CARVE: Ecosystem Scale CH4 Emission Derived from Aircraft Observations 2012-2014

This dataset provides methane flux estimates derived from airborne measurements collected over Alaska and the western Yukon Territory during the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) between 2012 and 2014. The state-scale methane fluxes were calculated using a combination of atmospheric profiles and lagrangian transport modeling. The methane flux estimates were used in a simple linear regression model to estimate the fluxes from the tundra and boreal ecosystems. Methane fluxes were also used with a combination of environmental variables to derive a statistical relationship between domain-wide flux and soil temperature. Soil temperature products from North American Regional Reanalysis and derived parameters from a Boltmann-Arrhenius model were used to model methane flux and related uncertainties within the domain at monthly and daily frequencies.

This dataset includes three files in CSV format and two files in NetCDF format. 

This dataset provides methane flux estimates derived from airborne measurements collected over Alaska and the western Yukon Territory during the Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) between 2012 and 2014. Methane fluxes were calculated using a combination of atmospheric profiles and lagrangian transport modeling. The methane flux estimates were used in a simple linear regression model to estimate the fluxes from the tundra and boreal ecosystems. Methane fluxes were also used with a combination of environmental variables to derive a statistical relationship between domain-wide flux and soil temperature. Soil temperature products from North American Regional Reanalysis and derived parameters from a Boltmann-Arrhenius model were used to model methane flux and related uncertainties within the domain at monthly and daily frequencies.

Project: Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE)

The Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) is a NASA Earth Ventures (EV-1) investigation designed to quantify correlations between atmospheric and surface state variables for Alaskan terrestrial ecosystems through intensive seasonal aircraft campaigns, ground-based observations, and analysis sustained over a 5-year mission. CARVE collected detailed measurements of greenhouse gases on local to regional scales in the Alaskan Arctic and demonstrated new remote sensing and improved modeling capabilities to quantify Arctic carbon fluxes and carbon cycle-climate processes. CARVE science fills a critical gap in Earth science knowledge and satisfies high priority objectives across NASA’s Carbon Cycle and Ecosystems, Atmospheric Composition, and Climate Variability & Change focus areas as well as the Air Quality and Ecosystems elements of the Applied Sciences program. CARVE data also complements and enhances the science return from current NASA and non-NASA sensors.

Related Publication:

Hartery, S., Commane, R., Lindaas, J., Sweeney, C., Henderson, J., Mountain, M., Steiner, N., McDonald, K., Dinardo, S. J., Miller, C. E., Wofsy, S. C., and Chang, R. Y.-W. 2018. Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska, Atmos. Chem. Phys., 18, 185-202, https://doi.org/10.5194/acp-18-185-2018

Related Data:

A full list of data products from the CARVE campaign is available at: https://carve.ornl.gov/dataproducts.html

Budney, J.W., R.Y-W. Chang, R. Commane, B.C. Daube, A. Dayalu, S.J. Dinardo, E.W. Gottlieb, A. Karion, J.O.W. Lindaas, C.E. Miller, J.B. Miller, S. Miller, M. Pender, J.V. Pittman, J. Samra, C. Sweeney, S.C. Wofsy, and B. Xiang. 2016. CARVE: L2 Merged Atmospheric CO2, CO, O3 and CH4 Concentrations, Alaska, 2012-2015. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1402

Spatial Coverage: Alaska and western Yukon Territory 

Spatial Resolution: 0.5-degree

Temporal Coverage: 20120501 - 20141130

Temporal Resolution: Daily to monthly 

Study Area (These coordinates are the approximate locations of the study sites and may not match the extent of the data files. All latitude and longitude are given in decimal degrees.)

Site	Northern Extent	Western Extent	Eastern Extent	Southern Extent
Alaska and Yukon Territory	74.75	-169.75	-130.25	50.25

 

Date File Information

There are three files in CSV format and two files in NetCDF format (*.nc) included in this dataset. The two NetCDF files contain 0.5-degree gridded monthly and daily methane flux estimates. The three CSV files provide these monthly and daily methane flux estimates for the entire study area and divided between boreal and tundra ecosystems. 

