Climatology Ajs

7/28/2019 Climatology Ajs

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: CLIMATOLOGY:(Lecture notes prepared by Prof. A.J.Sanyal, H.O.D; Architecture, KITS, Ramtek)

Atmosphere, Weather & Climate:

We can study our earth planet in basically three spheres namely Lithosphere, Hydrosphere &Atmosphere. Atmosphere can be defined as gaseous layer surrounding earth extendinghundreds of kilometers in space (Approx. 6000 miles or 9000 kms).

It consists of: a) a mixture of gases called pure dry air; b) water vapour; & c) dust particles. Fisttwo is in gaseous state, where as the third one consists of solid particles much larger thanmolecules, but mixes freely with gases & stay in atmosphere indefinitely. Clouds & fog which aretiny water droplets or ice crystals. They cannot be considered as part of the atmosphere, eventhough they are present much of the time word over.

Atmosphere mainly consists of the following gases:i) Nitrogen- nearly 78%, which is fairly constant up to 45 mile( 72 kms.) & is chemically

inactive space filler, extracted from air naturally to form nitrogen compounds vital forplant growth.

ii) ii) Oxygen-21%. It is chemically very active, combining with rock forming minerals,with metals for rusting, with fuel in burning, with food to provide the heat etc. Despiteits chemical activity, the quantity of O2 in air remains constant because the amount ofused is exactly balanced by or given back to atmosphere by plants.

iii) Remaining 1% consists of gases like argon, CO2, H2, Methane, Nitrous oxide,Ozone, SO2, NO2, ammonia etc,

iv) CO2 is extremely important both in climate control & in sustaining life on earth.Chemically it is important as an absorber of heat & as an insulating blanket, helpingto regulate air temperature near earths surface. It is also important for plant growth &% of it increased more than 10% due to industrial activities.

v) Ozone is present in traces in lower atmosphere but in larger quantities/concentratedin upper layers.

vi) SO2, NO2, ammonia is present in lower layer of air of industrial cities/towns.

b) Water vapour: Gaseous state of water vapour is not visible to eye. Fogs & clouds are in liquidforms or solid state of water vapour. Amount of water vapour varies from place to place, time totime 25% weight of air or 10,000 parts of air). Water vapour supplies water for all clouds & rains &during condensation it releases latent heat which is supplies the energy for the storms.

c) Dust: Small particles of earth surface (25,000 of them placed side by side may occupy 2.54cms. Space) Smoke in may be due to industrial activities, forest fires. Wind over desert areacarries lots of dust particles & which remains in atmosphere for considerable period.

Weather:Weather is the sum total of atmospheric condition at a given place at a given time, where asclimate is generalization or integration of weather condition for a given period of time of givenarea. Weather is a every day experience, where as climate is an abstract concept.

Climatology:It may be defined as the scientific study of climate; its concern includes practical application ofsuch study. Aim of the climatology is to discover, explain and exploit for the benefit of humanbeings normal behaviors towards atmospheric phenomenon, bearing in mind that irregularities in

atmospheric behavior are not the rule but exceptions.

The variation in earths surface has profound effects on the interchange of heat, moisture &momentum between land, water, and atmosphere which are vital in determining specific climaticconditions. Weather


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There are three methods of working within the field of Climatology & they are as under:a) Climatography : It is presentation of climatic data verbally or cartographically or in the

form of tables & charts.b) Physical or dynamic climatology : Explanation of climatic phenomenon in terms of

physics & dynamics i.e. application of physical-even experimental physics to climaticphenomenon & dynamic climatology as the application of mathematical concepts.

c) Applied Climatology : It is scientific analysis of climatic data in order to apply it insolving specific design or operational problems within the field as industry, technology,buildings etc.

Climatology can be subidividesd as under:i) Descriptive climatology : Providing the climatological information in easily

understood form.ii) Statistical climatology : The reduction of mass of climatic data in concise & easily

usable form.iii) Mathematical climatology: Isolation of those aspects of climate that can be given

an exact mathematical explanation or representation.iv) Synoptic climatology : Isolation of those aspects of climatology that are of use in

weather forecasting.v) Micro-climatology : The discovery of features of climate that are characteristic of the

lowest few meters of of the atmosphere & isolation of factors controlling them.vi) Macro-climatology : It is study of climate on worldwide scale.vii) Meso-climatology : The isolation of the atmospheric entities that control the climate

of few hundreds of sq. miles or sq. kms in extent. ( Say state or district level)viii) Local-climatology : It is study of climate of a specific place.ix) Topo-climatology : Study of climate of a specific place, where local climate is closely

related to surface conditions.

