Atmospheric Stability Questions and Answers

Answer: B

The Brunt Vaisala or buoyancy frequency has a square proportional to the vertical gradient of potential temperature, and its value near 0.01 per second in the troposphere corresponds to a period of about ten minutes. The inertial frequency involves rotation instead and gives a period of seventeen hours at mid-latitudes. Both appear together in the dispersion relation for inertia-gravity waves. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: C

A superadiabatic layer is unstable, a dry adiabatic layer neutral, an isothermal layer stable and an inversion the most stable of all, giving 3, 2, 1, 4. Laying the four out along a single axis of lapse rate makes the classification immediate, and each has a characteristic appearance on a sounding that can be recognised at a glance.

Answer: D

Convective instability requires an unstable stratification, Kelvin-Helmholtz instability requires shear sufficient to overcome a stable one, and symmetric instability requires a slanted displacement in a rotating baroclinic flow. Each produces a characteristic structure, respectively cells, billows and bands, which is how they are identified in observations. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: A

Stable stratification suppresses vertical motion, so any cloud that forms spreads horizontally into layers and precipitation is light and continuous rather than heavy and showery. Fog, stratus and drizzle are the characteristic products. Convective showers and thunderstorms require instability, which is precisely the opposite condition, so both of those options invert the relationship. Clear skies occur only when the air is also dry, since stability alone does not prevent cloud from forming.

Answer: B

Instability permits vertical motion, so cloud grows upward into cumulus and cumulonimbus and precipitation falls as showers separated by bright intervals. Good visibility between the showers is another characteristic. Drizzle, fog and persistent overcast are all products of stable stratification and would not survive in an unstable air mass.

Answer: C

Vertical mixing dilutes pollutants and moisture through a deep layer, so the air between the showers is exceptionally clear, which is why distant hills become visible in a polar maritime airstream. Stable conditions trap haze near the surface and give poor visibility. The contrast is one of the most reliable everyday indicators of the stability of the air mass. Working one numerical case through both cases side by side fixes the distinction better than any rule of thumb.

Answer: D

Cold air travelling over a warmer ocean is heated and moistened from below, which steepens the lapse rate and produces the showers characteristic of the airstream. The instability deepens with the length of the sea track. Air arriving directly from the pole over ice remains stable, which is the arctic rather than the polar maritime case.

Answer: A

Warm moist air moving over cooler water or land is cooled from below, which stabilises it and produces the sea fog, low stratus and drizzle characteristic of a tropical maritime airstream. It is stable despite its tropical origin because of the cooling it undergoes on the journey. The contrast with polar maritime air illustrates that the track matters as much as the source region. Reading the definition literally, rather than recalling a formula, is the reliable route through questions of this shape.

Answer: B

Surface heating steepens the lapse rate from below, so a stable maritime airstream can become unstable inland during a summer afternoon and produce thunderstorms far from the coast. This airmass modification is why the same air can bring drizzle on the coast and thunder inland on the same day. Relative humidity does fall on warming but the moisture content is unchanged. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.

Answer: C

An air mass acquires the properties of its source region and is then progressively modified by the surfaces it crosses, gaining or losing heat and moisture and changing its stability. The concept is central to the Norwegian school's classification. Advection describes the transport itself rather than the change in properties that accompanies it.