Increased temperature in urban ground as source of sustainable energy

This paper is part of the Proceedings of the 10th International Conference on Urban Regeneration and Sustainability (Sustainable City 2015). http://www.witconferences.comDensely urbanized areas are characterized by special microclimatic conditions with typically elevated temperatures in comparison with the rural surrounding. This phenomenon is known as the urban heat island (UHI) effect, but not restricted exclusively to the atmosphere. We also find significant warming of the urban subsurface and shallow groundwater bodies. Here, main sources of heat are elevated ground surface temperatures, direct thermal exploitation of aquifers and heat losses from buildings and other infrastructure. By measuring the shallow groundwater temperature in several European cities, we identify that heat sources and associated transport processes interact at multiple spatial and temporal scales. The intensity of a subsurface UHI can reach the values of above 4 K in city centres with hotspots featuring temperatures up to +20°C. In comparison with atmospheric UHIs, subsurface UHIs represent long-term accumulations of heat in a relatively sluggish environment. This potentially impairs urban groundwater quality and permanently influences subsurface ecosystems. From another point of view, however, these thermal anomalies can also be seen as hidden large-scale batteries that constitute a source of shallow geothermal energy. Based on our measurements, data surveys and estimated physical ground properties, it is possible to estimate the theoretical geothermal potential of the urban groundwater bodies beneath the studied cities. For instance, by decreasing the elevated temperature of the shallow aquifer in Cologne, Germany, by only 2 K, the obtained energy could supply the space-heating demand of the entire city for at least 2.5 years. In the city of Karlsruhe, it is estimated that about 30% of annual heating demand could be sustainably supplied by tapping the anthropogenic heat loss in the urban aquifer. These results reveal the attractive potential of heated urban ground as energy reservoir and storage, which is in place at many places worldwide but so far not integrated in any city energy plans.This work was supported by the Swiss National Science Foundation (SNSF) under grant number 200021L 144288, and the German Research Foundation (DFG), under grant number BL 1015/4-1

Survey on solar X-ray flares and associated coherent radio emissions

The radio emission during 201 X-ray selected solar flares was surveyed from 100 MHz to 4 GHz with the Phoenix-2 spectrometer of ETH Zurich. The selection includes all RHESSI flares larger than C5.0 jointly observed from launch until June 30, 2003. Detailed association rates of radio emission during X-ray flares are reported. In the decimeter wavelength range, type III bursts and the genuinely decimetric emissions (pulsations, continua, and narrowband spikes) were found equally frequently. Both occur predominantly in the peak phase of hard X-ray (HXR) emission, but are less in tune with HXRs than the high-frequency continuum exceeding 4 GHz, attributed to gyrosynchrotron radiation. In 10% of the HXR flares, an intense radiation of the above genuine decimetric types followed in the decay phase or later. Classic meter-wave type III bursts are associated in 33% of all HXR flares, but only in 4% they are the exclusive radio emission. Noise storms were the only radio emission in 5% of the HXR flares, some of them with extended duration. Despite the spatial association (same active region), the noise storm variations are found to be only loosely correlated in time with the X-ray flux. In a surprising 17% of the HXR flares, no coherent radio emission was found in the extremely broad band surveyed. The association but loose correlation between HXR and coherent radio emission is interpreted by multiple reconnection sites connected by common field lines.Comment: Solar Physics, in pres

Temporal Correlation of Hard X-rays and Meter/Decimeter Radio Structures in Solar Flares

We investigate the relative timing between hard X-ray (HXR) peaks and structures in metric and decimetric radio emissions of solar flares using data from the RHESSI and Phoenix-2 instruments. The radio events under consideration are predominantly classified as type III bursts, decimetric pulsations and patches. The RHESSI data are demodulated using special techniques appropriate for a Phoenix-2 temporal resolution of 0.1s. The absolute timing accuracy of the two instruments is found to be about 170 ms, and much better on the average. It is found that type III radio groups often coincide with enhanced HXR emission, but only a relatively small fraction ($\sim$ 20%) of the groups show close correlation on time scales $<$ 1s. If structures correlate, the HXRs precede the type III emissions in a majority of cases, and by 0.69$\pm$0.19 s on the average. Reversed drift type III bursts are also delayed, but high-frequency and harmonic emission is retarded less. The decimetric pulsations and patches (DCIM) have a larger scatter of delays, but do not have a statistically significant sign or an average different from zero. The time delay does not show a center-to-limb variation excluding simple propagation effects. The delay by scattering near the source region is suggested to be the most efficient process on the average for delaying type III radio emission

First analysis of solar structures in 1.21 mm full-disc ALMA image of the Sun

Various solar features can be seen on maps of the Sun in the mm and sub-mm wavelength range. The recently installed Atacama Large Millimeter/submillimeter Array (ALMA) is capable of observing the Sun in that wavelength range with an unprecedented spatial, temporal and spectral resolution. To interpret solar observations with ALMA the first important step is to compare ALMA maps with simultaneous images of the Sun recorded in other spectral ranges. First we identify different structures in the solar atmosphere seen in the optical, IR and EUV parts of the spectrum (quiet Sun (QS), active regions (AR), prominences on the disc, magnetic inversion lines (IL), coronal holes (CH) and coronal bright points (CBPs)) in a full disc solar ALMA image. The second aim is to measure the intensities (brightness temperatures) of those structures and compare them with the corresponding QS level. A full disc solar image at 1.21 mm obtained on December 18, 2015 during a CSV-EOC campaign with ALMA is calibrated and compared with full disc solar images from the same day in H\alpha, in He I 1083 nm core, and with SDO images (AIA at 170 nm, 30.4 nm, 21.1 nm, 19.3 nm, and 17.1 nm and HMI magnetogram). The brightness temperatures of various structures are determined by averaging over corresponding regions of interest in the ALMA image. Positions of the QS, ARs, prominences on the disc, ILs, CHs and CBPs are identified in the ALMA image. At 1.21 mm ARs appear as bright areas (but sunspots are dark), while prominences on the disc and CHs are not discernible from the QS background, although having slightly less intensity than surrounding QS regions. ILs appear as large, elongated dark structures and CBPs correspond to ALMA bright points. These results are in general agreement with sparse earlier measurements at similar wavelengths. The identification of CBPs represents the most important new result.Comment: 9 pages, 3 figure

