Northern Annular Mode effects on the land surface phenologies of Northern Eurasia
Kirsten
M
de Beurs, Virginia Tech University, kdebeurs@vt.edu
Geoffrey
M
Henebry, South Dakota State University, geoffrey.henebry@sdstate.edu
(Presenting)
Land surface phenology (LSP) is the spatio-temporal development of the vegetated land surface as revealed by synoptic sensors. Modeling LSP across Northern Eurasia reveals the magnitude, significance, and spatial pattern of the influence of the Northern Annular Mode. Here we fit simple LSP models to two Normalized Difference Vegetation Index (NDVI) datasets and calculate the Spearman rank correlations to link the start of the observed growing season (SOS) and the timing of the peak NDVI with the North Atlantic Oscillation (NAO) and Arctic Oscillation (AO) indices. We investigate the relationships between the Northern Annular Mode and weather station data, accumulated precipitation derived from the CPC Merged Analysis of Precipitation (CMAP) dataset, accumulated growing degree-days (AGDD) derived from the NCEP/DOE II Reanalysis and the number of snow days from the National Snow and Ice Data Center.
Our analyses confirm strong relationships between the temporal behavior of temperature and precipitation and large-scale climatic variability across Eurasia. We found widespread influence of the NAM on the land surface phenologies across Northern Eurasia affecting 200-300 Mha. The tundra ecoregions were especially impacted with significant results for about a quarter of the biome. The influence of the AO was also extensive (> 130 Mha) for the boreal forests. AO appears to affect the Asian part of northern Eurasia more strongly than NAO, especially for the NDVI peak position as a function of AGDD. Significant responses of vegetation timing to NAO and AO in northeastern Russia have not been as well documented as the seasonal advancement in Europe. The two AVHRR NDVI datasets yield fields of LSP model parameter estimates that are more similar in dates of peak position than in dates for SOS and more similar for AO than for NAO. As a result, we conclude that peak position appears to be a more robust characteristic of land surface phenology than SOS to link vegetation dynamics to variability and change in regional and global climates.
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