scholarly journals Large impact of tiny model domain shifts for the Pentecost 2014 MCS over Germany

2019 ◽  
Author(s):  
Christian Barthlott ◽  
Andrew I. Barrett
Keyword(s):  
Initial Conditions ◽  
Grid Point ◽  
Large Impact ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Convective System ◽  
Simple Method ◽  
Model Domain ◽  
Cosmo Model ◽  
Whole Life Cycle

Abstract. The mesoscale convective system (MCS) that affected Germany at Pentecost 2014 (9 June 2014) was one of the most severe for decades. However, the predictability of this system was very low as the operational deterministic and ensemble prediction systems failed to predict the event with sufficiently long lead times. We present hindcasts of the event using the COnsortium for Small-scale MOdeling (COSMO) model at convection-permitting (2.8 km) resolution on a large (1668 × 1807 km) grid, which allowed us to simulate the whole life cycle of the system originating from the French Atlantic coast. Results show that this model configuration successfully reproduces the convective events of that day. However, the low predictability of the event was evident by the surprisingly large impact of tiny changes to the model domain. We systematically shifted the model domain by one grid point in eight different directions, from which three did not simulate any convection over Germany. The analyses show that no important differences in domain-averaged initial conditions nor in the preconvective environment ahead of the convective system exist. That one-third of these seemingly identical initial conditions fails to produce any convection over Germany is intriguing. The main reason for the different model results seems to be the proximity of the track of the initial convective system to the coast and colder sea surface. The COSMO model simulates small horizontal displacements of the precursors of the MCS which then determine if the cells dissipate close to the sea or reach a favourable area for convective development over land and further evolve into an MCS. This study demonstrates the potentially huge impact of tiny model domain shifts on forecasting convective processes in this case, which suggests that the inclusion of this simple method in convective-scale ensemble forecasting systems should be evaluated for different cases, models and weather regimes.

scholarly journals Large impact of tiny model domain shifts for the Pentecost 2014 mesoscale convective system over Germany

2020 ◽  
Vol 1 (1) ◽  
pp. 207-224
Author(s):  
Christian Barthlott ◽  
Andrew I. Barrett
Keyword(s):  
Initial Conditions ◽  
Mesoscale Convective System ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Convective System ◽  
Large Domain ◽  
Model Domain ◽  
Cosmo Model ◽  
Mesoscale Convective ◽  
Whole Life Cycle

Abstract. The mesoscale convective system (MCS) that affected Germany at Pentecost 2014 (9 June 2014) was one of the most severe for decades. However, the predictability of this system was very low as the operational deterministic and ensemble prediction systems completely failed to predict the event with more than a 12 h lead time. We present hindcasts of the event using the COnsortium for Small-scale MOdeling (COSMO) model at a convection-permitting (2.8 km) resolution on a large (1668 km×1807 km) domain. Using this large domain allowed us to successfully simulate the whole life cycle of the system originating from the French Atlantic coast. However, even with the large domain, the predictability of the MCS is low. Tiny changes to the model domain produced large changes in the MCS, removing it completely from some simulations. To demonstrate this we systematically shifted the model domain by just one grid point in eight different directions, from which three did not simulate any convection over Germany. Our analysis shows that there were no important differences in domain-averaged initial conditions or in the preconvective environment ahead of the convective system. The main reason that one-third of these seemingly identical initial conditions fail to produce any convection over Germany seems to be the proximity of the track of the initial convective system to the coast and colder sea surface. The COSMO model simulates small horizontal displacements of the precursors of the MCS which then determine if the cells dissipate close to the sea or reach a favorable area for convective development over land and further evolve into an MCS. This study demonstrates the potentially huge impact of tiny model domain shifts on forecasting convective processes in this case, which suggests that the sensitivity to similarly small initial-condition perturbations could be a helpful indicator of days with low predictability and should be evaluated across other cases, models, and weather regimes.

