Microwavephysics and Atmospheric Physics
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Last update: 22.11.2018
HS 2016: Seminare über Microwavephysics and Atmospheric Physics
Friday 10-12
Vorträge, die innerhalb der nächsten Tage stattfinden, sind speziell markiert.
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Freitag, 23.09.2016

Master's thesis: Cloud Effect on Temperature Profiles from Microwave Radiometry

Zeit: 10:15 Uhr
Hörsaal: B5
Leonie Bernet
Institute of Applied Physics
and Oeschger Centre for Climate Change Research
University of Bern

Freitag, 07.10.2016

Lidar and Microwave Radiometer Synergy for High Vertical Resolution Thermodynamic Profiling

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Maria Barrera Verdejo
Institute for Geophysics and Meteorology
University of Cologne, Germany

Continuous monitoring of thermodynamic atmospheric profiles is important for many applications, e.g. assessment of atmospheric stability and cloud formation. Nowadays there is a wide variety of ground-based sensors for atmospheric profiling. Unfortunately there is no single instrument able to provide a measurement with complete vertical coverage, high vertical and temporal resolution, and good performance under all weather conditions, simultaneously. For this reason, in the last decade instrument synergies have become a strong tool used by the scientific community to improve the quality and usage of the atmospheric observations. Aiming to overcome the specific sensor limitations, the microwave radiometer (MWR) and lidar synergy has been developed.

On the one hand, lidar measurements can provide water vapor or temperature measurements with a high vertical resolution albeit with limited vertical coverage, due to overlapping function (OVF) problems, sunlight contamination and the presence of clouds. On the other hand, MWRs receive water vapor, temperature and cloud information throughout the troposphere though their vertical resolution is poor. The retrieval algorithm combining these two instruments is called Lidar and Microwave Synergetic Optimal Atmospheric Profiler (LIME SOAP) and is based on an Optimal Estimation Method (OEM). The main advantage of this technique with respect to other retrieval algorithms, e.g. neural networks, Kalman filters, etc., is that an OEM allows for an uncertainty assessment of the retrieved atmospheric products.

LIME SOAP combines measurements, i.e. MWR brightness temperatures and lidar water vapor mixing ratio and/or temperature profiles, with a priori atmospheric information taking the uncertainty of both into account. The method is applied to two different scenarios, i.e. ground based measurements during a two months campaign in Germany, and airborne measurements over tropical and subtropical Atlantic Ocean, for retrieving high vertical resolution profiles of absolute humidity (AH), temperature (T), relative humidity (RH) and liquid water path (LWP). For all retrievals, the studies in terms of theoretical error and degrees of freedom per signal reveal that the information of the two sensors is optimally combined. In addition, the vertical resolution of the products is improved when the MWR+lidar combination is performed with respect to the instruments working alone.

Results show that, for example, when applying the LIME SOAP for ground-based AH profiling, on average the theoretically determined absolute humidity uncertainty is reduced by 60% (38%) with respect to the retrieval using only-MWR (only-Raman lidar) data, for two-months data analysis. For temperature, it is shown that the error is reduced by 47.1% (24.6%) with respect to the only-MWR (only-Raman lidar) profile, when using a collocated radiosonde as reference.

The benefits of the sensor combination will be shown, being especially strong in regions where lidar data is not available, whereas if both instruments are available, the lidar measurements dominate the retrieval.

Freitag, 21.10.2016

Microwave radiometer observations of dynamical processes in the middle atmosphere

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

We present an overview of recent observations of changes in the dynamics and atmospheric composition of the middle atmosphere which are related to sudden stratospheric warmings, planetary wave breaking and geomagnetic activity. The aim of the presentation is to foster the discussion and interpretation of the observations.

Freitag, 04.11.2016

Middle atmospheric wave signatures in ground-based observed water vapor

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

After giving a short overview about past studies on middle atmospheric water vapor variability at the IAP, the focus is firstly put on the variability of mesospheric water vapor observed by the MIAWARA microwave radiometer above Bern in relation to the 27-day solar rotation cycle and secondly put on H2O oscillations in the period range from 15 to 21 hours, what is within the wave spectrum of low-frequency gravity waves. Many studies investigated solar–terrestrial responses (thermal state, O3, OH, H2O) with emphasis on the tropical upper atmosphere, but observations at mid-latitudes found less attention. Eight years of water vapor profile measurements above Bern are investigated to study oscillations with the focus on periods between 10 and 50 days. Different spectral analyses revealed prominent features in the 27-day oscillation band, which are enhanced in the upper mesosphere during the rising sunspot activity of solar cycle 24. Local as well as zonal mean Aura MLS observations support these results by showing a similar behavior. The MIAWARA H2O oscillation is negatively correlated to the solar Lyman-Alpha oscillation, and the phase lag is 6-10 days. The competition between advective transport and photodissociation loss of mesospheric water vapor may explain the sometimes variable phase relationship of mesospheric H2O and solar Lyman-Alpha oscillations. A wavelet coherence analysis indicates that solar variability causes observable photochemical and dynamical processes in the mid-latitude mesosphere. In the second part of the presentation we report on MIAWARA water vapor measurements over 12 months in two time periods from October to March (winter 2014/15 and 2015/16). Oscillations with periods between 6 and 30 hours are analyzed in the pressure range 0.01-10 hPa. Seven out of twelve months have the highest wave amplitudes between 15 and 21 hour periods in the upper mesosphere. The quasi 18-hour wave is studied in more detail. The temporal behavior of the wave is investigated and SD-WACCM simulations are used for comparison and to derive characteristic wave features considering low-frequency gravity-waves being involved. A brief overview about atmospheric gravity waves and some idealized mountain wave simulations with the all-scale geophysical flow solver EULAG are given for illustration.

