Lesson 9: Homework answer key
Answer key for homework problems in Lesson 9
Questions
Q: In the La Soufriere volcano eruption video, one can see the structures of cloud/smoke: can you circle out areas that you think are modulated by gravity waves? (hint: colors are from infrared channels, with red/yellow being warm and green/blue being cold)
A: The bands to the left are probably associated with gravity waves generated by the volcano eruption (circled). The upwind propagating gravity waves quickly became stalked and help forming the cloud bands while the downwind ones can go to the stratosphere and mesosphere. The large wavy structure to the right of this screenshot is actually associated with the intermittent nature of this eruption.
Q: Do you think atmospheric gravity waves are usually linearly or circularly polarized? Why?
A: Circularly polarized. Gravity waves have two orthogonal component: one with up-down buoyancy oscillation resulted from a balance between buoyancy and gravity. And a horizontal rotation due to Coriolis force.
Q: Is sunlight polarized?
A: Sunlight can be approximated as unpolarized. But that’s for direct sunlight. After scattering, absorption and other processes happen in the atmosphere, the sunlight you receive is usually partially polarized.
Q: What type of gravity waves are single radiosonde profiles particularly sensitive to?
-
- (A) Long vertical wavelength, short horizontal wavelength, vertically propagating ones
- (B) Long vertical wavelength, long horizontal wavelength ones
- (C) Short vertical wavelength, long horizontal wavelength, slantwisely propagating ones
- (D) Short vertical wavelength, short horizontal wavelength, small ones
A: The answer is C
Q: Our 2017, 2019 and 2020 solar eclipse campaigns all launch balloons hourly. If we make a time series, what is the smallest wave period can it resolve? In 2024, we aim at 15 minutes cadence at some sites. What is the smallest wave period can we resolve if we are successful?
A: 4X rule applies here. The smallest period of gravity waves that an hourly launching schedule can resolve is 4 hours. If we shrink the cadence to 15 mins, we can resolve ~ 1 hour period gravity waves. However, please note that this is only for the case of timeseries. For single radiosonde profile, we may resolve higher-frequency waves ( ~ 10s mins) if ascending rate perturbation is analyzed.