Microwavephysics and Atmospheric Physics
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HS 2010: Seminare über Microwavephysics and Atmospheric Physics
Friday 10-12
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Freitag, 24.09.2010

Masterthesis: A novel 142-GHz-radiometer for mesospheric wind measurements

Zeit: 10:15 Uhr
Hörsaal: A97
Rolf Rüfenacht
Institute of Applied Physics, University of Bern

The aim of this thesis was the conception and putting into operation of a new radiometer for mesospheric wind measurements using the Doppler shift of the 142 GHz ozone emission line. The talk will comprise three parts. In the first one the measurement principle is elucidated and the atmospheric simulations are commented. The second part consists in the illustration of the most important properties of the instrument. In the last part the results of the first atmospheric measurements will be shown.

Freitag, 08.10.2010

Alpine precipitation measurements with a polarimetric X-Band radar and additional sensors

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Marc Schneebeli
EPFL, Lausanne

The alpine region is vulnerable to natural disasters which are mostly caused by heavy precipitation events. Due to their orography, the Alps itself also have a huge impact on the flow patterns of air masses, hence influencing directly the precipitation distribution in all seasons. Therefore, accurate rain- and snowfall observations are needed to minimize disaster impact and to further the understanding on small-scale precipitation dynamics. However, the complex alpine topography as well as the fact that precipitation occurs as rain and snow induces difficulties for accurate quantitative estimations. In order to address such problems, a mobile X-Band polarimetric weather radar (MXPol) was deployed in September 2009 on the slope of a mountain valley near Davos in the eastern Swiss Alps, at an altitude of about 2200 m. The opposite side of the valley was equipped with a network of different disdrometers (three optical Parsivel disdrometers aligned in a transect from the bottom of the valley up to 2600 m and one video disdrometer at 2600 m with the capability of measuring the shape of raindrops and snowflakes). These measurements were complemented with snow accumulation and snow density measurements as well as several weather stations. The installation and operation of this unprecedented sensor assembly is described and difficulties caused by the harsh environmental conditions are discussed. A significant number of snowfall events, ranging from dry and cold to warm and wet snow, as well as rain events were detected. I will present several case studies and show how the polarimetric capability of our radar can be used to correct for attenuation and to identify different hydrometeor classes.

Freitag, 29.10.2010

SOMORA ozone profiles: from acousto-optical to fast Fourier transform spectrometers

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Eliane Maillard Barras
MeteoSwiss, Payerne

Ozone vertical profiles are measured since 2000 by the microwave radiometer SOMORA developed by IAP/Bern. The ARTS/Qpack package is used for the retrieval of the ozone profiles since 2 years. The characterization of the retrieval performances and the determination of the optimal tuning parameters adapted to SOMORA will be presented. Comparison with ozone profiles measured by Payerne radiosounding and by AURA/MLS satellite will be discussed. First steps of a study on combining ozone radiosounding and microwave radiometer SOMORA measurements of Payerne in a composite ozone vertical profile from ground to 60 km will be presented. During one year, parallel measurements of ozone profiles have been performed using digital Fast Fourier Transform (FFT) and acousto-optical spectrometers (AOS). The retrieval has been adapted to the new FFT acquisition mode. Ozone profiles retrieved from FFT acquisition mode will be compared to ozone profiles retrieved from AOS and to radiosounding ozone profiles. Open questions concerning the resolution of the raw FFT spectrum and the frequencies distribution will be discussed.

Freitag, 05.11.2010

The restless atmosphere - wind, turbulence, and waves

Zeit: 10:15 Uhr
Hörsaal: A97
Prof. Dr. Hans Richner
Institut für Atmosphäre und Klima
ETH Zürich

The atmosphere is constantly in motion. This is true for all scales, i.e., for the Earth's dimension where the global circulation distributes the incoming solar energy, as well as for the dimension of centimeters where the motion of turbulent elements achieve the flux of heat, mechanical energy and atmospheric constituents. Between these two extremes, atmospheric waves are almost constantly present. After an overview of the dynamic features, their effects on the propagation of electromagnetic waves are discussed. While these might be an annoyance for astronomy, geodesy, telecommunication, etc., they are widely used for observing the state of the atmosphere and, consequently, an important tool for atmospheric research. The principles of some observing systems - among them the scintillation anemometer and ray-tracing of gravity waves - are briefly discussed.

