INTERANNUAL VARIATIONS IN SATELLITE-SENSED VEGETATION INDEX DATA FROM1981 TO 1991

Normalized difference vegetation index (NDVI) data processed from meas urements of advanced very high resolution radiometers (AVHRR) onboard the afternoon-viewing NOAA series satellites (NOAA 7, 9, and 11) were analyzed for spatial and temporal patterns comparable to those observe d in atmospheric CO2, near-surface air temperature, and sea surface te mperature (SST) data during the 1981-1991 time period. Two global data sets of NDVI were analyzed for consistency: (1) the land segment of t he joint NOAA/NASA Earth Observing System AVHRR Pathfinder data set an d (2) the Global Inventory Monitoring and Modeling Studies AVHRR NDVI data set. The impact of SST events was found to be confined mostly to the tropical latitudes but was generally dominant enough to be manifes t in the global NDVI anomaly. The vegetation index anomalies at latitu des north of 45 degrees N were found to exhibit an increasing trend. T his linear trend corresponds to a 10% increase in seasonal NDVI amplit ude over a 9 year period (1981-1990). During the same time period, ann ual amplitude in the record of atmosphere CO2 measured at Point Barrow , Alaska, was reported to have increased by about 14%. The increase in vegetation index data between years was especially consistent through the spring and early summer time periods. When this increase was tran slated into an advance in the:timing of spring green-up, the measure ( 8 +/- 3 days) was similar to the recently published estimate of about 7 days in the advance of the midpoint of CO2 drawdown between spring a nd summer at Point Barrow, Alaska. The geographical distribution of th e increase in vegetation activity was consistent with the reported pat terns in springtime warming and decline of snow cover extent over the northern hemisphere land area.