111 research outputs found
The solar wind disappearance event of 11 May 1999: source region evolution
Context. A recent, detailed study of the well-known solar wind disappearance
event of 11 May 1999 traced its origin to a coronal hole (CH) lying adjacent to
a large active region (AR), AR8525 in Carrington rotation 1949. The AR was
located at central meridian on 05 May 1999 when the flows responsible for this
event began. We examine the evolution of the AR-CH complex during 5-6 May 1999
to study the changes that apparently played a key role in causing this
disappearance event. Aims. To study the evolution of the solar source region of
the disappearance event of 11 May 1999. Methods. Using images from the Soft
X-ray Telescope (SXT), the Extreme-ultraviolet Imaging Telescope (EIT) and the
Michelson Doppler Imager (MDI) to examine the evolution of the CH and AR
complex at the source region of the disappearance event. Results. We find a
dynamic evolution taking place in the CH-AR boundary at the source region of
the disappearance event of 11 May 1999. This evolution, which is found to
reduce the area of the CH, is accompanied by the formation of new loops in EUV
images that are spatially and temporally correlated with emerging flux regions
as seen in MDI data. Conclusions. In the period leading up to the disappearance
event of 11 May 1999, our observations, during quiet solar conditions and in
the absence of CMEs, provide the first clear evidence for Sun-Earth connection
originating from an evolving AR-CH region located at central meridian. With the
exception of corotating interacting regions (CIR), these observations provide
the first link between the Sun and space weather effects at 1 AU, arising from
non-explosive solar events.Comment: The paper has recently been accepted in A&A letters and this version
is an 8 page article with 4 figure
УМЕНЬШЕНИЕ ВОЗДЕЙСТВИЯ РАДИАЦИОННОГО ФАКТОРА НА ТЕРРИТОРИЯХ С ПОВЫШЕННОЙ СТЕПЕНЬЮ РИСКА
The article is devoted to the modern problems of radioecology. The study reveals the problems of radioecological situation in some regions of the Republic of Uzbekistan. The main attention of the authors is paid to the ecologically hazardous objects in the uranium mining industry. The characteristics of wastes from uranium mining and stages of development of the mining industry are described. The historical background of the accumulation of the wastes in dumps, the ore-bearing rocks, and other off-balance ores is given. The practical experience and directions radio-ecological safety are generalized, achieving improvements of the environmental quality in areas with high risk. In conclusion, the authors recommend carrying out some measures to reduce an impact of the radiation factor on human health and to stabilize the radioecological situation at the studied regions.Статья посвящена актуальной на сегодняшний день проблеме радиоэкологии. В материалах раскрываются проблемы радиоэкологической обстановки в отдельных регионах Республики Узбекистан. Основное внимание в работе авторы акцентируют на радиационно и экологически опасных объектах урандобывающей промышленности. Выделяются и описываются характерные особенности образования отходов добычи урановых руд и этапы развития горнорудной промышленности. Приводится историческая справка накопления отходов в отвалах рудовмещающих пород и забалансовых руд и пр. Обобщаются практический опыт и направления радиоэкологической безопасности, достижения улучшения качества окружающей среды на территориях с повышенной степенью риска. В заключение авторы рекомендуют проведение мероприятий по уменьшению воздействия на организм человека радиационного фактора и стабилизации радиоэкологической системы
Magnetic Field Line Random Walk and Solar Energetic Particle Path Lengths: Stochastic Theory and PSP/ISoIS Observation
Context:In 2020 May-June, six solar energetic ion events were observed by the
Parker Solar Probe/ISoIS instrument suite at 0.35 AU from the Sun. From
standard velocity-dispersion analysis, the apparent ion path length is 0.625 AU
at the onset of each event. Aims:We develop a formalism for estimating the path
length of random-walking magnetic field lines, to explain why the apparent ion
pathlength at event onset greatly exceeds the radial distance from the Sun for
these events. Methods:We developed analytical estimates of the average increase
in pathlength of random-walking magnetic field lines, relative to the
unperturbed mean field. Monte Carlo simulations of fieldline and particle
trajectories in a model of solar wind turbulence are used to validate the
