Hwa Chong Institution (High School) Term 1-2010 Sec 4 Geography Revision Notes INSTRUCTIONS TO READERS You do not need to write your name, class and index number in the spaces at the top of this page. Read ALL the content carefully in the Sections provided in this revision paper You can open the booklet at any time you want INFORMATION FOR READERS Memorize all the content if possible This note consists of 12 printed pages (including this page)
Content page Lighthouse of this note Section I: Terms and conditions Section A: Atmosphere, Weather and Climate Section B: Elements of weather and climate Section C: Humidity and precipitation Section D: Planetary Wind and pressure TERM AND CONDITIONS The content of the pages of this note is for your general information and use only. It is subject to change without notice. Neither Cao Yu nor anyone whom you can think off provide any warranty or guarantee as to the accuracy, timeliness, performance, completeness or suitability of the information and materials found or offered on this note for you to score an A1. You acknowledge that such information and materials may contain inaccuracies or errors. Your use of any information or materials on this note is entirely at your own risk, for which I shall not be liable. From time to time this note may also include links to other websites. These links are provided for your convenience to provide further information. They do not signify that I endorse the website(s) nor I have visited the website(s). Hence, I have no responsibility for the content of the linked website(s). You may not upload this note to any website or email it to anyone whom you can think off without Cao Yu s prior written consent.
Section A: Atmosphere, Weather and Climate The more original a discovery, the more obvious it seems afterwards. STRUCTURE OF EARTH S ATMOSPHERE Atmosphere An envelope of transparent, odorless gases It is held in place by the pull of Earth s gravitational forces Earth s gravity is strongest nearer to the surface, therefore, most of the atmosphere is found near the surface. Consists mostly of: Nitrogen (78%) Oxygen (21%) Water vapor Dust particles STRUCTURE AND COMPOSITION OF ATMOSPHERE Using temperature, atmosphere can be divided into 4 distinct layers: 1. Troposphere 2. Stratosphere 3. Mesosphere 4. Thermosphere TROPOSPHERE Approximately 0 to 14 km above sea level Temperature decreases by 6.4 degrees for every 1000m increase in altitude Temp is due to solar radiation which keeps earth warm Falls in pressure due to the decreasing effect of gravity The most unstable layer Topped by an isothermal layer STRATOSPHERE Steady rise in temp caused by ozone Pressure continues to fall Dry air; little or no weather Acts as a protective shield against meteorite which usually burns out as it enters earth s gravitational field MESOSPHERE Temperature falls rapidly due to no water vapor, cloud or dust or ozone to absorb incoming radiation Lowest temperature 90 degrees Strongest winds 3000km/hr THERMOSPHERE Temperature rise rapidly with height to reach 1500 degrees Due to atomic oxygen which has the same function as ozone.
Hwa Chong Institution 2010 Term 1 IHE Geography Revision Notes ENERGY IN THE ATMOSPHERE 3 ways in which solar radiation is treated by atmosphere: Absorption: mainly my ozone, dust, water vapour and carbon dioxide, greenhouse gases Reflection: reflection radiation back into space Scattering: Incoming radiation is diverted by molecules of gas and becomes diffused
IMPORTANCE OF THE ATMOSPHERE Helps sustain life Protects the Earth WEATHER VS CLIMATE Weather When this happens, we experience a change in weather Meteorologists define weather as the condition of the atmosphere at a particular place over a short period of time Climate Weather pattern of a place over a long period of time, usually 30 years The basic elements of weather and climate: Sunshine Temperature Humidity Clouds Rainfall Air pressure Wind HOW WEATHER AND CLIMATE AFFECT PEOPLE Weather affects our daily life Climate affects how people live generally Where people choose to live Types of houses people live in Climate affects food and water supply
