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SLCSS/GEOGRAPHY/CE/LAND/3 Weather and Climate Contents: A. World climatic system B. Heat energy balance of the earth C. Heat energy transfer D. Interpretation of weather and climate E. Climatic elements 1. Temperature 2. Pressure 3. Wind 4. Relative Humidity 5. Precipitation F. Climatic regions of the world G. Measurements of climatic and weather elements H. Climate of Hong Kong I. Interpretation of Honk Kong weather chart J. Weather of Hong Kong SLCSS/GEOGRAPHY/CE/LAND/4 A. World climatic system INPUTS Solar radiation Gases Water vapour Dust PROCESSES OUTPUTS Heat energy transfer Air circulation Water cycle Ocean current Pattern of temperature Pattern of pressure Pattern of wind Pattern of precipitation B. Heat energy balance of the earth When insolation from the sun reaches the earth, heat is released and transferred from the earth’s surface through radiation, conduction, convection and advection. Shortwave solar radiation Insolation 100 -6 -27 -2 Reflection Scattering Absorption +14 Atmosphere +17 Ground +34 Longwave earth radiation Radiated from earth -17 +6 Radiated from atmosphere -48 Atmosphere +9 +19 Radiation from earth -23 Convection -9 Condensation -19 Ground SLCSS/GEOGRAPHY/CE/LAND/5 The in-coming solar energy and out-going longwave heat radiation from the earth are maintained in balance on a global scale. Such balance is called the heat energy balance or heat energy budget of the earth. C. Heat energy transfer D. Interpretation of climate and weather Difference: Climate – the average conditions of the atmosphere over a long period of time (usually more than 30 years) at any one place. Weather – the conditions of the atmosphere over a short period of time at any one place. SLCSS/GEOGRAPHY/CE/LAND/6 E. Climatic elements 1. Temperature Contents: I. Factors affecting temperature a. Latitude b. Altitude c. Distance from sea d. Ocean current e. Prevailing wind f. Aspect g. Cloud cover h. Maintain barrier i. Nature of surface j. Seasons and length of day II. World distribution of temperature a. Temperature pattern in July b. Temperature pattern n January III. Recording of temperature SLCSS/GEOGRAPHY/CE/LAND/7 1. Temperature Definition: a measure of the degree of hotness or coldness of the atmosphere. I. Factors affecting temperature a. Latitude Under normal conditions, temperature decreases polewards. This is because : 1. The angle of incidence at the poles is smaller. the sun’s rays spread over a larger area 2. the amount of energy received is less concentrated. The sun’s rays have to pass through a longer __________________ through the atmosphere before they reach the poles a lot of insolation is absorbed by the air particles and water vapour in the air the amount of insolation received at the poles is ___________. Lower Latitude Angle of incidence Sun’s rays Amount of energy received Thickness of the atmosphere traveled Energy loss through cloud absorption, reflection and scattering Air temperature Higher Latitude SLCSS/GEOGRAPHY/CE/LAND/8 b. Altitude Altitude refers to the height of the land. Temperature usually decreases with increasing altitude at a rate of 6.4 oC per 1000m. (i.e., the environmental lapse rate) This is because: 1. Air nearer the ground is _______________ and contains (more/less) water vapour and dust particles. heat absorption is quicker temperature is higher. 2. Conversely, air higher up is generally becoming _________and contains less ___________________ and ___________________________, heat absorption is slower temperature is lower. c. Distance from the sea Coastal areas have a ___________ annual range of temperature than inland, i.e. they are cooler in summer and warmer in winter. This is because : 1. 2. Land absorbs heat faster than sea. Land losses heat faster than sea. as the ______________________ of the sea water allows heat to penetrate deep under sea. sea can retain heat for a longer period in winter. Onshore winds bring this moderating effect to coastal areas and this is known as _________________________ influence. Effect of onshore winds is weaken in inland, so inland is under __________________________ influence. SLCSS/GEOGRAPHY/CE/LAND/9 Coastal areas Inland areas Moderation effect of onshore wind / Maritime influence Summer temperature Winter temperature Annual temperature range Climate Examples d. Ocean current Ocean current refers to the movement of surface water in the ocean. Ocean currents are moving along the coast and onshore winds help to bring their effects to coastal areas and finally affect the temperature there. There are two types of ocean currents having opposite effects on temperature of coastal areas : Cold ocean currents Movement Air brought by onshore wind Effect on temperature Warm ocean currents Equatorward Polarward (from high to low latitudes) (from low to high latitudes) SLCSS/GEOGRAPHY/CE/LAND/10 e. Prevailing winds ________________________ winds raise winter temperature and lower summer temperature of land surface ___________ annual range of temperature. ________________________ winds raise summer temperature and lower winter temperature of land surfaces f. ___________ annual range of temperature. Aspect Aspect