Climatology scope and principles

Nazmun Nahar
Associate Professor
Department of Geography & Environment
303 Climatology

Introduction to Climatology:
Principles and Scope

Introduction
The study of the Earth falls into four broad categories:
 The solid lithosphere
 The liquid hydrosphere
 The gaseous atmosphere
 The life biosphere
 Climatology studies the gaseous atmosphere
 Climatology is the science of climate which study the
Physical state of the atmosphere:
 over a specific region
 during a specific period
 on the basis of climatic data

Introduction …
 Climatology is compounded of two Greek words,
 Klima - inclination that is latitude
 Logos - science of study
 So, climatology is a science that seeks to describe
and explain:
 the nature of climate
 why it differs from place to place
 how it is related to other elements of the natural
environment and human activities
 It is the study of the verities of climates found on the Earth
and their distribution over the surface of the Earth

Climatology & Meteorology
 Climatology is closely related to meteorology
 Meteorology deals with the day to day atmospheric conditions
and their causes
 Meteorology is defined as the Physics of the atmosphere
 Meteorology uses the methods of Physical science to interpret
and explain the atmospheric processes
 Climatology collects and interpret the data observed by
meteorology to investigate the spatial patterns of climate and
its interaction
 Meteorologically it deals with the meteorological techniques
and geographically it deals with the spatial aspects of climatic
phenomena

Climatology & Geography
 Since geography studies the Earth as the habitat of Man it is
closely related with climatology;
 Climatology studies the atmospheric conditions
 Geography studies the spatial distribution of these climatic
condition
 Through the study of climate, it serves the ends of
geography, while the means employed by it are those of
meteorology
 Climatology is a science whose methods are strictly
meteorological and whose aims and results are geographical.

Definitions of Climatology
Climatology is the science of climate which study the Physical
and spatial state of the atmospheric conditions
 According to Critichfield
‘climatology is the science that seeks to describe and
explain the nature of climate, how it differs from place to
place and how it is related to man’s activities.’
 According to Austin Miller:
‘Climatology is that branch of science which discusses the
average conditions of weather.’
 According to Koppen and De Lang:
‘Climatology is a summery, a composition of weather
conditions over a long period of time.’

Definitions of Climatology …
 According to Thornthwaite
Thornthwaite broadens the scope of climatology and suggest
that it is the study of the atmosphere as well as the Earth’s
surface.’
 Climatology is applied to five fields:
 Climatological records
 Theory of climate
 Energy and moisture balance
 Study of climate as the environment of living organisms
 Study of climate as the direct environment of Man

Branches of Climatology
1. Physical climatology:
 Physical climatology seeks to explain the factors responsible
for bringing out the temporal and spatial variations in heat
exchange, moisture exchange and air movement
 Physical climatology is closely related to meteorology
 Physical climatology is closely related to meteorology
 Physical climatology is a main aspect meteorology from which
most of its basic principles are drawn the focus is on:
 The study of solar energy-its transformation at a location and its
transfer through the atmosphere
 The complicated patterns and exchange of energy from one
phase to another-from solid state to liquid state and from liquid
state to vapor and vice versa

Branches of Climatology …
2. Dynamic climatology:
 Dynamic climatology is global in scope
 it studies the thermodynamic processes in the atmosphere and
the resultant atmospheric motions
 it investigate the impact of changes in various physical
 parameters on climate
 this branch of climatology includes:
 The effect of the increase of greenhouse gases in global
temperature
 the role of mountains in determining the dynamics of the
atmosphere
 An investigation into sea-surface temperature

3. Synoptic climatology:
 Synoptic climatology deals with local or hemispheric climate
from the view point of atmospheric circulation
 different circulation patterns lead to differences in climates
 it studies the relationship between circulation features and
severe weather conditions e.g. the effect of El Nino and La
Nina in creating severe weather conditions
 Synoptic climatology is a new approach to regional
climatology.

