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- High-resolution ensemble LES energy balance closure study of the
LITFASS-2003 campaign-
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Abstract:  High-resolution ensemble LES energy balance closure study of the LITFASS-2003 campaignHuq, Sadiq; De Roo, Frederik; Sühring, Matthias; Wanner, Luise; Mauder, Matthias
Meteorologische Zeitschrift, (2024), p. - Abstract The imbalance between the measured available energy and the sum of the turbulent fluxes lead to the energy balance closure problem. In spite of several experimental and modelling studies, the reasons for the lack of closure are not fully understood, particularly, in a heterogeneous terrain. The LITFASS-2003 campaign in Northeastern Germany was designed to develop and to assess different area-averaging strategies of the surface fluxes over a heterogeneous land surface. The micrometeorological measurements of the campaign were targeted at local fluxes over different types of land surface that are essential to study the energy balance closure problem for a complex land surface where the secondary circulations induced by surface heterogeneity are suspected to influence the surface energy budget imbalance. To assess the influence of the secondary circulations we perform large-eddy simulations of a 5.4 × 5.4 km2 sub-region of the LITFASS area with a flat topography and composed mainly of agricultural land. The boundary conditions for the simulation domain is derived from the experimental data collected on 30 May 2003. To capture the spatial variation of the fluxes, the surface fluxes of latent and sensible heat flux in the simulated domain are prescribed by composite fluxes derived from multiple surface flux stations operated during the experiment. A grid resolution of 1 m in the vertical and 2 m in the horizontal directions up to 72 m from the ground is achieved by employing a nested large-eddy simulation model. A total of five realizations of the domain is performed to calculate ensemble averages to separate the heterogeneity effect from the turbulence fluctuations and the 30-minute time-averaging ensures more representative statistics. We find the underestimation to be systematic and to increase with height. At a typical eddy covariance tower height of 10 m, we find the dispersive flux represents up to 5% of the prescribed surface fluxes, which partially explains the imbalance in the field measurements.
PubDate: Wed, 14 Aug 2024 00:00:00 +000
- Observations and forecasting of a low visibility event in Hong Kong on New
Year’s Eve-
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Abstract:  Observations and forecasting of a low visibility event in Hong Kong on New Year’s EveXie, Jielan; Chan, Pak-Wai; Ng, Wai-yin; Tam, Hiu-fai
Meteorologische Zeitschrift, (2024), p. - Abstract This paper investigates a unique low visibility event induced by haze in Hong Kong on New Year’s Eve 2023, characterized by significant spatial differences in visibility across Victoria Harbour. The study discusses the meteorological conditions, including weak northeast monsoon and localized wind variations, leading to the rapid fluctuation in visibility. Ground observations, remote-sensing data, and Aerosol Optical Depth (AOD) from satellites were utilized to analyze the phenomenon. The research highlights the impact of surface winds, boundary layer stability, and aerosol dispersion in understanding the visibility variation. Additionally, the study assesses the effectiveness of the current forecasting techniques, especially the high-resolution numerical weather prediction model utilized by Hong Kong’s Environmental Protection Department. The paper serves as a valuable resource for weather forecasters in the region and suggests further studies using high-resolution models to better understand localized visibility deterioration events.
PubDate: Tue, 13 Aug 2024 00:00:00 +000
- Effect of volcanic sulfur dioxide on solar UV irradiance during the 2023
Fagradalsfjall eruption in Reykjavík, Iceland-
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Abstract:  Effect of volcanic sulfur dioxide on solar UV irradiance during the 2023 Fagradalsfjall eruption in Reykjavík, IcelandČížková, Klára; Láska, Kamil; Tichopád, David; Metelka, Ladislav; Staněk, Martin; Sigurðsson, Árni
Meteorologische Zeitschrift, (2024), p. - Abstract Sulfur dioxide is an important atmospheric gas that can attenuate solar ultraviolet radiation. It can be found in greater quantities in highly polluted areas and especially in volcanic plumes. During the eruption of the Icelandic volcanic system Fagradalsfjall, which lasted between 10 July and 5 August 2023, the sulfur dioxide plume reached the capital city Reykjavík on 24 July 2023, resulting in almost 50 DU column of this gas, as measured by a B199 MkIII Brewer spectrophotometer. The increased sulfur dioxide concentration resulted in ~25 % reduction in UV Index, compared to only 1 % decrease on 23 July 2023, when up to 3.6 DU sulfur dioxide were recorded. In the UV spectrum, sulfur dioxide affected mostly short wavelengths up to approximately 325 nm, above which the effects were negligible. On 24 July 2023, a 50 DU sulfur dioxide column lead to more than 79 % reduction of UV irradiance at 296 nm. Model simulations showed that a 100 DU column sulfur dioxide would attenuate 96 % of UV irradiance at this wavelength. The effects of sulfur dioxide on vitamin D weighted solar UV irradiance were even greater than on UV Index, as a 50 DU sulfur dioxide column caused a 37 % decline in vitamin D weighted solar UV irradiance, and a potential 100 DU column of this gas would lead to a 58 % reduction of vitamin D production.
