Overall Goals



Climate model PArameterizations informed by RAdar (PARA)



Joint project between Uni Bonn and Uni Leipzig

University of Leipzig: Sabine Hörnig (project PhD candidate) and Johannes Quaas (PI)
University of Bonn: Nikolaos Papaevangelou (project PhD candidate) and Silke Trömel (PI)


The idea of PARA is to improve the representation rain originating from the ice phase in climate models thanks to the information provided by polarimetric radar. Specifically, PARA will make rigorous use of subgrid-scale variability to revise the parameterisation of four relevant processes (illustrated in the Figure) in the ICON atmospheric general circulation model.


Figure 1: Schematic of investigated processes in PARA.



current status

The work in the first year addresses the horizontal variability of cloud ice (WP 1) as well as accounting for this in the snow formation process via aggregation (WP 2).


Contribution of University Leipzig
At ULEI, an evaluation of the Sundqvist et al. (1989) variability parameterisation that was assessed for liquid-water clouds by Quaas (2012) was performed for the upper troposphere focusing on the in-cloud specific ice variability in comparison to satellite radar retrievals from the raDAR-liDAR (DARDAR; Delanoë and Hogan, 2010) approach. Revisions to the parameterisation of the ice variability were implemented and evaluated. In the next step, this revised horizontal variability of ice clouds within each grid-box is now applied for the aggregation parameterisation following earlier work by Weber and Quaas (2011) and Mewes (2001). First results show success in reducing the artificial tuning factor.




Contribution of University Bonn
At the university of Bonn the polarimetric radar measurements at C and X – band and the most recent ice microphysical retrievals (Murphy et al. 2018) are used to investigate the ice variability above the melting layer. Additional techniques are implemented in order to disentangle statistical errors and subgrid variability. Assuming an exponential distribution for ice particles aloft and distinguishing between cloud ice and snow based on the smallest size a particle is assigned to snow (100µm), observation-based retrievals of number concentration, particle size and ice water content can be provided as a function of height for ice and snow, respectively.




References

Delanoë, J., and Hogan R. J, Combined CloudSat-CALIPSO-MODIS retrievals of the proper¬ties of ice clouds, J. Geophys. Res., 115, D00H29, doi:10.1029/2009JD012346, 2010.

Mewes, D., Stochastic Parameterization of Precipitation in the ECHAM6 General Circulation Model, Master‘s thesis, University of Leipzig, 29 pp., available at http://research.uni-leipzig.de/climate/mewes_daniel__masterarbeit__2016.pdf, 2016.

Ryzhkov, A., Bukovčić P., Murphy A., Zhang P., and McFarquhar G., 2018: Ice microphysical retrievals using polarimetric radar data. Proceedings of the 10th European Conference on Radar in Meteorology and Hydrology (ERAD 2018): 1-6 July 2018, Ede-Wageningen, The Netherlands, 2018. Available online at: projects.knmi.nl/erad2018/ERAD2018_extended_abstract_040.pdf.

Quaas, J., Evaluating the “critical relative humidity” as a measure of subgrid-scale variability of humidity in general circulation model cloud cover parameterizations using satellite data. J. Geophys. Res., 117, D09208, doi:10.1029/2012JD017495, 2012.

Sundqvist, H., et al., Condensation and cloud parameterization studies with a mesoscale numerical weather prediction model, Mon. Weather Rev., 117, 1641–1657, 19

Weber, T., and Quaas J., Incorporating the subgrid-scale variability of clouds in the autoconver¬sion parameterization. J. Adv. Model. Earth Syst., 4, M11003, doi:10.1029/2012MS000156, 2012.


Contribution of University of Leipzig, July 2019
A first goal of the Univ. Leipzig contribution to PARA was the evaluation of the subgrid-scale variability of cloud ice. In the ICON general circulation model (Giorgetta et al., 2018), the cloud horizontal subgrid-scale variability is represented in terms of a “critical relative humidity” framework (Sundqvist et al., 1989) that corresponds to a uniform distribution of total-water specific humidity around its grid-box mean value (Quaas, 2012). In the present study, only ice clouds are considered, and the cloudy part of each grid box is isolated, i.e. the total-water amount that is beyond the saturation specific humidity with respect to ice.

