Weather and climate

Changes in climate

- Global records since 1880 show a significant, but irregular upward trend in temperature with fluctuations of 0.3°C to 0.6°C - Global warming over the last century: world is warming on average by 0.74°C, with most of the increase since the 1970s - Global temperatures in the last decade reached the highest levels on record

Elements of weather

- Temperature - Air humidity, clouds and rainfall - Pressure and winds

Explain the formation of convectional rain and relief rain.

Convectional rain- When the earth's surface is heated by conduction, moisture-laden vapour rises because heated air always expands and becomes lighter. Air rises in a convection current after a prolonged period of intense heating. In ascending, its water vapour condenses into cumulonimbus clouds with a great vertical extent. This probably reaches its maximum in the afternoon when the convectional system is well developed. Hot, rising air has a great capacity for holding moisture, which is abundant in regions of high relative humidity. As the air rises, it cools and when saturation point is reached, torrential downpours occur, often accompanied by thunder and lightning. Relief (orographic) rain is formed whenever moist air is forced to ascend a mountain barrier. It is best developed on the windward slopes of mountains where the prevailing moisture laden winds come from the sea. The air is compelled to rise and is thereby cooled by expansion in the higher altitudes and the subsequent decrease in atmospheric pressure. Further ascent cools the air until the air is completely saturated. Condensation takes place forming clouds and eventually rain. On descending the leeward slope, a decrease in altitudes increases both the pressure and the temperature; the air is compressed and warmed. Consequently, the relative humidity will drop. There is high evaporation and little or no precipitation.

Describe and explain the distribution and characteristics of equatorial, monsoon and cool temperate climates.

Equatorial climate Distribution: Between 10°N and 10°N of the equator e.g. Singapore, Johor in Malaysia Characteristics: High mean temperature of about 27°C throughout the year because of the high angle of incidence of the sun's rays concentrating at the Equator. The temperature range is small, about 2 to 3°C. High relative humidity of over 80% experienced throughout the year. Due to the high temperatures, water evaporates quickly into the air, forming clouds and convectional rain. Total annual rainfall is high at more than 2000mm throughout with no dry month. Tropical Monsoon climate Location: Between 5°N and 25°N and S of the equator e.g. Mumbai, India Characteristics: High temperatures around 29°C in the hot season due to the midday sun being overhead at the Tropic of Cancer in June. Mean temperatures are lower in the cool season ranging from 20°C. to 24°C in Dec and Jan, the coolest months. The annual range of temperature is larger than that of the equatorial, ranging from 5°C to 17°C. The rainfall is mainly affected by the monsoon winds which cause a distinct wet and dry season. The onshore monsoon brings the rainy season while the offshore monsoon causes the dry season. In India the offshore NE monsoon does not bring rain except areas close to the Bay of Bengal and therefore it is relatively dry towards the end and beginning of the year. The SW monsoon brings heavy rain to the coastal areas as the wind is laden with moisture it had picked up when crossing the Indian Ocean. Cool Temperate Location: Between 45°N and 60°N and S of the equator e.g. Paris in France, Moscow in Russia Characteristics: Four distinct seasons of spring, summer, autumn and winter due to the tilt of the earth and its revolution around the sun. During winter, these places have a shorter day and less energy from the sun, This results in a large temperature range with winter temperature below 0°C. Total annual rainfall is lower between 300mm and 900mm. There are no distinct wet or dry seasons.

Explain the greenhouse effect.

Greenhouse gases (CO2, water vapour, nitrous oxide, methane, ozone and halocarbons) trap heat in the atmosphere resulting in a greenhouse effect. Incoming shortwave radiation from the sun passes through the greenhouse gases in the atmosphere. Most of the shortwave radiation is absorbed by the earth's surface which heats up as a result. The warmed surface of the earth emits longwave radiation to the atmosphere. Greenhouse gases absorb longwave radiation and warm the atmosphere. Enhanced greenhouse effect is a rise in global temperatures due to the increase in the concentration of the greenhouse gases.

Explain how coastal temperatures are moderated by land and sea breezes.

In coastal regions, the land is heated up faster than the sea during the day and the hot air rises resulting in lower pressure over the land than the sea. The air pressure over the sea is higher and thus the air moves towards the land as sea breeze. At night, the land cools faster and thus the air pressure over the land is higher than the sea. The air moves towards the sea as land breeze. Sea breezes usually blow at about mid-afternoon when the temperature difference between the land and the sea is the greatest. This lowers the relatively warmer temperature of the land. Land breezes, on the other hand, cool the warm air over the sea at night. Thus land and sea breezes help to regulate the temperatures of the land and the sea, keeping it at a moderately constant level.

