Microwavephysics and Atmospheric Physics
HS 2018  ·  FS 2018
HS 2017  ·  FS 2017
HS 2016  ·  FS 2016
HS 2015  ·  FS 2015
HS 2014  ·  FS 2014
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Biomedizinische Photonik
Ultrafast Science and Technology
Last update: 22.11.2018
HS 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, 21.09.2018

Irregularities in the Ionosphere and Thermosphere

Zeit: 10:15 Uhr
Hörsaal: A97
 
PD Dr. Klemens Hocke
Institute of Applied Physics
University of Bern

Gravity waves and ionospheric irregularities in the lower and middle thermosphere are investigated by using data from the GOCE satellite and the satellite constellation COSMIC. The talk gives a short overview on activities of the Astronomical Institute of University of Bern. Then an introduction of the radio occultation measurement principle and the data analysis are given. Finally I present results for gravity wave activity in the lower thermosphere and ionospheric irregularities in the middle thermosphere.

 
Freitag, 28.09.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 05.10.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 12.10.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 19.10.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 26.10.2018

Interstellar dust in the heliosphere

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Veerle Sterken
Institute of Applied Physics

University of Bern

Interstellar dust (ISD) from the Local Interstellar Cloud traverses the solar system at 26 km/s, owing to the relative motion of the Sun and the Local Interstellar Cloud. These particles are messengers from interstellar space that can be studied in situ with dust detectors on space missions inside the solar system.

In 1993, the first such ISD particles were detected using the Ulysses cosmic dust detector. The mission provided a total of 16 years of ISD data and thus covered almost one 22-year solar magnetic cycle. This is important since the dust trajectories are shaped by the solar radiation pressure, gravity and Lorentz force, as they are charged and move through the interplanetary magnetic field that changes throughout the solar cycle. Interpretation of these data is carried out using Monte Carlo simulations of dust trajectories, which allows us to constrain the particle properties and it teaches us about the role of the heliosphere.

Finally, in 2006, Stardust brought a few samples of interstellar dust material back to Earth, and in 2016, the Cassini mission provided the first time-of-flight mass spectra of 36 ISD impacts on the Cassini Cosmic Dust Analyzer.

In this talk, we review the latest developments in the study of “local” interstellar dust with astronomical, in-situ, and sample return techniques. The dynamics of the ISD as it moves through the heliosphere will be explained and finally, we elaborate on what we can gain from computer simulations and spacecraft data for constraining both the ISD properties as well as for studying the heliosphere.

 
Freitag, 02.11.2018

Stratospheric ozone recovery at mid-latitudes: improved ground-based time series and trend estimations

Zeit: 10:15 Uhr
Hörsaal: A97
 
Leonie Bernet
Institute of Applied Physics

University of Bern

Monitoring the recovery of stratospheric ozone is essential to verify the effectiveness of the Montreal Protocol. After the protocol banned ozone depleting substances, first signs of an ozone recovery in the stratosphere were observed starting in 1997. Recent studies have confirmed that mid-latitudinal ozone is increasing in the middle stratosphere due to chemical and dynamical effects, whereas evidence for a continuous decrease in the lower stratosphere exists. To improve trend estimations of stratospheric ozone profiles, continuous and stable time series are crucial and trend uncertainties need to be addressed. We present an updated and improved 23-years time series of stratospheric ozone from the GROMOS (GROund-based Millimeter-wave Ozone Spectrometer) microwave radiometer located at Bern, Switzerland, that provides ozone profiles from 20-60km. We compared the data with other ground-based instruments in central Europe from the Network for the Detection of Atmospheric Composition Change (NDACC). Based on the different data sets we estimated trends of stratospheric ozone volume mixing ratios (VMR) with a multilinear trend model that can handle uncertainties in a flexible way. The datasets show positive ozone VMR trends of 2-4% in the middle stratosphere (25-40km), and biased results in the lower stratosphere. Our study further elucidates how trend estimates of stratospheric ozone are influenced by factors such as uncertainties of the underlying ozone data, sampling rate and period length. The GROMOS data are well suited to investigate such factors thanks to the long and complete time series and the high temporal resolution.

 
Freitag, 09.11.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 16.11.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Mittwoch, 21.11.2018

Quantifying ozone variability and long-term changes using observations and chemistry climate models

Zeit: 14:15 Uhr
Hörsaal: B78
 
Dr. William T. Ball, Institute for Atmospheric and Climate Science (IAC), ETH Zürich and PMOD/WRC, Davos

 
Freitag, 30.11.2018

PhD defense; Radiometric Calibration of the Submillimetre Wave Instrument SWI/JUICE

Zeit: 10:15 Uhr
Hörsaal: B78
 
Karl Jacob
Institute of Applied Physics
University of Bern

 
Freitag, 07.12.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 14.12.2018

Can a mm-wave detector’s sensitivity approach the quantum limit at room temperature?

Zeit: 10:15 Uhr
Hörsaal: A97
 
Prof. Luis Enrique García Muñoz, Universidad Carlos III de Madrid

The cosmic microwave background (CMB) radiation is a relic from the recombination epoch of the early universe. Its intensity anisotropies and near black body spectrum were predicted and observed, allowing the refinement of the cosmological standard model. However, extremely weak hypothesized signatures such as spectral distortions with respect to a black body, and the B-mode polarization due to primordial gravitational waves are yet undetected. The CMB intensity, spectrum, and polarization, are currently observed with radio telescopes on earth and in space whose instrumentation (radiometers) require cryogenic conditions in order to minimize the internally generated thermal noise. Here we show that microwave-to-optical up-conversion in high Q nonlinear whispering-gallery mode (WGM) resonators can be used for ultra-low-noise radiometry of the CMB at room temperature. We found that radiometers with similar or better sensitivity than a 85K-cooled high-electron-mobility transistor (HEMT) receiver can be achieved at room temperature with high efficiency up-converters and photodetectors. We experimentally demonstrate up- conversion of 80 GHz microwave signals into 194 THz optical signals inside lithium niobate cavities, showing two orders of magnitude higher efficiency than the best reported so far. These results demonstrate the versatility of WGM cavities made of nonlinear crystals, as ultra-low-noise and highly efficient electro-optic up-converters for frequencies ranging from microwave to THz. And the question arises: “Can a mm-wave detector’s sensitivity approach the quantum limit at room temperature?”

 
Freitag, 21.12.2018

No seminar

Zeit: 10:15 Uhr
Hörsaal: A97