images were created using Wimsoft (http://wimsoft.com)
software and monthly satellite date described in http://www.spg.ucsd.edu/Satellite_Projects/Monthly_global_time_series/Monthly_global_time_series.htm.
wam_series for was used for subsetting the global data and wam_anomaly for calculating the
anomalies. The monthly anomalies are calculated relative to the respective
monthly means. A tutorial for calculating anomalies is available
A tutorial for calculating anomalies is available here.
· The limits for the area were: 20-40 N; 128-105 W.
· The chlorophyll-a anomalies were composed from 7 years of SeaWiFS data using standard Version 4 Level-3 monthly data (Standard Mapped Images). The nominal pixel resolution is 9 km. The chlorophyll anomalies are calculated from a ratio of a monthly composite to the respective monthly mean. The full range for the ratio is from 0.1 to 10.
· The SST anomalies were composed from almost 20 years (1985-2004) of AVHRR Pathfinder Version 5 monthly ascending (daytime) data. The nominal pixel resolution is 4 km. The SST anomalies are calculated by subtracting the respective monthly mean from a monthly composite. The full range for the difference is from -5.0 to +5.0.
· The color scheme to visualize the anomalies uses blue tones for negative anomalies and red tones for positive anomalies. The intensity (saturation) shows the intensity of the anomaly. Values close to the mean are shown in pale colors and mean and no valid data are both shown as white.
example of SST anomalies in January, 1998 shows the effects of the strong
1997/1998 El Niño: most of the area shown has positive (red) SST anomaly. The
positive SST anomaly is strongest in the central Gulf of California and
offshore of the
corresponding chlorophyll-a anomaly image for January,
1998 shows that most of the California Current had lower than normal surface
chl-a concentration with the exception of the warm waters off
· An animated GIF showing the 7-year chl-a anomalies is shown at link given below. Please be patient as this is a 2 MB file that takes time to download!
· An animated GIF showing the nearly 20-year SST anomalies is shown at a link given below. Please be patient as this is a 20 MB file that takes time to download!
Kahru, M., B.G. Mitchell, Influence of the 1997-98
El Niño on the surface chlorophyll in the
Kahru, M., B.G. Mitchell, Influence of the El Niño –
La Niña cycle on satellite-derived primary production in the