Weather and Climate
Weather
State of atmosphere at a particular place over a short period of time
Climate
Average state/condition of a place over a long period of time (30-35 yrs)
Temperature
Degree of hotness or coldness of the place
Factors that Affect Weather & Climate
Temperature
Energy from the sun mostly travels through the atmosphere and is absorbed by the earth’s
surface. This causes it to warm up which in turn heats the atmosphere
Things to note about Temperature:
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mean daily temperature
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diurnal temperature range
o
diff between max and min in a day
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mean monthly temp range
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mean annual temp range
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annual temp range
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max temp
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min temp
Heat Budget
Absorption
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of incoming radiation is mainly by ozone, water vapour, carbon dioxide and particles
of ice and dust
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insolation is retained by the particles and converted into heat
• Occurs in and is limited to the infrared part of the spectrum
Radiation
•
Solar radiation is either reflected back to space or reaches the Earth as diffused
radiation
• Shortwave solar radiation = energy from the sun
• Longwave radiation = outgoing (terrestrial) radiation that is radiated from the
ground after solar radiation is absorbed and converted to heat energy
•
Incoming radiation is converted to heat energy
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Heat is absorbed by water vapour/carbon dioxide, other gases, pollutants to retain
heat near the surface (Greenhouse Effect)
Reflection
•
By clouds and the earth’s surface back to space
• dependent on the albedo of clouds and earth’s surface
• The albedo of an object is the extent to which it reflects light from the sun.
• Ratio between insolation and the amt reflected  represented by %
• Varies with cloud type
• Thing clouds  30-40%
• Thicker stratus  50-70%
• 90%  cumulonimbus only 10% reaches teh atmosohere
below cloud level
• Albedo also differ over land surfaces
• Oceans/dark soil  Less than 10%
• Deforestation and overgrazing occur, the albedo increases 
reduces the chances of cloud formation and precipitation and
increases the risk of desertification
• Coniferous and urban  less than 15%
• Grassland and deciduous forest  25%
• Light coloured deserts  40%
• Reflecting fresh snow  85%
•
Gas molecules also scatter radiation back to space. The rest reaches surface by
diffused radiation (scattered energy).
• Diffuse radiation= scattering occurs when insolation is diverted by particles of dust
(volcanoes/deserts) or by molecules of gas  Takes place in all direction Some of
the radiation reach the E’s surface as diffuse radiation
• Due to absorption, reflection and scattering, only 24% of incoming radiation reaches
the E’s surface directly
• Further 21% arriving at ground level as diffuse radiation
• Hence, only 45% of incoming radiation reaches the E’s surface
Words to Note:
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•
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net radiation: difference between all incoming and outgoing (terrestrial) radiation
• there is a net gain in radiation everyw on E’s surface except in polar latitudes
which have high albedo surfaces
• positive heat balance within the tropics
• negative heat balance both at high altitudes and latitudes (polar regions)
• after balancing the incoming and outgoing radiation, there is a net surplus
between 35 S and 40 N (the difference in latitudes is due to the larger
land masses in the northern hemisphere) and a net deficit to the poleward
sides of those latitudes
•
surplus: radiant energy flowing in faster than it is flowing out
deficit: radiant energy flowing out faster than it is flowing in
Type of Heat Transfers
Horizontal Heat Transfers = transfer of heat energy away from the tropics, thus preventing
tropics from overheating and the poles from getting colder
Example:
• Winds, air movements (80%)
 Oceans hold a smaller percentage (20%)
Vertical Heat Transfers = radiation, conduction, convection and transfer of latent heat. This
prevents the surface from overheating and atmosphere from getting colder
 Radiation, conduction, convection and the transfer of latent heat
Latent heat the amount of energy needed to change the state of a substance without
affecting its temperature (ie. When ice changes into water and there isn’t a change in the
temperature as energy is used up in the change of state)
Factors affecting Temperature
Latitude (Long Term)
The latitude = distance of any point on earth measured from north or south from the
Equator. Each degree is made up of 60 minutes. (eg. Singapore 1 degree 22N = 1 degree 22
minutes north from the equator)
The earth tilts at 23.5 degrees on its own axis. Hence, the sun’s rays strike at various angles at
different parts of the earth. Angle of incidence = angle rays hit
The greater the angle of incidence, the more concentrated the rays are. Meanwhile, in certain
areas, solar radiation spreads out over a wider area, hence making it cooler.
