The Spiral Structure of the Milky Way, Cosmic Rays, and Ice Age Epochs on Earth

The short term variability of the Galactic cosmic ray flux (CRF) reaching Earth has been previously associated with variations in the global low altitude cloud cover. This CRF variability arises from changes in the solar wind strength. However, cosmic ray variability also arises intrinsically from variable activity of and motion through the Milky Way. Thus, if indeed the CRF climate connection is real, the increased CRF witnessed while crossing the spiral arms could be responsible for a larger global cloud cover and a reduced temperature, thereby facilitating the occurrences of ice ages. This picture has been recently shown to be supported by various data (Shaviv, 2001). In particular, the variable CRF recorded in Iron meteorites appears to vary synchronously with the appearance ice ages. Here we expand upon the original treatment with a more thorough analysis and more supporting evidence. In particular, we discuss the cosmic ray diffusion model which considers the motion of the Galactic spiral arms. We also elaborate on the structure and dynamics of the Milky Way's spiral arms. In particular, we bring forth new argumentation using HI observations which imply that the galactic spiral arm pattern speed appears to be that which fits the glaciation period and the cosmic-ray flux record extracted from Iron meteorites. In addition, we show that apparent peaks in the star formation rate history, as deduced by several authors, coincides with particularly icy epochs, while the long period of 1 to 2 Gyr before present, during which no glaciations are known to have occurred, coincides with a significant paucity in the past star formation rate.Comment: 33 pages, 11 figures. To Appear in New Astronom

Seasonal observations of floe-scale sea-ice deformation during MOSAiC : Scaling ice in space and time

Sea-ice dynamics is becoming increasingly essential for the modelling warming climate as the extent and thickness of the ice cover are decreasing along with increasing drift speeds and mechanical weakening. The description of the sea-ice dynamics involves an enormous variety of spatial and temporal scales from meters to the scale of the Arctic Basin and from seconds to years in the geophysical approaches. The complex coupled spatio-temporal scaling laws prohibit the commonly utilized procedures for scale linkage of ice mechanics. Currently, deformation scaling presents one of the principal open questions in sea ice dynamics for which the thesis aims to provide observational analysis. The high-resolution ship-radar imagery gathered during the MOSAiC expedition from October 2019 to September 2020 for which deformation component rates were calculated to generate a seasonal deformation time series. Current research of deformation scaling commonly relies on satellite imagery and drift buoys for which the spatial and temporal resolutions often tend to be considerably lower than for the ship-radar data. The formerly observed dominant deformation mode of shear and the strong spatial correlation of divergence and shear in the Arctic sea ice were confirmed with no signs of seasonal variation. The temporally averaged deformation variations were found to coincide with satellite derived deformation events rather poorly. A strong length scale dependence of deformation was confirmed in the ship-radar data. The spatial scaling law exponents were found to show unexpectedly high values with the behaviour of both spatial and temporal scaling law exponents disobeying the previously observed large-scale characteristics. The seasonal variation of both scaling law exponents were found to exhibit the commonly observed trends following the progression of total deformation rate. The obtained results showed unexpected values and behaviour for the deformation scaling law exponents, which was suggested to be due to the technical faults in the ship-radar data. The faults were often spatially local and lasted merely for a single time step leading to a possible increase in the localization and intermittency of the deformation rates. Additionally, the new ice conditions of the Arctic Ocean and drift route along the Transpolar Drift were suggested as a possible physical source of the unexpected results. Further studies with different methodologies were suggested for the verification and possible the dismissal of the unexpected results

Summer Atmospheric Circulation Anomalies over the Arctic Ocean and Their Influences on September Sea Ice Extent: A Cautionary Tale

Numerous studies have addressed links between summer atmospheric circulation patterns and inter-annual variability and the downward trend in total September Arctic sea ice extent. In general, low extent is favored when the preceding summer is characterized by positive sea level pressure (SLP) anomalies over the central Arctic Ocean north of Alaska. High extent is favored when low pressure dominates. If such atmospheric patterns could be predicted several months out, these links provide an avenue for improved seasonal predictability of total September extent. We analyze de-trended September extent time series (1979-2015), atmospheric reanalysis fields, ice age and motion, and AIRS data, to show that while there is merit to this summer circulation framework, it has limitations. Large departures in total September extent relative to the trend line are preceded by a wide range of summer circulation patterns. While patterns for the four years with the largest positive departures in September extent have below average SLP over the central Arctic Ocean, they differ markedly in the magnitude and location of pressure and air temperature anomalies. Differences in circulation for the four years with the largest negative departures are equally prominent. Circulation anomalies preceding Septembers with ice extent close to the trend also have a wide range of patterns. In turn, years (such as 2013 and 2014) with almost identical total September extent, were preceded by very different summer circulation patterns. September ice conditions can also be strongly shaped by events as far back as the previous winter or spring

