Weather Parameters Information

Weather

      Weather is the condition of the atmosphere in one area at a particular time. Weather is made up of multiple parameters, including:
  • Air temperature
  • Humidity
  • Atmospheric pressure
  • Solar radiation
  • Wind
  • Rainfall

      Each of these factors can be measured to define typical weather patterns and to determine the quality of local atmospheric conditions. Weather monitoring can establish a database of typical conditions. When one or more weather elements deviate from this standard, the information can be used to explain or predict weather events.
(Source:fondriest.com)

Air Temperature

Air temperature is a measure of how hot or cold the air is. Temperature describes the kinetic energy, or energy of motion, of the gases that make up air. As gas molecules move more quickly, air temperature increases. Air temperature also affects nearly all other weather parameters. For instance, air temperature affects:

  • The rate of evaporation
  • Relative humidity
  • Atmospheric pressure
  • Precipitation
  • Solar radiation
  • li>Wind
  • Rainfall

      Temperature is usually reported in one of four different scales, Celsius, Fahrenheit, Kelvin and Reamur.The conversion equations for the four temperature scales are:

  • 1 Reamur = 4/5 Celsius
  • 1 Farenheit = (9/5) Celsius + 32
  • 1 Kelvin = Celsius + 273.15

      Celsius or Centigrade, with 0oC as the melting point of ice and 100oC as the boiling point of water;

Humidity

      Relative humidity is a measure of the amount of moisture in the air relative to the total amount of moisture that the air can hold. Humidity is simply water vapor in the air, which is needed to form rain. Additionally, water vapor holds heat in the air. Relative humidity is reported as a percentage (%) of the total amount of moisture that could be held in the air. Relative humidity is influenced by temperature and geographic location. Warmer air holds more moisture than cooler air, and warmer weather promotes evaporation.
(Source:fondriest.com)

Pressure

      Barometric pressure is the weight of the overlying air pressing down on the earth. It is also known as air pressure. Low barometric pressure means the overlying air is rising, whereas high pressure means the overlying air is sinking. Barometric pressure is usually reported in milibar (mb). The conversion equations for pressure scales are:

  • 1 mb = 1 hPa
  • 1 Pa = 10-5 bar = 10-2 milibar = 9.8692 x 10-6 atm = 1.450377 x 10-4 psi
  • 1 bar = 103 milibar = 105 Pa = 0.98692 atm = 14.50377 psi

      Barometric pressure is mainly influenced by temperature and altitude. Barometric pressure is lower at higher altitudes because there is less air pushing down on the earth. Barometric pressure also decreases with increasing temperature. This is because air is less dense at warmer temperatures. This makes warm air rise, and cold air sink.

Wind Velocity

      Wind velocity consists of wind speed and wind direction.Wind speed describes how fast the air is moving past a certain point. This may be an averaged over a given unit of time, such as miles per hour, or an instantaneous speed, which is reported as a peak wind speed, wind gust or squall. Wind speed and direction play a large role in predicting weather patterns.

      Wind speed and direction play a large role in predicting weather patterns. Wind direction describes the direction on a compass from which the wind emanates, for instance, from the North or from the West. Wind speed is typically reported in miles per hour, knots, or meters per second.

  • 1 knot = 1.852 km/h
  • 1 km/h = 0.278 m/s

      Wind direction and speed are caused by differences in air temperature and variations in barometric pressure. Wind moves from areas of high air pressure to low air pressure. The larger the difference in pressure, the faster the wind will move. Land forms and topography also influence wind speed and direction. Large bodies of water, such as the Great Lakes and oceans, promote high wind speeds.

Wind speed is sometimes assigned a number (1-12) on the Beaufort Scale, a measure that relates wind speed to observed conditions at sea or on land. The Beaufort scale, however, is usually described in terms of how it affects things, not people.

Beaufort wind scale

Wind descriptive terms

km/h

m/s

knot

Appearance of Wind Effects

0
Calm
<1
<0.3
<1
Calm, smoke rises vertically
1
Light air
1-5
0.3–1.5
1–3
Direction shown by smoke drift but not by wind vanes
2
Light breeze
6-11
1.6–3.3
4–6
Wind felt on face; leaves rustle; wind vane moved by wind
3
Gentle breeze
12–19
3.4–5.5
7–10
Leaves and small twigs in constant motion; light flags extended
4
Moderate breeze
20–28
5.5–7.9
11–16
Raises dust and loose paper; small branches moved
5
Fresh breeze
29–38
8–10.7
17–21
Small trees in leaf begin to sway; crested wavelets form on inland waters
6
Strong breeze
39–49
10.8–13.8
22–27
Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty
7
High wind, moderate gale,near gale
50–61
13.9–17.1
28–33
Whole trees in motion; inconvenience felt when walking against the wind
8
Gale,fresh gale
62–74
17.2–20.7
34–40
Twigs break off trees; generally impedes progress
9
Strong/severe gale
75–88
20.8–24.4
41–47
Slight structural damage (chimney pots and slates removed
10
Storm, whole gale
89–102
24.5–28.4
48–55
Seldom experienced inland; trees uprooted; considerable structural damage
11
Violent storm
103–117
28.5–32.6
56–63
Very rarely experienced; accompanied by widespread damage
12
Hurricane force
>118
>32.7
>64
Devastation

Rainfall

      Rainfall is the amount of rain that falls on a single occasion. Rainfall is reported in mm. One millimeter of rainfall is the equivalent of one liter of water per square meter. 1mm rainfall means every one square meter area is filled with the water of height 1mm. 1 square meter = 1000mm length ×1000mm breath. So 1mm rain means 1000mm length × 1000mm breath × 1mm height = 1litre of water. Every square meter has one litre of water.