Atmospheric Circulation and Weather Systems


1. Multiple choice questions.

(i) If the surface air pressure is 1,000 mb, the air pressure at 1 km above the surface will be:

(a) 700 mb (c) 900 mb

(b) 1,100 mb (d) 1,300 mb

Ans: (c) 900 mb

(ii) The Inter Tropical Convergence Zone normally occurs:

(a) near the Equator (b) near the Tropic of Cancer

(c) near the Tropic of Capricorn (d) near the Arctic Circle

Ans: (a) near the Equator.

(iii) The direction of wind around a low pressure in northern hemisphere is:

(a) clockwise (c) anti-clock wise

(b) perpendicular to isobars (d) parallel to isobars

Ans: (c) anti-clock wise.

(iv) Which one of the following is the source region for the formation of air masses?

(a) the Equatorial forest (c) the Siberian Plain

(b) the Himalayas (d) the Deccan Plateau

Ans: (c) the Siberian Plain.

2. Answer the following questions in about 30 words.

(i) What is the unit used in measuring pressure? Why is the pressure measured at station level reduced to the sea level in preparation of weather maps?

Ans: Pressure is measured in pascals (Pa) or millibars (mb). Weather maps use sea-level pressure for comparison, even at higher altitudes, to eliminate the effect of altitude variations and focus on weather patterns.

(ii) While the pressure gradient force is from north to south, i.e. from the subtropical high pressure to the equator in the northern hemisphere, why are the winds north easterlies in the tropics.

Ans: Two forces affect wind direction: pressure pushing south and the Coriolis effect deflecting east. The Coriolis effect wins in the tropics, bending the southwards breeze into north easterlies.

(iii) What are the geotrophic winds?

Ans: Geostrophic winds are theoretical winds blowing parallel to pressure lines (isobars) when pressure and Coriolis forces perfectly balance, providing a simplified atmospheric flow model.

(iv) Explain the land and sea breezes.

Ans: Daytime: Land heats faster, warms air, creates low pressure. Sea breeze blows from cool ocean to replace rising warm air. Nighttime: Land cools faster, high pressure forms. Land breeze blows cool air out to sea, replacing sinking warm air.

3. Answer the following questions in about 150 words.

(i) Discuss the factors affecting the speed and direction of wind.

Ans: Three main forces tango to dictate wind's speed and direction:

1. Pressure Gradient: Air rushes from high pressure (calm) to low pressure (gusty) like water downhill. Stronger gradient, faster wind.

2. Coriolis Effect: Earth's spin bends winds! In the Northern Hemisphere, it curves them right, making winds blow slightly left of the pressure gradient (e.g., northeast trade winds).

3. Friction: Ground slows down winds near the surface, like slowing down in mud. Higher altitude, less friction, stronger winds.

These forces play together, shaping wind's wild dance across the globe!

(ii) Draw a simplified diagram to show the general circulation of the atmosphere over the globe. What are the possible reasons for the formation of subtropical high pressure over 30॰ N and S latitudes?

Ans: Unfortunately, I cannot directly draw diagrams within this interface. However, I can describe a simplified diagram and explain the formation of subtropical high pressure:

Simplified diagram:

*Imagine a globe with arrows representing wind movement.

*At the equator, rising warm air from the Intertropical Convergence Zone (ITCZ) creates low pressure.

*Trade winds blow from the subtropics towards the equator (northeast in the Northern Hemisphere, southeast in the Southern).

*At approximately 30° N and S, trade winds converge and sink, creating subtropical high pressure belts.

*Sinking air warms adiabatically and becomes drier, further contributing to high pressure.

*Westerlies blow at mid-latitudes towards the east, driven by pressure differences and the Coriolis effect.

*Polar highs near the Arctic and Antarctic complete the global circulation loop.

Reasons for subtropical high pressure:

1. Convergence of trade winds: As trade winds meet at 30° N and S, they pile up, increasing air pressure.

2. Sinking air: Descending air warms and compresses, further elevating pressure.

3. Adiabatic warming: Sinking air warms without exchanging heat, enhancing the high pressure zone.

4. Diverging air: Sinking air spreads out at the surface, contributing to lower pressure elsewhere, further strengthening the high pressure belt.

    Remember, this is a simplified picture, and real-world circulation involves complex interactions and seasonal variations.

(iii) Why does tropical cyclone originate over the seas? In which part of the tropical cyclone do torrential rains and high velocity winds blow and why?

Ans: Origin over seas:

*Warm water: Cyclones need sea surface temperatures above 26°C to fuel evaporation and release energy. Cold land cannot provide enough heat.

*Low pressure: Warm water evaporates readily, creating low pressure systems that are prime environments for cyclone formation.

Winds and rain:

*Eye wall: This swirling ring surrounding the calm eye has the highest wind speeds due to intense rising warm air and condensation.

*Spiral bands: Rain and gusty winds occur in these bands formed by rising moist air, cooling, condensing, and releasing latent heat.

In short: warm seas provide fuel, low pressure is the starting point, and the eye wall and spiral bands are the engines of wind and rain in tropical cyclones.




Answer Type By:k Himashree Bora.