Aviation Meteorology: Indian Climatology for the DGCA Paper

DGCA Meteorology does not stop at generic theory. A chunk of the paper draws directly on how weather behaves over the Indian subcontinent, because that is the environment you will actually be dispatching and flying in. This guide walks through the seasonal systems that matter most for the exam: the two monsoons, western disturbances and the fog they leave behind, pre monsoon thunderstorm activity, tropical cyclones on both coasts, and local wind effects at coastal and hilly aerodromes. We close with a full worked example reasoning through a fog formation scenario the way an examiner expects you to.

Why India specific climatology matters

Global meteorology theory explains the mechanisms, adiabatic cooling, pressure gradients, moisture condensation. Indian climatology tells you when and where those mechanisms actually produce hazards over Indian aerodromes. A CPL candidate needs both, and DGCA questions frequently blend them, describing a scenario (clear winter night, calm wind, high humidity) and asking you to identify the resulting phenomenon (radiation fog) or the month it is most likely (December to January), or a scenario over the Bay of Bengal in October and asking what hazard is developing (tropical cyclone).

India's climatological seasons

The two monsoon systems

India experiences two monsoon systems in a year, and DGCA candidates sometimes only remember the summer one.

The southwest monsoon

This is the main monsoon, arriving as a moisture laden southwesterly flow off the Arabian Sea. It makes landfall over Kerala typically around the last week of May or the first week of June, then advances northward across the country over the following weeks, usually covering the whole country by early to mid July. It brings widespread cloud, sustained rain, embedded thunderstorms and reduced visibility across most Indian aerodromes through to September, with monsoon depressions forming over the Bay of Bengal periodically and tracking inland, intensifying rainfall along their path.

The northeast monsoon

After the southwest monsoon withdraws, usually completing its retreat by around mid October, a reversed flow sets in: dry, cool, northeasterly winds off the Asian landmass. Over most of India this brings dry weather, but as this flow crosses the Bay of Bengal it picks up moisture and delivers a distinct rainy season to Tamil Nadu, coastal Andhra Pradesh and parts of Sri Lanka from October to December. This period also overlaps with peak cyclone season in the Bay of Bengal, so the northeast monsoon and cyclone risk are often tested together.

Western disturbances and north India winter fog

A western disturbance is an extratropical low pressure system that originates over the Mediterranean or Caspian region and tracks eastward across Iran, Pakistan and into north India, mainly during the winter months. As it approaches, it brings increased cloud, a chance of rain or snow over the western Himalaya, and a temporary rise in low level wind. Once it passes and clears out, it typically leaves calm, clear, cold conditions behind it, and this post frontal calm clear state is exactly the setup that produces radiation fog over the Indo Gangetic plain the following night or two.

Radiation fog needs four ingredients together: a clear sky (so the ground radiates heat away efficiently), light or calm wind (so the cooled air near the surface does not mix upward), high relative humidity (so the air is close to saturation already), and a long night (so there is enough time for the ground and the air layer above it to cool to the dewpoint). North India's winter nights are long, skies are often clear after a western disturbance clears, and humidity tends to be high after recent rain or under a moist low level layer, which is why Delhi and the surrounding plain see persistent dense fog disrupting flight operations from late November through January, peaking in December and early January.

Pre monsoon thunderstorms and squall lines

In the weeks before the southwest monsoon arrives, strong surface heating over land builds intense instability, and this produces some of the most violent convective weather of the Indian year. Over eastern India, particularly West Bengal, Bihar, Odisha and Assam, this appears as nor'westers, severe thunderstorms that develop through the afternoon and evening and move from the northwest, often bringing squall line gusts, hail and heavy rain with very little warning. Over the northwest plains, the same instability more often produces dust storms and dry thunderstorms with strong gust fronts but comparatively little rain. Both patterns are hazardous to aircraft on approach and departure because of the sudden wind shear and turbulence a squall line's gust front produces, and DGCA questions on this topic usually test recognising the gust front's arrival as a wind shift and temperature drop that precedes the rain itself.

Tropical cyclones on both coasts

India's two coastlines both see tropical cyclones, but with different frequency and timing. The Bay of Bengal, on the east coast, produces roughly four times as many cyclones as the Arabian Sea on the west coast, partly because of warmer sea surface temperatures and a more favourable monsoon trough position. Cyclone activity on both coasts has two peak windows: the pre monsoon period from April to June, and the post monsoon period from October to December, with the post monsoon window generally producing the more frequent and intense systems, particularly over the Bay of Bengal. Cyclones bring extreme wind, torrential rain and often force complete closure of coastal aerodromes for the duration of landfall and its immediate aftermath, so a candidate should be able to identify the coast, the likely months, and the operational response (airport closure, diversion planning) associated with a described cyclone scenario.

Local wind effects

Land and sea breeze

At coastal aerodromes such as Mumbai, Chennai and Goa, differential heating between land and sea produces a daily wind cycle. During the day, land heats faster than the adjacent sea, air rises over land and is replaced by cooler air flowing in from the sea, giving a sea breeze that typically sets in through the late morning and strengthens into the afternoon. At night the reverse happens, land cools faster than the sea, and a weaker land breeze flows from land to sea, usually developing after midnight and through the early morning. These are shallow, locally confined winds, but they routinely determine runway in use at coastal airports and can arrive as a sudden wind shift that catches an unprepared approach.

Mountain and valley winds

At hill aerodromes such as those in the Himalayan foothills, slopes heat during the day and generate an upslope, up valley wind called an anabatic wind. At night, slopes cool faster than the valley floor and cold air drains downhill as a katabatic, down valley wind. These local winds can be strong enough to matter for approach and departure planning at valley airports, particularly where terrain also channels the flow along the valley axis, and DGCA occasionally tests the correct terminology (anabatic for upslope daytime flow, katabatic for downslope nighttime drainage) rather than the operational detail itself.

Worked example: reasoning through a fog formation scenario

Evening conditions at Delhi (VIDP), 18 December:
Sky: clear, no cloud
Wind: 03 knots, becoming calm after sunset
Relative humidity: 85 percent at 1800 local
Temperature: 14C, dewpoint: 11C at 1800 local
Forecast overnight low: 6C
Sunset 1730 local, sunrise 0715 local (long winter night)

Exam tips for climatology questions

• Learn the four fog ingredients as a set (clear sky, light or calm wind, high humidity, long night) rather than in isolation, since scenario questions test whether you can spot all four together.
• Keep the two monsoons straight: southwest monsoon is the main summer rain system arriving via Kerala, northeast monsoon is the dry winter flow that turns wet only over the southeast coast.
• Remember which coast sees more cyclones (Bay of Bengal, east coast) and the two peak windows (April to June, October to December), since this is a frequently repeated question shape.
• Distinguish western disturbances (a winter, extratropical system from the west that often precedes fog) from monsoon depressions (a summer, tropical system from the Bay of Bengal).
• Know the correct terms for local winds: sea breeze and land breeze for coastal daily cycles, anabatic and katabatic for mountain slope flows.

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AviationGrade editorial team

From India Meteorological Department climatology and ICAO Annex 3

We build the DGCA question banks these guides link to. Corrections welcome and credited.