S. K. Meilinger

Size-dependent stratospheric droplet composition in lee wave temperature fluctuations and their potential role in PSC freezing

Rapid temperature fluctuations are shown to cause liquid H2SO4/HNO3/H2O stratospheric aerosols to depart considerably from thermodynamic equilibrium. While HNO3 uptake by larger droplets is diffusively hindered, small droplets can approach the composition of a pure binary HNO3/H2O solution with up to 52 wt% HNO3, 48 wt% H2O and very small amounts of H2SO4. The stoichiometry of these droplets is close to that of nitric acid trihydrate (NAT) and freezing experiments suggest that this could be a suitable pathway for the formation of frozen polar stratospheric clouds (PSCs) of type-Ia.

On the impact of heterogeneous chemistry on ozone in the tropopause region

We examine the impact of heterogeneous chemistry involving liquid aerosol and ice particles on net ozone (O3) production rates under conditions representative of the midlatitude upper troposphere (UT) and lowermost stratosphere (LS). We demonstrate that heterogeneous effects are controlled by nitrogen oxides (NOx) and by the location of the air masses relative to the tropopause (TP). The net effect of heterogeneous chemistry is to decrease net O3 production below the TP (via heterogeneous HO2 loss) and to cause O3 destruction above the TP (via heterogeneous chlorine (Cl) activation). In the UT, gas phase chemistry due to non-methane hydrocarbons (NMHCs) can become as important for O3 chemistry as heterogeneous reactions, and removal of HO2 by particles can become more important than changes of hydrogen oxides (HOx) through heterogeneous bromine (Br) chemistry. In the humid LS, Cl activation can become sufficiently large, so that O3 depletion occurs at all conceivable values of NOx. Such cold and humid conditions occur frequently enough to reduce the average ozone production rates in the midlatitude LS by more than 10%.

HNO3 Partitioning in Cirrus Clouds

During the 1997 POLSTAR-1 winter campaign in northern Sweden a flight was performed across a cold trough of air (≃ 196 K) in the tropopause region. Measurements of total water vapour, nitric acid, particles and reactive nitrogen (NOy) were taken. The particle measurements indicate that about 3% of the particles in the moist tropospheric air were ice particles. Forward and backward facing NOy inlets were used simultaneously to determine condensed phase HNO3. The combined NOy and particle measurements reveal that less than 1% of a monolayer of NOy could have resided on the ice particles. This casts doubt on the hypothesis that sedimenting cirrus particles generally lead to a strong downward flux of NOy. In addition to the NOy measurements, independent HNO3 measurements were used to determine total HNO3. Although quantitative uncertainties do not allow to completely rule out that the NOy uptake on ice was limited by total HNO3, the combined NOy and HNO3 data suggest that there was low uptake of NOy on ice despite abundant HNO3 in the gas phase. Model studies indicate, that the most likely explanation of the measured nitric acid partitioning is given by HNO3 in ternary solution droplets coexisting with almost HNO3 free ice in the same air mass.

Non‐equilibrium compositions of liquid polar stratospheric clouds in gravity waves

On 25 January 1998 mountain induced gravity waves developed over Scandinavia leading to the formation of mesoscale polar stratospheric clouds (PSCs). Balloon-borne mass spectrometric measurements of particle composition and optical backscatter measurements were performed above Kiruna/Sweden. PSCs were encountered twice, showing a correlated increase in the condensed phase water, nitric acid and the backscatter ratio. Thermodynamic modeling allows the PSC particles to be unambiguously identified as supercooled ternary solution (STS) droplets, but cannot account for the measured scatter in the particulate HNO3∶H2O mole ratio. Simultaneous temperature measurements show that the particles were subject to rapid atmospheric temperature fluctuations of ±1 K and cooling/heating rates exceeding 1 K/min caused by the gravity waves. Micro-physical non-equilibrium modeling of STS droplet distributions reveals that the observed temperature perturbations cause particle compositions in close agreement with the measured HNO3∶H2O variations. Non-equilibrium compositions of liquid PSC particles are thus a principal stratospheric characteristic related to gravity waves affecting particle evolution.