4. Regional climatology:
 This branch of climatology seeks to determine and describe
the various types of world climates
 it is also known as descriptive climatology because it is
concerned with the identification of important climatic
characteristics and the interaction of weather and climatic
elements upon the life, health and economic conditions of the
people and areas

5. Applied climatology:
 This branch of climatology is concerned with the application
of the climatological knowledge to practical problems
 It analyses the relationship of climatology to other sciences
 The main purpose is to find out the ways and means to make
use of our knowledge of climatic elements for the betterment
of human life on the Earth
6. Historical climatology:
 Historical climatology studies the development of climate through
time

Aims and objectives
 Climatology seeks to explain:
 The causes of different types of climates
 The reasons for their variations
 Their effects on natural vegetation
 The processes that produce different climates
 Climatology makes a detail analysis of the interaction of
weather and climatic elements upon human societies
 Climatology discusses the various climatic elements, the
factors that control the distribution of climate over the Earth

Lesson Summary
 The activities of man are influenced by the weather;
 Weather is the state of the atmosphere at a given time and
place;
 Climate is the average weather situation of a place over a
period of 30-35 years;
 Climatology is the scientific study of climate;
 Meteorology is the study of the atmosphere and its
phenomena;
 Climatology has a wide scope and can be subdivided into
regional, synoptic, physical, dynamic, applied and historical
climatology.

Assignment (Optional)
Discuss the following statement (200-250 words):
‘Without the atmosphere there cannot be climatology’
Or
‘The activities of man are influenced by the weather’

The Atmosphere:
Structure and Present Composition

Atmosphere of Earth
 The atmosphere of Earth is a layer of gases surrounding the
planet Earth that is retained by Earth's gravity.
 The atmosphere is an important part of what makes Earth
livable.
 It blocks some of the Sun's dangerous rays from reaching
Earth.
 It traps heat, making Earth a comfortable temperature.
 The oxygen within our atmosphere is essential for life.
 The common name given to the atmospheric gases used in
breathing and photosynthesis is air.

Composition of Atmosphere
 Dry air contains roughly (by volume)
 78.09% nitrogen,
 20.95% oxygen,
 0.93% argon,
 0.039% carbon dioxide, and
 small amounts of other gases.
 Air also contains a variable amount of
water vapor, on average around 1%.
 A small amount of dust of mineral and
organic composition, pollen and
spores, sea spray, and volcanic ash.

Structure of Atmosphere
 The atmosphere has a mass of about
5×1018 kg, three quarters of which is
within about 11 km (6.8 mi; 36,000 ft)
of the surface.
 The atmosphere becomes thinner and
thinner with increasing altitude, with no
definite boundary between the
atmosphere and outer space.
 Several layers can be distinguished in
the atmosphere, based on
characteristics such as temperature
and composition.

 n
Layers of the Atmosphere

Troposphere
 The troposphere begins at the surface and extends to
between 9 km (30,000 ft) at the poles and 17 km (56,000 ft)
at the equator with some variation due to weather.
 The troposphere is mostly heated by transfer of energy from
the surface, so on average the lowest part of the
troposphere is warmest and temperature decreases with
altitude.
 This promotes vertical mixing (hence the origin of its name in
the Greek word "τροπή", trope, meaning turn or overturn).
 The troposphere contains roughly 80% of the mass of the
atmosphere.
 The tropopause is the boundary between the troposphere
and stratosphere.

Stratosphere
 The stratosphere extends from the tropopause at about 12
km (7.5 mi; 39,000 ft) to about 51 km (32 mi; 170,000 ft).
 Temperature increases with height due to increased
absorption of ultraviolet radiation by the ozone layer, which
restricts turbulence and mixing.
 While the temperature may be −60 °C (−76 °F; 210 K) at
the tropopause, the top of the stratosphere is much
warmer, and may be near freezing.
 The stratopause, which is the boundary between the
stratosphere and mesosphere, typically is at 50 to 55 km
(31 to 34 mi; 160,000 to 180,000 ft). The pressure here is
1/1000 sea level.

Mesosphere
 The mesosphere extends from the stratopause at about 50
km (31 mi; 160,000 ft) to 80–85 km (50–53 mi; 260,000–
280,000 ft).
 It is the layer where most meteors burn up upon entering
the atmosphere.
 Temperature decreases with height in the mesosphere.
 The mesopause, the temperature minimum that marks the
top of the mesosphere, is the coldest place on Earth and
has an average temperature around −85 °C (−120 °F; 190
K).
 At the mesopause, temperatures may drop to −100 °C
(−150 °F; 170 K) and aid forming ice clouds.

Thermosphere
 Temperature increases with height in the thermosphere from
the mesopause up to the thermopause, then is constant with
height.
 The temperature of this layer can rise to 1,500 °C (2,700 °F),
though the gas molecules are so far apart that temperature
in the usual sense is not well defined.
 The International Space Station orbits in this layer, between
320 and 380 km (200 and 240 mi). Because of the relative
infrequency of molecular collisions, air above the
mesopause is poorly mixed compared with air below.
 While the composition from the troposphere to the
mesosphere is fairly constant, above a certain point, air is
poorly mixed and becomes compositionally stratified.

