# Presentation: 037829

## Deriving Daytime Variables from the Ameriflux Standard Eddy Covariance Data Set

- Catharine van Ingenac (vaningen@microsoft.com), Deb Agarwalabd  (daagarwal@lbl.gov), Marty Humphreye (humphrey@cs.virginia.edu) , Jie Lie (jl3yhhrey@cs.virginia.edu)
-  Berkeley Water Centera; Lawrence Berkeley National Laboratoryb; Microsoft Researchc; University of California, Berkeleyd; University of Virginiae

- Abstract
- A gap-filled, quality assessed eddy covariance dataset has recently become available for the AmeriFlux network. This dataset uses standard processing and produces commonly used science variables. This shared dataset enables robust comparisons across different analyses. Of course, there are many remaining questions. One of those is how to define "during the day" which is an important concept for many analyses. Some studies have used local time – for example 9am to 5pm; others have used thresholds on photosynthetic active radiation (PAR). A related question is how to derive quantities such as the Bowen ratio. Most studies compute the ratio of the averages of the latent heat (LE) and sensible heat (H). In this study, we  use different methods of defining "during the day" for GPP, LE, and H. We evaluate the differences between methods in two ways. First, we look at a number of statistics of GPP. Second, we look at differences in the derived Bowen ratio.  Our goal is not science per se, but rather informatics in support of the science.

- The daytime values computed with local time daytime differ from those computed with PAR > 5 or solar elevation. The computed daytimes always give a higher value of GPP.

- URL:  http://www.fluxdata.org/

- 203 site-years of data from 53 AmeriFlux sites were used in this study

- B31A-0286

- Annual values of GPP computed with local time daytime tend to be  consistent. The 9am to 5pm daytime values tend to be 25% larger – a bit less than simple linear scaling of the time window. The differences are larger with smaller annual GPP values.

| site ID | Name | Tower PI | PI E-Mail |
| --- | --- | --- | --- |
| US-ARb | ARM Southern Great Plains burn site- Lamont | Margaret Torn | mstorn@lbl.gov |
| US-ARc | ARM Southern Great Plains control site- Lamont | Margaret Torn | mstorn@lbl.gov |
| US-ARM | ARM Southern Great Plains site- Lamont | Margaret Torn | mstorn@lbl.gov |
| US-Bar | Bartlett Experimental Forest | Andrew Richardson | andrew.richardson@unh.edu |
| US-Blo | Blodgett Forest | Allen Goldstein | ahg@nature.berkeley.edu |
| US-Bo2 | Bondville (companion site) | Carl Bernacchi | bernacch@uiuc.edu |
| US-Dk1 | Duke Forest-open field | Gaby Katul | gaby@duke.edu |
| US-Dk2 | Duke Forest-hardwoods | Gaby Katul | gaby@duke.edu |
| US-Dk3 | Duke Forest - loblolly pine | Gaby Katul | gaby@duke.edu |
| US-Fmf | Flagstaff - Managed Forest | Sabina Dore  | Sabina.Dore@nau.edu |
| US-FR2 | Freeman Ranch- Mesquite Juniper | Marcy Litvak | mlitvak@unm.edu |
| US-Fuf | Flagstaff - Unmanaged Forest | Sabina Dore  | Sabina.Dore@nau.edu |
| US-Fwf | Flagstaff - Wildfire | Sabina Dore  | Sabina.Dore@nau.edu |
| US-Ha1 | Harvard Forest EMS Tower (HFR1) | Bill Munger | jwmunger@seas.harvard.edu |
| US-Ha2 | Harvard Forest Hemlock Site | Julian Hadley | jhadley@fas.harvard.edu |
| US-Ho1 | Howland Forest (main tower) | Dave Hollinger | davidh@hypatia.unh.edu |
| US-Ho2 | Howland Forest (west tower) | Dave Hollinger | davidh@hypatia.unh.edu |
| US-IB1 | Fermi National Accelerator Laboratory- Batavia (Agricultural site) | Roser Matamala | matamala@anl.gov |
| US-IB2 | Fermi National Accelerator Laboratory- Batavia (Prairie site) | Roser Matamala | matamala@anl.gov |
| US-KS1 | Kennedy Space Center (slash pine) | Bert Drake | drakeb@si.edu |
| US-KS2 | Kennedy Space Center (scrub oak) | Bert Drake | drakeb@si.edu |
| US-Los | Lost Creek | Ken Davis | davis@essc.psu.edu |
| US-LPH | Little Prospect Hill | Julian Hadley | jhadley@fas.harvard.edu |
| US-Me1 | Metolius - Eyerly burn | Bev Law | bev.law@oregonstate.edu |
| US-Me2 | Metolius-intermediate aged ponderosa pine | Bev Law | bev.law@oregonstate.edu |
| US-Me3 | Metolius-second young aged pine | Bev Law | bev.law@oregonstate.edu |
| US-Me4 | Metolius-old aged ponderosa pine | Bev Law | bev.law@oregonstate.edu |
| US-MMS | Morgan Monroe State Forest | Danilo Dragoni | ddragoni@indiana.edu |

