Signatures of the Higgs mode in transport through a normal-metal--superconductor junction

A superconductor subject to electromagnetic irradiation in the terahertz range can show amplitude oscillations of its order parameter. However, coupling this so-called Higgs mode to the charge current is notoriously difficult. We propose to achieve such a coupling in a particle-hole-asymmetric configuration using a DC-voltage-biased normal-metal--superconductor tunnel junction. Using the quasiclassical Green's function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. (ii) The AC charge current amplitude exhibits a characteristic nonmonotonic behavior with increasing voltage bias. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias. These signatures provide an electric detection scheme for the Higgs mode.Comment: 5.2+3 page

Orographically induced spontaneous imbalance within the jet causing a large-scale gravity wave event

To better understand the impact of gravity waves (GWs) on the middle atmosphere in the current and future climate, it is essential to understand their excitation mechanisms and to quantify their basic properties. Here a new process for GW excitation by orography–jet interaction is discussed. In a case study, we identify the source of a GW observed over Greenland on 10 March 2016 during the POLSTRACC (POLar STRAtosphere in a Changing Climate) aircraft campaign. Measurements were taken with the Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) instrument deployed on the High Altitude Long Range (HALO) German research aircraft. The measured infrared limb radiances are converted into a 3D observational temperature field through the use of inverse modelling and limited-angle tomography. We observe GWs along a transect through Greenland where the GW packet covers ≈ 1/3 of the Greenland mainland. GLORIA observations indicate GWs between 10 and 13 km of altitude with a horizontal wavelength of 330 km, a vertical wavelength of 2 km and a large temperature amplitude of 4.5 K. Slanted phase fronts indicate intrinsic propagation against the wind, while the ground-based propagation is with the wind. The GWs are arrested below a critical layer above the tropospheric jet. Compared to its intrinsic horizontal group velocity (25–72 m s$^{-1}$) the GW packet has a slow vertical group velocity of 0.05–0.2 m s$^{-1}$. This causes the GW packet to propagate long distances while spreading over a large area and remaining constrained to a narrow vertical layer. A plausible source is not only orography, but also out-of-balance winds in a jet exit region and wind shear. To identify the GW source, 3D GLORIA observations are combined with a gravity wave ray tracer, ERA5 reanalysis and high-resolution numerical experiments. In a numerical experiment with a smoothed orography, GW activity is quite weak, indicating that the GWs in the realistic orography experiment are due to orography. However, analysis shows that these GWs are not mountain waves. A favourable area for spontaneous GW emission is identified in the jet by the cross-stream ageostrophic wind, which indicates when the flow is out of geostrophic balance. Backwards ray-tracing experiments trace into the jet and regions where the Coriolis and the pressure gradient forces are out of balance. The difference between the full and a smooth-orography experiment is investigated to reveal the missing connection between orography and the out-of-balance jet. We find that this is flow over a broad area of elevated terrain which causes compression of air above Greenland. The orography modifies the wind flow over large horizontal and vertical scales, resulting in out-of-balance geostrophic components. The out-of-balance jet then excites GWs in order to bring the flow back into balance. This is the first observational evidence of GW generation by such an orography–jet mechanism

Coupling of stratospheric warmings with mesospheric coolings in observations and simulations

AbstractThe vertical coupling between the stratosphere and the mesosphere is diagnosed from polar cap temperatures averaged over 60°–90°N with a new method: the joint occurrence of a warm stratosphere at 10 hPa and a cold mesosphere at 0.01 hPa. The investigation of an 11-yr-long dataset (2004–15) from Aura-MLS observations shows that such mesospheric coupling days appear in 7% of the winter. During major sudden stratospheric warming events mesospheric couplings are present with an enhanced average daily frequency of 22%. This daily frequency changes from event to event but broadly results in five of seven major warmings being classified as mesospheric couplings (2006, 2008, 2009, 2010, and 2013). The observed fraction of mesospheric coupling events (71%) is compared with simulations of the Kühlungsborn Mechanistic Circulation Model (KMCM), the Hamburg Model of the Neutral and Ionized Atmosphere (HAMMONIA), and the Whole Atmosphere Community Climate Model (WACCM). The simulated fraction of mesospheric coupling events ranges between 57% and 94%, which fits the observations. In searching for causal relations weak evidence is found that major warming events with strong intensity or split vortices favor their coupling with the upper mesosphere. More evidence is found with a conceptual model: an effective vertical coupling between 10 and 0.01 hPa is provided by deep zonal-mean easterlies at 60°N, which are acting as a gravity-wave guide. The explained variance is above 40% in the four datasets, which indicates a near-realistic simulation of this process

On the upper tropospheric formation and occurrence of high and thin cirrus clouds during anticyclonic poleward Rossby wave breaking events