scholarly journals Hydro-meteorological evaluation of a convection-permitting ensemble prediction system for Mediterranean heavy precipitating events

2012 ◽  
Vol 12 (8) ◽  
pp. 2631-2645 ◽  
Author(s):  
B. Vié ◽  
G. Molinié ◽  
O. Nuissier ◽  
B. Vincendon ◽  
V. Ducrocq ◽  
...  
Keyword(s):  
Initial Conditions ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Model Errors ◽  
Ensemble Prediction System ◽  
Probabilistic Evaluation ◽  
Convective Scale ◽  
Prediction Systems ◽  
Data Assimilation Technique ◽  
The Impact

Abstract. An assessment of the performance of different convection-permitting ensemble prediction systems (EPSs) is performed, with a focus on Heavy Precipitating Events (HPEs). The convective-scale EPS configuration includes perturbations of lateral boundary conditions (LBCs) by using a global ensemble to provide LBCs, initial conditions (ICs) through an ensemble data assimilation technique and perturbations of microphysical parameterisations to account for part of model errors. A probabilistic evaluation is conducted over an 18-day period. A clear improvement is found when uncertainties on LBCs and ICs are considered together, but the chosen microphysical perturbations have no significant impact on probabilistic scores. Innovative evaluation processes for three HPE case studies are implemented. First, maxima diagrams provide a multi-scale analysis of intense rainfall. Second, an hydrological evaluation is performed through the computation of discharge forecasts using hourly ensemble precipitation forecasts as an input. All ensembles behave similarly, but differences are found highlighting the impact of microphysical perturbations on HPEs forecasts, especially for cases involving complex small-scale processes.

scholarly journals Predictability of Deep Convection in Idealized and Operational Forecasts: Effects of Radar Data Assimilation, Orography, and Synoptic Weather Regime

2019 ◽  
Vol 148 (1) ◽  
pp. 63-81 ◽  
Author(s):  
Kevin Bachmann ◽  
Christian Keil ◽  
George C. Craig ◽  
Martin Weissmann ◽  
Christian A. Welzbacher
Keyword(s):  
Data Assimilation ◽  
Deep Convection ◽  
Radar Data ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Model Errors ◽  
Ensemble Prediction System ◽  
Beneficial Impact ◽  
The Impact ◽  
Radar Data Assimilation

Abstract We investigate the practical predictability limits of deep convection in a state-of-the-art, high-resolution, limited-area ensemble prediction system. A combination of sophisticated predictability measures, namely, believable and decorrelation scale, are applied to determine the predictable scales of short-term forecasts in a hierarchy of model configurations. First, we consider an idealized perfect model setup that includes both small-scale and synoptic-scale perturbations. We find increased predictability in the presence of orography and a strongly beneficial impact of radar data assimilation, which extends the forecast horizon by up to 6 h. Second, we examine realistic COSMO-KENDA simulations, including assimilation of radar and conventional data and a representation of model errors, for a convectively active two-week summer period over Germany. The results confirm increased predictability in orographic regions. We find that both latent heat nudging and ensemble Kalman filter assimilation of radar data lead to increased forecast skill, but the impact is smaller than in the idealized experiments. This highlights the need to assimilate spatially and temporally dense data, but also indicates room for further improvement. Finally, the examination of operational COSMO-DE-EPS ensemble forecasts for three summer periods confirms the beneficial impact of orography in a statistical sense and also reveals increased predictability in weather regimes controlled by synoptic forcing, as defined by the convective adjustment time scale.

scholarly journals Evaluation of the Added Value of Regional Ensemble Forecasts on Global Ensemble Forecasts

2012 ◽  
Vol 27 (4) ◽  
pp. 972-987 ◽  
Author(s):  
Yong Wang ◽  
Simona Tascu ◽  
Florian Weidle ◽  
Karin Schmeisser
Keyword(s):  
Horizontal Resolution ◽  
Added Value ◽  
Ensemble Prediction ◽  
Small Scale ◽  
Initial Condition ◽  
Weather Variables ◽  
Single Model ◽  
Ensemble Forecasts ◽  
Model Based ◽  
Surface Weather

