Faculty of Physics University of Warsaw > Events > Seminars > Atmospheric Physics Seminar

Atmospheric Physics Seminar

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room B0.14, Pasteura 5 at 13:15

mgr Dongxiang Wang (IGF UW)

Aerosol and cloud properties from synergy of lidar, radar and radiometer measuremnets

The EMORAL lidar (UW), the BASTA cloud radar (LATMOS), and the HATPRO-G2 microwave radiometer (INOE) observations were conducted jointly over the PolWET peatland site in Rzecin (PULS) during the POLIMOS field campaigns (ESA).The EMORAL lidar measures in 8 channels: elastic (355/532/1064 nm), inelastic Raman (387 and 607 nm for N2, and 408 nm for H2O) and elastic cross-polarized (355 and 532 nm), with 3.75 m vertical resolution and adjustable temporal resolution (2s to 10 min). A 95-GHz Doppler cloud radar called the Bistatic Radar System for Atmospheric Studies (BASTA) uses a frequency–modulated continuous wave (FMCW) technique. The main products are reflectivity and Doppler velocity, obtained with 12.5 m, 25 m and 100 m vertical resolution and 3 s time resolution. The HATPRO-G2 microwave radiometer consists of two working bands at 22–31 and 51–58 GHz, each with seven channels. Measurements with a temporal resolution of 15 s and a height-dependent vertical resolution provide integrated water vapor, liquid water path and vertical profiles of relative humidity and temperature.During my talk the POLIMOS campaigns and the instruments will be introduced. Then I will focus on the algorithms for aerosol and cloud classification and the synergetic data products. All will be demonstrated on a case study basis.

room B0.14, Pasteura 5 at 13:15

mgr Dominika Szczepanik (IGF UW)

Lidar measurements at the EARLINET site in Warsaw in view of ACTRIS QA & QC recommendations

The PollyXT-type lidar at the Remote Sensing Laboratory provides unique data for the EARLINET/ACTRIS Data Base. Specifically, the delivered profiles are evaluated for both day and nighttime solely with the classical Raman retrieval. Moreover, those profiles comprise complete sets of wavelength-dependent particle backscatter and extinction coefficients and depolarization ratios (3β+2α+2δ), all averaged with the same temporal and height resolution and smoothing. The number of data files provided form July 2013 to December 2018 is impressive being of 1348 high-resolution, so-called, b-files and 851 low-resolution e-files.Firstly, a short description of the EARLINET/ACTRIS Data Base will be given, including discussion of the quality assurance procedures and quality control tests, the uniqueness of the climatology category measurements and the rules of providing the profiles to the database. Then, the seminar will be focused on the Warsaw RS-Lab data and evaluation chain, uncertainty estimation, as well as the results of the international lidar intercomparison campaign which took place in June 2018. Finally, the average Warsaw profiles derived over the different categories in the EARLINET/ACTRIS Data Base will be discussed.

room B0.14, Pasteura 5 at 13:15

Konstantina Nakoudi (Alfred Wegener Institute, Potsdam, Germany)

Aerosol investigation in the Arctic by means of Lidar remote sensing

As anthropogenic climate change drives major changes in the Arctic environment, the loss of sea ice is resulting in significant changes in both natural and anthropogenic Arctic aerosol. Aerosol can have significant impact on Arctic climate through aerosol-cloud and aerosol-radiation interactions.However,aerosol still entail high uncertainty in the estimation of their radiative forcing, especially in the Arctic region. Thus, a better understanding of the aerosol-related feedbacks is crucial especially in the rapidly changing Arctic environment, where near-surface temperature increase is higher compared to mid-latitudes (Arctic Amplification). The Arctic atmosphere is characterized by high aerosol load during spring due to intensified advection of air-masses from mid-latitudes (Arctic Haze season). Recently, persistent air-masses from North East Asia, have been identified over different regions of the European Arctic by the synergy of ground-based and air-borne Lidar systems. The retrieved optical properties revealed relatively small particles of spherical shape, with Lidar Ratios indicating aged biomass burning particles. The derived aerosol properties were utilized to estimate the aerosol radiative impact. In my talk I will present insights from this aerosol transport event and discuss its impact on the local radiative budget. This work has been conducted within the frame of my PhD project in the Alfred Wegener Institute for Polar and Marine Research.

