Theme 2d Weather

Question 1

Definition of weather

Answer 1

The day to day changes in the atmosphere e.g precipitation, temperature

Question 2

Definition of climate

Answer 2

The overall pattern of weather, usually based on an average over 35 years e.g arid, tropical, mild/temperate

Question 3

What are the characteristics of a Stevenson Screen

Answer 3

• Painted white to reflect sun’s rays
• Made of wood to prevent conduction of heat
• Sides are slatted to allow free movement of air
• Raised above ground to avoid heat radiated from ground
• Roof is double-layered with airspace for insulation

Question 4

What is the the use of Stevenson Screen and its site ?

Answer 4

• Contains six’s thermometer (min-max), hygrometer and barometer
• Door should face away from sun, should place on grass to reduce ground heat & kept in weather station behind locked gates (away from buildings &not affected by heat)

Question 5

What is a rain gauge, where to place, how to operate ?

Answer 5

• Use to measure precipitation (mm)
• Place on grass & away from buildings/trees
• At same time each day, water collected is poured into a tapered measuring cylinder on flat surface
• Water level is then read with the eye at the same level as the lowest part of the meniscus of the water

Question 6

What is a maximum-minimum thermometer and how it works ?

Answer 6

• To record the daily maximum and minimum temperature (°C)
• When temp rises => alcohol in left arm expands & alcohol in right arm evaporates into space in bulb
• Expanding alcohol on left pushes mercury up right =>pushes an index at maximum temperature reaches
• When temp cools => alcohol in left arm contracts => alcohol/vapour in bulb returns to liquid => mercury moves up left push an index indicates minimum temp reach

Question 7

What is a hygrometer/wet and dry bulb thermometer and how it works ?

Answer 7

• Measure relative humidity using wet and dry bulb thermometers (°C)
• Dry-bulb thermometer is an ordinary thermometer measure air temperature
• Bulb of wet-bulb thermometer has fine muslin cloth wrapped around it, beneath has a container of water
• A wick of cloth transfer moisture keep muslin moist
• If air not saturated => water evaporate from muslin &temp lowers
• Take dry-bulb reading minus wet-bulb reading to get depression & compare data in a table to get RH

Question 8

What is a Campbell-Stokes recorder and how does it work ?

Answer 8

• Measures sunshine hours
• Glass sphere refracts sun’s rays onto a card which burn & leaving a mark => measure length of mark & convert to hours get sunshine hours
• Must be bright to burn card => place it away from anything that block sunlight => facing south in northern hemisphere & vice versa

Question 9

What is a barometer and how many types are there ?

Answer 9

• Measures pressure in millibars (mb)
• There are 3 types of barometer:
  + Mercury barometer
  + Aneroid barometer
  + A barograph

Question 10

What is an anemometer and how does it work and where to place?

Answer 10

• Measures wind speed (m/s)/(km/h)
• Has 3 or 4 cups on metal arms that spin freely on a 10 m vertical shaft (reduce friction of wind with ground)
• The speed at which cups rotate when driven by wind in measured & shown on a meter/dial

Question 11

What is a wind vane and how does it work ?

Answer 11

• Measure wind direction N/S/E/W
• Arrow points to the direction from which wind has come from
• Placed at a top of long pole 10m high or 3m above buildings (reduce friction of wind with ground/surface)
• Broad end of the shaft catches the wind & swings in line with it

Question 12

What is an Okta scale ?

Answer 12

• Measures cloud cover (oktas); 0 oktas = clear sky, 8 oktas = total coverage, 9 = obstructed from view
• Each okta represents an eighth of the sky that is cloud-covered
• Cut a card to 8 equal squares, hold to the sky at arm’s length & read
• The number of full/partial squares are counted

Question 13

What is a Beaufort scale ?

Answer 13

Measure wind speed (knots)

Question 14

How does a mercury barometer work ?

Answer 14

• A hollow tube with all the air extracted, open end place in a bath of mercury
• Atmospheric pressure on the mercury in the bath push & force it up the tube
• Mercury rises until air pressure equals weight of the mercury column
• Height of the column mercury shows air pressure (higher => higher pressure)

Question 15

How does an aneroid barometer work ?

Answer 15

• A sealed metal capsule inside the barometer (aneroid cell)
• Air inside capsule is partially removed => can easily change shape
• High air pressure compress the capsule, low air pressure expand the capsule
• Movements transferred by a system of lever & springs, levers move a pointer on a calibrated scale showing air pressure

Question 16

How does a barograph work ?

Answer 16

• Contains a stack of sealed metal capsule (aneroid cell)
• Air inside the capsule is partially removed
• When air pressure increase, capsule is compressed, when air pressure decrease, capsule is expanded
• Movement is transferred through levers & levers move pen which records pressure changes on graph paper wrapped around a cylinder

Question 17

What is cloud ?

Answer 17

A collection of water droplets /ice crystals in the sky

Question 18

How does cloud form ?

Answer 18

1. Incoming solar radiation (insolation) heats the ground
2. Warm ground transfer heat to the air above it through conduction
3. Warm air (less dense) rises up and cool as it rises higher to the air
4. Cooler air hold less moisture & will reach dew point and condense to tiny water droplets/ice crystals
5. Water vapour condenses onto condensation nuclei (salt, dust) and droplets group together form clouds

Question 19

What are 4 main types of cloud and their characteristics ?

Answer 19

1. Cirrus cloud: thin, wispy, high
2. Stratus cloud: layer, uniform, low, produce light rain & snow
3. Cumulus cloud: heaped (cotton wool), thick, domed top, produce light rain
4. Cumulonimbus cloud: up to 10 Km high & wide; produce rain, thunder & lightning in spring and summer

Question 20

What is nimbus ?

Answer 20

Rain bearing

Question 21

What is alto ?

Answer 21

Middle (level)

Question 22

What does wind direction mean ?

Answer 22

The compass direction from which the wind originates, not where it is blowing to