Weather & Climate

Weather

  • Temperature, pressure, wind, humidity and precipitation, interact with each other.
  • They influence the atmospheric conditions like the direction and velocity of wind, amount of insolation, cloud-cover and the amount of precipitation. These are known as the elements of both weather and climate.
  • The influence of these elements differs from place to place and time to time. It may be restricted to a small area and for a short duration of time.
  • Very often this influence is described in the name of weather as sunny, hot, warm, cold, fine, etc depending upon the dominant element of weather at a place and at a point of time.
  • Therefore, weather is the atmospheric condition of a place for a short duration with respect to its one or more elements.
  • Two places even a short distance apart may have different kind of weather at one and the same time.

Seasons

Weather & Climate

  • Seasons are specified periods in a year which have similar weather conditions.
  • Season is a period of the year characterized by a particular set of weather conditions resulting from the inclination of the earth’s axis and the revolution of the earth round the sun.
  • The same cycle of season is repeated year after year.
  • Four seasons, each of three months duration have been recognized in temperate regions.
  • They are spring, summer, autumn and winter.
  • In our country, we have three distinct seasons which are summer, winter and monsoons.
  • The Indian Meteorological Department has recognized four main seasons.
  • They are
    • Cold weather season (December to February.)
    • Hot weather seasons (March to May)
    • Advancing monsoon season or rainy season (June to September.)
    • Retreating monsoon season (October to November.)
  • The rays of the sun are more or less direct on the equator throughout the year. Hence, equatorial regions experience the same temperature all the year round. Therefore, seasons are insignificant on or near the equator.
  • Near the coast, the oceanic influence reduces the seasonal variations.
  • In the polar regions, there are only two seasons i.e. long winter and short summer.

Climate

  • The average weather conditions, prevalent from one season to another in the course of a year, over a large area is known as climate.
  • The average of these weather conditions is calculated from the data collected for several years (about 35 years) for a larger area.
  • Rajasthan, for example, experiences hot and arid climate, Kerala has tropical rainy climate, Greenland has cold desert climate and the climate of Central Asia is temperate continental.

Climate of a region is considered more or less permanent.

Weather is nothing more than the different elements it is composed of, as well as the way they interact with each to create different atmospheric conditions or weather events. Eight primary elements/factors drive all weather:

    • Temperature
    • Air (Atmospheric) Pressure
    • Wind (Speed & Direction)
    • Humidity
    • Precipitation
    • Visibility
    • Clouds (Type & Cover)
    • Sunshine Duration

Temperature

  • Temperature is a measurement of the amount of kinetic energy present in the air, which manifests itself physically through the experience of heat or cold.
  • The scales typically used to measure temperature, is Celsius, Fahrenheit, and Kelvin.
  • The instrument used to measure temperature is called a thermometer.
  • In more practical terms, it means that the particles in the air move or vibrate at a certain speed, which creates kinetic energy.
  • When the particles start to move/rotate around faster, temperature increases.
  • When the particles begin to slow down, the temperature also starts to decrease

Air Pressure

  • Air pressure is another essential element of weather, especially when it comes to creating or changing atmospheric conditions.
  • It is also one of the critical variables used to make accurate weather forecasts.
  • Air Pressure is the result of the pressure created by the weight of the air in the Earth’s atmosphere.
  • It is also called a barometric pressure, named after the instrument used to measure air pressure.
  • Although it may not be visible, air has weight since it is not empty. It is filled with small particles of nitrogen, oxygen, argon, carbon dioxide and a few other gases.
  • The weight of the particles in the air creates pressure due to the gravitational force of the Earth.
  • Since more air is present above the air close to the ground, air pressure is the highest on the planet’s surface and decreases as altitude increase.
  • The barometer is the instrument used to measure air pressure.

Wind (Speed & Direction)

  • The movement of air (wind) is one of the main driving forces of weather.
  • The majority of major and even extreme weather events like cold & warm fronts, clouds, thunderstorms, and hurricanes are all driven by wind.
  • Wind is the large-scale movement of air from an area of high to an area of low pressure in the atmosphere.
  • The speed and strength of wind are determined by the distance between the low pressure and high-pressure areas, as well as the difference in air pressure.
  • The anemometer is the instrument used to measure wind speed.
  • A wind vane (or weather vane) is the instrument used to measure wind direction.

Humidity

  • Humidity is another weather element that cannot be seen but can be felt.
  • It not only plays a big part in weather formation but also directly influence our physical comfort levels.
  • Humidity is the amount of water vapor that is present in the atmosphere at any specific time.
  • Water vapor is nothing more than water in a state of gas (after the liquid has evaporated).
  • Although humidity and its effects can usually be felt, it is normally invisible to the naked eye.
  • Humidity can be challenging to understand and interpret correctly.
  • The hygrometer is the instrument used to measure wind speed.

Precipitation

  • Precipitation is water in all its different states, which is formed after condensation turned water vapor into its solid form, which falls to the ground after it becomes too heavy to stay suspended in the air.
  • Precipitation can take the form of rain, snow, hail, or graupel.
  • Precipitation is primarily the result of evaporation and condensation.
  • Instrument for Measuring Rainfall :A rain gauge is the instrument used to measure rainfall. It is essentially a measured container that captures rain and measures the amount that falls over a set period of time.

Visibility

  • Visibility is the measurement of the degree through which an object can be observed over a certain distance.
  • This measurement is crucial when conditions like mist, haze, fog, and freezing drizzle are present, which can severely impede visibility.
  • The importance to be able to measure this element is often underestimated.
  • It is especially applicable in areas where visibility plays a crucial role, like airports and harbors where it can literally be a matter of life or death.
  • Instrument for Measuring Visibility :Visibility sensors like “forward scatter sensor” are the instruments used to measure visibility.