Altitude (Long Term)
Temperature decreases with altitude as the atmosphere is mostly heard by the earth’s
surface. When solar radiation enters the atmosphere and reaches the earth’s surface in the
form of shortwave radiation, about 45% if this radiation is directly absorbed by the surface,
heating it up. The warm surface then emits heat in the form of long wave radiation.
The higher up the atmosphere u go, the further u are from the surface and hence, less heat
transfer and less temp.
Long wave radiation is emitted by the earth and is absorbed by greenhouse gases such as
carbon dioxide. Hence, air nearer to the surface absorbed more heat from long wave
radiation than air at higher altitudes.
In addition, air is less dense at higher altitudes. Denser air is then able to absorb more heat
from long wave radiation. The less dense air on top has less ability to absorb heat than the
denser air at sea level, hence, air at higher altitudes will be cooler as well.
Distance from Sea (Long Term)
Specific Heat Capacity (SHC)
•
•
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Land and water differ in their abilities to absorb heat
Water has a higher Specific Heat Capacity than land/soil, so takes a longer time to
heat up.
Water body seems cooler as compared to land surfaces.
Maritime Effect
Maritime effect = effect that large ocean bodies have on the climate of coastal
areas. It causes coastal areas to have a smaller annual temperature ra nge
During summer  the air over the sea is cooler than the air over the land as the
land heats up more quickly than the sea. The cooler air over the sea helps lower
the temperature of coastal areas.
During winter the air over the sea remains warmer than the air over the land.
Hence, the warmer air over the sea heated up the temperature of flatland areas,
making it warmer.
Continental Effect
Continental effect = effect that continental surfaces have on the climate of inland areas 
large annual temperature range
As inland areas are further away from the sea, the temp of these areas are not influenced by
the sea. Therefore, inland areas experience warmer summers and colder winters and a larger
annual temp range
Water body has higher albedo  higher reflection  lower temperature.
Continental areas therefore are more responsive to temperature changes as compared to
water bodies.
Prevailing Winds (Long Term)
Winds blowing from sea tend to be warmer. Hence, coastal areas experiencing such breezes
will be warmer than areas not experiencing such breezes.
For example:
Examples: The Mistral in France is a cold, strong, and usually dry wind, usually occurring in
the winter and spring, blowing from the northwest or north of Europe through the valley of
the Rhône River to the Mediterranean. Can cause local temperature to drop drastically 
damage vineyards.
Ocean Currents(Long Term)
Notice how all the cooler arrows
flow towards the equator, and the
warmer arrows towards the poles!
Ocean currents flowing from the Equator is warm and conversely water flowing away from
the polar area is cold. Warm currents carry polewards and raise the air temperature of the
maritime environments where they flow. Cold currents carry water towards the Equator and
lower the temperature of coastal areas.
The main ocean currents follow circular routes (clockwise in the northern hemisphere, anti
clockwise in the southern hemisphere).
Examples:
United Kingdom is warmer due to the North Atlantic Drift flowing from the Caribbean
Sea to the North Sea.
Hokkaido in North Japan is colder due to the presence of the cold Oyashio current
flowing from the Barents Sea to the Sea of Japan. This results in anomalies from the uneven
cooling and heating rates of land and sea, which are intensified by the horizontal transfer of
energy by ocean currents and prevailing winds. Areas can have higher or lower temperature
than the average of other locations of that latitude.
Warm Ocean Currents
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•
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Increases temp of coastal area
Keep harbours free from ice
Warm onshore winds raises temp of coastal areas
Cold Ocean Currents
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•
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Lower temp of coastal area
Labrador Current carries large icebergs to the Atlantic
Cool the onshore winds and lower temp of coastal lands
Temperature anomaly = temperature differences from a mean.
Anomaly = something that doesn’t fit the general pattern
Seasonal Changes (Short Term)
Lengths of Days and Nights (Short Term)
Areas experiencing longer days tend to have higher temperatures. Areas near the Equator
tend to have equal lengths of day and night every 24 hours. However elsewhere, they may
experience longer days than nights or vice versa. This would affect the amount of insolation
that would be absorbed. Longer days  warmer
Cloud cover (Local Influence)
Cloud cover= extent of the sky that is covered by clouds.
