Thesis symposium 30 June 2020

13:20-14:00 Thesis talk Katherine Mesdag

Methane Emissions from the Dutch Wadden Sea

Methane concentrations in the water and the atmosphere in, and above, the Dutch Wadden Sea have never been measured before.
During this thesis project I joined two cruises to the Wadden Sea, spent two weeks at the NIOZ to see what type of measurements and analysis they do there, measured isotopic signatures in the IMAU lab and of course analysed the data. The variables I measured were water temperature, salinity, density, methane concentration, methane isotopic signatures, methane oxidation rates, methane concentrations in the sediment, methane mixing ratios in the atmosphere, the rate of methane increase in a bucket placed over the water, and methane isotopic signatures in air samples. All of this to quantify methane emissions from the Wadden Sea, to determine temporal variations in the emissions and the possibly related variables, and to investigate what causes enhanced or decreased methane emissions.
Drew your attention? Please join my talk on the 30th of June at 13:20 to hear all about my process and my results.


14:00-14:40 Thesis talk Grant Francis

Deposition of Organic compounds on Alpine Snow

Currently, little is understood about the deposition and re-volatilization of organic matter (OM) in snow. Understanding this balance for individual organic compounds has the potential to provide important information about present and past conditions in our atmosphere and biosphere. This research investigates in detail the deposition and re-volatilization rates for specific atmospheric OM that are present in alpine snow. Once their deposition and re-volatilization rates are known, OM captured in the blank canvas of surface snow can reflect the relative abundances in the atmosphere. Likewise, surface snow containing OM that is eventually preserved in glacial ice can also express relative atmospheric composition of past climates. A recent pilot study by D. Materic et al.[1] investigates the post-precipitation change of OM in snow near the Sonnblick Observatory in the Austrian Alps. Using proton transfer reaction mass spectrometry, surface snow samples taken over several days were analyzed, and any organics found were grouped by their similar dynamics. This research expands on this study by analyzing snow samples encompassing a larger spatial domain around Sonnblick over a five-day duration. Both filtered and unfiltered processing methods were used to differentiate and identify OM of different sizes that are present within each sample. This research also compares long-term atmospheric measurements leading up to and overlapping the sampling period. Analysis of these data reveals correlated dynamics of surface and atmospheric OM, and provides evidence for specific deposition and re-volatilization rates.

 [1] Materic, Dusan. et al. Jan. 30, 2019: Briefcommunication: Analysis of organic matter in surface snow by PTR-MS - implications for dry deposition dynamics in the Alps. The Cryosphere, 13, 297–307, 2019


15:00-15:40 Thesis talk Wessel Boosman

Baroclinic energy conversion as driver for Rossby wave breaking

There is very little confidence on the future of blocking events. This uncertainty is fuelled by a lack of comprehension of the importance of different processes involved. This study focuses on one of this processes, the lowering of the atmo- sphere’s center of mass in order to produce eddy kinetic energy. It is found that this process, called baroclinic energy conversion, is a self maintaining mecha- nism in a jet stream with a meridional direction. Air parcels moving through a zone where the conditions for baroclinic energy conversion are fulfilled, get accelerated within the jetstream. This may play an important process in steer- ing the jetstream in a meandering way and eventually Rossby wave breaking. Future climate predictions could favor the conditions for baroclinic energy con- version in the upper troposphere while this may not be the case in the lower troposphere due to polar amplification.


Thesis talk Irene Kruse

Characterizing cold pool interactions over land with observational data from the Netherlands

When precipitation evaporates in a sub-saturated boundary layer, it cools the air and produces dense downdrafts, which flow towards the surface and can spread horizontally as a gust front. These spreading “cold pools” (CPs) can trigger convection and thus new precipitation events due to dynamical and thermodynamical lifting mechanisms. Due to their role in the local organization of convection, CP properties are currently being studied with the use of high-resolution numerical simulations. Measurement campaigns have been conducted over the ocean to validate the models. However, fewer studies have specifically targeted cold pools over land. We use the observational network of the Netherlands (meteorological stations and radar) to study CPs developing from summer convection and their role in triggering new convective events over land. Detailed information about CP gust fronts in terms of temperature, wind speed, heat fluxes and moisture at high vertical resolution is obtained from time series, measured at the 213-meter Cabauw tower. We create an algorithm that detects the passage of a CP from the tower time series to automatize the finding of CPs from a point measurement. We further study the properties of the detected CPs in connection to the surrounding rain events with imagery from the Herwijnen Doppler radar, situated in proximity to the Cabauw tower. We expect to learn more about the CP spreading velocity and lifetime in dependence of precipitation intensity of the generating precipitation cell. This link will help gain more insight into the role of CPs in organizing convection over land.


16:20-17:00 Thesis talk Tosca Kettler

Fog forecasting in HARMONIE: a case study to current issues with the overestimation of fog in HARMONIE

A recurring issue in HARMONIE-AROME is the overestimation of the occurrence of dense fog over the Netherlands. In this thesis, the performance of Harmonie on simulating radiation fog is studied by comparison of simulated fog to observed fog at the Cabauw observatory. By evaluating the representation of physical processes related to radiation fog formation in HARMONIE-AROME, acute issues are addressed that may lead to erroneous forecasting. The main focus lies on the representation of fog in the longwave radiation scheme and its dependence on the amount of cloud condensation nuclei. After analysis of a fog case study in which the fog simulated by HARMONIE-AROME is compared to Cabauw observations, the 1D model MUSC is used to evaluate the fog evolution in more detail for testing the performance of new parametrizations. From these experiments appears that the overestimation of fog is correlated to too strong longwave cooling by the fog. Based on the outcomes of many MUSC experiments, the HARMONIE-AROME case study is rerun in experiments with adaptations based on cloud longwave emissivity (0.096 instead of 0.144), longwave cloud inhomogeneity (0.7 instead of 1) and the number of cloud condensation nuclei (10-50 cm-3 instead of 300 cm-3 over land and 100 cm-3 over sea). The results of this study show that a reduction of the longwave emissivity combined with reduced CCN leads to a large improvement in the behavior of simulated fog.

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