Subject: photosynthesis calculations
From: Ranga Myneni (rmyneni@crsa.bu.edu)
Date: Wed Jul 02 1997 - 13:45:49 MDT
Dear CCM-LSM User:
I have a monthly-averaged field of vegetation canopy photosynthesis
(FPSN) in micro mols CO2 per square meter per second, at T31x15
resolution (48x48 matrix) for 1 model year (12 such matrices).
I would like to evaluate annual photosynthesis for the globe from
this data set (units: Giga Tons Carbon). So, I
(1) Evaluated the average size of the grid cell by latitude (km*km). The
numbers I got are appended at the bottom of this email. Can someone
please check if these numbers are correct?
(2) Using surfdat.t31x15.0696, the fraction of each pixel on land not
covered by lakes and wetlands was estimated ("land pixel").
(3) The area of the "land pixel" covered by vegetation was then
evaluated (basically excluding the bare areas here).
(4) The photosynthetic rate (FPSN) of each pixel was then multiplied
by the area of the pixel (in square meters). This, I then summed and
multiplied by (44.0/10**6) to obtain the global photosynthetic
rate in grams Carbon per second.
(5) I then multiplied this quantity by the number of seconds in a month,
and summed it over the year.
I am getting estimates of global photosynthesis well over 470 Giga Tons
of Carbon! Nooooooooo....
Can someone help? THANKS!
-ranga myneni
-------------------------
T31x15 Resolution
CCM LAT GRID CELL
INDEX AREA (km*km)
1.0 17786.436
2.0 38618.434
3.0 61657.043
4.0 82551.648
5.0 104251.828
6.0 123638.258
7.0 146742.266
8.0 166945.391
9.0 183080.344
10.0 203013.562
11.0 223097.047
12.0 233510.953
13.0 252889.047
14.0 269640.344
15.0 283298.781
16.0 289961.750
17.0 306747.812
18.0 310479.312
19.0 325074.094
20.0 332272.688
21.0 331511.656
22.0 342349.906
23.0 338603.125
24.0 346720.000
25.0 346694.969
26.0 338583.656
27.0 342316.531
28.0 331485.219
29.0 332229.562
30.0 318848.000
31.0 316588.531
32.0 300880.688
33.0 295668.875
34.0 283208.344
35.0 264485.562
36.0 253001.734
37.0 238305.391
38.0 223014.953
39.0 202932.875
40.0 182978.781
41.0 166843.828
42.0 143294.609
43.0 126853.562
44.0 104118.258
45.0 82393.047
46.0 61470.609
47.0 38393.043
48.0 17380.174
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