Amt of cloud cover influences the temperature on the earth’s surface in the day and night.
More clouds = smaller difference
Presence of clouds  during the day, clouds reflect a large amount of the suns energy back
to Space. This keeps the earth’s surface cool at the same time; clouds also absorb heat
radiated from the surface.
During the night, cloud absorbs more heat that is radiated from the earth’s surface or reflects
it, preventing it from escaping into slave, thus keeping the air near the E’s surface warm
Aspect (Local Influence)
ASPECT = the direction a slope faces in relation to the Sun
In the Northern Hemisphere, the south facing slope will be warmer as it receives more direct
solar radiation. It is also protected by cold polar winds from the North pole. The opposite
occurs in the Southern Hemisphere, where north facing slopes are warmer.
Houses in the equator tend to build houses facing the east as it’ll be cooler. Morning sun
cooler
North facing and south facing slopes  adret and ubac
Urbanisation (Local Influence)
Urbanisation alters the albedo of natural landscapes. This is because buildings, concrete and
black roads tend to reflect less insolation and hence, absorb more heat and heat up the
surrounding area. The phenomenon is called the Urban Heat Island Effect. It causes urban
areas to experience higher temperatures than grass or natural landscapes.
Generally, towns and cities generate a lot of heat. New York alone generates 7 times
as much heat as what it receives from the sun. It is found that generally, larger cities have >
urbanisation effects. Man made asphalt surfaces like our roads stores up heat during the say
and releases during the cool night. Homes and factories or buildings heat up during the
night, but take very long to cool down at night.
The contribution of pollutants too make the temperature fluctuate even more. It is found
that generally, haze and dust in the air above the city reflects back the heat generated, but it
also traps the heat in. With 200x So2 , 200x CO, 5 dust particles.
They make the air warmer by 1 to 2 degrees, creating more fog, or smog, and hecen cloud
cover.
Relative humidity
Ratio between the actual amount of water vapour present in a mass of air and
the maximum amount of water vapour the air could hold at a given tempera ture
Relative humidity (%) = (actual amount of war er vapour in the air (g/m^3)/
(max amt of water vapour the air can hold (g/m^3) x 100
Higher the %,  moisture the air is carrying
Factors that affect RH

amount of water vapour

temperature
o
Warm air can hold more water vapour than cool air. When the temp increases,
the amt of water vapour stays the same. Hence, RH decreases as temp
increases.
o
When the air holds the max amt of water vapour, it is said to be saturated
(100%) the temperature at which saturation occurs is known as the dew point
temperature
o
Condensation starts to occur at dew point temperature, where water vapour
changes to a liquid by cooling
Sling Psychrometre
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

Dry bulb is a normal thermometer
o Shows air temp
Wet bulb thermometre has a muslin wrapped round the bulb.
o Capillary action draws water up from the tiny bottle of water up the muslim cloth
onto the wet bulb. The reading must be less than the temperature because this just
tests for the rate of evaporation. If more evaporates, then the temperature for the wet
bulb will be lower. This is because as it evaporates, it takes heat with it. However, if
the air is already saturated, the air cannot evaporate and take latent heat with it.
Hence, the wet bulb swinging motion.
Take the diff bet the 2 temp.
o DB – WB = wet bulb depression
o Read from table
o Greater the diff / bigger the depression…
o lower the RH (drier the air)
Precipitation
Clouds
When the earth’s surface is heated up water is converted to water vapour during evaporation.
As water vapour rises, it starts to cool. When the water vapour cools to dew point
temperature condensation takes place if there are tiny particles for the water vapour to
condense on, these tiny particles such as dust = condensation nuclei. Water droplet will
bump into each other and become larger in a process called COALESCENCE. Clouds thus
forms.
Cloud = visible mass of water droplets/ice crystals that are suspended in the atmosphere. It
may eventually grow large enough to fall to the earth’s surface as precipitation
Brief Description of Types of Clouds
High altitude clouds: cirrus, thin wispy clouds. Indicates clear weather.
