Electromagnetic ion cyclotron (EMIC) waves are an important mechanism for particle energization and losses inside the magnetosphere. In order to better understand the effects of these waves on ...particle dynamics, detailed information about the occurrence rate, wave power, ellipticity, normal angle, energy propagation angle distributions, and local plasma parameters are required. Previous statistical studies have used in situ observations to investigate the distribution of these parameters in the magnetic local time versus L‐shell (MLT‐L) frame within a limited magnetic latitude (MLAT) range. In this study, we present a statistical analysis of EMIC wave properties using 10 years (2001–2010) of data from Cluster, totaling 25,431 min of wave activity. Due to the polar orbit of Cluster, we are able to investigate EMIC waves at all MLATs and MLTs. This allows us to further investigate the MLAT dependence of various wave properties inside different MLT sectors and further explore the effects of Shabansky orbits on EMIC wave generation and propagation. The statistical analysis is presented in two papers. This paper focuses on the wave occurrence distribution as well as the distribution of wave properties. The companion paper focuses on local plasma parameters during wave observations as well as wave generation proxies.
Key Points
A statistical study of EMIC waves is conducted over all MLATs and MLTs
Off‐equator peaks in wave occurrence are observed in the outer magnetosphere
Wave ellipticity, normal angle, propagation angle, and wave power are also investigated
Background.
To investigate the association between hearing loss and cognitive function in a nationally representative sample of older adults.
Methods.
We analyzed data from the 1999 to 2002 cycles of ...the National Health and Nutritional Examination Survey during which participants aged 60-69 years (n = 605) underwent both audiometric and cognitive testing. Hearing loss was defined by a pure tone average of hearing thresholds at 0.5, 1, 2, and 4 kHz in the better hearing ear. Cognitive testing consisted of the Digit Symbol Substitution Test (DSST), a nonverbal test that assesses executive function and psychomotor processing. Data on hearing aid use, demographics, and medical history were obtained from interviews. Regression models were used to examine the association between hearing loss and cognition while adjusting for confounders. Analyses incorporated sampling weights to yield results that are generalizable to the U.S. population.
Results.
Greater hearing loss was significantly associated with lower scores on the DSST after adjustment for demographic factors and medical history (DSST score difference of −1.5 95% confidence interval: −2.9 to −0.23 per 10 dB of hearing loss). Hearing aid use was positively associated with cognitive functioning (DSST score difference of 7.4 95% confidence interval: −0.62 to 15.4). The reduction in cognitive performance associated with a 25 dB hearing loss was equivalent to the reduction associated with an age difference of 7 years.
Conclusions.
Hearing loss is independently associated with lower scores on the DSST. Further research is needed to determine whether hearing loss is a modifiable risk factor or an early marker of cognitive decline.
To estimate the age- and severity-specific prevalence of hearing impairment in the United States.
We conducted cross-sectional analyses of 2001 through 2010 data from the National Health and ...Nutrition Examination Survey on 9648 individuals aged 12 years or older. Hearing loss was defined as mild (> 25 dB through 40 dB), moderate (> 40 dB through 60 dB), severe (> 60 dB through 80 dB), or profound (> 80 dB).
An estimated 25.4 million, 10.7 million, 1.8 million, and 0.4 million US residents aged 12 years or older, respectively, have mild, moderate, severe, and profound better-ear hearing loss. Older individuals displayed a higher prevalence of hearing loss and more severe levels of loss. Across most ages, the prevalence was higher among Hispanic and non-Hispanic Whites than among non-Hispanic Blacks and was higher among men than women.
Hearing loss directly affects 23% of Americans aged 12 years or older. The majority of these individuals have mild hearing loss; however, moderate loss is more prevalent than mild loss among individuals aged 80 years or older.
Our estimates can inform national public health initiatives on hearing loss and help guide policy recommendations currently being discussed at the Institute of Medicine and the White House.
To determine if age-related hearing loss is associated with social isolation and whether factors such as age, gender, income, race, or hearing aid use moderated the association.
Cross-sectional.
...Randomly sampled United States communities.
Cross-sectional data on adults 60 to 84 years old from the 1999 to 2006 cycles of the National Health and Nutrition Examination Survey were analyzed. The dependent variable was social isolation, which was defined using the social isolation score (SIS), a 4-point composite index consisting of items pertaining to strength of social network and support. SIS scores ≥2 were considered indicative of social isolation. The independent (predictor) variable was the pure tone average of speech frequency (0.5-4 kHz) hearing thresholds in the better-hearing ear. Covariates included potential medical, demographic, and otologic confounders. We used multivariate logistic regression to evaluate the association between hearing loss and the odds of having social isolation. An exploratory analysis was performed to assess the strength of associations between hearing loss and individual items of the SIS scale.
Greater hearing loss was associated with increased odds of social isolation in women aged 60 to 69 years (odds ratio OR, 3.49 per 25-dB of hearing loss; 95% confidence interval, 1.91, 6.39; P < .001). Effect modification by gender was significant in this age group (P = .003). Hearing loss was not significantly associated with social isolation in other age and gender groups.
Greater hearing loss is associated with increased odds of being social isolated in a nationally representative sample of women aged 60 to 69 years.
Hearing loss has been associated with cognitive and functional decline in older adults and may be amenable to rehabilitative interventions, but national estimates of hearing loss prevalence and ...hearing aid use in older adults are unavailable.
We analyzed data from the 2005-2006 cycle of the National Health and Nutritional Examination Survey, which is the first cycle to ever incorporate hearing assessment in adults aged 70 years and older. Audiometry was performed in 717 older adults, and data on hearing aid use, noise exposure, medical history, and demographics were obtained from interviews. Analyses incorporated sampling weights to account for the complex sampling design and yield results that are generalizable to the U.S. population.