PubDate: Tue, 13 Aug 2024 00:00:00 +000
- Characteristics of rain cells over the northwest Pacific warm pool
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Abstract:  Characteristics of rain cells over the northwest Pacific warm poolYe, Ping; Zhang, Aoqi
Meteorologische Zeitschrift, (2024), p. - Abstract The importance of precipitation morphology has been emphasized by recent studies. However, the specific morphological characteristics of rain cells (RCs) and their impact on rainfall intensity over the oceans remain unclear. In this study, using 15-year observations from Tropical Rainfall Measurement Mission (TRMM) Precipitation Radar (PR), more than 600 thousand RCs in the northwest Pacific warm pool were identified and approximated by rectangle. The results showed that the horizontal scale of RCs was negatively correlated with their occurrence frequency, while there was a logarithmic correlation between the length and width of the approximated rectangle. The morphology of RCs presented huge zonal differences but small meridional differences over the study region. RCs had larger scale, narrower 2-D shape, and slender 3-D shape in the southern region compared with ones in the northern region. Precipitation intensity generally increased with the enlargement of the horizontal scale. The relationships between precipitation intensity and shape of RCs were very complex. Moderate shape of RCs had the weakest precipitation, whereas 2-D narrower or 3-D slender RCs had the strongest precipitation. The results would be helpful for monitoring and predicting precipitating clouds over the oceans.
PubDate: Tue, 13 Aug 2024 00:00:00 +000
- Exploring the ability of regional extrapolation for precipitation
nowcasting with deep learning-
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Abstract:  Exploring the ability of regional extrapolation for precipitation nowcasting with deep learningBeutler, Tarek; Rudolph, Annette; Goehring, Daniel; Vercauteren, Nikki
Meteorologische Zeitschrift, (2024), p. - Abstract Precipitation nowcasting refers to the prediction of precipitation intensity in a local region and in a short timeframe up to 6 hours. The evaluation of spatial and temporal information still challenges state-of-the-art numerical weather prediction models. The increasing possibilities to store and evaluate data combined with the advancements in the developments of artificial intelligence algorithms make it natural to use these methods to improve precipitation nowcasting. In this work, a Trajectory Gated Recurrent Unit (TrajGRU) is applied to radar data of the German Weather Service. The impact of finetuning a network pretrained at a different location and for several precipitation intensity thresholds with respect to the training time is evaluated. In cases with little availability of training data at the target location, for example when heavy rainfall is rare, the finetuned model can benefit from the original model performance at the pretraining location. Furthermore, the skill scores for the different thresholds are shown for a prediction time up to 100 minutes. The results highlight promising regional extrapolation capabilities for such neural networks for precipitation nowcasting.
