Chlorophyll dynamics in the Santa Barbara Basin

Mati Kahru, mkahru@ucsd.edu

· This is a “quick-and-easy” exercise that shows what can be done in about 30 minutes. Wimsoft (http://wimsoft.com) software is applied to monthly composited and mapped global images at 9 km resolution of the OCTS (1996/11 – 1997/06) and SeaWiFS (1997/09 – 2004/12) and 4-km resolution images of Aqua-MODIS (2005/01 – 2005/02). For more information please see a related article at http://spg.ucsd.edu/Satellite_Projects/Monthly_global_time_series/Monthly_global_time_series.htm.

· The Santa Barbara Basin is too small for using 9-km data and for better results the full-resolution data should be used (see, for example, a related document “SeaWiFS time series for the California current”). To improve the visual appearance the images were zoomed about 4 times (remapped to higher resolution) but this fake improved resolution results in noticeable pixelation effect (visible square pixels).

· An animated GIF using monthly images is shown below. Using monthly data makes the transitions from one month to another too sharp. A better but more time consuming way would be using 8-day data with interpolation.

· The Santa Barbara Basin area was defined as shown in white color below. The image shows bottom depth and coastlines are also shown in white.

· A time series of the chlorophyll-a concentration was constructed for the Santa Barbara Basin using WAM program wam_statist. The median Chl values are shown below.

· The time series image is based on a table in the following form:

Image

SYear

EYear

SDay

EDay

Mask

Nin

Nout

Min

Max

Mean

StDev

Median

This table is the standard output from a wam_statist. The meaning of the table columns is the following:

Image – image file name

SYear, SDay – start year and day, respectively

EYear, EDay – end year and day, respectively

Mask – mask number (could be up to 255), only one mask used here

Nin, Nout – the number of valid (in) and invalid (out) pixels used

Min, Max, Mean, StDev, Median – the statistics parameters of the valid pixels

· To see the full table of statistics click on the time series image or here.

· Another way of looking at the monthly dynamics is to look at the monthly anomalies. Monthly anomalies are derived by first creating the monthly means for each of the twelve months using all available data (1986-2005) and then expressing each month as a ratio to the mean or as a difference from the mean. For chlorophyll we the ratio of the actual month values to the mean month values whereas for SST we subtract the mean month from the actual month. The calculation of monthly means and all the anomalies is done with a single command of a WAM script wam_anomaly. An animated GIF of the monthly anomaly images is shown below. Areas shown in red are significantly above the corresponding monthly mean whereas areas shown in blue are significantly below the corresponding monthly mean. A time series plot shown above for the median chlorophyll values in the Santa Barbara Basin could also be made for the anomal;ies.