Freitag, 12.11.2010

Ion-neutral chemistry coupling during excess ionization events in middle atmosphere

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Esa Turunen
Director, EISCAT Scientific Association
Kiruna, Sweden

Excess ionisation events in upper and middle atmosphere, due to solar proton events, high-energy auroral electron precipitation at high latitudes, relativistic electron precipitation from radiation belts and solar extreme X-ray events, cause ionosphere - neutral atmosphere coupling, where it appears that also the ion chemistry reactions are relevant when considering variations in neutral composition. Recently several studies have pointed out the need to study even possible existence of climatological effects, due to originally Space Weather related drivers.

In this talk, a detailed coupled ion and neutral chemistry model for the lower ionosphere and upper stratosphere, mesosphere and lower thermosphere, the Sodankyla Ion Chemistry Model (SIC), as an essential tool in such studies, is presented. Chemistry, physics, mathematics and software implementation of the model are described in schematic level. Recent results of applying the model during solar proton events, auroral electron precipitation, relativistic electron precipitation and solar X-ray flares in order to study variations in ionisation and changes in concentrations of odd nitrogen, odd hydrogen, ozone and nitric acid, as well as comparisons with satellite, radio and radar experiments are shown.

The ESFRI Roadmap Infrastructure facility EISCAT_3D will be Europe's next-generation radar for the high-latitude atmosphere and geospace research, with capabilities going beyond anything currently available. The facility will consist of large phased arrays in three countries. Depending on funding, EISCAT_3D will comprise tens of thousands, up to more than 100 000, antenna elements. EISCAT_3D combines volumetric imaging and tracking, aperture synthesis imaging, multistatic configuration, improved sensitivity and transmitter flexibility. At the passive sites, the design allows the full extent of the transmitted beam to be imaged using holographic techniques. The technical specifications and science case for EISCAT_3D will be briefly discussed. Studies of the atmospheric energy budget, exploration of small-scale and large-scale processes, as well as geospace environment monitoring and service applications are discussed.

Freitag, 26.11.2010

Fire detectors

Zeit: 14:15 Uhr
Hörsaal: B116
Dr. Aleksandar Duric
Siemens, Zug

Earth, water, air and fire, the four basic elements in the hellenic science, even more than in the past, pose threats to human lives and property. Thus, systems that provide early warning to emerging danger and ensure enough time to escape and introduce countermeasures became very important. This is the role of fire detection systems, particularly fire detectors - expected to be unremarkable most of their life, but acting quickly and resolutely when fire danger becomes significant. After an overview of working principles of various types fire detectors, a brief discussion of major challenges in their development and industrialization will follow.

Freitag, 03.12.2010

Masterthesis: Measurement of middle atmospheric water vapor and integrated water vapor by MIAWARA-C

Zeit: 10:15 Uhr
Hörsaal: A97
Brigitte Tschanz
Institute of Applied Physics, University of Bern

The talk presents an overview of the results of my work with the 22 GHz radiometer for middle atmospheric water vapor MIAWARA-C. After an introduction of the physical basics of microwave radiometry the instrument and its calibration scheme are described. The retrieval linking the measured spectrum to a water vapor profile is discussed. The importance of a good choice of observation angle is pointed out and the effect on the temporal resolution is illustrated with measurements from MIAWARA and MIAWARA-C. In addition profiles from MLS, MIAWARA and MIAWARA-C are compared. In the last part the estimation of integrated water vapor from measured opacity is presented together with its limitation.

Freitag, 10.12.2010

Promotions-Vortrag VERSCHOBEN auf Mittwoch 22. Dezember 14:15 Uhr

Zeit: 10:15 Uhr
Hörsaal: A97
Stefan Wacker
Physikalisch-Meteorologisches Observatorium

Freitag, 17.12.2010

Ground based lidar observations of stratospheric ozone and temperature at Dumont D'Urville, Antarctica

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Alexander Haefele

Since the early 90's a lidar system is installed at the french antarctic station Dumont D'Urville to measure stratospheric temperature and ozone profiles in the frame of the network for the detection of atmospheric composition change, NDACC. It is a multiwavelength system and the DIAL (differential absorption lidar) technique is applied to determine the ozone concentration at altitudes between 15 and 45 km. Temperature profiles between 20 and 60 km are derived from Rayleigh scattering signals by the integration technique. The system has been updated in 2005 and is back into operation since 2008. Design and performance of the new system and the retrieval of temperature and ozone are discussed followed by an evaluation of the data, collected since 2008, based on comparisons with radiosoundings and satellite data.

Mittwoch, 22.12.2010

Promotions-Vortrag: LIRAS - Longwave Infrared Radiative forcing Trend Assimilation over Switzerland

Zeit: 14:15 Uhr
Hörsaal: A97
Stefan Wacker
Physikalisch-Meteorologisches Observatorium