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