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P27

P27. Piia Post University of Tartu Institute of Physics. P27 - a simple eigenvector based classification scheme (Kruizinga 1978, 1979). Uses only 500 hPa heights on a regular grid (original one 6 x 6 points with the step of 5 ° in latitude and 10 ° in longitude)

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P27

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  1. P27 Piia Post University of Tartu Institute of Physics

  2. P27 - a simple eigenvector based classification scheme (Kruizinga 1978, 1979) • Uses only 500 hPa heights on a regular grid (original one 6 x 6 points with the step of 5° in latitude and 10° in longitude) • ptq= htq - ht , q=1,... n; n – the number of gridpoints, t=1,...N, N – the number of days • The vector of 500 hPa heights is approximated as: • pt ≈s1t a1+ s2t a2 +s3t a3 • a-s are the first principal component vectors (eigenvectors of the second-moment matrix of pt) and s-s are their amplitudes or scores. The flow pattern of a particular day is described by three amplitudes: s1t, s2t,s3t

  3. s1ta1 characterizes the east-west component of the flow s2ta2 – thenorth-south component and s3ta3 – the cyclonicity (or anticyclonicity) The range of each amplitude is divided into three equiprobable intervals, then each pattern is on the basis of its amplitudes uniquely assigned to one of the 3 x 3 x 3 = 27 possible interval combinations.

  4. 1) Which parameters are used for the calculations? 500 hPa gph 2) Is a specific program/software available for the application and use of the method, or a program must be developed by the user? Is code reproducible? No special software needed. Code is reproducible. 3) Must the researcher have a computer programming background for the application of the method (e.g. in order to develop software)? A little, if to compute the types himself. 4) How much time and computer power is roughly required for the computations? 5) Which method is used for deciding the number of classes/patterns? Is any number possible? The number is decided earlier, depends how many principal components are taken into account and to how many probability classes they are divided.

  5. 6) List the 5 main articles related to this method Kruizinga, S., 1979. Objective classification of daily 500 mbar patterns. Preprints Sixth Conference on Probability and Statistics in Atmospheric Sciences, 9-10 October 1979, Banff, Alberta, American Meteorological Society, Boston, MA, 126-129. Buishand, T.A., Brandsma, T., 1997. Comparison of circulation classification schemes for predicting temperature and precipitation is the Netherlands. Int. J. Climatol., 17, 875-889. 7) How are key-patterns defined? Just first three components 8) Which distance/similarity measure is used (possible)? Usual Euclidian distance

  6. Hemispheric circulation patterns

  7. Dzerdzeevski (1968) • Elementary circulation mechanisms (ECM) operate over a short time interval and govern the circulation pattern over the entire hemisphere • 2 postulates: • The hemispheric circulation is determined by a finite number of characteristic circulation mechanisms. The number of mechanisms is small over short time period, but their characteristics differ greatly with season. • The features of each circulation mechanism persist longer than the time scale of synoptic processes. Hemispheric circulation is a real macroprocess, not a chance combination of indipendent synoptic processes. Individual disturbances and fronts are regarded as ‘noise’.

  8. Cyclone and anticyclone tracks at the 700 or 500 hPa level are used as an indicator of the main mid-tropospheric steering currents. • Charts averaged over several days provide the best view of the various types. • Special attention is given to polar intrusions and associated blocking in the westerlies in six hemspheric sectors of 50-60°.

  9. Vangengeim (1935, 1946) • Elementary synoptic processes • Three basic types of circulation: • W – westerly • E – easterly • C – meridional • Each type is characterized by a particular distribution of depressions and anticyclones at the surface and by an organization of the major long wave pattern

  10. W E C

  11. Frequency of occurrence of circulation types (in days) 1891-1998

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