Abstract The regional single-model-based Aire Limitée Adaptation Dynamique Développement International–Limited Area Ensemble Forecasting (ALADIN-LAEF) ensemble prediction system (EPS) is evaluated and compared with the global ECMWF-EPS to investigate the added value of regional to global EPS models. ALADIN-LAEF consists of 16 perturbed members at 18-km horizontal resolution, while ECMWF-EPS includes 50 perturbed members at 50-km horizontal resolution. In ALADIN-LAEF, the atmospheric initial condition uncertainty is quantified by using blending, which combines large-scale uncertainty generated by the ECMWF-EPS singular-vector approach with small-scale perturbations resolved by the ALADIN breeding technique. The surface initial condition perturbations are generated by use of the noncycling surface breeding (NCSB) technique, and different physics schemes are employed for different forecast members to account for model uncertainties. The verification and comparison have been carried out for a 2-month period during summer 2007 over central Europe. The results show a quite favorable level of performance for ALADIN-LAEF compared to ECMWF-EPS for surface weather variables. ALADIN-LAEF adds more value to precipitation forecasts and has greater skill for 10-m wind and mean sea level pressure results than does ECMWF-EPS. For 2-m temperature, ALADIN-LAEF forecasts have larger spread, are statistically more consistent, but also have less skill than ECMWF-EPS due to the strong cold bias in the ALADIN forecasts. For the upper-air weather parameters, the forecast of ALADIN-LAEF has a larger spread, but the forecast skill of ALADIN-LAEF is from neutral to slightly inferior compared to ECMWF-EPS. It may be concluded that a regional single-model-based EPS with fewer ensemble members could provide more added value in terms of greater skill for near-surface weather variables than the global EPS with larger ensemble size, whereas it may have limitations when applied to upper-air weather variables.

Gas Cooling and Humidification: Design of Packed Towers from Small-Scale Tests

1950 ◽  
Vol 163 (1) ◽  
pp. 41-53 ◽  
Author(s):  
W. F. Carey ◽  
G. J. Williamson
Keyword(s):  
Operating Conditions ◽  
Total Heat ◽  
Small Scale ◽  
Water Cooling ◽  
Packed Tower ◽  
Simple Method ◽  
Worked Example ◽  
Gas Cooling ◽  
Heat Method ◽  
Working Out

On plants in which gases are processed, the gases are often brought into direct contact with water—usually in packed towers. The purpose may be to cool a hot gas, to increase the humidity of a gas, or, in the well-known special case of water-cooling towers, to cool water by contact with atmospheric air. These processes involve simultaneous transfers of sensible heat and water vapour, and existing methods of analysis are complex and laborious, except for the cooling of water, for which Merkel's total-heat method has long been available. Merkel's approximate solution offers the engineer a simple method of working out, for any operating conditions, the amount of heat transferred and the “driving force” available for transferring it. The present paper generalizes the total-heat method and, with a permissible sacrifice in accuracy, preserves the essential simplicity of the water-cooling treatment for gas-cooling and humidification processes. To complete the design of a packed tower, a knowledge is required of the characteristics of the packing. Information obtained in small towers is given for a number of packings, and a worked example shows how to apply the method of treatment, and the packing data presented, to the design of a large plant tower.

scholarly journals Saturation of Zeldovich stretch–twist–fold map dynamos

2015 ◽  
Vol 81 (5) ◽  
Author(s):  
Amit Seta ◽  
Pallavi Bhat ◽  
Kandaswamy Subramanian
Keyword(s):  
Initial Conditions ◽  
Reynolds Numbers ◽  
Small Scale ◽  
Saturation Properties ◽  
Field Amplification ◽  
Saturated State ◽  
Shape Invariant ◽  
Fold Map ◽  
Scale Fluctuation ◽  
The Magnetic Field