Low-altitude clouds: cumulus, clouds that look like bales of cotton. Indicates fair weather.
Cumulonimbus clouds: bring heavy thunderstorm. Look like a huge mushroom.
Rainfall
Precipitation = water in any form that falls from the atmosphere of I the surface of the earth
They can come in the form of hail (balls of ice), snow (white or translucent ice crystals), sleet
(mixture of rain and snow) and rain, which is the most common form
The main form of precipitation in the tropics is rain. Areas with rainfall above 1500
millimetres are classified high. 250 and below = low. The amt of precipitation is measured in
millimetres using a rain gauge.
Rainfall is the result of air instability, which is their tendency of a parcel of air to rise (unstable)
rather than remain in its original position (stable) . When a parcel of air is cooler than its
surrounding air, it sinks and reminds near the ground. This parcel of air is stable. However,
when it is heated, it expands, becomes less dense and rises, making it unstable.
The water droplets are so tiny and weigh so little that they are kept buoyant by the rising air
currents which created them.
Ice crystal mechanism
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temp of air between -5 and -25 degrees Celsius, supercooled water droplets and ice
crystals exist together
o
supercooling  takes place when water remains in the atmosphere after
temps have fallen below 0 degrees Celsius , usually due to the lack of
condensation nuclei
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ice crystals are in minority as they require freezing nuclei  less abundant
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relative humidity of air is ten times greater above an ice surface than over water. This
means that the water droplets evaporate and the resultant vapour condenses
(sublimes) back onto the ice crystals which then grow into hexagonal shaped
snowflakes.
o
They grow in size  further condensation/fusion of numerous edges
interlocked on collision with other flakes
o
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Increase in number as ice splinters break off and form new nuclei
As the snow falls to the ground, flakes melt into raindrops.
Collision and Coalescence
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Warm clouds (no ice crystals) as found in the tropics contain numerous water droplets in
differing sizes
Different sized droplets are swept upwards at different velocities and in doing so collide with
other droplets
It is thought that the larger the droplet the greater the chances of collision and coalescence
with smaller droplets
The thicker the cloud (cumulonimbus), the greater the time the droplets have in which to
grpw and the faster it will fall  thunder storms
CONVECTIONAL RAIN
Convectional rain occurs when the earth’s surface is heated intensely. Hence, this form of
rain is common in the tropics where it receives a large amount of solar radiation.
As the suns energy heats up the earth’s surface, the warm surface heats the air around it. The
parcels of air becomes unstable, causing it to expand and rise in pockets known as thermals.
As the air rises, its temperature drops. When the air then cools to the dew point temperature,
condensation occurs and clouds form. Water droplets in the clouds become large and heavy
enough; they fall to the ground as rain.
They are usually associated with lightning and thunder. They last for a short period of time
but bring intense rainfall during that time in a small area.
OROGRAPHIC/REFLIEF RAIN
This occurs when warm moist air is forced to rise over landforms suh as a mountain rage.
Moist air passes over the sea and arrives at the coast. The air then rises up the windward side
of the mountain and is forced to cool. When the temperature reaches dew point,
condensation occurs and clouds form. When the water droplets become large and heavy
enough, they fall as rain on the windward side of the mountain where air had risen up.
The other side, known as the leeward or rain shadow side, is usually dry because most of the
moisture would have fallen on the windward side.
Pressure and winds
Air Pressure
Air pressure is the force exerted on a unit area of the earth’s surface by the weight of a
column of air above it.
Air pressure millibars (mb) using a barometre. The average sea level value of air pressure is
1013 mb . Air pressure is considered high if it is above the sea level value, and low if it is
below the sea level. The measurement can then be presented in a weather map/synoptic
chart. Isobars, which are lines joining places of equal air pressure, are represented on these
charts.
Air pressure decreases as altitude increases as air is less dense at higher altitudes. Why? This
is because gravity pulls air molecules towards the surface of the earth. Hence, air pressure is
higher at sea level and lower at higher altitudes.
Wind
Air moves from an area of high pressure to an area of low pressure. This movement of air =
wind. Pressure gradient is the difference in air pressure between two locations. The great the
difference in air pressure (steeper pressure gradients), the faster the wind speed.
Wind is described in terms of speed, direction and frequency.
