Douglas Chan

Modeling and Scaling Coupled Energy, Water, and Carbon Fluxes Based on Remote Sensing: An Application to Canada's Landmass

Abstract Land surface models (LSMs) need to be coupled with atmospheric general circulation models (GCMs) to adequately simulate the exchanges of energy, water, and carbon between the atmosphere and terrestrial surfaces. The heterogeneity of the land surface and its interaction with temporally and spatially varying meteorological conditions result in nonlinear effects on fluxes of energy, water, and carbon, making it challenging to scale these fluxes accurately. The issue of up-scaling remains one of the critical unsolved problems in the parameterization of subgrid-scale fluxes in coupled LSM and GCM models. A new distributed LSM, the Ecosystem–Atmosphere Simulation Scheme (EASS) was developed and coupled with the atmospheric Global Environmental Multiscale model (GEM) to simulate energy, water, and carbon fluxes over Canada’s landmass through the use of remote sensing and ancillary data. Two approaches (lumped case and distributed case) for handling subgrid heterogeneity were used to evaluate the effect ...

Regional source/sink impact on the diurnal, seasonal and inter-annual variations in atmospheric CO2 at a boreal forest site in Canada

Time series of in-situ CO2 data from Fraserdale (50°N, 81°W) in the northern Ontario boreal forest is described, together with an analysis of observed variations occurring on daily to interannual timescales. Atmospheric CO2 measurements at Fraserdale reflect a complex interaction between the daily cycle of the vegetative carbon flux and the daily evolution of the boundary layer mixing dynamics. This is particularly evident during the growing season, when CO2 concentrations are influenced strongly by local and regional biospheric activities. In addition, the atmospheric CO2 measurements at Fraserdale are greatly influenced by the direction of atmospheric transport, and reflect the complex heterogeneous distribution of ecosystem types around the site. Averaged over the 7-yr period from 1990 to 1996, the seasonal cycle associated with air from west and northwest of the site shows an amplitude of ~19 ppm, while that associated with air from the south and southwest shows an amplitude of ~23 ppm; the seasonal minimum, on average, occurs about a week earlier in the latter case than in the former. This is reflective of the fact that many of the deciduous trees are located to the south and southwest of Fraserdale. Furthermore, its location in the boreal forest causes the seasonal minimum to occur on average in early August at Fraserdale, compared to late August observed at Alert and at many other background stations in the high-latitude Northern Hemisphere. At the Fraserdale site there is no statistically significant indication, during the 1990–1996 study period, of changes in the length of the growing season (as measured by zero crossing points in the seasonal cycle).

Global monthly CO2 flux inversion with a focus over North America

A nested inverse modelling system was developed for estimating carbon fluxes of 30 regions in North America and 20 regions for the rest of the globe. Monthly inverse modelling was conducted using CO2 concentration measurements of 3 yr (2001–2003) at 88 sites. Inversion results show that in 2003 the global carbon sink is -2.76 ± 0.55 Pg C. Oceans and lands are responsible for 88.5% and 11.5% of the sink, respectively. Northern lands are the largest sinks with North America contributing a sink of -0.97 ± 0.21 Pg C in 2003, of which Canada’s sink is -0.34 ± 0.14 Pg C. For Canada, the inverse results show a spatial pattern in agreement, for the most part, with a carbon source and sink distribution map previously derived through ecosystem modelling. However, discrepancies in the spatial pattern and in flux magnitude between these two estimates exist in certain regions. Numerical experiments with a full covariance matrix, with the consideration of the error structure of the a priori flux field based on meteorological variables among the 30 North America regions, resulted in a small but meaningful improvement in the inverted fluxes. Uncertainty reduction analysis suggests that new observation sites are still needed to further improve the inversion for these 30 regions in North America.

Temporal variations of atmospheric CO2 concentration in a temperate deciduous forest in central Japan