formalism and study the path lengths of particle guiding-center and
full-orbital trajectories. The formalism is implemented in a global solar wind
model, and results are compared with ion pathlengths inferred from ISoIS
observations. Results:Both a simple estimate and a rigorous theoretical
formulation are obtained for fieldlines' pathlength increase as a function of
pathlength along the large-scale field. From simulated fieldline and particle
trajectories, we find that particle guiding centers can have pathlengths
somewhat shorter than the average fieldline pathlength, while particle orbits
can have substantially larger pathlengths due to their gyromotion with a
nonzero effective pitch angle. Conclusions:The long apparent path length during
these solar energetic ion events can be explained by 1) a magnetic field line
path length increase due to the field line random walk, and 2) particle
transport about the guiding center with a nonzero effective pitch angle. Our
formalism for computing the magnetic field line path length, accounting for
turbulent fluctuations, may be useful for application to solar particle
transport in general
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
Acute viral hepatitis morbidity and mortality associated with hepatitis E virus infection: Uzbekistan surveillance data
<p>Abstract</p> <p>Background</p> <p>In Uzbekistan, routine serologic testing has not been available to differentiate etiologies of acute viral hepatitis (AVH). To determine the age groups most affected by hepatitis E virus (HEV) during documented AVH epidemics, trends in AVH-associated mortality rate (MR) per 100,000 over a 15-year period and reported incidence of AVH over a 35-year period were examined.</p> <p>Methods</p> <p>Reported AVH incidence data from 1971 to 2005 and AVH-associated mortality data from 1981 to 1995 were examined. Serologic markers for infection with hepatitis viruses A, B, D, and E were determined from a sample of hospitalized patients with AVH from an epidemic period (1987) and from a sample of pregnant women with AVH from a non-epidemic period (1992).</p> <p>Results</p> <p>Two multi-year AVH outbreaks were identified: one during 1975–1976, and one during 1985–1987. During 1985–1987, AVH-associated MRs were 12.3–17.8 per 100,000 for the general population. Highest AVH-associated MRs occurred among children in the first 3 years of life (40–190 per 100,000) and among women aged 20–29 (15–21 per 100,000). During 1988–1995 when reported AVH morbidity was much lower in the general population, AVH-associated MRs were markedly lower among these same age groups. In 1988, AVH-associated MRs were higher in rural (21 per 100,000) than in urban (8 per 100,000) populations (RR 2.6; 95% CI 1.16–5.93; p < 0.05). Serologic evidence of acute HEV infection was found in 280 of 396 (71%) patients with AVH in 1987 and 12 of 99 (12%) pregnant patients with AVH in 1992.</p> <p>Conclusion</p> <p>In the absence of the availability of confirmatory testing, inferences regarding probable hepatitis epidemic etiologies can sometimes be made using surveillance data, comparing AVH incidence with AVH-associated mortality with an eye to population-based viral hepatitis control measures. Data presented here implicate HEV as the probable etiology of high mortality observed in pregnant women and in children less than 3 years of age in Uzbekistan during 1985–1987. High mortality among pregnant women but not among children less than 3 years has been observed in previous descriptions of epidemic hepatitis E. The high mortality among younger children observed in an AVH outbreak associated with hepatitis E merits corroboration in future outbreaks.</p
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Assessing the quality of models of the ambient solar wind
In this paper we present an assessment of the status of models of the global Solar Wind in the inner heliosphere. We limit our discussion to the class of models designed to provide solar wind forecasts, excluding those designed for the purpose of testing physical processes in idealized configurations. In addition, we limit our discussion to modeling of the ‘ambient’ wind in the absence of coronal mass ejections. In this assessment we cover use of the models both in forecast mode and as tools for scientific research. We present a brief history of the development of these models, discussing the range of physical approximations in use. We discuss the limitations of the data inputs available to these models and its impact on their quality. We also discuss current model development trends
Global Retinoblastoma Presentation and Analysis by National Income Level