Wind speed = rate which air is moving  km/hr using an anemometer. It may also be
represented by the Beaufort Scale which is a scale for measuring wind speed based on
observations of the impacts of wind on land.
Wind Direction = direction from which wind blows. A wind vane is used to determine the
wind direction. It points to the direction the wind is blowing FROM. For example, if the wind
is blowing from the south south west, the wind vane will point there.
Wind frequency = percentage of time the wind blows from a particular direction. Wind
direction and frequency can be recorded using wind roses. The numbers represent teh dates
in a month in which the wind blew from a particular direction. The number of calm days
without wind is stated in the circle in the wind rose.
Wind systems
Land and Sea Breeze
Land and sea breezes are local winds that occur in coastal areas. These winds lower the
temperature of coastal areas during the day and regulate the temperature during the night,
leading to a smaller diurnal temperature range.
Land Breeze
Land breeze = wind that blows from the land to the sea. It is formed by differences in air
pressure due to the different rates at which land and water bodies cool. The land loses heat
and cools down faster. Hence, the sea has a higher temperature. As it air above the sea
would hence be of a higher temperature, it will expand and rise. This causes a lower air
pressure over the sea than the land. As the air moves from an area of high pressure to an
area of lower pressure, a land breeze is formed.
Sea Breeze
Sea breeze= wind blows from the sea to land. It is formed by the difference in air pressure as
well. Exact opposite happens as the sea gains heat slower than the land.
Monsoon Winds
Monsoon winds = regional wind patterns that reverse directions seasonally; seasonal
movements of large air masses across the Earth, as the NH and SH experience different
seasons. Musim in Arabic. This is brought about by the differences in temperature and hence,
air pressure. They modify prevailing planetary winds and result in large scale seasonal
changes in the wind pattern
It will bring rainfall when it is onshore monsoon, meaning it blows over a water body to pick
up moisture. When it blows dry air, it is offshore monsoon because it did not pass through a
water body before passing over the land.
How does the water pick up moisture?
As the sea takes a longer time to cool down, it’ll be warmer than the wind. As the parcel of
air blows over, it will slowly gain heat. This will increase its capacity to contain moisture, and
hence pick up the water vapour to form warm moist wind optimal for bringing rain.
This brings seasonal changes in precipitation. The level of precipitation can either increase or
decrease with the occurrence of monsoons and lead to wet/dry seasons.
Monsoon winds and other winds are affected by the Coriolis effect, which is a force
produced by the earth’s rotation. As the earth rotates, the coriolos effect changes the course
of moving objects on the earth’s surface. It causes the bending/deflection of winds. Generally,
the winds in the southern hemisphere are deflected to the left and those in the northern
hemisphere deflect to the right.
The Coriolist effect is strongest at the poles, weak in the tropics and not felt atall at the
Equator.
Monsoons occur in a number of locations in the world. The major monsoons affect Asia and
Australia. Eg. Singapore commonly experiences high rainfall in December because of the
northeast monsoon. India  due to the southwest monsoon, rainfall between June and Sept,
supplies nearly 80% of India’s annual rainfall
Southwest monsoon
It takes place between June and September, when it is summer in the northern hemisphere.
The air over Central Asia heats up, expands and rises, forming a region of low pressure over
the area. During the same period, the southern hemisphere is experiencing winter. The low
temperature causes the air to be cold and dense, exerting a greater force on the earth’s
surface. Hence, there is an area of higher pressure over Australia.
Due to the difference in pressure between Central Asia and Australia, air from Australia
moves to the Indian subcontinent and Central Asia as the southeast monsoon winds. As the
winds cross the Equator, the Coriolis Effect deflects the wind to the right. These winds
become the south west monsoon winds as it warms up and heads towards central Asia. The
warm air picks up heavy moisture as it travels over the Indian Ocean and brings heavy rain to
the Indian subcontinent.
Asia North Hemisphere Winter / Nn Winter (Oct – Jan)
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Central Asia (China)
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Rapid cooling on land
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Dev extensive area of Higher pressure
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Punjab (another area of Higher pressure … lowlands of Himalayas)
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Summer in Central Australia
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Area of Lower pressure
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Winds blow out from HP to LP, crosses ocean, equator and to Australia
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In the Northern hemisphere, deflect to the right
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NE monsoon in S China and SEA
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Picks up moisture from S China Sea, blows onshore to eastern coast of Peninsular
Malaysia and Singapore.
