Atmosphere: Air Masses, Fronts, and Tropical Cyclones

The Earth’s atmosphere is a dynamic and interconnected system, where various components work in harmony to shape our weather patterns. Among the key players in this atmospheric ballet are air masses, fronts, tropical cyclone, thunderstorms, and tornadoes. Each element contributes to the intricate dance of atmospheric circulation, influencing the climate and weather conditions we experience.

Air Masses: Exploring the Link to Tropical Cyclones

• Definition: The air with distinctive characteristics in terms of temperature and humidity and having a large body of air with little horizontal variation is called an air mass.
• Source Regions: These are the homogeneous surfaces, over which air masses form. Air Masses are classified on the basis of source regions as follows:
  • Warm tropical and subtropical oceans
  • The subtropical hot deserts
  • The relatively cold high latitude oceans
  • The very cold snow covered continents in high latitudes
  • Permanently ice covered continents in the Arctic and Antarctica
• Accordingly, following types of air masses are recognised:

(i) Maritime tropical (mT); 

(ii) Continental tropical (cT);

(iii) Maritime polar (mP); 

(iv) Continental polar (cP);

(v) Continental arctic (cA).

Fronts: Exploring the Dynamics with a Tropical Cyclone Twist

• Frontogenesis: When two distinct air masses converge, the region where they meet is termed a front, and this formation process is called frontogenesis. 
  • Location: These fronts, typically found in mid-latitudes, feature sharp temperature and pressure gradients, resulting in sudden temperature shifts and the ascent of air to create clouds and precipitation.
• Types of Fronts:
• Stationary Front: When a front doesn’t move, it’s termed a stationary front. 
• Cold and Warm Front: When cold air advances toward warm air, it’s a cold front.
• • When warm air advances toward cold air, it’s a warm front. 
• Occluded Front: If an air mass is lifted entirely off the land surface, it’s known as an occluded front.

Extra Tropical Cyclones: Beyond the Tropics Cyclones

• The systems developing in the mid and high latitude, beyond the tropics are called the middle latitude or extra tropical cyclones.
• Process of Formation:
  • As the pressure drops along the polar front, the warm air (coming from south) moves northwards and the cold air (coming from north) moves towards south setting in motion an anticlockwise cyclonic circulation.
  • This cyclonic circulation leads to a well developed extra tropical cyclone, with a warm front and a cold front.
  • The warm air glides over the cold air and a sequence of clouds appear over the sky ahead of the warm front and cause precipitation.
  • As the cold front pushes the warm air up completely the front gets occluded and the tropical cyclone dissipates.

Tropical Cyclones: Unleashing the Power of Tropical Cyclones

• Meaning: Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas.
• Characteristics: This is one of the most devastating natural calamities as they bring about large scale destruction caused by violent winds, very heavy rainfall and storm surges.
• Nomenclature: They are known as Tropical Cyclones in the Indian Ocean, Hurricanes in the Atlantic, Typhoons in the Western Pacific and South China Sea, and Willy-willies in the Western Australia.
• The conditions favorable for the formation and intensification of tropical storms are:

(i) Large sea surface with temperature higher than 27° C;

(ii) Presence of the Coriolis force;

(iii) Small variations in the vertical wind speed; 

(iv) A pre-existing weak low-pressure area or low-level-cyclonic circulation;

(v) Upper divergence above the sea level system.

• • The condensation process in the towering cumulonimbus clouds, surrounding the center of the storm along with continuous supply of moisture from the sea keep feeding the storm’s intensity.

• Once a tropical cyclone reaches the land the moisture supply is cut off and the storm dissipates this phenomenon is called the landfall of the tropical cyclone.
• A schematic representation of the vertical structure of a mature tropical cyclonic storm is shown in figure.
  • Strong spirally circulating wind around the center is called the eye, which is a region of calm with subsiding air.
  • Around the eye is the eye wall, where there is a strong spiraling ascent of air reaching a velocity of 250 km/hr resulting in torrential rains.

Thunderstorms, Tornadoes, and Atmospheric Turmoil

Thunderstorms and tornadoes are brief but highly destructive, typically limited to a small area.

• Thunderstorms: Thunderstorms result from intense convection during hot, humid conditions, featuring mature cumulonimbus clouds that produce thunder and lightning. 
  • When these clouds reach altitudes with sub-zero temperatures, hailstones form and fall as hailstorms. 
  • In cases of limited moisture, thunderstorms can create dust storms.
  • Thunderstorms are identified by strong updrafts of warm, rising air, causing cloud growth and increased altitude, resulting in precipitation.
• Tornadoes:
  • Sometimes severe thunderstorms generate a spiraling wind with very low pressure at the center that descends like the trunk of an elephant, causing massive destruction on its way. 
  • Such a phenomenon is called a tornado.
  • Location: Tornadoes generally occur in middle latitudes. 
  • The tornados over the sea are called waterspouts.

Atmospheric circulation and weather systems are intricately connected, driving the complex dynamics of our planet’s climate. The movement of air masses, the formation of pressure systems, and the interaction of various factors like temperature, humidity, and geography all play crucial roles in shaping our weather patterns. Understanding these processes is essential for meteorologists and climate scientists to predict and study weather events, from the daily forecast to severe storms and long-term climate trends.

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