Importance: Early diagnosis of retinoblastoma, the most common intraocular cancer, can save both a child's life and vision. However, anecdotal evidence suggests that many children across the world are diagnosed late. To our knowledge, the clinical presentation of retinoblastoma has never been assessed on a global scale. Objectives: To report the retinoblastoma stage at diagnosis in patients across the world during a single year, to investigate associations between clinical variables and national income level, and to investigate risk factors for advanced disease at diagnosis. Design, Setting, and Participants: A total of 278 retinoblastoma treatment centers were recruited from June 2017 through December 2018 to participate in a cross-sectional analysis of treatment-naive patients with retinoblastoma who were diagnosed in 2017. Main Outcomes and Measures: Age at presentation, proportion of familial history of retinoblastoma, and tumor stage and metastasis. Results: The cohort included 4351 new patients from 153 countries; the median age at diagnosis was 30.5 (interquartile range, 18.3-45.9) months, and 1976 patients (45.4%) were female. Most patients (n = 3685 [84.7%]) were from low- A nd middle-income countries (LMICs). Globally, the most common indication for referral was leukocoria (n = 2638 [62.8%]), followed by strabismus (n = 429 [10.2%]) and proptosis (n = 309 [7.4%]). Patients from high-income countries (HICs) were diagnosed at a median age of 14.1 months, with 656 of 666 (98.5%) patients having intraocular retinoblastoma and 2 (0.3%) having metastasis. Patients from low-income countries were diagnosed at a median age of 30.5 months, with 256 of 521 (49.1%) having extraocular retinoblastoma and 94 of 498 (18.9%) having metastasis. Lower national income level was associated with older presentation age, higher proportion of locally advanced disease and distant metastasis, and smaller proportion of familial history of retinoblastoma. Advanced disease at diagnosis was more common in LMICs even after adjusting for age (odds ratio for low-income countries vs upper-middle-income countries and HICs, 17.92 [95% CI, 12.94-24.80], and for lower-middle-income countries vs upper-middle-income countries and HICs, 5.74 [95% CI, 4.30-7.68]). Conclusions and Relevance: This study is estimated to have included more than half of all new retinoblastoma cases worldwide in 2017. Children from LMICs, where the main global retinoblastoma burden lies, presented at an older age with more advanced disease and demonstrated a smaller proportion of familial history of retinoblastoma, likely because many do not reach a childbearing age. Given that retinoblastoma is curable, these data are concerning and mandate intervention at national and international levels. Further studies are needed to investigate factors, other than age at presentation, that may be associated with advanced disease in LMICs
Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics
We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) ows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several special applications in heliophysics and astrophysics, assessing triumphs, challenges,and future directions
Heliolatitude and time variations of solar wind structure from in situ measurements and interplanetary scintillation observations
The 3D structure of solar wind and its evolution in time is needed for
heliospheric modeling and interpretation of energetic neutral atoms
observations. We present a model to retrieve the solar wind structure in
heliolatitude and time using all available and complementary data sources. We
determine the heliolatitude structure of solar wind speed on a yearly time grid
over the past 1.5 solar cycles based on remote-sensing observations of
interplanetary scintillations, in situ out-of-ecliptic measurements from
Ulysses, and in situ in-ecliptic measurements from the OMNI-2 database. Since
the in situ information on the solar wind density structure out of ecliptic is
not available apart from the Ulysses data, we derive correlation formulae
between solar wind speed and density and use the information on the solar wind
speed from interplanetary scintillation observations to retrieve the 3D
structure of solar wind density. With the variations of solar wind density and
speed in time and heliolatitude available we calculate variations in solar wind
flux, dynamic pressure and charge exchange rate in the approximation of
stationary H atoms.Comment: Accepted for publication in Solar Physic
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