Elements of Climate

  Elements of Climate


Elements of climate means the factors/parameters which decides the climate; they can be also said to be constituents of climate. However, Control of Climate consist of geographical features that can control the climate.

All these parameters are called Meteorological parameters and they are observed daily in a Meteorological Observatory.

  Cloud Cover


Clouds are suspended water in the atmosphere, give us a clue about what is going on in our atmosphere and how the weather might change in the hours or even days to come

Every cloud is formed in a different way, and each brings its own kind of weather. They efficiently reflect light to space and thus contribute to the cooling of the planet. Clouds are the base for precipitation

Type of Clouds 

The cloud cover is measures by instrument OKTAS

Cloud Cover (OKTAS)

In summer cloudy days provide protection from the rays of the sun.  In winter cloudy skies at night diminish nocturnal radiation and check the fall of temperature

 

The amount of could controls the duration of sunshine, the brightness of the sky and the amount of diffused day-light

Okta is a unit of measurement used to describe the amount of cloud cover at any given location. Sky conditions are estimated in terms of how many eighths of the sky are covered in cloud, ranging from 0 oktas (completely clear sky) through to 8 oktas (completely overcast). In addition, in the SYNOP code there is an extra cloud cover indicator '9' indicating that the sky is totally obscured (i.e. hidden from view), usually due to dense for or heavy snow.

  Temperature and Humidity


Temperature is a very important factor in determining the weather, because it influences or controls other elements of the weather, such as precipitation, humidity, clouds and atmospheric pressure

Temperature shows how hot or cold a body is

Temperature is the intensity that is, as to how hot or cold the atmosphere is, how many degrees Celsius(centigrade) it is above or below freezing (0°C)

Temperature Measurement

A Stevenson screen or instrument shelter is a shelter or an enclosure to shield meteorological instruments against precipitation and direct heat radiation from outside sources, while still allowing air to circulate freely around them

Maximum thermometer: This is a mercury thermometer and records the highest or maximum temperature reached during past 24 hours or since last setting. Maximum temperature generally occurs in the world between 14.00 to 1600 hrs (-20°C to 55°C.)

Minimum thermometer: This thermometer (alcohol thermometer) records the lowest temperature of air reached during last 24 hours or since last setting. Lowest temperature of the day generally occurs just before sunrise or clear day and after sun rise on cloudy day(-40°C to 50°C)

Dry bulb thermometer: This is a mercury thermometer which gives the prevailing temperature of air at 4' 3' to 4' 6' height. It is required to calculate relative humidity and vapour pressure

Wet bulb thermometer: This is similar to dry bulb thermometer but the bulb of thermometer acts as a evaporating surface. It is used for calculating dew point, relative humidity and vapour pressure

Wet bulb thermometer

It is like dry bulb thermometer whose bulb is wrapped by a piece of muslin cloth just sufficient to cover the bulb and is looped by cotton thread (Cruex thread) that remains the bulb in wet conditions so it is called wet bulb thermometer

When water evaporates from the wet surface, the latent heat requirement is drawn from the bulb of the thermometer and so the mercury column comes down indicating a reduction of temperature

Cooling causes the temperature difference in dry and wet bulb thermometers that is used to calculate relative humidity by using relative humidity tables

Once the temperature of the dry and wet bulb thermometers a re obtained, hygrometric tables are used to determine the dew point temperature and relative humidity

Humidity

Atmospheric moisture is the most important element of the atmosphere which modifies the air temperature. Humidity is the measurable amount of moisture in the air of the lower atmosphere

Absolute humidity: The total amount of water vapor present in per volume of air at a definite temperature

Relative humidity: Is the ratio of the water vapors present in air having a definite volume at a specific temperature compared to the maximum water vapors that the air is able to hold without condensing at that given temperature

Specific humidity:-Is defined as the mass of water vapor in grams contained in a kilogram of air and it represents the actual quantity of moisture present in a definite air.

