|From||Silke Trömel <firstname.lastname@example.org>|
|Date||Fri, 20 Nov 2015 13:00:30 +0100|
Two open PhD positions at University of Bonn (Germany)
The Meteorological Institute is inviting applications for two PhD positions (3/4 TV-L E13) in the field of radar meteorology and high impact weather. Both positions are offered for three years, starting January 2016, a fourth year as Post Doctoral researcher is possible. The Extramural Research Programme of the German Weather Service (DWD) funds the positions and the work will be done in close cooperation with DWD. Strong cooperation is planned with NOAA/NSSL.
Applicants should have master degree in geosciences or physics, preferably in meteorology, atmospheric physics, geophysics or hydrology, or written their thesis on a topic related to the planned research. Basic knowledge in radar polarimetry is highly appreciated.
1) A cover letter including your research interests and motivation
2) A detailed curriculum vitae
3) Certificates (BSc and MSc)
Deadline: A first cut-off date for the collection of the applications is foreseen on December 10, 2015.
Position 1: Improvement of hail detection and nowcasting by synergetic combination of information from polarimetric radar, model predictions and in-situ observations
Hail, the occurrence of which can be easily spotted especially in polarimetric radar observations, is a quite frequent phenomenon especially in summertime convective events. The identification especially of large hail, which is considered dangerous and potentially damaging, and its distinction from smaller hail is crucial for warnings but still difficult achieve. The hydrometeor classification scheme Hymec of DWD currently only discriminates one hail class besides hail together with rain. An experimental (Hail Size Discrimination Algorithm HSDA for S band based on polarimetry by Ryzhkov et al. (2013) and Ortega et al. (2013) distinguishes between small (ᴓ < 2.5 cm), large (2.5 cm < ᴓ < 5.0 cm), and giant hail (ᴓ > 5.0 cm). The prime goal of this project is the extension of Hymec by adapting the HSDA methodology to C-band and by exploiting its even larger potential at this wavelength for hail detection. In addition, the potential of the Circular Depolarization Ratio (CDR), which might be detectable also from DWDs C-Band radars will be exploited in addition to differential polarization (ZDR) for nowcasting of hail events. To better understand the hail and hail size signatures and its precursors above the melting layer, we will also use the overlapping observations of the Bonn and Jülich X-band radars for independent remote sensing information. Observations of hail occurrence and size for algorithm tuning and evaluation will be taken from DWDs and our own disdrometer network and from the growing European Severe Weather Database (ESWD) from ESSL.
Position 2: Improvement of nowcasting for winter precipitation by synergetic combining information from polarimetric radar, model predictions and in-situ observations
It is extremely important to know the precise location of rain/snow boundary at the surface and its progression in time, and also to know where and when e.g. freezing rain changes to ice pellets or vise versa. The project will derive an improved methodology to delineate this boundary and its progression in near future based on a synergetic use of dual-polarization observations of the DWD radar network, in-situ surface observations from meteorological stations, disdrometers and radiosondes, NWP fields, and a 1D bin microphysical model. The Hymec hydrometeor typing scheme will be evaluated in a first step for winter precipitation cases. In a second step the project will – based on the evaluation results and an extended use of polarimetric observations including the underutilized variable circular depolarization ratio CDR - try to improve on the estimators for precipitation type, phase and intensity. The third step will further improve Hymec by using current radiosonde observations and NWP model predictions by involving a 1D bin microphysics model, which predicts ensembles of physically consistent hydrometeor profiles including their polarimetric moments. The comparison between the ensemble and the polarimetric observations will be used to derive a probabilistic hydrometeor analysis. The fourth step will aim at nowcasting the precipitation field by advection methods and exploiting the uncertainty involved in the phase and the advection vectors for an ensemble approach. The fifth step will use the in-system tendencies of polarimetric fingerprints in the precipitation generating layers and NWP predictions of the thermodynamic state to include system evolution including uncertainty in the nowcasting.
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