The growth of snow bedforms

2020 ◽  
Author(s):  
Kelly Kochanski ◽  
Robert Anderson ◽  
Gregory Tucker
Keyword(s):  
High Speed ◽  
Conceptual Models ◽  
Time Lapse ◽  
Colorado Front Range ◽  
Polar Regions ◽  
Front Range ◽  
Aeolian Transport ◽  
The Past ◽  
Aeolian Geomorphology ◽  
Snow Deposition

<p>Wind-blown snow does not lie flat. It self-organizes into dunes, waves, ripples, and anvil-shaped sastrugi. These features, called snow bedforms, are high-speed analogues of sand features barchans, ripples, and yardangs. Snow bedforms appear within hours or days after a blizzard, and may migrate as fast as several meters per hour. They are widespread, and affect the albedo and thermal properties of snow across the polar regions, but thus far they have attracted little attention within aeolian geomorphology.</p><p>For the past three winters, I have documented the growth of snow bedforms in Colorado Front Range. I present time-lapse footage showing the movement of snow dunes, ripples and sastrugi (see tinyurl.com/bedform-videos). These observations show that (1) snow is only flat when winds are slower than 6.4 m/s (2) snow dunes adjust minute-by-minute to changes in wind speed, (3) the most widespread bedform, sastrugi, evolve by migrating and eroding downwind, and (4) snow waves and dunes deposit layers of cohesive snow in their wakes, and thus aid snow deposition in windy conditions. These observations provide the basis for new conceptual models of bedform evolution based on the rates of snowfall, aeolian transport, erosion, and snow sintering across the snowscape.</p>

scholarly journals The evolution of snow bedforms in the Colorado Front Range and the processes that shape them

2019 ◽  
Vol 13 (4) ◽  
pp. 1267-1281 ◽  
Author(s):  
Kelly Kochanski ◽  
Robert S. Anderson ◽  
Gregory E. Tucker
Keyword(s):  
Conceptual Models ◽  
Time Lapse ◽  
Colorado Front Range ◽  
Snow Surface ◽  
Front Range ◽  
Aeolian Transport ◽  
Complex Interactions ◽  
Barchan Dunes ◽  
First Time

Abstract. When wind blows over dry snow, the snow surface self-organizes into bedforms such as dunes, ripples, snow waves, and sastrugi. These bedforms govern the interaction between wind, heat, and the snowpack, but thus far they have attracted few scientific studies. We present the first time-lapse documentation of snow bedform movement and evolution, as part of a series of detailed observations of snow bedform movement in the Colorado Front Range. We show examples of the movement of snow ripples, snow waves, barchan dunes, snow steps, and sastrugi. We also introduce a previously undocumented bedform: the stealth dune. These observations show that (1) snow dunes accelerate minute-by-minute in response to gusts, (2) sastrugi and snow steps present steep edges to the wind and migrate downwind as those edges erode, (3) snow waves and dunes deposit layers of cohesive snow in their wake, and (4) bedforms evolve along complex cyclic trajectories. These observations provide the basis for new conceptual models of bedform evolution, based on the relative fluxes of snowfall, aeolian transport, erosion, and snow sintering across and into the surface. We find that many snow bedforms are generated by complex interactions between these processes. The prototypical example is the snow wave, in which deposition, sintering, and erosion occur in transverse stripes across the snowscape.

scholarly journals The evolution of snow bedforms in the Colorado Front Range and the processes that shape them

2019 ◽  
Author(s):  
Kelly Kochanski ◽  
Robert S. Anderson ◽  
Gregory E. Tucker
Keyword(s):  
Conceptual Models ◽  
Time Lapse ◽  
Colorado Front Range ◽  
Snow Surface ◽  
Front Range ◽  
Aeolian Transport ◽  
Complex Interactions ◽  
Barchan Dunes ◽  
First Time

Abstract. When wind blows over dry snow, the snow surface self-organizes into bedforms such as dunes, ripples, snow-waves, and sastrugi. These bedforms govern the interaction between wind, warmth, and the snowpack, but thus far they have far attracted few scientific studies. We present the first time-lapse documentation of snow bedform movement and evolution, as part of a series of detailed observations of snow bedform movement in the Colorado Front Range. We show examples of the movement of snow ripples, snow-waves, barchan dunes, snow-steps, and sastrugi. We also introduce a previously undocumented bedform: the stealth dune. These observations show that (1) snow dunes accelerate minute-by-minute in response to gusts; (2) sastrugi and snow-steps present steep edges to the wind, and move by retreating downwind; (3) snow-waves and dunes deposit layers of cohesive snow in their wakes; and (4) bedforms evolve along complex, cyclic trajectories. We use these observations to build new conceptual models of bedform evolution, based on the relative fluxes of snowfall, aeolian transport, erosion, and snow sintering across and into the surface. We find that many snow bedforms are generated by complex interactions between these processes. The prototypical example is the snow-wave, in which deposition, sintering, and erosion occur in transverse stripes across the snowscape.