: BASIC CLIMATIC ELEMENTS AT A PARTICULAR PLACE:

a) Solar radiation : Intensity and duration of sunshine.b) Temperature : It depends on the radiation, influences cloud coverc) Cloud cover : Determines how much of solar radiation reaches ground & how much is

radiated back into the space from the earths surface.d) Wind & its pressures : Former represents the air movement & later weight of the

atmosphere.e) Humidity :Amount of water in vapour form present in the atmosphere.f) Precipitations :Amount of water vapour present in atmosphere in its liquid / solid form.g) Topography : Characteristics of earth surface such as hills, water bodies, forest etc.

: SOLAR RADIATION AND INSOLATION PATTERN:

Flux density of solar radiation is defined as the amount of radiant energy passing the through unitarea in unit time, decreases with the sq. of distance from the sun.Q = k.1/ R2

Where Q = General indicators for flux density of solar radiation (1.95 Cal / Cm2 / Min.) = 1300 W / M2

R = Earth sun distance &K = Constant.

SOLAR PARAMETER/SOLAR CONSTANT: Radiant energy passing through 1Sq. cms/ min. iscalled solar parameter / constant. Hence total amount of solar radiation received = S r2 wherer = mean radius of earth = 6.37x 108 .

The radiation that survives its passage through the earths atmosphere & arrives at the surface ofthe earth is called INSOLATION i.e. contraction of incoming solar radiation.


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The amount of insolation received on any date at a place on earths surface is governed by:a) Solar radiation reaching the outer limits of atmosphere. It again depends on: (i) Energy

output of the sun; (ii) Distance of earth from sun & (iii) Interstellar dust.b) Transparency of the atmosphere.c) Duration & intensity of daily sunlight period.d) Angle at which the sun rays strikes the surface of the earth.e) Orbital characteristics e.g. revolution, rotation, inclination of earths axis & parallelism etc.

Solar radiation is produced due to continuous atomic explosion which is going on same isradiated in all directions in space. Energy output at the sun is not always constant & it is againaffected due variation in distance of earth from sun in Summer & Winter Solstice. Due to thisradiation which reaches earths surface varies by 3.5% from the mean.

Extraterrestrial dust in space is negligible & hence its effect on radiation reaching earth surface isalso negligible.

Transparency of the atmosphere is the most important factor. Effect of dust, clouds, water vapourand certain gases reflect, scatter & absorb part of radiation.

Transparency is also function of latitude, for middle & high latitude the solar beam must penetrate

the reflecting & absorbing atmosphere at a lower angle than in tropical latitudes. This effect varieswith the seasons, being greater in winter when noon sun is lowest on the horizon.

The duration of daylight (Photoperiod) also varies with the latitude & season. The longer thephotoperiod the greater is the total possible insolation.

: TABLE-1:

Latitude 0 17 41 49 63 66 67 90

Daylight 12 hrs. 13 hrs. 15 hrs. 16 hrs. 20 hrs. 24 hrs. 1 month 6 month

At equator days & nights are always equal. In Polar Regions the daily photoperiod reaches amax. of 24 hours in summer & mi. of zero hours in winter. At its summer solstice, under clearskies a polar area receives more radiation per 24 hrs./day than lower latitudes, although the net

radiation used in heating is reduced because of high ALBEDO factor.

