Evaluating the ability of a microwave radiometer and wrf to detect and simulate in-cloud icing conditions

2020 ◽  
Author(s):  
Jose Luis Sanchez ◽  
Pablo Melcon ◽  
Guillermo Merida ◽  
Andres Merino ◽  
Eduardo Garcia-Ortega ◽  
...  
Keyword(s):  
Liquid Water ◽  
Weather Forecasting ◽  
Freezing Point ◽  
Microwave Radiometer ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Indirect Detection ◽  
Liquid Droplets ◽  
Aircraft Icing ◽  
Cloud Droplets

<p>Icing occurs when an unheated solid structure is exposed to liquid cloud droplets at temperatures below the freezing point. Supercooled liquid water (SLW) in the atmosphere can persist in a physically metastable state until coming into contact with a solid object “In-cloud icing” occurs when super cooled liquid droplets (SLD) like clouds collide with a structure or object and freezes.</p><p>Atmospheric icing prediction has gain attention in the last years. Despite the progress made in meteorology, both weather forecasting modelling and atmospheric observations through advanced experimental technologies, there are still limitations in the accurate forecast and detection of icing conditions. The GFA‐ULE group has carried out some NWPs. In a previous work, we investigated the capability of the Weather Research and Forecasting model to detect regions containing supercooled cloud drops, proposing a multiphysics ensemble approach. Four microphysics and two planetary boundary layer schemes were used. Morrison and Goddard parameterizations with the YSU scheme, yielded superior results in evaluating the presence of liquid water content.</p><p>Concerning the remote detection of icing conditions, some European research centres (i.e. DLR, CIRA, ONERA, INCAS) as well as University of Leon (GFA-ULE) already have nowcasting or forecasting activities for detection of clouds and icing conditions. In this work a multichannel, microwave radiometer (MMWR) was used to detect the appearance of SLW. Consequently, we present both comparison between indirect detection of SLW and the output obtained by WRF with the two combination of parametrizations selected.</p><p>In our work we have taken into account:</p><ol><li>The comparison has been made at different levels, from the ground up to 5000 meters high</li> <li>We have taken different thresholds of the SLW: 0.05, 0.1, 0.15, 0.20, 0.25 and 0.30 g m<sup>-3</sup> because of the flight campaigns carried out previously, which revealed that the presence of low concentrations of SLW could lead to the appearance of aircraft icing.</li> </ol><p>The results show a good concordance between the number of events found by the MMWR and the result of the two numerical modeling performed. Therefore, everything seems to indicate that indirect detection by MMWR can be an accurate technology to detect the appearance of SLW and that the models can be qualitatively validated.</p><p>Acknowledgments: Data support came from the Atmospheric Physics Group, IMA, University of León, Spain, and the National Institute of  Aerospace Technology (INTA). This research was carried out in the framework of the SAFEFLIGHT project, financed by MINECO (CGL2016‐78702) and LE240P18 project (Junta de Castilla y León). We also thank R. Weigand for computer support.</p>

scholarly journals The ability of the ICE-T microphysics scheme in HARMONIE-AROME to predict aircraft icing

2021 ◽  
Author(s):  
Tim Carlsen ◽  
Morten Køltzow ◽  
Trude Storelvmo
Keyword(s):  
Water Content ◽  
Numerical Weather Prediction ◽  
Liquid Water ◽  
Prediction Models ◽  
Weather Prediction ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Aircraft Icing ◽  
Microphysics Scheme ◽  
Numerical Weather

Abstract In-cloud icing is a major hazard for aviation traffic and forecasting of these events is an important task for weather agencies worldwide. A common tool utilised by aviation forecasters is an icing intensity index based on supercooled liquid water from numerical weather prediction models. We seek to validate the modified microphysics scheme, ICE-T, in the HARMONIE-AROME numerical weather prediction model with respect to aircraft icing. Icing intensities and supercooled liquid water derived from two 3-month winter season simulations with the original microphysics code, CTRL, and ICE-T are compared with pilot reports of icing and satellite retrieved values of liquid and ice water content from CloudSat-CALIPSO and liquid water path from AMSR-2. The results show increased supercooled liquid water and higher icing indices in ICE-T. Several different thresholds and sizes of neighbourhood areas for icing forecasts were tested out, and ICE-T captures more of the reported icing events for all thresholds and nearly all neighbourhood areas. With a higher frequency of forecasted icing, a higher false-alarm ratio cannot be ruled out, but is not possible to quantify due to the lack of no-icing observations. The increased liquid water content in ICE-T shows a better match with the retrieved satellite observations, yet the values are still greatly underestimated at lower levels. Future studies should investigate this issue further, as liquid water content also has implications for downstream processes such as the cloud radiative effect, latent heat release, and precipitation.

scholarly journals Supercooled liquid water and secondary ice production in Kelvin–Helmholtz instability as revealed by radar Doppler spectra observations

