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Britton Stephens

General Information

Britton Stephens

EOL : RAF - TIIMES
Scientist II
BEACHON & BGS

Contact Information:
PO Box 3000, Boulder, CO 80307-3000
Office: Jeffco-143
Telephone: 303-497-1018
Email: stephens@ucar.edu
Home Page - Vita

Research Focus FY08:

Figure 1: The project HIAPER Pole-to-Pole Observations of Atmospheric Tracers (HIPPO) will conduct five global loops over the next three years, profiling from the tropopause to the surface. Investigators from Harvard, NCAR, Scripps, and NOAA will measure CO2, O2, CH4, CO, N2O, H2, SF6, COS, CFCs, HCFCs, O3, H2O, black carbon, and selected hydrocarbons - High resolution figure

Figure 2: The NCAR Airborne Oxygen Instrument (AO2) measures O2 concentration (reported as O2:N2 ratio) using a vacuum-ultraviolet absorption technique. It consists of a pump module, a cylinder module, and an instrument module - High resolution figure

Figure 3: Measurements of atmospheric O2 and CO2, made by the AO2 instrument on the NCAR GV during the START-08/pre-HIPPO campaign, while descending from the stratosphere to the surface over Grand Forks, ND in the mid afternoon. Correlated O2 and CO2 variations reflect the influence of stratospheric air age across the tropopause, pollution and boundary-layer air plumes in the free troposphere, and photosynthetic CO2 drawdown and O2 enhancement in the boundary layer - High resolution figure

Figure 4: Summertime RACCOON data averaged over the months June-August. a) Calibrated CO2 values from three heights at NWR b) Boxplot of the distribution of hourly standard deviations at NWR. c) Boxplot showing the distribution of 3.5 m to 5.1 m vertical gradients at NWR. d) Filtered diurnal cycles from four sites are generally representative of concentrations over large regions - High resolution figure

Figure 5: Monthly mean RACCOON CO2 concentrations at four sites and differences from marine boundary layer concentrations interpolated to the same latitude. The differences indicate strong CO2 uptake during spring in the Central Rocky Mountains - High resolution figure

Figure 6: Nighttime valley CO2 buildup measured at the Fraser Experimental Forest site. The decreasing trend indicates reduced ecosystem respiration following widespread beetle mortality - High resolution figure

Britton Stephens’ TIIMES research is focused on advancing our understanding of global carbon cycling and supporting the biogeosciences research community. This work has included airborne and ground-based field observations targeting regional scale carbon fluxes, analyses of background observations to investigate global carbon cycling, and instrument development for tower and aircraft applications.

 

HIAPER Pole-to-Pole Observations of Atmospheric CO2 and Related Tracers (HIPPO)

There exists > 100 % uncertainty in localizing the terrestrial uptake of anthropogenic carbon to specific latitudinal zones and this uncertainty is directly linked to vertical transport biases in the coarse-resolution atmospheric transport models used in CO2 inversion studies. Comprehensive measurements of atmospheric CO2 and related tracers, particularly at altitude and in previously undersampled regions, are needed to challenge these models and improve our understanding of global carbon cycling. This is the aim of the project HIAPER Pole-to-Pole Observations of Atmospheric CO2 and Related Tracers (HIPPO), a Harvard-NCAR-Scripps-NOAA collaboration to measure cross sections of atmospheric concentrations approximately pole-to-pole, from the surface to the tropopause, five times during different seasons over the next three-years (see Figure 1).

A comprehensive suite of tracers of the carbon cycle and related species will be measured: CO2, O2:N2 ratio, CH4, CO, N2O, 13CO2:12CO2, H2, SF6, COS, CFCs, HFCs, HCFCs, black carbon, and selected hydrocarbons. HIPPO will transect the mid-Pacific ocean and return over the Eastern Pacific. The program will provide the first comprehensive, global survey of atmospheric trace gases, covering the full troposphere in all seasons and multiple years. HIPPO will quantify the sources of major carbon cycle and greenhouse gases by region at the global scale.

Britt Stephens is supporting several key systems on these flights, including the NCAR Airborne Oxygen instrument (AO2, see Figure 2) and the MEDUSA flask sampler. These systems flew during the START-08/pre-HIPPO campaign in April-June of 2008. In this campaign, AO2 made the first successful airborne measurements of oxygen variations. This vacuum-ultraviolet absorption instrument is based on an existing NCAR laboratory instrument, but has been designed specifically for airborne use to minimize motion and thermal sensitivity and with a pressure and flow controlled inlet system. AO2 has a precision of +/- 2 per meg on a 4-second measurement which is the equivalent to detecting the removal of one O2 molecule from 2.5 million molecules of air. Such measurements are very useful in discriminating various influences on atmospheric CO2 (see Figure 3). The flasks collected during this campaign are being analyzed at Scripps for O2, Ar, and isotopes of CO2.

