Microwavephysics and Atmospheric Physics
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Last update: 13.09.2017
HS 2014: Seminare über Microwavephysics and Atmospheric Physics
Friday 10-12
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Freitag, 19.09.2014

Exoplanet and Earth system simulations with the chemistry-climate model CESM-WACCM

Zeit: 10:15 Uhr
Hörsaal: A97
 
Elisavet Proedrou
Institute of Applied Physics, and
Center for Space and Habitability
University of Bern

I present two numerical experiments with the climate model CESM-WACCM. The first experiment investigates how a soil colour change of the eastern region of the Sahara affects the dynamics of the troposphere. The soil colour perturbation generates a circular wave radially propagating away from the Sahara. After nine hours, the wave front reaches the convection zone in Brazil where a secondary wave is generated and can be clearly seen until 23:00 UT. Analysis of the simulation data gives new results on land-atmosphere interactions, global teleconnections and wave dynamics. The second experiment investigates how would the middle atmosphere and the ozone layer react if the Earth became suddenly tidally locked. A first analysis shows that the ozone concentration would be affected by both the dynamics and photochemistry. After 25 days a significant decrease of the ozone concentration at 34 km altitude can be seen on the night side of the planet and an increase on the day side. The atmospheric circulation is greatly altered, with the strong zonal winds being replaced by strong meridional winds instead. Also the value of the horizontal wind is greatly reduced. This is a new topic, which has not been investigated by the exoplanet community.

 
Freitag, 03.10.2014

The useful use of microwave noise

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Jiri Polivka
Spacek Labs
Santa Barbara, CA

During 1970s the author developed microwave radiometers for 12, 18 and 35 GHz, to study atmospheric water emission. To calibrate the instruments, the new avalanche noise diodes had a high excess-noise ratio that had to be attenuated. Before a directional waveguide coupler was machined, an idea led to making a noise radiator of a noise generator and a small horn antenna. Such calibration system worked but the near-field interference was missing. The concept of microwave noise field developed in several interesting applications and even in new concept in coherence. The contribution is devoted to the "active radiometry" development and interesting uses of the noise field, to measure insertion loss and reflectivity of materials (while the samples can move), measuring field distribution inside and close to antenna radiators, combining noise radiators in a matrix, and more.

 
Freitag, 10.10.2014

Trajectory mapping of middle atmospheric water vapour

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

The important task to observe the global coverage of middle atmospheric trace gases like water vapor or ozone usually is accomplished by satellites. Climate and atmospheric sciences rely upon the knowledge of horizontal trace gas distributions on various altitude levels up to the earth's mesosphere. A potential future lacking of highly needed remote sensing instruments on satellite platforms, which are dedicated to trace gas measurements, could lead to a significant knowledge gap of the state of the atmosphere.

We explore the possibilities of mapping middle atmospheric water vapor in the northern hemisphere by using Lagrangian trajectory calculations and water vapor profile data from a small network of five ground-based microwave radiometers. Four of them are operated within the frame of NDACC (Network for the Detection of Atmospheric Composition Change). The measurements from all the instruments are processed by use of different retrieval algorithms. Keeping in mind that the instruments are based on different hardware and calibration setups, a height dependent bias of the retrieved water vapor profiles has to be expected among the microwave radiometers. In order to correct and harmonize the different datasets, the Microwave Limb Sounder (MLS) on NASA's EOS (Earth Observing System) Aura satellite is used to serve as a kind of travelling standard. A domain/pixel filling trajectory mapping method is applied, which simplifies the subsequent validation of the quality of the trajectory mapped water vapor distribution towards direct satellite observations (e.g. Aura MLS). Trajectories are calculated in a forward and backward time line up to 10 days from 6 hourly meteorological analyses fields. Overall, a total of four case studies of trajectory mapping in different synoptic/dynamical atmospheric regimes including a day during a major sudden stratospheric warming, randomly chosen from the year 2012, will be presented, showing the high potential of a network of ground based remote sensing instruments to synthesize hemispheric maps of water vapor.

