CBM Atmospheric Thermodynamics 5 — Questions and Answers
Question 1: Which conditions most favor a strong surface-based radiation inversion overnight?
- Overcast skies and strong winds
- Clear skies, light winds, and dry air (Correct answer)
- Heavy rain and a cold front passage
- Warm air advection with high humidity aloft
Correct answer: Clear skies, light winds, and dry air
Clear, calm, dry nights let the ground lose longwave radiation efficiently and cool the air just above it.
Question 2: A subsidence inversion is most commonly associated with which feature?
- A deep low-pressure system
- Sinking air within a high-pressure system (Correct answer)
- A squall line
- A tropical wave
Correct answer: Sinking air within a high-pressure system
Air sinking under high pressure warms by compression and dries, creating a warm, dry inversion aloft.
Question 3: What is the convective temperature on a sounding?
- The temperature at the equilibrium level
- The surface temperature needed for a parcel to rise freely and form cumulus without forced lifting (Correct answer)
- The 500 mb temperature at which thunderstorms dissipate
- The dewpoint at the LCL
Correct answer: The surface temperature needed for a parcel to rise freely and form cumulus without forced lifting
Once the surface reaches the convective temperature, surface heating alone can start free convection and cumulus formation.
Question 4: A 'loaded gun' sounding typically features what?
- A saturated column with no inversion
- Moist low levels capped by a warm, dry elevated mixed layer with steep lapse rates above (Correct answer)
- An isothermal layer throughout the troposphere
- A deep surface-based inversion with dry low levels
Correct answer: Moist low levels capped by a warm, dry elevated mixed layer with steep lapse rates above
A cap holds back rich low-level moisture under steep mid-level lapse rates, so large instability builds until the cap breaks.
Question 5: Why do forecasters watch the wet-bulb zero height for hail?
- It sets the cloud base height
- A lower wet-bulb zero means less melting, so hail is more likely to reach the ground (Correct answer)
- It shows the level of maximum wind
- It sets the tropopause height
Correct answer: A lower wet-bulb zero means less melting, so hail is more likely to reach the ground
A low wet-bulb zero, often about 7,000-10,000 ft, reduces melting of falling hailstones.
Question 6: Which vertical temperature profile produces freezing rain?
- Below freezing through the whole column
- A deep warm layer aloft above a shallow subfreezing layer at the surface (Correct answer)
- A shallow warm layer aloft above a deep subfreezing surface layer
- Above freezing through the whole column
Correct answer: A deep warm layer aloft above a shallow subfreezing layer at the surface
Snow fully melts in a deep warm layer, then the drops supercool in a shallow cold surface layer and freeze on contact.
Question 7: On a sunny summer afternoon, the lowest few hundred meters often show a lapse rate greater than 9.8°C/km. What is this called?
- Isothermal layer
- Superadiabatic lapse rate (Correct answer)
- Moist adiabatic lapse rate
- Subsidence inversion
Correct answer: Superadiabatic lapse rate
Strong surface heating can make temperature drop faster than the dry adiabatic rate near the ground, which is absolutely unstable.
CBM Atmospheric Thermodynamics 5
Which conditions most favor a strong surface-based radiation inversion overnight?