Questions: Stratospheric Thermal Structure and Ozone

Question 1

If all ozone were suddenly removed from the stratosphere while everything else remained constant, what would happen to the stratospheric temperature profile?

• A. Temperatures would increase further, because without ozone absorbing UV, more energy reaches the lower stratosphere to heat it by other mechanisms
• B. The temperature inversion would collapse — stratospheric temperatures throughout would decrease, because ozone absorption is the primary heat source creating the warm upper stratosphere
• C. The temperature profile would be unchanged, because stratospheric heating is primarily driven by longwave IR emission from the warm troposphere below
• D. Only the upper stratosphere would cool; the lower stratosphere would be unaffected because ozone concentration is low there

Answer: (B)

The stratospheric temperature inversion exists because ozone absorbs UV radiation and converts that energy to heat. Without ozone, no UV is absorbed in the stratosphere — the primary heat source disappears. Temperatures would decrease throughout the layer, the inversion would vanish, and the stratosphere would behave like an extension of the troposphere (temperature decreasing with altitude). This demonstrates that ozone doesn't merely filter surface UV — it actively creates the thermal structure that defines the stratosphere as a distinct atmospheric layer.

Question 2

Why does ozone depletion over Antarctica strengthen the polar vortex rather than weakening it?

• A. Ozone depletion increases surface wind speeds, which mechanically spin up the stratospheric vortex from below
• B. Less ozone means less UV absorption, cooling the polar lower stratosphere further and enhancing the temperature contrast with warmer mid-latitude air — this strengthens the thermal wind driving the vortex
• C. Ozone depletion causes increased longwave emission to space, cooling the troposphere globally and intensifying all atmospheric circulation
• D. Ozone depletion reduces polar stratospheric clouds, which normally disrupt the vortex through latent heat release

Answer: (B)

The polar vortex is a ring of westerly winds driven by the temperature contrast between cold polar and warm mid-latitude stratospheric air. When ozone depletes over the pole, less UV is absorbed, cooling the polar lower stratosphere by 10°C or more. This enhanced temperature contrast increases the thermal wind — the vortex tightens and strengthens. A stronger vortex then isolates polar air more effectively, preventing mixing with warmer mid-latitude air, maintaining cold temperatures, and perpetuating conditions for further ozone destruction on polar stratospheric cloud surfaces. This is the chemistry-radiation-dynamics feedback loop.

Question 3

The stratospheric temperature inversion suppresses convection, which is why the stratosphere is almost cloudless and why volcanic aerosols injected into it persist for years.

• T. True
• F. False

Answer: True

The temperature inversion (warm air above cooler air) creates strong static stability. An air parcel rising into the stratosphere encounters progressively warmer — and therefore less dense — surroundings, making the parcel negatively buoyant and pushing it back down. This suppresses convective mixing entirely. Without convection to redistribute materials vertically, volcanic aerosols, CFCs, and other tracers injected into the stratosphere can persist for years before slowly dispersing through weaker stratospheric circulation. The same stability that makes the stratosphere chemically persistent also isolates it from tropospheric weather.

Question 4

The upper stratosphere is warmer than the lower stratosphere because it is physically closer to the sun and receives more direct solar heating.

• T. True
• F. False

Answer: False

The ~50 km altitude difference between the upper and lower stratosphere is negligible compared to the Earth-Sun distance of ~150 million km — proximity to the sun cannot explain this pattern. The upper stratosphere is warmer because UV radiation is progressively attenuated as it passes downward through the ozone layer: more UV energy is absorbed at higher altitudes where ozone first encounters unattenuated solar radiation. This is an atmospheric absorption effect. If physical proximity drove heating, every atmospheric layer above the surface would be warmer than those below — the opposite of what is observed in the troposphere.

Question 5

Explain why ozone is responsible for the existence of the stratosphere as a distinct atmospheric layer, rather than merely protecting Earth's surface from harmful UV radiation.

Model answer: Ozone actively creates the stratosphere. By absorbing UV radiation and releasing heat, ozone establishes a temperature inversion — warm air sitting above cooler air — that is the defining feature of the stratosphere. This inversion creates strong static stability, suppressing vertical mixing and isolating the stratosphere from the troposphere. The cloudlessness, long residence times, and dynamic properties of the stratosphere all follow from this ozone-driven thermal structure. Without ozone, the temperature inversion disappears, and the stratosphere ceases to exist as a distinct layer.

Reframing ozone from a passive UV filter to an active thermal engine changes how we understand stratospheric ozone depletion. Loss of ozone doesn't just increase surface UV — it cools the polar lower stratosphere, strengthens the polar vortex, and creates a feedback that perpetuates further ozone destruction. This is why stratospheric ozone depletion is a climate issue as well as a public health issue: it alters the thermal structure and dynamics of an entire atmospheric layer, with downstream effects on tropospheric circulation and climate. The Montreal Protocol's success in halting ozone depletion thus protected both the climate system and human health.