Humidity, Clouds, Precipitation and Cyclones: GK Notes

The correct answer is C, the eye. The eye of a tropical cyclone is the roughly circular column of calm, descending air at its centre, usually a few tens of kilometres across, where the pressure is lowest, the winds are light and the sky is often nearly clear. Around it stands the eye wall, a ring of tall cumulonimbus clouds carrying the strongest winds and the heaviest rain, so the passage of a cyclone over a place gives violent weather, then an interval of calm, then violent weather again from the opposite direction. Option A is wrong because base is not a term used for any part of a cyclone. Option B is wrong because focal point belongs to optics and to earthquake studies, not to meteorology. Option D is wrong because trigger point is not a recognised term in the structure of a storm.

The correct answer is B, Tauktae. Tauktae formed in the Arabian Sea in May 2021, intensified into an extremely severe cyclonic storm, moved north along the Konkan coast and made landfall in Gujarat, which is why it is remembered as an Arabian Sea system of the western coast. Option A is wrong because Vardah struck the Tamil Nadu coast near Chennai in December 2016 and came from the Bay of Bengal. Option C is wrong because Titli hit Odisha and Andhra Pradesh in October 2018, again a Bay of Bengal storm of the eastern coast. Option D is wrong because Hudhud crossed the coast at Visakhapatnam in October 2014. Note the useful contrast: the Bay of Bengal produces far more cyclones than the Arabian Sea, so an Arabian Sea landfall such as Tauktae is the one examiners pick out.

The correct answer is B. The local names of the tropical cyclone are a standing favourite: baguio belongs to the Philippines, hurricane to the United States and the wider Atlantic and Caribbean region, typhoon to China and the north-western Pacific, and willy-willy to Australia. That gives A with 3, B with 4, C with 2 and D with 1, which is option B. Option A is wrong because it pairs typhoons with Australia and willy-willies with China, reversing the last two. Option C is wrong because it begins by sending baguio to China. Option D is wrong because it pairs hurricanes with Australia and willy-willies with the United States. Add two more names to the list while revising: the storm is simply called a cyclone in the Indian Ocean and taifu in Japan.

The correct answer is B, Julia. Julia was a storm of the Atlantic basin and never approached India, so it cannot belong to a list of Indian landfalls. Option A is wrong because Yaas crossed the Odisha coast near Balasore in May 2021, only days after Tauktae struck the opposite coast. Option C is wrong because Tauktae formed in the Arabian Sea in May 2021 and made landfall in Gujarat. Option D is wrong because Gulab crossed the north Andhra Pradesh coast in September 2021 and its remnant later re-formed in the Arabian Sea as Shaheen. The point of the question is that the names of the north Indian Ocean storms come from a panel of countries of the region, so a name from the Atlantic list, where the storms are named separately, is the odd one out.

The correct answer is C, a hygrometer. A hygrometer measures the humidity of the air, and the common working form is the psychrometer, a pair of wet and dry bulb thermometers whose difference in reading is converted into relative humidity with a table. Option A is wrong because a barometer measures atmospheric pressure, the mercury barometer and the aneroid barometer being its two forms. Option B is wrong because an anemometer measures wind speed. Option D is wrong because a hydrometer, whose name differs by a single letter, measures the relative density of a liquid and has nothing to do with the atmosphere; this near-identical pair is the trap in the question. Remember the related definitions as well: air that holds all the vapour it can at a given temperature is saturated, and the temperature at which it becomes saturated is the dew point.

The correct answer is B, relative humidity. Relative humidity compares the water vapour actually present in the air with the maximum amount the air could hold at that temperature, so it is a ratio and is stated as a percentage; air at a hundred per cent relative humidity is saturated. Option A is wrong because absolute humidity is the actual weight of vapour in a given volume of air and is stated in grams per cubic metre. Option C is wrong because specific humidity is the weight of vapour in a unit weight of air, stated in grams per kilogram, and it is preferred in weather work because it does not change as the air expands or contracts. Option D is wrong because the dew point is a temperature, stated in degrees. Note also that heating air lowers its relative humidity even when no vapour has been added or removed.