scholarly journals Recent Glacial History of an Alpine Area in the Colorado Front Range, U.S.A.: II. Dating the Glacial Deposits

1968 ◽  
Vol 7 (49) ◽  
pp. 77-87 ◽  
Author(s):  
James B. Benedict
Keyword(s):  
Local Development ◽  
Colorado Front Range ◽  
Front Range ◽  
Glacial History ◽  
Glacial Deposits ◽  
Radiocarbon Dates ◽  
The Past ◽  
Rhizocarpon Geographicum ◽  
History Of ◽  
Mountain Glaciation

AbstractRecent glacial deposits in the Indian Peaks area of the Colorado Front Range have been dated lichenometricaily, using a growth curve developed locally forRhizocarpon geographicum. Radiocarbon dates, where available, tend to support the lichen chronology. Three distinct intervals of glaciation, each consisting of several minor pulsations, have occurred in the area during the past 4500 years. The earliest advance (Temple Lake Stade) is dated at 2500–700 b.c. A later advance (Arikaree Stade) began in about a.d. 100 and ended in a.d. 1000. The most recent advance (Gannett Peak Stade) is dated at a.d. 1650–1850. It remains to be seen whether the Arikaree Stade was purely a local development or whether glaciers were advancing elsewhere in the cordilleran region during this interval. Alluviation on the plains east of the Colorado Front Range seems to have occurred during the waning stages of mountain glaciation.

scholarly journals CoCoRaHS: The Evolution and Accomplishments of a Volunteer Rain Gauge Network

2016 ◽  
Vol 97 (10) ◽  
pp. 1831-1846 ◽  
Author(s):  
Henry W. Reges ◽  
Nolan Doesken ◽  
Julian Turner ◽  
Noah Newman ◽  
Antony Bergantino ◽  
...  
Keyword(s):  
Daily Precipitation ◽  
Weather Forecasting ◽  
Heavy Rain ◽  
Rain Gauge ◽  
Colorado Front Range ◽  
Front Range ◽  
The Past ◽  
Leading Role ◽  
Rain Gauge Network ◽  
Expansion Period

Abstract The Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) is a large and growing community of volunteers measuring and reporting precipitation and is making this information broadly available for the research and operational community. CoCoRaHS has evolved through several phases since its beginnings in 1998, first starting as a flood-motivated local Colorado Front Range project, then through a 5-yr nationwide expansion period (2005–09), followed by five years (2010–14) of internal growth and capacity building. As of mid-2015, CoCoRaHS volunteers have submitted over 31 million daily precipitation reports and tens of thousands of reports of hail, heavy rain, and snow, representing over 1.5 million volunteer hours. During the past 10 years, there has been wide demand for and use of CoCoRaHS data by professional and scientific users with an interest in its applicability to their different areas of focus. These range from hydrological applications and weather forecasting to agriculture, entomology, remote sensing validation, city snow removal contracting, and recreational activities, just to name a few. The high demand for CoCoRaHS data by many entities is an effective motivator for volunteer observers, who want to be assured that their efforts are needed and appreciated. Going forward, CoCoRaHS hopes to continue to play a leading role in the evolution and growth of citizen science while contributing to research and operational meteorology and hydrology.

scholarly journals Recent Glacial History of an Alpine Area in the Colorado Front Range, U.S.A.: II. Dating the Glacial Deposits

1968 ◽  
Vol 7 (49) ◽  
pp. 77-87 ◽  
Author(s):  
James B. Benedict
Keyword(s):  
Local Development ◽  
Colorado Front Range ◽  
Front Range ◽  
Glacial History ◽  
Glacial Deposits ◽  
Radiocarbon Dates ◽  
The Past ◽  
Rhizocarpon Geographicum ◽  
History Of ◽  
Mountain Glaciation

AbstractRecent glacial deposits in the Indian Peaks area of the Colorado Front Range have been dated lichenometricaily, using a growth curve developed locally for Rhizocarpon geographicum. Radiocarbon dates, where available, tend to support the lichen chronology. Three distinct intervals of glaciation, each consisting of several minor pulsations, have occurred in the area during the past 4500 years. The earliest advance (Temple Lake Stade) is dated at 2500–700 b.c. A later advance (Arikaree Stade) began in about a.d. 100 and ended in a.d. 1000. The most recent advance (Gannett Peak Stade) is dated at a.d. 1650–1850. It remains to be seen whether the Arikaree Stade was purely a local development or whether glaciers were advancing elsewhere in the cordilleran region during this interval. Alluviation on the plains east of the Colorado Front Range seems to have occurred during the waning stages of mountain glaciation.

