Cb-TRAM: Tracking and monitoring severe convection from onset over rapid development to mature phase using multi-channel Meteosat-8 SEVIRI data

Cb-TRAM is a new fully automated tracking and nowcasting algorithm. Intense convective cells are detected, tracked and discriminated with respect to onset, rapid development, and mature phase. Finally, short range forecasts are provided. The detection is based on Meteosat-8 SEVIRI (Spinning Enhanced Visible and Infra-Red Imager) data from the broad band high resolution visible, infra-red 6.2 micrometer (water vapour), and the infra-red 10.8 micrometer channels. Areas of convection initiation, of rapid vertical development, and mature thunderstorm cells (cumulonimbus Cb) are identified. For the latter, tropopause temperature data from ECMWF operational model analyses is utilised as an adaptive detection criterion. The tracking is based on geographical overlap between current detections and first guess patterns of cells detected in preceeding time steps. The first guess patterns as well as the short range forecasts are obtained with the aid of a new image matching algorithm providing complete fields of approximate differential cloud motion. Based on the so called pyramid matcher an interpolation and extrapolation technique is presented which can also be used to generate synthetic intermediate data fields between two known fields as well as nowcasts of motion and development of detected areas. Examples of application are presented for thunderstorm tracks over the Mediterranean

Influence of cloud microphysics schemes on weather model predictions of heavy precipitation

Cloud microphysics is one of the major sources of uncertainty in numerical weather prediction models. In this work, the ability of a numerical weather prediction model to correctly predict high-impact weather events, i.e., hail and heavy rain, using different cloud microphysics schemes is evaluated statistically. Polarimetric C-band radar observations over 30 convection days are used as observation dataset. Simulations are made using the regional-scale Weather Research and Forecasting Model (WRF) with five microphysical schemes of varying complexity (double moment, spectral bin (SBM), and particle property prediction (P3)). Statistical characteristics of heavy rain and hail events of varying intensities are compared between simulations and observations. All simulations, regardless of the microphysical scheme, predict heavy rain events that cover larger average areas than those observed by radar. The frequency of these heavy rain events is similar to radar-measured heavy rain events, but still scatters by a factor of 2 around the observations, depending on the microphysical scheme. The model is generally unable to simulate extreme hail events with reflectivity thresholds of 55 dBZ and higher, although they have been observed by radar during the evaluation period. For slightly weaker hail/graupel events, only the P3 model is able to reproduce the observed statistics. Analysis of the raindrop size distribution in combination with the model mixing ratio shows that the P3, Thompson 2-mom, and Thompson aerosol-aware models produce large raindrops too frequently, and the SBM model misses large rain and graupel particles.</p

Fernerkundung inhomogener Bewölkung und deren Einfluss auf die solare Strahlungsbilanz

