Atmospheric Stability Questions and Answers

Answer: C

Cloud suppresses both the daytime heating and the nocturnal cooling, and strong wind generates mechanical turbulence, so the profile approaches neutral and class D applies day or night. This is the most predictable dispersion regime and the one for which the classical formulae work best. Class A requires strong sunshine and light wind. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: D

Light winds with a strong inversion give minimal dilution in both the vertical and the horizontal, so concentrations from ground level sources such as traffic build up over many hours. Winter anticyclonic episodes combine both conditions. Unstable classes give high but brief peaks rather than the sustained accumulation that damages health. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

A ground level release in a shallow stable layer is confined to that layer and accumulates, whereas an elevated release fans out aloft and reaches the ground only weakly. This is why urban roadside concentrations peak on calm winter mornings. The contrast between ground level and elevated sources under stable conditions is the central practical result of dispersion meteorology. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: B

Vertical mixing through a deep layer combined with horizontal ventilation gives the greatest dilution, which is why air quality is best in unsettled windy weather. Anticyclonic conditions with subsidence and light winds are precisely the worst case. This inverse relationship between pleasant weather and good air quality is a recurring public communication difficulty. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: C

Cold air drains into the valley and is trapped beneath the inversion, so the effective mixing depth is even smaller than over flat terrain and pollutants accumulate for days. Alpine valleys and Mexico City suffer for exactly this reason. Foehn events can flush the pool out, which is one of the few natural clearance mechanisms available. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: D

Only a substantial change in the synoptic flow, bringing strong wind or warm descending air aloft, can scour out a well established cold pool, and radiative processes alone tend to reinforce it. Fog makes matters worse by reflecting sunlight. Cold pools in deep basins have persisted for weeks in extreme cases.

Answer: A

The ventilation coefficient is the product of the mixing depth and the transport wind, giving a measure of the volume of air available per unit time to dilute the emissions. Low values indicate poor dispersion and are used to issue air quality warnings. It combines the two independent controls in a single index, which is why it is preferred to either alone. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: B

Snow has a high albedo, so it absorbs little solar radiation, and a high emissivity, so it radiates efficiently at night, and its low conductivity insulates it from the ground beneath. The combination produces extremely strong surface inversions and the lowest temperatures recorded on the continents. Reflection cools rather than warms the surface. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: C

The Antarctic plateau combines high altitude, continuous darkness, extreme dryness and a snow surface, and satellite measurements have recorded surface temperatures below minus 90 degrees. Vostok holds the air temperature record at minus 89.2 degrees. The Siberian record of about minus 68 degrees is the northern hemisphere extreme.

Answer: D

Water vapour is the principal source of downward long wave radiation, so extremely dry air returns very little energy to the surface and allows it to cool far below what a moist atmosphere would permit. This is why deserts and polar plateaus both show extreme nocturnal cooling. Sublimation is far too slow to contribute measurably.