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Atmospheric Physics Seminar

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room 17, Pasteura 7 at 13:15

dr Marta Wacławczyk (IGF UW)

Statistical description of turbulent fields and their invariant modelling

Although the evolution of turbulent velocity field is governed by the deterministic Navier-Stokes equations, due to its sensitivity to small variations in the initial and boundary conditions turbulent field may be treated as a stochastic field. For its statistical description joint probability density functions (pdf's) of velocities in different points of the flow are needed. Transport equations for such pdf's form a system of infinitely many equations where in the n-th equation for n-point pdf an unknown pdf in (n+1) points is present.
In this respect, statistical turbulence closures like, e.g. k-ε or the Reynolds-stress models (RSM) provide only very limited information on a turbulent stochastic field. The Reynolds-stresses are one-point second-order moments of turbulent velocity, hence, the effect of all higher-order and multipoint correlations have to be replaced by a proper closure. Analogously, in Large Eddy Simulations (LES) a closure for the correlations on subgrid scales is sought for.
In the first part of the talk theoretical description of turbulent flows and mathematical analysis of the infinite system for pdf's with the use of the Lie-group method will be addressed. Next, possible applications of this theoretical study for the modelling of turbulence will be discussed.

room 17, Pasteura 7 at 13:15

dr Jun-Ichi Yano (Meteo France, Toulouse)

Theoretical Challenges of the NWP at Convection-Permitting Scale

With increasing horizontal resolutions, European operational weather forecast models have now begun to explicitly resolve individual elements of convective storms. However, the change may not improve the weather forecast as optimistically anticipated, but its performance may even worsen. This presentation systematically discusses various basic scientific challenges that we face under this convection-permitting NWP.

room 17, Pasteura 7 at 13:15

dr Andrzej Z. Kotarba (Centrum Badań Kosmicznych PAN)

Źródła zanieczyszczenia światłem w Polsce

Nadmiar sztucznego światła nocą początkowo stanowił problem tylko dla astronomów. W ostatnich dekadach zanieczyszczenie świetlne ewoluowało jednak do rangi kolejnego, globalnego źródła nadmiernej presji człowieka na środowisko. Zanieczyszczenie to wywiera negatywny wpływ na świat roślin i zwierząt, w tym także na funkcjonowanie organizmu ludzkiego (szczególnie w obszarach wielkomiejskich, gdzie noc astronomiczna w zasadzie już nie występuje). W czasie referatu przedstawiona zostanie definicja zanieczyszczenia światłem i omówione zostaną sposoby ilościowego określania stopnia zanieczyszczenia świetlnego (naziemne, satelitarne, modelowe). Opisany zostanie stan zanieczyszczenia świetlnego w Polsce według dostępnych danych. Na tym tle nakreślone zostaną kierunki badań, jakie planowanie są w ramach projektu „Źródła zanieczyszczenia światłem w Polsce” (przewidziany okres realizacji: lata 2016-2021).

room 17, Pasteura 7 at 13:15

prof. Jarosław BOSY, dr hab. Witold ROHM (Instytut Geodezji i Geoinformatyki, Uniwersytet Przyrodniczy we Wrocławiu)