| site ID | Name | Tower PI | PI E-Mail |
| --- | --- | --- | --- |
| US-Me1 | Metolius - Eyerly burn | Bev Law | bev.law@oregonstate.edu |
| US-Me2 | Metolius-intermediate aged ponderosa pine | Bev Law | bev.law@oregonstate.edu |
| US-Me3 | Metolius-second young aged pine | Bev Law | bev.law@oregonstate.edu |
| US-Me4 | Metolius-old aged ponderosa pine | Bev Law | bev.law@oregonstate.edu |
| US-MMS | Morgan Monroe State Forest | Danilo Dragoni | ddragoni@indiana.edu |
| US-MOz | Missouri Ozark Site | Lianhong Gu | lianhong-gu@ornl.gov |
| US-NC1 | NC_Clearcut | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-NC2 | NC_Loblolly Plantation | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Ne1 | Mead - irrigated continuous maize site | Shashi Verma | sverma@unlnotes.unl.edu |
| US-Ne2 | Mead - irrigated maize-soybean rotation site | Shashi Verma | sverma@unlnotes.unl.edu |
| US-Ne3 | Mead - rainfed maize-soybean rotation site | Shashi Verma | sverma@unlnotes.unl.edu |
| US-NR1 | Niwot Ridge Forest (LTER NWT1) | Russ Monson | Russell.Monson@colorado.edu |
| US-Oho | Oak Openings | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-PFa | Park Falls/WLEF | Ken Davis | davis@essc.psu.edu |
| US-SRM | Santa Rita Mesquite | Russ Scott | rscott@tucson.ars.ag.gov |
| US-Syv | Sylvania Wilderness Area | Ken Davis | davis@essc.psu.edu |
| US-Ton | Tonzi Ranch | Dennis Baldocchi | baldocchi@nature.berkeley.edu |
| US-UMB | Univ. of Mich. Biological Station | Peter Curtis | curtis.7@osu.edu |
| US-Var | Vaira Ranch- Ione | Dennis Baldocchi | baldocchi@nature.berkeley.edu |
| US-WCr | Willow Creek | Ken Davis | davis@essc.psu.edu |
| US-Wi0 | Young red pine (YRP) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi1 | Intermediate hardwood (IHW) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi2 | Intermediate red pine (IRP) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi4 | Mature red pine (MRP) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi5 | Mixed young jack pine (MYJP) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi6 | Pine barrens #1 (PB1) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi7 | Red pine clearcut (RPCC) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi8 | Young hardwood clearcut (YHW) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wi9 | Young Jack pine (YJP) | Jiquan Chen | Jiquan.Chen@utoledo.edu |
| US-Wkg | Walnut Gulch Kendall Grasslands | Russ Scott | rscott@tucson.ars.ag.gov |

- Our thanks to Tower Primary Investigators
- and their sponsors

- US-HO1
- lat. = 45.2041
- biome = ENF
- 2003

- Example computations of daytime GPP over a site year.

- US-Ne1
- lat. = 41.1651
- biome = CRO
- 2004

- US-KS2
- lat. = 28.6086
- biome = CSH
- 2004

- Local time based daytimes are simple time windows of 9am to 5pm and 10am to 4pm.

- PAR (or PPFD) daytime uses the observed photosynthetic active radiation flux data. “Daytime” is when PAR > is above 5 or above 20.

- Solar elevation (or daylength equation) daytime is centered at local noon with a length of day (Daylength) computed as:

- Declination = 23.5 * cos(2p *
-          (DayOfYear – 172) /365)
- Daylength = acos(- tan(p * Latitude /180) * tan(p * Declination/180)) * 2/15 *180/p

- While the annual values of GPP computed with the PAR > 5 and solar elevation tend to be the same, the actual duration of the “daytime” are different.
- The plots at left show the number of site-days with a given length of daytime. Season are defined with 3 month duration; winter begins in December.

- Daytime values of Bowen Ratio computed by solar elevation and PAR>5 differ more than the daily GPP values. We’re don’t yet know why.