Exosphere
 The exosphere is the outermost layer of Earth's
atmosphere, extending beyond the exobase at an altitude
of about 600 km.
 It is mainly composed of hydrogen, helium and some
heavier molecules such as nitrogen, oxygen and carbon
dioxide closer to the exobase.
 The atoms and molecules are so far apart that they can
travel hundreds of kilometers without colliding with one
another, so the atmosphere no longer behaves like a gas.
 These free-moving particles follow ballistic trajectories and
may migrate in and out of the magnetosphere or the solar
wind.

Lesson Summary
 The atmosphere of Earth is a layer of gases surrounding the
planet Earth and makes the planet livable.
 The atmosphere becomes thinner and thinner with increasing
altitude, with no definite boundary between the atmosphere and
outer space.
 The troposphere contains roughly 80% of the mass of the
atmosphere.
 Temperature increases with height in Stratosphere due to
increased absorption of ultraviolet radiation by the ozone layer.
 Exosphere is mainly composed of hydrogen, helium in the upper
level and nitrogen, oxygen and carbon dioxide closer to the
exobase.

The Atmosphere:
Characteristics of Atmospheric Gases

Carbon dioxide (CO2)
 Carbon dioxide (CO2) is a naturally occurring chemical
compound composed of two oxygen atoms bonded to a single
carbon atom.
 It is a gas at standard temperature and pressure and exists in
Earth's atmosphere in this state, as a trace gas at a
concentration of 0.039 per cent by volume.
 Plants photosynthesize carbohydrate from atmospheric CO2 and
water (H2O) and release oxygen (O2 ) in the air.
 CO2 is a major source of ocean acidification since it dissolves in
water to form carbonic acid (H2CO3).
 CO2 is an important greenhouse gas, warming the Earth's
surface to a higher temperature by reducing outward radiation.

Ozone (O3)
 Ozone (O3) is a triatomic molecule, consisting of three oxygen
atoms.
 O3 is much less stable than dioxygen (O2) which breaks down in
the lower atmosphere to
 Ozone is formed from O2 by the action of ultraviolet light and also
atmospheric electrical discharges.
 The highest levels of ozone in the atmosphere are in the
stratosphere, also known as the ozone layer between about 10
km and 50 km above the surface
 Ozone in the ozone layer filters out sunlight wavelengths from
about 200 nm UV rays to 315 nm
 Ozone acts as a greenhouse gas, absorbing some of the infrared
energy emitted by the earth.

 According to the National Academy of Sciences, the Earth's
surface temperature has risen by about 1 degree Fahrenheit
in the past century, with accelerated warming during the past
two decades.
 There is new and stronger evidence that most of the warming
over the last 50 years is attributable to human activities.
 Human activities have altered the chemical composition of
the atmosphere through the buildup of greenhouse gases –
primarily carbon dioxide, methane, and nitrous oxide.
 The heat-trapping property of these gases is undisputed
although uncertainties exist about exactly how earth's climate
responds to them.
Global Temperature Change

 There are many possible mechanisms that can cause the
warming of the global atmosphere, for example:
 Natural variation – the climate becomes warmer by internal
chaotic dynamics of the earth-atmosphere system (that is, no
external influence).
 Solar activity – either direct increase of solar energy output or
indirect “trigger” mechanisms due to solar activity (though nobody
knows how) may cause the surface temperature to go up.
 Greenhouse effect – increasing “greenhouse” gases such as
CO2, CH4, NO, CFC,…etc. (actually H2O is very efficient, too, but
at present it is assumed to be in steady state).
Causes for Temperature Change

Earth’s Atmospheric Gases
Nitrogen (N2)
Oxygen (O2)
Water (H2O)
Carbon Dioxide (CO2)
Methane (CH4)
Non-
Greenhouse
Gases
99%
Greenhouse
Gases
1%

 Carbon Dioxide (CO2)
– Source: Fossil fuel burning, deforestation
 Anthropogenic increase: 30%
 Average atmospheric residence time: 500 years
 Methane (CH4)
– Source: Rice cultivation, cattle & sheep ranching, decay from
landfills, mining
 Average atmospheric residence time: 7-10 years
 Nitrous oxide (N2O)
– Source: Industry and agriculture (fertilizers)
 Average atmospheric residence time: 140-190 years
Selected Greenhouse Gases

