12 Topics.
0 of 33 Concepts Done
Asked in UPSC PrelimsUPSC 2001
What to Study: What is atmospheric pressure, and in which unit is it expressed? Remember the average value at sea level and the two barometers used to measure it. Understand why air near the surface is denser and so has higher pressure.
What to Study: How fast does pressure fall as one goes up in the lower atmosphere, and does it fall at the same rate everywhere? Remember the approximate rate and the rough pressure at 1 km, 5 km and 10 km in a standard atmosphere. You should be able to apply the rate to a simple case.
What to Study: The pressure gradient upward is much larger than the one along the ground. Why, then, do we not feel strong upward winds? Understand how gravity balances it.
What to Study: Be clear about what isobars are. Why is pressure measured at a station reduced to sea level before it is shown on weather maps? Understand why even small pressure differences matter for wind direction and speed.
What to Study: How do a low-pressure system and a high-pressure system look on a map of isobars? Remember where the lowest and the highest pressure lie in each.
Asked in UPSC PrelimsUPSC 2002UPSC 2007UPSC 2011
What to Study: Remember the four pressure belts from the equator to the poles, whether each is high or low, and its approximate latitude. Remember the other name for the equatorial low and the weather it brings. Why are these belts neither permanent nor continuous?
What to Study: Which pressure belts arise from heating and cooling of the surface (thermal), and which from the movement of air (dynamic)? Remember how many belts are usually counted and how they divide between the two kinds.
What to Study: Why do the pressure belts move during the year, and in which direction in each season of the northern hemisphere? Understand where they lie at the equinoxes and roughly how far they shift. How does this shift cause the winter rain of the Mediterranean latitudes (about 30° to 45°)?
What to Study: Which three forces act on horizontal winds near the surface, and where does gravity come in? Understand how these forces together decide wind speed and direction.
What to Study: What is the pressure gradient? Understand how the spacing of isobars shows whether it is strong or weak, and how this force sets both the speed and the direction of wind. In what direction does it act in relation to the isobars?
What to Study: Where is friction greatest, and up to roughly what height does it matter? Why is it minimal over the sea, and why are winds faster over oceans than over land? Understand why winds a few kilometres up are free of friction.
Asked in UPSC PrelimsUPSC 2005UPSC 2010UPSC 2024
What to Study: What causes the Coriolis force? Remember the direction of deflection in each hemisphere. How does the force change with latitude, where is it strongest and where is it absent? Understand how wind speed affects it, why it changes only direction and not speed, and why it is called an apparent force.
What to Study: Why does a low-pressure area at the equator fill up instead of deepening? Understand what happens to the Coriolis force there, and how the wind then crosses the isobars. Roughly how far from the equator do cyclones usually form, and are there rare exceptions?
What to Study: Under what conditions does a geostrophic wind form, and which two forces are in balance? Remember how it blows in relation to the isobars. Why is it found only above the layer where friction acts, and why can it not form at the equator?
Asked in UPSC PrelimsUPSC 2001UPSC 2002
What to Study: Which pressure condition gives cyclonic circulation and which gives anticyclonic circulation? Remember the direction of rotation of each in the northern and southern hemispheres. Why are the winds in the tropics north-easterlies, even though the pressure gradient points from north to south?
What to Study: What happens to air above a low and above a high? Understand how eddies, convection, orographic uplift and fronts also make air rise, and why rising air is needed for clouds and rain.
What to Study: Remember the five factors on which the pattern of planetary winds depends. Understand what keeps the circulation going, and how it sets ocean water moving.
Asked in UPSC PrelimsUPSC 2015
What to Study: Why does air rise at the Inter Tropical Convergence Zone (ITCZ), and how does the Hadley cell close? Explain the two reasons for the formation of the subtropical high near 30° N and S. Where does the ITCZ normally lie?
What to Study: Where do the Ferrel cell and the polar cell lie, and where does air rise and sink in each? Remember the surface wind that goes with each cell. Why is the Ferrel cell called less well defined than the other two?
Asked in UPSC PrelimsUPSC 2000UPSC 2011UPSC 2015
What to Study: Remember for each planetary wind the belt it blows from, the belt it blows towards and its direction. What did the word "trade" originally mean, and why does it suit a steady wind? Remember the nicknames of the strong westerlies in the southern hemisphere, and explain why those westerlies are stronger there.
Asked in UPSC PrelimsUPSC 2020
What to Study: What are jet streams, and at what height do they blow? Distinguish the polar and subtropical jets by latitude, and the permanent jets from the temporary ones (Tropical Easterly and Somali). Understand their effect on storms, aviation, the Indian monsoon and western disturbances.
What to Study: What are Rossby waves, and what is the polar vortex? Understand how a weak, wavy jet stream can let cold polar air move into lower latitudes. Is the link between climate change and weaker jet streams settled, or still being studied?
What to Study: How do large-scale winds start ocean currents? Understand what the oceans give back to the air, and why this exchange is slow.
Asked in UPSC PrelimsUPSC 2002UPSC 2010UPSC 2011UPSC 2017
What to Study: What is El Niño? What happens to the trade winds, which way does the warm water move across the Pacific, and what happens to the cold upwelling off Peru? Why is the warming of the Pacific so important for the general circulation of the atmosphere?
Asked in UPSC PrelimsUPSC 2002
What to Study: What is the Southern Oscillation, and over which regions do its pressure changes occur? Distinguish El Niño, the Southern Oscillation and ENSO from one another.
What to Study: In a strong El Niño year, what happens to the weather in the arid west coast of South America, Australia, India and China? Does the Indian monsoon always fail in such years? Understand why ENSO is closely watched and how it helps long-range forecasting.
Asked in UPSC PrelimsUPSC 2011
What to Study: What is La Niña? Distinguish it from El Niño in sea surface temperatures in the Pacific and in the strength of the trade winds. What is its usual effect on the Indian monsoon?
What to Study: Remember the classes of winds (planetary, seasonal, diurnal and local) with one example of each. By what rule is a wind named: by the direction it blows from, or the direction it blows towards?
Asked in UPSC PrelimsUPSC 2014
What to Study: Why does the wind pattern change with the seasons, and where is the change most strongly felt? Understand the idea of seasonal reversal of winds. The detailed mechanism of the Indian monsoon is not needed here.
What to Study: Explain how uneven heating of land and sea gives a sea breeze by day and a land breeze by night. Be clear about the pressure difference that drives each.
What to Study: How do slope winds blow by day and by night? Distinguish the valley breeze from the mountain wind. What is a katabatic wind, and where does it come from?
What to Study: How does air lose its moisture on the windward side of a range, and why does it become warm and dry as it comes down the other side? Understand why such winds can melt snow quickly. Remember the Foehn and the Chinook as examples.
Asked in UPSC PrelimsUPSC 2001UPSC 2006
What to Study: Remember, for each of these winds, the region where it blows and its character (hot or cold, dry or moist): Chinook, Foehn, Sirocco, Khamsin, Harmattan, Mistral, Bora, Loo, Santa Ana and Bise.