 
Freitag, 17.10.2014

Precise Science Orbit Determination for ESA's GOCE Mission

Zeit: 10:15 Uhr
Hörsaal: A97
 
Prof. Adrian Jäggi
Astronomical Institute
University of Bern

The Gravity field and steady-state Ocean Circulation Explorer (GOCE), ESA's first Earth Explorer Core Mission, was launched on March 17, 2009 into a sun-synchronous dusk-dawn orbit and re-entered into the Earth's atmosphere on November 11, 2013. It was equipped with a three-axis gravity gradiometer for high-resolution recovery of the Earth's gravity field, as well as with a 12-channel, dual-frequency Global Positioning System (GPS) receiver for precise orbit determination (POD), instrument time-tagging, and the determination of the long wavelength part of the Earth's gravity field. A precise science orbit (PSO) product was provided during the entire mission by the Astronomical Institute of the University of Bern (AIUB) in the frame of the GOCE High-level Processing Facility (HPF) from the GPS high-low Satellite-to-Satellite Tracking (hl-SST) data. After a general introduction of the mission I will present the reduced-dynamic and kinematic PSO results for the entire mission period. Orbit comparisons and validations with independent Satellite Laser Ranging (SLR) measurements demonstrate the high quality of both orbit products being close to 2 cm 1-D RMS, but also reveal a correlation between solar activity, GPS data availability, and the quality of the orbits. We used the 1-sec kinematic positions of the GOCE PSO product for gravity field determination and I will present GPS-only solutions covering the entire mission period. The generated gravity field solutions reveal severe systematic errors centered along the geomagnetic equator, which may be traced back to the GPS carrier phase observations used for the kinematic orbit determination. The nature of the systematic errors is further investigated and reprocessed orbits free of systematic errors along the geomagnetic equator are derived. Eventually, the potential of recovering time variable signals from GOCE kinematic positions is briefly assessed.

 
Freitag, 24.10.2014

CO and CH4 retrievals from spaceborne FTIR nadir measurements

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Evelyn De Wachter
Belgian Institute for Space Aeronomy (BIRA-IASB)
Brussels, Belgium

The IASI nadir looking thermal infrared (TIR) sounder onboard MetOp-A enables the monitoring of atmospheric trace gases on a global scale. For this seminar I will present a quality assessment of retrieved IASI CO profiles, by an inter comparison with airborne in-situ CO profiles from the MOZAIC program. This validation exercise will show that TIR sounders are particularly suited to monitor mid-tropospheric concentrations of trace gases like CO, but have limited sensitivity to the boundary layer when the thermal contrast between the surface and the first atmospheric layer is low. Observations in the Shortwave infrared (SWIR) on the other hand provide trace gas column concentrations with high sensitivity near the ground, but are unable to resolve its vertical distribution. The TANSO-FTS instrument onboard GOSAT is the first instrument that measures simultaneously the same field of view in the SWIR (CH4) and TIR (CH4) spectral range with a high spectral resolution. In this context, the ESA SIROCCO project aims at retrieving the near-surface concentrations of CH4 by combining SWIR and TIR passive remote sensing measurements in a synergistic way. As part of the SIROCCO activities, I will present a performance analysis and the validation results of the non-synergistic SWIR and TIR and synergistic SWIR-TIR CH4 retrievals at 6 TCCON stations. With this work we want to better exploit the available data to provide information on CH4 as close as possible to its associated sources, and thereby provide a better understanding and quantification of its budget.

 
Freitag, 31.10.2014

Smoothing Error Pitfalls

Zeit: 10:15 Uhr
Hörsaal: A97
 
PD Dr. Thomas von Clarmann
Institute of Meteorology and Climate Research
Karlsruhe Institute of Technology
Karlsruhe, Germany

Often remote measurements do not contain sufficient information to reconstruct the atmospheric state from the measurements alone. Instead, usually some kind of prior information is used to constrain the inversion involved in the retrieval of atmospheric state variables from the measurements. The constraint, however, can push the retrieval away from the actual atmospheric state. The related retrieval error is traditionally referred to as 'smoothing error'. In the first part of the talk traps associated with the use of prior information are discussed, using intuitive examples. In the second part it will be shown that the smoothing error is not compatible with Gaussian error propagation and that it is thus misleading to include it in the error budget.

 
Freitag, 07.11.2014

no seminar, NORS workshop

Zeit: 10:15 Uhr
Hörsaal: A97
 

 
Freitag, 14.11.2014

Zeeman effect of oxygen at 60 GHz

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Francisco Navas
Institute of Applied Physics
University of Bern

In the work presented in this seminar we study the Zeeman effect on stratospheric O2 using ground-based microwave radiometer measurements. The interaction of the Earth magnetic field with the oxygen dipole leads to a splitting of O2 energy states which polarizes the emission spectra. A special campaign was carried out in order to measure this effect in the oxygen emission line centered at 53.07 GHz. Both a fixed and a rotating mirror were incorporated to the TEMPERA (TEMPERature RAdiometer) radiometer in order to be able to measure under different observational angles. This new configuration allowed us to change the angle between the observational path and the Earth magnetic field direction. Moreover, a high resolution spectrometer (1 kHz) was used in order to measure for the first time the Zeeman effect in the main isotopologue of oxygen from ground-based microwave measurements. The measured spectra showed a clear polarized signature when the observational angles were changed evidencing the Zeeman effect in the oxygen molecule. In addition, simulations carried out with the Atmospheric Radiative Transfer Simulator (ARTS) allowed us to verify the microwave measurements showing a very good agreement between model and measurements. The results suggest some interesting new aspects for research of the upper atmosphere.

