Weather and climate (KQ1) Flashcards
What is weather defined as?
- the condition of the atmosphere at a particular place and time
- affects how we live from day to day
atmosphere defined as: a layer of air surrounding the earth
What is climate defined as?
- the average condition of the atmosphere of a specific place over a long period of time (usually 30 years)
What are the different elements of weather?
- temperature
- relative humidity
- clouds
- rainfall
- air pressure
- wind
What is the most important factor affecting temperature?
- latitude
What are the factors affecting temperature?
- cloud cover
- latitude
- altitude
- distance from sea
(remember CLAD)
How does cloud cover affect temperature?
- more cloud cover causes cooler days and warmer nights
- smaller difference between day and night temperatures
- smaller diurnal temperature range
How does the presence of clouds affect temperature?
- during the day: clouds reflect a large portion of the sun’s energy back into space
- this keeps the earth’s surface cool
- at the same time, clouds also absorb heat radiated from the earth’s surface
- during the night: clouds absorb more of the heat radiated from the earth’s surface
- it prevents it from escaping into space
- thus, air near the earth’s surface is kept warm at night
How does the absence of clouds affect temperature?
- during the day: the absence of clouds allows large amounts of solar energy to reach the earth
- earth’s surface heats up quickly
- thus, the air near the earth’s surface is warmer
- during the night: the absence of clouds allows more heat radiated from the earth’s surface to escape into space
- thus, the earth’s surface becomes cooler at night
What is latitude defined as?
- latitude is the distance of anywhere on earth measured north or south of the equator
What is the latitude of the equator?
- 0 degrees
How does latitude affect temperature?
- the sun’s rays strike different parts of the world at different angles
- thus, temperature differs between places with higher and lower altitude
Why does the sun’s rays strike at different angles at different parts of the earth?
- the earth tilts at 23.5 degrees on its own axis
What does the solar angle refer to?
- is refers to the angle at which the sun’s rays reach the earth
How does solar angle affect the concentration of the sun’s rays on an area?
- the higher the solar angle, the more concentrated the sun’s rays are on an area
What does the earth’s tilt result in?
- it results in some places not receiving sunlight for months
What is the relationship between temperature and latitude?
- temperatures are lower at higher latitudes due to lower solar angle
What is altitude defined as?
- the height of a place in relation to the sea level
What is the relationship between altitude and temperature?
- temperature generally decreases by 6.5 degrees with every 1000 metre increase in altitude
Why does temperature decrease as altitude increases?
- temperature decreases with increasing altitude as the atmosphere is mostly heated by the earth’s surface
What is the process of solar energy reaching the earth’s surface?
- solar energy from the sun enters the atmosphere and reaches the earth’s surface in the form of shortwave radiation
- 45% of shortwave radiation is directly absorbed by the earth’s surface, heating it up
What is the process of the warm surface of the earth emitting heat?
- the warm surface of the earth emits heat in the form of longwave radiation
- the higher up the atmosphere, the further the surface of the earth heated by the sun
- thus, temperature decreases as altitude increases
Why does air nearer the earth’s surface absorb more heat from longwave radiation than air at higher altitudes?
- the air nearer the surface of the earth is denser compared to air higher up in the atmosphere
- denser air absorbs more heat from longwave radiation
How does longwave radiation warm the earth’s surface?
- longwave radiation is absorbed by greenhouse gases in the atmosphere
- thus, the solar energy is trapped, warming the earth
How does distance from the sea affect temperature
- sea heats up and cools down slower than land
- the difference in the rate of warming and cooling of the sea and land affects the temperature
- this results in the maritime and continental effects
What does the maritime effect refer to?
- it refers to the effect large bodies of water have on the climate of coastal areas
What causes coastal areas to have a smaller annual temperature range compared to inland areas?
- during summer, the air over the sea is cooler than the air over the land
- this is due to the sea cooling down and heating up slower than land
- the cooler air over the sea helps lower the temperature of coastal areas
- during winter, the air over the sea is cooler than the air over land
- refer to pt 2
- the warmer air over the sea increases the temperature of coastal areas during winter
- thus, due to the maritime effect, coastal areas receive cooler summers and warmer winters
What does the continental effect refer to?
- it refers to the effect continental surfaces have on the climate of inland areas
What causes inland areas to have a larger annual temperature range compared to coastal areas?
- inland areas are further from sea
- thus, their temperatures are not influenced by the sea
- warmer summers, cooler winters
- larger annual temperature range
Why do some places have the same latitude but different temperatures?
- although latitude strongly affects temperature
- factors such as altitude, distance from sea and cloud cover are also significant in influencing temperature
What is relative humidity?
- its the ratio (usually expressed in percentage)
- its between the actual amount of water vapour present in a mass of air and the maximum amount of water vapour the air can hold at a given temperature
How is relative humidity measured?
