64 research outputs found
Global filtered tropospheric NO2 slant column densities derived from 6-year averages of TROPOMI measurements over water for shipping signal detection
No full textThis dataset contains 6-year averages of global filtered tropospheric NO2 slant column densities (tSCDs) retrieved from the Sentinel-5 Precursor (S5P) satellite sensor TROPOMI (Tropospheric Monitoring Instrument) for the period from 1 May 2018 to 30 April 2024. All data are available on a 0.03° x 0.03° grid. The NO2 tSCDs are derived from the total slant columns by subtracting the across-track NO2 slant column stripe offset and spatially averaged stratospheric vertical column densities (VCDs) multiplied with the stratospheric air mass factor (AMF), provided in the TROPOMI NO2 product. The filtered NO2 tSCDs are developed to detect global shipping signals in the NO2 TROPOMI data. Therefore, only pixels over water are available in this dataset. The filtering methods include a high-pass filter with different box sizes (1°, 0.5°, 0.25°) and a Fourier filter. In addition, different flagging criteria are applied to the data with the standard box size of 1° for the high-pass filtering: no flagging, quality (qa) flagging, cloud fraction (CF) flagging, cloud height (CH) flagging, wind speed (wind) flagging, and sun glint (sg) flagging
Ground-based remote sensing of aerosol properties using the emission FTS in Ny-Ålesund, Spitsbergen (78°N)
No full textArctic amplification, the rapid warming of the Arctic compared to the global average, re
mains partially understood. Key processes include temperature feedback, surface albedo feedback, and cloud and water vapor feedback, with aerosols playing a critical role. Since 2019, a Fourier-Transform Infrared Spectrometer (FTS) at the AWIPEV research base in Ny-Ålesund, Spitsbergen, has been used to measure aerosol components. An algorithm based on the Line-by-Line Radiative Transfer Model and DIScrete Ordinate Radiative Transfer model (LBLDIS) was developed for retrieving aerosol composition.
In order to show this measurement technique in details, a case study for an aerosol-only
case is presented with data from the 10th of June 2020. In the aerosol-only case, the retrieval results show that sulfate (τ900cm−1=0.007 ± 0.0027) is the dominant aerosol during the whole day, followedbydust(τ900cm−1=0.0039 ± 0.0029) and black carbon (τ900cm−1=0.0017 ± 0.0007). Sea salt (τ900cm−1=0.0012 ± 0.0002), which has the weakest emission ability in the infrared waveband, shows the lowest AOD value. Such proportions of sulfate, dust and BC also show good agreement with MERRA-2 reanalysis data. Additionally, the comparison with a sun-photometer (AERONET) shows the daily variation of aerosol AOD retrieved from FTS to be similar with that of the sun-photometer. Based on this retrieval method, long time period observations dataset using FTS is retrieved and presented in this study.
Based on the observed data, the infrared radiation effects of different aerosol compo
sition are analyzed. The results show that the hygroscopic aerosols, such as sea salt and sulfate, have a warming effect in the Arctic during winter. These aerosols absorb atmospheric water vapor, leading to wet growth, increased size, and enhanced longwave downward radiation emission, defined as the Aerosol Infrared Radiation Effect (ARE). Observations of aerosols, especially their composition, are challenging during the Arctic winter. We use an emission Fourier Transform Spectrometer to measure aerosol composition. Observations show that the ARE of dry aerosols is limited to about 1.45 ±2.00 Wm−2. Wet growth significantly increases the ARE of aerosols. During winter, at relative humidity levels between 60% and 80%, wet aerosols exhibit the ARE approximately 10 times greater than dry aerosols. When relative humidity exceeds 80%, the effect can be up to 50 times higher (30- 100 Wm−2). Sea salt aerosols in Ny-Ålesund demonstrate high effect values, while non-hygroscopic aerosols like black carbon and dust show consistently low values. Reanalysis data indicates increased water vapor and sea salt aerosol optical depth in Ny-Ålesund after 2000, correlating with significant positive temperature anomalies in this area. Besides, wet aerosols can remain activated even in dry environments, continuously contributing high effects, thereby expanding the area affected by aerosol-induced warming. This warming effect may exacerbate Arctic warming, acting as a positive feedback mechanism.