Zeldovich’s stretch–twist–fold (STF) dynamo provided a breakthrough in conceptual understanding of fast dynamos, including the small-scale fluctuation dynamos. We study the evolution and saturation behaviour of two types of generalized Baker’s map dynamos, which have been used to model Zeldovich’s STF dynamo process. Using such maps allows one to analyse dynamos at much higher magnetic Reynolds numbers $\mathit{Re}_{M}$ as compared to direct numerical simulations. In the two-strip map dynamo there is constant constructive folding, while the four-strip map dynamo also allows the possibility of a destructive reversal of the field. Incorporating a diffusive step parametrized by $\mathit{Re}_{M}$ into the map, we find that the magnetic field $B(x)$ is amplified only above a critical $\mathit{Re}_{M}=R_{\mathit{crit}}\sim 4$ for both types of dynamos. The growing $B(x)$ approaches a shape-invariant eigenfunction independent of initial conditions, whose fine structure increases with increasing $\mathit{Re}_{M}$. Its power spectrum $M(k)$ displays sharp peaks reflecting the fractal nature of $B(x)$ above the diffusive scale. We explore the saturation of these dynamos in three ways: via a renormalized reduced effective $\mathit{Re}_{M}$ (case I) or due to a decrease in the efficiency of the field amplification by stretching, without changing the map (case IIa), or changing the map (case IIb), and a combination of both effects (case III). For case I, we show that $B(x)$ in the saturated state, for both types of maps, approaches the marginal eigenfunction, which is obtained for $\mathit{Re}_{M}=R_{\mathit{crit}}$ independent of the initial $\mathit{Re}_{M}=R_{M0}$. On the other hand, in case II, for the two-strip map, we show that $B(x)$ saturates, preserving the structure of the kinematic eigenfunction. Thus the energy is transferred to larger scales in case I but remains at the smallest resistive scales in case II, as can be seen from both $B(x)$ and $M(k)$. For the four-strip map, $B(x)$ oscillates with time, although with a structure similar to the kinematic eigenfunction. Interestingly, the saturated state in case III shows an intermediate behaviour, with $B(x)$ similar to the kinematic eigenfunction at an intermediate $\mathit{Re}_{M}=R_{\mathit{sat}}$, with $R_{M0}>R_{\mathit{sat}}>R_{\mathit{crit}}$. The $R_{\mathit{sat}}$ value is determined by the relative importance of the increased diffusion versus the reduced stretching. These saturation properties are akin to the range of possibilities that have been discussed in the context of fluctuation dynamos.

Identification of the best topology of delta configured three phase induction generator for distributed generation through experimental investigations

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Vanka Bala Murali Krishna ◽  
Sandeep Vuddanti
Keyword(s):  
Distributed Generation ◽  
Reactive Power ◽  
Voltage Regulation ◽  
Reactive Power Compensation ◽  
Induction Generator ◽  
Experimental Investigations ◽  
Small Scale ◽  
Empirical Formulas ◽  
Simple Method ◽  
Main Challenge

Abstract Research on Self –excited induction generator (SEIG) brings a lot of attentions in the last three decades as a promising solution in distributed generation systems with low cost investment. There are two important fixations to attend in the operation of SEIG based systems, a) excitation and b) voltage regulation. Many procedures are reported regarding selection of excitation capacitance in the literature, based on state-state analysis, dynamic modeling, empirical formulas and machine parameters which involve various levels of complexity in findings. Moreover, the voltage regulation is the main challenge in implementation of SEIG based isolated systems. To address this problem, many power electronic-based schemes are proposed in the literature and but these solutions have few demerits importantly that additional cost of equipment and troubles due to failure of protection schemes. In particular, the installation of SEIG takes place at small scale in kW range in remote/rural communities which should not face such shortcomings. Further in case of off-grid systems, the maximum loading is fixed based on connected rating of the generator. This paper presents the various methods to find excitation capacitance and illustrates an experimental investigation on different possible reactive power compensation methods of delta connected SEIG and aimed to identify a simple method for terminal voltage control without power electronics. In this experimental work, the prime-mover of the generator is a constant speed turbine, which is the emulation of a micro/pico hydro turbine. From the results, it is found that a simple delta connected excitation and delta configured reactive power compensation limits voltage regulation within ±6% while maintaining the frequency of ±1%, which make feasible of the operation successfully in remote electrification systems.