Wave modelling - the state of the art

This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered. The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments

Evaluation of ERTS-1 data for certain hydrological uses

The author has identified the following significant results. ERTS-1 MSS data have been used in a variety of hydrologic research including snow-extent mapping; studies of snowmelt, snowmelt runoff, spectral reflectance of snow for assessing snowpack conditions, and snow albedo; lake ice formation, breakup, and migration; lake current measurements; multispectral studies of lake ice; and flood studies. MSS sensing of soil moisture over a well-vegetated test site was unsuccessfully attempted. Although a powerful research tool, ERTS-1 has very limited use as an operational system for hydrologic communities because of its 18-day revisit cycle and its lack of a quick look capability

Sublimation rates of carbon monoxide and carbon dioxide from comet nuclei at large distances from the Sun

One of the more attractive among the plausible scenarios for the major emission event recently observed on Comet Halley at a heliocentric distance of 14.3 AU is activation of a source of ejecta driven by an icy substance much more volatile than water. As prerequisite for the forthcoming detailed analysis of the imaging observations of this event, a simple model is proposed that yields the sublimation rate versus time at any location on the surface of a rotating cometary nucleus for two candidate ices: carbon monoxide and carbon dioxide. The model's variable parameters are the comet's heliocentric distance r and the Sun's instantaneous zenith angle z

RELATIONSHIPS BETWEEN ARCTIC ICE WATER FRACTION AND LOCAL 2D WIND STRESSES AT THE SURFACE OF THE CRYOSPHERE

Includes Supplementary MaterialA study of the Marginal Ice Zone (MIZ) in the Central Arctic was sponsored by the Office of Naval Research (ONR) in 2014. This experiment used clusters of buoys equipped with autonomous sensors. As the 2014 arctic season progressed, the buoy GPS locations were collected to produce estimates of local divergence of the ice field, and a resulting measurement of equivalent Open Water Fraction (eOWF). In this research, changes in eOWF within the MIZ were compared with local two-dimensional 10 m wind fields extracted from the local European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis wind products. A cross-correlation analysis between the mean field surface stresses (wind stress, divergence, and curl) and eOWF ice divergence was conducted along the buoy GPS tracks using a Lagrangian sampling method. OWF from the NASA Team Special Sensor Microwave/Imager (SSMI) satellite measurements algorithm was compared with the eOWF ice divergence calculation method. Results revealed that wind stress goes through a relaxation period of about one day prior to large eOWF changes. For convergent events starting with high eOWF, changes are seen < 24 hours after a relaxation period. A strong cross correlation between eOWF and wind stress was confirmed with mean r-values of 0.91 and 0.89 across two clusters of buoy data. Timelag between the maximum wind stress and the point of lowest wind stress when eOWF rate of change is highest is about 60 hours.Lieutenant Commander, United States NavyApproved for public release. Distribution is unlimited

Tracking icebergs with time-lapse photography and sparse optical flow, LeConte Bay, Alaska, 2016–2017

We present a workflow to track icebergs in proglacial fjords using oblique time-lapse photos and the Lucas-Kanade optical flow algorithm. We employ the workflow at LeConte Bay, Alaska, where we ran five time-lapse cameras between April 2016 and September 2017, capturing more than 400 000 photos at frame rates of 0.5–4.0 min−1. Hourly to daily average velocity fields in map coordinates illustrate dynamic currents in the bay, with dominant downfjord velocities (exceeding 0.5 m s−1 intermittently) and several eddies. Comparisons with simultaneous Acoustic Doppler Current Profiler (ADCP) measurements yield best agreement for the uppermost ADCP levels (∼ 12 m and above), in line with prevalent small icebergs that trace near-surface currents. Tracking results from multiple cameras compare favorably, although cameras with lower frame rates (0.5 min−1) tend to underestimate high flow speeds. Tests to determine requisite temporal and spatial image resolution confirm the importance of high image frame rates, while spatial resolution is of secondary importance. Application of our procedure to other fjords will be successful if iceberg concentrations are high enough and if the camera frame rates are sufficiently rapid (at least 1 min−1 for conditions similar to LeConte Bay).This work was funded by the U.S. National Science Foundation (OPP-1503910, OPP-1504288, OPP-1504521 and OPP-1504191).Ye