Atmospheric Waves Questions and Answers

Answer: C

Long lived tracers whose tropospheric concentration is increasing steadily provide a clock: the lag between a stratospheric measurement and the matching tropospheric value gives the mean transit time. Ages of up to six years are found at high latitudes. Ozone is chemically active, water vapour is modified by the cold trap, and nitrous oxide is destroyed rather than produced in the stratosphere. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: D

Air entering the stratosphere through the tropical tropopause is dehydrated to the saturation mixing ratio at the cold point, typically a few parts per million, which sets the humidity of the whole stratosphere. This is the Brewer mechanism, proposed to explain the observed dryness. Tropopause height and ozone influence the temperature but the freeze drying is the direct control. Checking the units of each quantity catches a wrong formula before the arithmetic begins.

Answer: A

The tropical tropopause layer between about 14 and 19 kilometres is a transition region with properties intermediate between troposphere and stratosphere, and it is where air is dehydrated as it enters the stratosphere. Its detailed structure controls the stratospheric water vapour budget. The boundary layer, Ekman layer and entrainment zone all lie within the lowest kilometres of the atmosphere and have nothing to do with stratospheric entry.

Answer: B

The annual cycle of tropical cold point temperature imprints alternating moist and dry layers on the ascending air, and these propagate upward over several years like the signal on a tape recorder. Tracking them gives a direct measurement of the ascent rate of the Brewer-Dobson circulation. Methane oxidation does add water vapour with height, which makes that a plausible distractor, but the tape recorder signal is the striking observation.

Answer: C

By following the upward progress of a given annual maximum or minimum through successive years of observation, the mean vertical velocity of the tropical branch of the Brewer-Dobson circulation can be read off directly. Values around 0.3 millimetres per second are found. It is one of the few direct measurements of a large scale vertical velocity anywhere in the atmosphere.

Answer: D

The mid-latitude surf zone is where planetary waves break irreversibly, mixing potential vorticity and forming a broad region of weak gradients between the tropics and the vortex edge. The vortex edge itself acts as a transport barrier. The name captures the analogy with ocean waves breaking on a shelving beach, and the sharp gradients at its edges are a striking feature of potential vorticity maps.

Answer: A

Strong potential vorticity gradients at the vortex edge inhibit mixing, so air inside remains isolated for months, which is what allows the chemical processing responsible for the ozone hole to proceed undiluted. The barrier is not perfect but is remarkably effective. The jet is associated with the edge but the two are not exactly coincident at every level.

Answer: B

Because the vortex is isolated, air depleted of ozone by heterogeneous chemistry on polar stratospheric clouds is not replaced, and the depletion accumulates through the winter and spring. This is why the ozone hole is a southern hemisphere phenomenon, the southern vortex being colder and more isolated than the northern one. Descent does occur but the air remains extremely cold.

Answer: C

The southern vortex is colder, stronger and far less disturbed by planetary waves, because the southern hemisphere has weaker stationary wave forcing from topography and land-sea contrast. That is precisely why the ozone hole forms over Antarctica and not over the Arctic. The vortex is a winter feature, forming as the pole enters polar night.

Answer: D

Breaking planetary waves can decelerate and reverse the vortex within a few days, raising polar stratospheric temperatures by tens of kelvin and sometimes splitting the vortex in two. Such major warmings occur in roughly half of northern winters and very rarely in the south. The spring reversal is the ordinary seasonal transition, and volcanic and tropospheric influences act far more slowly.