| Jungle Research Group | |
| at the Atmospheric Sciences Research Center |
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|
NIGEC/Harvard Forest
We continue our efforts to understand the physics of subcanopy flows and their connection to potential CO2 flux deficits. Fluxnet carbon budgets now rely on an empirical rule of thumb to account for respiration on calm nights. To understand flows on calm nights, we developed a microkinematic approach, the DRAINO experiments performed from 1999-2002.
Canopy structure. In 2002, subcanopy measurements of the wind and CO2 fields in a 120x120m grid around the EMS tower were conducted from mid-April to early December, covering the whole growing season. In addition, in collaboration with G. Parker of SERC, detailed canopy structure measurements were made using the methods of Parker et al. [2002], walking horizontal transects through the forest with an upward-looking laser range finder. Laser return readings were taken at 170Hz and binned in horizontal 2m sections along the path walked, equivalent to about 680 data points. Corrections were performed to correct for the bias to closer targets by assuming that leaves are Poisson randomly distributed [MacArthur and Horn, 1969]. An absolute canopy area density (CAD) is then derived using an empirical relationship between leaf area indices measured by leaf litter collection and laser return signals [Parker and Lefsky, 2003].
|
1999 |
2000 |
2001 |
2002 |
Total |
|
|
Study period |
27Jul-8 Nov |
22Aug-24Nov |
9Oct-26 Nov |
19 Apr–4 Dec |
|
|
Number of nights with all
data |
70 |
66 |
46 |
128 |
310 |
|
Number with CO2
flux deficit (N) |
40 (57%) |
38 (57%) |
24 (52%) |
79 (62%) |
181 (58%) |
|
Number of these N with u* <
0.2 m/s |
15 (38%) |
15 (39%) |
9 (38%) |
36 (46%) |
75 (41%) |
|
Number of these N with
drainage flow |
27 (68%) |
27 (71%) |
20 (83%) |
51
(65%) |
125
(69%) |
|
Number of these N with
stress flow |
1 (3%) |
2 (5%) |
0 (0%) |
7
(9%) |
10
(6%) |
|
Number of these N with
pressure flow |
10 (25%) |
6 (16%) |
4 (17%) |
17
(22%) |
37
(20%) |
Table 1: Summary of nightly conditions. The last four rows refer to the subset of nights with CO2 flux deficits. Drainage, stress and pressure flows refer to nights when the corresponding terms in Eq. (1) ([5], [4] and [6]) were dominant. Note that the last three rows may not always sum to 100% because on some nights no one of the forcing terms clearly dominated.
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Harvard Forest is approximately 3000 acres of forest in Petersham, Massachusetts (65 miles west of Cambridge). Above are two maps depicting the location of Harvard Forest. Images from http://www-as.harvard.edu/chemistry/hf/.
The Jungle Research Group, in association with Harvard Forest, takes atmospheric measurements from a 30m tower, which extends 6m above the forest canopy. The tower is located at 42.537755 N latitude and 72.171478 W longitude. The elevation at this location is 340m (ASL). Images of this tower can be found on the Harvard Forest Images page.
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Archived Plots: HF plots
HF NIGEC data sets.
The raw data files for HF/NIGEC project acquired in 2002-2005 were processed.
To view the listing of available processed data files, please click here.
If you have questions about this project or want to obtain some of these data sets please contact the project director Dr. David R. Fitzjarrald
His e-mail address is listed on the personnel page.
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