 Subjects -> METEOROLOGY (Total: 106 journals)
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- Thermal loads in two different urban quarters – perspectives from
mobile measurements and mental maps-
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Abstract:  Thermal loads in two different urban quarters – perspectives from mobile measurements and mental mapsModerow, Uta; Ziemann, Astrid; Goldberg, Valeri; Sinning, Heidi
Meteorologische Zeitschrift, (2023), p. 447 - 470 The fact that different urban structures have different climatic effects and therefore differ in their thermal loads for people is well known. However, there is a lack of quantitative and qualitative surveys in specific districts that are suitable to derive accepted adaptation measures. This paper addresses the research questions where thermally stressed areas in public space are identified by mobile measurements and by mental maps and what are the causes of each, where both methods agree or disagree, and what are the benefits and the limitations of using both methods for prioritizing adaptation measures. Mobile measurements in an urban quarter over a whole day can supply needed data for determining thermal loads of urban structures and their temporal development. Mental maps give information about the perception of urban dwellers and – based on the spatial distribution of obtained data – the user frequency. Both methods provide information concerning where and when measures should be taken in order to facilitate adaptation to heat. The paper presents the results of mobile measurements and mental maps of two different urban quarters in Germany. Thermal loads were assessed by using the Universal Thermal Climate Index (UTCI) for three selected summer days. Results indicated that the different urban structures can differ by up to 7 K or by two stages of thermal stress during a hot summer day. Surface material with high albedo can overcompensate smaller sky view factors resulting in high thermal loads. Street trees caused changing thermal loads but reduced them on average. Identified hot spots based on mobile measurements mostly correlated with hot spots identified by mental maps, if they were frequently used. However, hottest spots identified by measurements were not necessarily most frequently named as hot spots in the mental maps. Most often named hot spots of mental maps coincided with major traffic routes suggesting that user frequency is important. We conclude that the combination of both methods can be valuable for identifying locations with high priority for climate adaptation in cities.
PubDate: Tue, 05 Dec 2023 00:00:00 +000
- Towards higher accuracy in wind farm deficit decay modelling –
a comparison-
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Abstract:  Towards higher accuracy in wind farm deficit decay modelling – a comparisonMauz, Moritz; Emeis, Stefan; Hoeckh, Frederick; van Kesteren, Bram; Platis, Andreas; Bange, Jens
Meteorologische Zeitschrift, (2023), p. 471 - 486 Wind farm wake behaviour and forecasting is gaining the importance recently. It is especially relevant in the German Bight where space for wind farm clusters is limited, and wind farm wake lengths of up to 60 km have been measured. In this investigation newly proposed simple wind farm far-field recovery analytical wake model called SWIFFR is compared to the analytical EFFWAKE ( Emeis, 2010) (Efficiency and Wake) wind farm wake model and the established Frandsen model ( Frandsen et al., 2006). The models in this study are compared to measured in‑situ airborne data, captured during the WIPAFF (wind park far field) project. Three specific flights are shown and compared to the respective model result of each analytical model. The SWIFFR model is derived from the Reynolds-averaged Navier-Stokes equation for the momentum conservation. It describes the wind speed recovery, as for example, in the wake of a wind farm from an atmospheric point of view, by acknowledging turbulent momentum from the atmosphere aloft of the wind farm wake and from the sides as well. A gain in accuracy in comparison to the EFFWAKE model is achieved. Analytical models provide computationally inexpensive results based on some assumptions and simplifications of the governing equations, which distinguishes this approach from purely empirical models.
PubDate: Tue, 05 Dec 2023 00:00:00 +000
- A machine learning approach on the investigation of the scale dependent
relation of CAPE and precipitation-
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Abstract:  A machine learning approach on the investigation of the scale dependent relation of CAPE and precipitationRudolph, Annette; Névir, Peter
Meteorologische Zeitschrift, (2023), p. 487 - 497 The temporal and spatial scale dependent relation of Convective Available Potential Energy (CAPE) and precipitation is investigated. Using the COSMO-REA6 data set, we ask which of the standard machine learning algorithms: perceptron, support vector machine, decision tree, random forest, k-nearest neighbor and a simple kept deep neural network algorithm can best relate these two variables. Then, we concentrate on decision trees and evaluate the relation of CAPE and precipitation across different scales. We investigate temporal resolutions of 1 hour to 24 hours and horizontal resolutions of 6 km up to 768 km. Regarding ten CAPE and two precipitation classes we find accuracy scores mostly of about 0.7 across all scales. Taking the Dynamic State Index (DSI) as additional predictor into account leads to an overall increase of the scores. We further introduce a theoretical relation of CAPE and precipitation based on the works of Hans Ertel (1933), which will be analyzed in future studies. Today it is natural to tackle complex atmospheric processes using machine learning methods. These data based methods are suggested as additional tool to complement the results gained by the governing equations of atmospheric motion.
