Predictability of springcold spells in Europe

M. E. Shongwe, G. J. van Oldenborgh, C. Ferro and C. A. S. Coelho

Outline

Motivation

Model verification

Possible source of model skill

Skill scores relative to a simple statistical model

The KNMI Climate Explorer

Summary

2006 Spring 2m temperature

Whereas global warming is a topical issue world wide, there is still a need to investigate the predictability of cold extremes in e.g Europe (spring 2006 a good illustration)

Operational GCMs verified

MODEL RESOLUTION REFERENCE

ECMWF-2 T95L40 van Oldenborgh et al.(2005a,b)

NCEP-CFS T62L64 Saha et al. (2005)

UKMO 3.75° x 2.5° L55 Scaife et al. (2000)

Model ROC curves

Model ROC scores normal seasons

All three models show some skill in predicting near-average seasons in Eastern Europe, but……..

Models verified against NCEP-NCAR Reanalysis

Model ROC scores coldest seasons

The skill is even much higher over the same area for the coldest springs…..suggesting that there is some physical mechanism responsible.

Data source: NCEP-CPC Monitoring and data

Snow Cover ClimatologyAmongst other candidate land surface processes influencing cold spells in NE Europe is the presence or absence of snow and its effect on the albedo and sensible heat exchange

Snow cover climatology expresses the fraction of time with snow on the ground.Interannual standard deviations of the probability of the presence of snow on the ground early in March-April

Scatter plotsSpatial averaged early February snow water equivalent (mm) versus boreal spring near-surface (2m) temperature.The three coldest MAMs were characterised by high snow-depth on the ground.The effect of snow on the center of the temperature distribution is smaller

Verification of Principal Regression model?

Using the regression model the area of highest skillshifts is more southward?

The KNMI Climexp (http:climexp.knmi.nl)

SummaryThere is an obvious incentive for investigating the predictability of cold outbreaks in Europe as demonstrated during last spring.The GCMs verified seem to be predicting these extremes skillfully over Eastern Europe.Snow-related feedbacks are in part responsible for colder spring seasons.More accurate analysis of snow is expected to improve colder temperature predictions.To do....Methods of improving GCM prediction (e.g. statistical recalibration).