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Reena H.

on 20 November 2014

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What is weather?
The state of the ATMOSPHERE at a particular time

Made up of 6 different components: - Precipitation
- Temperature
- Humidity
- Air pressure
- Wind
- Clouds

any form of water that falls from clouds
includes rain, hail, sleet, snow and drizzle
measured using a rain gauge, recorded in millimetres (mm)
Tropical storms
Must be read same time each day
Melt all snow or frost first
Pour water from the collecting jar into the measuring cylinder
Place on FLAT surface
Read at EYE LEVEL - to avoid parallax error
A)Concave meniscus - read at bottom

B)Convex meniscus - read at top
Reading a meniscus
*amounts too small to measure should be recorded as a trace
Degree of warmth in the air
measured in degrees Celsius
-Six's thermometer
-Minimum thermometer
-Maximum thermometer (2 types)
Ensuring a fair test
Calculating Statistics
Mean annual temperature
- total of monthly means divided by 12
Daily range of temperature
- max. minus min. temperature of the day
Mean daily temperature
- max. plus min. temperature of the day divided by 2
Mean monthly temperature
- total of average temp. divided by the number of days in the month
Annual range

- mean temp.of warmest month minus mean temp. of coldest month
Amount of water vapour in a given volume of air
Used to forecast occurrence of precipitation
- max. amount of water vapour that can be held at that temperature. (air is saturated)
Temperature rises, water evaporates, humidity increases
Relative humidity
actual amount of water vapour in the air

maximum amount of water vapour that the air can hold at that temperature
* saturated air, relative humidity = 100%
Wet and dry bulb thermometers (hyGROmeter)
Done by: Chloe, Trudy, Marissa and Reena
Wet bulb
- muslin cloth wrapped around it, wick of cloth from a container of water leads to the muslin (keeps the bulb moist)
Dry bulb -
gives air temperature
- If air not saturated, water evaporates from muslin = causes cooling of the bulb = mercury contracts
temp. of wet bulb - temp. of dry bulb = depression of wet bulb
^larger this is, lower the relative humidity will be.
* If air saturated, evaporation not possible. Thermometers show same temp.
* If air not saturated, relative humidity can be found using table on pg 172 (not required to learn table)
how heavy the atmosphere is
measured in millibars (mb)
pressures below sea level pressure is low and above is high

(less air above ground)
3 instruments used to measure atmospheric pressure:
- Mercury barometer
- Aneroid barometer
- Barograph

measured with anemometer
metres per second
Beaufort scale used for classifications of wind speeds and effects
speed displayed on a meter/dial
wind vane
points of compass
wind catches thick end of arrow
points to direction where wind has COME from
influences weather due to temp. and moisture of areas it has passed

should be 10 metres above ground to avoid gusts and ground fiction.
open space (x3 height of nearest obstacle away from it)
urban areas- on top of buildings
PREVAILING wind: most frequently occurring wind in an area
Digital Hygrometer
Digital maximum-minimum thermometers (data may be lost if instrument gets wet, must be kept out of direct sunlight)
Tipping bucket rain gauge - uses a bucket with a known volume that tips over when full.
-Total volume = no. of times bucket tips X volume of bucket.
-measures distribution of rainfall through the day
Shield from DIRECT sunlight and sources of heat
Raise so bulbs are 1.25m above ground to avoid heat being RADIATED from ground or being CHILLED
Away from buildings that radiate heat
consist of water droplets suspended in the atmosphere
formed when water vapour condenses
type of cloud and amount of sky it covers are recorded
Main types
Further subdivision
High clouds could be in layers called CIRRostratus or globules called CIRRocumulus (prefixed by cirro)
Middle-level called ALTOstratus or ALTOcumulus (prefixed by alto)
Low-level is stratus or cumulus. I it has traits of both, its called stratocumulus
Cumulonimbus - biggest cloud
-sea-level to top of troposphere
-cannot rise higher than
tropopause so it spreads out to
form a distinctive ANVIL shape at
the top of the cloud
How cloud extent is measured
measured by eye
expressed in oktas (eights)
Grass reflects and radiates heat less than concrete
Stores wet and dry bulb thermometers, maximum-minimum thermometers and barometer
has to open away from the sun (facing north in northern hemisphere and south in southern
Double layered roof with air space for insulation
Slatted sides (louvres) allow free movement of air
Raised above ground to avoid heat radiation (If screen on concrete, placed higher)
Box made out of wood to avoid conduction of heat
Painted white to reflect the sun's rays
(according to shape)
(with greater vertical extent)
Synoptic charts
Pressure over area shown by ISOBARS
Circles represent weather stations
Shading in circle is cloud extent
Arrow at station shows wind direction
Symbol by circle shows type of precipitation (if any)
Temperature written above station circle
Stratus - little vertical uplift, over wide are, form in LAYERS
Cumulus - flat bases, globular upper surfaces, more vertical but localised
Cirrus - feather-like, wispy, appears when condensation is high
Nimbostratus (up to 5000 metres deep)
equivalent to categories 8-11 on Beaufort scale
last about 7-14 days
form over oceans between May and November in Northern hemisphere and between November and May in Southern
surface of sea must be minimum 27 degrees Celsius
do NOT form at equator or higher latitudes
Heated warm air rising from ocean creates low pressure at the surface
air cools and sinks, forming the EYE at the centre of the storm
Thick cumulonimbus clouds produced, heavy rain
Spiraling mass rises quickly
More warm, moist air moves in to replace air that has risen
calm, sunny area
longer than usual period of dry weather
occur almost everywhere
can cause desertification
cause destruction of homes, rapid rises in sea-level, torrential rain, flooding, landslides
refer to page 185
refer page 183
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