From this, the variance of the subgrid-scale variability is computed (Quaas, 2012) and analysed at several isobaric levels. As a reference for the global distributions, satellite retrievals from the raDAR-liDAR approach by Delanoë and Hogan (2010) are used. From the high-resolved satellite data along the track within each 2.8° length, the variance of the ice specific mass is computed on the isobaric surfaces. The multi-year mean is compared to the ICON simulations.

The results show a relatively consistent geographical pattern between the model and the observations. However, some adjustments to the “critical relative humidity” parameter allow to improve the simulation in the middle-to-upper troposphere. These new results will now be used to improve the representation of precipitation processes, and radar data will be used for an in-detail evaluation at a regional scale.





References Delanoë, J., and R. J. Hogan, Combined CloudSat-CALIPSO-MODIS retrievals of the properties of ice clouds, J. Geophys. Res., 115, D00H29, doi:10.1029/2009JD012346, 2010.

Giorgetta, M.A., R. Brokopf, T. Crueger, M. Esch, S. Fiedler, J. Helmert, C. Hohenegger, L. Kornblueh, M. Koehler, E. Manzini, T. Mauritsen, C. Nam, S. Rast, C. Reick, D. Reinert, M. Sakradzija, H. Schmidt, R. Schnur, L. Silvers, H. Wan, G. Zaengl, and B. Stevens, ICON-A, the atmospheric component of the ICON Earth System Model.
Part I: Model Description, J. Adv. Model. Earth Syst., 10, 1613– 1637, doi:10.1029/2017MS001242, 2018. Quaas, J., Evaluating the “critical relative humidity” as a measure of subgrid-scale variability of humidity in general circulation model cloud cover parameterizations using satellite data. J. Geophys. Res., 117, D09208, doi:10.1029/2012JD017495, 2012.

Sundqvist, H., et al., Condensation and cloud parameterization studies with a mesoscale numerical weather prediction model, Mon. Weather Rev., 117, 1641–1657, 1989.

Spectrally resolved Polarimetric Observation and Computation of Clouds (SPOCC)


Joint project between Uni Bonn and TROPOS

TROPOS: Majid Hajipour, Junghwa Lee project (PhD candidate) Patric Seifert (PI) and Oswald Knoth (PI)



Contribution of TROPOS, July 2019


Mixed-phase clouds can contain a variety of different hydrometeor types in the same volume. The PROM project Spectrally resolved Observations and Modelling of Clouds (SPOMC) is dedicated to the development of advanced polarimetric methods for the retrieval of hydrometeor ratios in clouds and their evaluation against cloud-resolved simulations with a spectral-bin microphysics model.
Basis for the technical developments are observations of a hybrid-mode 35-GHz cloud radar from the Analysis of the Compositions of Clouds with Extended Polarization Techniques (ACCEPT) campaign conducted in fall 2014 in Cabauw, NL.
Goal is to associate signatures of prolate, isometric and oblate particles in a Doppler spectrum with the occurrence of hydrometeor types such as, pristine crystals, droplets, aggregates, and graupel.
Spectral-bin microphysical modeling of selected case studies with COSMO-SPECS will on the one hand be evaluated against the radar observations. On the other hand, the simulations and forward-modeled radar variables will show to which extent cloud radar is in principle capable to distinguish different hydrometeors in a complex, turbulent atmospheric environment.

Two Phd students work within SPOMC at TROPOS. One (Majid Hajipour) is developing the polarimetric retrieval, the other one (Junghwa Lee) is working with COSMO-SPECS.
Both will work on radar forward operators.






Figure 1: Current work of Junghwa Lee: Quasi-steady state for 4h of simulation for a mixed-phase stratocumulus cloud in a 1D kinematic system. (a) Temperature [K] (b) Vertical motion [m/s] © Liquid water path [kg m-2] for cloud (blue) and rain (red) (d) ice water path [kg m-2] for crystal (blue), snow (green), and graupel (red).