 

NetCDF Data Files

• CARVE-CH4.model.daily.nc --- 0.5-degree gridded daily CH4 emissions estimates calculated from atmospheric profiles and lagrangian transport modeling (Boltzmann-Arrhenius model)
• CARVE-CH4.model.monthly.nc --- 0.5-degree gridded monthly CH4 emissions estimates calculated from atmospheric profiles and lagrangian transport modeling (Boltzmann-Arrhenius model)

Table 1. Variables in each of the NetCDF files

Variable name	Units	Description
area	m2	Land surface area of domain
ch4_flux	kg per m2	Total CH4 emitted during time interval
ch4_flux_u	kg per m2	Uncertainty of total CH4 emitted during time interval. See Section 4 for details.
boreal	Flag: 0 or 1	Boreal ecoregion (Boreal = 1, other = 0)
latitude	degrees_north	Latitude coordinate
longitude	degrees_east	Longitude coordinate
time	days since 1990-01-01	Time in days since 1990-01-01 00:00:00 UTC
tundra	Flag: 0 or 1	Tundra ecoregion (Tundra = 1, other = 0)

 

Tabular Data Files

• CARVE-CH4.aircraft.csv

Estimates of CH4 from atmospheric profiles for the boreal and tundra ecosystems of Alaska and the Yukon.

Column name	Units	Description
profile_date	YYYY-MM-DD	Profile date
profile_number		Profile number
start_datetime	YYYY-MM-DD HH:MM:SS UTC	Start date and time
end_datetime	YYYY-MM-DD HH:MM:SS UTC	End date and time
ch4_flux	mg m-2 d-1	CH4 flux
total_column_footprint_influence	ppm (nmol-1 m-2 s-1)-1	Total column footprint influence
ch4_background	ppb	CH4 background
boundary_layer_height	m	Boundary layer height
flag1 *	Flag: 0 or 1	1 = Large variability in free tropospheric CH4
flag2 **	Flag: 0 or 1	1 = Difficulty estimating boundary layer height
flag3 ***	Flag: 0 or 1	1 = Boundary layer influence anomalously low

* Refers to an observed problem in constraining the background value of CH4 in the free troposphere which is used to calculate the mixed layer enhancement.

** Reported when the refractivity method for determining the mixed layer height significantly differed from observations of the profiles of water vapor, potential temperature and other trace gases. 

*** Indicates when the average domain integrated footprint influence throughout the mixed layer was less than 5% of the campaign average (~ 1 ppm nmol^-1 m^-2 s^-1). This indicates that the air was likely of foreign origin (i.e. not within the domain of study).

 

• CARVE-CH4.aircraft.monthly.csv

Monthly regional average flux of CH4 for the boreal and tundra ecosystems of Alaska and the Yukon. 

Column name	Units	Description
month	YYYY-MM	Month number (MM; Jan = 01, Feb = 02, etc.), recorded for growing season only.
weighted_average_ch4_flux	mg m-2 d-1	Weighted average CH4 flux
weighted_average_uncertainty	mg m-2 d-1	Weighted average uncertainty of CH4 flux. See Section 4 for details.
average_uncertainty	mg m-2 d-1	Average uncertainty of CH4 flux. See Section 4 for details.
weighted_standard_deviation	mg m-2 d-1	Weighted standard deviation of CH4 flux. See Section 4 for details.
standard_deviation	mg m-2 d-1	Standard deviation of CH4 flux. See Section 4 for details.
flag	Flag: 0 or 1	Flag = 1 whenever there were consistent differences between observed CH4 background used to estimate CH4 enhancements and the CH4 background observed at in situ sites within Alaska

 

• CARVE-CH4.ecosystem.csv

Monthly average flux of CH4 for each of the domain ecosystems, tundra and boreal. 

Column name	Units	Description
month		Month number (Jan = 1, Feb = 2, etc.), recorded for growing season only.
tundra_ch4_flux	mg m-2 d-1	Tundra CH4 flux
uncertainty_in_tundra_ch4_flux	mg m-2 d-1	Uncertainty in tundra CH4 flux. See Section 4 for details.
boreal_ch4_flux	mg m-2 d-1	Boreal CH4 flux
uncertainty_in_boreal_ch4_flux	mg m-2 d-1	Uncertainty in boreal CH4 flux. See Section 4 for details.

The estimates of regional scale CH4 budget included in this dataset can be used to investigate the relationship between land surface properties and atmospheric CH4 observations.

Uncertainties in the estimated CH4 flux from individual profiles were determined through bootstrapping both observational measurements and the integrated model footprints involved in their calculation by sampling each variable with replacement 500 times. Explicit variables included were as follows:

• matching observations of CH4, T, P, and Pw at each 250-m altitude bin to estimate uncertainties associated with the observations and spatial variability; 
• the footprint sensitivity at each 250-m altitude bin, approximating the uncertainty of releasing particles within neighboring grid cells - it should be emphasized that this is not a true posterior variability and may underestimate full modelling uncertainties, although it is still a useful approximation of a type of model uncertainty;
• the mixed layer height, which was varied by +/- 250 m and propagated through the calculations of flux by either adding or removing another 250-m bin to the integration of the column enhancement of CH4, but without varying the CH4 background, representing the uncertainty due to height;
• same as above but changing the CH4 background; and
• all of the above propagated through the entire calculation, representing the total methodological uncertainty in our calculations of CH4 flux.

