Weather Gateway 1 Flashcards
What is weather
Specific condition of the atmosphere at a particular place and a specified time
What is climate
The average condition of the atmosphere of a region over a long period of time, usually 30 years.
Factors influencing the temperature at a location: Latitude
-The sun’s rays strike the Earth’s curved surface at different angles
-This results in an unequal distribution of solar energy over the earth
-Places near the equator receive more direct sunlight and hence higher temperatures
-Places nearer the poles, the solar energy is spread over a larger area and hence lower temperatures
-Therefore, there is a drop in mean annual temperature as latitude increases
Factors influencing the temperature at a location: Altitude
-Temperature drops an average of 6.5 degrees celsius for every 1000m gained in altitude
-The earth’s surface is heated by the sun and transfers heat to the air
-The greater the number of air molecules present, the greater the amount of heat transferred.
-This is due to the greater concentrations of greenhouse gases which absorbs heat radiated from the earth’s surface
-There are more air molecules closer to sea level than at the top of a mountain
-As altitude increases, the amount of air molecules decreases and therefore the transfer of heat is less effective.
-Thus, temperature decreases as altitude increases
Factors influencing the temperature at a location: Distance from sea
-Temperate areas by the coast experience lower annual temperature ranges than places inland.
-The sea heats up and cools down slower than the land.
-In temperate regions during winter, the sea is warmer than the land.
-Thus, air temperature over the sea is also warmer than over the land
-Cold winter temperatures in coastal areas are moderated by the warm air over the sea
-Places further inland do not experience this warming effect
-Therefore, coastal areas experience warmer winters than areas inland
-In summer, the sea is cooler than the land
-Thus, the air over the sea is also cooler than the air above the land
-Warm summer temperatures in coastal areas are moderated by the cool air over the sea.
-Places further inland do not experience cooler summers than areas inland.
Factors influencing the temperature at a location: Cloud cover
-Places with higher cloud cover experience lower daily/diurnal temperature ranges than places with low cloud cover.
-Higher cloud cover reflects a large portion of solar radiation
-This reduces the amount of solar radiation reaching the ground
-Therefore, temperatures are lower in places with high cloud cover than in places with low cloud cover
-At night, cloud cover prevents heat from escaping into space
-It absorbs and re-radiates head back towards the earth
-Therefore, nighttime temperatures are warmer in places with high cloud cover and lower in places with low cloud cover
Relative Humidity
-RH is the ratio between the actual amount of water vapour in the air to the maximum amount of water vapour the air can hold at a given temperature
-RH varies with temperature. Warmer air can hold more water vapour than cooler air.
-If the amount of water vapour remains constant, an increase in temperature will cause a decrease in RH
-Satuation occurs when the RH is equal to 100%
-Dew point temperature is the temperature at which 100% RH occurs.
Clouds
A visible mass of water droplets or ice crystals that are suspended in the atmosphere. Clouds are formed when water vapour in the air condenses to form cloud droplets.
Convectional rain
-On hot days, air near the earth’s surface gets heated up
-The air beneath becomes unstable, expands and rises upwards.
-As air rises, it cools and the amount of water vapour it can hold decreases.
-Air reaches dew point temperature and condensation occurs.
-The cloud droplets combine to form heavier droplets and fall as rain
-This is known as convectional rain
Relief rain
-Parcels of moist air coming in from the sea may encounter coastal mountain ranges
-The warm, moist air from the sea is forced to rise up the side of the mountain range
-Air cools as it rises
-When dew point temperature is reached, condensation occurs and clouds form
-The cloud droplets combine to form heavier droplets and fall as rain
-The clouds and rain normally form on the side facing the income wind
-This is known as the windward side of the mountain
-By the time the winds pass over the mountain range, it has lost most of its moisture
-It descends down the leeward side of the mountain, the air is dry and no rain forms
Air pressure
-Air pressure is the force exerted per unit area on the earth’s surface by the weight of a column of air above it
-Measured in millibars (mb) with a barometer
-Air pressure decreases with increasing altitude
-Air pressure also decreases when warm air rises and increases when cold air sinks
Winds
-Winds are moving air created when neighboring locations have different air pressures
-Air moves from high to low pressure
-The larger the difference in pressure, the faster the wind speed
Sea breeze (wind blows from sea)
-During the day, the land heats up faster than the sea.