The correct answer is D, cumulonimbus. The cumulonimbus is a cloud of great vertical extent that can rise from near the ground almost to the top of the troposphere, and the strong updraughts inside it produce thunder, lightning, heavy showers and hail; it is the cloud of the thunderstorm and the eye wall of a cyclone is built of such clouds. Option A is wrong because cirrus is a high, thin, feathery cloud of ice crystals that gives no rain. Option B is wrong because altostratus is a middle cloud forming a grey sheet through which the sun shows faintly. Option C is wrong because stratus is a low, uniform, layered cloud associated with drizzle and dull weather. Remember the height classes: high clouds about six to twelve kilometres, middle clouds two to six, low clouds up to two.

The correct answer is A, convectional rainfall. In the equatorial belt the ground is strongly heated through the morning, the warm moist air rises in powerful convection currents, cools as it rises, condenses into towering cumulonimbus and falls as a short, very heavy shower in the afternoon, which is why it is nicknamed four o'clock rain. Option B is wrong because orographic rainfall needs a mountain barrier to force the moist air upward, and it leaves a rain shadow on the leeward slope. Options C and D are wrong because frontal or cyclonic rainfall is produced where a warm air mass rides over a cold one along a front; it is slow, widespread and typical of temperate latitudes, as in the western disturbances that water north-west India in winter. The three types to keep apart are therefore convectional, orographic and cyclonic.

The correct answer is C. The Coriolis force, which arises from the rotation of the earth, is zero at the equator and very weak for a few degrees on either side, so converging air cannot be deflected into the spiral that makes a cyclone; the belt within about five degrees of the equator is therefore free of tropical cyclones even though it is warm. Option A is wrong because the equatorial seas are the warmest in the world, well above the twenty-seven degrees Celsius a cyclone needs. Option B is wrong because the equatorial air is the most humid on earth. Option D is wrong because the equatorial belt is a zone of rising air and low pressure, not of descending air; descending air belongs to the subtropical high-pressure belts near thirty degrees. The other conditions are a wide warm sea, weak change of wind with height and divergence aloft.

The correct answer is D. The India Meteorological Department grades a system of the north Indian Ocean by its sustained wind speed, and the highest grade, the super cyclonic storm, begins at two hundred and twenty-two kilometres per hour. Option A is wrong because sixty-two to eighty-seven kilometres per hour is the band of an ordinary cyclonic storm, the stage at which the system is given a name. Option B is wrong because eighty-eight to one hundred and seventeen kilometres per hour is a severe cyclonic storm. Option C is wrong because one hundred and eighteen to one hundred and sixty-six kilometres per hour is a very severe cyclonic storm, and the band above it, up to two hundred and twenty-one, is the extremely severe cyclonic storm. Below the storm stages lie the depression at thirty-one to forty-nine and the deep depression at fifty to sixty-one kilometres per hour.

The correct answer is A. A temperate or extra-tropical cyclone is a frontal system: it forms between about thirty-five and sixty-five degrees latitude where a cold polar air mass meets a warm subtropical one, and the warm air is forced to rise along the front, giving slow and widespread rain over a large area. Option B is wrong because the eye and the eye wall belong only to the tropical cyclone; a temperate cyclone has no eye. Option C is wrong because it is the tropical cyclone that dies quickly over land, having lost its supply of warm moist air, while a temperate cyclone travels across continents from west to east. Option D is wrong because the five-degree rule describes where tropical cyclones cannot form; temperate cyclones form far from the equator in any case, so the statement does not distinguish them.

The correct answer is B, frost. When the surface on which condensation occurs is below the freezing point and the dew point is also below it, the vapour changes directly into tiny ice crystals instead of water droplets, and that white deposit is frost; it is common on clear, calm winter nights when the ground loses heat rapidly by radiation. Option A is wrong because dew forms in the same way but when the dew point is above freezing, so the moisture settles as drops of water. Option C is wrong because fog is condensation on dust and smoke nuclei in the air near the ground, which reduces visibility sharply. Option D is wrong because mist is the thinner, less dense form of the same phenomenon, with better visibility than fog. The essential conditions for dew and frost are a clear sky, still air, high relative humidity and a cold long night.