Effect of Atlantic Sea Surface Temperature in May on Intraseasonal Variability of Eurasian NDVI in Summer
Liuqing Ji, Ke Fan
Abstract
Abstract Intraseasonal variabilities exist in terms of Eurasian vegetation growth in summer, as estimated by the Normalized Difference Vegetation Index (NDVI). The spatiotemporal patterns of Eurasian NDVI in June are significantly different from those in July and August (JA), especially over eastern Europe and western Siberia (50°–70°N, 30°–90°E; abbreviated as EEWS). Meanwhile, June and JA EEWS‐NDVI respond differently to the Atlantic sea surface temperature in May over coastal regions (35°–60°N, 20°W–20°E; abbreviated as ACSST). During 1982–2015, the JA EEWS‐NDVI is significantly related to May ACSST (correlation coefficient: 0.44, significant at the 1% level), whereas the June EEWS‐NDVI shows only a slight and nonsignificant relationship (correlation coefficient: 0.23). In June, the EEWS‐NDVI is primarily influenced by the local 2‐m temperature (correlation coefficient: 0.62, significant at the 1% level), whereas in JA it is more closely linked with soil moisture (correlation coefficient: 0.38, significant at the 5% level). Increased May ACSST corresponds to lower surface air temperature and increased precipitation, which is accompanied by higher soil moisture over the EEWS region, and a persistently high soil moisture from May to JA is favorable for the growth of vegetation. However, the surface air temperature in June responding to higher ACSST is slightly lower, which is not conducive to the vegetation growth in June. Numerical experiments are carried out using CAM5, and the results support the proposed physical mechanisms. Therefore, May ACSST is a possible climatic factor responsible for the intraseasonal variabilities of EEWS‐NDVI, which may serve as a predictor of JA vegetation over Eurasia.