The influence of cloud inhomogeneity on the remote sensing of cloud parameters and the consequences for the determination of the radiation budget in the solar spectral range are studied. Standard techniques of remote sensing are based on simplifying assumptions on radiative transport: clouds are assumed to be homogeneous throughout each pixel and the interaction between pixels is neglected. The quantification of the resulting uncertainties is of major concern considering the potential of remote sensing for a global characterisation of clouds and their interaction with the radiation field. For this purpose, the three-dimensional radiative transport (using a Monte Carlo model) and remote sensing are simulated for a number of realistic cloud structures. The latter are based on high resolution measurements (15 m horizontal resolution) of marine stratus and stratocumulus from the airborne spectrometer CASI. The development of a novel method is described that allows for the derivation of a horizontal distribution of liquid water path, of a profile of microphysics, and of a realistic cloud top geometry. Based on these cloud structures a systematic investigation of a standard remote sensing technique for the simultaneous derivation of optical thickness and effective droplet size is conducted for different sensor geometries (resolution, viewing angle). While the systematic deviation for the optical thickness of overcast pixels is always lower than 5%, the bias increases for partially covered pixels (10-30%). In contrast, the uncertainty for individual pixels can reach more than 50%. The effective radius is systematically underestimated by 3 to 5%. If the solar part of the radiation budget, e.g. the scene reflection, is determined based on these data, deviations from the actual situation between 3 and 10% do occur.Der Einfluss von Wolkeninhomogenität auf die Fernerkundung von Wolkenparametern und die Konsequenzen für die Ableitung der solaren Strahlungsbilanz wird untersucht. Konventionelle Fernerkundung beruht auf vereinfachenden Annahmen über den Strahlungstransport: Zum einen wird die Bewölkung innerhalb eines Bildelementes als homogen betrachtet, zum anderen wird die Wechselwirkung zwischen benachbarten Bildelementen ausgeschlossen. Die Quantifizierung der daraus resultierenden Fehler ist von großer Bedeutung angesichts der Möglichkeiten, die die Fernerkundung für die globale Charakterisierung von Wolken und ihrer Wechselwirkung mit dem Strahlungsfeld bietet. Dazu wurde der dreidimensionale Strahlungstransport mit einem Monte Carlo Modell sowie die Fernerkundung für eine Anzahl realistischer Wolkenstrukturen simuliert. Diese wurden aus Messungen maritimen Stratus und Stratocumulus des flugzeuggetragenen Spektrometers CASI in hoher Auflösung (15 m) abgeleitet. Ein neuartiges Verfahren wurde entwickelt, das eine solche Ableitung der horizontalen Verteilung des Flüssigwasserpfades, eines Profils der Mikrophysik und einer realistischen Oberkantengeometrie ermöglicht. Auf der Basis dieser Wolkenstrukturen wurden systematische Untersuchungen eines Standard-Fernerkundungsverfahrens für verschiedene Sensorgeometrien (Auflösung, Blickwinkel) zur gleichzeitigen Bestimmung von optischer Dicke und effektivem Tröpfchenradius durchgeführt. Während die systematischen Fehler der optischen Dicke bei vollständig bedeckten Bildelementen unter 5% betragen, wachsen die systematischen Fehler für teilweise bedeckte Bildelement an (10-30%). Werte einzelner Bildelemente sind allerdings mit weit größerer Unsicherheit belastet (mehr als 50%). Der effektive Radius wird systematisch um 3 bis 5% überschätzt. Bei der Ableitung der solaren Strahlungsbilanz, z.B. der Reflexion einer Szene, aus diesen Daten ergeben sich Abweichungen von den tatsächlichen Verhältnissen von 3 bis 10%

Lifetime nowcasting of thunderstorms over Germany using a multi-source data-based fuzzy-logic approach

Due to technical progress in sensor technology and computer power, observation and model data are operationally available today with a high spatial and temporal resolution, suitable for thunderstorm detection and prediction. However, nowcasting the remaining lifetime of an observed thunderstorm is still a challenge to date. To improve nowcasting of deep convective cells, we developed the algorithm LOC-lifetime that predicts the remaining lifetime of thunderstorms based on life-cycle signatures present in satellite, radar, lightning and numerical weather prediction model data. We use the mathematical method “fuzzy logic” to combine this multi-source input and to categorize the thunderstorm evolution into the life-cycle sets growth and decay. We analyzed a data set of almost 1,800 thunderstorms that occurred during the summer months June 2016, May, June, July 2017 and June 2018. The data reveal highly variable life cycles which make it difficult to predict the remaining lifetime on basis of life-cycle statistics. Nevertheless, LOC-lifetime offers an improved nowcasting quality compared to a simpler nowcasting method as it increases the probability of correct prediction and reduces the root-mean-square error. Therefore, we propose the lifetime prediction via LOC-lifetime as a useful tool in combination with other existing algorithms to nowcast and forecast thunderstorm

Ground-based imaging remote sensing of ice clouds: uncertainties caused by sensor, method and atmosphere