 
Freitag, 21.11.2014

Age of Air decadal trends from MIPAS SF6 observations and the displacement of the subtropical mixing barriers as their potential cause

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Gabriele Stiller
Institute of Meteorology and Climate Research
Karlsruhe Institute of Technology
Karlsruhe, Germany

We have derived the first data set of SF6 with global coverage over ten years from MIPAS/Envisat spectral measurements. SF6 is an inert tracer in the stratosphere that allows to derive mean stratospheric age of air (AoA) as long as the tropospheric growth rate of SF6 is sufficiently well known. Analysis of global distributions of AoA from MIPAS data provides a latitude-altitude pattern of positive and negative decadal trends that are not easy to understand and to interpret in terms of acceleration or deceleration of the Brewer-Dobson circulation. We show that a displacement of the subtropical mixing barriers, leading to a position shift of the tropical pipe and the surf zones, over the ten years of MIPAS observation, can explain the observed AoA trends, and, moreover, most of the trend patterns of tracers derived from MIPAS observations. (G. Stiller, F. Fierli, F. Ploeger, F. Haenel, T. Reddmann, B. Funke, and T. von Clarmann)

 
Freitag, 28.11.2014

Numerical scattering analysis of aircraft for radar applications

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Arne Schröder
Institute of Applied Physics
University of Bern

This talk deals with the numerical radar cross section (RCS) analysis of aircraft for typical radar applications such as air traffic control. The possibilities and limitations of electromagnetic simulation tools for scattering investigations are demonstrated. Various radar scenarios, including mono- and bistatic RCS computations as well as inverse scattering aperture radar examinations, are discussed for different types of airplanes. Here, modeling aspects and issues are shown with regard to a real life medium-sized aircraft. Moreover, quasi-periodic surfaces, as used for radar absorbing structures, are investigated. An efficient analytical-based technique for period structures is presented and the results are compared with measurements and full-wave numerical results.

 
Freitag, 05.12.2014

Characteristics of gravity waves resolved by ECMWF: results from the PREMIER GW study

Zeit: 10:15 Uhr
Hörsaal: A97
 
Dr. Peter Preusse
Forschungszentrum Juelich
Juelich, Germany

Global model data from the European Centre for Medium-Range Weather Forecasts (ECMWF) are analyzed for resolved gravity waves (GWs). Based on fitted 3-D wave vectors of individual waves and using the ECMWF global scale background fields, backward ray tracing from 25 km altitude is performed. Different sources such as orography, convection and winter storms are identified. Gravity waves which originate from regions of strong convection are frequently excited around the tropopause and have in the ECMWF model low phase and group velocities as well as very long horizontal wavelengths compared to measurements. Gravity waves generated by storms and mountain waves show large day-to-day variability, which has a strong influence also on total hemispheric fluxes; from one day to the next the total hemispheric flux may increase by a factor of 3. Implications of these results are discussed. In particular, the techniques developed for this paper shall be used for flight-planning in an upcoming aircraft campaign in January 2016 at Kiruna to investigate the life cycle of GWs.

 
Freitag, 12.12.2014

Harmonisation and trend analysis of the time series of stratospheric ozone profiles observed by GROMOS microwave radiometer at Bern

Zeit: 10:15 Uhr
Hörsaal: A97
 
Lorena Moreira
Institute of Applied Physics
University of Bern

The ozone radiometer GROMOS (GROund-based Millimeterwave Ozone Spectrometer) performs continuous observations of stratospheric ozone profiles since 1994 above Bern, Switzerland. GROMOS is part of the Network for the Detection of Atmospheric Composition Change (NDACC) and contributes to the EU project NORS. From November 1994 to October 2011, the ozone line spectra were measured by a digital filter bench (FB). In July 2009, a Fast-Fourier-Transform spectrometer (FFTS) has been added as backend to GROMOS. The new FFTS and the original FB measured parallel for over two years. The FFTS results from October 2009 to August 2011 are compared to ozone profiles retrieved by FB. The ozone profiles of FB and FFTS agree within 5% at pressure levels from 30 to 0.5 hPa. A careful harmonisation of both time series is performed by taking the FFTS as benchmark for the FB. Finally we discuss preliminary results of long-term trends derived from the 20 years of stratospheric ozone observations at Bern.