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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 SVs only intensify weather systems; just as often they weaken or displace them.  A

A special (tropical) version of the SV is created for use used in the tropics to deal with uncertainties in the moisture processes typical of low latitudes, in particular of in tropical cyclones.  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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