PubDate: Tue, 13 Aug 2024 00:00:00 +000
- Evaluation of the Urban Climate Model PALM-4U over Hilly Terrain Using
Wind and Turbulence Observations-
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Abstract:  Evaluation of the Urban Climate Model PALM-4U over Hilly Terrain Using Wind and Turbulence ObservationsKiseleva, Olga; Gantner, Leonhard; Kalthoff, Norbert; Kossmann, Meinolf; Holst, Christopher
Meteorologische Zeitschrift, (2024), p. 177 - 198Abstract We used boundary layer observations in the Stuttgart area from two summer episodes for model evaluation of the urban climate model PALM-4U. In summer 2017, radiosondes and Doppler lidars were operated, and the lidar virtual tower technique was applied to provide vertical profiles of wind speed and direction at different sites. In summer 2018, two Doppler lidars were operated in vertical stare mode providing vertical wind speeds and their variances. PALM-4U with grid spacings of 10 m in 2018 and 40 m in 2017 was driven by COSMO analysis data. The PALM-4U output data were evaluated with the observations at the corresponding sites. For 14 to 15 August 2017, the normalised root mean square error (NRMSE) between simulated and measured wind speed time series at 100 m agl is about 0.5, except for the last hours of the investigated period. The RMSE for wind direction is 30–35°. At 700 m agl, the NRMSE for wind speed is 0.2–0.3 and the RMSE for wind direction is about 15°. The greater NRMSE differences found in the night and morning of 15 August can be explained by differences between the observed and simulated height of the low-level jet which caused stronger simulated turbulent downward mixing of momentum in the morning. On 20 June 2018, the daytime convective boundary-layer evolution was well represented in the model. However, as the wind speed was low, 1-h integration times turned out to be not suitable for model evaluation because the uncertainty in variances of the vertical wind is considerable (50%). To overcome the poor statistics due to the low number of eddies dominating, 3-h integration times turned out to be necessary. For these time intervals, the simulated profiles lie within the error bars of the observations. Theoretical considerations provide suggestions for experimental set-ups and synoptic conditions to capture vertical profiles allowing model evaluations under convective conditions based on 1-h intervals.
PubDate: Mon, 29 Jul 2024 00:00:00 +000
- The TEAMx‑PC22 Alpine field campaign – Objectives, instrumentation,
and observed phenomena-
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Abstract:  The TEAMx‑PC22 Alpine field campaign – Objectives, instrumentation, and observed phenomenaPfister, Lena; Gohm, Alexander; Kossmann, Meinolf; Wieser, Andreas; Babić, Nevio; Handwerker, Jan; Wildmann, Norman; Vogelmann, Hannes; Baumann-Stanzer, Kathrin; Alexa, Almut; Lapo, Karl; Paunović, Ivan; Leinweber, Ronny; Sedlmeier, Katrin; Lehner, Manuela; Hieden, Alexander; Speidel, Johannes; Federer, Maria; Rotach, Mathias W.
Meteorologische Zeitschrift, (2024), p. 199 - 228Abstract The multi‑scale transport and exchange processes in the atmosphere over mountains—programme and experiment (TEAMx) wants to advance the understanding of transport and exchange processes over mountainous terrain as well as to collect unique multi‑scale datasets that can be used, e.g., for process studies, model development and model evaluation. The TEAMx Observational Campaign (TOC) is planned to take place between 2024 and 2025. In summer 2022 a TEAMx pre‑campaign (TEAMx‑PC22) was conducted in the Inn Valley and one of its tributaries, the Weer Valley, to test the suitability and required logistics of measurement sites, to evaluate their value for the main campaign, and to test new observation techniques in complex terrain. Scientifically, this campaign focused on resolving the mountain boundary layer and valley wind systems on multiple scales. Through the combined effort of six institutions the pre‑campaign can be deemed successful. A detailed description of the setup at each sub‑target area is given. Due to the spatial distribution of instruments and their spatio-temporal resolution, atmospheric processes and phenomena like valley winds have been investigated at different locations and on different scales. Furthermore, scale interactions were detected and are discussed in detail in example cases. Additionally, observational gaps were determined which should be closed for the TOC. Data of the pre‑campaign are publicly available online and can be used for process studies, demonstrating the utility of new observation methods, model verification, and for data assimilation.