Compare and explain the variations in temperature between different locations.(Factors influencing the temperature of locations)

Latitude - Temperature generally decreases with increasing latitude. Places in low latitudes have higher temperatures because they receive vertical sunrays and hence more concentrated insolation. Temperatures are higher as the vertical sunrays travel through shorter distance of the atmosphere and smaller amount of insolation is lost through reflection and scattering. Altitude - The atmosphere is mainly heated by long wave radiation (heat energy) from the earth's surface (land or sea surfaces). Thus, the higher the altitude, the cooler the air temperature. With increasing altitude or elevation, air becomes less dense and contains less dust and water vapour. . Heat from the earth's surface thus escapes more rapidly, thereby lowering the air temperature. In general, air temperature decreases with increasing altitude at a rate of about 0.6°C to 0.65°C per 100 metres (or 6°C to 6.5°C per 1000 m) in a free atmosphere. This change of temperature gradient is called the normal lapse rate (or vertical lapse rate). Distance from the sea- Land heats up and cools faster than water or the sea. Maritime effect - onshore winds blowing from the sea or ocean to coastal regions tend to lower summer temperatures and raise winter temperatures. Such moderating influence is called maritime influence and is confined to coastal areas. Thus, coastal regions have a cooler summer and a warmer /milder winter than inland regions. The annual range of temperature in coastal regions is therefore smaller than that in inland regions. This is particularly felt in temperate regions. Continental effect - Inland regions situated at a great distance from the sea have hotter summers and colder winters than coastal regions. The annual range of temperature in inland regions is greater, and the climate is thus more extreme than that of coastal areas Cloud cover - Blanket effect of cloud produces small diurnal and annual ranges of temperature. Clouds reduce the amount of solar radiation that reaches the earth's surface and re-radiation that leaves the earth's surface. The dense cloud cover in equatorial / tropical regions reduces intense solar heating of the land in the daytime. At night thick clouds prevent rapid loss of long wave radiation (heat energy) from the earth's surface. . The result is that daytime temperatures in tropical equatorial regions do not rise too high (rarely exceeding 33°C) even though the angle of the mid-day sun is high. On the other hand, night temperatures in these regions do not fall too much. The diurnal range and annual range of temperature are therefore small. e.g. Singapore and other equatorial regions. Absence of cloud cover leads to great diurnal range of temperature. The cloud cover in deserts tends to allow maximum solar heating of the land in the daytime. Thus daytime temperatures rise high (often exceeding 38°C). At night there is little cloud cover in desert regions. There is rapid and maximum loss of heat energy by radiation from the heated land surface, and temperatures fall to 21°C or below 0°C. This produces a great diurnal temperature range in desert regions. e.g. Sahara Desert

Explain the use of the following weather instruments:

Maximum and minimum thermometer to measure the maximum and minimum temperatures When temperature rises, the mercury expands, pushing the metal index along the tube. When temperature falls, the alcohol contracts and pulls the metal index along the tube. For the Six's thermometer (U-shape maximum and minimum thermometer), the temperatures are obtained by reading the values indicated at the bottom of the metal index (indicators). Rainfall Gauge to measure the rainfall It consists of a funnel that collects and channels rainwater into a container. The rainwater that is collected is emptied after every 24 hours into a measuring cylinder. It should be placed in an open area where there are no obstructions to block the rain and also avoid concrete surfaces as splashing may occur leading to an inaccurate reading. Hygrometer / psychrometer to measure relative humidity Read and record the temperature on the dry bulb thermometer. Refer to the relative humidity chart. Read the temperature of the dry bulb thermometer on the left column. The depression of the wet bulb is the difference between the wet bulb thermometer and the dry bulb temperature. Find the value at which the dry bulb temperature intersects with the depression of the wet bulb. Wind vane and wind sock to measure wind direction Wind direction refers to the direction that the wind is blowing from. It is shown by a freely moving pointer on a wind vane. The wind vane is usually placed on a high, open place with little or no obstruction to the flow of wind. The direction the wind vane is pointing to is the direction where the wind is blowing from. A windsock is a kite made from a tube of cloth. One end of the tube is held open by a ring. Windsocks point in the direction opposite of the wind's direction of origin. For example, if a windsock is pointing west, the wind is coming from the east. The faster the wind blows the straighter and more horizontally the wind extends. A 15-knot (28 km/h; 17 mph) wind will fully extend the properly functioning windsock. A 3-knot (5.6 km/h; 3.5 mph) breeze will cause the windsock to orient itself according to the wind. Anemometer / pocket weather tracker to measure wind speed An anemometer is used to measure wind speed and direction. It includes 3 to 4 cups mounted on a vertical pole. The cups catch the blowing wind and turn the pole. Each time the anemometer makes a full rotation, the wind speed is measured by the number of revolutions per minute (RPM). The number of revolutions is recorded over time and an average is determined. Wind rose to record wind A wind rose records the number of days with and without wind, as well as wind direction. The number in the centre records the number of calm days in the month. The rectangles point in the direction the wind is blowing from and the numbers represent the dates in a month in which the wind blew from a particular direction. Barometer to measure air pressure A barometer has two hands. The hand on the inside is called the measuring hand. The hand on the outside directly over the measuring hand is called the movable pointer.The moveable pointer is arranged over the measuring hand to mark the current pressure. The measuring hand will move according to the air pressure. Take the reading to see whether the hand moves to right which is rising or to the left which is falling. The dial expresses mercury in measurements in millibars (Mb).

