A document by Benjamin Rodenkirch. Click on the document to view its contents.

Below the equator, the preeminent tourist attraction in the late nineteenth century was the White Terraces of Lake Rotomahana in New Zealand.

A document by Zechao Zhuo. Click on the document to view its contents.

A document by Niklas Grimmich. Click on the document to view its contents.

A document by Grzegorz Kwiatek. Click on the document to view its contents.

Hamiltonian Monte Carlo (HMC) is known to be highly efficient when sampling high-dimensional parameter spaces. This high efficiency can be attributed to Hamilton’s equations, which guide the sampling of the model space. In the case of weakly non-linear problems, this efficiency can be increased even further by linearizing the forward problem. In this study, we exploit this for the purpose of estimating source parameters of a 3.4 magnitude induced event that originated in the Groningen gas field in 2019. In total, we estimate ten earthquake parameters: centroid (three coordinate components), moment tensor (six elements), and origin time. We demonstrate that, in the absence of a sufficiently accurate centroid prior, the linearization of the forward model necessitates multiple initial centroid priors. Here, we consider two sets of initial centroid priors. The first set is based on the known fault geometry in the Groningen reservoir, whereas the second set is obtained by placing initial centroid priors on a uniform horizontal grid at a depth of 3 km (the approximate depth of the gas reservoir). In general, the results from both sets are in good agreement with each other. Most important, however, is their agreement with the geological knowledge of the area: the posterior peaks for model vectors containing a centroid near a major fault and a moment tensor that corresponds to normal faulting along a plane which has a strike almost coinciding with the strike of that major fault.

Sand dunes are ubiquitous in nature, and are found in abundance on Earth and other planetary environments. One of the most common types are crescent-shaped dunes known as barchans, whose mid-line could be assumed to behave as 2D dunes. In this work, we (i) compare the morphology of the mid-line of 3D barchans with 2D dunes; and (ii) track the evolution of 3D barchan and 2D dunes under bi-modal changes in the flow direction. We performed experiments in a 2D flume on 2D dunes and Euler-Lagrange simulations of 3D bedforms. The reversal experiments start with an initial heap deforming into a steady-state dune, which is then perturbed by reversing the flow, resulting in an inverted dune. We show that during the reversal the grains on the lee side immediately climb back onto the dune while its internal part and toe remain static, forming a new lee face on the previous stoss slope of varying angle. We determine that (i) the characteristic time for the development of 2D dunes scales identically with that for 3D barchans, (ii) that the time for dune reversal is twice the time necessary to develop an initial heap to steady-state, and (iii) that a considerable part of grains remain static during the entire process. Our findings reveal the mechanisms for dune reversal, and highlight that numerical computations of 2D barchans, which are more feasible in geophysical scales, predict realistic outcomes for the relevant time-scales.

Low-gradient coastal watersheds are susceptible to flooding caused by various flows such as rainfall-runoff, astronomical tides, storm surges, and riverine flows. Compound flooding occurs when at least one coastal flood driver occurs simultaneously or in close succession with a pluvial and/or fluvial flood driver, such as during a tropical cyclone event. This study presents a one-dimensional (1-D), reduced-order physics compound inundation model tested over an idealized coastal watershed transect under various forcing conditions (e.g., storm surge, astronomical tides, and rainfall) that varied in magnitude, time, and space. This study aims to evaluate each flooding mechanism and the associated hydrodynamic responses to identify generalized coastal transition zones and enhance the production of flood maps for varying regions in a coastal watershed. Compound inundation levels are affected by the magnitude and timing of each flooding mechanism. The desire is a more holistic compound inundation model that can be a critical tool for decision-makers, stakeholders, and authorities who provide evacuation planning to save human lives and enhance resilience.

A document by Yan-Ning Kuo. Click on the document to view its contents.