Freitag, 11.11.2016

WCOM: A Synergetic Water Cycle Observation Mission

Zeit: 10:15 Uhr
Hörsaal: A97
Prof. Xiaolong DONG
Key Laboratory of Microwave Remote Sensing
National Space Science Center
Beijing, China

Satellite observations play a critical role in providing information for understanding the global water cycle, which dominates the Earth-climate system. However, limitations in observations will restrict our current ability to reduce the uncertainties in the information used to make decisions regarding to water use and management. Under the support of “Strategic Priority Program on Space Sciences” of the Chinese Academy of Sciences, the Water Cycle Observation Mission (WCOM) is proposed aiming to provide higher accuracy and consistent measurements of key elements of water cycle from space. WCOM is a mission dedicated to synergetic observations of global water cycle parameters, with emphasis on soil moisture, ocean surface salinity, snow water equivalent and frozen/thaw. WCOM implements its observation requirements by measurement of microwave emission/scattering of both the frequencies sensitive to the key parameters and also the auxiliary frequencies providing necessary atmospheric and surface roughness corrections. In order to satisfy this measurement requirements, WCOM is equipped with payloads with combination of active and passive microwave sounding capabilities of frequency from L-band to W-band. In this talk, the scientific objectives, mission and satellite design and also the expected data product will be introduced. The expected more consistent and accurate datasets would be used to refine existing long-time series of satellite measurements, to constrain hydrological model projections and to detect the trends necessary for global change studies. The WCOM is expected to be implemented during the 13th five-year-plan period (2016-2020).

Freitag, 18.11.2016

Microwave temperature profiles from ground to the stratopause

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

The thermal structure of the atmosphere is one of the most important atmospheric characteristics for determining chemical, dynamical and radiative processes in the atmosphere. In the lowest part of the atmosphere, temperature profiles are a key input for the weather forecast models. In the stratosphere, temperature can influence chemical processes, and its vertical distribution is fundamental for investigating other atmospheric species as for example ozone or water. In addition, stratospheric temperature is also a very important indicator of climate change. The temperature trends can provide evidence of the roles of natural and anthropogenic climate change mechanisms. Several studies have shown a detectable observed pattern of tropospheric warming and lower stratospheric cooling during the last few decades of the twentieth century which is very likely related to anthropogenic emissions of trace gases, ozone and aerosols.

Despite the importance of the knowledge of the temperature from ground to the tropopause there are few measurement techniques that are able to cover the whole range. A relatively new temperature radiometer (TEMPERA) has been designed and built by the microwave group at the Institute of Applied Physics (IAP), University of Bern, Switzerland. This is the first ground-based radiometer that measures temperature profiles in the troposphere and in the stratosphere simultaneously. Microwave radiometers present the main advantage of having the capacity of providing atmospheric profiles with a high temporal resolution and a reasonable vertical resolution. In addition, long-term measurements in a fixed location allow the local atmospheric thermodynamics to be characterized.

In this seminar, the validation of the tropospheric and stratospheric temperature profiles from TEMPERA radiometer will be presented. These measurements were compared with the ones from different measurement techniques as radiosondes, satellite, lidar and also with WACCM model.

Freitag, 25.11.2016

The new COSMO forecasting system of MeteoSwiss

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Jean-Marie Bettems
senior scientist

MeteoSwiss initiated the COSMO-NExT project in 2012 to further develop the system for numerical weather prediction with a forecast range of up to five days. After four years of research and development, the new system, which includes the ensemble-based data assimilation system, COSMO-1, and COSMO-E, is operational since spring 2016. COSMO-1 is the high resolution component of the forecasting system, calculated 8 times a day, up to 45 hours lead time, with a horizontal grid box size of 1.1. km; COSMO-E comprises an ensemble of 21 forecasts calculated twice a day, up to 5 days lead time, with a horizontal grid box size of 2.2 km. These systems are computed on the same geographical region, with the Alpine Arc fully included. The boundary conditions are provided by the global forecast of the European Centre for Medium-Range Weather Forecasts (ECMWF).