room B0.14, Pasteura 5 at 13:15

dr Stanisław Gepner (Warsaw University of Technology, MEiL)

Various instabilities and chaotic mixing in channel flows

Improvements in the performance of various flow-based devices, such oxygenators or DNA microarrays can be reduced to decreasing hydraulic drag and increasing achievable mixing efficiency. In case of fluids, mixing can be seen as an inter-material transport process (such as diffusion) overlaid on top of “mechanical” stirring that results from kinematics of the flow. Since, in general diffusion is relatively slow, the role of stirring is to cause generation of small-scale structures that can be quickly smoothed out by diffusion. This can be efficiently achieved via turbulization. Still, there are a few problems for which this is unfeasible, either due to size constraints or fragile nature of processed materials. In case of laminar flows effective stirring can be achieved by principles of chaotic advection. Chaotic advection is a phenomenon in which fully laminar, relatively simple velocity fields (in the Eulerian representation) result in chaotic response in the Lagrangian view. High complexity of motion, in case of such flows, results from the fact that dynamical system that describes motion of individual fluid particles might be non-integrable leading to the onset of chaotic trajectories and in consequence improved stirring. The objective of this work is to study the onset of chaotic advection due to amplification of naturally occurring hydrodynamic instabilities resulting from large-scale wall corrugations. At the same time, we plan to examine and quantify possible improvements of mixing due to chaotic character of advection.

room B0.14, Pasteura 5 at 13:15

prof. dr hab. Wojciech Grabowski (National Center for Atmospheric Research, Boulder, CO)

Modeling condensation inside Pi Chamber with Eulerian bin and Lagrangian particle-based microphysics schemes

An idealized simulation setup is developed motivated by laboratory experiments with the Pi Chamber and previous model simulations of the Pi Chamber dynamics and microphysics. Pi Chamber experiments consider interaction between turbulence, CCN activation, and cloud droplet growth in moist Rayleigh-Bénard convection driven by the temperature and moisture difference between homogeneous horizontal boundaries. The focus here is on comparison of simulations applying traditional Eulerian bin microphysics scheme with simulation using a novel particle-based Lagrangian approach to simulate CCN activation and droplet growth. The Eulerian bin microphysics solve the evolution equation for the spectral density function, whereas Lagrangian approach follows evolution in time and space of computational particles referred to as super-droplets. Each super-droplet represents a multiplicity of natural droplets that makes the Lagrangian approach computationally feasible.The two schemes apply identical representation of CCN activation and use the same droplet growth equation; these make the direct comparison between the two schemes practical. Steady-state droplet spectra averaged over the entire chamber are similar, with the mean droplet concentration, mean radius and spectral width close in Eulerian and Lagrangian simulations. The differences are explained by the inherent differences between the two schemes and their numerical implementation. However, as one might expect, the local droplet spectra differ substantially, again in agreement with the inherent limitations of the theoretical foundation behind each approach. Comparison between simulations, laboratory experiments, and previous theoretical studies of droplet growth in the turbulent environment will be discussed.

room B0.14, Pasteura 5 at 13:15

dr Dennis Niedermeier (Leibniz Institute for Tropospheric Research, Leipzig, Germany)

LACIS-T - A moist air wind tunnel for investigating the interactions between turbulence and cloud microphysics