A Simple Method to Find a Neighboring Grid Point on the Cubed-sphere

2018 ◽  
Vol 54 (S1) ◽  
pp. 413-419 ◽  
Author(s):  
Ki-Hwan Kim ◽  
Pyoung-Seop Shim ◽  
Seoleun Shin ◽  
Junghan Kim
Keyword(s):  
Grid Point ◽  
Simple Method ◽  
Cubed Sphere

scholarly journals SEJARAH, KENDALA DAN HAMBATAN INVESTASI SEKTOR RIIL TERHADAP PERKEMBANGAN EKONOMI MASYARAKAT PESISIR (Studi Kasus Pabrik Pengolahan Ikan)

2013 ◽  
Vol 1 (2) ◽  
Author(s):  
Eddy Mantjoro
Keyword(s):  
Scientific Explanation ◽  
Initial Conditions ◽  
Fishing Effort ◽  
Small Scale ◽  
Processing Plant ◽  
Fish Processing ◽  
Case Study Method ◽  
Processing Industry ◽  
North Sulawesi

Abstract Goals to be achieved through this research are as follows: (1) the scientific explanation about the initial conditions of fishing effort in the area of ​​research in this area is South Minahasa; (2) To obtain information on the historical development of the fish processing industry in North Sulawesi and Minahasa south in particular; (3) To be informed of the obstacles and challenges faced by the fisheries sector investors, especially fish processing timber. This research focuses on one unit of the fish processing industry wooden fish processing plant, and then in the case study method is relevant. The case study method is expected that researchers can examine more detailed and focused on problems experienced by fish processing company. As a consequence the results can not be generalized as like which would otherwise require science. Unless some case studies on the same topic on other companies and the result is the same, the efforts generalizations can be made. However the results of the case study can paint a picture on the history, constraints and barriers to investment that occur in similar industries and other industries. The initial condition of fisheries business investment in South Minahasa in 1995 was still dominated by small-scale businesses, which is limited to household livelihoods of fishermen. How governance is still very traditional in terms of business objectives just to meet daily food needs. Wooden fish processing technology already existed and developed since the year 700 BC in Japan. In Indonesia, especially in North Sulawesi started introduced in 1927 by a Japanese man named Hara Ko. The new investment started in 1971 until now. Investment in fish processing faces many obstacles and challenges, namely (1) the limited market share, (2) Legal certainty is not guaranteed, (3) Investors from outside the region and abroad to invest by holding on minimal information about the culture and traditions of local communities (4 ) morale of local residents very traditional if not arguably worse. (5) The investment policy is supported by the local government level only at the Regent while Assiten level, down to the village more displays of terror and intimidation to investors. Keywords: fish factory, investment, history, constraints, obstacles Abstrak Tujuan yang ingin dicapai melalui penelitian ini ialah sebagai berikut: (1) Penjelasan ilmiah tentang kondisi awal usaha perikanan di wilayah penelitian dalam hal ini Daerah Minahasa Selatan. (2) Memperoleh informasi tentang sejarah perkembangan industri pengolahan ikan di Sulawesi Utara dan Minahasa selatan khususnya. (3) Mendapatkan informasi mengenai kendala dan tantangan yang dihadapi oleh investor bidang perikanan khususnya pengolahan ikan kayu. Penelitian ini berfokus pada satu unit industri pengolahan ikan yakni pabrik pengolahan ikan kayu, maka metode studi kasus di pandang relevan. Metode studi kasus diharapkan peneliti dapat mengkaji lebih rinci dan fokus pada masalah yang dialami oleh perusahan pengolahan ikan. Sebagai konsekwensinya hasil penelitian tidak dapat digeneralisir sebagai layaknya yang di syaratkan oleh ilmu pengetahuan. Kecuali beberapa studi kasus dengan topik yang sama pada perusahan lain dan hasilnya sama maka upaya generalisasi dapat dilakukan. Walau demikian hasil studi kasus dapat melukiskan gambaran mengenai sejarah, kendala dan hambatan investasi yang terjadi pada industri sejenis dan industri lainnya. Kondisi awal usaha perikanan di wilayah Minahasa selatan pada tahun 1995 ketika investasi pabrik pengolahan ikan kayu di mulai masih didominasi oleh usaha skala kecil, yaitu sebatas mata pencaharian rumah tangga nelayan. Cara kelola pun masih sangat tradisional dalam pengertian tujuan usaha hanya untuk memenuhi kebutuhan makanan harian. Teknologi pengolahan ikan kayu sudah ada dan berkembang sejak tahun 700 sebelum masehi di Jepang. Di Indonesia khususnya di Sulawesi Utara mulai di perkenalkan pada tahun 1927 oleh orang Jepang bernama Hara Ko. Investasi baru dimulai pada tahun 1971 hingga sekarang. Investasi bidang pengolahan ikan menghadapi banyak kendala dan tantangan, yaitu (1) keterbatasan pangsa pasar, (2) Kepastian hukum tidak terjamin, (3) Investor dari luar daerah dan luar negeri berinvestasi dengan berpegang pada informasi minim mengenai budaya dan tradisi masyarakat lokal (4) moral kerja penduduk lokal amat tradisional jika tidak boleh dikatakan buruk.(5) Kebijakan investasi ditunjang oleh pemerintah daerah hanya pada level Bupati sedangkan level assiten, ke bawah sampai kelurahan lebih banyak menampilkan teror dan intimidasi kepada investor. Kata Kunci : pabrik ikan, investasi, sejarah, kendala, hambatan