Emerging Global Navigation Satellite Systems based tropospheric products

Witold Rohm, Jarosław Bosy, Jan Kapłon, Tomasz Hadaś, Karina Wilgan, Paweł Hordyniec, Krzysztof Sośnica, Kamil Kaźmierski, Jan Sierny
GNSS&Meteo Working Group, Institute of Geodesy and Geoinformatics, Wroclaw University of Environmental and Life Sciences.
GNSS were not designed and build for remote sensing applications, as of now positioning and navigation are still a corner stone of everyday use of such satellite systems. Surprisingly though, the GNSS data are marked by International Radio Occultation Working Group among top five techniques reducing weather forecasts errors, and the most efficient one in per observation term. There are two major reasons for such high rank: 1) GNSS measurements are all-weather, microwave and based solely on uniform time scale provided by precise atomic clocks observations, 2) high-precision, high-fidelity requirements imposed on the receivers and positioning processing strategies resulted in careful bias removal and uncertainty quantification procedures in place. Currently, there are three major types of observation platforms and associated signal physical effects that are employed in atmosphere remote sensing using GNSS signals: 1)ground-based GNSS observations using permanent networks, where slowing down of signal phase and group velocity is the most dominant effect, 2)space-based limb-looking GNSS observations that record and utilise bending of rays paths, 3)space-based or ground-based reflected signals polarization and group velocity delay with respect to the reference signal is used. The first two play an important role in the GNSS & Meteo research portfolio, as we are at the forefront of ground-based GNSS investigation, advancing troposphere delay estimation techniques in near real time real time, in the zenith direction as well as into the direction of satellite, 4D modelling (GNSS tomography), Numerical Weather Prediction models GNSS assimilation procedures. In collaboration with our Taiwanese partners National Central University and National Space Organisation we also take active role in the COSMIC II research looking into low troposphere radio occultation retrievals, in a near future this collaboration will mature into Joint Processing Centre (PL-TW) established at WUELS.

room 17, Pasteura 7 at 13:15

prof. dr hab. Szymon P. Malinowski (IGF UW)

Turbulent Inversion: A Missing Piece in the Puzzle of Stratocumulus Entrainment?

We investigate high-resolution airborne data collected in the course of the Physics of Stratocumulus Top (POST) project. Analysis of 8 different cases of marine stratocumuli, based on ~400 aircraft penetrations across the Entrainment Interfacial Layer (EIL), reveals a fine-layered structure of the cloud top and capping inversion. Despite very high static stability, the inversion and the whole EIL remain turbulent with maximum turbulence intensity just below the cloud top. The thickness of the EIL corresponds to the thickness of the shear layer in the cloud top region, and adapts to the velocity- and buoyancy-jump between the cloud layer and the free troposphere in such a way, that the gradient Richardson Number across EIL sublayers remains critical. Estimates of Ozmidov and Corrsin scales indicate significant anisotropy turbulence in scales governing turbulent transport across the EIL.

room 17, Pasteura 7 at 13:15

prof. dr hab. Wojciech Grabowski, profesor afiliowany przy Uniwersytecie Warszawskim (National Center for Atmospheric Research, Boulder, Colorado, USA)

Untangling microphysical impacts on deep convection applying piggybacking methodology

Formation and growth of cloud and precipitation particles (“cloud microphysics”) affect cloud dynamics and such macroscopic cloud field properties as the mean surface rainfall, cloud cover, and liquid/ice water paths. Traditional approaches to investigate the impacts rely on parallel simulations with different microphysical schemes or with different scheme parameters. Such methodologies are not reliable because of the natural variability of a cloud field that is affected by the feedback between cloud microphysics and dynamics. A novel modeling methodology, microphysical piggybacking, was developed to assess the impact of cloud microphysics on cloud dynamics and to separate purely microphysical effects from the impact on the dynamics. The main idea is to use two sets of thermodynamic variables driven by two microphysical schemes (or by the same scheme with different parameters), with one set coupled to the dynamics and driving the simulation, and the other set piggybacking the simulation, that is, responding to the simulated flow but not affecting it. I will discuss application of this methodology to cloud field simulations of deep convection focusing on the so-called convective invigoration in polluted environments. I will show that the methodology allows assessing the impact of cloud microphysics on cloud field properties with unprecedented accuracy. By switching the sets (i.e., the set driving the simulation becomes the piggybacking one, and vice versa), the impact on cloud dynamics can be isolated from purely microphysical effects. Applying single-moment and double-moment bulk microphysics, I will show that the methodology documents a rather small indirect aerosol impact on convective dynamics for the case of scattered unorganized deep convection, but a significant microphysical effect.

room 17, Pasteura 7 at 13:15

dr Jesper Pedersen (Instytut Geofizyki, Wydział Fizyki UW)

On the Influence of Grid Resolution and Domain Size on the Structure and Evolution of the Stratocumulus-Topped Boundary Layer: A Large-Eddy Simulation Study