refers to the direction of a slope faces. Sun-facing slopes receive more insolation than shaded slopes, because : Northern hemisphere Aspect of slopes Southern hemisphere South-facing North-facing South-facing North-facing slopes slopes slopes slopes Sun-facing Shaded Sun-facing Shaded Angle of incidence Insolation Exposure to cold polar winds Air temperature In fact, effect of aspect is obvious in temperate latitudes since in the tropics, the angle of elevation of the sun is always high. SLCSS/GEOGRAPHY/CE/LAND/11 g. Cloud cover Cloud cover can lower temperature range, because: Cloudy sky Clear sky Insolation received Daytime temperature Loss of radiation Nighttime temperature Daily and annual range of temperature Example h. Mountain barrier Mountain ranges will restrict the movement of cold winds and prevent onshore SLCSS/GEOGRAPHY/CE/LAND/12 winds from bring maritime influence to the leeward side of mountains. i. Nature of surfaces nature of surfaces affect temperature and range of temperature by different reasons as shown below: Snow surface Grassland Reflection of insolation Temperature Sandy, rocky surface Grassland, woodland Heat absorption and heat release Daily and annual range of temperature j. Length of daytime and seasons Air temperature increases with increasing length of daytime summer temperature of a place is usually higher than its winter temperature : Overhead sun Length of daytime Air temperature in northern hemisphere Air temperature in southern hemisphere In January In July At Tropic of Capricorn, 23½°S At Tropic of Cancer, 23½°N Increases from 0 hour of Decreases from 24 hours sunlight in N. Pole to 24 of daytime in N. Pole to 0 hours of daytime in S. Pole hour of sunlight in S. Pole SLCSS/GEOGRAPHY/CE/LAND/13 Shade the area with night-time in the two globes of the above figure. II. World distribution of temperature a. Temperature pattern in July Warm current Cold current Characteristics Temperature decreases poleward in the two hemispheres Reasons Effect of latitude The sun is overhead at the northern hemisphere Daytime is longer in the northern hemisphere In the Northern Hemisphere: Temperature is generally higher Isotherms bend northward over continents as they are hotter than the sea Land heats up faster than the sea Less moderating effect from the sea / Weaker maritime influence towards inland Isotherms bend southward along NE Asia and the west coast of North America as these areas are cooler Effect of cold ocean current Greater sea surface reduces the effect of differential heating and cooling of the land and sea Effect of cold ocean current In the Southern Hemisphere: Isotherms have a uniform pattern Isotherms bend northward along west coast of South America and Africa SLCSS/GEOGRAPHY/CE/LAND/14 b. Temperature pattern in January Characteristics Temperature decreases poleward in the two hemispheres Reasons Effect of latitude Sun is overhead at southern hemisphere Shorter daytime in northern hemisphere In the northern hemisphere: Temperature is generally lower Isotherms bend southward over continents as they are colder than the sea Land cools down faster than sea Less moderating effect from sea towards inland Isotherms bend northward along the west coast of Europe as this area is warmer Effect of warm ocean current Effect of warm ocean current Effect of cold ocean current The high altitude of Andes Mountains(thinner air with less vapour and dust particles) In the southern hemisphere: Isotherms bend southward along east coast of South America as this area is warmer Isotherms bend northward along the west coasts of South America and South Africa as these areas are cooler than the sea Temperature is especially low near the west coast of South America SLCSS/GEOGRAPHY/CE/LAND/15 III. Recording of temperature Mean daily temperature Maximum temperatu re - Minimum temperatu re 2 b. Diurnal (daily) range of temperature = maximum temperature – minimum temperature c. Mean monthly temperature a. d. Sum of mean daily mean tempe rature of the month Number of days of the month Annual temperature Sum of mean monthly te mperature for that year 12 e. Mean annual temperature f. It is obtained by averaging the annual temperature of a place for at least 30 years Annual range of temperature = highest mean monthly temperature – lowest mean monthly temperature for a year Temperature map – this can be done by drawing isotherms. Isotherm a line drawn joining all points with the same temp. What is the temperature indicated by the maximum thermometer? ____________________________ What is the temperature indicated by the minimum thermometer? ____________________________ SLCSS/GEOGRAPHY/CE/LAND/16 Brief summery of factors affecting temperature: Raise Lower Raise annual Lower annual temperature temperature temperature range temperature range a. Latitude b. Altitude c. Distance from sea d. Ocean current e. Prevailing wind f. Aspect g. Cloud cover h. Maintain barriers i. Nature of surface j. Length of daytime SLCSS/GEOGRAPHY/CE/LAND/17 Exercise: Study the climatic graph carefully. Try to match them with the cities marked on the map, pay attention to the latitudes, altitudes, distribution of land and sea, pressure and wind. ___________ ____________ ____________ ___________ ____________ ______________ ___________ SLCSS/GEOGRAPHY/CE/LAND/18 2. Air Pressure and Wind Definition : Air pressure is the weight of air exerts on the Earth’s surface. Pressure pattern tells whether the air condition is stable or not. It also controls the general wind direction and strength of wind. I. Factors Affecting Pressure a. Altitude b. Temperature c. Air Movement d. Distribution of Land and Sea II. Planetary Pressure Belts a. Equatorial low b. Subtropical high c. Temperate low d. Polar high III. World Patterns of Air Pressure a. Pressure pattern in July b. Pressure pattern in January IV. Measurement and Recording of Air Pressure V. Factors Affecting Wind a. Temperature and Pressure b. Rotation of the Earth VI. Planetary Wind System VII. Secondary Wind System a. Monsoon b. Anticyclone and Cyclone c. Ridge and Trough VIII. Local Winds IX. World Pattern of Prevailing Winds X. Measurement and Recording of Wind SLCSS/GEOGRAPHY/CE/LAND/19 I. Factors Affecting Air Pressure a. Altitude Air pressure generally _____________________ with increasing altitude because Places at higher altitude support a ________________ weight of air, and The density of air is ____________________ at lower altitude. At sea level, average air pressure is 1,013 hPa, and at about 5,500 metres high, it drops to about half of that at sea level b. Temperature High Temperature Low Temperature Effect on air Air density at ground level Air pressure at ground level Low pressure is formed Air expands and rises Air is heated Air is cooled Air contracts and sinks High pressure is formed SLCSS/GEOGRAPHY/CE/LAND/20 c. Air movement Convergence of air Types of movement Air pressure at ground level Example in the world Divergence of air Two air masses______ Two air masses______ and _______________ and _______________ SLCSS/GEOGRAPHY/CE/LAND/21 II. Planetary Pressure Belts Assuming that the Earth’s surface is an uniform body of water/land, pressure belts develop over different latitudes. Pressure belts shift according to the shift of _______________________________ at different periods of time within a year. Pressure Belts Location Causes Equatorial / Doldrum Low Pressure Belt _____________ temperature convergence of air at ____________ level Subtropical / Horse latitudes High Pressure Belts ____________________ of air at high level and air _______________ Temperate / Subtropical Low Pressure Belts Convergence of air at ____________ level Polar High Pressure Belts and air _________________ ________________ temperature convergence of air at __________ level SLCSS/GEOGRAPHY/CE/LAND/22 Overhead sun shifts to __________ ___________________________ on June 21st . The pressure belts shift _________________________ Overhead sun shifts to ___________________________ __________ on December 22nd. The pressure belts shift _________________________ III. World Patterns of Air Pressure The Earth’s surface is actually not uniform. It is composed of continents, mountains and oceans. The distribution of land and sea will modify the planetary pressure belts. The heating and cooling of land is ___________________ than sea. Therefore, Temperature over continents is ________________ than oceans in summer and then _____________ pressure centres will develop over continents. Temperature over continents is ________________ than oceans in winter and then _____________ pressure centres will develop over continents. SLCSS/GEOGRAPHY/CE/LAND/23 Pressure Patterns in July Overhead sun shifts to Tropic of Cancer Pressure belts shift northward Northern Hemisphere Southern hemisphere Summer in Northern Hemisphere Winter in Southern Hemisphere Doldrum low pressure shifts to north of Subtropical high pressure belt and the Equator and extends northward and temperate low pressure belt are continuous inland over Asia and North America because landmasses are relatively small because continents are hotter in summer Subtropical high pressure belt is broken by large continents Pressure pattern in January Overhead sun shifts to Tropic of Capricorn Pressure belts shift southward Northern Hemisphere Winter in Northern Hemisphere Subtropical high pressure belt is continuous and extends northwards and inland over Asia and North America Because of the intense cooling of land Southern hemisphere Summer in Southern Hemisphere Equatorial low pressure belt shifts to the south of equator and extends over continents because intense heating of land Subtropical high pressure belt is broken by large continents SLCSS/GEOGRAPHY/CE/LAND/24 IV. Measurement and Recording of Air Pressure Air pressure is usually measured with barometer or barograph. The unit to show air pressure is hPa. Air pressure is usually shown with isobars on weather charts. An isobar of 1012 hPa V. Factors Affecting Wind Wind is horizontal movement of air. a. Temperature and Pressure Temperature affects air pressure which in turn affects wind. Air _____________ at low pressure centre and ____________ at high pressure centre. Therefore, on ground surface, air moves from area with ____________ pressure to area with _____________ pressure. Sinking air High pressure Rising air Surface wind Low temperature Low pressure High temperature Ground surface SLCSS/GEOGRAPHY/CE/LAND/25 The spacing of isobars shows the pressure gradient. The steeper the pressure gradient (i.e. the closer the isobars on weather charts), the _________________ the wind speed. b. Rotation of the Earth The Earth rotates from ________________ to ________________ . The rotation of the Earth produces ________________ force. Coriolis force leads to the ___________________ of wind (turning the direction of air movement). According to the Ferrel’s Law, winds are deflected to the ______________ in the Northern Hemisphere and to the _________________ in the Southern Hemisphere. 