首页|Monthly variations of the spring greenness response across boreal Eurasia to the preceding wintertime northern annular mode during 1982–2022
Monthly variations of the spring greenness response across boreal Eurasia to the preceding wintertime northern annular mode during 1982–2022
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NETL
NSTL
Springer Nature
Abstract The Northern Annular Mode (NAM) represents the primary form of atmospheric variability in the northern extratropics, significantly influencing the climate in the northern mid-high latitudes. In this study, the linkages between the previous wintertime (December-January-February-March) NAM (WNAM) and springtime vegetation growth across North Eurasia (NEUA), as measured by the normalized difference vegetation index (NDVI), were investigated. Results indicate vegetation cover tends be higher than normal over Europe (western Siberia) in March (May) during or after WNAM’s positive phase, and the opposite for WNAM’s negative phase. However, reduced April vegetation growth across central NEUA is apparent after both the positive and negative phases of the WNAM. In March, the WNAM anomaly excites a Rossby wave from the North Atlantic to western NEUA, generating anomalous high pressure and an anticyclone across western NEUA during WNAM’s positive phase. Consequently, there is a notable increase in 2-m air temperature in the region, which favors vegetation growth. In April, a North Atlantic tripole pattern of sea surface temperature (SST) anomalies preserves the previous WNAM signal and triggers atmospheric wave trains from the North Atlantic to central NEUA after WNAM’s positive phase. This in turn leads to anomalous low pressure and increased cloudiness in central NEUA, which results in a reduction in temperature and solar radiation, thereby inhibiting vegetation growth in the region. However, in April after WNAM’s negative phase, positive snow cover anomalies reduce the turbulent heat flux to the south of Lake Baikal, altering the temperature gradient and triggering an anomalous cyclone, which also leads to reduced temperatures and solar radiation, thereby suppressing vegetation growth in central NEUA in April. WNAM’s impact on vegetation in May mirrors the physical processes after its positive phase in April, particularly in connection with the North Atlantic tripole SST. The findings offer new insights into WNAM’s impact on climate and vegetation in the northern mid-high latitudes, suggesting that WNAM could serve as a reliable predictor for spring vegetation growth anomalies in NEUA.
NETL
NSTL
Springer Nature