MeteoSwiss is developing the COSMO numerical forecasting model on an ongoing basis in collaboration with international partners. The national weather services of Germany, Greece, Italy, Poland, Romania, Russia and Switzerland are working together closely within the framework of the Consortium for Small-Scale Modelling (COSMO, see http://www2.cosmo-model.org/). This consortium was founded in October 1998 with the objective to develop further an operational and research mesoscale model-system for the short to very short range, aimed especially at high-impact weather forecast and having ensemble prediction methodology at its core. At the KIT (Karlsruhe Institute for Technology) the COSMO-Model was extended to treat secondary aerosols, directly emitted components like soot, mineral dust, sea salt and biological material as pollen; the online coupling enables calculation of the interactions of gases and aerosols with the state of the atmosphere (http://www.imk-tro.kit.edu/english/3509.php). The CLM Community extended the COSMO-Model to be able to run long-term simulations, the so-called climate mode (http://www.clm-community.eu/). My talk will present an overview of the new COSMO forecasting system of MeteoSwiss, with a focus on the capabilities of the system and with some insights on future developments.

Freitag, 02.12.2016

Return glider radiosonde for in-situ upper-air research measurements

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Andreas Kräuchi

Upper-air balloon soundings for weather predictions have been made since the beginning of the 20th century. New radiosonde instruments for in situ humidity-, radiation and gas-profile measurements in the troposphere and the lower stratosphere, were introduced in recent years for atmospheric research and climate monitoring, but such instruments are often expensive and it is desired they be reused on multiple flights. Here, we introduce the return glider radiosonde (RGR), which enables flying and retrieving valuable in situ upper-air instruments. The RGR is lifted with weather balloons similar to traditional Radiosondes to a pre-set altitude, where a built-in autopilot flies the glider autonomously back to the launch site or a desired pre-programmed location. The motivation for this project was to measure radiation profiles throughout the atmosphere with the same instrument multiple times and with a rapid turn-around time. This allowed measuring radiation flux profiles and the radiation budget from the Earth’s surface to above 24 km in the stratosphere. Several successive flights measuring radiation profiles demonstrate the reliability and the operational readiness of the RGR, allowing new ways for atmospheric in situ research and monitoring with payloads up to several kg depending on the specific size of the glider.

Freitag, 09.12.2016

Single and dual-frequency millimetre-wave radar measurement of rain

Zeit: 10:15 Uhr
Hörsaal: A97
Dr. Peter Speirs
EPFL Lausanne

As a result of Mie-scattering and high attenuation, millimetre-wave radars are not the typical go-to solution for horizontally-pointing measurements of liquid precipitation. However, there are some circumstances in which it may be necessary or even beneficial to make such measurements, and this talk will show how they can be made.

I will present single-and dual-frequency attenuation- and reflectivity-based algorithms for estimating rainfall rate from millimetre radars, based on disdrometer data. As part of this, I will present the importance of using an ellipsoidal (or better) approximation for the scattering from raindrops at millimetre-wave frequencies, and the relatively poor performance of polarisation-based methods at these frequencies. I will then present some experimental results demonstrating the performance of these techniques in the real world. This will include a brief presentation the the 38 and 94 GHz radars that were used for validating these methods, and their calibration.

The talk will also briefly cover the possibility of using millimetre-wave radars to measure volcanic ash plumes, and the possible advantages of using such radars.

Finally, I will also present very briefly some of the work of the University of St Andrews' Millimetre-Wave and High-field ESR group, and the EPFL's Environmental Remote Sensing lab, including my own current work evaluating the performance of the Global Precipitation Monitoring Mission's dual-frequency precipitation radar's performance across Switzerland.

Freitag, 16.12.2016

Middle Atmospheric Ozone and Water Vapour Observations at Ny-Ålesund since September 2015

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

The ground based microwave radiometers GROMOS-C (ground based ozone monitoring system) and MIAWARA-C (middle atmospheric water vapour radiometer) are located at Ny-Ålesund (78°N/12°E) in the Arctic since September 2015 and provide vertical profiles of middle atmospheric ozone and water vapour respectively. Both microwave radiometers have been developed at the University of Bern, Switzerland. The advantage of ground based microwave radiometry is the continuous observation of atmospheric constituents like water vapour and ozone with a high time resolution, depending on tropospheric opacity. In case of ozone, hourly profiles are available whereas in the case of water vapour two to four hourly profiles are realistic. Photochemical and dynamical effects in the middle atmosphere like the diurnal cycle of ozone, the tertiary ozone maximum and deformations of the polar vortex have been observed. As the ozone radiometer is able to measure in the four cardinal directions it is possible to have observations inside and outside of the polar vortex in case the vortex edge is close to Ny-Ålesund. Inter-comparisons are performed with the microwave radiometer of the University of Bremen (OZORAM) which is also located at Ny-Ålesund, with satellite data and with ozonesonde measurements. The results are further compared to simulations with the specified dynamics version of the whole atmosphere community climate model (SD-WACCM).