 

Regional Atmospheric Continuous CO2 Network in the Rocky Mountains (Rocky RACCOON)

In order to improve our understanding of regional carbon fluxes in the Rocky Mountain West, Britt Stephens has developed and deployed autonomous, inexpensive, and robust CO2 analyzers (AIRCOA) at six sites throughout Colorado, Utah, and Arizona over the past three years (http://raccoon.ucar.edu).  Analysis of the diurnal cycles in CO2 concentration and CO2 variability at these sites provide insight as to when and under what conditions mountaintop CO2 signals are regionally representative, as well as first-order constraints on boundary-layer heights and flux rates for use in evaluating model fidelity (Figure 4).  Comparisons between the RACCOON measurements and estimates of free-tropospheric background concentrations reveal regional-scale CO2 flux signals that are generally consistent with one another and our expectation of peak CO2 uptake in mountain forests during spring (Figure 5).  Combining these differences with information on boundary-layer mixing can lead to quantitative estimates of monthly regional CO2 fluxes.  These data have also been used in the NOAA CarbonTracker flux estimation system as well as the GlobalView data product used by modeling groups around the world, and are a key NCAR contribution to the multi-agency North American Carbon Program (NACP).

The RACCOON observations at Fraser Experimental Forest have occurred while the trees in the St. Louis creek drainage have experienced widespread mortality due to mountain pine bark beetle infestation. The CO2 measurements at the base of this valley show large increases in CO2 at night as the valley drainage flow pools respiration from a large area.  This nocturnal build-up has decreased over the past three years (Figure 6), suggesting a decrease in ecosystem respiration in response to the insect outbreak.  This decrease indicates that the reduction in autotrophic respiration is greater than any short-term increase in litter fall, and will be a valuable test of models predicting the impact of the recent outbreaks on regional scale carbon fluxes.  

 

Plans for FY09 and beyond

Britt Stephens will deploy AO2 and the MEDUSA sampler on the NCAR GV as part of the first HIPPO global campaign in January of 2009, then again in 4 more campaigns in 2009-2011.  Both AO2 and MEDUSA are planned for long-term availability to community researchers.
 
Future plans to address regional carbon fluxes include in depth analysis of ACME-07 and Rocky RACCOON data and synthesis with modeling efforts to

  1. Define regional-scale monthly to interannual carbon fluxes for the U.S. Central Rocky Mountains and Southwest
  2. Assess key drivers of variability and trends including drought, fires, and insects
  3. Optimize community CO2 observational efforts across the Mountain West

 

Community Service FY08:

  • Graduated Research Advisor & Thesis Committee: Sherri Heck, University of Boulder
  • member: Wallowa Mountain Institute Advisory Board
  • Scientific Steering Committee: 8th International Carbon Dioxide Conference
  • U.S. National Ecological Observatory Network (NEON) Fundamental Instrument Unit Tiger Team, 2007 - present.
  • North American Carbon Program (NACP) Mid-Continent Intensive (MCI) working groups: MCI Science Team, MCI Coordination, MCI Topic 2 Region-wide Inversion Analyses, 2006 – present.
  • The Surface Ocean - Lower Atmosphere Study (SOLAS) Implementation Group 3, 2003 - present.
  • SOLAS/Integrated Marine Biogeochemistry and Ecosystem Research (IMBER) Carbon Group (SIC), 2005 - present.

Scientific Talks FY08:

  • Atmospheric Oxygen Measurements during HIPPO: HIAPER Pole-to-Pole Observations of Atmospheric Tracers (NCAR EOL Science Group meeting, Boulder, CO, September, 2008)
  • HIAPER Pole-to-Pole Observations of Atmospheric Tracers (NCAR TIIMES Science Advisory Committee meeting, Boulder, CO, June, 2008)
  • HIAPER Pole-to-Pole Observations of Atmospheric Tracers: Global Carbon Cycle (START-08 planning meeting, Boulder, CO, January, 2008)
  • Closing in on the Missing Carbon Sink: Implications for Climate Research and Mitigation (U.N. Climate Change Conference, Bali, Indonesia, December, 2007)

Publications FY08:

Obrist, D., A. Hallar, I. McCubbin, B. B. Stephens, T. Rahn, 2008: Atmospheric mercury concentrations at Storm Peak Laboratory in the Rocky Mountains: Evidence for long-range transport from Asia, boundary layer contributions, and plant mercury uptake. Atmos. Environ., doi: 10.1016/j.atmosenv.2008.06.051. (In Press)

Burns, S. P., A. Delany, J. Sun, B. B. Stephens, S. P. Oncley, G. D. Maclean, S. R. Semmer, J. Schroter, J. Ruppert, 2008: An evaluation of calibration techniques for in-situ carbon dioxide measurements using a programmable portable trace-gas measuring system. J. Atmos. Ocean. Technol., doi: 10.1175/2008JTECHA1080.1. (In Press)

Kort, E.A., Eluszkiewicz, J., Stephens, B.B., Miller, J.B., Gerbig, C., Nehrkorn, T., Daube, B.C., Kaplan, J.O., Houweling, S., Wofsy, S.C., Emissions of CH_4 and N_2 O over the United States and Canada based on a receptor-oriented modeling framework and COBRA-NA atmospheric observations, /Geophysical Research Letters/, 35, L18808, doi:10.1029/2008GL034031, 2008.