The interactions between turbulence and cloud microphysical processes have been investigated primarily through numerical simulation and field measurements over the last ten years. However, only in the laboratory we can be confident in our knowledge of initial and boundary conditions, and are able to measure under statistically stationary and repeatable conditions. In this talk, a unique turbulent moist-air wind tunnel will be presented, called the Turbulent Leipzig Aerosol Cloud Interaction Simulator (LACIS-T) which has been developed in order to study cloud physical processes in general and interactions between turbulence and cloud microphysical processes in particular. Investigations take place under well-defined and reproducible turbulent and thermodynamic conditions covering the temperature range of warm, mixed-phase and cold clouds (25°C > T > -40°C). The continuous-flow design of the facility allows for the investigation of processes occurring on small time (up to a few seconds) and spatial scales (micrometer to meter scale) and with a Lagrangian perspective. The experimental studies using LACIS-T are accompanied and complemented by Computational Fluid Dynamics (CFD) simulations which are helpful to design experiments as well as to interpret experimental results.In this talk, I will present the fundamental operating principle of LACIS-T, the numerical model as well as results concerning the thermodynamic and flow conditions prevailing inside the wind tunnel combining both characterization measurements and numerical simulations. Finally, results are depicted from deliquescence/hygroscopic growth as well as droplet activation and growth experiments.

room B0.14, Pasteura 5 at 13:15

Prof. Timo Vesala (Institute for Atmospheric and Earth System Research Physics, Faculty of Science, University of Helsinki, Finland)

Forest harvesting and climate and a public discourse

We have participated in several acts of writings, public discourses and seminars concerning the effects of forest utilization on climate and biodiversity (e.g. EASAC 2017; EURACTIV 2017a, b). Writings include, among other things, long reports (multiple authors), newspaper columns and public letters (multiple authors). Finland is planning to increase substantially harvesting of timber, which leads, in the short-term (by mid 2000 century), increased carbon dioxide emissions into the atmosphere. Based on best available scientific understanding, these communications and writings have criticized these plans, which eventually lead to situation where the forest management actions in Finland are against the targets set by the Paris Climate Agreement and endanger the present level of biodiversity.The core of the criticism has been in the planned massive intensification of forest use as bioenergy, leading to increased harvests in the expense of carbon storage and sinks, and possibly even harvesting previously economically non-profitable stands with the help of government subsidies. This view has been based on the proposed carbon neutrality of forest biomass, however it is not accounting for e.g. the poor energy content of forest biomass in comparison to other energy sources, nor the climate relevant emissions from forest harvesting which last for decades after clear-cut. Therefore, the climate neutrality of forest-based bioenergy can be questioned.The comments and feedback we have obtained have varied greatly, depending on the perspective of the commenting persons and organisations. The discussion fora for replies have ranged from social media to newspaper articles and policy debates in scientific arena. On the one hand, we have been acknowledged for participating in the important socio-economic debate, for bringing the scientific arguments to the discussion and for clarifying the complex problem, where the terms and concepts are sometimes presented very vaguely. On the other hand, we have been accused for, e.g., being extremely narrow-minded and biased, for forgetting the economic realities and being unpatriotic, in addition to presenting dangerous things towards Finland and the finnish pulp and paper industry. Our statements are blamed to be post-truth politics and representing green left values without scientific facts.In this presentation we aim at clarifying the background of this public dialogue and argue that a scientists’ responsibility is to participate also in public debates that concern the research field (s)he is working with. Scientists are often in a position where they are able to provide strong scientific argumentation on the climate change questions, and thus effectively contribute to the policy-relevant dialogue. ReferencesEASAC (2017) Multi-functionality and sustainability in the European Union’s forests. EASAC policy report 32, April 2017. ISBN: 978-3-8047-3728-0Euractiv (2017a) Science-based forest policies urgently needed for effective climate action. www.euractiv.com/section/climate-environment/opinion/science-based-forest-policies-urgently-needed-for-effective-climate-action/ Euractiv (2017b) EU’s climate credibility is at risk under forest accounting rules. www.euractiv.com/section/climate-environment/opinion/forest-accounting-rules-put-eus-climate-credibility-at-risk/