weather, climate and atmosphere-lecture 1

7/27/2019 Weather, Climate and Atmosphere-lecture 1

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Lecture 1

WEATHER, CLIMATE AND THE

ATMOSPHERE


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Introduction

Weather influences our everyday activities, our jobs,and our health and our comfort. Many of us pay littleattention to the weather unless we are inconveniencedby it.

Nevertheless, there are few other aspects of thephysical environment that affects our lives more thanthe phenomena we collectively call the weather.

Weather clearly influences our lives a great deal. Yet itis also important to realize that people influence theatmosphere and its behaviour as well.


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What is Weather?

Weather is the current atmosphericconditions, including temperature, rainfall,wind, and humidity at a given place.

Weather is what's happening right now or islikely to happen tomorrow or in the very nearfuture.

You can tell how hot it is by taking atemperature reading.


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What is Climate? (I)

Climate, on the other hand, is thegeneral weather conditions over a longperiod of time.

For example, on any given day in June,

we expect it to be rainy in Axim, WesternRegion and sunny and hot in Tamale,Northern Region.


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What is Climate? (II)

Climate is sometimes referred to as "average" weather

for a given area. Most National Weather Services usedata such as temperature highs and lows andprecipitation rates for the past thirty years to compilean area's "average" weather.

However, some atmospheric scientists think that youneed more than "average" weather to accuratelyportray an area's climatic character - variations,patterns, and extremes must also be included.

Thus, climate is the sum of all statisticalweather information that helps describe a placeor region. The term also applies to large-scale weatherpatterns in time or space such as an 'Ice Age' climate or

a 'tropical' climate.


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Weather vrs Climate

Some meteorologists say that "climate iswhat you expect and weather is what youget." According to one middle school

student, "weathertells you what to weareach day, but the climate helps you figureout what should be in yourcloset


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Climate Variability

Although an area's climate isalways changing, the changes donot usually occur on a time scalethat's immediately obvious to us.

While we know how the weatherchanges from day to day, subtleclimate changes are not as readilydetectable.

Weather patterns and climatetypes take similar elements intoaccount, the most important of

which are:

The temperature of the air

The humidity of the air

The type and amount of

cloudiness

The type and amount ofprecipitation

Air pressure

Wind (speed and direction)


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Relationship between Weatherand Climate

Although weather and climate are different, theyare very much interrelated. A change in oneweather element often produces changes in theothers - and in the region's climate.

For example, if the average temperature over aregion increases significantly, it can affect theamount of cloudiness as well as the type andamount of precipitation that occur.

If these changes occur over long periods of time,the average climate values for these elements willalso be affected.


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THE EARTHS ATMOSPHERE

It's a thin layer of gases surrounding ourplanet. Many of the planets in this solar system haveatmospheres, but none that we know of has anatmosphere quite like ours - one that can support life.

The atmosphere is held to the planet by the force ofgravity, which also determines what gases are presentin it.

The Earth's primitive atmosphere was much differentfrom today's and consisted primarily of ammonia,methane, and trace amounts of carbon dioxide andwater vapor. There was little, if any, free oxygenpresent.


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Earth System Concept

The Earth

System

operateswithin four

spheres


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Atmosphere - thin layer of gases surrounding the earth;

held by gravity; mixture of N, O, Ar, CO2

Lithosphere - earths crust & portion of mantel;sometimes thought of as the entire solid planet

Hydrosphere - water in all parts; liquid, solid, & gaseousform; two forms - fresh and salt. The Earth issometimes called the blue planet

Biosphere - intricate web that connects all organismswith their physical environment; physical and chemicalfactors make the context of life; continually changing.

The Earths Systems


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Examination of theAtmosphere

The atmosphere is structured. Threecriteria to examine atmosphere

Composition

Temperature (Structure)

Function


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Composition of theAtmosphere


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Pressure/Altitude I

0.000031000.00179.20.0165.10.148.1131.2 1016.2

505.61000

Percent sea level pressureAltitude(km)

The atmosphere decrease in concentration,and hence pressure, as you rise above the

surface of the earth.


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Pressure/Altitude (II) The earth's outermost atmosphere, the part above a few

hundred kilometers, is a region of extremely lowdensity. Near sea level, the number of atoms and moleculesin a cubic centimeter of air is about 2x1019; near 600 km it isonly about 2x107, which is the sea level value divided by a

million million.

At sea level, an atom or molecule can be expected, on theaverage, to move about 7x10-6 cm before colliding withanother particle; at the 600 km level this distance, called the"mean free path," is about 10 km.

Near sea level, an atom or molecule, on the average,undergoes about 7x109 such collisions each second; near 600km, this number is about 1 each minute.


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90% of atmospheres massis within 15 km of the

surface (the Troposphere)

Atmospheric

Pressure Changes


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Temperature/Altitude

Not only does the pressure change with altitude,but temperature does as well.

Originally, scientists thought that temperaturedecreased continuously with increasing heightuntil reaching absolute zero (-273.16C). Thisdecrease of temperature with increasing altitude is

known as the normal lapse rate and isapproximately 6.5C/1000 m (3.5F/1000').