Ground-based lidar measurements and balloon soundings were employed to examine the dynamical link between anticyclonic Rossby wave breaking and cirrus clouds from 13 to 15 February 2006. For this event, an air mass with low Ertel's potential vorticity appeared over Central Europe. In the tropopause region, this air mass was accompanied with both an area of extreme cold temperatures placed northeastward, and an area of high specific humidity, located southwestward. ECMWF analyses reveal a strong adiabatic northeastward and upward transport of water vapour within the warm conveyor belt on the western side of the ridge over Mecklenburg, Northern Germany. The backscatter lidar at Kühlungsborn (54.1°N, 11.8°E) clearly identified cirrus clouds at between 9 and 11.4 km height. In the tropopause region high-vertical resolution radiosoundings showed layers of subsaturated water vapour over ice but with a relative humidity over ice >80%. Over Northern Germany radiosondes indicated anticyclonically rotating winds in agreement with backward trajectories of ECMWF analyses in the upper troposphere, which were accompanied by a relatively strong increase of the tropopause height on 14 February. Based on ECMWF data the strong link between the large-scale structure, updraft and ice water content was show

Signatures of the Higgs mode in transport through a normal-metal--superconductor junction

A superconductor subject to electromagnetic irradiation in the terahertz range can show amplitude oscillations of its order parameter. However, coupling this so-called Higgs mode to the charge current is notoriously difficult. We propose to achieve such a coupling in a particle-hole-asymmetric configurations using a DC-voltage-biased normal-metal--superconductor tunnel junction. Using the quasiclassical Green's function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. (ii) The AC charge current amplitude exhibits a characteristic nonmonotonic behavior with increasing voltage bias. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias. These signatures provide an electric detection scheme for the Higgs mode and in more complex devices pave the way for advanced functionalities.publishe

High‐Resolution Observations of Turbulence Distributions Across Tropopause Folds

In this study, we interpret two vertical turbulence measurements. We acquired these uninterrupted high‐resolution dissipation rate profiles with the balloon‐borne instrument LITOS (Leibniz Institute Turbulence Observations in the Stratosphere) from velocity measurements using a spectral technique. The meteorological situation is characterized using ECMWF’s integrated forecast system (IFS) as breaking Rossby waves showing significant tropospheric jets and a developed tropopause fold. In both cases, dissipation rates in the shear zone above the upper‐tropospheric jet are three orders of magnitude larger than below, reaching severe turbulence strengths (1,000 mW kg−1) in a deep tropopause fold and moderate turbulence strengths in a medium tropopause fold (10 mW kg−1). These turbulent spots are shown to create a tripole shaped pattern of PV modification across the tropopause. Furthermore, tracer‐tracer correlations exhibit mixing of tropospheric and stratospheric air masses in the medium‐fold case. While the strength of turbulence corresponds to the depth of the tropopause fold, its asymmetric vertical distribution is possibly related to the tropopause fold life cycle. The observed asymmetry in the vertical turbulence distribution is consistent across both tropopause folds and in overall agreement with measured Richardson numbers. In the medium‐fold case however, it is neither expected from conceptual models nor from Richardson numbers in the IFS. This calls for further field campaigns to investigate the role of turbulence and its implications for the meteorological understanding as well as for aviation safety.Plain Language Summary: Tropopause folds are areas where air from higher altitudes is submerged under the jet stream. These areas are important for the vertical exchange of trace gases and are known for creating aviation hazards due to enhanced turbulence. In our study, we use high‐resolution turbulence measurements from balloons to study the phenomenon. For further understanding, these observations are compared to data from weather forecast models. While we generally find a quantitative agreement between our measurements and other studies, the observed turbulence pattern is unexpected: we find turbulence strengths above the jet stream to be 1,000 times stronger than below. As conceptional models predict a strengthening of tropopause folds due to turbulence, this result has a likely influence on our understanding of the phenomenon as well as it highlights potential hazards for high flying passenger aircraft.Key Points: High‐resolution turbulence measurements show severe (moderate) turbulence strength in deep (medium) tropopause fold. Eddy heat fluxes are found to modify potential vorticity distribution across tropopause fold comparable to other studies. Unexpectedly, in both cases dissipation rates above the jet are three orders of magnitude larger than below.Deutsche Forschungsgemeinschaft (DFG) http://dx.doi.org/10.13039/50110000165

Signatures of the Higgs mode in transport through a normal-metal--superconductor junction

A superconductor subject to electromagnetic irradiation in the terahertz range can show amplitude oscillations of its order parameter. However, coupling this so-called Higgs mode to the charge current is notoriously difficult. We propose to achieve such a coupling in a particle-hole-asymmetric configurations using a DC-voltage-biased normal-metal--superconductor tunnel junction. Using the quasiclassical Green's function formalism, we demonstrate three characteristic signatures of the Higgs mode: (i) The AC charge current exhibits a pronounced resonant behavior and is maximal when the radiation frequency coincides with the order parameter. (ii) The AC charge current amplitude exhibits a characteristic nonmonotonic behavior with increasing voltage bias. (iii) At resonance for large voltage bias, the AC current vanishes inversely proportional to the bias. These signatures provide an electric detection scheme for the Higgs mode and in more complex devices pave the way for advanced functionalities.publishe

Trägheitsschwerewellen und ihre Verbindung zu brechenden Rossbywellen : Schlussbericht

[no abstract available