1,401 research outputs found
Forest albedo in the context of different cloud situations derived from irradiance measurements at the Leipzig floodplain crane: A pilot study
The surface albedo significantly modulates the atmospheric energy budget
and, thus, vertical radiation, energy, and mass fluxes. Therefore, it regulates the local
and regional effects of climate warming. Over a forest canopy, the surface albedo mainly
depends on the seasonal leaf state. Furthermore, for certain surface types, such as snow,
it has been shown that the surface albedo changes as a function of cloudiness. A similar
effect is expected over forest surfaces, leading to complex feedback loops between forest
surfaces and climate. To investigate these processes, a pilot study was performed at the
Leipzig floodplain crane to observe the forest canopy albedo under different atmospheric
conditions in 2021. First analyses revealed a dependency of the forest albedo from the
cloud state, which is slightly stronger in the near-infrared wavelength range compared to
the visible wavelength range.Der atmosphärische Strahlungshaushalt und damit auch die vertikale
Strahlungsverteilung, Energie- und Massenflüsse werden signifikant durch die
Bodenalbedo gesteuert. Diese regulieren somit lokale und regionale Effekte der Klimaerwärmung.
Über einem Wald hängt die Bodenalbedo hauptsächlich vom saisonalen
Blattstatus ab. Zudem wurde für bestimmte Bodentypen wie Schneeoberflächen gezeigt,
dass die Bodenalbedo eine Funktion der Bewölkung ist. Ähnlicher Effekte werden für
Waldoberflächen erwartet, welche zu komplexen Rückkopplungseffekten zwischenWaldoberflächen
und dem Klima führen. Um diese Prozesse zu untersuchen wurde im Jahr
2021 eine Vorstudie am Leipziger Auwaldkran durchgeführt, um die Waldalbedo unter
verschiedenen atmosphärischen Bedingungen zu beobachten. Erste Analysen zeigen,
dass auch die Albedo des Waldes von den Bewölkungsbedingungen abhängt. Der Effekt
ist dabei etwas stärker im nah-infrarotem als im sichtbaren Wellenlängenbereich zu
beobachten
Empirical H/V spectral ratios estimated in two deep sedimentary basins using microseisms recorded by short-period seismometers
In this work, we analyse continuous measurements of microseisms to assess the reliability of
the fundamental resonance frequency estimated by means of the horizontal-to-vertical (H/V)
spectral ratio within the 0.1–1 Hz frequency range, using short-period sensors (natural period
of 1 s). We apply the H/V technique to recordings of stations installed in two alluvial basins
with different sedimentary cover thicknesses—the Lower Rhine Embayment (Germany) and
the Gubbio Plain (Central Italy). The spectral ratios are estimated over the time–frequency
domain, and we discuss the reliability of the results considering both the variability of the
microseism activity and the amplitude of the instrumental noise. We show that microseisms
measured by short period sensors allow the retrieval of fundamental resonance frequencies
greater than about 0.1–0.2 Hz, with this lower frequency bound depending on the relative
amplitude of themicroseism signal and the self-noise of the instruments. In particular,we show
an examplewhere the considered short-period sensor is connected to instruments characterized
by an instrumental noise level which allows detecting only fundamental frequencies greater
than about 0.4 Hz. Since the frequency at which the peak of the H/V spectral ratio is biased
depends upon the seismic signal-to-instrument noise ratio, the power spectral amplitude of
instrumental self-noise should be always considered when interpreting the frequency of the
peak as the fundamental resonance frequency of the investigated site
Airborne observations of clouds in the Central Arctic during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition
Microlocal analysis of quantum fields on curved spacetimes: Analytic wavefront sets and Reeh-Schlieder theorems
We show in this article that the Reeh-Schlieder property holds for states of
quantum fields on real analytic spacetimes if they satisfy an analytic
microlocal spectrum condition. This result holds in the setting of general
quantum field theory, i.e. without assuming the quantum field to obey a
specific equation of motion. Moreover, quasifree states of the Klein-Gordon
field are further investigated in this work and the (analytic) microlocal
spectrum condition is shown to be equivalent to simpler conditions. We also
prove that any quasifree ground- or KMS-state of the Klein-Gordon field on a
stationary real analytic spacetime fulfills the analytic microlocal spectrum
condition.Comment: 31 pages, latex2
Single track coincidence measurements of fluorescent and plastic nuclear track detectors in therapeutic carbon beams
In this paper we present a method for single track coincidence measurements
using two different track detector materials. We employed plastic and
fluorescent nuclear track detectors (PNTDs and FNTDs) in the entrance channel
of a monoenergetic carbon ion beam covering the therapeutically useful energy
range from 80 to 425 MeV/u. About 99 % of all primary particle tracks detected
by both detectors were successfully matched, while 1 % of the particles were
only detected by the FNTDs because of their superior spatial resolution. We
conclude that both PNTDs and FNTDs are suitable for clinical carbon beam
dosimetry with a detection efficiency of at least 98.82 % and 99.83 %
respectively, if irradiations are performed with low fluence in the entrance
channel of the ion beam. The investigated method can be adapted to other
nuclear track detectors and offers the possibility to characterize new track
detector materials against well-known detectors. Further, by combining two
detectors with a restricted working range in the presented way a
hybrid-detector system can be created with an extended and optimized working
range.Comment: 14 pages, 8 figures, 2 table
Climate-Based Suitability Assessment for Methane Mitigation by Water Saving Technology in Paddy Fields of the Central Plain of Thailand
The alternate wetting and drying (AWD) water management technique has been identified as one of the most promising options for mitigating methane (CH) emissions from rice cultivation. By its nature, however, this option is limited only to paddy fields where farmers have sustained access to irrigation water. In addition, large amounts of rainfall often make it difficult to drain water from paddy fields. Therefore, it is necessary to understand the specific conditions and suitability of an area in which AWD is foreseen to be applied before its CH mitigation potential can be assessed in view of planning regional and national mitigation actions. In this study, we applied a methodology developed for assessing the climatic suitability of AWD to paddy fields in the central plain of Thailand in order to determine the potential spatial and temporal boundaries given by climatic and soil parameters that could impact on the applicability of AWD. Related to this, we also assessed the CH mitigation potential in the target provinces. Results showed that the entire area of the six target provinces was climatically suitable for AWD in both the major (wet) and second (dry) rice seasons. A sensitivity analysis accounting for uncertainties in soil percolation and suitability classification indicated that these settings did not affect the results of the suitability assessment, although they changed to some extent the distribution of moderate and high climatic suitability areas in the major rice season. Following the methodologies of the Intergovernmental Panel on Climate Change Guidelines, we estimated that the AWD scenario could reduce annual CH emissions by 32% compared with the emissions in the baseline (continuously flooded) scenario. The potential of AWD for annual CH emission reduction was estimated to be 57,600 t CH year, equivalent to 1.61 Mt CO-eq year, in the target provinces. However, we recognize the possibility that other parameters not included in our current approach may significantly influence the suitability of AWD and thus propose areas for further improvement derived from these limitations. All in all, our results will be instrumental in guiding practitioners at all levels involved in water management for rice cultivation
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