The on-line use of histogram data for high-speed correction and alignment of electron microscope images

1984 ◽  
Vol 42 ◽  
pp. 556-557
Author(s):  
William Krakow
Keyword(s):  
Power Spectrum ◽  
High Speed ◽  
Direct Memory Access ◽  
Digital Television ◽  
Contrast Transfer Function ◽  
The Past ◽  
High Resolution Tem ◽  
On Line ◽  
Correction Of Astigmatism ◽  
The Fourier Transform

In the past few years on-line digital television frame store devices coupled to computers have been employed to attempt to measure the microscope parameters of defocus and astigmatism. The ultimate goal of such tasks is to fully adjust the operating parameters of the microscope and obtain an optimum image for viewing in terms of its information content. The initial approach to this problem, for high resolution TEM imaging, was to obtain the power spectrum from the Fourier transform of an image, find the contrast transfer function oscillation maxima, and subsequently correct the image. This technique requires a fast computer, a direct memory access device and even an array processor to accomplish these tasks on limited size arrays in a few seconds per image. It is not clear that the power spectrum could be used for more than defocus correction since the correction of astigmatism is a formidable problem of pattern recognition.

An atomic-resolution microscope study of Al contracts on GaAs

1986 ◽  
Vol 44 ◽  
pp. 726-727
Author(s):  
Z. Liliental-Weber ◽  
C. Nelson ◽  
R. Ludeke ◽  
R. Gronsky ◽  
J. Washburn
Keyword(s):  
High Speed ◽  
Schottky Contacts ◽  
Detailed Knowledge ◽  
The Past ◽  
Semiconductor Interfaces ◽  
Deposited Metal ◽  
Microwave Applications ◽  
Free Interfaces ◽  
Potential Use

The properties of metal/semiconductor interfaces have received considerable attention over the past few years, and the Al/GaAs system is of special interest because of its potential use in high-speed logic integrated optics, and microwave applications. For such materials a detailed knowledge of the geometric and electronic structure of the interface is fundamental to an understanding of the electrical properties of the contact. It is well known that the properties of Schottky contacts are established within a few atomic layers of the deposited metal. Therefore surface contamination can play a significant role. A method for fabricating contamination-free interfaces is absolutely necessary for reproducible properties, and molecularbeam epitaxy (MBE) offers such advantages for in-situ metal deposition under UHV conditions

Five-Dimensional Microscopy using Widefield-Deconvolution: Practical Considerations and Biological Applications

1996 ◽  
Vol 54 ◽  
pp. 268-269
Author(s):  
W.F. Marshall ◽  
K. Oegema ◽  
J. Nunnari ◽  
A.F. Straight ◽  
D.A. Agard ◽  
...  
Keyword(s):  
Confocal Microscopy ◽  
High Speed ◽  
Laser Scanning ◽  
Ccd Camera ◽  
Image Plane ◽  
Time Lapse ◽  
Laser Scanning Confocal Microscopy ◽  
Three Dimensions ◽  
Excitation Light ◽  
Cooled Ccd

The ability to image cells in three dimensions has brought about a revolution in biological microscopy, enabling many questions to be asked which would be inaccessible without this capability. There are currently two major methods of three dimensional microscopy: laser-scanning confocal microscopy and widefield-deconvolution microscopy. The method of widefield-deconvolution uses a cooled CCD to acquire images from a standard widefield microscope, and then computationally removes out of focus blur. Using such a scheme, it is easy to acquire time-lapse 3D images of living cells without killing them, and to do so for multiple wavelengths (using computer-controlled filter wheels). Thus, it is now not only feasible, but routine, to perform five dimensional microscopy (three spatial dimensions, plus time, plus wavelength).Widefield-deconvolution has several advantages over confocal microscopy. The two main advantages are high speed of acquisition (because there is no scanning, a single optical section is acquired at a time by using a cooled CCD camera) and the use of low excitation light levels Excitation intensity can be much lower than in a confocal microscope for three reasons: 1) longer exposures can be taken since the entire 512x512 image plane is acquired in parallel, so that dwell time is not an issue, 2) the higher quantum efficiently of a CCD detect over those typically used in confocal microscopy (although this is expected to change due to advances in confocal detector technology), and 3) because no pinhole is used to reject light, a much larger fraction of the emitted light is collected. Thus we can typically acquire images with thousands of photons per pixel using a mercury lamp, instead of a laser, for illumination. The use of low excitation light is critical for living samples, and also reduces bleaching. The high speed of widefield microscopy is also essential for time-lapse 3D microscopy, since one must acquire images quickly enough to resolve interesting events.

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