENERAL budget,

memorizing ALL these numbers won’t be

necessary….

These numbers are being revised constantly based

on more current observations, new studies

and research findings.

Latitudinal Heat Balance

Why don’t the tropics keep getting hotter and the poles keep getting colder?

The atmosphere and oceans MOVE and transfer energy from the equator towards the poles!

The energy imbalance drives ocean currents and winds!

Latitudinal Heat Balance The actual amount of energy

received fluctuations based on cloud cover, atmospheric composition and seasons

Dust, ash and pollutants can block radiation too…

Seasonal variations in Sun angle and length of daylight alter heating too…

ESCI 106 – Weather and Climate Lecture 2 8-25-2011 Jennifer D. Small Jennifer D. Small.

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