Calculate the following

Mean daily temperature - sum of hourly temperatures divided by 24 hours Diurnal temperature range -maximum temperature minus minimum temperature Mean monthly temperature - sum of mean daily temperatures in the month divided by number of days in the month Mean annual temperature - sum of mean monthly temperatures in the year divided by 1 Annual temperature range - maximum temperature minus minimum temperature recorded in a year Daily rainfall - the amount of rain that falls over 24 hours Monthly rainfall - total amount of rainwater collected throughout the month Annual rainfall - total amount of rainwater collected throughout the year.

Explain the formation of monsoon winds.

Monsoon winds are regional wind patterns that reverse direction seasonally due to the Coriolis effect produced by the rotation of the earth. The Coriolis effect cause the wind to be deflected. In the northern hemisphere, the wind is deflected to the right and to the left in the southern hemisphere. Between June and September, the northern hemisphere experience summer and the air over Central Asia heats up, expands and rises, forming a region of low pressure over the area. The southern hemisphere experience winter and the low temperature causes the air to be cold and dense, resulting an area of high pressure over Australia. Air from Australia moves towards Central Asia as the southeast monsoon due to the difference in pressure between Central Asia and Australia, As the wind cross the Equator, the Coriolis effect deflects the wind to the right and it become the southwest monsoon. Between October and February, the southern hemisphere experience summer and an area of low pressure forms over Australia. The northern hemisphere experience winter and the low temperature causes the air to be cold and dense, resulting an area of high pressure over Central Asia. Air from Central Asia moves towards Australia due to the difference in pressure between Central Asia and Australia. The Coriolis effects deflect the wind to the right in the northern hemisphere as the northeast monsoon. As the wind crosses the equator, the Coriolis Effect deflects the wind to the left and it becomes the northwest monsoon in the southern atmosphere. https://sites.google.com/a/moe.edu.sg/sec3geog/ weather-and-climate/wc-k1-lesson-6 for images

Explain the impact of climate change such as sea level rise, extreme weather events and human health.

Sea level rise - threatens low lying areas and islands, increases risk of damage to homes and buildings from storm surges that accompany tropical cyclones. More frequent extreme weather events e.g. heat waves, flood, drought and tropical cyclones. Increased land and sea surface temperatures resulted in greater amounts of water vapour and latent heat in a warmer atmosphere causing more extreme weather events. Spread of some infectious insect-borne diseases e.g. heavy rainfall allows mosquitoes to grow resulting in spread of malaria and dengue fever. Higher temperatures may lengthen the growing season in certain regions e.g. fruit production in Eastern Canada, vineyards in Europe. Increase in the types of crops such as blackberries and maize that can be grown in UK. However in China, production of fruits such as apples and cherries or nuts such as almonds and walnuts is reduced as these fruits and nuts require cool weather temperature. Similarly in Canada, the production of wheat is reduced

Describe and explain the weather and climate of Singapore with reference to rainfall, relative humidity and temperature.

Singapore experiences the hot, wet equatorial climate. Mean annual temperature is high at about 27.5°C. Surrounded by water and accompanied by the high temperatures, especially at mid-day, leads to a high evaporation rate. The air is humid or saturated with water vapour by late afternoon. The dry- bulb reading will fall with temperatures towards night, closing the gap between the readings on the two thermometers. Since the wet bulb depression becomes very low, relative humidity is very high at around 84.2%. Total annual rainfall is high at about 2, 200mm. Most of the rain in Singapore comes from convectional rain. However the northeast monsoon does bring more rain to Singapore from Oct to Feb amounting to about 1,125mm as it crosses the South-china sea and picks up more moisture.