HErZ: The German Hans-Ertel Centre for Weather Research

AbstractIn 2011, the German Federal Ministry of Transport, Building and Urban Development laid the foundation of the Hans-Ertel Centre for Weather Research [Hans-Ertel-Zentrum fur Wetterforschung (HErZ)] in order to better connect fundamental meteorological research and teaching at German universities and atmospheric research centers with the needs of the German national weather service Deutscher Wetterdienst (DWD). The concept for HErZ was developed by DWD and its scientific advisory board with input from the entire German meteorological community. It foresees core research funding of about €2,000,000 yr−1 over a 12-yr period, during which time permanent research groups must be established and DWD subjects strengthened in the university curriculum. Five priority research areas were identified: atmospheric dynamics and predictability, data assimilation, model development, climate monitoring and diagnostics, and the optimal use of information from weather forecasting and climate monitoring for the benefit ...

Perturbation of the aerosol layer by aviation-produced aerosols: A parametrization of plume processes

The perturbation of the sulfate surface area density in the tropopause region and the lower stratosphere by subsonic and supersonic aircraft fleets is examined. The background aerosol surface area, the conversion of fuel sulfur into new sulfate particles in aircraft plumes, and the plume mixing with ambient air control this perturbation. Results from an analytic expression for the surface area changes are presented which contains the dependences on these parameters and can be employed in large-scale atmospheric models.

Multi-stage evolution of single- and multi-objective MCLP: Successive placement of charging stations

Maximal covering location problems have efficiently been solved using evolutionary computation. The multi-stage placement of charging stations for electric cars is an instance of this problem which is addressed in this study. It is particularly challenging, because a final solution is constructed in multiple steps, stations cannot be relocated easily and intermediate solutions should be optimal with respect to certain objectives. This paper is an extended version of work published in Spieker et al. (Innovations in intelligent systems and applications (INISTA), 2015 international symposium on. IEEE, pp 1–7, 2015). In this work, it was shown that through problem decomposition, an incremental genetic algorithm benefits from having multiple intermediate stages. On the other hand, a decremental strategy does not profit from reduced computational complexity. We extend our previous work by including multi-objective optimization of multi-stage charging station placement, allowing us to not only optimize toward (weighted) demand location coverage, but also to include a second objective, taking into account traffic density. It is shown that the reachable part of the full Pareto front at each stage is bound by the solution that was chosen from the respective previous front. By careful choice of the selection strategy, a particular focus can be set. This can be exploited to comply with concrete implementation goals and to adjust the evolved strategy to both static and dynamic changes in requirements.

Successive evolution of charging station placement

An evolving strategy for a multi-stage placement of charging stations for electrical cars is developed. Both an incremental as well as a decremental placement decomposition are evaluated on this Maximum Covering Location Problem. We show that an incremental Genetic Algorithm benefits from problem decomposition effects of having multiple stages and shows greedy behaviour.

Size-dependent stratospheric droplet composition in rapid temperature fluctuations

Publisher Summary Rapid temperature fluctuations in the vicinity of the nitric acid trihydrate (NAT) equilibrium temperature can lead to substantial deviations of the acid concentrations from the thermodynamic equilibrium values. Stoichiometry of NAT can be reached in the smallest droplets, which possibly leads to nucleation of NAT. This size-selective NAT nucleation mechanism is in contrast to previous studies, which postulated that the largest droplets would freeze first. This new mechanism would lead to the formation of two distinct radial modes, as the few frozen particles take up HNO3 at the expense of the numerous larger droplets, which would finally revert to almost binary H2SO4/H20. Clearly, further experiments are necessary to determine whether cooling of stratospheric air in lee waves is an important pathway for the formation of frozen polar stratospheric cloud (PSC) above the frost point. Whether they freeze or not, it is clear that mesoscale temperature fluctuations can strongly influence liquid aerosol composition and size distributions. Even synoptic temperature changes influence the composition of the droplets, whereas the total volume is hardly affected.