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When NE Monsoon crosses the equator, to SH
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Deflects to the left, NW monsoon in Australia.
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Punjab (same concept except)
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Blows across sub continent of India … no source of moisture… dry monsoon /
offshore wind … dry winter for India
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A bit of relief rain on Himalayas and hence have highest rainfall there
Northeast monsoon
When: October to February the opposite happens and the wind goes the other side
However, sometimes it is not just the corealis effect. Wind can also be deflected/redirected
because of the Specific Heat Capacity of land and water. The water bodies, such as the sea,
will take a longer time to cool down/warm up, thus creating areas of instable air parcels. The
HP and LP causes the wind to be deflected.
Asia South Hemisphere Winter / Sn Winter (June – Sept)
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Central Asia heated up more intensely than the ocean
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Dev area of LP
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Similar in Punjab
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But in Australia … freezing winter … area of Higher pressure
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Winds blows out in an anticlockwise direction, Higher pressure to Lowerpressure ,
across Pacific / Indian Ocean
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Across the equator and reach Central Asia
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Deflected to the left, SE monsoon in Southern hemisphere
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Crosses E, deflected to right, SW monsoon in SEA
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Presence of obstacle… island of Sumatra, SWM does not bring much rain to PM
and Singapore.
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As it blows into the NH, changes direction … SW monsoon in Central Asia
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Punjab
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Receives onshore SW monsoon, picks up moisture from Indian Ocean + Bay of
Bengal
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Wet monsoon --- SW India + Bangladesh have a wet summer.
Atmosphere
Tropopause: Transition
between troposphere and
other layers
Troposphere
The troposphere is the lowest layer of the atmosphere. Here, the temperature
decreases with increasing height and contains the most water vapour, cloud, dust and
pollution. The Environmental Lapse Rate = temperature decreases by 6.4 degrees Celsius for
every 1000m increase in height  Average Lapse Rate
Home to the world’s biosphere, it is the atmospheric layer that supports life and
region of principal weather activity. However, the tropopause marks a change from a positive
one to a negative lapse rate in the stratosphere. However, the troposphere is the upperlimit
to the E’s climate and weather. It is marked by an isothermal layer where temperature
remains constant despite any changes in height
Funfact: Lapse Rates
Average/Environmental Lapse Rate = 6.4°C/km
The average atmospheric lapse rate results in a temperature decrease of 6.4°C/km of altitude.
Dry Adiabatic Lapse Rate = 10°C/km
A dry lapse rate of 10°C/km is often used to calculate temperature changes in air not at 100%
relative humidity.
Wet/Saturated Adiabatic Lapse Rate
A wet lapse rate of 5.5°C/km is used to calculate the temperature changes in air that is saturated
(i.e., air at 100% relative humidity).
Stratosphere
The stratosphere extends from 19km to 50km from the E’s Surface. The temperatures
in that area increase with altitude throughout with warmer layers higher up and the cooler
layers further down. (Eg. -57°C at 18km (at the tropopause) to 0°C at 50km at the
stratopause.)
The layer is heated by the absorption of UV radiation from the sun by the ozone layer.
Currently, it serves as a protective shield against meteorites which usually burn out as they
enter the E’s gravitational field. Most planes cannot fly into his area. In fact, only Jets can do
so stably.
It is also a isothermal layer which temperatures cannot change with increasing height.
Mesosphere
Temperature defreases with increasing altitudes
Thermosphere
Interpreting Climographs
Things to look out for the following to identify the type of climate.
•
mean annual temperature (high / low)
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annual temperature range (high / low)
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uniformity of temperature
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total precipitation (high / moderate / low)
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distribution of rainfall (even / seasonal)
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summer time / winter time
When describing climographs
Temperature
1. highest temperature
2. lowest temperature
3. temperature range
4. mean annual temperature
5. identify the time period
a. winter/summer?
b. Hence deduce the location
i. Northern/southern hemisphere
Rainfall
1. Highest rainfall
2. Lowest rainfall
3. Distribution of rainfall
4. Annual rainfall