2.4 - Weather Flashcards
Weather
The short-term day to day changes in the atmosphere for a place.
Meteorologists
Measure the weather and predict the forecast.
Why do we need to know the weather? (name 3)
- Been able to gather information about the weather is extremely important to society
- The weather can have huge impacts on what people do
- It can even have a national or even global impact (e.g. flights, floods etc.)
- It is very important to gather accurate data for the weather, small mistake can create hazards
- It is very useful to predict weather conditions for the future (e.g. trade, commercial usage, industry, for individual people)
What is describing weather conditions based on?
- temperature
- percipitation
- moisture
- air pressure
- wind speed
- wind direction
- amount of sunshine
- cloud type/cover
- visibility
Percipitation
Moisture that falls from the sky
(rain, snow, hail, sleet)
Easiest measuring instrument for temperature
A digital thermometer
* measured in Celcius
Measuring instrument for maximum and minimum temperature
Six’s thermometer/maximum minimum thermometer measures current temperature and the temperature range in a period of time
* measures in celcius
How is Six’s thermometer used?
- Shade temperature is measured, as air temperature is variable due to direct insolation and cloud cover
- If the temperature rises, the alcohol in the right tube evaporates and fills the air space.
* This allows the mercury to move upwards
* The index is pushed upwards and its bottom marker marks the maximum temperature. - If the temperature falls, the mercury retreats but the index stays in place.
* The antagonistic movement can be noticed in the left tube. - Can have a diurnal temperature range
Insolation
Incoming Solar Radiation: the incoming shortwave radiative energy received from the sun
Diurnal temperature range
Differences between the hottest and coldest temperature in a 24 hour range (min - max)
Formula to calculate daily average temperature
(max + min) / 2
Measuring instrument to measure percipitation
Rain gauge
* measured usually in mm
How is percipitation measured?
- The rain gauge is usually anchored in the ground with the top of the gauge
- around 30cm above the ground surface to ensure that rain splash does not affect the results.
- The depth of the rain in millimetres can be read from the side of the container (or the rain gathered can be poured into a measuring cylinder)
Measuring instrument to measure wind direction
Wind vane
* using compass directions
How is wind direction measured?
It is reported by the direction it is blowing from not to (e.g. blowing from the west to the east, it is a westerly wind)
Measuring instrument to measure wind speed
Anenometer
* measured in knots, km/h or m/s
How is wind speed measured?
- The anemometer consists of 3 or 4 cups fixed on metal arms that rotate freely on a 10m vertical shaft
* The stronger the wind, the faster the cups rotate, and more rotations are recorded on the counter - The digital handheld anemometers need to be held into the oncoming wind with outstreched arms and as the fan rotates, the number is shown on the screen
- Wind vanes and anemometers are placed well away from any buildings or trees that can interfere with air movement
Measuring instrument to measure humidity
Hygrometer
* as a percentage
Measuring instrument to measure air pressure
Barometer
* in millibars
General properties of air humidity
- Warm air can hold more water vapour than cold air
- When the air is holding as much moisture as it can, it’s said to be saturated
- Relative humidity: how much water vapour the air is holding in relation to the maximum amount of water vapour it could hold at a specific temperature
How is a mercury barometer used?
- The open end is placed in a bath of mercury
- Mercury is forced up the tube by atmospheric pressure on the mercury in the bath
- When the two pressures equalise, mercury will stop rising in the tube
- The height of the column of mercury will change with air pressure:
* Rising as air pressure rises
* Dropping as air pressure falls
How is an aneroid barometer used?
- There is a strong metal spring within the chamber that prevents it from collapsing
* The spring will expand and contract with changes in atmospheric pressure - Levers magnify these changes
* a pointer moves across a calibrated scale to show atmospheric pressure at that time
What is an aneroid barometer?
It has a partly vacuumed, corrugated metal chamber inside
What is a mercury barometer?
A hollow tube with all the air extracted
What is normal air pressure?
Normal pressure is 1000mb with a reading above this being regarded as high pressure and a reading below regarded as low pressure
* low air pressure means a higher chance for rain
Measuring instrument to measure visibility (and how)
Sensors send off light signals and see how far they can be seen for
* in metres
Measuring instrument to observe cloud cover (and how)
A table split into eight squares is held up into an area of the sky
* in oktas which represent one eight of the sky covered by clouds
Measuring instrument to measure sunshine
Campbell-Stokes sunshine recorder
* in hours and minutes
How is sunshine measured?
- Sunshine recorder is placed in an open space, south-facing in northern hemisphere or north-facing in southern hemisphere
* making sure that the sunshine is not covered by anything - The recorder is a glass sphere partly surrounded by a metal frame
- Sunlight is concentrated through the sphere onto a recording card placed beneath the focal point
* The rays burn a trace on the card - The length of the trace shows the sunshine duration at that location
* At day’s end, the card is replaced
Clouds and how rain forms and falls
- Clouds consist of tiny water droplets or ice particles that are too light to fall to Earth
- Clouds will form when air rises, cools and condenses into water droplets or ice crystals if cold enough
- The tallest clouds form in the tropical regions, as the tropopause is at its highest and clouds do not form beyond it
- Clouds produce precipitation if they have enough water or ice particles that can collide and join together
* The particles will then grow too big and heavy to be supported in the air and will fall through the rising air currents
Tropopause
The atmospheric dividing line between the troposphere and the stratosphere
Cirrus
- Level: High above 6km
- Description: Thin, white and made of ice crystals. Forms narrow wisps, threads or feathers (cirrus means hair-like)
- Weather: fine
Cirrostratus
- Level: high above 6km
- Description: Thin, white layers made of ice crystals with a wide horizontal spread, often covers whole sky
- Weather: fine
Altostratus
- Level: medium 2-6 km
- Description: Can be thin and white or grey and thick with layer of water droplets
- Weather: fine