Homework questions (answers below)

  1. When a rising balloon passes through a gravity wave front, which way do you think its trajectory will look like?
    1. up-down oscillation   
    2. slantwise oscillation
    3. spiral oscillation

2.The vertical oscillation component of gravity wave originates from a balance between gravity and buoyancy. What forces balance on the horizontal direction?

3. Can you name a few atmospheric gravity wave sources? Can you name a few oceanic gravity wave sources?

4. Can you lay-out a few reasons why gravity waves are important, so we need to study them?

5. Can you lay-out a few challenges for models to simulate gravity wave impacts?

6. Can you think of some processes that a typical climate model cannot resolve other than the ones listed in the slides?

7. Given a global climate model (GCM) grid size of 100 km, and the earth radius of 6371 km, theoretically what are the smallest and largest wavelength of waves that this GCM can resolve?

Answers

  1. C
  2. We only need Coriolis force for the horizontal oscillation. Remember Coriolis force is always to the right in the Northern hemisphere and to the left in the Southern hemisphere of the moving direction, so itself forms the so-called inertial oscillation. You can see marine debris often gradually aggregate together into big piles. That’s not only because they follow the general ocean current, but also the inertial motion looping in smaller areas at the same time.
  3. Atmosphere: mountain/topography, deep convection (including typhoon, hurricane, tornado), jet, frontal system, solar eclipse (yes, that’s one of the major drives of this campaign!), volcano eruption, tsunami, missile launch, rocket launch, …

        Ocean: ocean surface topography, wind blowing at the ocean surface (e.g., by storms, hurricane, etc.), tsunami, underwater volcano eruption, torpedo, throwing a rock into water, tides, …

4. (1) Gravity waves in the troposphere impact weather. They often play a role in modulating the formation of new convective cells and the propagation of the convective system. They are often associated with hazardous aviation scenarios like triggering clear-air turbulence, forming dangerous downdraft flow or forming cloud bands. (2) They serve as a key mechanism for the lower-upper atmosphere coupling because they transport energy and momentum from the source to the sink. (3) They perturb the temperature (and hence relative humidity or other chemical reactions that are sensitive to temperature) in the stratosphere and mesosphere, which serves as an important mechanism for the formation of PSCs and PMCs, both have strong climate impact (e.g., worsen ozone depletion). (4) gravity waves in the thermosphere and ionosphere are coupled with other variations, e.g., tides, magnetic storm, and impact communication, space weather and spacecraft operations.

5. The major challenge is that none of the model can resolve all gravity waves. Ultra-high resolution is rather a curse than a bless for resolving gravity waves as they cause instability and chaos. Modelers strive to parameterize the impact from unresolved waves, while making sure the resolved waves are reasonable and do not breakdown other things. (See slide 19 & 20 for more complete answers)

6. Open answer. Any processes that are smaller than ~ 100 km scale, or very fast/transient or very slow, but in the meantime are important to weather prediction or climate projection.

7. )Smallest wave = 4 X grid size = 400 km (again, in reality 600 km is a more practical answer. Both correct)

          Largest wave = Earth’s circumference / 4 = 2* pi * radius / 4 ~ 10, 000 km

 

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