Baroclinic Instability Questions and Answers

Answer: C

Quasi-geostrophic turbulence conserves both energy and enstrophy, which forces energy towards larger scales, and the accumulation of energy at planetary scale can organise into a persistent block. The enstrophy cascade runs the other way and ends in dissipation. Friction removes energy rather than concentrating it, and molecular effects are negligible at these scales. The shared properties explain why these belong to one family, and the differences explain why more than one exists.

Answer: D

Once established a block is persistent and therefore relatively predictable, but the transitions into and out of the blocked state remain among the hardest forecasting problems in mid-latitudes. Models also show systematic errors in block frequency and duration. Blocks are prominent features easily identified in analyses, and they are more common in the northern hemisphere than the southern. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: A

Subsidence within the anticyclone suppresses cloud and the diverted storm track keeps fronts away, giving prolonged dry weather that can become a heatwave in summer or a cold spell in winter. Heavy rain and gales occur instead in the diverted flow around the flanks. The European heatwave of 2003 and the Russian heatwave of 2010 were both associated with persistent blocking. The quantity that varies and the quantity that does not are worth naming before any substitution is attempted.

Answer: B

Persistence is what turns ordinary weather into an extreme, and a block that holds the same pattern for two weeks produces heatwaves in summer and severe cold in winter. The 2003 European and 2010 Russian heatwaves are the standard examples. Tornado outbreaks and flash floods require strong dynamical forcing of the kind a block suppresses.

Answer: C

The Northern Annular Mode, closely related to the North Atlantic Oscillation, describes the north-south seesaw of mass that accompanies a strong or weak polar vortex and westerly flow. Its positive phase brings mild wet winters to northern Europe. The other indices listed describe tropical phenomena on interannual and intraseasonal timescales.

Answer: D

A strong polar vortex and a northward shifted storm track bring frequent Atlantic depressions to northern Europe, giving mild wet winters, while southern Europe is drier. The negative phase reverses this, with blocking and cold outbreaks. Understanding the index as a shift of the storm track rather than a change in its intensity is what makes the regional pattern predictable. Naming the cost of a choice alongside its benefit is what turns a fact into a design decision.

Answer: A

A major warming weakens or reverses the polar vortex, and the anomaly propagates downward over the following weeks, favouring the negative phase with an equatorward shifted storm track and cold outbreaks. This downward influence is exploited in extended range forecasting. Ozone depletion and volcanic aerosol act on much longer timescales and the quasi-biennial oscillation modulates rather than forces the mode.

Answer: B

Tropospheric memory is lost after about a week, but a stratospheric anomaly persists and influences the surface for several weeks, adding skill in exactly the range where deterministic forecasting has failed. This is now exploited operationally. Short range forecasts depend on the tropospheric initial state, and multi-year prediction depends on the ocean.

Answer: C

Rossby wave energy propagating downstream faster than the individual troughs seeds new development ahead of an existing system, producing the observed families of cyclones following one another along a track. Bjerknes described the pattern observationally long before the group velocity explanation was available. Formation is systematic rather than random or simultaneous. Most errors here come from carrying a result across from a neighbouring case where it does not hold.

Answer: D

Because energy travels at the group velocity, which can be substantially faster and in the opposite sense to the phase, a disturbance in one place seeds development well downstream within a day or two. Westward phase propagation is real but is not what carries the energy. Rossby waves are strongly dispersive, which is precisely why the two velocities differ.