In order to examine the temporal variation of the atmospheric CO2 concentration in a temperate deciduous forest, and its relationship with meteorological conditions, continuous measurements of CO2 and meteorological parameters have been made since 1993 on a tower at Takayama in the central part of Japan. In addition to an average secular increase in atmospheric CO2 of 1.8 ppm yr−1, diurnal variation with a maximum during the night-time to early morning and a minimum in the afternoon is observed from late spring to early fall; the diurnal cycle is not so clearly observed in the remaining seasons of the year. A concentration difference between above and below the canopy, and its diurnal variation, can also be seen clearly in summer. Daily mean concentration data show a prominent seasonal cycle. The maximum and the minimum of the seasonal cycle occur in April and from mid August to mid September, respectively. Day-to-day changes in the diurnal cycle of CO2 are highly dependent on the day-to-day variations in meteorological conditions. However, CO2 variations on longer time scales (>10 d) appear to be linearly related to changes in respiration. At Takayama, variations in the 10-d standard deviation of daily mean CO2 data and 10-d averaged respiration show distinct relationships with soil temperature during spring and fall seasons. In spring, respiration has a stronger exponential dependence on soil temperature than in fall. Interestingly, in summer when soil temperature becomes greater than about 15 °C, biological respiration becomes more variable and independent of the soil temperature. Thus, at the Takayama site, the Q10 relationship is seasonally dependent, and does not represent well the biological respiration process when the soil temperature rises above 15 °C.

On the CO2 exchange between the atmosphere and the biosphere: the role of synoptic and mesoscale processes

Estimating global carbon fluxes by inverting atmospheric CO2 through the use of atmospheric transport models has shown the importance of the covariance between biospheric fluxes and atmospheric transport on the carbon budget. This covariance or coupling occurs on many time scales. This study examines the coupling of the biosphere and the atmosphere on the meso- and synoptic scales using a coupled atmosphere—biosphere regional model covering Canada. The results are compared with surface and light aircraft measurement campaigns at two boreal forest sites in Canada (Fraserdale and BERMS). Associated with cold and warm frontal features, the model results showed that the biospheric fluxes are strongly coupled to the atmosphere through radiative forcing. The presence of cloud near frontal regions usually results in reduced photosynthetic uptake, producing CO2 concentration gradients across the frontal regions on the order of 10 parts per million (ppm). Away from the frontal region, the biosphere is coupled to the mesoscale variations in similar ways, resulting in mesoscale variations in CO2 concentrations of about 5 ppm. The CO2 field is also coupled strongly to the atmospheric dynamics. In the presence of frontal circulation, the CO2 near the surface can be transported to the mid to upper troposphere. Mesoscale circulation also plays a significant part in transporting the CO2 from the planetary boundary layer (PBL) to the mid-troposphere. In the absence of significant mesoscale or synoptic scale circulation, the CO2in the PBL has minimal exchange with the free troposphere, leading to strong gradients across the top of the PBL. We speculate that the ubiquity of the common synoptic and mesoscale processes in the atmosphere may contribute significantly to the rectifier effect and hence CO2 inversion calculations.

Aircraft vertical profiling of variation of CO 2 over a Canadian Boreal Forest Site: a role of advection in the changes in the atmospheric boundary layer CO 2 content

During the period of July 8–13, 2002, we collected vertical profiles by aircraft of meteorological variables and atmospheric CO2 over the OBS (old black spruce) site located in Boreal Ecosystem Research and Monitoring Sites in Northern Saskatchewan, Canada.We have used the data from the morning and afternoon flights to calculate the regional daily afternoon CO2 flux for the days July 8–11. These daily fluxes were then compared to those obtained by the boundary layer budget method and by the eddy covariance measurements on the tower at the OBS site.We identified the importance of changes in the CO2 concentration by advection to the flux estimates. In addition, we provide arguments to suggest that subseasonal temporal averaging might not, at least in some cases, eliminate advective bias contribution to the flux estimates. Because the advective influence is large and highly directional, even on seasonal and interannual timescales, it is advisable that flux estimates based on CO2 concentration change at a site contain dynamic description of an air parcel transport history.

Regional non-CO2 greenhouse gas fluxes inferred from atmospheric measurements in Ontario, Canada

Independent verification of bottom-up greenhouse gas (GHG) emission inventories is crucial for a reliable reporting of Kyoto gases to the United Nations Framework Convention on Climate Change. Here, we use a pseudo-data experiment to test if our improved version of the well-known Radon tracer method (RTM) is able to quantitatively retrieve regional GHG fluxes. Using in-situ observations in Egbert, Canada, from 2006 to 2009 for the RTM, we derive night-time fluxes of CH4 and N2O in southern Ontario. The N2O fluxes found have a inter-quartile range of 7.6–31.2 μgN2O/(m2h) with an overall mean of 24.4 ± 5.6 μgN2O/(m2h). Comparison with the EDGAR4.1 inventory revealed an underestimation by a factor of 1.7 ± 0.4 in the inventory, which is explainable by missing natural sources and a missing seasonal cycle in the inventory. Our RTM-based fluxes of CH4 with a inter-quartiles range of 0.19–0.49 mgCH4/(m2h) and a mean of 0.36 ± 0.08 mgCH4/(m2h) lie significantly below the inventory-based estimates of 0.79 ± 0.06 mgCH4/(m2h). Using a Stochastic Time-Inverted Lagrangian Transport (STILT) model this difference can be attributed to an overestimation of CH4 emissions in a specific region, the highly urbanized Greater Toronto Area. This study displays how the application of the RTM in future monitoring networks could help to assess high-resolution emission inventories.