2021 ◽  
Author(s):  
Haoran Li ◽  
Alexei Korolev ◽  
Dmitri Moisseev
Keyword(s):  
Liquid Water ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Radiation Budget ◽  
Doppler Spectrum ◽  
Droplet Growth ◽  
Liquid Droplets ◽  
Cloud Droplets ◽  
Ice Particles

Abstract. Mixed-phase clouds are globally omnipresent and play a major role in the Earth's radiation budget and precipitation formation. The existence of liquid droplets in presence of ice particles is microphysically unstable and depends on a delicate balance of several competing processes. Understanding mechanisms that govern ice initiation and moisture supply are important to understand the life-cycle of such clouds. This study presents observations that reveal the onset of drizzle inside a ∼600 m deep mixed-phase layer embedded in a stratiform precipitation system. Using Doppler spectra analysis, we show how large supercooled liquid droplets are generated in Kelvin-Helmholtz (K-H) instability despite ice particles falling from upper cloud layers. The spectral width of supercooled liquid water mode in radar Doppler spectrum is used to identify a region of increased turbulence. The observations show that large liquid droplets, characterized by reflectivity values larger than −20 dBZ, are generated in this region. In addition to cloud droplets, Doppler spectral analysis reveals the production of the columnar ice crystals in the K-H billows. The modelling study estimates that the concentration of these ice crystals is 3 ∼ 8 L−1, which is at least one order of magnitude higher than that of primary ice nucleating particles. Given the detail of the observations, we show that multiple populations of secondary ice particles are generated in regions where larger cloud droplets are produced and not at some constant level within the cloud. It is therefore hypothesized that K-H instability provides conditions favorable for enhanced droplet growth and formation of secondary ice particles.

scholarly journals Supercooled liquid water and secondary ice production in Kelvin–Helmholtz instability as revealed by radar Doppler spectra observations

2021 ◽  
Vol 21 (17) ◽  
pp. 13593-13608
Author(s):  
Haoran Li ◽  
Alexei Korolev ◽  
Dmitri Moisseev
Keyword(s):  
Spectral Analysis ◽  
Liquid Water ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Doppler Spectrum ◽  
Liquid Droplets ◽  
Cloud Droplets ◽  
Ice Particles ◽  
Doppler Spectral Analysis

Abstract. Mixed-phase clouds are globally omnipresent and play a major role in the Earth's radiation budget and precipitation formation. The existence of liquid droplets in the presence of ice particles is microphysically unstable and depends on a delicate balance of several competing processes. Understanding mechanisms that govern ice initiation and moisture supply are important to understand the life cycle of such clouds. This study presents observations that reveal the onset of drizzle inside a ∼ 600 m deep mixed-phase layer embedded in a stratiform precipitation system. Using Doppler spectral analysis, we show how large supercooled liquid droplets are generated in Kelvin–Helmholtz (K–H) instability despite ice particles falling from upper cloud layers. The spectral width of the supercooled liquid water mode in the radar Doppler spectrum is used to identify a region of increased turbulence. The observations show that large liquid droplets, characterized by reflectivity values larger than −20 dBZ, are generated in this region. In addition to cloud droplets, Doppler spectral analysis reveals the production of columnar ice crystals in the K–H billows. The modeling study estimates that the concentration of these ice crystals is 3–8 L−1, which is at least 1 order of magnitude higher than that of primary ice-nucleating particles. Given the detail of the observations, we show that multiple populations of secondary ice particles are generated in regions where larger cloud droplets are produced and not at some constant level within the cloud. It is, therefore, hypothesized that K–H instability provides conditions favorable for enhanced droplet growth and formation of secondary ice particles.

scholarly journals Photomineralization mechanism changes the ability of dissolved organic matter to activate cloud droplets and to nucleate ice crystals

2019 ◽  
Vol 19 (19) ◽  
pp. 12397-12412 ◽  
Author(s):  
Nadine Borduas-Dedekind ◽  
Rachele Ossola ◽  
Robert O. David ◽  
Lin S. Boynton ◽  
Vera Weichlinger ◽  
...  
Keyword(s):  
Organic Matter ◽  
Organic Carbon ◽  
Dissolved Organic Matter ◽  
Organic Acids ◽  
Liquid Water ◽  
Supercooled Liquid ◽  
Ice Nucleation ◽  
Ice Crystals ◽  
Cloud Droplets ◽  
Photochemical Processing