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In this figure, theenvironmental lapse ratecan be seen graphicallyas the decrease intemperature withincreasing height.

The normal lapse rate isobserved until thetropopause is reached.


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Temperature/Altitude in Different

Geographic Regions


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Composition


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Homosphere composition

Why so muchNitrogen?

It is volatile in mostforms

Eg. Ammonia gas

It is unreactive withmost solid earthmaterial

It is stable in sunlight.


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Homosphere Composition

Why so muchOxygen?

Produced by

photosynthesis.


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Why so muchArgon?

It slowly degasses

from rocks

It is unreactive sostays in the

atmosphere Argon is a noble gas


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Why so littlecarbon dioxide? Original

atmosphere was

probably about25% CO2

It dissolves in

water

It is used by plantsin photosynthesis

Th l St t f th


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Thermal Structure of theAtmosphere


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Troposphere

The bottom layer, where temperature decreases withaltitude, is known as the troposphere (from the Greekfor "turning layer"). The troposphere is approximately12 kilometers thick, but there are slight variations.

If the temperature increases with increasing altitude inthe troposphere, then a temperature inversionexists. All the weather that we are primarily interested

in, occurs in the troposphere.

The top of the troposphere is marked by thetropopause.


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Stratosphere

Above the tropopause lies the stratosphere. It gets it'sname from the Greek meaning "stratified layer." The layeris stratified with the denser, cooler air below the warmer,lighter air. This leads to an increase in temperature withheight.

Since the stratosphere isn't turbulent this is where mostplanes like to fly. The temperature increases with heightuntil it reaches about 10C at an altitude of 48 km. Theprimary reason that there is a temperature increase with

altitude is that most of the ozone is contained in thestratosphere.

Ultraviolet light interacting with the ozone causes thetemperature increase. The boundary between the

stratosphere and the next layer is called the stratopause.


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Mesosphere & Thermosphere

Above the stratopause, the temperature again decreaseswith altitude. This layer is called the mesosphere, or"middle layer." The temperature drops to ~-90C nearthe top of the mesosphere where the mesopause islocated.

Above the mesopause is the thermosphere, or "warmlayer." In the thermosphere the temperature doesincrease with height (to >1000C), but as we havealready seen, the number of molecules present are so few

that even thought they are very energetic, they have sucha low density, that temperature as we call it means verylittle.


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Exosphere

Above the thermosphere lies the exosphere ("outerlayer"). The boundary between the two is verydiffuse. Molecules in the exosphere have enough kineticenergy to escape the earth's gravity and thus fly off into

space. This is where helium "disappears."

The outer part of the mesosphere and the thermosphereare sometimes called the ionosphere since most of themolecules and atoms are ionized by the ultraviolet light

and other high energy particles at this height. Theionosphere is what radio signals bounce off.


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Vertical Composition

The atmosphere also change composition withheight and can be divided into two layers. Thelower layer is called the homosphere and has thecomposition we talked about earlier. It's top isapproximately the mesopause.

Above the homosphere lies the heterosphere, alayer in which the gases are stratified into four

shells. The lowermost shell is dominated bymolecular nitrogen (N2); next, a layer of atomicoxygen (O) is encountered, followed by a layerdominated by helium atoms (He), and finally, a layerconsisting of hydrogen atoms (H).


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The Ionosphere

The ionosphere lies from about 80-400 km in height and iselectrically charged as short wave solar radiation ionizesthe gas molecules. The electrical structure of theatmosphere is not uniform and is arranged into threelayers, D, E, and F. Since the production of chargedparticles requires solar radiation, the thickness of each

layer, particularly the D and E layers, changes from nightto day. The layers weaken and disappear at night andreappear during the day. The F layer is present duringboth day and night. This change in height of the variouselectrically charged layers doesn't effect the weather, butdoes effect radio signals.

The auroras also take place in the ionosphere since this isthe electrically charged layer. The aurora borealis(northern lights) and aurora australis (southern lights) isclosely correlated to solar flare activity.


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Ozone hole

Ozone

concentration on

September 7th,

2003.


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Formation of Ozone

Oxygen that we breathe (and plantsproduce) is O2

UV radiation breaks down O2

into 2O.

O bonds with other O2 to give O3.

O h l


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Ozone hole

Breakdown of ozone

CFCs are broken down by strong ultravioletradiation to create chlorine atoms.

Cl acts as a catalyst to destroy O3 molecules.

Chlorine is not consumed by the reaction. One Cl atom can destroy 100,000 O3

molecules.

Timescales CFCs take about 1 year to mix in with the

troposphere

They take 2-5 years to mix in with the

stratosphere

Wh A i


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Why over Antarctica

Homogeneous versus Heterogeneous O3

depletion

Homogeneous depletion occurs over the

ozonosphere. There has been a 5-10% drop in O3 levels over

the US.

Heterogeneous depletion occurs overAntarctica.Atmospheric circulation over Antarctica is

isolated during the winter.

Cold temperatures encourage ozone depletion

weather, climate and atmosphere-lecture 1

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