PubDate: Tue, 05 Dec 2023 00:00:00 +000
- Lifetime nowcasting of thunderstorms over Germany using a multi-source
data-based fuzzy-logic approach-
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Abstract:  Lifetime nowcasting of thunderstorms over Germany using a multi-source data-based fuzzy-logic approachZöbisch, Isabella; Zinner, Tobias; Wapler, Kathrin
Meteorologische Zeitschrift, (2023), p. 499 - 511 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 thunderstorms.
PubDate: Tue, 05 Dec 2023 00:00:00 +000
- Revisiting the early instrumental temperature records of Basel and Geneva
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Abstract:  Revisiting the early instrumental temperature records of Basel and GenevaBrugnara, Yuri; Brönnimann, Stefan
Meteorologische Zeitschrift, (2023), p. 513 - 527 Basel and Geneva have two of the longest meteorological records in Switzerland, covering more than two and a half centuries. The respective monthly temperature series were published over 60 years ago and are part of todays main global temperature data sets. After digitizing the raw sub-daily measurements, we rebuilt the early instrumental part (i.e., before 1864) of the two series at daily resolution using modern methods and additional data sources that were not considered in previous efforts. A comparison with the old series and with other existing recontructions show a generally good agreement only for the last 30 years. Before the 1830s a few systematic differences appear, particularly in summer, suggesting that both new and old versions contain residual inhomogeneities. We use the new series together with other reconstructions to analyze the periods 1791–1807 and 1808–1824, which have been described, respectively, as a warm and cold period in summer in previous studies. Our results suggest that most existing instrumental data sets tend to overestimate summer temperature in Switzerland during the former period, confirming previous results based on proxy records. The overestimation is particularly large (almost 1 °C) in the old Geneva series. On the other hand, we find a probable systematic underestimation of summer temperature in our Basel series. Before the 1780s the agreement between existing reconstructions is poor, so that it is hardly possible to make confident statements about climate variability for the first few decades covered by the series. Nevertheless, the daily resolution of the data allows an insight into individual meteorological events such as cold spells and heat waves.
PubDate: Tue, 05 Dec 2023 00:00:00 +000
- Spatial scaling of extreme rainfall from radar QPE in Germany
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Abstract:  Spatial scaling of extreme rainfall from radar QPE in GermanyPöschmann, Judith Marie; Kronenberg, Rico; Bernhofer, Christian
Meteorologische Zeitschrift, (2023), p. 353 - 365 The study analyses 19 years of hourly quantitative precipitation estimates (RADKLIM-RW) concerning the spatial scaling behaviour of extreme rainfall for Germany as well as general heavy rainfall patterns. Four regions with the same size of 256 km × 256 km were selected with varying characteristics. For each region, spatial rainfall maxima for different aggregation steps with box length of 2, 4, 8, 16, 32, 64, and 128 km were retrieved using sliding and fixed window methods. Rainfall was classified with two parameters into patterns dominated by convection or advection, respectively. Based on the calculated spatial maxima, potential maximum rain rates were extrapolated for sub-pixel scale. Though the power laws of the resulting scaling relationship have a very good fit, no mono-scale power law could be derived from the data due to different rainfall mechanisms on different spatial scales. Typical power laws exist for more convective characteristics up to a scale of 8 km box length and for more advective characteristics with larger box lengths. A regional power law for maxima of convective rainfall could be used to statically refine the radar resolution to 250 m or even 125 m box length. However, when scaled to smaller box lengths or to the size of a Hellmann gauge (200 cm2) the values become increasingly unrealistic. The results indicate that radar derived areal precipitation values are limited to the radar scale (here 1 km2), despite the fact that they are scaled to fit observed values from rain gauges.
PubDate: Mon, 16 Oct 2023 00:00:00 +000
- Is it foehn or sea breeze' Eulerian and Lagrangian analysis of the
flow in the Jordan Valley-
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Abstract:  Is it foehn or sea breeze' Eulerian and Lagrangian analysis of the flow in the Jordan ValleyLezuo, Tobia; Jansing, Lukas; Rostkier-Edelstein, Dorita; Sprenger, Michael
Meteorologische Zeitschrift, (2023), p. 367 - 381 For more than one century, the penetration of the Mediterranean Sea Breeze into the Jordan Valley has been studied. At times, the associated downslope westerlies in the Dead Sea area exhibit foehn characteristics, leading to a warming and drying upon arrival and therefore contradicting the typical characteristics of a sea breeze. In this paper, a particular summer day (16 August 2014) is analyzed using a kilometre-scale model simulation. For the first time, the Mediterranean Sea Breeze penetration is investigated with Lagrangian backward trajectories and its characterization is extended to the entire Jordan Valley. Along the western slopes of the valley, two well-distinguishable layers are detected in the afternoon: a moist and cold sea breeze layer, and a dry and warm foehn layer above. While the air parcels of both layers cover similar pathways in the hours before reaching the Jordan Valley, they originate from strikingly different altitudes. For this reason, significant differences in their temperature evolution and humidity content are detected. In the evening, the Mediterranean Sea Breeze layer is eroded, enabling the foehn layer to reach the surface. The arrival of foehn retards the afternoon cooling and leads to a decrease in relative humidity. This unique imprint of foehn breakthrough is confirmed by in situ measurements. Therefore, the two-layered flow pattern is found to be a key element in understanding the mesoscale wind system and the surface signals in the Dead Sea area. The foehn layer is spatially confined to the Dead Sea area since the locally elevated upstream Judean Mountains cause a major disturbance of the westerly flow. This work extends the knowledge on summer mesoscale flows in the Jordan Valley and on different types of foehn-breeze interactions.
