Kiran Alapaty

and 5 more

Different functions are used to account for turbulence in the atmospheric boundary layer for different stability regimes. These functions are one of the sources for differences among different atmospheric models’ predictions and associated biases. Also, turbulence is underrepresented in some of the resistance formulations. To address these issues with dry deposition, firstly we take advantage of three-dimensional (3-D) aspects of turbulence in estimating resistances by proposing and validating a 3-D turbulence velocity scale that is relevant for different stability regimes of boundary layer. Secondly, we hypothesize and prove that 3-D sonic anemometer measured friction velocity, used in 0-D and 1-D models, can be effectively replaced by the new turbulence velocity scale multiplied by the von Karman constant. Finally, we (1) evaluate a set of resistance formulations for ozone (O3), based on the 3-D turbulence velocity scale; and (2) intercompare estimations of such resistances with those obtained using the existing formulations and also evaluate simulated O3 fluxes using a single-point dry deposition model against long-term observations of O3 fluxes at the Harvard Forest site. Results indicate that the new resistance formulations work very well in simulating surface latent heat and O3 fluxes when compared to respective existing formulations as well as measurements at decadal time scale. Findings from this research may help to improve the capability of dry deposition schemes for better estimation of dry deposition fluxes and create opportunities for the development of a community dry deposition model for use in regional/global air quality models.

JIALIN LIU

and 7 more

With over 700 million km2 Siberia is the largest expanse of the northern boreal forest—deciduous-needleleaf larch. Temperatures are increasing across this region, but the consequences to carbon balances are not well understood for larch forests. We present flux measurements from a larch forest near the southern edge of Central-Siberia where permafrost degradation and ecosystem shifting are already observed. Results indicate net carbon exchanges are influenced by the seasonality of permafrost active layers, temperature and humidity, and soil water availability. During periods when surface soils are fully thawed, larch forest is a significant carbon sink. During the spring-thaw and fall-freeze transition, there is a weak signal of carbon uptake at mid-day. Net carbon exchanges are near-zero when the soil is fully frozen from the surface down to the permafrost. We fit an empirical ecosystem functional model to quantify the dependence of larch-forest carbon balance on climatic drivers. The model provides a basis for ecosystem carbon budgets over time and space. Larch differs from boreal evergreens by having higher maximum productivity and lower respiration, leading to an increased carbon sink. Comparison to previous measurements from another northern larch site suggests climate change will result in an increased forest carbon sink if the southern larch subtype replaces the northern subtype. Observations of carbon fluxes in Siberian larch are still too sparse to adequately determine age dependence, inter-annual variability, and spatial heterogeneity though they suggest that boreal larch accounts for a larger fraction of global carbon uptake than has been previously recognized.