- sling psychrometer
- consists of a wet bulb thermometer and a dry bulb thermometer
What is the formula to calculate relative humidity?
relative humidity (%) = (actual amount of water vapour in the air/maximum amount of water vapour the air can hold) x 100%
How does temperature affect relative humidity?
- warm air can hold more water vapour than cool air
- as temperature increases, the amount of water vapour in the air remains the same
- but the rise in temperature makes the air able to hold more water vapour
What happens when the air holds the maximum amount of water vapour it can hold?
- saturation occurs
- saturation occurs when relative humidity is at 100%
What is the temperature saturation occurs at known as?
- dew point temperature
What first starts to occur at dew point temperature?
- condensation
What is the process of condensation?
- condensation is a process in which water vapour changes to a liquid form by cooling
What is a cloud?
- a cloud is a visible mass of water or ice crystals
- they are suspended in the atmosphere due to the condensation of water vapour
- the water droplets grow large enough to fall to the earth’s surface
- this is known as precipitation
How are clouds formed?
- when the surface of the earth is heated up
- liquid water evaporates to become water vapour
- as water vapour rises, it cools
- when it cools at dew point temperature, condensation occurs when there are tiny particles for the water to condense on
- tiny particles such as dust, are known at condensation nuclei
- water droplets in the air will merge and become larger through coalescence
- cloud are formed
What is precipitation?
- precipitation refers to water in any form that falls from the atmosphere to the earth’s surface
What does precipitation include?
- hail
- snow
- sleet (mixture of rain and snow)
- rain
What is classified as high rainfall and what is classified as low rainfall?
- high rainfall: above 1500 mm
- low rainfall: below 250 mm
How is the amount of precipitation measured?
- in millimeters
- using a rain gauge
What does a rain gauge consist of?
- funnel
- copper cylinder
- outer casing
- glass bottle
What is rainfall the result of?
- air instability
What is air instability?
- it is the tendency of a parcel of air to rise (unstable)
- instead of remaining in its original position (stable)
- when a parcel of air is cooler than the surrounding air, it sinks and remains near the ground (stable)
- when the air is heated, it expands and becomes less dense than the surrounding air and rises (unstable)
When does convectional rain occur?
- it occurs when the earth’s surface is heated intensely
Where does convectional rain mainly occur and why?
- they receive a great amount of sunlight
- the tropics
What is the process of convectional rain?
- as the sun’s energy heats up the earth’s surface
- the warm surface heats the air surrounding it
- the air becomes unstable, causing it to rise
- as the air rises, its temperature begins to drop
- when the rising air cools to dew point temperature, condensation occurs and clouds are formed
- when the water droplets become large and heavy enough, they fall to the ground as rain
What is convectional rain associated with?
- lightning
- thunder
How long does convectional rain last?
- a short period of time
- it brings intense rainfall over an area
When does relief rain occur
- relief rain occurs when warm, moist air is forced to rise over landforms
- e.g. mountain range
What is the process of relief rain?
- moist air passes over the sea and arrives at the coast
- the air rises up the windward side of the mountain and is forced to cool
- when the temperature reaches dew point temperature, condensation occurs and clouds are formed
- when the water droplets become large and heavy, they fall as rain on the windward side of the mountain, where the air has risen
What happens on the leeward side of the mountain?
- its usually dry
- most of the moisture would have fallen on the windward side
What is air pressure?
- the force exerted on a unit area of the earth’s surface by the weight of a column of air above it
- we do not notice it as clearly as temperature, but its effects are felt
How is air pressure measured?
- barometer
- measured in millibars
What is the average sea level value of air pressure?
- 1013 mb
What is considered high and low air pressure?
- high: above sea level value
- low: below sea level value
What is the relationship between air pressure and altitude?
- air pressure decreases as altitude increases
Why does air pressure decrease as altitude increases?
- air is denser at lower altitudes as it tends to be more compressed at lower elevations
- where the larger overlying mass exerts a large gravitational force
What is wind?
- it is a movement of air when it moves from an area of high pressure to one of low pressure
What is pressure gradient?
- it is the difference in air pressure between 2 locations
What is the relationship between wind speed and pressure gradient?
- the greater the difference in air pressure, the faster the wind speed
How is wind described?
in terms of
- speed
- direction
- frequency
What is wind speed?
- the rate at which air is moving and is measured in kilometers per hour
How is wind speed represented?
- an anemometer
- beaufort scale (refer to tb pg 160)
What is the Beaufort scale?
- it is a scale for measuring wind speed based on observations of the impacts of wind on land
What does wind direction refer to?
- it refers to the direction from which the wind blows
What is used to determine wind direction?
- wind vane
If the wind is blowing from south-southwest, in which direction will the wind vane point in?
- south-southwest
What does wind frequency refer to?
- the percentage of time the wind blows from a particular direction
What are prevailing winds?
- winds that blow frequently from a specific direction
How are wind direction and frequency recorded?
- wind roses
What is land breeze?