Abstract. An organic aerosol particle has a lifetime of approximately 1 week in the atmosphere during which it will be exposed to sunlight. However, the effect of photochemistry on the propensity of organic matter to participate in the initial cloud-forming steps is difficult to predict. In this study, we quantify on a molecular scale the effect of photochemical exposure of naturally occurring dissolved organic matter (DOM) and of a fulvic acid standard on its cloud condensation nuclei (CCN) and ice nucleation (IN) activity. We find that photochemical processing, equivalent to 4.6 d in the atmosphere, of DOM increases its ability to form cloud droplets by up to a factor of 2.5 but decreases its ability to form ice crystals at a loss rate of −0.04 ∘CT50 h−1 of sunlight at ground level. In other words, the ice nucleation activity of photooxidized DOM can require up to 4 ∘C colder temperatures for 50 % of the droplets to activate as ice crystals under immersion freezing conditions. This temperature change could impact the ratio of ice to water droplets within a mixed-phase cloud by delaying the onset of glaciation and by increasing the supercooled liquid fraction of the cloud, thereby modifying the radiative properties and the lifetime of the cloud. Concurrently, a photomineralization mechanism was quantified by monitoring the loss of organic carbon and the simultaneous production of organic acids, such as formic, acetic, oxalic and pyruvic acids, CO and CO2. This mechanism explains and predicts the observed increase in CCN and decrease in IN efficiencies. Indeed, we show that photochemical processing can be a dominant atmospheric ageing process, impacting CCN and IN efficiencies and concentrations. Photomineralization can thus alter the aerosol–cloud radiative effects of organic matter by modifying the supercooled-liquid-water-to-ice-crystal ratio in mixed-phase clouds with implications for cloud lifetime, precipitation patterns and the hydrological cycle.Highlights. During atmospheric transport, dissolved organic matter (DOM) within aqueous aerosols undergoes photochemistry. We find that photochemical processing of DOM increases its ability to form cloud droplets but decreases its ability to form ice crystals over a simulated 4.6 d in the atmosphere. A photomineralization mechanism involving the loss of organic carbon and the production of organic acids, CO and CO2 explains the observed changes and affects the liquid-water-to-ice ratio in clouds.

scholarly journals How to estimate total differential attenuation due to hydrometeors with ground-based multi-frequency radars?

2020 ◽  
Author(s):  
Frédéric Tridon ◽  
Alessandro Battaglia ◽  
Stefan Kneifel
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Particle Growth ◽  
Vertical Gradient ◽  
Liquid Droplets ◽  
Dual Frequency ◽  
Liquid Water Path ◽  
W Band ◽  
Frequency Ratios ◽  
Attenuation Corrected

Abstract. At millimeter wavelengths, attenuation by hydrometeors, such as liquid droplets or large snowflakes, is generally not negligible. When using multi-frequency ground-based radar measurements, it is common practice to use the Rayleigh targets at cloud top as a reference in order to derive attenuation-corrected reflectivities and meaningful dual-frequency ratios (DFR). By capitalizing on this idea, this study describes a new quality-controlled approach aiming at identifying regions of the cloud where particle growth is negligible. The core of the method is the identification of a Rayleigh plateau, i.e. a large enough region near cloud top where the vertical gradient of DFR remains small. By analyzing collocated Ka-W band radar and microwave radiometer (MWR) observations taken at two European sites under various meteorological conditions, it is shown how the resulting estimates of differential path-integrated attenuation (DeltaPIA) can be used to characterize hydrometeor properties. When the DeltaPIA is predominantly produced by cloud liquid droplets, this technique alone can provide accurate estimates of the liquid water path. When combined with MWR observations, this methodology paves the way towards profiling the cloud liquid water and/or quality flagging the MWR retrieval for rain/drizzle contamination and/or estimating the snow differential attenuation.

scholarly journals Wind tunnel experiments on the retention of trace gases during riming: nitric acid, hydrochloric acid, and hydrogen peroxide

2011 ◽  
Vol 11 (6) ◽  
pp. 17447-17472
Author(s):  
N. von Blohn ◽  
K. Diehl ◽  
S. K. Mitra ◽  
S. Borrmann
Keyword(s):  
Hydrogen Peroxide ◽  
Wind Tunnel ◽  
Hydrochloric Acid ◽  
Liquid Water ◽  
Trace Gases ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Ice Particles ◽  
Trace Species ◽  
Ice Phase

Abstract. Laboratory experiments were carried out in a vertical wind tunnel to study the retention of different atmospheric trace gases during riming. In the experiments, the rimed ice particles floated in a laminar air stream carrying a cloud of supercooled droplets with radii between 10 and 20 μm. Ice particles, dendritic ice crystals, and snow flakes with diameters between 6 mm and 1.5 cm were allowed to rime at temperatures between −5 and −12 °C where riming mainly proceeds in the atmosphere and with cloud liquid water contents between 1 and 1.5 g m−3 which are values typically found in atmospheric mixed phase clouds. Three trace species were investigated, nitric and hydrochloric acid, and hydrogen peroxide. They were present in the supercooled liquid droplets in concentrations from 1 to 120 ppmv, i.e. similar to the ones measured in cloud drops. The chemical analyses of the rimed ice particles allow to determine the trace species concentration in the ice phase. Together with the known liquid phase concentration the retention coefficients were calculated in terms of the amount of the species which remained in the ice phase after freezing. It was found that the highly soluble trace gases nitric and hydrochloric acid were retained nearly completely (98.6 ± 8 % and 99.7 ± 9 %, respectively) while for hydrogen peroxide a retention coefficient of 64.3 ± 11 % was determined. No influence of the riming temperature on the retention was found which can be explained by the fact that in the observed range of temperature and liquid water content riming proceeded in the dry growth regime.

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