Climate feedbacks are vital in shaping the extent of global warming. While directly observing climate feedbacks is hardly feasible, it is possible to establish a relationship between them and top-of-the-atmosphere flux changes in response to natural fluctuations in surface temperature. In this study, we explore this method to potentially constrain climate feedbacks in climate models using observations. Our findings reveal significant correlations for longwave and shortwave feedbacks within a period of 14 years. This allows for utilizing satellite observations and reanalysis to show that models exhibiting moderate negative longwave and moderate positive shortwave internal variability feedbacks demonstrate better consistency with observations. The emergence of the relationship for the net feedback requires a longer time, about 60 years. Continuous satellite records need to be maintained minimum until the mid-2040s before estimates of observed net internal variability feedback can be used to constrain net forced climate feedback, and thereby climate sensitivity.

The slow water renewal endows the Baltic Sea a strong retention of pollutants/nutrients. Constraining water age is a practical way to depict the transport pathways/timescales for water masses and accompanying soluble substances. Although the water ages in the Baltic Sea have been resolved by 3D ocean models 20 year ago, the simulated results have not been verified. In this work, we exploited two anthropogenic radionuclides (129I and 236U) as an age marker to constrain the ages of inflowing North Sea saline waters into the Baltic Sea. Our results indicate that the Baltic Sea has a highly stratified structure with distinctly different timescales for surface-water and deep-water circulations (3{plus minus}2 and 20 {plus minus} 3 years, respectively), providing the first observation-based proof for the multi-decadal retention of (radioactive) pollutants within the Baltic Sea. This work demonstrates the power of anthropogenic radiotracers in investigating hydrodynamic processes in the Northwestern European coastal areas.

A document by Xiaoran Dong. Click on the document to view its contents.

A document by Lubor Ostrihansky. Click on the document to view its contents.

Mohan [email protected]

We investigated whether hydrologic restoration at Sturgeon Lake, Oregon, USA has sufficiently increased water flux and reduced stagnation, improving environmental conditions for juvenile salmon and waterfowl. This 19.2km2 lake is a pivotal environmental feature in the area, providing a haven for salmon on the Columbia River before reaching the Pacific Ocean and winter habitat for hundreds of thousands of waterfowl and migratory birds on the Pacific Flyway. The Oregon Conservation Strategy names restoring natural hydrology to Sturgeon Lake as a key step toward conservation in this area. We use stable isotopes of water from the lake, surrounding water bodies, and precipitation to understand the restoration work’s efficacy and whether further efforts are necessary to restore healthy habitats. Because of its importance to bird migration and salmon spawning, we focus on seasonal patterns in lake hydrology. We determined that approximately 36.5% and 9.5% of water input was lost to evaporation during the summer and winter, respectively, after restoration. We estimate the residence time of water in the lake to average ~43.2 days during the study period. Based on these results, we determined that the lake habitat is being adequately maintained in the winter, when it is most valuable to local fauna, but that some stagnation and potential ecosystem degradation occurs in the summer. Neither juvenile salmonids nor migratory birds utilize the lake during the summer, therefore the restoration work is effective at maintaining habitat for these species, but further summer-focused work could be beneficial.

Dust emissions related to anthropogenic activities (i.e., anthropogenic dust (AD)) is not represented in most global climate models and its radiative impact remains unassessed. In this study, we develop a new and physically based method to parameterize AD emission based on the DOE’s Energy Exascale Earth System Model version 1 (E3SMv1). This method relates AD emission to the crop land use fraction in the E3SMv1 land component. Major AD sources simulated by our parameterization include those over Central America, the Sahel, North India, and North China. The annual averaged AD emission is 567 Tg yr-1 in present-day (year 2000), which contributes to 13.3 % of total dust emission. Model evaluation against satellite and ground-based observations shows that the new parameterization can represent AD emissions and global dust cycle reasonably well. We find that the total dust emission increases by 13 % (495 Tg yr-1) from 1850 to 2000 mainly due to the cropland land use fraction changes, which induces a net dust direct effective radiative forcing of -0.041 W m-2 at top of the atmosphere. This AD-induced cooling exceeds 10% of the total anthropogenic aerosol direct effective radiative forcing from 1750 to 2014 estimated by the Intergovernmental Panel on Climate Change Sixth Assessment Report. Our findings indicate an important role of AD in the regional and global climate changes, which should be included in future climate change assessments.

A document by Aida D. Arik. Click on the document to view its contents.

A document by Karl Mitchell. Click on the document to view its contents.