Montane ecosystem productivity responds more to global circulation patterns than climatic trends

Desai, A. R.*; Wohlfahrt, G.*; Zeeman, M. J.*; Katata, Genki; Eugster, W.*; Montagnani, L.*; Gianelle, D.*; Mauder, M.*; Schmid, H. P.*

Environmental Research Letters, 11(2), p.024013_1 - 024013_9, 2016/02

AA2015-0882.pdf:2.25MB

https://doi.org/10.1088/1748-9326/11/2/024013

Regional ecosystem productivity is highly sensitive to inter-annual climate variability, both within and outside the primary carbon uptake period. However, Earth system models lack sufficient spatial scales and ecosystem processes to resolve how these processes may change in a warming climate. Here, we show, how for the European Alps, mid-latitude Atlantic ocean winter circulation anomalies drive high-altitude summer forest and grassland productivity, through feedbacks among orographic wind circulation patterns, snowfall, winter and spring temperatures, and vegetation activity. Therefore, to understand future global climate change influence to regional ecosystem productivity, Earth systems models need to focus on improvements towards topographic downscaling of changes in regional atmospheric circulation patterns and to lagged responses in vegetation dynamics to non-growing season climate anomalies.

Comparison of the spatial and temporal structure of type-I ELMs

Kirk, A.*; Asakura, Nobuyuki; Boedo, J. A.*; Beurskens, M.*; Counsell, G. F.*; Eich, T.*; Fundamenski, W.*; Herrmann, A.*; Kamada, Yutaka; Leonard, A. W.*; et al.

Journal of Physics; Conference Series, 123, p.012011_1 - 012011_10, 2008/00

https://doi.org/10.1088/1742-6596/123/1/012011

A comparison of the spatial and temporal evolution of the filamentary structures observed during type I ELMs is presented from a variety of diagnostics and machines. There is evidence that these filaments can be detected inside the LCFS prior to ELMs. The filaments do not have a circular cross section instead they are elongated in the perpendicular (poloidal) direction and this size appears to increase linearly with the minor radius of the machine. The filaments start rotating toroidally/poloidally with velocities close to that of the pedestal. This velocity then decreases as the filaments propagate radially. It is most likely that the filaments have at least their initial radial velocity when they are far out into the SOL. The dominant loss mechanism is through parallel transport and the transport to the wall is through the radial propagation of these filaments. Measurements of the filament energy content show that each filament contains up to 2.5 % of the energy released by the ELM.

Deactivation of nitrogen donors in silicon carbide

Schmid, F.*; Reshanov, S. A.*; Weber, H. B.*; Pensl, G.*; Bockstedte, M.*; Mattausch, A.*; Pankratov, O.*; Oshima, Takeshi; Ito, Hisayoshi

Physical Review B, 74(24), p.245212_1 - 245212_11, 2006/12

https://doi.org/10.1103/PhysRevB.74.245212

Hexagonal SiC is co-implanted with silicon Si, carbon C, or neon Ne ions along with nitrogen N ions. Also hexagonal SiC irradiated with electrons e of 200 keV energy. During the subsequent annealing step at temperatures above 1450 C a deactivation of N donors and a reduction of the compensation are observed in the case of the Si/N co-implantation and e irradiation. Using Hall measurement, the N donor deactivation is studied as a function of the concentration of the co-implanted species and the annealing temperature. The formation of energetically deep defects is analyzed with deep level transient spectroscopy. A detailed theoretical analysis based on the density functional theory is conducted; it takes into account the kinetic mechanisms for the formation of N interstitial clusters and N-vacancy complexes. In accordance with all the experimental results, this analysis distinctly indicates that the (N)-V complex, which is thermally stable at high temperatures, is responsible for the N donor deactivation.

Ecosystem greenhouse gas fluxes respond directly to weather not climate; A Case study on the relationship of global atmospheric circulation, foehn frequency, and winter weather to northern alps regional grassland phenology and carbon cycling

Desai, A. R.*; Wohlfahrt, G.*; Zeeman, M.*; Katata, Genki; Mauder, M.*; Schmid, H. P.*

no journal, , 

The impact of climate change on regional ecosystem has two important aspects: (1) ecosystems don't respond directly to climate, but indirectly via frequency and occurrence of weather systems, (2) many responses of ecosystems to these weather patterns and extremes are lagged in time. Here, we examine these aspects for northern Alpine grasslands. Long-term flux and phenology observations in Austria and Germany and biophysical models reveal a strong influence of winter air temperature, snowfall, and snowmelt frequency on winter grass mortality and spring grassland carbon uptake. Further, the mode of climate variability that drives winter air temperature and snow depth patterns is primarily the frequency of strong regional southerly Foehn flow. Finally, we demonstrate that much of the interannual variance in Foehn frequency and southerly flow is driven by statistics and climatic trends of 500 hPa pressure patterns in Greenland, part of the Arctic Oscillation.