Climatology

By: Fasihud Din Nauman

Book Reference: Meteorology Today Chapter# 1.Encyclopedia of world climatology

Weather

• Atmospheric state prevailing at a particular time (few hours- few days or even weeks) over a specified area (usually 30 Km across). Weather is expressed in terms of atmospheric pressure, temperature, relative humidity, light intensity, precipitation (rain, snow) and winds etc.

• weather indicates changes in these atmospheric characteristics within a short period of time.

Climate

• Atmospheric characteristics of an area recorded for a long duration (many years, e.g. standard thirty years by WMO for comparison).

• Climate is aggregate or composite of the weather and involves both the extremes and variability of the weather.

• Various atmospheric processes and surface features explain the weather, which over a longer period explains the climate.

• Surface features include latitude, elevation, landform, orientation to the sun and distance from the sea. Other feature are also important like

Radiation

Temperature

Leaching

Immobilisation

Mineralization

C & NUptake

Fertilisation

volatilization

Conceptual model of weather-crop-soil system

Transpiration

Irrigation

Rain

Evaporation

DrainageCapillary rise

UptakeH2O

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Temperature (oC)

Visibility (miles)

Current Weather

Dewpoint (oC) Sky

CoverStation ID (MULTAN)

3 hour precipitation

3 hour pressure change

Station Pressure

Wind speed, direction, and peak gust

Earth’s Atmosphere

• Atmosphere: The earth’s atmosphere is a thin envelop of air.

• It consists of a physical mixture of gases and particle matter

• Atmosphere is extended upward to many hundred kilometers.

• Around 99% of the atmosphere lies within 30 km (19 miles) of the earth’s surface.

• Functions of Atmosphere: This thin blanket constantly shields the surface and its inhabitants from the dangerous UV (Ultraviolet) radiations from the sun.

• It also protects materials form outer space to enter earth.

• Boundary of Atmosphere: There is no definite upper limit to the atmosphere. It becomes thinner and thinner and eventually merging with empty space, which surrounds the earth.

• Aerosols: Tiny solid or liquid particles suspended in the atmosphere are called Aerosols.

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Gas Characteristics

• Expand or compress due to pressure, containers, etc

• Easily mixed• Individual molecules far apart• Individual molecules have distinct mass• Most common measurements:

– temperature, pressure, and volume

Gas characteristics

• Density: The density of the air (or any substance) is determined by its mass and its volume.

• Density=mass/volume.• Air molecules are in constant motion.

Bounces of air molecules creates a tiny push. The force which air molecules on a unit area is called pressure or air pressure.

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Atmospheric Pressure• Pressure = force / area.

Measure of the weight of air above you Force = push or pull, especially on other air molecules

Compressible More air (mass) above means more compression Air closer to the surface more dense, because compressed

by the “weight” of the air above it

Pressure decreases with height exponentially BAR: A force of 0.1 million newton (N) acting on a

surface area of 1 square meter (1 m2).

SI (System International) unit of pressure is Pascal (Pa). Where 1 Pa is the force of 1 N acting on a surface of 1 m2.

common unit is hPa (hecto-pascal) (100 Pa)

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Chemical (Gas) Composition

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Chemical (Gas) Composition

• Each constituent has a – Source: Production – Sink : Destruction

• N Source– Decaying of plants and animals

• N Sink– Biological processes through bacterial activity

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Hydrostatic Balance We tend to make the assumption that

the atmosphere is in Hydrostatic Balance.