Albedo is the ratio of the amount of radiation reflected to the amount received on the surface.Typical approximate values of ALBEDO of various surfaces are as under:

: TABLE-2:

Sr. No. Type of surface Albedo factor i

01. Ever green forest 7%

02. Water 8%

03 Deciduous forest 9%

04. Dry pasture 10%

05. Built areas 10%

06. Fresh grass 11%07. Sand 15%

08. Clouds 55%

09. Fresh snow 85%

The effect of varying angle of the solar beam can be seen in daily march of sun across the sky. Ator near solar noon the intensity of insolation at the earths surface is greatest, but in the morningand in the evening hours when the sun angle is low, the intensity is reduced. The same principleapplies to the latitudes & seasons. In winter & high latitudes the suns noon angle is low, in


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summer & at low latitude it is more nearly perpendicular. The oblique rays of the low angle sunsrays are spread over a greater surface than perpendicular rays & therefore produce less heatingper unit area.

The angle at which solar radiation strikes the earths surface also depends on the terrain features.In northern hemisphere southern slopes receive more direct solar beam, whereas northern slopesmay be entirely in the shade. The possible hours of direct sunshine during winter in deep valleymay be reduced to zero by surrounding hills.

From the foregoing it is evident that the world distribution of possible insolation at the surface ofthe earth is closely related to the latitude. At the equator the annual amount is about 4 times thatat either pole. Direct solar beam shifts seasonally from one hemisphere to the other, the zone ofmaximum possible daily insolation moves with it. In tropical latitude the amount of possibleinsolation is constantly great, and there is little variation with the season. But in its annual journeythe sun passes over all places between the tropic of cancer & tropic of Capricorn twice, causing

two maximum. In latitude between 23 & 66, max. & min. periods of insolation occur shortlyafter the summer & winter solstice, respectively. Beyond Artic & Antarctic circles the max.coincides with the summer solstice, but there is a period during which insolation is lacking. Thelength of period increases towards the poles, where it is of six months.

Observation of actual insolation at the earths surface shows a distribution that departs slightlyfrom simple latitudinal pattern. Max. annual values are at about 20 latitude where the lower airpermits a greater proportion of the radiant energy to penetrate to surface level. Cloudy regionsreceive less insolation at the surface level. Cloudy regions receive less insolation at the surface


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than do areas with predominantly clear weather. In general, high plateaus & mountains arefavoured by more effective insolation because of the relatively clearer & less dense air at highaltitudes.

Orbital characteristics: (Revolution, Rotation, Inclination of earths axis & Parallelism)

Earth revolves around the sun in an elliptical orbit in 365 days approximately. Earth sunsdistance varies from 147 million kms. (At the perihelion i.e. near sun) during 1week of January to152 million kms. (At aphelion i.e. away fro sun) during 1st week of July.

Earth also rotates on its axis, counter-clockwise when viewed from over N-pole, with one rotationtaking in 24 hours.

The earths orbit around sun describes a geometrical plane, called the plane of the ecliptic. Theearths axis is inclined 23 from the perpendicular to this plane. This inclination remainsconstant throughout a revolution & the axis is parallel to itself at all the times i.e. poles are alwaysdirected towards same point (North star) in deep space.

If the earth-sun distance is scaled down to the length of football field (100 yards or 90 mts.) thenearth will be about or 8 mm & sun will be 29 or 850 mm. in diameters.

On 21st March & 23rd September sun rays are perpendicular to the equator & sun is at its zenith &is called Equinoxes as days & nights are equal.

Figure 1 Sun and Earth Positions


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March 21st to June 21st the latitude at which the noon rays of the sun are overhead moves innorthern hemisphere as far as 23 N (Uttarayana as per Hindu Panchang). Then sun movesbackwards towards equator which it passes on 23 rd September & continues its as far as 23 S(Known as dakshinayana as per Hindu Panchang), which it reaches on 22nd Dec. Then again itmoves back to starting point of March, 21st. This latitudinal variation of the noon rays pf the sun isthe "SOLAR INCLINATION".

Solstices occur when the noon rays are farthest from the equator: at summer solstices (21 st June)and the winter solstices (21st Dec.) During equinoxes the circle of illumination passes through thepoles & thus every latitude experiences a day & night of 12 hours.

On 21st June the circle of illumination divides the earth in such a way that all the latitudes in thenorthern hemisphere have greater than 12 hours day. At equator it is 12 hours & at 66 it is 24hours. From there to pole sun never sets. Same condition applies to southern poles on 22nd Dec.solstice (winter).

