Weather:weather describes the atmospheric conditions at a particular place and time together with change taking place over short term. E.g. hour-by-hour or day by day.Climate: climate is the average weather conditions of a place or area, the result of weather data recorded over a long period of time (normally 30 years)

Maximum and minimum

thermometer Wet and dry bulb thermometer Hygrometer Barometer Stevenson's Screen Thermometer wind vane Anemometer Rain guage

Weather station instruments:

Latitude Distance from the sea Prevailing winds Ocean currents Altitude cloud cover

Factors affecting temperature

Temperature: Air temperature is recorded in the shade ( in a

Stevenson’s Screen) It is recorded using a maximum/minimum

thermometer ( highest and lowest temperatures in the last 24 hours)

It is recorded in degrees Centigrade (Celsius) or Fahrenheit.

Solar radiation or insolation, is the main source of heat energy to the atmosphere

The atmosphere is warmed mainly from long wave radiation emitted by the earth.

Temperature therefore decreases with height at an average rate of 6.5°C per 1000 Meter

A Range Of Data Is Recorded

Air pressure:

• Air pressure is the weight of the atmosphere at the earth’s surface

• Air pressure is recorded using an aneroid barometer

• It is measured in millibars (mb), reduced to sea level( average pressure at sea level is 1013mb)

Air pressure varies with: (1)TEMPERATURE; warmer lighter air is forced

to rise creating areas of low pressure; heavier, colder air descends creating areas of high pressure

(2)HEIGHT- As the atmosphere becomes thinner pressure decrees.

Uses Of Weather Station Instruments

Maximum and minimum

thermometer

Maximum thermometer is also a mercury-in-glass thermometer having a constriction near the bulb end. When the temperature of air rises, the mercury in the thermometer expands and forces its way into the stem past this constriction. But when the bulb cools none of the mercury above the constriction will get back into the bulb and then the length of the mercury remains the same. The end of the mercury thread farthest from the bulb registers the highest temperature reached in a day.

Minimum Thermometer: The liquid used in minimum thermometer is alcohol in which a dumb-bell-shaped index is set. When the temperature falls, the alcohol column drags the index towards the bulb end but when the temperature rises the alcohol column expands and runs past the index without disturbing it. Thus the end of the index farthest from the bulb gives the lowest temperature attained in a day.

Wet & Dry Bulb Thermometer:This instrument will be used to measure the air temperature

Hygrometer:This instrument will be used to measure the humidity (moisture) in the air

Barometer:A barometer is a scientific instrument used in meteorology to measure atmospheric pressure.Stevenson’s Screen Thermometer:

Wind Direction: wind vane is used to recorded as the direction from which direction wind is blowing Wind Speed:Anemometer is used to measure wind speed. Speed is measured in Knots or kilometers per hour.

PRECIPITATION: (RAIN FALL)Precipitation mainly occurs when air is forced to rise. Precipitation is the deposition of moisture from the atmosphere as rain drizzle, hail, snow, fog or dew. Rainfall is measured by using a RAINGUAGE

Characteristics of Stevenson screen:• Thermometers (and sometimes other instruments)

are housed in a white, louvered box called the Stevenson Screen.

• It is painted white to reflect incoming radiation from the Sun and is set at a height of 1.25 metres above the ground, so as not to be affected by the Earth's low-level radiation. The screen should be kept clean from dust and dirt.

• In order to prevent direct sunlight falling on and affecting the instruments when the door is opened it is designed so that the door opens to the north in the northern hemisphere. This is because the Sun never shines from the north.

• The thermometers inside are usually the dry bulb, wet bulb, maximum and minimum, they are read in that order.

Characteristics of Stevenson screen:• The dry thermometer is a mercury filled

thermometer, recording changes in temperature in degrees and tenths Centigrade. The temperature rises and falls as the temperature changes.

• The maximum thermometer is filled with mercury, which moves up the central tube as the temperature increases. There is a constriction just above the bulb of the thermometer, which stops the mercury returning to the bulb when the temperature falls. Therefore, the highest temperature (the max) is recorded regardless of the temperature at the observation.

TYPES OF CLOUDSThe main types of clouds can be separated into three broad categories according to the height of their base above the ground: HIGH CLOUDS, MEDIUM CLOUDS LOW CLOUDS.

High clouds: are usually composed solely of ice crystals and have a base between 5500 and 14,000 meter.

There are 3 types of High Clouds

CirrusCirrocumulusCirrostratus

white filamentssmall rippled elements

transparent sheet, often with a halo

Medium clouds: are usually composed of water droplets or a mixture of water droplets and ice crystals, and have a base between 2000 and 7000 meter.

There are 3 types of Medium clouds

Altocumulus cloudsAltostratus cloudsNimbostratus clouds

layered, rippled elements, generally white with some shading

thin layer, gray, allows sun to appear as if through ground glass

thick layer, low base, dark, rain or snow may fall from it.

Low clouds: are usually composed of water droplets though cumulonimbus clouds include ice crystals, and have a base below 2000 meter

There are 4 types of low clouds:Cumulonimbus cloudsCumulus cloudsStratus cloudsStratocumulus clouds

1. large, cauliflower-shaped towers, often ‘anvil tops’ something giving thunderstorms, or showers of rain or snow.

2.individual cells, vertical rolls or towers, flat base

3.ayered, uniform base, grey

4. layered, series of rounded rolls, generally white with some shading.

BY:Suresh Kumar Kundur