Rectifier effect in an atmospheric model with daily biospheric fluxes: impact on inversion calculation

Atmospheric CO2 measurements showstrong synoptic variability. To understand the contribution of the synoptic signals on atmospheric CO2 inversion, we simulate the cases of biospheric fluxes with and without synoptic variations (referred to as ‘Synoptic’ and ‘Reference’, respectively) using an atmospheric transport model, and then perform inversion analyses with these biospheric CO2 concentration fields. Results show the monthly and annually averaged CO2 concentration anomalies (Synoptic–Reference) are functions of the distance from the continental biospheric source regions. Remote sites (like Mauna Loa) show averaged monthly amplitude of ∼0.2 ppm, while continental sites show averaged monthly amplitudes of 1–2 ppm with maximum monthly amplitudes up to 7 ppm. Spatial scales of these monthly mean synoptic anomaly patterns may exceed 1000 km. These CO2 concentration patterns are the results of the interaction of the synoptic CO2 flux field and atmospheric transport, and may be referred to as the synoptic Rectifier Effect. Inversion CO2 fluxes for 1992–1995 are obtained using biospheric background fields with and without synoptic biospheric flux variations. The maximum magnitude differences in estimated monthly flux for land and ocean regions are ∼0.4 and ∼0.2 GtC month-1, respectively. The average land sink increases by 0.19 GtC yr-1 while the average ocean sink decreases by 0.30 GtC yr-1.

North American influence on atmospheric carbon dioxide data collected at Sable Island, Canada

Continuous and flask measurements of atmospheric CO2 taken at Sable Island from August 1992 to April 1993 are presented and characterised as a function of air mass origin. The atmospheric environment over Sable Island (43°56ʹN, 60°01ʹW) is continuously influenced by the complex meteorology of synoptic systems moving off North America. This makes the interpretation of the Sable Island CO2 data difficult. However, trajectory analysis shows distinct quantitative differences between the statistics of CO2 measurements associated with air masses from “North America” (regions of high anthropogenic and terrestrial biospheric fluxes associated with much of the United States and the southern half of Canada) and of those associated with air masses from the “Arctic/North Atlantic” (regions of few terrestrial fluxes and oceans associated with the northern half of Canada and the Atlantic Ocean). When the continuous CO2 data are segregated into these two trajectory sectors for the period of observation, air masses originating in the North American sector show a higher CO2 mixing ratio by ~2 ppm in winter and lower by ~3 ppm in summer, compared to air masses arriving from the other sector. Furthermore, the continuous Sable Island CO2 measurements show a detectable monthly mean (August/September) diurnal cycle with an amplitude of ~2 ppm, with a minimum occurring on average around noon local time. Given the timing of the observed diurnal minimum and the lack of vegetation on the island, this indicates that the diurnal pattern observed at Sable Island is a diffused remnant of diurnal cycles transported from the main North American continent. These characteristic details are not captured by the discrete flask sampling program on the island.

The Sensitivity of the Simulated Normal and Enhanced C02 Climates to Different Heat Transport Parameterizations in a Two-Dimensional Multilevel Energy Balance Model

Abstract Atmospheric sensible and latent heat fluxes constitute an important component of the total poleward energy transport in the climate system. The authors investigate the relative role of these heat fluxes in normal and enhanced C02 warming scenarios, using a two-dimensional latitude-height multilayer energy balance climate model. The model uses a diffusive scheme to parameterize the heat transports, where the diffusion coefficients are calculated as a function of the temperature gradient. Results of various numerical experiments show that changes in the diffusion coefficients of both the latent and sensible heat fluxes can significantly affect the present (1×C02) equilibrium climate. The difference between the 2×C02 and 1×C02 climate, however, as measured by the simulated difference temperature field, is much more sensitive to changes in the latent heat rather than the sensible beat diffusion coefficients, particularly in the Tropics. The parameterization scheme with temperature-dependent diffusion...