Kepler's Laws

Johannes Kepler, working with data painstakingly collected by Tycho Brahe without the aid of atelescope, developed three laws which described the motion of the planets across the sky.

1. The Law of Orbits: All planets move in elliptical orbits, with the sun at one focus.

2. The Law of Areas: A line that connects a planet to the sun sweeps out equal areas in equaltimes.

3. The Law of Periods: The square of the period of any planet is proportional to the cube of thesemimajor axis of its orbit.

Kepler's laws were derived for orbits around the sun, but they apply to satellite orbits as well.

The Law of Orbits

All planets move in elliptical orbits, with the sun at one focus.
http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c6%23c6http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c6%23c6http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c2%23c2http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c5%23c5http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c6%23c6


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This is one ofKepler's laws. The elliptical shape of the orbit is a result of the inverse square forceofgravity. The eccentricity of the ellipse is greatly exaggerated here.

Orbit EccentricityThe eccentricity of an ellipse can be defined as the ratio of the distance

between the foci to the major axis of the ellipse. The eccentricity is zero for a circle. Of theplanetary orbits, only Pluto has a large eccentricity.

The Law of Areas

A line that connects a planet to the sun sweeps out equal areas in equal times.

This is one ofKepler's laws.This empirical law discovered by Kepler arises from conservation ofangular momentum. When the planet is closer to the sun, it moves faster, sweeping through alonger path in a given time.
http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html#isqghttp://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#gravhttp://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#amphttp://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#amphttp://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#amphttp://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/forces/isq.html#isqghttp://hyperphysics.phy-astr.gsu.edu/hbase/grav.html#gravhttp://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c3%23c3http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html#c1%23c1http://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#amphttp://hyperphysics.phy-astr.gsu.edu/hbase/amom.html#amp


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:THE CELESTIAL SPHERE CONCEPTS:Ptolemaic concept of a fixed earth about which the heavenly bodies revolve is useful in explainingthe celestial sphere concepts. When you look at the sky on a clear, dark night you might think thatyou can see millions of stars. In reality, the human eye can only detect about 6000 stars over theentire sky. However, for those of us in the northern hemisphere we can only see the stars that areabove our horizon, which means that we can only see about 3000 stars. The earth rotates fromwest to east once every 24 hours, which is why we have day and night, so the stars rise in theeast and set in the west, as do the Sun and the Moon. This daily, or diurnal, motion of the stars isvery apparent in time exposure photographs.

Many ancient societies believed the Earth to be the center of the universe. They also imaginedthe stars to be attached to the surface of a huge sphere centered on the Earth. This imaginarysphere, called the celestial sphere, is quite a useful concept.

The stars are, in actuality, scattered at various distances from the Earth. Several of the brighteststars that are visible to the naked eye are in the range of 10 to 1000 light years away. These arevery large distances indeed, so far in fact that the stars appear to be fixed to a sphericalbackdrop. In fact astronomers use this idea of a spherical backdrop to locate objects andimportant positions in the sky.

Lets picture the Earth at the center of huge sphere. The sphere is called the celestial sphere.Lets project some of Earth's key geographic features outward into space to provide the celestialsphere with some features as well to establish directions and our bearings on the celestialsphere.

Let us extend the following Earth's features outward.

Extend the Earth's equator outward, thus forming the celestial equator.

Extend the North geographic pole upward, thus forming the north celestial pole

Extend the South geographic pole downward, thus forming the south celestial pole

The celestial equator divides the sky into northern and southern hemispheres, just as the Earth'sequator divides the Earth into two hemispheres.

Declination measures how high a star is in the sky. Declination of an object is the angulardistance north or south of the celestial equator. For example, a star that in on the north celestialpole has a declination of 90o degrees and a star on the celestial equator has a declination of0o,and a star on the south celestial sphere has a declination of -90 o.. Right ascension measureswhere a star is positioned around the celestial sphere. The right ascension of an object is theangular distance from the vernal equinox eastward. Right ascension is measured in hours,minutes and seconds.


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The Sun and the Earth's orbit form a plane called the ecliptic. You can also think of this as thepath the Sun follows across the sky when viewed from the Earth.