1012 High 1010 1012 High 1010 1008 1008 Low Northern Hemisphere Low Southern Hemisphere SLCSS/GEOGRAPHY/CE/LAND/26 VI. Planetary Wind System Assuming the Earth’s surface is a uniform body of water / land, pressure gradient force and cause Coriolis the force planetary wind system. Wind Belt Trades Westerlies Origin From Types Characteristics NE trades in the They blow between 30oN northern and 30oS __________ hemisphere They are constant in SE trades in the direction and strength pressure belt southern Trades from the two hemisphere hemispheres converge to to form the intertropical Convergence Zone (ITCZ) __________ When trades blow from one hemisphere to another, the pressure belt direction of deflection changes From South-westerlies in They blow between 30o and the northern 60oN/S __________ hemisphere Westerlies meet polar North-westerlies in easterlies along a polar front pressure belt the southern Owing to great sea surface in hemisphere the southern hemisphere, to westerlies are more constant in strength and direction than __________ in northern hemisphere pressure belt Polar easterlies From North-easterlies in the northern __________ hemisphere South-easterlies in pressure belt the southern hemisphere to __________ pressure belt They blow between 60o and 90oN/S Owing to great sea surface in the southern hemisphere, polar easterlies are more constant in strength and direction than in northern hemisphere SLCSS/GEOGRAPHY/CE/LAND/27 Because of the shift of overhead sun, planetary pressure belts shift ____________________ in June but ________________ in December. With the northward shift of the equatorial low pressure belt in June, SE trades cross the Equator and are deflected as _________________________ . With the southward shift of the equatorial low pressure belt in December, NE trades cross the Equator and are deflected as ___________________________ . VII Secondary Wind System The Earth’s surface is not uniform as it is composed of continents, mountains and ocean. Differential rates of heating and cooling of the land and sea affect pressure patterns. Therefore, planetary wind system is modified by uneven distribution of land and sea. a. Monsoon Wind System The absorption and loss of heat over land is much _______________ than sea. Therefore, temperature over land is _________________ than sea in summer but _________________ than sea in winter. This then causes extensive area of ___________ pressure in summer and __________ pressure in winter over land . Thus wind direction _____________________ . is reversed seasonally, this system is called SLCSS/GEOGRAPHY/CE/LAND/28 In January Overhead sun shifts to the _______________ _______________________________ . It is ______________ in the northern hemisphere. Air over Asian inland cools more ______________ than over the ocean. Cold air over land sinks and an extensive ___________ pressure centre develops over central Asia. Warm air over the ocean rises, so the pressure is ______________ . Australia is in summer, then an intensive ______________ pressure centre develops over central Australia because land is heated up _________________ than sea in summer. Winds blow from the Asian high pressure centre to the ocean and across the equatorial low pressure belt to the low pressure centre of central Australia. Because of deflection, wind direction over North China is ______________________ but becomes _________________ over South China(including Hong Kong) and SE Asia. After crossing the Equator, winds are deflected to the ___________ in the southern hemispere by Coriolis force. Wind direction over northern Australia is ____________________ . Effect on Weather South China(including Hong Kong) Northern Australia Cold offshore wind in NE direction wet Relief rain Unstable weather SLCSS/GEOGRAPHY/CE/LAND/29 In July Overhead sun shifts to the _______________ _______________________________ . It is ______________ in the northern hemisphere. Air over Asian inland heats more ______________ than over the ocean. Hot air over land rises and an extensive ___________ pressure centre develops over central Asia. Cool air over the ocean sinks, so the pressure is ______________ . Australia is in winter, then an intensive ______________ pressure centre develops over central Australia because land is cooled down _________________ than sea in winter. Winds blow from the Australia high pressure centre to the ocean and across the equatorial low pressure belt to the low pressure centre of central Asia. Because of deflection, wind direction over northern Australia is ____________________ . After crossing the Equator, winds are deflected to the ___________ in the northern hemisphere by Coriolis force. Therefore wind direction over SE Asia is _____________________ . Wind direction over South China(including Hong Kong) is ____________________ . Effect on Weather South China(including Hong Kong) Northern Australia Cold offshore wind in NE direction Dry Very little rain Fine weather SLCSS/GEOGRAPHY/CE/LAND/30 b. Anticyclone and Cyclone Anticyclone Cyclone Shape Pressure Centre Movement of air In the northern hemisphere Wind In the southern hemisphere Origin Associated weather Other characteristics Northern Hemisphere Slow movement Long lasting Large in extent calm condition in centre close isobars at the edge and the resulting wind is strong 1022 fast-moving short-lived small in extent close isobars near the centre and the resulting wind of a tropical cyclone is strong Northern Hemisphere 1004 1024 1026 1002 1028 998 1000 Southern Hemisphere 1022 Southern Hemisphere 1004 1024 1002 1026 1028 998 1000 Use arrows to show the wind directions in the above cyclones and anticyclones SLCSS/GEOGRAPHY/CE/LAND/31 c. Ridge and Trough 1004 1006 1024 1022 1020 1002 1018 Ridge of High Pressure 1004 1006 1008 Trough of Low Pressure Pressure system Air movement Wind direction Associated weather VIII. Local Winds a. Land and Sea breezes Land and sea breezes are resulted from differential heating of land and sea during day and night. Day pressure temperature Land pressure temperature Sea SLCSS/GEOGRAPHY/CE/LAND/32 Night pressure temperature pressure temperature Sea Land b. Mountain and Valley Winds IX. World Pattern of Prevailing Winds Prevailing winds are winds which blow most frequently at a place. In the northern hemisphere, prevailing winds are greatly affected by _________________ system because there are large continents and ocean. In the southern hemisphere, prevailing wind almost follow ________________________ system because relatively small difference between land and sea. SLCSS/GEOGRAPHY/CE/LAND/33 X. Measurement and Recording of Wind Wind Direction Wind Speed Instrument Symbol / diagram Prevailing wind : _____________ Wind direction : _________ No. of days with calm condition : ________ Wind speed : ____________ SLCSS/GEOGRAPHY/CE/LAND/34 4. Relative humidity Contents: I. Interpretation of humidity II. Interpretation of condensation III. Forms of condensation a. Dew and frost b. Mist and fog Advection fog Radiation fog c. Cloud IV. Recording of relative humidity I. Interpretation of humidity Humidity = the amount of water vapour in the air Relative Humidity (R.H.) = percentage expression of the actual amount of water vapour the air is holding as compared with the maximum amount of water vapour it can hold. Relative humidity 100% where, Absolute Humidity = actual amount of water vapour that the air is holding Water Holding Capacity = the maximum amount of water vapour it can hold it depends on its temperature the higher the temperature, the greater the capacity i.e. warm air can hold more water vapour than cool air Therefore, decrease in temperature will decrease its water holding capacity, and thus increase its R.H, given its absolute humidity unchanged. II. Interpretation of condensation When absolute humidity = water holding capacity → R.H. = 100% → air is _______________________ _____________________ = the process by which water vapour (gaseous state) changes into water droplets (liquid state). ______________________= the temperature at which air becomes saturated and condensation occurs. SLCSS/GEOGRAPHY/CE/LAND/35 Conditions for condensation a. b. c. III. Cooling of air to the dew point Relative humidity = 100% Presence of condensation nuclei Therefore, relative humidity is a good indicator of the possibility of rainfall, as it shows how far condensation will occur. Forms of condensation There are several forms of condensation and usually occur at different levels of atmosphere: Forms of condensation Levels in atmosphere Dew and frost Mist and fog Clouds a. Dew and frost Descriptions: small water droplets (dew) or ice crystals (frost) form on cool surfaces, e.g. leaves or ground surface. Conditions favouring their formation: 1. At night or early ___________________ (Reason: low temperature) 2. __________ sky (Reason: allow rapid radiation rapid decrease in temperature) 3. Calm condition (Reason: prohibit water droplets, which are form by condensation, being evaporated by wind) Formation: Rapid loss of _______________ through radiation Temperature of rock and plant surface become low The air above the cool surface is ___________________ . Water holding capacity decrease Relative humidity increase to 100% at dew point Condensation occurs If dew point is _____________ 0 °C, water vapour condenses into small water droplets on cool surfaces, dew is formed. If dew point is _____________0 °C, water vapour condenses into ice crystals on cool surfaces, frost is formed. Dew or ice crystals disappear through evaporation shortly after sunrise SLCSS/GEOGRAPHY/CE/LAND/36 Impact on human: Dew may provide crops with moisture in farmland (positive impact) Frost may cause damage/loss to crops (negative impact) b. Mist and fog Descriptions: small condensed water droplets around dust in the air near ground surface. There are two kinds of fog: radiation and advection fog i) Radiation fog Conditions favouring its formation: 1. At night or early morning 2. Clear sky 3. Cooling of air 4. Calm conditions 5. In valley (Reason: restrict air movement) Formation: After sunset, rapid earth radiation and _______________ of ground occurs lower layer of warm air near the cool ground surface is cooled to the _________ point condensation occurs and ____________________ fog is formed. Clear sky Rapid radiation Fog Air is cooled To condense C Cool ground surface SLCSS/GEOGRAPHY/CE/LAND/37 ii) advection fog Formation: When warm moist air passes horizontally over a _____________ sea or land surface the lower layer of the warm air in contact with the cold surface is cooled to ________________ point. condensation occurs and ___________________fog is formed. Advection fog in Hong Kong: Commonly found in ____________________ During spring, the sea water is still _________________ when warm moist ___________________ wind from south Pacific Ocean moves horizontally over the sea surfaces warm and moist air contacts with _______________ sea and land surface ______________________ occurs and advection fog is formed. fog Warm moist southerlies Cold surface sea Impact on human: They may cause poor visibility, which means the distance that a person can see an object. Poor visibility hinders air and water transport. it may also cause traffic accidents on roads. In polluted industrial areas, smog may be formed and it may be hazardous to SLCSS/GEOGRAPHY/CE/LAND/38 health. They may provide crops with moisture in farmland. c. Clouds Descriptions: it consists of small water droplets or ice crystals floating in the atmosphere. Formation: Clouds are formed when the air is cooled to the dew point at a certain high level— condensation level.. Cooling of air to dew point at high level is either the result of: 1. 2. 3. 4. earth radiation strong conventional movement of air warm air is forced to rise by cold air air rises along slope of mountain The height of condensation level depends on the temperature and humidity of the moving air, i.e. this level will be lower if the air is _____________________and _______________________. Types of cloud SLCSS/GEOGRAPHY/CE/LAND/39 IV. Measurement and Recording of Relative Humidity If on day X, the dry bulb thermometer shows 22°C and the wet bulb thermometer shows 19°C, what is the relative humidity of day X? ___________________________ If on day Y, the dry bulb thermometer shows 25°C and the wet bulb thermometer shows 19°C, what is the relative humidity of day Y? ___________________________ If on day Z, the dry bulb thermometer shows 20°C and the wet bulb thermometer shows 20°C, what is the relative humidity of day X? ___________________________ , the dry bulb thermometer shows 22°C and the wet bulb thermometer shows 19°C, what is the SLCSS/GEOGRAPHY/CE/LAND/40 relative humidity of day X? 5. Precipitation Contents: I. Interpretation of precipitation II. Forms of precipitation a. Rain Types i) Relief rain (Orographic rain) ii) Convectional rain iii) Cyclonic rain (Frontal rain) 2. Factors affecting world distribution of rainfall 3. Measurement and recording of rainfall 4. Hazards brought by rainstorm b. Snow 1. c. Hailstone 1. Precipitation I. Interpretation of precipitation Formation: When rising air cooled below the dew point temperature, _______________________takes place at that level which is called condensation level. The water vapour in air condenses around dust or tiny particles which act as _______________________________________. Tiny water droplets or ice crystals gather to form _____________________. When clouds become too heavy to remain suspended, they fall as ________________________________. II. Forms of precipitation a. Rain 1. Types of rain SLCSS/GEOGRAPHY/CE/LAND/41 i) Relief Rain (Orographic Rain) Places of Occurrence: Commonly occurs when prevailing _______________ wind is blocked by a _________________________barrier which runs parallel to the coast Formation: When wet, onshore wind meets coastal mountains, it is forced to ________________ along the windward slope. When air rises, it expands and the temperature _____________ . Relative humidity __________________ as temperature drops. If the air is cooled below ____________________________ (i.e. above condensation level), water vapour condenses into water droplets. Clouds form. When water droplets in clouds grow too heavy to be suspended, _____________ begins to fall on windward slope. The air loses much moisture when it reaches the mountain top. When the air sinks along the leeward slope, it is warmed by compression. Since warm air has a greater water holding capacity, its relative humidity drops and becomes dry. The leeward slope is called a _________________________ region because of little rainfall. Warm and wet Onshore wind Cloud is formed Condensation takes place Air is saturated Relative humidity rises Temperature decreases Air expands Air rises along slope Mountain Sea ii) Convectional Rain Rain shadow SLCSS/GEOGRAPHY/CE/LAND/42 Places of Occurrence: 1. Hot and wet areas, e.g. ____________________________________ 