1. NWP Symposium University of Maryland June 2004 The 1954 start of operational Numerical Weather Prediction in Sweden

2. NWP Symposium University of Maryland June 2004 Why Sweden? -C. G. Rossby back from the US 1947 (home-longing, management and politics) -Swedish state-of-art computers (BARK 1950, BESK 1953) -International support (from the USA and Belgium)

3. NWP Symposium University of Maryland June 2004 1953 BESK= Binary Electronic Sequence Calculator

4. NWP Symposium University of Maryland June 2004 BESK In 1953 the world’s “best” computer Electrostatic drum memory “Williams tube” memory Control desk Arithmetic unit

5. NWP Symposium University of Maryland June 2004 The International Meteorological Institute Rossby wanted, like V. Bjerknes after WWI, to play an international role in the political reconstruction after WWII Eady V. Mieghem Rossby Steyer Hubert Vuorela

6. NWP Symposium University of Maryland June 2004 Baroclinic or barotropic models? …yes, but the large scale motion can kinematically be described by a barotropic model The atmospheric motions are driven by thermal processes as reflected in baroclinic developments R. C. Sutcliffe C. G. Rossby

7. NWP Symposium University of Maryland June 2004 Common misinterpretations of Rossby’s barotropic concept -Only valid for stationary waves -Can only perform linear extrapolations -Only valid for barotropic features -Group velocity….

8. NWP Symposium University of Maryland June 2004 The concept of group velocity tells us that any boundaries have to be placed far enough away from the verification region 24-hour compu- tational areas for - MISU - UKMO

9. NWP Symposium University of Maryland June 2004 A +24 hour forecast from the UKMO system winter 1953-54 Boundary errors and numericalinstability

10. NWP Symposium University of Maryland June 2004 Only in 1965 did the UKMO go operational with NWP after a personal intervention by the new Director General John Mason Oh dear... Dear members of the press, radio and TV...

11. NWP Symposium University of Maryland June 2004 In Stockholm tendency calculations were carried out, first by hand in 1952, later on BESK in 1953 The Swedish tabloid “Expressen” published the results almost a year before “Tellus” (forecast left, analysis right)

12. NWP Symposium University of Maryland June 2004 +24 h baro- tropic forecast 3 January 1954 00 UTC 2 January 1954 00 UTC Barotropic re-run of the “tree-feller” storm the 2-3 January 1954

13. NWP Symposium University of Maryland June 2004 First real time NWP in late September 1954 Not quite the 72 hour computational area 72 hour verification area

14. NWP Symposium University of Maryland June 2004 -Professor Dahlqvist, when is Spring coming? From the operational period Dec 1954-May 1955

15. NWP Symposium University of Maryland June 2004 -Tomorrow at 2 pm! +72 hours

16. NWP Symposium University of Maryland June 2004 …and Spring came!

17. NWP Symposium University of Maryland June 2004 Why Sweden succeeded: -C. G. Rossby back from the USA 1947 -Swedish state-of-art computers -International support -Choice of barotropic model (skilful and providing operational experience) -Efficient automatic analysis system (Bergthorsson-Döös, 1955) -Not too small NWP area (but not too big either, avoiding retrogression of the planetary waves!)

18. NWP Symposium University of Maryland June 2004 From wheat to bread! Bert Bolin shows automated 500 mb forecasts for Ragnar Fjørtoft (Norway) and George Corby (UK) around 1956