The humidity element of weather makes the day feel hotter and can be used to predict coming storms. The humidity element of climate is the prolonged moisture level of an area that can affect entire ecosystems

Relative Humidity

The pressure of air is the total weight of all the gases including water vapour in small proportions. Since water vapour also contributes to this air pressure, the partial pressure due to water vapour alone is called vapour pressure. It is expressed in millibars or millimeters of Hg.

Water evaporates into water vapour. As more and more water is evaporated, amount of water vapour increases in air. However, at any particular temperature, there is a maximum capacity for water vapour that air can hold. The pressure exerted by water vapour under such a saturated condition is called saturated water vapour pressure. SVP increases with increasing temperature

The pressure exerted by water vapour actually present in air is called the actual vapour pressure(AVP) of air. The ratio of actual water vapour pressure and saturation vapour pressure under fixed condition of temperature is called relative humidity

Relative humidity can be calculated from the difference in temperature between two thermometers, one normally exposed and one kept moist by a wick drawing water from a small container

The moist thermometer is cooled by evaporation; the amount of cooling depending on the humidity

Dew Point

The dewpoint temperature is the temperature at which the air can no longer "hold" all of the water vapor which is mixed with it, and some of the water vapor must condense into liquid water. The dew point is always lower than (or equal to) the air temperature 
If the air temperature cools to the dew point, or if the dew point rises to equal the air temperature, then dew, fog or clouds begin to form

At this point where the dew point temperature equals the air temperature, the relative humidity is 100%

  Precipitation


Precipitation is the term given to moisture that falls from the air to the ground

Precipitation is defined as the particles of liquid water or ice dropping from the clouds and reaching on the ground in the form of rain, drizzle, snow hail, etc. and is measured as the depth or thickness of layer on the surface of the earth if there were no loss by evaporation

Precipitation is simply any water form that falls to the Earth from overhead cloud formations

As an element of weather, precipitation determines whether outdoor activities are suitable or if the water levels of lakes and rivers will rise

As an element of climate, precipitation is a long term, predictable factor of a region's makeup. For instance, a desert may experience a storm (weather) though it remains a typically dry area (climate)

 

Precipitation Measurement

It is measured in mm. The simplest and most common method of measuring rainfall is to use a raingauge. These are of two types:

Non-recording raingauge : Simons rain gauge or ordinary raingauge and FRP ( Fibre Glass Reinforced Polyster) rain gauge

Self recording raingauge : Recording weighing rain gauge, Tipping bucket rain gauge and natural siphoning float type self recording rain gauge

Symon’s Rain Gauge

Automatic rain gauge and Wetness sensors are also used for precipitation measurement

 

  Winds


The horizontal movement of the atmosphere is called wind, Wind can be felt only when it is in motion

Wind is the result of the horizontal differences in the air pressure. Wind is simply the movement of air from high pressure to low pressure

The speed of the wind is determined by the difference between the high and low pressure. The greater the difference the faster the wind speed.  Closer the isobars stronger the winds

The wind brings with it the temperature of the area it is coming from,

Wind Measurement Site

The site for wind instruments must be as open as possible and should be away from tall structures

The instruments namely anemometer and wind vane should be placed on wooden posts or masonry pillars so that the height of the centre of the cup in case of anemometer and the arrow head should be 10 feet above the ground level

The pillars should be vertical to the ground surface

In order to maintain natural rotations of wind vane and anemometer, the instruments should be regularly lubricated by oiling

Wind Measurement Instruments

  • Anemoscope: This records the direction of the wind continuously
  • Aerovane : This measures the velocity and direction of the wind simultaneously
  •  Wind vane : This is used in observatories to find the wind direction
  • Anemometer: It measures speed of the wind

Wind Vane

It is a balanced lever which turns freely about a vertical axis. One end of the lever exposes a broad surface to the wind, while the other end is narrow and points to the direction from which the wind blows