The ecliptic and the celestial equator intersect in only two points. These two points are calledequinoxes (from the Latin word meaning equal), because when the Sun appears at either ofthese points, daytime and nighttime are each 12 hours long at all locations on Earth.


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The Vernal Equinox marks the beginning of spring in the northern hemisphere and occurs aboutMarch 21. The autumnal equinox is when autumn starts in the north hemisphere and is aboutSeptember 21.

Between the dates of the two equinoxes are two other important dates. These dates occur whenthe Sun reaches the lowest and highest points in the sky. On about June 21 the sun is reaches its

highest position in the sky when viewed from the north hemisphere. This point is called thesummer solstice. When the sun reaches the lowest point in the sky when viewed from thenorthern hemisphere the winter solstice occurs. Note that the ecliptic is titled 23.5o relative to thecelestial equator, why do think this is the case?

The inclination of the ecliptic to the celestial equator produces some interesting effects at certainlocations on the Earth. For example, on any date during the year the Sun appears directlyoverhead at "high noon" along a band of locations encircling the Earth. The northernmost placewhere this happens is called the Tropic of Cancer (what is the southern most point?). The tropicof cancer is at latitude of 23.5o north of the equator. On the date of the summer solstice, the Sunis at the zenith at high noon as seen from anywhere along the tropic of Cancer. Can the sun ever

be at the zenith as viewed from Bloomington?

The corresponding southern location is called the Tropic of Capricorn, 23.5o south of the equator.On the date of the winter solstice, when the Sun has reached its southernmost declination at highnoon, as viewed from any location along this tropic. Can you demonstrate this in your model?

There are also regions on Earth near the two poles where the Sun spends many consecutivedays either above or below the horizon. For example, as seen by someone standing at the NorthPole, the Sun rises on the day of the vernal equinox and stays above the horizon for six months,


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setting on the day of the autumnal equinox. During the next six months the arctic does not seethe sun, because the Sun is too far south to be seen from the North Pole.

The region around the north pole where can see the Sun for 24 continuous hours on at least oneday of the year is bounded by the Arctic Circle. The Arctic Circle lies at 23.5 o south of the NorthPole. What is the latitude of the Arctic Circle? Well, since the North Pole is 90o latitude that must

mean that the Arctic Circle has latitude of 90o

- 23.5o

which is 66.5o

north.

The Earth's inclination to its rotation axis and our latitude conspire together to keep someconstellations permanently from our view. That is some constellations are always below ourhorizon. For example, as viewed from the United States, the north celestial pole is always abovethe horizon. In fact, the elevation of the north celestial pole is exactly equal to our latitude(Bloomington's latitude is about 37o north). As the Earth turns, constellations near the northcelestial pole circle/revolve about the pole, never rising or setting. Similarly, there areconstellations around the south celestial pole that are too far south to be seen from Bloomington.

Another poignant example of these phenomena is the Magellanic Clouds. The magellanic cloudsare small satellite galaxies of our Milky Way galaxy. We can't see them because they are belowthe horizon. Further, the great supernovae of 1987 (called 1987a) occurred in a region of the skythat is also unavailable to us, so we missed out on one of the greatest events the Universe can

produce.

Thoughts to keep in mind when modeling your Celestial Sphere

When scientists begin study on a phenomenon they begin with certain known facts or theories,then create a model based upon what they know which in several cases is very little. Once theyhave a model of the phenomenon a good scientist asks questions that then use the model todemonstrate or obtain solutions to their questions. If the model does not provide satisfactorysolutions, that are solutions that are physically reasonable, then the model is thrown away and anew model is developed and the scientist starts the process again. Therefore one must always beasking questions, or using your model to demonstrate a physical law, relationship or concept. Foryour celestial sphere model can it:

Demonstrate the path of the Sun across the sky. Demonstrate the point the Sun rises on the Vernal Equinox.

Demonstrate the zenith of the Sun at different points during the year.

Demonstrate the path of the Earth when viewed from the Sun.

Demonstrate the position of the Solstices.

Demonstrate your astronomical horizon.

There are other questions or demonstrations that you will think of. Feel free to develop your ownset of questions and concepts to test with your model. It is important to ask questions if yourmodel will prove to be successful.


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Climatology Ajs