65 research outputs found
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Heliospheric Observations of STEREO-Directed Coronal Mass Ejections in 2008--2010: Lessons for Future Observations of Earth-Directed CMEs
We present a study of coronal mass ejections (CMEs) which impacted one of the
STEREO spacecraft between January 2008 and early 2010. We focus our study on 20
CMEs which were observed remotely by the Heliospheric Imagers (HIs) onboard the
other STEREO spacecraft up to large heliocentric distances. We compare the
predictions of the Fixed-Phi and Harmonic Mean (HM) fitting methods, which only
differ by the assumed geometry of the CME. It is possible to use these
techniques to determine from remote-sensing observations the CME direction of
propagation, arrival time and final speed which are compared to in situ
measurements. We find evidence that for large viewing angles, the HM fitting
method predicts the CME direction better. However, this may be due to the fact
that only wide CMEs can be successfully observed when the CME propagates more
than 100 deg from the observing spacecraft. Overall eight CMEs, originating
from behind the limb as seen by one of the STEREO spacecraft can be tracked and
their arrival time at the other STEREO spacecraft can be successfully
predicted. This includes CMEs, such as the events on 4 December 2009 and 9
April 2010, which were viewed 130 deg away from their direction of propagation.
Therefore, we predict that some Earth-directed CMEs will be observed by the HIs
until early 2013, when the separation between Earth and one of the STEREO
spacecraft will be similar to the separation of the two STEREO spacecraft in
2009--2010.Comment: 21 pages, accepted to Solar Physic
Coronal Field Opens at Lower Height During the Solar Cycles 22 and 23 Minimum Periods: IMF Comparison Suggests the Source Surface Should Be Lowered
Powerscapes
Thesis (M. Arch.)--Massachusetts Institute of Technology, Dept. of Architecture, 2012.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 149-151).In 2050, global oil supply will decline to 1/8 of today's. Migrating to the Post-Oil Era, over 10000's km2 of Powerscapes - the solar-collecting infrastructure - will be gradually constructed across the arid desert, for the indispensable production of solar energy to sustain Middle East's economy and global energy supply. The contingency of introducing the Powerscapes is a spatial problem. Unlike a powerplant that burns coal or oil, the scale of the Powerscapes is dramatically extensive. The inserted Powerscapes will interiorize the desert landscape and shelter the ground from the harsh direct sunlight that will be captured for power supply. Transformation in biological development, meteorological activity and geological phenomena will be inevitable, but the change that reduces the heat and evaporation rate will make its climatatic dynamics more habitable for human, animals and plants - an invaluable opportunity for the synthesis of energy production and climate conditioning. This thesis investigates the strategic programming and spatial configuration of such constructed landscape, capitalized by its new temporal characteristics, and sensitively adapting to it. Layers of material will be organized to form "Strata" of temporal conditions to be stretched across the landscape. To forge a symbiotic relationship between Solar Collection, human habitation, agricultural production and wild nature, the layers of material will delineate, push, flip, intersect, puncuate, wrap and merge, responding to programmatic needs and geographical dynamics that the natural geology and the Powerscapes together create. Such adaptive organization also permits certain geometrical and configuration logic to reiterate themselves in multiple scales, formulating a fractalic field with recursive part to whole relationships.by Chun Lun Otto Ng.M.Arch
The Physical Processes of CME/ICME Evolution
As observed in Thomson-scattered white light, coronal mass ejections (CMEs) are manifest as large-scale expulsions of plasma magnetically driven from the corona in the most energetic eruptions from the Sun. It remains a tantalizing mystery as to how these erupting magnetic fields evolve to form the complex structures we observe in the solar wind at Earth. Here, we strive to provide a fresh perspective on the post-eruption and interplanetary evolution of CMEs, focusing on the physical processes that define the many complex interactions of the ejected plasma with its surroundings as it departs the corona and propagates through the heliosphere. We summarize the ways CMEs and their interplanetary CMEs (ICMEs) are rotated, reconfigured, deformed, deflected, decelerated and disguised during their journey through the solar wind. This study then leads to consideration of how structures originating in coronal eruptions can be connected to their far removed interplanetary counterparts. Given that ICMEs are the drivers of most geomagnetic storms (and the sole driver of extreme storms), this work provides a guide to the processes that must be considered in making space weather forecasts from remote observations of the corona.Peer reviewe
The Cholecystectomy As A Day Case (CAAD) Score: A Validated Score of Preoperative Predictors of Successful Day-Case Cholecystectomy Using the CholeS Data Set
Background
Day-case surgery is associated with significant patient and cost benefits. However, only 43% of cholecystectomy patients are discharged home the same day. One hypothesis is day-case cholecystectomy rates, defined as patients discharged the same day as their operation, may be improved by better assessment of patients using standard preoperative variables.
Methods
Data were extracted from a prospectively collected data set of cholecystectomy patients from 166 UK and Irish hospitals (CholeS). Cholecystectomies performed as elective procedures were divided into main (75%) and validation (25%) data sets. Preoperative predictors were identified, and a risk score of failed day case was devised using multivariate logistic regression. Receiver operating curve analysis was used to validate the score in the validation data set.
Results
Of the 7426 elective cholecystectomies performed, 49% of these were discharged home the same day. Same-day discharge following cholecystectomy was less likely with older patients (OR 0.18, 95% CI 0.15–0.23), higher ASA scores (OR 0.19, 95% CI 0.15–0.23), complicated cholelithiasis (OR 0.38, 95% CI 0.31 to 0.48), male gender (OR 0.66, 95% CI 0.58–0.74), previous acute gallstone-related admissions (OR 0.54, 95% CI 0.48–0.60) and preoperative endoscopic intervention (OR 0.40, 95% CI 0.34–0.47). The CAAD score was developed using these variables. When applied to the validation subgroup, a CAAD score of ≤5 was associated with 80.8% successful day-case cholecystectomy compared with 19.2% associated with a CAAD score >5 (p < 0.001).
Conclusions
The CAAD score which utilises data readily available from clinic letters and electronic sources can predict same-day discharges following cholecystectomy
Overview of recent physics results from the National Spherical Torus Experiment (NSTX)
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