Additionally, the rapid Arctic warming, which is occurring faster than in other regions,
leads to a meandering atmospheric circulation pattern. Recently, a new pathway for African dust transport to the Arctic has been identified. This study provides a detailed description of the Rapid Pathway (RP) and investigates the temporal variation of African dust influx into the Arctic via this route. Using GEOS-Chem model simulations, we demonstrate the RP’s enhanced efficiency in accelerating African dust transport to the Arctic within approximately one week, compared to other pathways. Our analysis reveals a significant shift in African dust transport routes after 2000, with a marked increase in dust transport through the central North Atlantic (RP region), particularly in March and April. ERA5 wind field data reveal significant positive anomalies in poleward winds over the North Atlantic in March and April after 2000, facilitating northward dust transport via the RP region. In contrast, negative wind anomalies over Europe suggest a diminished role for the European pathway in Arctic dust transport
Machine-Learning Based Observational Cloud Products for Process-Oriented Climate Model Evaluation
No full textThe importance of clouds in regulating the Earth’s energy balance as well as moisture and heat distributions cannot be overstated. Consequently, clouds have a considerable influence on the trajectory of anthropogenic climate change, of which possible scenarios are being studied with global climate models (GCMs). Uncertainties from the representation of clouds in GCMs have been identified as a leading cause of inter-model spread in climate projections.
Our current understanding of clouds and the processes relevant to their formation and effect on climate is informed partly by observations from remote sensing instruments aboard orbital satellites. This thesis introduces new methods of characterizing clouds from space with the help of machine learning and neural networks. The purpose of these methods is to improve the understanding of and reduce the uncertainties in climate projections by providing satellite products that are objectively interpretable and consistently comparable to GCM output.
The methods explored in this thesis highlight that machine learning and especially neural networks have the potential to improve multiple aspects of climate science. The presented results show that cloud classes can be reliably obtained from low-resolution data to improve their interpretability. They further show that comparison between climate models and observations can potentially be simplified with machine learning
On the impact of transport model errors for the estimation of CO2 surface fluxes from GOSAT observations
No full textA series of observing system simulation experiments is presented in which column averaged dry air mole fractions of CO2 (X-CO2) from the Greenhouse gases Observing SATellite (GOSAT) are made consistent or not with the transport model embedded in a flux inversion system. The GOSAT observations improve the random errors of the surface carbon budget despite the inconsistency. However, we find biases in the inferred surface CO2 budget of a few hundred MtC/a at the subcontinental scale, that are caused by differences of only a few tenths of a ppm between the simulations of the individual X-CO2 soundings. The accuracy and precision of the inverted fluxes are little sensitive to an 8-fold reduction in the data density. This issue is critical for any future satellite constellation to monitor X-CO2 and should be pragmatically addressed by explicitly accounting for transport errors in flux inversion systems. Citation: Chevallier, F., L. Feng, H. Bosch, P. I. Palmer, and P. J. Rayner (2010), On the impact of transport model errors for the estimation of CO2 surface fluxes from GOSAT observations, Geophys. Res. Lett., 37, L21803, doi:10.1029/2010GL044652.</p
Aerosols in the central Arctic cryosphere: satellite observations and model simulations during spring and summer
No full textMy doctoral thesis focuses on the variability of suspended atmospheric particles, known as aerosols, over the central Arctic cryospheric regions
Studies of the Stratospheric Nitrogen and Iodine Chemistry by Balloon-Borne DOAS Measurements and Model Calculations
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No full textThe research literature on one of the most famous literary texts of the Catalan Renaixença, the verse epic Canigó, repeatedly alludes to the symbolic and identity establishing function of the Pyrenees in the context of the development of the Catalan national consciousness in the 19th century. Unlike the interpretations of the Pyrenees motive, that are based on both the dramatic art of the plot and the context when the work was created, the contribution concentrates on analysing the linguistic-stylistic strategies of textualisation of this motive-complex. Taking into account the semantic implications of the Pyrenees-metaphoric in other works by this author, his aim is to develop superordinated categories for the rhetoric varieties of the motive and to highlight their text inherent functions
The Significance of Fast Radiative Transfer for Hyperspectral SWIR XCO2 Retrievals
No full textFast radiative transfer (RT) methods are commonplace in most algorithms which retrieve the column-averaged dry-mole fraction of carbon dioxide (XCO2) in the Earth’s atmosphere. These methods are required to keep the computational effort at a manageable level and to allow for operational processing of tens of thousands of measurements per day. Without utilizing any fast RT method, the involved computation times would be one to two orders of magnitude larger. In this study, we investigate three established methods within the same retrieval algorithm, and for the first time, analyze the impact of the fast RT method while keeping every other aspect of the algorithm the same. We perform XCO2 retrievals on measurements from the OCO-2 instrument and apply quality filters and parametric bias correction. We find that the central 50% of scene-by-scene differences in XCO2 between retrieval sets, after threshold filtering and bias correction, that use different fast RT methods, are less than 0.40 ppm for land scenes, and less than 0.11 ppm for ocean scenes. Significant regional differences larger than 0.3 ppm are observed and further studies with larger samples and regional-scale subsets need to be undertaken to fully understand the impact on applications that utilize space-based XCO2
Thrust Optimisation of an Oscillating Hydrofoil - By Non-Sinusoidal Sway and Yaw Motion
No full textPast research has shown that oscillating hydrofoils can enhance the propulsion efficiency significantly compared to traditional propellers. Dynamic stall plays an important role in the thrust generated by an oscillating hydrofoil, combining this with non-sinusoidal motion makes it an complicated phenomenon to investigate.