-This causes the air over the land to heat up faster than air over the sea
-The warm air rises, forming an area of low pressure over the land
-The cool air over the sea sinks forming an area of high pressure over the sea
-Air moves from an area of high pressure to low pressure
-Therefore, air moves from the sea to the land as a sea breeze
Land breeze (Wind blows from land)
-At night, the land cools down faster than the sea.
-This causes the air over the land to cool down faster than the air over the sea
-Cool air over the land sinks forming an area of high pressure
-Warm air over the sea rises forming an area of low pressure
-Air moves from an area of high pressure to low pressure
-Therefore, air moves from the land to the sea as a land breeze
Monsoon winds (middle of year)
-During the middle of the year, temperature in central Asia is heated up
-The air is warm and rises, forming an area of low pressure over Asia at sea level
-In Australia, it is winter and the cold, dense air sinks, forming an area of high pressure over Australia at sea level.
-Air moves from an area of high pressure to low pressure
-Therefore, air moves from Australia to Asia
-As the wind crosses the equator it is deflected to the right due to the Coriolis Effect and approaches India and parts of SEA as the south-west monsoon in Asia
Add only if required by qn
-As the southwest monsoon crosses the ocean it picks up moisture
-This brings rain to the coastal areas of western India
-Singapore does not receive as much rain during this time as it is sheltered by the mountain range that runs down the length of Sumatra
Monsoon winds (start and end of year)
-During the beginning and end of the year, temperature in central Asia is low
-The air sinks forming an area of high pressure over Asia at sea level
-In Australia, it is summer, and the warm air rises forming an area of low pressure over Australia at sea level
-Air moves from an area of high pressure to low pressure
-Therefore, air moves from Asia to Australia
-As the wind blows out from Asia it is deflected to the left due to the Coriolis Effect and approaches Australia as the northeast monsoon winds
Add only if required by qn
-As the northeast monsoon wind is cold and dry as it originates far inland
-India therefore experiences cool dry weather
-Singapore receives a lot of rain during this time as the wind blows over the open South China Sea, picking up a lot of moisture
Types of climate: Equatorial climate
Distribution:
-Tropical equatorial climate is found distributed between latitudes 10 degrees North and South of the equator
-Major regions include the Amazon lowlands of South America, the northern Congo Basin of equatorial Africa and the Southeast Asian region
Temperature:
-Temperatures are high and constant throughout the year
-Mean annual temperatures above 27 degrees celsius and small annual temperature range of 2 degrees celsius
Reasons for temperature:
-The sun’s rays strike places at or near the equator at high angles of incidence
-Thus solar energy is concentrated over a smaller area, resulting in high average annual temperatures
-However high humidity leads to an extensive cloud cover that prevents temperatures from becoming too high
Rainfall:
-No distinct wet and dry seasons (rains every month)
-Total annual rainfall of more than 2000mm (high)
Reason for rainfall:
-The large amount of rain is due to high temperatures that cause rapid evaporation from water bodies
-These clouds produce large amounts of rainfall evenly distributed throughout the year.
Types of climate: Monsoon climate
Distribution:
-Found between latitudes 5 degrees and 25 degrees north and south of the equator
-It includes many Asian countries like India, Bangladesh etc…
Temperature:
-It has high mean annual temperatures, which are slightly lower than in the equatorial region as it is slightly further away from the equator
-Temperatures in this climate are affected by the seasonal rainfall
-Temperatures during the rainy season are about 25 degrees celsius while in the dry season they are about 30 degrees celsius, resulting in an annual temperature range of about 5 degrees celsius
-This is due to the high cloud cover and heavy rainfall in the rainy season
Rainfall:
-There is a distinct wet and dry season
-High annual rainfall over 2000mm
-This is due to the seasonal onshore and offshore monsoon winds
Types of climate: Cool Temperate Climate (Marine west-coast)
Distribution:
-Located between 40 and 60 degrees north and south of the equator
-Found along the western coast of all continents e.g. Paris, Toronto etc…
Temperature:
-Experience four distinct seasons due to the tilt of the earth and its revolution around the sun
-They have mild winters and cool summers due to its proximity to the sea
-During winter they have shorter days and receive less solar radiation
-Results in a large annual temperature range of 25 degrees celsius
Rainfall:
-Rainfall is evenly distributed throughout the year (no distinct wet or dry seasons)
-Total annual rainfall ranges from 300mm to 900mm (low)
-Most rainfall is in summer due to convectional rain
