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Singular Vectors - SV

The Singular Vector(SV) technique seeks perturbations for wind, temperature and pressure that will maximize their impact on a 48 hour forecast as measured by the total energy over the hemisphere outside the tropics.  This maximization does not mean that the SV SVs only intensifies intensify weather systems; equally often it weakens them.  In addition, such systems can be displaced.  To specifically address just as often they weaken or displace them.

A special version of the SV is used in the tropics to deal with uncertainties in the moisture processes typical of low latitudes, in particular of in tropical cyclones, a special (tropical) version of the SV is created for use in the tropics.  These tropical SVs may also influence forecasts of extratropical extra-tropical developments, (e.g. when tropical cyclones enter mid-latitudes some days into the forecast and interact with the baroclinic developments in the westerlies).

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• they deliver rearward sloping baroclinic structures, which should generally be more realistic. 
  
• the spread of outcomes grows realistically.
• the code is fairly inexpensive to run (it has a low 320km resolution (320km) and there .  There is no evidence yet that higher resolution SVs would improve ensemble skill).
  

 The disadvantages of the Singular Vectors are:

• they don’t directly take into account analysis uncertainty, nor observation coverage or accuracy.
• they produce rather localized variability (in the very short range).
• they under-develop variability in tropical regions (tropical . Tropical singular vectors are employed used to try to offset this problem).

Points to note:

• Average SV total energy charts can be used to identify unstable regions. 
• SV perturbations SVs (i.e. the SV perturbations applied) tend to be localized in areas of strong barotropic and baroclinic instability.Average
• SV total energy charts can be used to identify unstable regions. SV growth tends to be characterized by characterized during the model run by:
  • an upscale
  and
  • energy transfer.
  • an upward energy transfer (most rapid for smaller scales)
  , with
  • .
  • initial
  -time
  • potential energy being converted
  , during the model run,
  • into kinetic energy.
• Information for the final-time synoptic-scale structure is contained in the sub-synoptic scale SVs.  At initial time:
  
  • SVs with sub-synoptic -scale wavenumbers at initial time scale wave numbers may grow very rapidly to reach synoptic scales.
    
  • SVs with large scale wavenumbers at initial time wave numbers grow much more slowly than unconstrained, smaller-scale perturbations; the .  The presence or absence of large scales has little effect on SV growth. 
• The atmospheric flow structure in winter tends to be more baroclinically unstable than it does in summer (and during .  During winter the flow over Pacific and Atlantic sectors is on average more unstable than it is in other regions).

Additional Sources of Information

(Note: In older material there may be references to issues that have subsequently been addressed)

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