Section B: Elements of Weather climate We have, I fear, confused power with greatness. DEFINITION OF TEMPERATURE Temperature is the degree of heat or cold in the atmosphere It is measured in ºC or ºF WARMING OF AIR Convection Conduction Radiation Hot air, being lighter than cold air, rises as a convection current Air receives heat from the ground it is in contact with Heat energy from the ground is sent back to space. This form of heat energy can travel in a vacuum Factor influencing Temperature Latitude Altitude Description Places near the Equator are hotter than places near the poles due to the angle at which sun s ray strike the Earth Amount of heat received by Earth s surfaces decreases with latitude due to the decreasing angle of incidence Angle at which sun s ray hits earth of the sun s ray Earth s axis is tilted at an angle of 23.5º from the vertical From June to Aug, there is a higher intensity of the sun s ray in the northern hemisphere The higher latitudes in the northern hemisphere experience higher temperature in summer while the higher latitudes in the southern hemisphere experience low temp in winter. Temperature falls by 6.4ºC for every 1000m increase in height. This fall in temperature is called the normal lapse rate. Air is warmed by the heat radiated from the ground due to conduction and convection. It is much warmer as there is larger land Most of Earth's surface gases are also concentrated at the Earth s surface. Temperature sometimes rise with altitude in the troposphere due to: Rapid outgoing terrestrial radiation on a cloudless night. Cold air rolling down slope displacing the Warmer air Warm air rises over cold air at a warm front Cold air undercutting warm air at a cold front
Distance from Sea heats up and loses heat more slowly than land the sea Coastal area temperature is influenced. In temperate latitudes, coastal areas have a smaller temperature range between summer and winter Inland areas far from the sea are not affected by the ocean thus having a larger annual temperature range. Ocean Change in temperature is due to ocean currents in the area currents Ocean current are set in motion by prevailing winds blowing over the surface 2 types of ocean currents: Warm Originates from equator Cold Originates from higher latitudes Aspect Refers to the direction of the slope of the land relative to the sun More obvious in temperate regions rather than tropical regions In northern hemisphere, south facing slope have higher temp than north facing slope Humidity Humidity is the state of the atmosphere with respect to its amount of water vapour The higher the humidity, the more clouds there will be as clouds are formed by condensation of water vapour. Thick cloud cover prevents solar radiation from entering in the day and outgoing terrestrial radiation escaping in the night. Therefore, equatorial areas which have high humidity and thick cloud cover have low diurnal temp range. Land surface An area with vegetation is much cooler than an area of concrete. Vegetation reduces the incoming radiation and prevents absorption of heat into the ground. Concrete surfaces absorb heat quickly in the day and releases heat lowly at night. SIX S THERMOMETER Maximum temperature is measured by the maximum thermometer It consists of a glass tube containing mercury and a metal index When temperature rises, the mercury expands and pushes the metal index upwards When temperature falls and the mercury contracts, the metal index stays in place The minimum thermometer works in the same way, but contains alcohol instead of mercury.
Section C: Humidity and precipitation The shortest distance between two points is always under construction. HUMIDITY The state of atmosphere with respect to its water vapor content Warm air can hold more water vapour than cold air Water vapour comes from the evaporation of water from ponds, lakes, rivers, seas and oceans. Saturation point is reached when air contains all the water vapour it is able to hold at a particular temperature RELATIVE HUMIDITY The ratio of the actual amount of water vapour in the air at a particular temperature to the maximum quantity of water vapor the air can hold at that temperature Usually measured as a % SATURATION POINT when the air reaches the maximum capacity to hold water vapor DEW POINT TEMPERATURE The temperature at which Saturation Point is reached; Name of the cloud Cirrus Description Thin and wispy Cumulus Round and wooly Stratus Flattish low clouds, occurs in layers Cumulonimbus Huge, towering
