Tropical cyclones facilitate recovery of forest leaf area from dry spells in East Asia

Forests disturbance by tropical cyclones is mostly documented by field studies of exceptionally strong cyclones and satellite-based approaches attributing decreases in leaf area. By starting their analysis from the observed damage, these studies are biased and may, therefore, limit our understanding of the impact of cyclones in general. This study overcomes such biases by jointly analyzing the cyclone tracks, climate reanalysis, and changes in satellite-based leaf area following the passage of 140 ± 41 cyclones. Sixty days following their passage, 18 ± 8 % of the cyclones resulted in a decrease and 48 ± 18 % showed no change in leaf area compared to nearby forest outside the storm track. For a surprising 34 ± 7 % of the cyclones, an increase in leaf area was observed. Cyclones resulting in higher leaf area in their affected compared to their reference area coincided with an atmospheric pressure dipole steering the cyclone towards a region experiencing a dry spell caused by the same dipole. When the dipole was present, the destructive power of cyclones was offset by their abundant precipitation enabling forest canopies in the affected area to recover faster from the dry spell than canopies in the reference area. This study documents previously undocumented widespread antagonist interactions on forest leaf area between tropical cyclones and droughts.</p

Compacte vlakke-golfgeleiderkoppelingen in silicium-op-isolator Compact planar waveguide spot-size converters in silicon-on-insulator

An optical chip is a planar component in which a light signal is guided by optical waveguides and in which light can be processed in various ways and for various purposes. Examples are splitting a light beam into its separate wavelengths, absorption of the light for sensor applications, modulating a high-content data signal onto a light beam, etc., all offering the possibility for cheaper and better optical systems. In these chips often connections occur between waveguides with different widths. Traditionally these connections are realized by long coupling sections having a linear or parabolic shape when viewed from above. If we want to shorten these coupling sections to gain precious chip surface area, innovative shapes should be applied. A general shape for an innovative coupler is proposed in this work and is optimized in various ways leading to a good coupling efficiency. In these simulations an in-house eigenmode expansion method, CAMFR, is used both for two- and three-dimensional waveguide calculations. At the optimization side, a successive line minimization and a standard genetic algorithm are successfully applied. Different initial assumptions for the shapes of these couplers can, after optimization, lead to similar structures, confirming the value of the applied methods. After simulation, a selection of optimized structures is realized in the material system silicon-on-insulator. For this manufacturing, standard deep-UV lithography with an illumination wavelength of 248 nm, normally used in the creation of CMOS chips, is applied. Optical measurements on these optical coupling structures confirm the calculated coupling efficiencies and lead us to the conclusion that couplers between planar optical waveguides with a different width can be shortened if, instead of the conventional linear or parabolic shapes, more complex structures are applied

Remote Sensing Technologies for Assessing Climate-Smart Criteria in Mountain Forests

Peer reviewe

A compact photonic horizontal spot-size converter realized in silicon-on-insulator

A

Reconciling different approaches to quantifying land surface temperature impacts of afforestation using satellite observations

Satellite observations have been widely used to examine afforestation effects on local surface temperature at large spatial scales. Different approaches, which potentially lead to differing definitions of the afforestation effect, have been used in previous studies. Despite their large differences, the results of these studies have been used in climate model validation and cited in climate synthesis reports. Such differences have been simply treated as observational uncertainty, which can be an order of magnitude bigger than the signal itself. Although the fraction of the satellite pixel actually afforested has been noted to influence the magnitude of the afforestation effect, it remains unknown whether it is a key factor which can reconcile the different approaches. Here, we provide a synthesis of three influential approaches (one estimates the actual effect and the other two the potential effect) and use large-scale afforestation over China as a test case to examine whether the different approaches can be reconciled. We found that the actual effect (ΔTa) often relates to incomplete afforestation over a medium-resolution satellite pixel (1 km). ΔTa increased with the afforestation fraction, which explained 89 % of its variation. One potential effect approach quantifies the impact of quasi-full afforestation (ΔTp1), whereas the other quantifies the potential impact of full afforestation (ΔTp2) by assuming a shift from 100 % openland to 100 % forest coverage. An initial paired-sample t test shows that ΔTa&lt;ΔTp1&lt;ΔTp2 for the cooling effect of afforestation ranging from 0.07 to 1.16 K. But when all three methods are normalized for full afforestation, the observed range in surface cooling becomes much smaller (0.79 to 1.16 K). Potential cooling effects have a value in academic studies where they can be used to establish an envelope of effects, but their realization at large scales is challenging given its nature of scale dependency. The reconciliation of the different approaches demonstrated in this study highlights the fact that the afforestation fraction should be accounted for in order to bridge different estimates of surface cooling effects in policy evaluation.</p

Silicon-on-insulator based nano-photonics: why, how, what for ? (invited paper)

Abstract Silicon-on-Insulator is rapidly emerging as a versatile platform for a variety of integrated nano-photonic components. This paper discusses the variety of merits offered by this system. The key technological challenges are discussed as well as the potential in multiple application fields