The 95 % confidence interval (CI) of the last step was used to estimate the uncertainty associated with the estimated CH4 flux from individual profiles. The mean, minimum, and maximum 95% CI for each of these steps reveal that the largest methodological uncertainty associated with the results is the combined uncertainty in identifying both the mixed layer height and the CH4 background.

Uncertainties in the monthly-mean CH 4 flux were estimated in four ways:

• average uncertainty, the 95% CI for each individual estimate is averaged for each month with no weighting;
• weighted average uncertainty, the 95%CI for each individual estimate is averaged for each month and weighted by the column-integrated total surface influence;
• standard deviation, the normal standard deviation is calculated from the residuals of the weighted monthly mean;
• and weighted standard deviation, the standard deviation of all CH4 flux estimates within a given month is calculated, weighting each residual by the total surface influence and the inverse of the square of the 95% CI.

Uncertainties calculated using the weighted standard deviation are given because they account for both monthly variability and the uncertainty in the flux estimated from each profile.

For the ecosystem and regression analysis, uncertainties in the net ecosystem emissions and monthly average fluxes were propagated using the uncertainties in regression parameters.

This dataset contains methane fluxes derived from in-situ gas measurements collected at ~2.5-second intervals by two ring-down spectrometers (Budney et al. 2016) using lagrangian transport modeling. The primary product of this dataset is the domain average fluxes in units of mg CH4 m^-2 d^-1. They were calculated on a profile-by-profile basis and are listed in CARVE-CH4.aircraft.csv.

Monthly average CH4 fluxes for the Alaska were estimated from the modeled methane fluxes. These are listed in CARVE-CH4.aircraft.monthly.csv. Monthly fluxes were translated into gridded monthly emissions in units of kg CH4 m^-2 (CARVE-CH4.aircraft.flux.nc) on a 0.5-degree lat/lon grid. Grid cells falling outside of the CARVE domain were masked from the map using a fill value of -999.

The CH4 flux estimates were also used in a simple linear regression model to estimate the fluxes from the tundra and boreal ecosystems (conglomerates of EPA Level III ecosystems) described in Hartery et al. (2018). The monthly ecosystem fluxes are listed in CARVE-CH4.ecosystem.csv. The 0.5-degree gridded boreal and tundra ecosystems are depicted on the map in Figure 2. 

Figure 2. Ecoregions derived from the Commission for Environmental Cooperation Level II Terrestrial Ecoregions. The study region is defined by the coastline and filled ecoregions (Hartery et al. 2018). 

The methane fluxes were used with a combination of environmental variables to derive a statistical relationship between domain-wide flux and soil temperature. These calculations use the soil temperature products from NARR and derived parameters from a Boltzmann-Arrhenius model to model CH4 flux within the domain. These calculations and related uncertainties are available in CARVE-CH4.model.monthly.nc and CARVE-CH4.model.daily.nc and are on the same 0.5-degree lat/lon grid. The monthly calculations were calculated using monthly averaged temperatures from NARR and daily temperatures from the daily files. 

Budney, J.W., R.Y-W. Chang, R. Commane, B.C. Daube, A. Dayalu, S.J. Dinardo, E.W. Gottlieb, A. Karion, J.O.W. Lindaas, C.E. Miller, J.B. Miller, S. Miller, M. Pender, J.V. Pittman, J. Samra, C. Sweeney, S.C. Wofsy, and B. Xiang. 2016. CARVE: L2 Merged Atmospheric CO2, CO, O3 and CH4 Concentrations, Alaska, 2012-2015. ORNL DAAC, Oak Ridge, Tennessee, USA. https://doi.org/10.3334/ORNLDAAC/1402

Hartery, S., Commane, R., Lindaas, J., Sweeney, C., Henderson, J., Mountain, M., Steiner, N., McDonald, K., Dinardo, S. J., Miller, C. E., Wofsy, S. C., and Chang, R. Y.-W. 2018. Estimating regional-scale methane flux and budgets using CARVE aircraft measurements over Alaska, Atmos. Chem. Phys., 18, 185-202, https://doi.org/10.5194/acp-18-185-2018