scholarly journals Ensemble forecasting with a stochastic convective parametrization based on equilibrium statistics

2011 ◽  
Vol 11 (11) ◽  
pp. 30457-30485 ◽  
Author(s):  
P. Groenemeijer ◽  
G. C. Craig
Keyword(s):  
Large Scale ◽  
Mesoscale Model ◽  
Initial Conditions ◽  
Deep Convection ◽  
Horizontal Resolution ◽  
Ensemble Forecasting ◽  
Total Variance ◽  
Ensemble Prediction ◽  
Ensemble Prediction System ◽  
The Impact

Abstract. The stochastic Plant-Craig scheme for deep convection was implemented in the COSMO mesoscale model and used for ensemble forecasting. Ensembles consisting of 100 48 h forecasts at 7 km horizontal resolution were generated for a 2000 × 2000 km domain covering central Europe. Forecasts were made for seven case studies and characterized by different large-scale meteorological environments. Each 100 member ensemble consisted of 10 groups of 10 members, with each group driven by boundary and initial conditions from a selected member from the global ECMWF Ensemble Prediction System. The precipitation variability within and among these groups of members was computed, and it was found that the relative contribution to the ensemble variance introduced by the stochastic convection scheme was substantial, amounting to as much as 76% of the total variance in the ensemble in one of the studied cases. The impact of the scheme was not confined to the grid scale, and typically contributed 25–50% of the total variance even after the precipitation fields had been smoothed to a resolution of 35 km. The variability of precipitation introduced by the scheme was approximately proportional to the total amount of convection that occurred, while the variability due to large-scale conditions changed from case to case, being highest in cases exhibiting strong mid-tropospheric flow and pronounced meso- to synoptic scale vorticity extrema. The stochastic scheme was thus found to be an important source of variability in precipitation cases of weak large-scale flow lacking strong vorticity extrema, but high convective activity.

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