Theory of phase-locking in generalized hybrid Josephson junction arrays

A recently proposed scheme for the analytical treatment of the dynamics of two-dimensional hybrid Josephson junction arrays is extended to a class of generalized hybrid arrays with ''horizontal'' shunts involving a capacitive as well as an inductive component. This class of arrays is of special interest, because the internal cell coupling has been shown numerically to favor in-phase synchronization for certain parameter values. As a result, we derive limits on the circuit design parameters for realizing this state. In addition, we obtain formulas for the flux-dependent frequency including flux-induced switching processes between the in-phase and anti-phase oscillation regime. The treatment covers unloaded arrays as well as arrays shunted via an external load.Comment: 24 pages, REVTeX, 5 Postscript figures, Subm. to Phys. Rev.

Phases of Josephson Junction Ladders

We study a Josephson junction ladder in a magnetic field in the absence of charging effects via a transfer matrix formalism. The eigenvalues of the transfer matrix are found numerically, giving a determination of the different phases of the ladder. The spatial periodicity of the ground state exhibits a devil's staircase as a function of the magnetic flux filling factor $f$. If the transverse Josephson coupling is varied a continuous superconducting-normal transition in the transverse direction is observed, analogous to the breakdown of the KAM trajectories in dynamical systems.Comment: 12 pages with 3 figures, REVTE

Collisional damping rates for plasma waves

The distinction between the plasma dynamics dominated by collisional transport versus collective processes has never been rigorously addressed until recently. A recent paper [Yoon et al., Phys. Rev. E 93, 033203 (2016)] formulates for the first time, a unified kinetic theory in which collective processes and collisional dynamics are systematically incorporated from first principles. One of the outcomes of such a formalism is the rigorous derivation of collisional damping rates for Langmuir and ion-acoustic waves, which can be contrasted to the heuristic customary approach. However, the results are given only in formal mathematical expressions. The present Brief Communication numerically evaluates the rigorous collisional damping rates by considering the case of plasma particles with Maxwellian velocity distribution function so as to assess the consequence of the rigorous formalism in a quantitative manner. Comparison with the heuristic ("Spitzer") formula shows that the accurate damping rates are much lower in magnitude than the conventional expression, which implies that the traditional approach over-estimates the importance of attenuation of plasma waves by collisional relaxation process. Such a finding may have a wide applicability ranging from laboratory to space and astrophysical plasmas.Comment: 5 pages, 2 figures; Published in Physics of Plasmas, volume/Issue 23/6. Publisher: AIP Publishing LLC. Date: Jun 1, 2016. URL: http://aip.scitation.org/doi/10.1063/1.4953802 Rights managed by AIP Publishing LL

X-ray Chemistry in the Envelopes around Young Stellar Objects

We have studied the influence of X-rays from a massive young stellar object (YSO) on the chemistry of its own envelope by extending the models of Doty et al. (2002) and Staeuber et al. (2004). The models are applied to the massive star-forming region AFGL 2591 for different X-ray luminosities and plasma temperatures. Enhanced column densities for several species are predicted. In addition we present first detections of CO+ and SO+ toward AFGL 2591. These molecular ions are believed to be high-energy tracers. Herschel-HIFI will be able to observe other tracers like CH and CH+ whereas ALMA is well suited to measure the size and geometry of the emitting region.Comment: To appear in "The Dusty and Molecular Universe: A Prelude to Herschel and ALMA", Eds.: A. Wilson. To be published in ESA Conference Serie

Technical Note: A numerical test-bed for detailed ice nucleation studies in the AIDA cloud simulation chamber

The AIDA (Aerosol Interactions and Dynamics in the Atmosphere) aerosol and cloud chamber of Forschungszentrum Karlsruhe can be used to test the ice forming ability of aerosols. The AIDA chamber is extensively instrumented including pressure, temperature and humidity sensors, and optical particle counters. Expansion cooling using mechanical pumps leads to ice supersaturation conditions and possible ice formation. In order to describe the evolving chamber conditions during an expansion, a parcel model was modified to account for diabatic heat and moisture interactions with the chamber walls. Model results are shown for a series of expansions where the initial chamber temperature ranged from &minus;20&deg;C to &minus;60&deg;C and which used desert dust as ice forming nuclei. During each expansion, the initial formation of ice particles was clearly observed. For the colder expansions there were two clear ice nucleation episodes. <br><br> In order to test the ability of the model to represent the changing chamber conditions and to give confidence in the observations of chamber temperature and humidity, and ice particle concentration and mean size, ice particles were simply added as a function of time so as to reproduce the observations of ice crystal concentration. The time interval and chamber conditions over which ice nucleation occurs is therefore accurately known, and enables the model to be used as a test bed for different representations of ice formation