Microwavephysics and Atmospheric Physics
HS 2018  ·  FS 2018
HS 2017  ·  FS 2017
HS 2016  ·  FS 2016
HS 2015  ·  FS 2015
HS 2014  ·  FS 2014
HS 2013  ·  FS 2013
HS 2012  ·  FS 2012
Biomedizinische Photonik
Ultrafast Science and Technology
Last update: 02.11.2018
FS 2018: Seminare über Microwavephysics and Atmospheric Physics
Friday 10-12
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Freitag, 02.03.2018

Unexpected behavior in resonant structures undergoing free space THz and GHz excitation

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Suchitra Ramani
Los Alamos National Laboratory
New Mexico, USA

Finite metamaterial arrays with varying split ring resonator sizes were excited in the Kretschmann ATR configuration using finite sized terahertz beams. The intent was to explore the behavior of two-dimensional planar metamaterials or metafilms and understand the various excitation schemes for application of metafilms to Terahertz-Attenuated Total Reflection spectroscopy (THz-ATR). The ATR measurements on metafilms with closely spaced rings showed an anomalous edge enhancement when the metafilm sample was illuminated near the edge. More recent work in the GHz regime investigating the relationship between highly-moded excitation (mode stirred chamber) and plane wave excitation (anechoic chamber) on slotted cylindrical cavities with high Q has yielded unexpected results.

 
Freitag, 16.03.2018

Optical Design of the Submillimeter Wave Instrument on JUICE

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Mikko Kotiranta
Institute of Applied Physics
University of Bern

The JUpiter ICy moons Explorer (JUICE) is a mission of the European Space Agency (ESA) to study Jupiter and its satellites Ganymede, Callisto and Europa. The launch is scheduled for 2022. The spacecraft will carry 10 instruments on board, one of them being the Submillimeter Wave Instrument (SWI). The SWI is a passive heterodyne radiometer that will observe the atmospheres and surface properties of the Jovian objects in the frequency bands 530– 625 GHz and 1080–1275 GHz. This paper reports the design and detailed analysis of the optical system of the SWI instrument. The instrument receives the radiation with a paraboloidal off-axis Cassegrain antenna with an aperture diameter of 29 cm. The telescope is able to scan an angular range of ±72° in the spacecraft orbital plane and ±4.3° perpendicular to it to allow mapping of the entire surface area of Jupiter. The signal from the hyperbolic secondary mirror of the Cassegrain antenna is guided via planar and elliptical mirrors to a polarizing beam splitter (PBS) that divides the signal into two orthogonal polarizations. The signal transmitted through the PBS is reflected from an elliptical mirror and is then coupled to a smooth-walled spline-profiled feed horn of a double side band (DSB) receiver of the 1200-GHz channel. Similarly, the signal reflected from the PBS undergoes a further reflection at another elliptical mirror after which it is received by a linear-profiled corrugated feed horn of the 600-GHz DSB receiver. The instrument is calibrated by observing a conical blackbody calibration target and cold space that act as the hot and cold temperature references, respectively. In order to allow the receivers to view the hot load, the beam path is redirected by activating a planar flip mirror. A view to the cold load is enabled by rotating the telescope. The telescope is required to provide an antenna pattern with a full width at half maximum of less than 1.3 Lambda/D, a side lobe suppression of less than -30 dB, and a cross-polarization level of less than -20 dB. We have designed an optical network that is frequency independent in both frequency bands using Gaussian beam mode analysis and simulated the far-field radiation pattern of the telescope with the physical optics (PO) method. In addition to the ideal configuration, we have evaluated the optical performance by including measured surface profiles of prototype mirrors into the simulations. As the optical elements will be exposed to temperatures down to 110 K during the mission, the effect of shape deformation and misalignment provided by thermo-elastic finite element method simulations has been studied as well. Finally, the effect of manufacturing and assembly tolerances on the optical performance has been determined by running several thousand PO simulations: first, each component was misaligned one at a time, then random misalignments were assigned to all of the components in a Monte Carlo fashion.

 
Freitag, 23.03.2018

Evidence for continued ozone layer reduction

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. William Ball
PMOD/WRC & IAC/ETH Zurich

Stratospheric ozone protects life from harmful ultraviolet radiation from the Sun. The Montreal Protocol, enacted to prevent ozone depletion from human activity, halted declines in column-integrated ozone in the 1990s; the upper stratosphere is recovering, but lower stratospheric trends are unknown. I will present clear evidence that lower stratospheric ozone continues to decline, preventing total ozone recovery. However, the result contradicts expectations given our understanding of these factors and, with no clear understanding of why this trend has emerged, implies that the problem of ozone depletion is not yet fully solved. The decline may impact future estimates of ozone layer recovery, and among other things, surface levels of solar ultraviolet radiation.

 
Freitag, 30.03.2018

No seminar (Good Friday)

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 20.04.2018

Planetary boundary layer detection by Remote Sensing instruments

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Martine Collaud Coen
MeteoSwiss Payerne

Continuous determination of planetary boundary layer (PBL) height is of prime importance for air quality analysis and prediction, and for model validation. The PBL top is characterized by a decrease of the aerosol and humidity concentrations and by increased turbulences. These physical properties can be measured either by Lidar, Windprofiler, microwave radiometer or radio-sounding. All these methods are synergistically used to obtain the most comprehensive picture of the various PBL layers. Comparisons with the PBL heights determined by the numerical weather prediction (NWP) model COSMO-2 as well as a two year climatology at Payerne and Schaffausen were also done. Finally a ceilometer at the Kleine Scheidegg associated with a new algorithm, PathFinderTurb, was developed to automatically derived the local convective boundary layer and the top of the continuous aerosol layer above the research station of the Jungfraujoch. The impact of the regional and of the meso-scale pollution on a high altitude site can then be assessed.

