Question 1

If an area has surface low pressure and upper-level divergence, why can the system intensify?

Accepted Answer

Upper-level divergence removes rising air and helps maintain surface convergence. In a developing low-pressure system, air converges near the surface and rises. If winds diverge at upper levels, they carry away the air that has risen. This removal prevents excessive accumulation aloft and allows continued surface convergence and ascent. The surface pressure can therefore fall further, strengthening the low and often increasing cloud development and storm activity.

Question 2

What inference does the ideal gas idea give about air temperature and pressure?

Accepted Answer

At constant volume, pressure may rise with temperature, but in the open atmosphere expansion and density changes are also important The ideal-gas relation pV = nRT shows that pressure, volume, temperature, and the amount of gas are linked. If volume and mass remain fixed, increasing temperature raises pressure. However, the atmosphere is open and mobile: heated air expands, becomes less dense, and may rise or be replaced. Consequently, surface pressure does not necessarily increase every time temperature rises, making option A the most accurate statement.

Question 3

What caution should be taken while explaining surface pressure when an air column contains more water vapour?

Accepted Answer

Pressure should not be inferred from humidity alone; temperature and vertical motion should also be considered Water vapour has a lower molecular mass than dry-air gases such as oxygen and nitrogen, so moist air can be less dense at the same temperature and pressure. However, a surface pressure observation depends on the weight of the entire air column, temperature structure, altitude, and vertical motion. Therefore, humidity alone cannot determine whether pressure will rise or fall; the other atmospheric conditions must also be examined.

Question 4

In which situation can falling surface pressure indicate an increasing possibility of bad weather soon?

Accepted Answer

When pressure is falling and moist-air convergence is increasing Falling surface pressure often indicates that air is converging toward a developing low-pressure system or that upward motion is increasing. If the converging air is moist, it can rise, cool adiabatically, reach saturation, and form clouds and precipitation. Pressure fall alone is not a complete forecast, but combined with moisture convergence it is a useful warning of unsettled or stormy weather.

Question 5

In a high-pressure centre, what upper-air process is generally associated with maintaining surface divergence?

Accepted Answer

Subsidence, or sinking of air from above In a high-pressure system, air commonly subsides from the upper troposphere toward the surface. On reaching lower levels, it spreads outward, producing surface divergence. This descending air also warms by compression and tends to reduce cloud formation, which is why anticyclones are often associated with stable and clearer weather. The complete circulation includes upper-level convergence and downward motion, not disappearance of air.

Question 6

If isobars change from 1016 hPa to 1000 hPa within 200 km, what would characterize this area?

Accepted Answer

Fairly steep pressure gradient and possibility of strong wind The pressure difference is 16 hPa, calculated as 1016 minus 1000, across only 200 km. A large pressure change over a short horizontal distance produces a steep pressure gradient. The pressure-gradient force drives air from higher toward lower pressure, and, with other conditions suitable, it can produce strong winds. Therefore, option B is correct.

Question 7

What is the main difference between thermal low pressure and dynamic low pressure?

Accepted Answer

Thermal low mainly forms by surface heating while dynamic low may form by convergence in circulation A thermal low develops primarily because intense surface heating warms the air, lowers its density, and encourages rising motion. A dynamic low is produced mainly by atmospheric circulation, such as convergence near the surface or divergence aloft, which causes air to rise and pressure to fall. Thus the essential difference is the dominant cause of formation, making option A correct.

Question 8

Why can pressure reduced to sea level be higher than actual station pressure?

Accepted Answer

Because calculation adds an imaginary air column from the station down to sea level Station pressure is the pressure actually measured at the station’s elevation. To compare observations from places at different heights, meteorologists reduce the value mathematically to mean sea level by estimating the pressure exerted by the air column between the station and sea level. Since pressure normally increases downward, this reduced sea-level value can be higher than the measured station pressure. Option A is correct.

Question 9

Why is cold, dry air at the same altitude more likely to have higher pressure?

Accepted Answer

It is denser and contains more air mass per unit volume At the same altitude, colder air is generally denser because its molecules move less vigorously and occupy less volume. Dry air is also denser than equally warm, moist air because water vapour has a lower molecular mass than the main gases of dry air. The greater density means more mass is concentrated in a given volume, favouring higher surface pressure. Therefore, option A is correct.

Question 10

Why does the human body feel oxygen shortage at high altitude even though the percentage of oxygen in air may remain nearly the same?

Accepted Answer

Because total air pressure and partial pressure of oxygen decrease The proportion of oxygen in dry atmospheric air remains close to 21 percent through the lower atmosphere, but total atmospheric pressure decreases with altitude. Oxygen partial pressure equals its fraction multiplied by total pressure, so its partial pressure also falls. Consequently, each breath contains fewer oxygen molecules and diffusion into the blood becomes less effective. Option A is correct.

Question 11

Why do pressure belts appear more broken over continents?

Accepted Answer

Because of unequal thermal behaviour of continents and oceans Ideal pressure belts are shown as broad, continuous zones arranged mainly according to latitude. In reality, continents heat and cool more rapidly than oceans, while landforms, seasonal contrasts, and unequal surface conditions modify air temperature and circulation. These regional differences distort and split the ideal belts, making them appear discontinuous over land. Thus, option A gives the correct explanation.

Question 12

What is the physical reason for the boiling point of water decreasing when atmospheric pressure decreases?

Accepted Answer

At lower external pressure it becomes easier for vapour pressure to equal it Boiling begins when the vapour pressure of a liquid becomes equal to the pressure exerted by the surrounding atmosphere. If external atmospheric pressure is lower, water needs to reach a lower temperature for its vapour pressure to match that pressure. Consequently, water boils at a lower temperature at high altitudes, although cooking may take longer because the boiling water is cooler. Option A is correct.

Question 13

Which statement gives the most integrated description of factors affecting atmospheric pressure?

Accepted Answer

Atmospheric pressure changes due to the combined effect of altitude, temperature, humidity, gravity, and air circulation Atmospheric pressure is not controlled by a single variable. It generally decreases with altitude, changes with temperature because warm and cold air have different densities, and is influenced by humidity because water vapour is lighter than dry air. Gravity determines the weight of the air column, while horizontal and vertical circulation redistribute air mass. Therefore, option C provides the most complete description.

Atmospheric pressure and factors affecting it

Practice questions

01 If an area has surface low pressure and upper-level divergence, why can the system intensify?

02 What inference does the ideal gas idea give about air temperature and pressure?

03 What caution should be taken while explaining surface pressure when an air column contains more water vapour?

04 In which situation can falling surface pressure indicate an increasing possibility of bad weather soon?

05 In a high-pressure centre, what upper-air process is generally associated with maintaining surface divergence?

06 If isobars change from 1016 hPa to 1000 hPa within 200 km, what would characterize this area?

07 What is the main difference between thermal low pressure and dynamic low pressure?

08 Why can pressure reduced to sea level be higher than actual station pressure?

09 Why is cold, dry air at the same altitude more likely to have higher pressure?

10 Why does the human body feel oxygen shortage at high altitude even though the percentage of oxygen in air may remain nearly the same?

11 Why do pressure belts appear more broken over continents?

12 What is the physical reason for the boiling point of water decreasing when atmospheric pressure decreases?

13 Which statement gives the most integrated description of factors affecting atmospheric pressure?

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