Wind direction is the direction from which the wind is approaching the observer. It is expressed in degrees, measured clockwise from geographical north. The codes and 16 point wind direction.Wind coming from the south has a wind direction of 180 degrees; one from the east is 90 degrees

Winds are described after the direction from which they come, followed by '-erly'. For example, winds from the north are called ‘northerly winds’(north +-erly)

Windward side i.e. from where the wind is coming. Leeward side where the win d is going is never reported

Anemometer

Robinson Cup anemometer Mechanical arrangement for converting the rotational motion into linear motion in kmph which is converted into average wind speed in kmph by dividing 24

This instrument consists of four hemispherical cups fixed at the end of metal arms from a central point. The cup wheel is pivoted at the centre to a vertical spindle passing through a brass tube attached to the anemometer box. The cup is set in motion due to the pressure differences occurring between the two faces of the cup

For example: If the first anemometer is 4005.6 and the second reading is 4006.8, the wind speed will be 20 x ( 4006.8-4005.6) = 20 x 1.2 = 24 kmph.

Vane anemometers

Wind rose

  • Wind rose is defined as graphical representation of wind speed and direction of a particular location
  • Wind speed less that 1.8 km/hr is called calm
  • Get data from IMD (Head office Pune)
  • Nearby IMD (80km vicinity)

 

  Air Pressure


Air pressure is the weight of air resting on the earth's surface

Air has specific weight. This weight exerted by the air is atmospheric pressure

Atmospheric pressure is defined as the force per unit area exerted against a surface by the weight of air above that surface in the Earth's atmosphere

The average pressure of the atmosphere at mean sea level is about 1 kg per square cm or a pressure of 1013.25 millibars (mb), and which is also referred to as 1 atmosphere. Atmospheric pressure is measured with a barometer

It is used primarily by meteorologists to monitor developing storms that can seem to come out of nowhere

Barometer is the device to measure atmospheric pressure

Mercury and Aneroid Barometer

Aneroid barometers

The aneroid metal capsule, which is the device that moves with changes in air pressure, is made from an alloy of beryllium and copper

Barometer cases are usually made out of brass (a mixture of copper and zinc). Mixture of 65% copper and 35% lead

Barometer dials can be made out of anything: aluminum, steel, brass, or paper

  Storms


Meteorologically terrestrial storm is a wind measuring 10 or higher on the Beaufort Scale (Beaufort wind force scale), meaning a wind speed of 24.5m/s (89 km/h, 55 mph) or more; however, popular usage is not so restrictive. Storms can last anywhere from 12 to 200 hours, depending on season and geography

Tornadoes, hail storms and fog are all examples of meteorological phenomena that are hard to predict

As an element of weather, these occurrences can seem random and are a result of a set of unique circumstances; However, some regions of the world can factor meteorological phenomena into their climate

Beaufort wind force scale (1 mph = 1.61 km/hr)

 

  Visibility


DefinitionThe greatest distance at which a black object of suitable dimensions, situated near the ground, can be seen and recognized when observed against a bright background;

The greatest distance at which lights of 1,000 candelas can be seen and identified against an unlit background

Visibility is one of the most critical weather element

Obstructions to visibility include clouds, fog, smoke, haze, and precipitation is represented by the meteorological optical range (MOR) and varies with the background illumination

In extremely clean air in Arctic or mountainous areas, the visibility can be up to 70 kilometres 100 kilometres

Visibility is often reduced somewhat by air pollution and high humidity. Fog and smoke can reduce visibility to near zero, making driving extremely dangerous

The same can happen in a sandstorm in and near desert areas, or with forest fires

Heavy rain (such as from a thunderstorm) not only causes low visibility, but the inability to brake quickly due to hydroplaning;

Blizzards and ground blizzards (blowing snow) are also defined in part by low visibility

 

 

Runway visual range (RVR) is in aviation meteorology the distance over which a pilot of an aircraft on the centreline of the runway can see the runway surface markings delineating the runway or identifying its centre line. RVR is normally expressed in feet or meters

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