CBM Radar & Satellite Meteorology 5 — Questions and Answers
Question 1: The radar reflectivity factor Z for Rayleigh scattering is proportional to the drop diameter raised to which power?
- Sixth power (D^6) (Correct answer)
- Fourth power (D^4)
- Third power (D^3)
- Second power (D^2)
Correct answer: Sixth power (D^6)
Z is the sum of D^6 over particles in a volume, so a few large drops dominate the return.
Question 2: Why do forecasters use storm-relative velocity (SRM) instead of base velocity when looking for mesocyclones?
- It corrects for range folding automatically
- It removes all ground clutter
- It converts radial velocity to vertical velocity
- Removing the storm's motion makes rotational couplets easier to see (Correct answer)
Correct answer: Removing the storm's motion makes rotational couplets easier to see
Subtracting storm motion removes the bulk flow, revealing the rotation pattern within the storm.
Question 3: On a WSR-88D, the Clear Air Mode volume coverage patterns (such as VCP 31/32/35) are mainly designed to:
- Disable Doppler velocity measurements
- Only scan the lowest 0.5 degree elevation
- Use slower scans to increase sensitivity for detecting light echoes and boundaries (Correct answer)
- Scan as quickly as possible for tornado detection
Correct answer: Use slower scans to increase sensitivity for detecting light echoes and boundaries
Clear Air VCPs use fewer elevation angles and longer dwell time to detect weak returns such as light snow and outflow boundaries.
Question 4: In GOES infrared imagery, which brightness temperature generally indicates the highest cloud tops?
- Temperatures close to the surface temperature
- The coldest brightness temperatures (Correct answer)
- The warmest brightness temperatures
- Temperatures that match the 850 mb level
Correct answer: The coldest brightness temperatures
Temperature usually decreases with height in the troposphere, so the coldest cloud tops are the highest.
Question 5: At night, which GOES product is commonly used to detect fog and low stratus?
- The 0.64 µm visible band alone
- The Geostationary Lightning Mapper flash density
- The difference between the 3.9 µm shortwave IR and 10.3 µm longwave IR bands (Correct answer)
- The 6.2 µm water vapor band alone
Correct answer: The difference between the 3.9 µm shortwave IR and 10.3 µm longwave IR bands
Water droplets emit less efficiently at 3.9 µm than at 10.3 µm, so liquid cloud stands out in the difference.
Question 6: A negative split-window difference (about 10.3 µm minus 12.3 µm) in satellite imagery is a classic signature of:
- Deep moisture in the boundary layer
- Clear sky over the ocean
- Thick cirrus composed of ice
- Volcanic ash (Correct answer)
Correct answer: Volcanic ash
Silicate ash particles absorb differently than ice or water, reversing the usual sign of the split-window difference.
Question 7: A broadcast meteorologist sees a strong velocity couplet only at the 0.5 degree slice far (about 120 miles) from the radar; what limitation should they consider?
- The radar cannot measure velocity beyond 60 miles
- The couplet must be ground clutter from superrefraction
- The beam is several thousand feet above ground and broadened, so low-level rotation may be missed or smoothed (Correct answer)
- Velocities at long range are always overestimated tenfold
Correct answer: The beam is several thousand feet above ground and broadened, so low-level rotation may be missed or smoothed
Beam height and beam width increase with range, so distant storms are sampled well above the surface at coarser resolution.
CBM Radar & Satellite Meteorology 5
The radar reflectivity factor Z for Rayleigh scattering is proportional to the drop diameter raised to which power?