As a supplement to measurements, numerical simulation is a widely used and valuable tool in studies of the stratocumulus-topped boundary layer (STBL). However, due to limited computational resources, simulations are often run at resolutions too coarse to account for the smallest eddies involved in e.g. the entrainment process, and possibly in computational domains too small to contain the largest relevant flow structures in the boundary layer. Here we investigate how changes in domain size and spatial resolution affect key parameters such as cloud cover and liquid water path in large-eddy simulations of the STBL. We use a modified version of the 3D nonhydrostatic anelastic Eulerian-semi-Lagrangian (EULAG) model, and the performed simulations are based on measurements from the second Dynamics and Chemistry of Marine Stratocumulus (DYCOMS-II) and Physics of Stratocumulus Top (POST) field campaigns. We show how refining the horizontal resolution facilitate development of small-scale turbulence in the cloud-top region, which enhance entrainment and tends to dissolve the cloud. Refining the vertical grid spacing, on the other hand, allows for stronger vertical temperature gradients which tend to strengthen the capping inversion and inhibit entrainment. The statistics of the flow and the evolution of the cloud is found to be more sensitive to changes in resolution than to changes in domain size. We do however observe still larger flow structures as the horizontal extent of the computational domain is increased.

room 17, Pasteura 7 at 13:15

dr Josef Schroettle (Institute for Atmospheric Physics, German Aerospace Center, DLR)

Latge-Eddy Simulations of Coherent Structures in the Atmospheric Surface Layer

Abstract

room 17, Pasteura 7 at 13:15

dr Sylwester Arabas, mgr Anna Jaruga i mgr Maciej Waruszewski (IGF WF UW)

What's new in libmpdata++ (towards the 2.0 release)

Over the last three years, in the aerosol-cloud modelling team at IGFUW (group of Hanna Pawłowska) we have been developing a new free/libre and open-source C++ library: libmpdata++. The project is carried out in collaboration with Piotr Smolarkiewicz (ECMWF) and it aims at implementing the MPDATA family of numerical solvers using novel programming techniques that help to improve researchers' productivity(researchers being both the users and developers of the software).

During the seminar, we will briefly introduce the library features included in the 1.0 release of the library which accompanied publication of the library manual in the Geosci. Model Dev. journal (Jaruga et al., 2015; doi: 10.5194/gmd-8-1005-2015).

We will then report on what new features the past months of development have brought to libmpdata++. These features are aimed for the upcoming 2.0 release and include:
- higher-order operators (for DNS/iLES simulations);
- implicit treatment of absorbers (for immersed-boundary method);
- adaptive timestepping;
- distributed-memory parallelisation using MPI.

room 17, Pasteura 7 at 13:15

prof. dr hab. Wojciech Grabowski (profesor afiliowany przy Uniwersytecie Warszawskim, National Center for Atmospheric Research, Boulder, Colorado, USA)

Towards global large eddy simulation: super-parameterization revisited

This talk will present the case for a global large eddy simulation model applying the super-parameterization (SP) methodology on massively parallel computers. I proposed SP about 15 years ago to improve representation of deep convection and accompanying cloud processes in large-scale models of weather and climate. The main idea behind SP is to embed---in all columns of the large-scale model with a horizontal gridlength of the order of 100 km---copies of a two-dimensional nonhydrostatic convection-permitting small-scale model with about 1 km horizontal gridlength and periodic lateral boundary conditions, and to couple them with the outer model. This methodology can be expanded by applying a high-spatial-resolution three-dimensional SP model, essentially a large-eddy simulation model, and by embedding its copies in all columns of a large-scale model with the horizontal gridlength in the range of 10 to 50~km. The outer model will then simulate processes down to the mesoscale (e.g., organized convection) and small-scale processes (e.g., boundary layer turbulence, convective drafts) will be simulated by LES models. Although significantly more expensive than the traditional SP, the SP LES is ideally suited to take advantage of parallel computers (e.g., applying GPU technology) because of the minimal communication between LES models when each processor runs a single LES model. Additional benefits of such a methodology will be discussed, and a simple computational example will be presented.