TYPE OF PRECIPITATION Type of Description precipitation Rainfall The air rises or is lifted The air that has risen or has been lifted cools The cool air becomes saturated at dew point ie, it is holding all the water vapour it can hold at a particular temp. When air is cooled further, it continues to rise, the water vapour in it condenses into water droplets around atmospheric particles The water droplets forms clouds When the water droplets in clouds are too heavy to be suspended in air rain falls Snow Forms under similar conditions to rain Except that as dew points temperatures are under 0ºC, then water vapour condenses directly into solid (Sublimation) Sleet Is a mixture of ice and snow formed when the upper air temperature is below freezing, allowing snowflakes to form and lower air temperature is around 2 to 4ºC which allows them to melt partially Hail Made up of frozen raindrops which exceeds 5mm in diameter It usually forms in cumulonimbus clouds resulting from the uplift of air by convection currents or at a cold front. More common in summer areas where more heat triggers off the uplifting of air. THEORY OF PRECIPITATION Minute water droplets (less than 0.05mm in diameter) or ice crystals (if dew point temperature is below freezing) are produced from condensation Very tiny and weigh very little Constantly kept buoyant by the same rising air currents that produce them Water droplets and ice crystals need to become sufficiently large to overcome this uplift COLLISION & COALESCENCe warm clouds (containing no ice crystals) are found in tropics contain numerous water droplets of differing sizes different-sized droplets swept upwards at varying velocities collide with other droplets the larger the droplet, the greater the chance of collision and coalescence with smaller droplets
when coalescing droplets reach a radius of 3mm, their motion causes them to disintegrate to form a fresh supply of droplets thicker clouds provide more time for droplets to grow, with them falling faster (thundery showers) TYPE OF RAINFALL Type of Description rainfall Convectional On a hot day, the air in contact with the warm ground is warmed by conduction. The warm air with higher temperature than the surrounding air rises and is said to be unstable. This unstable warm air which holds a lot of moisture rises in a convection current. As it rises to great height, it cools. Further cooling after it reaches dew point causes water vapor to condense into water droplets around particles such as dust and smoke. The water droplets form towering cumulonimbus clouds. When the water droplets are too heavy to be suspended, conventional rain falls. Relief Orographic rain occurs when near-saturated, warm maritime air is forced to rise when confronted by a coastal mountain barrier. As air rises, it cools. Air becomes saturated when dew point is reached at the level of condensation. Condensation occurs upon further cooling, forming water droplets that coalesce to form clouds. When the water droplets become too heavy, they fall as relief rain on the windward slop. The leeward side of the mountain forms a rain shadow area. After crossing the mountain, descending dry air is warmer. Forms warm dry wind on the leeward slope and it brings very little moisture Frontal Lighter warm air rises gently over heavier cold air which remains close to the ground. Warm air rises, cools and water vapor condenses to form low to mid-level clouds like nimbostratus/altocumulus clouds. Light rain over wide area for several hours Heavy cold air slips under lighter warm air. Warm air rises aggressively. Cumulonimbus clouds form with heavy rain over a small area with a short duration.
Section D: Planetary pressure system Life being what it is, one dreams of revenge. WINDS moving air- caused by difference in air pressure Wind always moves from area of high pressure to area of low pressure Air pressure is measured using a mercury barometer PLANETARY PRESSURE SYSTEM 1. Equatorial low pressure belt/doldrums (from 5 N to 5 S) 2. Polar high pressure belts (around 90 N to 90 S) 3. Sub-tropical high pressure belts/horse latitudes (around 30 N to 30 S)
4. Sub-polar low pressure belts (around 60 N to 60 S) CORIOLIS Due to rotation of the earth and the unequal distribution of land and sea surfaces, winds do not blow directly from areas of high pressure to low pressure. Moving air appears to be deflected to the right in the northern hemisphere and left in the southern hemisphere. MAJOR PLANETARY WINDS
Trade winds (Both northeast and southeast) Blow from sub-tropical high pressure belts (horse latitudes) to the equatorial low-pressure belt (doldrum). Zone of convergence: ITCZ Westerlies Blow from sub-tropical high pressure belts to sub-polar low pressure belts. Generally warm and dry Easterlies Blow from polar high-pressure belts to sub-polar low pressure belts. MONSOON IN SEA & HURRICANE KATRINA Regional winds which influence the climate of huge land masses. They are seasonal by nature and are caused by changes in pressure during the changing seasons between summer and winter LOCAL WIND