Hydrostatic Balance is when the net upward force on a slab of air equals the net downward force.

gdz

dP ρ−=

Review

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Temperature and Density Temp is the measure of

the kinetic energy of molecules (speed) KE = ½ mv2

Warmer air is less dense Consider the ideal gas law:

P=RT If we consider constant pressure, then:

P/R = TOr:

Constant = T We can see then, if the temperature increases,

density must decrease It follows: Colder air is more dense

Review

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Atmospheric Temperature

Complicated vertical profile Can depend on

atmospheric composition current conditions

lapse rate: the rate at which the air temperature decreases with height

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Layers of the Atmosphere

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Layers of the Atmosphere Defined by changes in temperature with height Troposphere

Sun warms surface, surface radiates Stratosphere

Ozone absorbs solar radiation, warming results Mesosphere

No ozone, molecules lose more energy than they absorb

Thermosphere O2 absorbs solar radiation

Composition of atmosphere

• Up to 85 km above the earth’s surface, major component of atmosphere includes Nitrogen (78%) and Oxygen (21%)

• At the earth’s surface, there is a balance between production (input) and destruction (output) of these gases.

• N is removed from the atmosphere primarily by soil bacteria. N is returned to the atmosphere by decaying of organic bodies.

Vertical Structure of Atmosphere

• Troposphere: 12 km above the earth surface is called troposphere where majority of the world’s weather occur.

• Temperature of the troposphere varies from 15 C (earth surface) to -54 C (at the top).

• Almost all of the processes of vertical transfer to atmospheric properties through turbulence and mixing occur in the troposphere.

• Tropopause: The boundary separating troposphere from the stratosphere is called tropopause.

• The height of the tropopause varies. Generally it is higher in summer and lower in winter.

• In some regions tropopause “BREAKS” and it is difficult to locate.

• Radiosonde: The instrument that measures the vertical profile of air temperature in the atmosphere up to an approximate elevation of 30 km is called RADIOSONDE.

• Pollutants: Human-made (and some natural) impurities in the atmosphere are a nuisance and health hazard. These impurities are called Pollutants. NO2, CO, SO2 and hydrocarbons.

Vertical Structure of Atmosphere

• Stratosphere: Between 12 and 48 km above the earth surface called STRATOSPHERE.

• Air temperature begins to increase with height , producing a temperature inversion.

• The inversion tends to reduce the amount of vertical motion in the stratosphere itself; hence it is a stratified layer.

• Tropopause: The boundary separating troposphere from the stratosphere is called tropopause.

• The height of the tropopause varies. Generally it is higher in summer and lower in winter.

• In some regions tropopause “BREAKS” and it is difficult to locate.

• Ozone: Ozone is the reason for the heating of stratosphere, as it absorbs energetic ultraviolet (UV) radiation from the sun.

• If ozone were not present, the air probably would become colder with height, as it does in the troposphere.

• Ozone Hole: Concentration of ozone in the atmosphere is reducing, creating ozone hole, which caused direct exposure of UV radiation, e.g. in Australia, it is a major concern.

Vertical Structure of Atmosphere

• Mesosphere: Vertical layer of the atmosphere above the stratosphere is mesosphere.

• The percentage of N2 and O2 in the mesosphere is about the same as at the sea level, but very low density. (less O2 breathing)

• We need breathing equipments otherwise prolonged exposure to such conditions may cause deficiency of O2 to brain leading to Hypoxia.

• Exposure to UV solar radiation may burn the body parts severely.

• Stratopause: The boundary separating stratosphere from the Mesosphere is called Stratopause.

• The air at this level is very thin and atmospheric pressure is very low 1mb or 1hPa.

• 99.9% of the atmospheric mass is located below stratopause.

• Temperature: The temperature in the mesosphere decreases with height up to 85 km, partially due to lack OZONE. (Less absorption of solar radiation).

• Temperature of the mesosphere may reach -90 C.

• Thermosphere: The hot layer above the mesosphere is thermosphere.

• In the thermosphere, oxygen molecules absorbs energetic solar radiation and warm the air.

• Absorption of small amount of solar radiation can cause large increase in air temperature.

• Mesopause: The boundary that separates colder mesosphere from the warmer thermosphere is called mesopause.

• As the density of thermosphere is very low, air molecules will move over 1 km distance before colliding another molecule.

• Similar molecules at the earth’s surface will move an average distance of less than one millionth of a centimeter before it collide another molecule.

• Exosphere: The region where atoms and molecules shoot off into space is sometimes referred to as the Exosphere.