 Humanity’s greenhouse gas emissions are expected to lead
to climatic changes in the 21st century and beyond. These
changes will potentially have wide-ranging effects on the
natural environment as well as on human societies and
economies.
 Scientists have made estimates of the potential direct
impacts on various socio-economic sectors, but in reality the
full consequences would be more complicated because
impacts on one sector can also affect other sectors indirectly.
 To assess potential impacts, it is necessary to estimate the
extent and magnitude of climate change, especially at the
national and local levels.
Potential climate change Impact

 Although much progress has been made in understanding
the climate system and climate change, projections of climate
change and its impacts still contain many uncertainties,
particularly at the regional and local levels.
Potential Impact …

Lesson Summary
 CO2 is an important greenhouse gas, warming the Earth's
surface to a higher temperature by reducing outward
radiation.
 Ozone acts as a greenhouse gas, absorbing some of the
infrared energy emitted by the earth.
 Human activities have altered the chemical composition of
the atmosphere through the buildup of greenhouse gases –
primarily carbon dioxide, methane, and nitrous oxide.
 Greenhouse gases absorb infrared radiation and prevent it
from escaping to space.

Insolation & Global Variation
 INSOLATION is the energy which drives the atmospheric
weather system. All winds, humidity and weather systems are
driven by variations in temperature.
 Climate (long term variations in the state of the atmosphere) is
related to global and continental location.
 Weather (short term variation) is related to small scale
changes in time and space.
 The amount of insolation emitted by the sun varies with sun
spot activity. This causes fluctuations of up to 2% on a time
scale of decades, or more.
 The amount of insolation reaching the earth’s outer
atmosphere varies with distance and variations of the earth’s
orbit. This causes fluctuations of up to 4% on a time scale of
centuries or more.

Insolation & Global Variation …
 Insolation received at the earth’s surface varies with latitude.
The higher angle of the sun in the sky at the equator conveys
more energy per unit area than at higher latitudes.
 Radiation passes through a greater length of atmosphere when
at a low angle in the sky than when overhead. Atmospheric
gases, dust and vapour absorb more energy before it reaches
the earth’s surface.

The atmosphere is heated primarily from below… from the surface

Earth’s Heat Balance …
Incoming energy
 The total rate at which the energy enters the Earth's
atmosphere is estimated at 174 petawatts (100%).
 Solar radiation (99.97%, or nearly 173 petawatts). This is equal to
the product of the solar constant and the area of the Earth's disc
as seen from the Sun.
 Geothermal energy (0.025%; or about 44 to 47 terawatts).
This is produced by stored heat and heat produced by radioactive
decay leaking out of the Earth's interior.
 Tidal energy (0.002%, or about 3 terawatts). This is produced by
the interaction of the Earth's mass with the gravitational fields of
other bodies such as the Moon and Sun.
 Waste heat from fossil fuel consumption (about 0.007%, or about
13 terawatts).

Outgoing energy
 The average albedo (reflectivity) of the Earth is about 0.3,
which means that 30% of the incident solar energy is reflected
into space, while 70% is absorbed by the Earth and reradiated
as infrared.
 30% of the incident energy is reflected, consisting of:
 6% reflected from the atmosphere
 20% reflected from clouds
 4% reflected from the ground (including land, water and ice)
 The remaining 70% of the incident energy is absorbed:
 51% is absorbed by land and water, and then emerges in the
following ways:
 23% is transferred back into the atmosphere as latent heat by the
evaporation of water, called latent heat flux

Outgoing energy …
 7% is transferred back into the atmosphere by heated rising air,
called Sensible heat flux
 15% is transferred into the atmosphere by radiation
 6% is radiated directly into space
 19% is absorbed by the atmosphere (16% by the air, 3% by
clouds).
 When the Earth is at thermal equilibrium, the absorbed and
radiated energy are equal: 70% of the incident solar energy =
64% radiates by the atmosphere and cloud + 6% radiates
directly from earth’s surface.

