Large, Long-Lived Convective Systems Over Subtropical South America and Their Relationships With Atmospheric Teleconnections

This study provides a climatological assessment of persistent elongated convective systems (PECS) over subtropical South America during the austral warm seasons of 1998-2007 and a comparison of PECS frequency and physical characteristics to mesoscale convective complexes (MCCs) in the region. Relationships between the Antarctic Oscillation (AAO) and El Niño – Southern Oscillation (ENSO) teleconnections and large, long-lived convective systems (LLCSs) are explored. An average of 143 PECS and 37 MCCs occurred per warm season. PECS lasted longer on average than MCCs (17 hrs. vs. 14 hrs.) and reached a greater average maximum cloud-shield extent than MCCs (297,300 km2 vs. 256,500 km2). PECS frequency was maximized over the La Plata river basin during December – February. The relative frequency of LLCS occurrence was greatest during negative AAO phases (0.906 LLCSs/day) and positive ENSO phases (28.1 LLCS/month). LLCS maximum cloud-shield extent was greatest during negative AAO phases and positive ENSO phases. LLCSs tended to be displaced southward during negative AAO phases and neutral ENSO phases. These results suggest that AAO and ENSO phases have at least some influence on LLCSs over SSA. Additionally, the high relative frequency of PECS compared to MCCs suggests they may contribute substantially to yearly precipitation totals in the region

Optimal enhanced dissipation and mixing for a time-periodic, Lipschitz velocity field on T2\mathbb{T}^2

We consider the advection-diffusion equation on $\mathbb{T}^2$ with a Lipschitz and time-periodic velocity field that alternates between two piecewise linear shear flows. We prove enhanced dissipation on the timescale $|\log \nu|$, where $\nu$ is the diffusivity parameter. This is the optimal decay rate as $\nu \to 0$ for uniformly-in-time Lipschitz velocity fields. We also establish exponential mixing for the $\nu = 0$ problem.Comment: 37 pages; 1 figur

Atmospheric triggers of the Brunt Ice Shelf calving in February 2021

The calving of Antarctic ice shelves remains unpredictable to date due to a lack of understanding of the role of the different climatic components in such events. In this study, the role of atmospheric forcing in the calving of the Brunt Ice Shelf (BIS) in February 2021 is investigated using a combination of observational and reanalysis data. The occurrence of a series of extreme cyclones around the time of the calving induced an oceanward sea surface slope of more than 0.08º leading to the calving along a pre-existing rift. The severe storms were sustained by the development of a pressure dipole on both sides of the BIS associated with a La Niña event and the positive phase of the Southern Annular Mode. Poleward advection of warm and moist low-latitude air over the BIS area just before the calving was also observed in association with atmospheric rivers accompanying the cyclones. Immediately after the calving, strong offshore winds continued and promoted the drift of the iceberg A-74 in the Weddell Sea at a speed up to 700 m day-1. This study highlights the contribution of local atmospheric conditions to ice-shelf dynamics. The link to the larger scale circulation patterns indicates that both need to be accounted for in the projections of Antarctic ice shelf evolution

Lorentz violating kinematics: Threshold theorems

Recent tentative experimental indications, and the subsequent theoretical speculations, regarding possible violations of Lorentz invariance have attracted a vast amount of attention. An important technical issue that considerably complicates detailed calculations in any such scenario, is that once one violates Lorentz invariance the analysis of thresholds in both scattering and decay processes becomes extremely subtle, with many new and naively unexpected effects. In the current article we develop several extremely general threshold theorems that depend only on the existence of some energy momentum relation E(p), eschewing even assumptions of isotropy or monotonicity. We shall argue that there are physically interesting situations where such a level of generality is called for, and that existing (partial) results in the literature make unnecessary technical assumptions. Even in this most general of settings, we show that at threshold all final state particles move with the same 3-velocity, while initial state particles must have 3-velocities parallel/anti-parallel to the final state particles. In contrast the various 3-momenta can behave in a complicated and counter-intuitive manner.Comment: V1: 32 pages, 6 figures, 3 tables. V2: 5 references adde

Greenland Ice Sheet late-season melt: investigating multi-scale drivers of K-transect events

