RELATIONSHIPS BETWEEN

CIRCULATION MODES AND SURFACE

CLIMATIC VARIABLES:

A COMPARISON OF REANALYSES

Martin HYNČICA and Radan HUTH

Department of Physical Geography and Geoecology

Charles University in Prague

MAIN OBJECTS

• The main goal is the comparison of relationships of circulation

modes identified from several reanalyses to temperature over

Northern Hemisphere at 650 stations

• Here, only two the most notable circulation modes are showed:

NAO (North Atlantic Oscillation) and PNA (Pacific North America)

• Five reanalyses: 20th Century Reanalyses (20CR); ERA20C;

ERA40; JRA-55; NCEP/NCAR

• Period: 1957-2002

• Seasons: winter, spring and autumn

METHODOLOGY

• Circulation modes are identified by rotated principal component

analyses (RPCA) of 500 hPa geopotential height

• RPCA = > results are loadings (spatial representation of modes)

and scores (index of circulation modes)

• 650 stations (GHCN), monthly temperature anomaly from long-

term climate is used

• Pearson correlation coefficient is calculated between monthly

score (=index of circulation mode) and temperature anomaly

Percentage of points (out of 734), where difference between

correlation of the 500 hPa and circulation mode is significant between

reanalyses. Higher values indicates higher differences in space

Fischer transformation is used for determination of statistical

significant differences (p<0.05)

NAO

PNA

WINTER

20CR ERA20 ERA40 JRA55 NCEP

WINTER – NAO AND PNA

CORRELATION

BETWEEN NAO

AND MONTLY

TEMPERATURE

ANOMALY

IN WINTER

20CR ERA20 ERA40

NCEP JRA55

CORRELATION

BETWEEN PNA

AND MONTLY

TEMPERATURE

ANOMALY

IN WINTER

20CR ERA20 ERA40

JRA55 NCEP

There are no stations, where differences in correlations between temperature and circulation modes are statistically different

SPRING NAO

PNA

SPRING NAO

PNA

High differences are mostly present between 20CR and remaining

reanalyses

Differences are caused by displacement and different shapes of some

centres

SPRING – NAO

20CR ERA20 ERA40

JRA55 NCEP

CORRELATION

BETWEEN NAO

AND MONTLY

TEMPERATURE

ANOMALY IN

SPRING

ERA40 ERA20 20CR

JRA55 NCEP

NAO - 20CR NAO - NCEP

STATIONS, WHERE CORRELATION OF NAO TO TEMPERATURE SIGNIFICANTLY DIFFERS BETWEEN REANALYSES

• Second column shows percentage of stations, where are statistical significant differences in correlations between temperature anomaly and NAO index calculated from different reanalyses

• High statistical significant differences in 500 hPa => high percentage of stations with st. significant differences in correlation between circulation mode and temperature

SPRING – NAO – 20CR

20CR ERA20 ERA40

JRA55 NCEP

SPRING – PNA

CORRELATION

BETWEEN PNA

AND MONTLY

TEMPERATURE

ANOMALY

IN SPRING

ERA40 ERA20 20CR

JRA55 NCEP

PNA – 20CR PNA – JRA55

STATIONS , WHERE CORRELATION OF PNA TO TEMPERATURE SIGNIFICANTLY DIFFERS BETWEEN REANALYSES

AUTUMN

NAO

PNA

AUTUMN– NAO

20CR ERA20 ERA40

JRA55 NCEP

CORRELATION

BETWEEN NAO

AND MONTLY

TEMPERATURE

ANOMALY

IN AUTUMN

ERA20 ERA40

JRA55 NCEP

20CR

AUTUMN–PNA

20CR ERA20 ERA40

JRA55 NCEP

CORRELATION

BETWEEN PNA

AND MONTLY

TEMPERATURE

ANOMALY

IN AUTUMN

20CR ERA20 ERA40

NCEP JRA55

There are no stations, where differences in correlations between temperature and circulation modes are statistically different , as it is in winter

CONCLUSIONS

• We compared relationships of NAO and PNA to monthly temperature

anomaly at 650 stations over the Northern Hemisphere in 5 reanalyses

between 1957 and 2002

• Negligible differences are present between reanalyses in winter, higher

differences are indentified in autumn. In both seasons, signigicant

differences in relationships of both circulation modes to temperature are

not found

• On the other hand, in spring, the spatial representation of NAO (in

20CR and ERA20) and PNA (in 20CR) is different compared to

remaining reanalyses. These differences are caused by different

shapes of centres and the consequence is higher amount of stations,

where correlation of 20CR with temperature differs significantly in

comparison with the other reanalyses (particularly over North America)