Lesson Summary
 All materials contain energy, which can radiate through
space as electromagnetic waves.
 The wavelengths of energy that come from the Sun include
visible light, which appears white but can be broken up into
many colors.
 Ultraviolet waves are very high energy. The highest energy
UV, UVC and some UVB, gets filtered out of incoming
sunlight by ozone.
 More solar energy reaches the low latitudes and the
redistribution of heat by convection drives the planet's air
currents.
 Incoming Solar Energy = Outgoing Radiation

Air Pressure
 Air pressure or Atmospheric pressure is the force per unit
area exerted on a surface by the weight of air above that
surface in the atmosphere of Earth.
 On a given plane, low-pressure areas have less atmospheric
mass above their location, whereas high-pressure areas
have more atmospheric mass above their location.
 A column of air, one square centimeter measured from sea
level to the top of the atmosphere, has a mass of about 1 kg
 Things that effect Air Pressure
 Altitude (Elevation)
 Temperature
 Humidity (moisture in the air)

Altitude / Temp. / Humidity
 The higher the altitude, the lower the air pressure.
 The lower the altitude, the higher the air pressure.
 As the temperature goes up, the air pressure goes down.
(hot molecules are further apart- less pressure).
 As the temperature goes down, the air pressure goes up.
(cold air is more dense than warm air).
 As the air becomes more humid, the air pressure goes down
(moist air weighs less than dry air).
 Drier air has higher pressure because dry air weighs more
than moist air, therefore it has greater pressure.

Pressure Gradient
 The pressure gradient force initiates movement of
atmospheric mass, wind, from areas of higher to areas of
lower pressure
 Horizontal wind speeds are a function of the strength of the
pressure gradient

Air pressure and Air density
The relationship between air
pressure and air density

In a high pressure area, air will sink because
the air is more dense. This is because the air is
Cold and sinks. Therefore, clouds
CANNOT form.
In a high pressure area, air will rise because the
air is less dense. This is because the air is
warm and rises. Therefore, clouds are
LIKELY to form.
Low vs High Pressure

Low vs High Pressure …
low pressure high pressure
warm or cold air
air rising or sinking
clouds or no clouds
clockwise or
counterclockwise wind
direction
winds toward or
away from the center

Sea and Land Breezes
 Caused by temperature
differences between
land and sea. Strongest
in spring/summer.
 During the day (night)
land is hotter (colder)
than water.
 A thermal low develops
over the warmer region.
 Air converges into the
low, ascends, and
produces clouds and
possibly precipitation.

Valley and Mountain Breezes
 Diurnal variation similar to a
land/sea breeze occur in
mountainous areas and are called
valley and mountain breezes.
 Mountains facing the sun heat more
intensely than shaded valley areas.
This develops a thermal low during
the day which produces a valley
breeze.
 At night the situation reverses
producing a mountain breeze.

Speed and Direction
 Horizontal pressure gradients are responsible for wind
generation
 Three factors affect wind speed and/or direction (velocity):
 Pressure Gradient Force (PGF)
 Coriolis Effect (CE)
 Friction Force (FF)
1. Pressure Gradient Force:
 High pressure  low pressure
 Pressure differences exits due to unequal heating of
Earth’s surface
 Spacing between isobars indicates intensity of gradient
 Flow is perpendicular to isobars

Speed and Direction …
2. The Coriolis Effect:
 Objects in the atmosphere are influenced by the Earth’s rotation
 Rotation of Earth is counter-clockwise looking down from N. Pole.
 Results in an ‘apparent’ deflection (relative to surface)
 Deflection to the right in Northern Hemisphere (left in S. H.)
 Greatest at the poles, 0 at the equator
 Increases with
speed of moving
object and distance
 CE changes
direction not speed

Speed and Direction …
3. Friction:
 Friction slows down wind speed and reduces Coriolis
deflection
 Friction is important for air within ~1.5 km of the surface (the
so-called planetary boundary layer).
 It varies with surface texture, wind speed, time of day/year
and atmospheric conditions.
 Friction above 1.5 km is often small (often called the free
atmosphere), except over regions with storms and gravity
waves

Lesson Summary
 Sea and land breezes. Caused by temperature difference
between land and sea.
 The pressure gradient force initiates movement of
atmospheric mass, wind, from areas of higher to areas of
lower pressure
 Horizontal pressure gradients are responsible for wind
generation
 Things that effect Air Pressure: 1. Altitude (Elevation)
2. Temperature, 3. Humidity (moisture in the air)
 Three factors affect wind speed and/or direction (velocity):
1. Pressure Gradient Force (PGF), 2. Coriolis Effect (CE),
3. Friction Force (FF)

Climatology scope and principles

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