Clouds (Type & Cover)

  • Clouds are water droplets or water in different states (like ice and snow crystals), which formed after water vapor reached condensation level and could no longer remain in gaseous form.
  • Knowing how to identify a certain type of cloud and the weather associated with it, can prove valuable when assessing weather conditions with only visual references.
  • Instrument for Measuring Clouds The advanced instruments meteorologists use to study clouds in detail are weather satellites and radars.
  • Satellite and radar images are able to accurately measure cloud density, the amount of moisture, the temperature, and movement of the clouds.

Sunshine Duration

  • Sunshine duration is the length of time the Earth’s surface is directly exposed to solar radiation.
  • It is also referred to as sunlight hours and measure the amount of exposure over a set period of time (generally in hours per day or year).
  • As already stated, sunshine duration influence other weather elements, which can change the whole makeup of the weather conditions.
  • This ability makes it a more powerful and influential factor than you might think.
  • Instrument for Measuring Sunshine :Sunshine recorders, more specifically Campbell–Stokes recorders, are the instruments used to record sunshine duration.
  • Campbell–Stokes recorders basically consist of a spherical lens that focuses sunlight on a specific type of tape to make its measurement.

Different regions of the world have differences in temperature, humidity and precipitation. These differences influence the lifestyle of the people living under different climatic conditions. To understand different climatic conditions, let us discuss the factors which cause the variations in the climate of a place or a region.

Weather Climate


Latitude or Distance from the Equator

  • The places near the equator are warmer than the places which are far away from it.
  • This is because the rays of the sun fall vertical on the equator and slanting in the temperate and polar regions.
  • The vertical rays are concentrated over a small area than the slanting one.
  • Again, the vertical rays pass through a shorter distance in the atmosphere before reaching the earth’s surface.
  • Therefore, lower the latitude higher is the temperature and vice versa.
  • Malaysia which is near the equator is warmer than England which is far away from the equator.

Altitude or the Height from the mean sea level

  • It is known that mountains are cooler than the plains.
  • Shimla situated on a higher altitude is cooler than Jalandhar, although both are almost on the same latitude.
  • The temperature decreases with the height of a place.
  • For a vertical rise of 165 metres there is an average decrease in temperature at the rate of 1°C.
  • Thus the temperature decreases with increase in height.

Continentally or the Distance from the Sea

  • The water is a bad conductor of heat i.e. it takes longer time to heat and longer time to cool.
  • Due to this moderating effect of the sea, places near the coast have low range of temperature and high humidity.
  • The places in the interior of the continent do not experience moderating effect of the sea. These places have extreme temperatures.
  • The places far from the sea have higher range of diurnal (daily) and annual temperatures.
  • Mumbai has relatively lower temperature and higher rainfall than Nagpur, although both are almost situated on the same latitude.

Nature of the Prevailing Winds

  • The on-shore winds bring the moisture from the sea and cause rainfall on the area through which they pass.
  • The off-shore winds coming from the land are dry and help in evaporation.
  • In India, the on-shore summer monsoon winds bring rains while off-shore winter monsoon winds are generally dry.

Cloud Cover

  • In areas generally of cloudless sky as in deserts, temperature even under shade are very high because of the hot day time sunshine.
  • At night this heat radiates back from the ground very rapidly.
  • It results in a large diurnal range in temperature.
  • On the other hand under cloudy sky and heavy rainfall at Thiruvananthapuram the range of temperature is very small.

Ocean Currents

  • Ocean waters move from one place to another partly as an attempt to equalize temperature and density of water.
  • Ocean currents are large movements of water usually from a place of warm temperature to one of cooler temperature or vice-versa.
  • The warm ocean currents raise the temperature of the coast and sometimes bring rainfall, while the cold currents lower the temperature and create fog near the coast.
  • Port Bergen in Norway is free from ice even in winter due to warm North Atlantic Drift while Port Quebec in Canada remains frozen during winter months due to chilling effect of the Cold Labrador Current in spite of the fact that Port Quebec is situated in much lower latitude than Port Bergen.
  • The on-shore winds passing over a warm current carry warm air to the interior and raise the temperature of the inland areas.
  • Similarly, the winds blowing over cold current carry cold air to the interior and create fog and mist.

Direction of Mountain Chains

  • The mountain chains act as natural barrier for the wind.
  • The on-shore moisture laden winds are forced to rise after striking against the mountain; and give heavy rainfall on the windward side.
  • These winds descending on the leeward side cause very low rainfall.
  • The great Himalayas check the moisture laden monsoon winds from crossing over to Tibet. This mountain chain also checks biting polar cold winds from entering into India.
  • This is the reason for which northern plains of India get rains while Tibet remains a perpetual rain shadow area with lesser amount of rainfall.

Slope and the Aspect

  • The concentration of heat being more on the gentler slope raises the temperature of air above them.
  • Its lesser concentration along steeper slopes lowers the temperature.
  • At the same time, mountain slopes facing the sun are warmer than the slopes which are away from the sun’s rays.
  • The southern slopes of Himalaya are warmer than the northern slopes.

The Nature of the Soil and Vegetation Cover

  • The nature of soil depends upon its texture, structure and composition. These, qualities vary from soil to soil.
  • Stony or sandy soils are good conductor of heat while black clay soils absorb the heat of the sun’s rays quickly.
  • The bare surface reradiates the heat easily.
  • The deserts are hot in the day and cold in the night.
  • The forest areas have lower range of temperature throughout the year in contrast to non-forested areas.