The prevalence of hearing loss defined as a speech frequency pure tone average of more than 25 dB in the better ear was 63.1% (95% confidence interval: 57.4-68.8). Age, sex, and race were the factors most strongly associated with hearing loss after multivariate adjustment, with black race being substantially protective against hearing loss (odds ratio 0.32 compared with white participants 95% confidence interval: 0.19-0.53). Hearing aids were used in 40.0% (95% confidence interval: 35.1-44.8) of adults with moderate hearing loss, but in only 3.4% (95% confidence interval: 0.8-6.0) of those with a mild hearing loss.
Hearing loss is prevalent in nearly two thirds of adults aged 70 years and older in the U.S. population. Additional research is needed to determine the epidemiological and physiological basis for the protective effect of black race against hearing loss and to determine the role of hearing aids in those with a mild hearing loss.
This is the second in a pair of papers discussing a statistical study of electromagnetic ion cyclotron (EMIC) waves detected during 10 years (2001–2010) of Cluster observations. In the first paper, ...an analysis of EMIC wave properties (i.e., wave power, polarization, normal angle, and wave propagation angle) is presented in both the magnetic latitude (MLAT)‐distance as well as magnetic local time (MLT)‐L frames. This paper focuses on the distribution of EMIC wave‐associated plasma conditions as well as two EMIC wave generation proxies (the electron plasma frequency to gyrofrequency ratio proxy and the linear theory proxy) in these same frames. Based on the distributions of hot H+ anisotropy, electron and hot H+ density measurements, hot H+ parallel plasma beta, and the calculated wave generation proxies, three source regions of EMIC waves appear to exist: (1) the well‐known overlap between cold plasmaspheric or plume populations with hot anisotropic ring current populations in the postnoon to dusk MLT region; (2) regions all along the dayside magnetosphere at high L shells related to dayside magnetospheric compression and drift shell splitting; and (3) off‐equator regions possibly associated with the Shabansky orbits in the dayside magnetosphere.
Key Points
A statistical study of EMIC waves is conducted using 10 years of Cluster observations
EMIC wave‐associated plasma conditions along with two wave generation proxies are analyzed
A high L shell region favorable for wave generation is observed for a broad range in MLATs
Size and shape of the distant magnetotail Sibeck, D. G.; Lin, R.-Q.
Journal of geophysical research. Space physics,
02/2014, Letnik:
119, Številka:
2
Journal Article
Recenzirano
Odprti dostop
We employ a global magnetohydrodynamic model to study the effects of the interplanetary magnetic field (IMF) strength and direction upon the cross section of the magnetotail at lunar distances. The ...anisotropic pressure of draped magnetosheath magnetic field lines and the inclusion of a reconnection‐generated standing slow mode wave fan bounded by a rotational discontinuity within the definition of the magnetotail result in cross sections elongated in the direction parallel to the component of the IMF in the plane perpendicular to the Sun‐Earth line. Tilted cross‐tail plasma sheets separate the northern and southern lobes within these cross sections. Greater fast‐mode speeds perpendicular than parallel to the draped magnetosheath magnetic field lines result in greater distances to the bow shock in the direction perpendicular than parallel to the component of the IMF in the plane transverse to the Sun‐Earth line. The magnetotail cross section responds rapidly to variations in the IMF orientation. The rotational discontinuity associated with newly reconnected magnetic field lines requires no more than the magnetosheath convection time to appear at any distance downstream, and further adjustments of the cross section in response to the anisotropic pressures of the draped magnetic field lines require no more than 10–20 min. Consequently, for typical ecliptic IMF orientations and strengths, the magnetotail cross section is oblate, while the bow shock is prolate.
Key Points
An ecliptic IMF causes prolate bow shock but oblate magnetotail cross sections
The oblate lunar magnetotail cross sections include broad slow‐mode fans
Lunar magnetotail and bow shock cross sections respond rapidly to IMF variations
RHESSI
measurements relevant to the fundamental processes of energy release and particle acceleration in flares are summarized.
RHESSI’s
precise measurements of hard X-ray continuum spectra enable ...model-independent deconvolution to obtain the parent electron spectrum. Taking into account the effects of albedo, these show that the low energy cut-off to the electron power-law spectrum is typically ≲tens of keV, confirming that the accelerated electrons contain a large fraction of the energy released in flares.
RHESSI
has detected a high coronal hard X-ray source that is filled with accelerated electrons whose energy density is comparable to the magnetic-field energy density. This suggests an efficient conversion of energy, previously stored in the magnetic field, into the bulk acceleration of electrons. A new, collisionless (Hall) magnetic reconnection process has been identified through theory and simulations, and directly observed in space and in the laboratory; it should occur in the solar corona as well, with a reconnection rate fast enough for the energy release in flares. The reconnection process could result in the formation of multiple elongated magnetic islands, that then collapse to bulk-accelerate the electrons, rapidly enough to produce the observed hard X-ray emissions.
RHESSI’s
pioneering
γ
-ray line imaging of energetic ions, revealing footpoints straddling a flare loop arcade, has provided strong evidence that ion acceleration is also related to magnetic reconnection. Flare particle acceleration is shown to have a close relationship to impulsive Solar Energetic Particle (SEP) events observed in the interplanetary medium, and also to both fast coronal mass ejections and gradual SEP events. New instrumentation to provide the high sensitivity and wide dynamic range hard X-ray and
γ
-ray measurements, plus energetic neutral atom (ENA) imaging of SEPs above ∼2 R
⊙
, will enable the next great leap forward in understanding particle acceleration and energy release is large solar eruptions—solar flares and associated fast coronal mass ejections (CMEs).
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