Explain the differences in relative humidity in different locations.

The amount of water vapour in the air affects relative humidity. For example, if the air at 15°C holds 5g/m³ of water vapour and can contain a maximum of 10 g/m³of water vapour, relative humidity will be 50%. If the actual amount of water vapour held by the air increases to 6 g/m³, relative humidity will be 60% instead. Relative humidity also varies with temperature. Warm air can hold more water vapour than cool air. When temperature increases, the amount of water vapour in the air stays the same, but the rise in temperature makes air more able to hold water vapour. Thus relative humidity decreases as temperature increases.

Differentiate between weather and climate.

Weather is the condition of the atmosphere at a particular place and time whereas climate is the average condition of the atmosphere of a specific place over a long period of time, usually over 30 years.

Discuss the natural causes of recent climate change.

What are some natural causes of climate change? Variations in solar output An increase in magnetic activity results in an increase in solar radiation. The magnetic activity of the sun has a cycle that lasts about 11 years. An increase in solar radiation is due to an increase in sunspots. Areas surrounding the sunspots radiate more energy to make up for the cooler sunspot areas. With higher solar radiation, earth's temperatures will increase. There was a peak in the number of sunspots in 2000 coincided with high solar activity and global temperatures increased during this period. Volcanic eruptions When a volcano erupts, large volumes of carbon dioxide, water vapour, sulphur dioxide, dust and ash are released into the atmosphere. Sulphur dioxide reacts with water to form sulphur-based particles in the atmosphere. Together with dust and ash, these particles reflect solar energy back into the space, resulting in global dimming. Global dimming is the gradual reduction in the amount of sunlight reaching the earth's surface. Temporarily cools the earth for months or years. For example, Mount Pinatubo in the Philippines erupted in 1991, released 17 million tonnes of sulphur dioxide into the atmosphere. This lowered temperatures in the northern hemisphere by as much as 0.6°C for as long as two years. Temporary global cooling effect will cease once the volcanic dust and ash settle.

Explain how human activities (Anthropogenic factors) such as deforestation, burning of fossil fuels, rice cultivation and cattle farming increase greenhouse gases and lead to enhanced greenhouse effect.

• Deforestation alters atmospheric composition e.g. carbon dioxide and nitrous oxide, and affecting hydrological cycle - Forest absorbs CO² via photosynthesis. Deforestation lead to increase in CO² level in the atmosphere. - Carbon oxidation is a process by which carbon in the soil reacts with oxygen in the atmosphere to produce CO². Deforestation exposes soil to sunlight and increase soil temperature and rate of carbon oxidation which release more CO² into the atmosphere. • Changing land use - Agriculture •Rice cultivation - tractors running on fossil fuels release CO². Use of chemical fertilisers increases the amount of nitrous oxide in soil which is then released when soil is ploughed or when rain flows through the soil. Methane is released when dead leaves and manure decompose rapidly in the rice field due to high level of moisture in the soil •Cattle ranching - cattle releases methane as a waste gas - Industries - burning of fossil fuel to produce energy release CO² as well as manufacturing of goods release CO² as by-product. - Urbanisation - burning of fossil fuels to produce energy for household activities in urban areas such as heating, cooling, cooking and lighting. More cars, buses and other transportation also increase greenhouse gas emissions. Constructing infrastructure and producing construction materials also release greenhouse gases.

Explain the daily and seasonal variations in temperature at a particular location.

•Temperature varies throughout the day in a place. The temperature rises and falls as the Earth rotates from west to east. The location facing the sun experience day and the location which is away from the sun experience night. Temperature rises during the day and falls at night. •Temperature generally increases with the length of the day. Places along the equator have equal lengths of day and night all the year. Beyond the equator, places have longer days and hence higher temperatures in summer, and shorter days and lower temperatures in winter. Temperatures are higher from June to August in the Northern Hemisphere due to the position of the sun in relation to the Earth's axis which is tilted at an angle of 23½° from the vertical. From June to August because of the position of the overhead sun, there is a higher intensity of the sun rays in the northern hemisphere. Thus the temperatures are higher during this period.

Factors influencing the temperature of locations

○ Latitude ○ Altitude ○ Distance from the sea ○ Cloud cover