Figure 2: Current work of Majid Hajipour: Calculation of the relationship between antenna elevation angle and differential reflectivity (b) for a radar Doppler spectrum (a) calculated from a given bi-modal size distribution of hydrometeors and using a spheroid scattering model


IcePolCKa



Joint project between Uni Bonn and Deutsches Zentrum für Luft- u.Raumfahrt(DLR), Ludwig-Maximilians-Universität (LMU)


LMU: Gregor Möller (PhD candidate),Tobias Zinner (PI)

DLR: Eleni Tetoni(PhD candidate), Martin Hagen (PI)

Investigation of the initiation of convection and the evolution of precipitation using simulations and polarimetric radar observations at C- and Ka-band

Abstract Aim of the project is to exploit the synergy of two full polarimetric radars, the C-band POLDIRAD at DLR, Oberpfaffenhofen and the Ka-band miraMACS at LMU,
Munich, to study convective initiation as well as ice particle growth and its role in precipitation formation.

At a distance of 23 km between DLR and LMU the use of the two research radar systems allows targeted observations and coordinated scan patterns. In order to study life-cycles of convective cells or precipitation development (e.g. fall streaks), object tracking will be applied using horizontal PPI and vertical RHI cross sections on or close to the line-of-sight.

An ice particle size retrieval will be developed for the dual-wavelength radar measurements, which will be used to advance established polarimetric hydrometeor classifications. Other processes observable will be drizzle formation, cloud glaciation, distinction between depositional growth of small ice particles and onset of quicker ice particle growth into precipitation sized particles by aggregation, and initiation of first precipitation at the surface.

Timing of these processes and their spatial distribution will be observed and compared to modeled processes. Using a numerical weather model (WRF) with a nested domain centered over Munich at high spatial resolution (∆x of around 100 m), we will analyze how microphysical parameterizations of different levels of complexity compare to the observations.


Contribution DLR, July 2019

A large number of coordinated RHI cross sections were performed with C-band POLDIRAD at Oberpfaffenhofen (λ = 5.5 cm) and the Ka-band miraMACS at Munich (λ = 0.8 cm).
RHI scans with a temporal resolution up to 3 minutes were performed along the axis between the two radars as well as off-axis targeting the evolution of individual precipitation cells.
The data were interpolated on the same grid for further processing. The retrieval of median diameter and ice water content was then possible with the measurements. T-matrix simulations of various kinds of ice particles were performed to generate look-up tables for the retrieval of particle habits and effective radius.




Figure: The reflectivity measurements of both radars are shown, differential reflectivity and the instrument mask from a coordinated measurement on 30 January 2019 at 10:08 UTC.

Polarimetry Influenced by CCN aNd INP in Cyprus and Chile (PICNICC)



Joint project between University Bonn, TROPOS and University of Leipzig

Uni Leipzig: Teresa Vogl (PhD candidate), Heike Kalesse (PI), Johannes Quaas (PI)
TROPOS: Audrey Teisseire (PhD candidate), Patric Seifert (PI)



Contribution TROPOS and University Leipzig,July 2019
In the frame of the PROM project Polarimetry Influenced by CCN aNd INP in Cyprus and Chile (PICNICC), W- and Ka-band cloud radar observations will be used to investigate the susceptibility of mixed-phase cloud processes to variations in the aerosol load. Based on a combination of radar polarimetry, dual-frequency Doppler radar and lidar observations from the clean, pristine site of Punta Arenas (Chile, 53°S,71°W) and the aerosol-burden site of Limassol (Cyprus, 35°N,33°E ), the contrasts in the microphysical fingerprints of mixed-phase clouds, specifically of pristine ice formation, riming and aggregation, will be studied. The investigations will be supported by high-resolved numerical weather simulations of ICON-NWP with 2-moment microphysics, which will be used to evaluate the impact of aerosol variations on cloud microphysics over the two field sites. Two PhD students work on the project, one (Audrey Teisseire, TROPOS) focusing on radar polarimetry and forward simulations and one (Teresa Vogl, Leipzig Institute for Meteorology, University of Leipzig) working with dual-frequency (Ka-W-band) radar, Doppler spectra analysis and the ICON-NWP model.


Figure: Explaining the Hypothesis worked on within the PICNICC project:






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