Post-doctoral Research Fellowship at Météo France
“Quantitative Microphysical Retrievals with a network of polarimetric X-band radars”
Application deadline: The selection process will start on 30 June 2010 and will continue until the position is filled. Candidates are invited to submit their application as soon as possible.
Duration: 18 months (6 to 12 months extension possible).
Start : starting ideally in September – October 2010
Salary: between 2.4 and 2.9 k€ net monthly pending on the experience of candidate
Place : Centre de Météorologie Radar, Direction des Systèmes d’Observation, Météo France, 42, Avenue Coriolis, 31057 Toulouse.
The MétéoFranceCenter in Toulouse is located about 6 km west of the town center (about 20 minutes by bike and 30 minutes by metro). Temporary lodging at the Météo France site is possible.
Work description
Météo France (the French National Weather Service) is seeking a post-doctoral researcher to work on microphysical retrievals from X-band polarimetric measurements in the frame of an ambitious project to deploy a network of 4 X-band Doppler polarimetric radars in the south-east region of France (RHYTMME Project).
The operational X-band radars will be spaced apart by about 60 km. There is also some overlap with existing S-band polarimetric radars (incl. a polarimetric one). The region is extremely rugged (with peaks reaching above 3,500 m) and prone to intense flooding, particularly in the falls season. Those two features make the operational use of X-band data quite challenging. A research polarimetric X-band radar is already installed and running. The first operational X-band radar will be installed in mid 2010, opening the way towards intelligent compositing and networking.
The RHYTMME project is funded by governmental agencies and by Météo France. Beside the radar component, the project aims at establishing a platform where hydrological models and alert systems are run in real-time.
This project is the continuation of Météo France long-term investment on operational radar polarimetry and R&D, which started several years ago. The first French polarimetric radar (C-band) was indeed installed in Trappes, near Paris about 4 years ago. Since then a significant amount of work has been carried out to make progress on: data quality assessment and monitoring, artefact removal, attenuation correction, bright band identification, hydrometeor classification, effect of orography and QPE evaluation. Those works are summarized in the following papers (+ numerous conference papers available upon request):
Tabary, P., Vulpiani, G., J.J. Gourley, A.J. Illingworth, R.J. Thompson and O. Bousquet, 2009 : Unusually high differential attenuation at C-band : results from a two-year analysis of the French Trappes polarimetric radar data, Journal of Applied Meteorology and Climatology , Volume 48, Issue 10 (October 2009) pp. 2037–2053
Friedrich, K., U. Germann and P. Tabary, 2008 : Influence of Ground Clutter Contamination on Polarimetric Radar Parameters, accepted in J. Atmos. Oceanic Technol.
Gourley, JJ., A.J. Illingworth and P. Tabary, 2008 : Absolute calibration of radar reflectivity using redundancy of the polarization observations and implied constraints on drop shapes, submitted to J. Atmos. Oceanic Technol.
Tabary, P., Vulpiani, G., J.J. Gourley, A.J. Illingworth and O. Bousquet, 2008 : Unusually high differential attenuation at C-band : results from a two-year analysis of the French Trappes polarimetric radar data, submitted to J. Appl. Meteor..
Vulpiani, G., P. Tabary, J. Parent-du-Chatelet and Frank S. Marzano, 2008 : Comparison of advanced radar polarimetric techniques for operational attenuation correction at C-band, J. Atmos. Oceanic Technol,, 25, Issue 7 (July 2008) pp. 1118–1135
Friedrich, K., U. Germann, J.J. Gourley, and P. Tabary, 2007: Effects of radar beam shielding on rainfall estimation for polarimetric C-band radar, J. Atmos. Oceanic Technol., 24, No 11, 1839 – 1859.
Gourley, JJ, P. Tabary, J. Parent-du-Chatelet, 2007: Empirical estimation of attenuation from differential propagation phase measurements at C-band, J. Appl. Meteor., 46, No. 3, 306 – 317.
Gourley, JJ, P. Tabary, J. Parent-du-Chatelet, 2007: A fuzzy logic algorithm for the separation of precipitating from non-precipitating echoes using polarimetric radar, J. Atmos. Oceanic Technol. Vol. 24, No. 8, 1439–1451.
Gourley, JJ, P. Tabary, J. Parent-du-Chatelet, 2006: Data quality of the Météo France C-band polarimetric radar, J. Atmos. Oceanic Technol , 23, No. 10, 1340–1356.
