MGG 005 Solved Guess Paper 2026 for IGNOU Climatology, Master of Science in Geography (MSCGG)

Vertical layers of the atmosphere by thermal properties

Question: Give a detailed description of the vertical layers of the atmosphere based on thermal properties, with a suitable diagram.

On thermal characteristics, the atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere and exosphere. The file pairs this answer with a temperature-altitude diagram.

1. Troposphere: The lowest layer. It holds three-fourths of the gaseous mass and almost all water vapour and dust. It was named by Teisserenc de Bort; "tropos" means mixing. All weather happens here. Temperature falls 6.5°C per 1000 m, the normal lapse rate. Its height is about 8 km at the poles and 16 km at the equator.
2. Tropopause: The top boundary of the troposphere, named by Sir Napier Shaw. Temperature here is about −50°C to −60°C, and it is coldest over the equator.
3. Stratosphere: From about 12 km to 50 km. It is stable, so aeroplanes fly here. Up to about 25 km it is isothermal. Above that, temperature rises to about 0°C at 50 km because ozone (15 to 35 km) absorbs UV rays.
4. Mesosphere: From 50 km to 80 km. Temperature falls with height and reaches about −100°C at the mesopause. Noctilucent clouds are seen here and meteors burn up.
5. Thermosphere: Above the mesopause. Its lower part (100 to 400 km) is the ionosphere, which reflects radio waves. Temperature rises sharply, but the air is so thin that the heat is not felt.
6. Exosphere: The outermost layer (500 to 1000 km), made mainly of hydrogen and helium.

Conclusion: Temperature falls in the troposphere, rises in the stratosphere, falls in the mesosphere and rises again in the thermosphere. This zig-zag is the key to the answer.

Coriolis force and the movement of prevailing winds

Question: Define Coriolis force. Explain how it influences the movement of prevailing winds. Support your answer with a neat sketch.

Coriolis force is the apparent deflection of moving air caused by the earth's rotation. It was first described by the French physicist G.G. Coriolis. On a non-rotating earth, winds would blow straight from high to low pressure; because the earth rotates, they follow curved paths. Wind direction is set by three forces: pressure gradient, Coriolis force and friction.

1. Direction: Winds turn to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. This is Ferrel's law.
2. Speed: Higher wind speed gives more deflection; lower speed gives less.
3. Latitude: Deflection is maximum at the poles and absent at the equator.
4. Trade winds: Air moving towards the equator turns and becomes the North-East and South-East Trades.
5. Westerlies: Air moving poleward turns and blows from the south-west in the north and the north-west in the south.
6. Geostrophic wind: When pressure gradient and Coriolis force balance, winds blow parallel to the isobars.

Sketch in the file: a globe showing the intended path and the actual deflected path in each hemisphere, with no deflection at the equator.

Conclusion: Coriolis force does not start the wind; it only turns it. That is why planetary winds blow diagonally.

Air masses: source regions, characteristics and classification

Question: Define air mass. List the major source regions of air masses. Discuss the characteristics of major air masses and their classification.

An air mass is a huge body of air whose temperature and humidity are more or less uniform horizontally (Petterssen). Critchfield and Trewartha and Horn give similar definitions. A cold air mass is colder than the surface below it; a warm air mass is warmer.

Source regions are large, uniform surfaces of land or ocean: maritime polar (mP) over oceans near 60°N and 60°S; continental polar (cP) over polar lands with intense winter cold; maritime tropical (mT) over tropical oceans; and continental tropical (cT) over tropical continents, mainly Asia and North Africa. Maritime equatorial (mE) air also forms all year at the ITCZ.

1. Continental polar: Forms over northern Canada and Siberia. Cold, dry and stable; it brings cold waves.
2. Maritime polar: Polar air that moves over warmer oceans. Its lower part is heated and turns unstable, giving rain on windward slopes.
3. Continental tropical: Forms over hot deserts at 20° to 30°. Very hot, very dry and stable; it rarely leaves its source.
4. Maritime tropical: Forms over warm oceans between 30°N and 30°S. Warm, moist and unstable; it gives heavy rain with fronts or mountains.

Classification: geographical (Trewartha) gives four types, cP, mP, cT and mT; thermodynamic adds cold (k) and warm (w) for eight types; composite adds stable (s) and unstable (u) for sixteen types, such as cPks and mTwu.

Conclusion: An air mass takes its character from its source region. Remember 4 geographical, 8 thermodynamic and 16 composite types.

Koppen's climatic types and the 'A' group in detail

Question: Mention the broad climatic types given by Koppen. Discuss in detail the 'A' type of climate and its sub-types given by Koppen.

Wladimir Koppen (1846 to 1940), a German botanist and climatologist, believed vegetation is the best expression of climate. He gave his first scheme in 1900, revised it in 1918 and produced a world map in 1931. His system is quantitative and empirical, built on monthly temperature and precipitation.

Five groups: A tropical rainy (megatherms), B dry (xerophytes), C warm temperate rainy (mesotherms), D cold forest (microtherms) and E polar (hekistotherms). A, C, D and E rest on temperature; B rests on the precipitation-evaporation ratio.

1. Af, tropical rainforest: The driest month gets 6 cm or more of rain, with no dry season and very low temperature ranges.
2. Aw, tropical savanna: Wet summer, dry winter; at least one month gets less than 6 cm.
3. Am, tropical monsoon: Total rain like Af, seasonal pattern like Aw; a short dry season but enough rain for dense forest.
4. As, tropical dry summer: Rare. In India it occurs on coastal Tamil Nadu, where rain falls mainly in winter.

Separating Am and Aw: a = 10 − R/25, where a is the rain of the driest month and R is annual rain in cm. For R = 200 cm, a = 2 cm; below that the climate is Aw.

Conclusion: Koppen gave five groups, A to E. Group A has four sub-types separated by the rain of the driest month.

Weather forecasting: significance, types and methods

Question: What is weather forecasting? Discuss its significance and its types based on different time scales. Discuss the methods of weather forecasting.

Weather forecasting is the prediction of air temperature, humidity, sky conditions, pressure and circulation for a place or region, using scientific tools and statistical techniques. It matters for tourism, fishing, sports and above all agriculture, from sowing and irrigation to harvesting and storage.

Types by time scale: long range (a fortnight to a season, for monsoon estimates), medium range (3 days to 3 weeks, for farming and floods), short range (a few hours to 72 hours, very accurate) and nowcast (a few hours, for cyclone and thunderstorm warnings).

1. Persistence method: Today equals tomorrow. It works where weather changes little.
2. Trends method: A cyclone 1500 km away moving at 300 km a day arrives in five days.
3. Climatology method: Uses the long-term average for that place and date.
4. Analog method: Finds a past day with a similar pattern; a perfect analog is rare.
5. Numerical weather prediction: Equations run on supercomputers; the most accurate method.

Conclusion: Forecasting has four time-scale types and five main methods. NWP is the most accurate and persistence the simplest.