2. Tropical deserts and inland in hot summer 3. During afternoon because of intense insolation from the sun Formation: When ground surface is intensely __________________ up Hot air then ________________ and ________________ up as strong convection currents. When air rises, air temperature ___________________ . Then, _________________________ increases. When air is cooled to dew point, water vapour condenses into ___________________________. Since the air rises as strong currents, water droplets are forced to rise and _______________________ cloud is formed. Convectional rain occurs when the rising air currents cannot support the dense water droplets or ice crystals of the cloud. Uprising air current Air is saturated and condensation starts Relative humidity _______________ air ____________ and ___________ Heated air rises Land is intensively ____________ up Characteristics: 1. ______________________ duration 2. usually occurs in ______________________________ SLCSS/GEOGRAPHY/CE/LAND/43 3. Heavy downpours 4. Often associated with thunderstorms, tropical cyclones or trough of low pressure. iii) Cyclonic Rain (Frontal Rain) Place of Occurrence: Often occurs along fronts(cold front and warm front) of temperate cyclones. In winter, it may affect lower latitudes, e.g. winter and early spring in Hong Kong. Formation: Cyclonic rain is caused by Temperate Cyclone. In fact, there are two kinds of fronts along the two sides of the cyclone, they are ________________ front and ___________ front. In both cases, denser and heavier cold air remains near the ground Lighter _________________air is forced to rise along the front When warm air rises, the temperaure ______________ Then relative humidity ____________________ . Warm air is cooled and condensed into water droplets Then cloud is formed and cyclonic rain occurs Warm, wet Air masss Cloud is formed Condensation takes place Reaching dew point temperature Relative humidity increases Air temperature decreases Air expands Warm air is force to Cold, dry Air mass rise Ground Characteristics: In fact, the rain characteristics that occur along warm and cold fronts are SLCSS/GEOGRAPHY/CE/LAND/44 different : Warm front Cold front Duration Intensity Kind of rain 2. Factors affecting world distribution of rainfall Factors Facilitate rainfall Prohibit rainfall Pressure belts 1. Equatorial low pressure 1. belt intensive heating strong uprising current heavy convectional rain 2. Temperature low pressure belts meeting of polar cold air mass and tropical Subtropical high pressure belts sinking air air is warmed by compression R.H. drops 2. Polar high pressure belts sinking air dry air warm air mass temperate cyclones cyclonic rain Wind Existence of mountain barriers ____________ wet wind Windward slope __________________ ____________ dry wind Leeward slope _____________________ Distance from Coastal area onshore wet Inland onshore wet wind wind reaches maritime cannot reach continental sea influence influence SLCSS/GEOGRAPHY/CE/LAND/45 3. Measurement and recording rainfall - A _____________________ is used to collect daily rainwater. Amount of daily rainfall is measured by measuring cylinder. The amount of rainfall is measured in mm. SLCSS/GEOGRAPHY/CE/LAND/46 4. Hazards brought by rainstorm 1. 2. 3. 4. 5. 6. 7. Serious road flooding Traffic congestion Landslide or rockfall Flooding on farmland Damage of crops and livestock, e.g. pigs and fish in pond Damage of man’s life and property, e.g. houses Temporary closure of schools, shops and offices b. Snow - It is a solid form of precipitation Water vapour condenses at a temperature below freezing point and becomes ice crystals directly When ice crystals become too heavy to remain suspended in the air, they fall to the ground as snow c. Hailstone - This falls from cumulonimbus during a thunderstorm. - It is caused by rapid ascent of warm and wet air currents, which carry the condensed water droplets upwards. These water droplets freeze at great heights and forms ice crystals. When the ice crystals fall, more water condenses around them, causing an increase in size. These crystals are again thrust upward by rising air currents and then a new layer of ice is formed around them. These processes continue until the hailstones have acquired sufficient weight to overweigh the ascending currents, then they fall to the ground when they have not melted and are known as hailstones. - SLCSS/GEOGRAPHY/CE/LAND/47 F. Climatic Region of the World SLCSS/GEOGRAPHY/CE/LAND/48 _________________ _____________________ ___________ _____________________ ___________ __________________ ____________ ________________________ _______________________ G. Climate of Hong Kong J Mean Air pressure (hPa) F M A M J J A S O N D 1020.2 1018.7 1016.2 1013.1 1009.1 1006.0 1005.3 1005.1 1008.8 1014.0 1017.9 1020.2 Mean daily maximum 18.6 18.6 21.3 24.9 28.7 30.3 31.5 31.3 30.3 27.9 24.2 20.5 13.6 13.9 16.5 20.2 23.9 25.9 26.6 26.3 25.5 23.1 19.2 15.4 15.8 15.9 18.5 22.2 25.9 27.8 28.8 28.4 27.6 25.2 21.4 17.6 5.5 5.1 5.0 5.0 5.0 4.8 5.3 5.3 5.3 5.2 5.5 5.6 71 78 81 83 83 82 80 81 78 73 69 68 58 73 76 78 74 75 65 66 63 56 53 49 Total rainfall (mm) 23.4 48.0 66.9 161.5 316.7 376.0 