1. LONG-TERM TALL TOWER CO 2 MONITORING IN HUNGARY László HASZPRA Hungarian Meteorological Service Zoltán BARCZA Eötvös Loránd University

2. Hegyhátsál is located at 46°57'N, 16°39'E, 248 m above the sea level 15 O E16 O E17 O E18 O E19 O E 48 O N 47 O N 46 O N

4. –1993 weekly NOAA flask sampling at 96 m –1994 CO 2 vertical profile measurements (10 m, 48 m, 82 m, 115 m) –1997 CO 2 vertical flux measurements (eddy covariance method, 82 m)  2001 regular aircraft meas- urements over the tower up to 3000 m above ground 

5. Early afternoon parallel in-situ measurements and flask samples (NOAA) can be used for quality control The slight deviation can be explained by the relatively high temporal variability, the non-perfect synchronization of the in- situ measurements and the flask sampling and by the difference in the sampling elevations

6. Combined data series of the two Hungarian CO 2 monitoring stations K-puszta (KPU, 46º58'N, 19º33'E, 125 m, 1981-1999) and Hegyhátsál (HHS, 46º57'N, 16º39'E, 248 m, 1994- ) black line = marine boundary layer (mbl)

7. Detrended data series Annual amplitude is decreasing (36.5 ppm → 28.7 ppm, 0.78 ppm/yr) Change is not symmetric

8. CO 2 deficit season Changing shape of the seasonal cycle Increase of the length of the CO 2 deficit season is approx. 1 day/year Increasing length of the growing season?

9. Possible reasons for the decreasing annual amplitude: decreasing anthropogenic emission in Hungary and in the neighbouring countries anthropogenic CO 2 emission hardly changed between 1994 and 2004 no sign of significant changes decreasing atmospheric stability, circulation decreasing biospheric uptake

10. winter:1.91 ppm/yr autumn:1.78 ppm/yr annual:1.85 ppm/yr spring:1.53 ppm/yr summer:2.17 ppm/yr mbl: 1.82 ppm/yr lower than average increase in spring (Mar-May), higher than average increase in summer (Jun-Aug) sign of earlier start of the growing season or more intensive biospheric uptake in spring sign of decreasing summer biospheric uptake

11. slightly increasing carbon uptake in March → earlier start of the growing season no change in April decreasing carbon uptake from May to August (especially in late summer [July-August]) daytime (08-16 h LST) NEE

12. -150 -100 -50 0 50 100 NEE (g C/m 2 /yr) 12 14 16 March – October temperature ( o C) 400 500 600 700 800 March - October precipitation (mm) 1960-1990 average vapour pressure deficit may give higher correlation Haszpra et al., 2005: Long term tall tower carbon dioxide flux monitoring over an area of mixed vegetation. Agricultural and Forest Meteorology 132, 58-77. no measurements

13. Conclusions: in addition to the results of other methods the changes in the temporal variation of CO 2 mixing ratio and the early spring trend in the biosphere-atmosphere carbon exchange rate also indicate the earlier start of the growing season the gradually drier and warmer than average weather in the growing season resulted in decreasing biospheric carbon uptake between the late 90’s and 2003, turning the region to net carbon source by 2003 this climate anomaly period seemed to be interrupted in the influence region of the station in 2004, and the region acted again as a net carbon sink the measurements give the experimental evidence that the expected drier and warmer future climate may turn the region into a significant net natural carbon source