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Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

Spatial Coherence of NEE Response of Different Ecosystems to the Same Climate Anomaly (A Spring 1998 Case Study). Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003. Premise.

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Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

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  1. Spatial Coherence of NEE Response of Different Ecosystems to the Same Climate Anomaly(A Spring 1998 Case Study) Martha P. Butler The Pennsylvania State University ChEAS Meeting June 29 – July 2, 2003

  2. Premise • Different ecosystems, separated in space, exposed to the same climate anomaly, may have similar responses. • If the climate anomaly includes a large area, the shared ecosystem response may be large enough to be detected globally. • Can flux tower measurements be combined to represent regional responses?

  3. Test • Pick a climate anomaly that might be expected to have a widespread response. [Spring 1998] • Locate FLUXNET sites within the anomaly area with data for Spring 1997 and Spring 1998. • Identify and quantify the common response. • MAM mean temperature, cumulative MAM NEE • Look for evidence in local and global CO2 signals.

  4. Why Spring? Why 1998? • In Spring there are detectable phenological changes, especially in deciduous forests. • Onset of photosynthesis, soil thaw • Change in relationship of latent heat flux to sensible heat flux • Spring 1998 was one of the warmest on record for parts of the Northern America. • An El Niño winter…

  5. Map shows the location of grid boxes with station data for January-July 1998 that contributed to our global land analysis. The size and color of the dots indicate how much warmer or colder January-July 1998 was compared to January-July 1997.

  6. Surface Temperature Anomalies in °C (1961-1990 base period) December 1997- February 1998 March 1998 – May 1998 Bell et al., BAMS, Vol.80, No. 5, 1999

  7. A Closer View Of the US Record May 1998 Climate Variations Bulletin National Climatic Data Center, NOAA

  8. Criteria for Choosing Sites • Availability of NEE Data for Spring 1997 and Spring 1998 • Gap-Filled FLUXNET Data Sets • Mirror Sites to PI-Maintained Data • Published Literature • Availability of Good Quality CO2 Mixing Ratio Time Series • Inside/Outside Boundaries of Warm Anomaly • Vegetation Type

  9. Sites Considered…

  10. Comparison of Spring 1998 to Spring 1997 Order of Magnitude of increase in carbon uptake: 50g C m-2 spring-1 (managed) (outside of anomaly) *Old Aspen data from Black et al., 2000; Mean Temperatures are for April-May; cumulative NEE is estimated from Figure 1 **CO2 Flux reported for Howland Forest (not NEE) ***All other data from FLUXNET monthly summary, gap-filled by look-up table method, ustar-screened, from http://daac.ornl.gov/FLUXNET/

  11. Timing of Spring Onset The “cross-over” of latent and sensible heat fluxes in these deciduous and mixed forests occurred earlier in 1998 than in 1997. Data are 15 day bin averages of mean daily fluxes. Source: FLUXNET gap-filled daily data

  12. Quality/Availability of CO2 Mixing Ratio Measurements

  13. Evidence in the Local CO2 Record Earlier spring decrease in mean daytime CO2 mixing ratios in 1998. An early spring is not necessarily a guarantee of a productive summer growing season. Data are 15-day bin averages for hours 10-14 LST. Howland Forest data courtesy of D. Hollinger. All other data from PI-maintained FLUXNET mirror sites.

  14. Questions • If much of North America is affected, can this signal be seen in the global CO2 measurement network? • Or… • What does the global measurement network show? • What is the magnitude of the land response that could account for the global observations? • First cut, simple approach, with many assumptions:

  15. An Order of Magnitude Scaling Exercise • Consider two sites in the CO2 global measurement network, at roughly 53N. • Assume a mean westerly wind, U = 10 ms-1 • Assume that any change in CO2 between the two sites is due to land interaction in North America (land traverse of d = 5 x 106 m). • Assume any change in CO2 is mixed through the depth of the troposphere, • h = 104 m.

  16. Scaling Exercise (continued)… • Find the mean difference in CO2 mixing ratio between SHM and MHD for Spring 1997 (March, April, May). • Find the net land flux, E – D (Emissions – Deposition), that would account for this CO2 difference using dC/dt = E/h – D/h, where • ΔC = [CO2] at MHD – [CO2] at SHM • Δt = d/U • Repeat for 1998. • Compare the net land flux differences for 1997 and 1998. • Compare this result to 50g C m-2 more terrestrial uptake for Spring 1998 that seems plausible from the flux tower results. • Ready? Let’s do it…. • ΔC for 1997 is -1.52 ppm • ΔC for 1998 is -2.05 ppm

  17. Scaling Exercise Results • For 1997: (E – D) = (h U ΔC)/d • (104 m)(10 ms-1)(-1.52 ppm) / (5 x 106 m) = -0.030 ppm ms-1 • Convert to gC m-2 day-1 (multiply by 35) = -1.06 gC m-2 day-1 • Multiply by 100 days = -100 gC m-2 spring-1 • For 1998: • (104 m)(10 ms-1)(-2.05 ppm) / (5 x 106 m) = -0.041 ppm ms-1 • -1.44 gC m-2 day-1 • -140 gC m-2 spring-1 • 40 gC m-2 more uptake in Spring 1998 compared to Spring 1997. • Challenges? • Implications?

  18. Next Steps • What about Europe? • Try another anomaly (more recent, with more operational flux towers) • Apply more rigorous geostatistical methods. • Make the scaling exercise more rigorous • Use the flux towers measurements (including CO2 data) to extend the global measurement network to include more land sites.

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