323.5 391.4 299.7 144.8 35.1 27.3 Sunshine (hr) 152.4 97.7 96.4 108.9 153.8 161.1 231.1 207.0 181.7 195.0 181.5 181.5 Prevailing wind direction ENE ENE ENE ENE E E WSW E E E ENE ENE Mean wind speed (km/hr) 24.0 23.8 22.1 19.7 19.2 21.6 20.0 18.5 21.9 27.6 27.2 25.5 temperature (oC) Mean daily minimum temperature (oC) Mean daily temperature (oC) Mean daily temperature range (oC) Mean reative humidity (%) Cloud cover (%) ( SLCSS/GEOGRAPHY/CE/LAND/49 )( ) ( Spring ) Summer ( )( ) Autumn Winter Months _____________ to ________ to mid Mid- __________ _____________ to _____________ Temperature ______________ to early ________ ______________ begin to _____________ begin to _____________ Air Pressure _____________ ______________ low pressure _______ pressure ______ pressure system over ________ system over central Asia pressure system begins to over central Asia system over central Asia begin central Asia to ___________ . _________ of low ___________ weak _________ pressure front ___________ and front ________ cyclone _________ of ______ pressure high pressure begins to develop begin to develop Wind warm and moist _________ and intense ________ onshore wind cold and dry __________ and offshore wind SLCSS/GEOGRAPHY/CE/LAND/50 _______ southerly from _________ ________ easterly from _________ wind wind Relative humidity _________ R.H. ____________ begins to generally _________ ________ ___________ fog Cloud cover generally _________ sky generally alternately ______ __________ sky _________ sky and _______ sky Condensation and precipitation ___________ and ________ rainfall _________ and generally ______ _____________ with occasionally _____________ _______ rainfall brought by trough _________ rain and tropical cyclone General weather alternate periods generally unstable begin to become generally stable conditions of cool, dry hot and wet cool and dry weather and warm wet weather begin to become unstable more stable cool and dry SLCSS/GEOGRAPHY/CE/LAND/51 H. Interpretation of Hong Kong Weather Chart SLCSS/GEOGRAPHY/CE/LAND/52 (1) Describe the weather conditions of Hong Kong on that day. The temperature on that day was ______________. The air pressure was ______________. Wind direction on that day was ___________ . Wind speed was _______________ . _________________________________________________________________________ (2) Name the pressure system over central China. ________________________________________________________________________ (3) Explain how this pressure is formed. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ (4) Account for the difference in wind speed between South China and Central China. _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ SLCSS/GEOGRAPHY/CE/LAND/53 (1) Describe the changes in weather condition in Hong Kong between 29 Jan and 30 Jan. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (2) Name the type of rain which can be found in South China on the two days. ________________________________________________________________________ (3) Describe the weather conditions of Hong Kong on 31 Jan. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _______________________________________________________________________ SLCSS/GEOGRAPHY/CE/LAND/54 (1) Describe the weather conditions of Hong Kong on that day. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (2) Account for the fine weather over South China. _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (1) Describe the weather conditions of Hong Kong on that day. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (2) Account for the unstable weather over South China. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (3) Which season does this weather chart show? ________________________________________________________________________ SLCSS/GEOGRAPHY/CE/LAND/55 (1) Name the pressure system over South China Sea. _______________________________________________________________________ (2) Which season is this pressure system usually found over South China? ________________________________________________________________________ (3) Describe the weather conditions of Hong Kong one day ago. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _______________________________________________________________________ (4) Describe the changes in weather condition in Hong Kong on the coming day. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ (5) Draw an annotated cross section of the pressure system. SLCSS/GEOG/Weather & Climate/56 Before Tropical cyclone Front vortex Eye Rear Vortex Air pressure Wind speed Wind direction Rainfall intensity Cloud amount Vortex Eye Vortex Tropical cyclone Left SLCSS/GEOG/Weather & Climate/57 (1) Which season does this weather chart represent? _______________________________________________________________________ (2) Describe the weather conditions of Hong Kong on that day. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________ (3) Explain the formation of the type of condensation found in Hong Kong on that day. _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ _________________________________________________________________________ ________________________________________________________________________