- wind that blows from the land to sea
How is land breeze formed?
- it is formed by differences in air pressure
- due to the different rates sea and land heat up and cool down at
- the land loses heat or cools down faster than sea bodies at night
- thus, the sea has a higher temperature and lower pressure while the land has a lower temperature and higher pressure
- as the air moves from an area of high pressure to an area of low pressure, land breeze is formed that blows from land to sea and night
What is sea breeze?
- wind that blows from sea to land
How is sea breeze formed?
- differences in air pressure
- due to the different rates land and sea cool down and heat up at
- in the day, land heats up faster than sea
- as a result, the air pressure over land is lower than that over sea
- thus, wind blows from sea to land during day forming sea breeze
What are monsoons?
- regional wind patterns that reverse directions seasonally
What do these direction changes result in?
- seasonal changes in precipitation
What are monsoon winds or other winds affected by?
- coriolis effect
What is the coriolis effect?
- a force produced by the earth’s rotation
How does the earth’s rotation affect the coriolis effect?
- as the earth rotates
- coriolis effect changes the course of moving objects on the earth’s surface
- causes deflection/bending of the winds
- coriolis effect changes the course of moving objects
Where is the coriolis effect the strongest, and where is it the weakest?
- strongest near the poles
- weak in the tropics
- felt at the equator
What happens to winds in the northern hemisphere?
- winds deflect to the right
What happens to winds in the southern hemisphere?
- winds deflect to the left (opposite of what happens in the northern hemisphere)
When do the southwest monsoons occur?
- between june and september
- this is when it is summer in the northern hemisphere
What is the process of the southwest monsoon?
- air over Central Asia heats up, expands and rises → region of low pressure over the area
- southern hemisphere: experiencing winter → low temperature → air to be cold and dense → exerts a greater force on the earth’s surface → high pressure over Australia
difference in pressure between Central Asia and Australia → air from Australia moves to the Indian sub-continent and Central Asia as southeast monsoon winds → as winds cross to the equator, the Coriolis effect deflects the winds to the right → winds became the southwest monsoon winds and warms up as they head to Central Asia → warm air picks up moisture as it travels over the Indian ocean → brings heavy rain to the Indian sub-continent
When does the northeast monsoon occur?
- between october and febuary
- when it is summer in the southern hemisphere (cuases an area of low pressure to form over australia)
What is the process of the northeast monsoon?
- northern hemisphere: experiencing winter → area of high pressure develops over the Indian sub-continent and Central Asia
- difference in pressure → air moves from the Indian subcontinent and Central Asia to Australia as the northeast monsoon winds → generally dry and cold as they blow across cold land → as the winds cross the Equator, the Coriolis effect deflects the winds to the left → winds become the northwest monsoon winds and warm up as they head for Australia → warm air picks up moisture as it travels over the Indian Ocean and brings heavy rain to Australia
What are the different climate types?
- equatorial
- monsoon
- cool temperate
Where are the different climate types found?
- equatorial: concentrated mostly 10 degrees north and south of the equator
- monsoon: usually located bewteen 5 degrees and 25 degrees north and south of the equator
- cool temperate: usually located near coastal areas found between 40 and 60 degrees north and south of the equator
What countries are these climate types found in?
- equatorial: Southeast Asia, Northwestern Brazil, Congo Basin, Indonesia
- monsoon: Chittagong, Bangladesh, Mumbai (India)
- cool temperate: London (England), Vancouver (Canada)
How does one describe climographs?
- Mean annual temperature
- Annual temperature range
- Total annual rainfall/precipitation
- Seasonal distribution
- remember MATS
How is temperature described in climographs?
- Mean annual temperature: high, moderate, low
- temperature range: large, small
What constitutes as high, moderate and low in mean annual temperature?
- high: more than 20 degrees celsius per month
- moderate: 10 - 19 degrees celsius per month
- low: 0 to 9 degrees celsius per month
What constitues as large and small in temperature range?
- large: more than 10 degrees celsius per day/month/year
- small: less than 10 degrees celsius per day/month/year
How is rainfall described in climographs?
- high
- moderate
- low
What constitutes as high, moderate or low rainfall?
- high: more than 1000mm
- moderate: 250 to 1000mm
- low: below 250mm
What is the latitude of Singapore?
- 1°22’N
What is Singapore’s climate type?
- equatorial
What are the characteristics of SIngapore’s climate?
- uniformly high temperatures
- abundant rainfall
- high relative humidity
How is Singapore’s mean annual temperature described as and what is it?
- high
- 27.5 degrees celsius
How is Singapore’s total annual rainfall described as and what is it?
- high
- about 2200mm
What is Singapore’s mean annual relative humidity?
- 84.2%
- air very humid
What is the total monthly rainfall in Singapore during the northeast monsoon?
- 1125mm
What is the total monthly rainfall in SIngapore during the southwest monsoon?
- 600mm