• Exosphere represents the upper limit of the earth’s atmosphere.

• At the top of the thermosphere (near exosphere) 500 km above the earth’s surface, molecules can move distances of 10 km before they collide another molecule.

• At this height, many of the lighter, faster-moving molecules traveling in the right direction escape the earth’s gravitational pull.

Atmospheric composition

• Homosphere: Below the thermosphere (0-95 km above the earth’s surface) the composition of air is fairly uniform (78% N, 21% O) and well mixed by turbulent. This region is called Homosphere.

• .

• Heterosphere: The region from the base of the thermospher (95+ km) is called heterosphere.

• In the thermosphere the collision between the molecules is infrequent and air is unable to mix, therefore atoms and heavier molecules (O2 and N2) tend to settle to the bottom of the layer, while lighter gasses (Hydrogen and Helium) float to the top.

Ionosphere

• Ionosphere: It is an electrified region within the upper atmosphere where fairly large concentrations of ions and free electrons exist.

• Ions are atoms and molecules that have lost (or gained) one or more electrons.

• Atoms lose electrons and become positively charged when they cannot absorb all of the energy transferred to them by a colliding energetic particle of solar energy.

• .

• The region from the base of the thermosphere (95+ km) is called heterosphere.

• Bulk of the ionosphere is in the atmosphere.

• Ionosphere plays a major role in AM radio communications. Lower part (D-region) reflects standard AM radio waves back to the earth.

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Station Pressure

Station Plot

Sea-level pressure is plotted in tenths of millibars (mb), with the leading 10 or 9 omitted. For reference, 1013 mb is equivalent to 29.92 inches of mercury. Below are some sample conversions between plotted and complete sea-level pressure values:

410: 1041.0 mb103: 1010.3 mb987: 998.7 mb872: 987.2 mb

1 kt = 0.514 ms-1 = 1.15 mph

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Deciphering Station Plot

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Deciphering Station Plot

important

GDD and Corresponding GSL

Climate-Water-Food Linkages

Crop Water Demand

Water Availability

Evapo-transpiration (ET)

Agriculture (Crop Yield)

Photosynthetic Activity

Climate

Temperature RainfallWind,

Sunshine, Solar Radiation

CO2 level

Canal/ground water

Jan FebMar Apr May Jun Jul Aug Sep Oct Nov Dec

Rainfall

Wet Period Dry Period

6 Months (Mar – Aug)…………… Wet Window6 Months (Sep – Feb)…………… Dry Window

Winter

Monsoon

Rainfall

Units, Conversions, and EquationsPeta P 1,000,000,000,000,000 1015

Tera T 1,000,000,000,000 1012

Giga G 1,000,000,000 109

Mega M 1,000,000 106

Kilo k 1,000 103

Hecto h 100 102

Deca da 10 101

No Prefix 1 100

Deci d 0.1 10-1

Centi c 0.01 10-2

Milli m 0.001 10-3

Micro µ 0.000001 10-6

Nano n 0.000000001 10-9

Pico p 0.000000000001 10-12

Femto f 0.000000000000001 10-15

Units, Conversions, and EquationsPhysical Quantity Name of SI Unit SymbolLength Meter mMass Kilogram kgTime Seconds sTemperature Kelvin KAmount of substance Mole molElectric current Ampere A

Quantity Name Derived Unit MKSForce Newton (N) kg m s-2

Pressure Pascal (Pa) (Nm-2) = kg m-1 s-2

Energy Joule (J) (Nm) = kg m2 s-2

Power Watt (W) (Js-1) = kg m2 s-3

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Energy Conduction: Energy transfer by molecular

collisions E.g.: The sun warms the ground, and this heats a thin

layer of air above the surface In general, air is a poor conductor

Convection: energy transfer by the motion of matter from one location to another e.g.: parcel of air rising Important in our atmosphere

Radiation: transfer of energy not requiring contact between bodies or a fluid between them e.g.: the sun warms the surface of the earth

Review