litpoint

Create a catalogue of atmospheric circulation types for a selected point, based on Litynski's modified classification

% [littable] = litpoint(latpoint,lonpoint,method,varargin) is a function that
% creates a catalogue of atmospheric circulation types for a selected point,
% in accordance with J. Litynski (1969) circulation types classification,
% modified by K. Kulesza (2019).
%
% This classification scheme is based on three indices calculated from
% gridded sea level pressure data from the NCEP/NCAR reanalysis:
% https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html
% The advection of air masses and cyclonicity (circulation) characteristics are
% estimated. Meridional (Wp) and zonal (Ws) indices are calculated as spatially
% averaged components of geostrophic wind vector, while cyclonicity index (Cp)
% is estimated as sea level pressure value over the central grid point of
% the domain. Threshold values divide the distribution of values in each index
% into three equally-likely classes (negative, indifferent and positive),
% where the indifferent category includes such values that:
%
% percentile 33 <= {indifferent category} <= percentile 67
%
% percentiles 33 and 67 are calculated based on one of the two
% possible methods (user's choice): 0 or 1 (see: Input variables).
%
% These threshold values are assigned to the middle day of each month. Between
% the middle days of two adjacent months, the threshold values are
% interpolated. As a result, the circulation types for the first half of the
% first month in a time series and the second half of the last month in a time
% series are not calculated. Circulation types are defined as distinct combinations of
% index categories for Wp and Ws leading to nine advection types (Adv). Adding Cp
% index categories (Circ) results in final division into 27 circulation types.
% For example: Circ = 1, Adv = 2 >> north-easterly anticyclonic type
% Circ = 0, Adv = 5 >> southerly indifferent type
%
% Output variable:
% littable is a 5-column table, where:
% y year,
% mt month,
% d day,
% Circ circulation, where: 1=A (anticyclonic), 0=0 (indifferent), -1=C (cyclonic)
% Adv advection, where: 0=0 (no advection), 1=N, 2=NE, 3=E, 4=SE, 5=S,
% 6=SW, 7=W, 8=NW
%
% Input variables:
% latpoint: indicate the latitude of the selected central grid point in a decimal format,
% e.g. 52.14
%
% lonpoint: indicate the longitude of the selected central grid point in a decimal format,
% e.g. 21.01
%
% method: chose one of two possible methods of calculating thresholds
% '0' for calculating percentiles 33 and 67 from all values
% (of an index) in a month in a given year and all values
% from this month from 19 previous years, i.e. running
% thresholds
% '1' for calculating percentiles 33 and 67 from all values
% (of an index) in a particular month from the period
% 1951-2000, i.e. fixed thresholds
%
% varargin: input NetCDF files, downloaded from:
% https://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.html
% (variable: Sea level pressure, statistic: 4 times Daily, level: sea-lvl)
% The input files consist of 3 dimensions: latitude; longitude; time (4 times
% daily individual observations); and 1 variable: sea level pressure;
% e.g. 'X95.160.154.129.39.0.33.57.nc'.
% In the case of using data from a very long time period (e.g. catalogue
% for 30 years + previous 20 years for calculations = 50 years),
% it is sometimes not possible to download one NetCDF.
% Instead, several NetCDFs with shorter time periods may be
% downloaded. In this case, input any number of comma-separated
% NetCDF files in a chronological order, e.g.
% (...,'example1.nc','example2.nc','example3.nc').
%
% References:
% Litynski J. (1969), 'A numerical classification of circulation patterns
% and weather types in Poland', Prace Panstwowego Instytutu Hydrologiczno-
% Meteorologicznego, 97, 3-15 (in Polish).
% Kulesza K. (2019), 'Modified, threshold-based circulation type
% classification for Central Europe, on the basis of Litynski's
% classification', Miscellanea Geographica, 23, 1, DOI:
% 10.2478/mgrsd-2018-0033.