Using images from the Cassini spacecraft, we analyzed three ribbon waves in Saturn's 42°N eastward jet at 45°N, 42°N, and 39°N planetocentric latitudes. In this report, we demonstrate that the ...morphology, wavelength, and propagation of the ribbon waves are consistent with barotropic Rossby waves with a smaller baroclinic component. We report on the appearance and disappearance of these waves during Cassini's mission. We suggest that the temporal evolution of these waves are related to the great Saturn storm of 2010–2011.
Plain Language Summary
During their 1980 and 1981 flybys of Saturn, the Voyager spacecraft imaged a dark, sinuous line encircling the planet. This feature, dubbed the ribbon wave after its visual appearance, was embedded in an atmospheric jet stream at 42N latitude. The Cassini spacecraft also discovered waves in the 42N jet during its 2004–2017 Saturn mission. Using images taken by Cassini, we have identified the ribbon waves as Rossby waves, that is, planet‐scale waves that are common in atmospheres, including that of the Earth. Unlike Earth's atmospheric Rossby waves, which are only visible as undulations on weather maps, Saturn's ribbons are visually striking and may be some of the most prominent examples of Rossby waves in the Solar System. The ribbons are composed of a number of wavelengths, each of which is affected differently by the atmosphere and move at different speeds. By measuring the differing speed of these wavelength components, we compared the behavior of the ribbons to theoretical predictions for Rossby waves and estimated basic properties of the atmosphere. Because the ribbons likely extend deep into the atmosphere, they may help shed light on the how the atmosphere behaves at depths that Cassini was not able to observe directly.
Key Points
Cassini observed three wave‐like ribbon features in Saturn's 42N atmospheric jet from 2005 to 2014
The ribbons' morphology, mean wavelengths, and propagation are consistent with Rossby waves
Their propagation places constraints on atmospheric conditions within the jet
Angular scattering measurements of cells can provide information about the organelles within. By fitting these measurements with scattering curves modeled with Mie theory, estimates for the size ...distribution of organelles have been obtained. While this has been done for ensembles of cells, we are interested in obtaining this information at the single-cell level. However, in order to be able to study many individual cells in parallel, complex-field information is required. This is because with traditional intensity-based measurements, without the phase information, the individual cell information is lost. Field-based measurements of angular scattering is a relatively unexplored area. In this thesis we present a new field-based angular scattering microscope system. This system uses a spatial light modulator placed in a Fourier plane to apply phase shifts to the unscattered light relative to the scattered light and obtains complex-field images of a sample through phase-shifting interferometry. Unlike similar systems developed for quantitative phase imaging, this system was optimized for angular scattering, with a focus on maximizing the range of angles that could be measured. The performance of this system was characterized by measuring the scattering from polystyrene beads of known sizes between 1 and 5 microns. Size estimates were obtained that were consistent with the manufacturer’s specifications and with an uncertainty on the scale of 10s of nanometers. To better approximate the refractive index contrast found in single cells, measurements of beads in glycerol were also performed. Cell measurements involved measurements of yeast cells, macrophages, and cardiomyocytes. The scattering measurements from these cells were all above the system background and served different purposes. Yeast cells in particular served as a first test of the scattering signal strength from cells while also having scattering patterns that were similar in appearance to beads. Measurements of macrophages at different stages of antibody-dependent cellular phagocytosis were performed to demonstrate the system’s ability to detect changes in the cell’s scattering caused by the presence of phagocytosed material within. Cardiomyocyte measurements demonstrated the system’s ability to extract plausible size estimates of the organelles that were consistent with those reported for mitochondria. The limiting factor to the accuracy of these size estimates was speckle noise. Future work with this system will involve mitigating this noise source as well as time-lapse studies of cells undergoing an induced process.
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