Anurag Dipankar

Last Name

Dipankar

First Name

Anurag

ORCID

0000-0002-1410-4324

Organisational unit

02260 - EXCLAIM / EXCLAIM

Show all metadata

Search Results

Publications 1 - 10 of 31

Resolution dependence of southern Atlantic Ocean stratocumulus decks
Canton, Jacopo; Dipankar, Anurag; Schär, Christoph (2024)
Quarterly Journal of the Royal Meteorological Society
Oceanic stratocumulus decks of clouds are among the largest contributors to the Earth’s radiation budget, covering around a fifth of the planet’s surface and reflecting a large part of the incoming solar radiation. Unfortunately, these clouds are not well represented in modern climate models, resulting in one of the leading causes of uncertainty in climate change projections. This con tribution analyses this issue from a novel perspective and sheds light on the mechanisms behind the misrepresentation and resolution dependence of these large clouds. The analysis is based on realistic week-long simulations performed over a 563 × 563 km2 oceanic domain. Four horizontal resolutions, between 4.4 and 0.55 km, are employed, resulting in a timely investigation, especially in light of the high resolutions employed by present and near-future climate projections. Results show that the liquid cloud water, the main contributor to the simulated grid-scale clouds, decreases with a power-law decay as the resolution increases, whereas the water vapour, responsible for subgrid-scale clouds, is much less affected by the grid spacing. The leading cause is identified as an imbalance between the rates of change of the advection and turbulence parametrisation terms. In order to verify this observation and provide a possible mitigation to the issue, a second set of simulations is performed where the turbulence parametri sation is tuned. The strategy proves to be successful, confirming the hypotheses and resulting not only in a resolution-independent radiation budget but also cloud coverage.
Scale‐Aware Evaluation of Complex Mountain Boundary Layer Flow From Observations and Simulations
Lapo, Karl; Dipankar, Anurag; Goger, Brigitta (2025)
Geophysical Research Letters
Boundary layers over complex, mountainous terrain are characterized by multi‐scale, complex flow structures, where the characterization of individual flow modes poses a fundamental challenge. We apply the novel multi‐resolution coherent spatio‐temporal scale separation (mrCOSTS) method to LIDAR observations and numerical data of the velocity components of complex mountain boundary‐layer flow. Using three distinct time scales (turbulent scales, mountain boundary layer, and diurnal scales) the underlying physical processes are explored. Furthermore, we identified the dominant flow patterns for each time scale, for example, down‐ and up‐valley flows, cross‐valley vortices, small‐scale turbulence, and large evening transition eddies. Applying mrCOSTS to simulated velocity components enables us to identify how coherent structures and the flow patterns are represented at various mesh sizes in the model. Using mrCOSTS we trivially retrieved complex dynamics that were previously difficult to resolve, enabling a direct, scale‐aware evaluation between the LIDAR observations and model results.
EXCLAIM: Extreme Scale Computing and Data Platform for Cloud-resolving Weather and Climate Modelling
Dipankar, Anurag; Bianco, Mauro (2023)
EXCLAIM aims at developing a modeling infrastructure that can allow the climate models to simulate the Earth’s climate at a substantially higher resolution. Explicit representation of key climate processes (e.g. moist convection) at such high resolution should allow for reduced uncertainty in the future climate projection simulated by these models. The climate model used for this exercise is ICON based that is developed jointly by the Max Planck Institute for Meteorology in Hamburg, Germany, and the German weather service. The approach taken by EXCLAIM to reach the performance target is to re-write the currently Fortran-based monolithic codes into a descriptive user code based on Python, which is then translated into standard imperative language (e.g., C++) for specific architectures using a toolchain based on GT4Py (GridTools for Python). However, performance gain alone doesn’t ensure sustainable software development for a code that is already too complex. A modularized code structure is therefore envisioned. Modularization is performed down to the smallest reasonable part of the code- termed granules- that can be tested in isolation, and in combination with other granules. Status of these developments and how they address the needs of ultra-high-resolution modeling while allowing for further innovation will be presented.
On the Applicability of Urban Canopy Parameterizations in Building Grey Zone
Dipankar, Anurag; Chen, Song (2022)
Towards Specialized Supercomputers for Climate Sciences: Computational Requirements of the Icosahedral Nonhydrostatic Weather and Climate Model
Hoefler, Torsten; Calotoiu, Alexandru; Dipankar, Anurag; et al. (2024)
arXiv
We discuss the computational challenges and requirements for high-resolution climate simulations using the Icosahedral Nonhydrostatic Weather and Climate Model (ICON). We define a detailed requirements model for ICON which emphasizes the need for specialized supercomputers to accurately predict climate change impacts and extreme weather events. Based on the requirements model, we outline computational demands for km-scale simulations, and suggests machine learning techniques to enhance model accuracy and efficiency. Our findings aim to guide the design of future supercomputers for advanced climate science.
The impact of decreasing horizontal grid spacing on the simulation of the mountain boundary layer in the hectometric range
Goger, Brigitta; Dipankar, Anurag (2024)
arXiv