The extremely positive results obtained have led to the extension of dual-polarisation to other radars of the network, which now counts 10 operational polarimetric elements (9 at C-band and 1 at S-band). A polarimetric processing chain including 1) polarimetric variable monitoring (including the monitoring of horizontal reflectivity ZH using the consistency relationship), 2) artefact removal, 3) attenuation correction, 4) bright band identification and 5) hydrometeor classification will be introduced in operations in the course of 2010.
There are still several challenges that need to be overcome to fully exploit polarimetry in a quantitative way, especially in mountainous areas:
-Identification and correction of partially blocked beams. Assessment of their impact on ZH, ZDR, HV, DP and estimation of the uncertainty on corrected variables.
-Wet Radome attenuation using close-range ground-clutter levels, noise emissions and radar – radar comparisons.
-Attenuation correction in non-rain precipitation (wet hail, melting snow, …). Use of noise emissions and ground-clutter intensities as Path-Integrated Attenuation constraints.
-Correction for Vertical Profile of Reflectivity (VPR) of ZH and ZDR. Combined use of radars and vertically pointing radars (MRR).
-Intelligent 2D and 3D polarimetric compositing between neighbouring radars.
-Microphysical retrievals in rain and non-rain (hail, snow, …) precipitation.
This last item will constitute the core of the work of the post-doc student. Emphasis will be laid on the development of quantitative microphysical retrievals (in rain, hail, snow, super-cooled water and even mixed phases) rather than applying basic dominant particle retrievals. This work can be seen as a preparatory work towards the assimilation of polarimetric variables into high-resolution NWP. The work will be carried out in close relationship with the Météo France mesoscale group (CNRM/GMME/MICADO, Dr. Olivier Caumont).
So far, the Météo France Radar Group has been active on polarimetric QPE studies in rain only. For instance, two so-called “integrated” polarimetric algorithms – only valid in rain – were compared – using 1 year of data collected by the Paris (Trappes) radar - against the classical conventional Marshall-Palmer estimator : ZZDR, which makes use of ZH and ZDR (Illingworth and Thompson 2005) only and ZPHI (Testud et al. 2000), which relies on ZH and DP.
Illingworth, A.J. and R.J. Thompson, 2005 : The estimation of moderate rain rates with operational polarisation radar, 32nd Int. Conf. On Radar Meteorology, Albuquerque, Paper P9R.1, Am. Meteorol. Soc.
Testud, J., E. Le Bouar, E. Obligis, and M. Ali-Mehenni, 2000: The rain profiling algorithm applied to polarimetric weather radar, J. Atmos. Oceanic Technol.,17, 332-356.
Both polarimetric algorithms were demonstrated to be superior to the conventional one but they were also shown to be strongly dependent upon the calibration of the variables (ZH and ZDR). The triggering conditions of the two algorithms appeared to be complementary, which calls for the development of a combination between the two approaches.
The work proposed here is novel in the sense that emphasis is laid on:
1)quantitative microphysical retrievals
2)non-rain precipitation.
To achieve that goal, it is proposed to build upon the following approach:
Hogan, R.J., 2007 : A Variational Scheme for Retrieving Rainfall Rate and Hail Reflectivity Fraction from Polarization Radar, J. Appl. Meteor., 46, 1544- 1563.
Additional information (e.g. vertical profiles of terminal fall speed retrieved from spectral analysis at 90°, Doppler-retrieved vertical velocities, model output, surface measurements, …) will be considered in the retrieval methodology.
Validation will be carried out using rain gauges, snow gauges, hail pads, disdrometers, Micro Rain Radars and radar – radar comparisons (at different wavelengths).
The selected post-doc student will join an enthousiastic team of about 15 people including 2 other talented post-docs working full time on polarimetry R&D at S, C and X bands.
Required qualification
Applicants should have or soon have a Ph.D. in Environment, Atmospheric Sciences or Remote Sensing.
A good knowledge of radars, radar data and their interpretation is required. Knowledge of polarimetric radars and related algorithms would definitely be an advantage.
Applicants should be fluent in oral and written English. Knowledge of UNIX / LINUX is required (FORTRAN, C, C++) and experience with IDL or PV-WAVE highly recommanded. The work will be supervised by Dr. Pierre Tabary (Météo France, Toulouse, France). This job is offered with no restriction on age, sex nor nationality, in accordance with French law.
Applicants should send:
-a letter of interest,
-a curriculum vitae (resume + list of publications),
-date of availability,
-names, fax numbers, e-mail and post addresses of two references to:
Dr. Pierre TABARY
Centre de Météorologie Radar - Direction des Systèmes d'Observation, Météo France
42, Avenue Coriolis 31057 Toulouse cedex (FRANCE)
Tel: (+33) 5 67 69 87 17 - Fax: (+33) 5 67 69 87 49 - Mail :