 
Freitag, 27.04.2018

Water vapor in the middle atmosphere: Long-term measurements to study the variability of quasi 2-day waves and trends

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Martin Lainer
Institute of Applied Physics
University of Bern

Atmospheric water vapor is a key climate parameter. Long-term observations from ground and space are required to study trends and the variability on different time scales. In the stratosphere and mesosphere, water vapor can be used as a tracer to study atmospheric waves. A mesospheric water vapor data set obtained by the middle atmospheric water vapor radiometer (MIAWARA) close to Bern, Switzerland (46.88°N, 7.46°E) between October 2010 and September 2017 is investigated to study the long-term evolution and variability of quasi 2-day waves (Q2DWs). We present a climatological overview and an insight on the dynamical behavior of these waves with the occurring spectrum of periods as seen from a mid-latitude observation site. The analysis of autobicoherence spectra gives evidence that Q2DWs occasionally are to a high degree phase coupled to diurnal oscillations and to waves with a period close to 18 hour. The second part of the talk presents results on a water vapor trend study in the middle atmosphere with 5 ground-based microwave radiometers operated in the scope of NDACC and with space-based observations by the Aura MLS satellite. The trend assessment is performed with a multi-linear parametric trend model which includes a linear term, the solar variability, the El Niño–Southern Oscillation (ENSO) index, the quasi-biennial oscillation (QBO), the annual and semi-annual oscillation.

 
Freitag, 04.05.2018

Results from stratospheric and mesospheric wind measurement campaigns from tropical, polar and mid-latitudes by microwave radiometry

Zeit: 10:15 Uhr
Hörsaal: A97
 
Jonas Hagen
Institute of Applied Physics
University of Bern

Passive Doppler microwave wind radiometry is a unique method to continuously measure wind profiles in the stratosphere and mesosphere. Currently, two instruments are operational, namely WIRA (WInd RAdiometer) and WIRA-C (WInd RAdiometer for Campaigns). Both instruments observe the rotational emission line of ozone at 142 GHz and exploit the classical Doppler shift introduced to this emission line due to the movement of the emitting molecules with the air flow. Thanks to the pressure broadening effect, altitude resolved wind profiles can be obtained between 30 and 70 km altitude. Currently, WIRA and WIRA-C are operated in the frame of the ARISE2 project that is funded by the European Commission Horizon 2020.

Since the development of microwave wind radiometry, the two instruments WIRA and WIRA-C have accomplished several campaigns in tropical, polar and mid-latitudes. We present a total of over 60 months of zonal and meridional wind measurements acquired between 2012 and 2018. This includes measurements from campaigns at the Observatoire de Haute-Provence (44° N), the Maïdo observatory on La Reunion island (21° S) and the ALOMAR observatory in Andenes (67° N). We sum up the atmospheric events represented in our dataset like for example sudden stratospheric warmings, the annual cycle and signatures of tropical dynamics. Further we elaborate on the differences between our measurements and the ECMWF model data when comparing the continuous time series for the different latitudes. In addition we compare our measurements to point-in-time measurements from the co-located lidar systems.

 
Freitag, 11.05.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 01.06.2018

Results from 3 years of middle atmospheric H2O and O3 observation by microwave radiometry at Ny-Ålesund

Zeit: 10:15 Uhr
Hörsaal: A97
 
Franziska Schranz
Institute of Applied Physics
University of Bern

The two ground-based microwave radiometers GROMOS-C for ozone and MIAWARA-C for water vapour have been located at the Arctic research station AWIPEV at Ny-Ålesund, Svalbard (79° N, 12° E) since September 2015. Both radiometers were built at the University of Bern, Switzerland and are specially designed for campaigns. The instruments measure the vertical distribution of ozone and water vapour in the middle atmosphere with a high time resolution and under most weather conditions. GROMOS-C provides hourly ozone profiles where for MIAWARA-C a resolution of 2–4 hours is realistic, depending on the atmospheric opacity. GROMOS-C additionally provides daily mean zonal and meridional wind profiles and can switch to carbon monoxide measurements. The unique datasets from these instruments are used to study dynamical events and the chemistry of ozone and water vapour in the middle atmosphere. We present an overview of the data from 3 years of continuous measurement and show characteristic events in the Arctic atmosphere. During winter the polar vortex dominates the dynamics in the Arctic middle atmosphere. At the latitude of Ny-Ålesund one is mostly inside of the vortex system and we are able to estimate the descent rate of water vapour during its formation. Two sudden stratospheric warmings took place and we measured the reversals of the zonal wind and changes in ozone. We spectrally analysed the water vapour and ozone time series by means of a Fast Fourier Transformation in order to find periodicities. Both time series show signatures of atmospheric waves with periodicities of 2, 5 and 10 days. Ozone has additionally a strong daily cycle. Special emphasis is given to the investigation of the link between ozone and water vapour concentrations in the upper stratosphere and lower mesosphere. The specified dynamics version of the Whole Atmosphere Community Climate Model (SD-WACCM) is used to support this investigation.