The horizontal grid spacing of numerical weather prediction models keeps decreasing towards the hectometric range. We perform limited-area simulations with the ICON model across horizontal grid spacings (1 km, 500 m, 250 m, 125 m) in the Inn Valley, Austria, and evaluate the model with observations from the CROSSINN measurement campaign. This allows us to investigate whether increasing the horizontal resolution automatically improves the representation of the flow structure, surface exchange, and common meteorological variables. Increasing the horizontal resolution results in an improved simulation of the thermally-induced circulation. However, the model still faces challenges with scale interactions and the evening transition of the up-valley flow. Differences between two turbulence schemes (1D TKE and 3D Smagorinsky) emerge due to their different surface transfer formulations, yielding a delayed evening transition in the 3D Smagorinsky scheme. Generally speaking, the correct simulation of the mountain boundary layer depends mostly on the representation of model topography and surface exchange, and the choice of turbulence parameterization is secondary.
Evaluating the Turbulence Representation in a NWP Model over Mountainous Terrain
Goger, Brigitta; Dipankar, Anurag (2023)
EGUsphere
Analysis of the Swiss urban climate over the past five years
Canton, Jacopo; Dipankar, Anurag (2023)
Switzerland is home to several medium to small cities, usually situated on lakes or large rivers and always in the proximity of mountains. Both size and location contribute to reducing the dominance of the urban climate over the local weather systems, e.g., lake breezes, mountain and valley winds, but the interaction between Swiss cities and the local climate has long been monitored with measurements [1]. This contribution presents a numerical analysis of the alpine country over the past five years (2017-2022). The focus is on the urban climate and urban heat island (UHI) effect. The simulations are performed with the Consortium for Small-Scale Modeling (COSMO) model at a resolution of 1.1km, with explicit convection, and are validated against measurements by the Federal Office of Meteorology and Climatology. The bulk scheme TERRA_URB [2] is employed for modelling urban areas and is provided with a 100m-resolution state-of-the-art database for the subdivision of the urban landscape into local climate zones (LCZ) [3]. Our findings show that the UHI of Swiss cities (i.e., the temperature delta between city centre and a rural reference) closely follows the weather patterns measured over the same period and does not show a net positive trend, despite the continuous urbanization of the country which is in line with the European average [4]. The number of tropical nights (i.e., nights when the temperature did not drop below 20C) and other “classic” measures show comparable trends. The only year exhibiting a clear variation is 2022, which was a record warm year for large parts of Europe. Regarding UHI the worst affected city is Zurich, with a time averaged maximum UHI of around 3C, while most other large cities have values of 2-2.5C and smaller cities between 0.5 and 2C. Lugano, the only city in our analysis south of the Alps, presents the highest number of tropical nights, followed by Geneva and Lausanne. Simulations allow us to investigate the space-dependent nature of the UHI effect, which is especially insightful for medium-small cities. We present such an analysis for the ten largest Swiss cities, providing an objective quantification of the effects caused by different LCZs and geographical features, as well as a direct intercomparison between similarly built-up areas in different cities. The seasonality of UHI as well as the influence of weather patterns on its magnitude are also analysed, completing the spatiotemporal picture of the country’s current urban climate.
On the applicability of urban canopy parametrization in building grey zone
Chen, Song; Dipankar, Anurag (2022)
Quarterly Journal of the Royal Meteorological Society
With increasing interest in urban meteorology and related services, the need to appropriately represent the urban environment in climate/weather models is rising. These regional weather/climate models typically use a km-scale horizontal grid, which is insufficient to resolve the flow around buildings. Effects of the urban environment on the atmosphere above are represented through a bulk approach using the Urban Canopy Parametrization (UCP) schemes. Existing UCPs usually use the repeating canyon-roof representation that assumes homogeneous distribution of buildings within the grid box. It is commonly accepted that the assumption of homogeneity holds at km-scale grid resolution but whether it also holds at sub-km scale, where the regional models are increasingly approaching, is questionable. For this reason, among others, the resolution ranges from a few hundred metres to tens of metres (i.e. building-resolving scales) is termed the building grey zone in the existing literature. This work shows that the assumption of homogeneity indeed does not hold at the building grey zone for the city-state Singapore. To understand the possible influences of the use of UCPs at scales from the building grey zone to the conventional mesoscale, we use an urban-grid method that allows us to estimate the parametrized fluxes from a typical UCP at varying resolutions over the urban landcover while keeping the same atmospheric model grid. Numerical results show that different urban-grid resolutions yield variations in the near-surface temperature and wind to a maximum of 0.5 K and 1 m center dot s(-1). Their impact on the boundary-layer parameters is found to be limited. Although these near-surface variations are small, they are comparable to the near-surface scaling variables and are thus physically significant.
Evaluation of ICON over complex terrain on the hectometric range
Goger, Brigitta; Dipankar, Anurag (2023)

Publications 1 - 10 of 31

Anurag Dipankar

Last Name

First Name

ORCID

Organisational unit

Filters

Search Results