One consequence of recent Arctic warming is an increased occurrence and longer seasonality of above-freezing air temperature episodes.There is significant disagreement in the literature concerning potential physical connectivity between high-latitude open water duration proximate to the Greenland Ice Sheet (GrIS) and unseasonal (i.e. late summer and autumn) GrIS melt events. Here, a new date of sea ice advance (DOA) product is used to determine the occurrence of Baffin Bay sea ice growth along Greenland’s west coast for the 2011–2015 period. For the unseasonal melt period preceding the DOA, northwest Atlantic Ocean and atmospheric conditions are analyzed and linked to unseasonal melt events observed at a series of on-ice automatic weather stations (AWS) along the K-transect in southwest Greenland. Mesoscale and synoptic influences on the above and below freezing surface air temperature events are assessed through analyses of AWS wind, pressure, and humidity observations. These surface observations are further compared against Modèle Atmosphérique Régional (MAR), Regional Atmospheric Climate Model (RACMO2), and ERA-Interim reanalysis fields to understand the airmass origins and (thermo)dynamic drivers of the melt events. Results suggest that the K-transect late season, ablation zone melt events are strongly affected by ridging atmospheric circulation patterns that transport warm, moist air from the sub-polar North Atlantic toward west Greenland. While thermal conduction and advection off south Baffin Bayopen waters impact coastal air temperatures, consistent with previous studies, marine air incursions from Baffin Bay onto the ice sheet are obstructed by barrier flows and the pressure gradient-driven katabatic regime along the western GrIS margin

Building Better Neighborhoods Identity Design

The City of Muncie has diverse communities with friendly people, interesting past, and outstanding cultural amenities that make it a desired place to live, do business, and to visit. Until Spring 2019, a lot of the neighborhoods in Muncie were lacking proper visual identification. A strong visual identity was needed to elevate the image of the neighborhood as well as provide a sense of pride within the residents. In partnership with Building Better Neighborhoods and Muncie Action Plan, we worked with a core group of committee members from various Muncie Neighborhoods to develop their visual identity. Check out the other neighborhood identities at the Studio 165+ website: www.studio165plus.com/bb

Industrial Byproducts as a Treatment for Bioretention Underdrain Effluent: A Benchtop Proof of Concept

Around the world, stormwater is a frequent and growing source of contamination for waterbodies. Common sources of pollution include heavy metals such as, but not limited to aluminum (Al), arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni), selenium (Se), and zinc (Zn). Nutrients such as phosphorus (P) also pose a large risk to waterbodies. Neonicotinoid pesticides are the most commonly used pesticide in the United States and are of growing concern to waterbodies, aquatic life, and non-aquatic life. Low impact development (LID) structures such as bioretention have been effective in the management of stormwater pollutants for decades. More recently, areas for improvement in bioretention have been identified and a need for additional water quality improvements has been recognized. Industrial byproducts have been suggested as an augmentation to bioretention design as a way to provide low-cost water quality improvement while giving an otherwise disposed byproduct a second and sustainable use. This study focused on using fly ash (a coal burning byproduct), steel slag (a steel smelting byproduct), and biochar (wood waste heated with little to no oxygen) in treating a complex synthetic stormwater. This proof of concept benchtop study looked at influent and effluent concentrations in flowthrough column studies for a suite of metals, phosphorus, and three selected neonicotinoids to identify which media yielded the best removal potential for the various contaminants. Columns were set up in two orientations, one vertical with constant flow and full saturation and another horizontal which included a bioretention simulation with head-driven flow which flowed into a treatment column filled with the experimental media. Results showed that aggregated fly ash and steel slag yielded a noticeably higher pH, likely from the dissolution of different -oxide species into solution. This dissolution also contributed to a noticeable increase in specific conductivity. These trends were observed for biochar as well but at noticeably lower magnitudes. In vertical columns, the small-sized fraction of steel slag proved to be the best to remove most contaminants from solution. Some exceptions existed where either the large-sized fraction of aggregated fly ash was more effective, or results were mixed. Removal is generally understood to be via sorption, however further studies would be required to confirm the mode of removal. Major cations such as Ca+2, Na+, Mg+2, and K+ were generally leached from the media with aggregated fly ash and steel slag as the most common culprits due to their high composition of these elements. Because biochar posed a lesser leaching risk and showed comparable contaminant removal to aggregated fly ash, vertical column experiments suggest biochar as the next best treatment media behind small steel slag. Horizontal column experiments had the additional condition of results being compared to the removal rates of a bioretention simulation control column. Where the control failed to treat all three neonicotinoids, P, As+5, and Na+, the experimental columns containing the media of study proved to be effective treatments. Small steel slag again showed to be the best medium to remove As+5, and P where biochar proved to yet again prevent meaningful major cation leaching and was a sink for Na and all three neonicotinoids. Depending on the contaminant of concern being treated, either biochar or small steel slag would be the standout options for bioretention effluent treatment. Further studies are recommended to confirm the mechanism by which contaminants are removed, the stability of the removed contaminants to stay out of solution, and the environmental safety of deploying these media into the real world. Modeling is also recommended to help guide future studies by predicting the state and species of contaminants in solution and their likelihood to sorb to the experimental media or precipitate as a result of treatment