Martha P. Butler

Estimates of net CO2 flux by application of equilibrium boundary layer concepts to CO2 and water vapor measurements from a tall tower

fluxes that affects the CO2 and water vapor mixing ratios. We apply quasi-equilibrium concepts for the terrestrial ABL to measurements of CO2 and water vapor made within the ABL from a tall tower (396 m) in Wisconsin. We suppose that CO2 and water vapor mixing ratios in the ABL approach an equilibrium on timescales longer than a day: a balance between the surface fluxes and the exchange with the free troposphere above. By using monthly averaged ABL-to-free-tropospheric water vapor differences and surface water vapor flux, realistic estimates of vertical velocity exchange with the free troposphere can be obtained. We then estimated the net surface flux of CO2 on a monthly basis for the year of 2000, using ABL-to-free-tropospheric CO2 differences, and our flux difference estimate of the vertical exchange. These ABL-scale estimates of net CO2 flux gave close agreement with eddy covariance measurements. Considering the large surface area which affects scalars in the ABL over synoptic timescales, the flux difference approach presented here could potentially provide regional-scale estimates of net CO2 flux. INDEX TERMS: 1615 Global Change: Biogeochemical processes (4805); 1818 Hydrology: Evapotranspiration; 3307 Meteorology and Atmospheric Dynamics: Boundary layer processes; 3322 Meteorology and Atmospheric Dynamics: Land/atmosphere interactions; KEYWORDS: boundary layer, CO2 exchange, evapotranspiration

Transport of Carbon Dioxide in the Presence of Storm Systems over a Northern Wisconsin Forest

Mixing ratios of CO2 often change abruptly in the presence of inclement weather and low pressure systems. Water vapor mixing ratio, temperature, wind speed, and wind direction data are used to infer that the abrupt changes in CO2 mixing ratios at a site in northern Wisconsin are due to tropospheric mixing, horizontal transport, or a combination of both processes. Four different scenarios are examined: the passage of a summer cold front, a summer convective storm, an early spring frontal passage, and a late autumn low pressure system. Each event caused CO2 mixing ratios to change rapidly when compared to biological processes. In one summer convective event, vertical mixing caused CO 2 mixing ratios to rise more than 22 ppm in just 90 s. Synoptic-scale transport was also evident in the presence of storm systems and frontal boundaries. In the cases examined, synoptic-scale transport changed CO2 mixing ratios as much as 15 ppm in a 1-h time period. The events selected here represent extremes in the rate of change of boundary layer CO2 mixing ratios, excluding the commonly observed venting of a shallow, stable boundary layer. The rapid changes in CO 2 mixing ratios that were observed imply that large mixing ratio gradients must exist, often over rather small spatial scales, in the troposphere over North America. These rapid changes may be utilized in inverse modeling techniques aimed at identifying sources and sinks of CO2 on regional to continental scales.

Inaction and climate stabilization uncertainties lead to severe economic risks

Climate stabilization efforts must integrate the actions of many socio-economic sectors to be successful in meeting climate stabilization goals, such as limiting atmospheric carbon dioxide (CO2) concentration to be less than double the pre-industrial levels. Estimates of the costs and benefits of stabilization policies are often informed by Integrated Assessment Models (IAMs) of the climate and the economy. These IAMs are highly non-linear with many parameters that abstract globally integrated characteristics of environmental and socio-economic systems. Diagnostic analyses of IAMs can aid in identifying the interdependencies and parametric controls of modeled stabilization policies. Here we report a comprehensive variance-based sensitivity analysis of a doubled-CO2 stabilization policy scenario generated by the globally-aggregated Dynamic Integrated model of Climate and the Economy (DICE). We find that neglecting uncertainties considerably underestimates damage and mitigation costs associated with a doubled-CO2 stabilization goal. More than ninety percent of the states-of-the-world (SOWs) sampled in our analysis exceed the damages and abatement costs calculated for the reference case neglecting uncertainties (1.2 trillion 2005 USD, with worst case costs exceeding

An Approximate Footprint Model for Flux Measurements in the Convective Boundary Layer

60 trillion). We attribute the variance in these costs to uncertainties in the model parameters relating to climate sensitivity, global participation in abatement, and the cost of lower emission energy sources.

Causes of interannual variability in ecosystem–atmosphere CO2 exchange in a northern Wisconsin forest using a Bayesian model calibration

Abstract An explicit footprint model for flux measurements of passive scalars in the lower part of the convective boundary layer (CBL) is introduced. A simple footprint model is derived analytically in an idealized CBL. The simple model can simulate the overall characteristics of the flux footprint. Then a method is proposed to adjust the analytical solutions to those from a Lagrangian stochastic model that considers more realistic atmospheric conditions in the vertical direction. The adjusted footprint model is a function of Monin–Obukhov length (L), roughness length, receptor height, and CBL depth (h). Comparison between the results from the adjusted footprint model and stochastic model suggests that the adjusted footprint model can well simulate the streamwise extent of the footprint within the dimensionless upwind distance X < 1, which accounts for a majority of the footprint. The model applies to stabilities of –L/h between 0.01 and 0.1 and roughness lengths between 10−5 and 2 × 10−3h in the lower pa...