38
J. Gower and S. King
0
0.2
0.4
0.6
0.8
1
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Start of year
Chlor (mg.m
-3
)
0
0.004
0.008
0.012
0.016
0.02
NFLH (mW.cm
-2
.
-1
.ster
-1
)
Chlor
Chlor'
NFLH
Fig. 2.2 Average surface chlorophyll concentrations (green) and normalized fluorescence (red)
from MODIS Aqua data in the Gulf of Guinea, from 3
◦ N to 3
◦ S and 20
◦ W to 0
◦
shown at right) in the months of January, April, July and October of 2011. Land is
masked as white. Ocean areas which are cloudy for the entire month, such as in the
Gulf of Guinea in January and in the Arabian Sea in July, are also masked to white.
The bright purple areas represent the lowest surface chlorophyll, less than 0.05 mg
m
−3 (see colour scale at right). A belt of high chlorophyll covers all latitudes at 40
◦ S
at all seasons. Areas of high chlorophyll along the equator especially in July in the
Gulf of Guinea in the Atlantic and to a lesser extent in the Indian Ocean, indicate the
effect of equatorial upwelling. Narrow bands of high chlorophyll near shore indicate
coastal upwelling in many areas, such as along the coasts of Namibia and western
South Africa near 30
◦ S, 15
◦ E, the Horn of Africa near 10
◦ N, 50
◦ E and west Africa
near 20
◦ N, 15
◦ W.
Figure 2.2 shows time series of MODIS Aqua data averaged by GIOVANNI over
the area 3
◦ N to 3
◦ S and 20 W to 0 W along the equator in the Gulf of Guinea. Of
the nine years for which MODIS Aqua so far provides data, maximum chlorophyll
(green line in Fig. 2.2) is in August in 5 years, July in three and September in one,
confirming the annual cycle apparent in Fig. 2.1. Fluorescence data (red line) peak
slightly earlier, in July of all years except 2003 to 2005 (June) and 2009 (August).
At the relative scaling of the two plots (50:1 when units are mg m
−3 and W m
−2
nm
−1 ster
−1 ), the green peaks tend to be higher than the red. When comparing the
green and red plots, allowance needs to be made for the expected self absorption of
fluorescence as expressed in Eq. 2.2. A modified chlorophyll (i.e. Chlor’: “fluorescing
J. Gower and S. King
0
0.2
0.4
0.6
0.8
1
2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Start of year
Chlor (mg.m
-3
)
0
0.004
0.008
0.012
0.016
0.02
NFLH (mW.cm
-2
.
-1
.ster
-1
)
Chlor
Chlor'
NFLH
Fig. 2.2 Average surface chlorophyll concentrations (green) and normalized fluorescence (red)
from MODIS Aqua data in the Gulf of Guinea, from 3
◦ N to 3
◦ S and 20
◦ W to 0
◦
shown at right) in the months of January, April, July and October of 2011. Land is
masked as white. Ocean areas which are cloudy for the entire month, such as in the
Gulf of Guinea in January and in the Arabian Sea in July, are also masked to white.
The bright purple areas represent the lowest surface chlorophyll, less than 0.05 mg
m
−3 (see colour scale at right). A belt of high chlorophyll covers all latitudes at 40
◦ S
at all seasons. Areas of high chlorophyll along the equator especially in July in the
Gulf of Guinea in the Atlantic and to a lesser extent in the Indian Ocean, indicate the
effect of equatorial upwelling. Narrow bands of high chlorophyll near shore indicate
coastal upwelling in many areas, such as along the coasts of Namibia and western
South Africa near 30
◦ S, 15
◦ E, the Horn of Africa near 10
◦ N, 50
◦ E and west Africa
near 20
◦ N, 15
◦ W.
Figure 2.2 shows time series of MODIS Aqua data averaged by GIOVANNI over
the area 3
◦ N to 3
◦ S and 20 W to 0 W along the equator in the Gulf of Guinea. Of
the nine years for which MODIS Aqua so far provides data, maximum chlorophyll
(green line in Fig. 2.2) is in August in 5 years, July in three and September in one,
confirming the annual cycle apparent in Fig. 2.1. Fluorescence data (red line) peak
slightly earlier, in July of all years except 2003 to 2005 (June) and 2009 (August).
At the relative scaling of the two plots (50:1 when units are mg m
−3 and W m
−2
nm
−1 ster
−1 ), the green peaks tend to be higher than the red. When comparing the
green and red plots, allowance needs to be made for the expected self absorption of
fluorescence as expressed in Eq. 2.2. A modified chlorophyll (i.e. Chlor’: “fluorescing