Genetic optimisation algorithms are employed to optimise the motion for thrust efficiency of a NACA0015 foil with a 7.5 cm chord oscillating in sway and yaw. The optimisation algorithm selects motion-parameters during model-scale experiments, and adjusts these to optimise thrust efficiency. Experiments are conducted in a circulating water tunnel (CWT) at the Norwegian University of Science and Technology (NTNU). Thrust efficiency was successfully increased compared to previous research, where traditional parametric search methods were applied.
Two different flow conditions are considered: one at low Reynolds number with a wide range of Strouhal number; and another with higher Reynolds number, and a turbulent boundary layer through turbulence stimulation. Thrust efficiency is measured to above 60 % for a wide range of thrust coefficients at: 0.02-0.6. If drag at zero angle of attack is disregarded, efficiencies above 90 % are observed for thrust coefficients below 0.2.
Previous experiments by J. Anderson, Streitlien, Barrett, and Triantafyllou (1998) were successfully repeated. Good agreement was found for many of their results, except for a few cases.
The phase between sway and yaw showed a tendency towards 75° if the Strouhal number is above 0.2, for which a reverse Von Karman vortex street is expected.
For further work, all results from the optimisation experiments are listed in the attached ".csv" file, raw-data is available on request. The data generated for the optimisation experiments is enormous. A lot can still be investigated regarding the ideal motion parameters, and how thrust and power consumption varies through one oscillation. Additionaly it would be very interesting to look for similarities between the genetic algorithm, and motions of the dorsal fin on thunniform swimmers (Dolphines, Tunas, etc.). For which the author was unable to find any literature concerning measurements of the exact sway and yaw motion
Children on the rims of a rich city : growing up in a marginalised neighbourhood of Munich
No full textWhereas childhood poverty was a very visible part of the German post-war period, the issue
soon decreased in obviousness and lost attention as the nation’s economy started to prosper
again. Yet, it is an inconvenient but persisting affair that also today children can be found on
the margins, even in the richest regions of Germany. This thesis takes the reader to Munich, a
city whose wealth shows a flip side to some of its residents: high living expenses and an outof-control housing market press children beneath poverty lines, to the societal and spatial rims
of the town. Responding to research gaps in this context, the work at hand is a qualitative study
with children as participants and a theoretical foundation in the field of Childhood Studies.
Children’s experiences, the resources available to them, as well as the challenges they encounter
in everyday life are thereby of special interest. The author spent five weeks as a guest in a day
care centre located in a disadvantaged neighbourhood of Munich, researching actively together
with girls and boys in first and second grade. Participant observation, interactive drawing and
discussing, as well as interviews with children and adults are applied to investigate this life
world. Children’s own interpretations find special recognition, but also the impact of political
and economic processes is kept in mind. The study illuminates rich social and cultural capacities
held by the boys and girls in the field. Children initiate varied peer cultures, possess
multicultural competences, and have wide social networks available. At the same time, they
meet constraints by being located outside the dominant cultures of the German mainstream.
Bourdieu’s theory of practice as well as the concept of agency help to see beyond a onedimensional understanding of childhood poverty as financial distress resulting in deprivation.
Eventually, the reader is supposed to win an understanding on how missing consideration for
children’s own notions, foreignness between different social classes, as well as structural
influences play a role in reaffirming children’s marginalised position in Munich
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