PubDate: Mon, 29 Jul 2024 00:00:00 +000
- Lagrangian transport based on the winds of the icosahedral nonhydrostatic
model (ICON)-
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Abstract:  Lagrangian transport based on the winds of the icosahedral nonhydrostatic model (ICON)Sonnabend, Jonas; Grooß, Jens-Uwe; Ploeger, Felix; Hoffmann, Lars; Jöckel, Patrick; Kern, Bastian; Müller, Rolf
Meteorologische Zeitschrift, (2024), p. 229 - 242Abstract Representing atmospheric transport of constituents accurately in a chemistry climate model is a challenge. This is true in particular for a realistic representation of atmospheric transport barriers, e.g. at the edge of the polar vortices or at the tropopause. When transport is represented employing Lagrangian methods, numerical problems representing transport barriers may be obviated. Here, we present a first implementation of a Lagrangian transport model (the Chemical Lagrangian Model of the Stratosphere, CLaMS) driven by horizontal winds and vertical velocities of the icosahedral nonhydrostatic model (ICON) using the Modular Earth Submodel System (MESSy). The diabatic heating rates deduced from the temperature tendencies in the (free-running) ICON model allow vertical velocities to be determined and transport calculations in isentropic (diabatic) coordinates. The deduced diabatic heating rates agree qualitatively well with ERA5 reanalysis values in the zonal annual mean, but some discrepancies remain. Further, there is an overall agreement between the simulation and N2O observations by the Microwave Limb Sounder (MLS) satellite instrument; in particular regarding N2O gradients at the edge of the polar vortex. Overall, the Antarctic vortex and the associated transport barrier at its edge are well represented in the simulation, although the simulated polar vortex is larger than observed. Some differences between the observations and the Lagrangian simulation may be caused by the underlying ICON winds. The coupled ICON/MESSy-CLaMS transport scheme allows realistic simulations of tracer distributions in the free troposphere and in the stratosphere, including the representation of tracer gradients across transport barriers, a feature generally more difficult to obtain by classical Eulerian schemes.
PubDate: Mon, 29 Jul 2024 00:00:00 +000
- Survey On Output Data From Obstacle Resolving Atmospheric Models
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Abstract:  Survey On Output Data From Obstacle Resolving Atmospheric ModelsVoss, Vivien; Schlünzen, K. Heinke; Grawe, David
Meteorologische Zeitschrift, (2024), p. 243 - 253Abstract Obstacle resolving micro-scale atmospheric models (ORMs) are important to assess atmospheric processes within urban areas. However, the data generated from such models are not standardised yet and existing data standards do not fit properly to those data. Standardised model data can help to prepare FAIR data publications, which foster the process of data reuse, sharing, comparison and distribution. Therefore, an online survey was distributed among ORM users and developers in the urban meteorology and urban climate community. The survey should help to assess, which models are currently in use and to collect suggestions and requirements from the participants on how a data standard should look like. The aim of the survey was not to test the knowledge of the participants about the model they use but rather to get an overview of how they understand, use and work with ORMs. Based on 14 finished survey entries, it shows that ORMs provide and handle their data differently. The participants are aware of the need for standardisation, preferring netCDF as data format and suggesting extending existing standards to the needs of ORM data.
PubDate: Mon, 29 Jul 2024 00:00:00 +000
- Observation and numerical simulation of terrain-induced airflow leading to
low level windshear at the Hong Kong International Airport based on
Range-Height-Indicator scans of a LIDAR-
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Abstract:  Observation and numerical simulation of terrain-induced airflow leading to low level windshear at the Hong Kong International Airport based on Range-Height-Indicator scans of a LIDARChan, Pak Wai; Cheung, P.; Lai, K. K.
Meteorologische Zeitschrift, (2024), p. - Abstract A Doppler Light Detection And Ranging (LIDAR) system is set up downstream of a small hill of Lantau Island near the Hong Kong International Airport to perform range-height-indicator (RHI) scans to monitor airflow disturbances by the terrain in a tropical cyclone case and to study the feasibility of alerting the low level windshear to be encountered by the aircraft leaving the airport. This is the first time that RHI scans are performed regularly downstream of the small hill. The scans show many interesting features of terrain-disrupted airflow, including tiny vortex of reverse flow and higher-speed wind streaks. The latter are found to be associated with the low level windshear reported by the pilots. The airflow features are simulated using a high resolution numerical weather prediction model. It turns out that the higher-speed wind streaks could be reproduced successfully. However, the reverse flow does not show up well in the simulation.
PubDate: Mon, 29 Jul 2024 00:00:00 +000
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