PubDate: Mon, 16 Oct 2023 00:00:00 +000
- Performance of large-eddy simulations for capturing low-level wind shear
at the Hong Kong International Airport for a whole wind-shear (spring)
season-
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Abstract:  Performance of large-eddy simulations for capturing low-level wind shear at the Hong Kong International Airport for a whole wind-shear (spring) seasonChan, P.W.; Lai, K.K.; Li, Q.S.
Meteorologische Zeitschrift, (2023), p. 383 - 394 The wind-shear reports from pilots from a particular springtime wind-shear season at the Hong Kong International Airport, namely, January to April 2021, are considered in order to study the performance of a meteorological model in large-eddy simulations in capturing the low-level wind shear and turbulent flow under a variety of weather conditions. It could be seen that, from a statistical comparison of the results, the low-level wind-shear reports are reasonably well captured. This is re-enforced in two selected cases of typical, low-level wind shear at the airport, namely, terrain-disrupted airflow and a sea breeze front. The turbulent flow feature is also reproduced reasonably well from the structure function and eddy dissipation rate (EDR). The scatter plot of actual and model-simulated EDR reveals a reasonable comparison. Through case studies, the major features of turbulent airflow are well reproduced. This paper suggests that large-eddy simulation could have reasonable skill in capturing the low-level wind shear using a large wind-shear sample.
PubDate: Mon, 16 Oct 2023 00:00:00 +000
- A stochastic model of the model error to improve the
ICON‑D2‑EPS ensemble forecasts-
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Abstract:  A stochastic model of the model error to improve the ICON‑D2‑EPS ensemble forecastsSprengel, Martin; Gebhardt, Christoph
Meteorologische Zeitschrift, (2023), p. 395 - 412 In this work, we aim at improving the operational regional ensemble forecast system ICON‑D2‑EPS at the German Meteorological Service (Deutscher Wetterdienst, DWD). To this end, we propose to describe the model error of the forecast with a random field generated by a linear stochastic partial differential equation (SPDE). The SPDE contains three terms to describe spatial and temporal correlations as well as amplitude of the model error with a coefficient for each of the terms controlling the strength of the corresponding process. To account for the weather dependence of the model error, the coefficients are flow-dependent through a dependency on the respective tendency of the perturbed variables. In order to find the coefficients, we first derive theoretical properties of the solution of the SPDE. Then we investigate historical model error fields and determine the three coefficients in such a way that the simulated perturbation fields have the same spatial and temporal correlations and amplitude as the historical model error fields. The SPDE is implemented into the ICON forecast model and an ensemble experiment for a full month has been performed. The SPDE is solved during the forecast and corrects the slow physics tendencies of the horizontal wind components and temperature in each time step with a different random field in each member. Using this approach, various ensemble verification scores such as the CRPS and spread/skill ratio both against surface synoptic observations and radiosondes measurements are improved without degrading the RMSE of the forecast.
PubDate: Mon, 16 Oct 2023 00:00:00 +000
- A Dynamic Mixed Model for General Circulation Models
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Abstract:  A Dynamic Mixed Model for General Circulation ModelsSchaefer-Rolffs, Urs
Meteorologische Zeitschrift, (2023), p. 413 - 429 An extension of the dynamic Smgarorinsky model (DSM) is presented. In the so-called dynamic mixed model (DMM), the Leonard stress (i.e., the resolved part of the Reynolds stress) is no longer parameterized in the test filter range by the Smagorinsky model. Instead, it is modeled by the so-called similarity model, which assumes close self-similarity of the resolved and unresolved flow. This implementation is derived first in general and then specifically for spectral models. In the latter case, spectral cut-off filters allow a simple reformulation of the basic tensor equation of the DSM, requiring only the modification of a particular term to obtain the DMM version of the turbulence model. The DMM is then examined in the Kühlungsborn Mechanistic general Circulation Model (KMCM), a spectral CGM, where, starting from the same initial condition, the flow fields are compared in a model run with the DMM and in a control run with the DSM on day zero and day eight. Although most of the results are comparable, there is, already at day zero, a significant difference at the poles: with the DSM, there are certain locations with large values of the Smagorinsky parameter that are not present in the DMM run. This can be explained mathematically by the fact that the convergence of the associated Legendre polynomials in the spectral representation is worse at the poles. Therefore, numerical errors can occur in the spectral transformation, which cancel out in the DMM due to its formulation, allowing the increase of the time steps.
PubDate: Mon, 16 Oct 2023 00:00:00 +000
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