In this study a method is introduced for the retrieval of optical thickness and effective particle size of ice clouds over a wide range of optical thickness from ground-based transmitted radiance measurements. Low optical thickness of cirrus clouds and their complex microphysics present a challenge for cloud remote sensing. In transmittance, the relationship between optical depth and radiance is ambiguous. To resolve this ambiguity the retrieval utilizes the spectral slope of radiance between 485 and 560aEuro-nm in addition to the commonly employed combination of a visible and a short-wave infrared wavelength. An extensive test of retrieval sensitivity was conducted using synthetic test spectra in which all parameters introducing uncertainty into the retrieval were varied systematically: ice crystal habit and aerosol properties, instrument noise, calibration uncertainty and the interpolation in the lookup table required by the retrieval process. The most important source of errors identified are uncertainties due to habit assumption: Averaged over all test spectra, systematic biases in the effective radius retrieval of several micrometre can arise. The statistical uncertainties of any individual retrieval can easily exceed 10aEuro-A mu m. Optical thickness biases are mostly below 1, while statistical uncertainties are in the range of 1 to 2.5. For demonstration and comparison to satellite data the retrieval is applied to observations by the Munich hyperspectral imager specMACS (spectrometer of the Munich Aerosol and Cloud Scanner) at the Schneefernerhaus observatory (2650aEuro-maEuro-a.s.l.) during the ACRIDICON-Zugspitze campaign in September and October 2012. Results are compared to MODIS and SEVIRI satellite-based cirrus retrievals (ACRIDICON - Aerosol, Cloud, Precipitation, and Radiation Interactions and Dynamics of Convective Cloud Systems;MODIS - Moderate Resolution Imaging Spectroradiometer;SEVIRI - Spinning Enhanced Visible and Infrared Imager). Considering the identified uncertainties for our ground-based approach and for the satellite retrievals, the comparison shows good agreement within the range of natural variability of the cloud situation in the direct surrounding

Evaluation of convective cloud microphysics in numerical weather prediction models with dual-wavelength polarimetric radar observations: methods and examples

The representation of cloud microphysical processes contributes substantially to the uncertainty of numerical weather simulations. In part, this is owed to some fundamental knowledge gaps in the underlying processes due to the difficulty of observing them directly. On the path to closing these gaps, we present a setup for the systematic characterization of differences between numerical weather model and radar observations for convective weather situations. Radar observations are introduced which provide targeted dual-wavelength and polarimetric measurements of convective clouds with the potential to provide more detailed information about hydrometeor shapes and sizes. A convection-permitting regional weather model setup is established using five different microphysics schemes (double-moment, spectral bin ("Fast Spectral Bin Microphysics", FSBM), and particle property prediction (P3)). Observations are compared to hindcasts which are created with a polarimetric radar forward simulator for all measurement days. A cell-tracking algorithm applied to radar and model data facilitates comparison on a cell object basis. Statistical comparisons of radar observations and numerical weather model runs are presented on a data set of 30 convection days. In general, simulations show too few weak and small-scale convective cells. Contoured frequency by altitude diagrams of radar signatures reveal deviations between the schemes and observations in ice and liquid phase. Apart from the P3 scheme, high reflectivities in the ice phase are simulated too frequently. Dual-wavelength signatures demonstrate issues of most schemes to correctly represent ice particle size distributions, producing too large or too dense graupel particles. Comparison of polarimetric radar signatures reveals issues of all schemes except the FSBM to correctly represent rain particle size distributions

The Liebherr Intelligent Hydraulic Cylinder as building block for innovative hydraulic concepts

We present hereafter the development of the Liebherr Intelligent Hydraulic Cylinder, in which the hydraulic component is used as smart sensing element providing useful information for the system in which the cylinder is operated. The piston position and velocity are the most important signals derived from this new measuring approach. The performance under various load and temperature conditions (measured both on dedicated test facilities and in field in a real machine) will be presented. An integrated control electronics, which is performing the cylinder state processing, additionally allows the synchronized acquisition of external sensors. Providing comprehensive state information, such as temperature and system pressure, advanced control techniques or monitoring functions can be realized with a monolithic device. Further developments, trends and benefits for the system architecture will be briefly analyzed and discussed

Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field

We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50m horizontal resolution and a large cumulus cloud field at 50 and 100m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day(-1). To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations. Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures;later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes. The cloud fields in the 100 and 50 m resolution simulations develop similarly;however, 3-D local effects are stronger in the 100m simulations which might indicate a limit of our 3-D radiation parameterization