WG2 MEETING 2008 WG2 MEETING 2008 AUGSBURGAUGSBURG

DO

MIN

GO

F.

RA

SIL

LA

ÁL

VA

RE

Z

Dp

to.

de

Geo

gra

fía,

Urb

an

ism

o y

OT

Un

iver

sid

ad

de

Can

tab

ria

Sp

ain

PREPROCESSING

QUESTION 1: VARIABLES

SLP, Z500, Z850

WINDOW SIZE

DENSITY OF GRID POINTS

¿Weighting?

¿Re-gridding?

S MODE

STANDARIZATION OF GRID POINTS

1014

1016

1018

1020

1022

1 31 61 91 121 151 181 211 241 271 301 331 361

Julian day

hP

a

Regional air pollution analysis

Multipurpose climate analysis

SPATIAL PATTERNS OF VARIABILITY

NUMBER PCs

Scree test-LEV

Rule N

North et al

ROTATIONVARIMAX

PRINCIPAL PRINCIPAL COMPONENT COMPONENT

ANALYSISANALYSIS

Cluster

Analysis

QUESTION 8: SIMILARITY MATRIX

EUCLIDEAN DISTANCE

CLUSTER ALGORITHM

Hierarchical (Ward)

Agglomerative

(K-means)

NUMBER OF CLUSTERS

OUTCOMEFollowing

slides

TRACK OF THE LOW !!

PETISCO’S PROCEDURE

HOW TO SELECT THE NUMBER OF CLUSTERS

• Hybrid method (Rasilla 2000)– Predefined number of groups (manual or

subjective)• Spanish climatology tradition on Syn Class

– Seed days selected through manual classification of a subset (10 years!!) + DA (statistical confirmation of reliability of the classification)

– K-means of the complete dataset (1946-1998)– Too much time consuming!!!

HOW TO SELECT THE NUMBER OF CLUSTERS

ftp://ftp.sas.com/techsup/download/sample/samp_lib/

• Pure statistical method (Rasilla 2006)– Several K-means

solutions with algorithm (reduces the influence of the initial partition)

• number of groups: subjective (analysis of climate fields) + mathematics (Pseudo-t CCC…)

– Disc Ann (validation CA classification)

• Cross-validation (bootstraping 2 halves)

• External validation:– Climate fields– Other classifications– ¿Common sense?

HOW TO SELECT THE NUMBER OF CLUSTERS

Sea level pressure fields Daily precipitation fields

An example of a SPSS syntax file developing

the procedure

QUESTION 2. Is a specific program/software available for the application and use of the method, or a program must be developed by the user? (addition: if not availabe, can we

produce the code to be published ("open source") or is it too complicated or are there not enough details known about the

technique?) SPSS with syntax file, SAS.

QUESTION 3. Must the researcher have a computer programming background for the application of the method

(e.g. in order to develop software)? NO

QUESTION 4. How much time and computer power is roughly required for the computations? NO MORE THAN 5´

Related papers

• Yarnal B (1993): Synoptic climatology in environmental analysis. Belhaven Press, London

• Comrie AC (1996): An all-season synoptic climatology of air pollution in the U.S.-Mexico border region. Professional Geographer 48(3), 237-251.

• Ekström M, Jönsson P & Bärring L (2002): Synoptic pressure patterns associated with major wind erosion events in southern Sweden (1973–1991). Climate Research, 23: 51–66.