Inherent length-scales of periodic solar wind number density structures

[1] We present an analysis of the radial length-scales of periodic solar wind number density structures. We converted 11 years (1995–2005) of solar wind number density data into radial length series segments and Fourier analyzed them to identify all spectral peaks with radial wavelengths between 72 (116) and 900 (900) Mm for slow (fast) wind intervals. Our window length for the spectral analysis was 9072 Mm, approximately equivalent to 7 (4) h of data for the slow (fast) solar wind. We required that spectral peaks pass both an amplitude test and a harmonic F-test at the 95% confidence level simultaneously. From the occurrence distributions of these spectral peaks for slow and fast wind, we find that periodic number density structures occur more often at certain radial length-scales than at others, and are consistently observed within each speed range over most of the 11-year interval. For the slow wind, those length-scales are L ∼ 73, 120, 136, and 180 Mm. For the fast wind, those length-scales are L ∼ 187, 270 and 400 Mm. The results argue for the existence of inherent radial length-scales in the solar wind number density

Are periodic solar wind number density structures formed in the solar corona?

[1] We present an analysis of the alpha to proton solar wind abundance ratio (AHe) during a period characterized by significant large size scale density fluctuations, focusing on an event in which the proton and alpha enhancements are anti-correlated. In a recent study using 11 years (1995–2005) of solar wind observations from the Wind spacecraft, N. M. Viall et al. [2008] showed that periodic proton density structures occurred at particular radial length-scales more often than others. The source of these periodic density structures is a significant and outstanding question. Are they generated in the interplanetary medium, or are they a relic of coronal activity as the solar wind was formed? We use AHe to answer this question, as solar wind elemental abundance ratios are not expected to change during transit. For this event, the anti-phase nature of the AHe variations strongly suggests that periodic solar wind density structures originate in the solar corona

Relative occurrence rates and connection of discrete frequency oscillations in the solar wind density and dayside magnetosphere

[1] We present an analysis of the occurrence distributions of statistically significant apparent frequencies of periodic solar wind number density structures and dayside magnetospheric oscillations in the f = 0.5–5.0 mHz range. Using 11 years (1995–2005) of solar wind data, we identified all spectral peaks that passed both an amplitude test and a harmonic F test at the 95% confidence level in 6-hour data segments. We find that certain discrete frequencies, specifically f = 0.7, 1.4, 2.0, and 4.8 mHz, occur more often than do other frequencies over those 11 years. We repeat the analysis on discrete oscillations observed in 10 years (1996–2005) of dayside magnetospheric data. We find that certain frequencies, specifically f = 1.0, 1.5, 1.9, 2.8, 3.3, and 4.4 mHz, occur more often than do other frequencies over those 10 years. Many of the enhancements found in the magnetospheric occurrence distributions are similar to those found in the solar wind. Lastly, we counted the number of times the same discrete frequencies were identified as statistically significant using our two spectral tests on corresponding solar wind and magnetospheric 6-hour time series. We find that in 54% of the solar wind data segments in which we identified a spectral peak, at least one of the same discrete frequencies was statistically significant in the corresponding magnetospheric data segment. Our results argue for the existence of inherent apparent frequencies in the solar wind number density that directly drive global magnetospheric oscillations at the same discrete frequencies, although the magnetosphere also oscillates through other physical mechanisms

The effect of magnetopause motion on fast mode resonance

The Earth's magnetosphere supports several types of ultralow frequency (ULF) waves. These include fast mode resonance (FMR): cavity modes, waveguide modes, and tunneling modes/virtual resonance. The magnetopause, often treated as the outer boundary for cavity/waveguide modes in the dayside magnetosphere, is not stationary. A rapidly changing outer boundary condition—e.g., due to rapid magnetopause motion—is not favorable for FMR generation and may explain the sparseness of FMR observations in the outer magnetosphere. We examine how magnetopause motion affects the dayside magnetosphere's ability to sustain FMR with idealized Space Weather Modeling Framework (SWMF) simulations using the BATS‐R‐US global magnetohydrodynamic (MHD) code coupled with the Ridley Ionosphere Model (RIM). We present observations of FMR in BATS‐R‐US, reproducing results from other global MHD codes. We further show that FMR is present for a wide range of solar wind conditions, even during periods with large and rapid magnetopause displacements. We compare our simulation results to FMR observations in the dayside magnetosphere, finding that FMR occurrence does not depend on solar wind dynamic pressure, which can be used as a proxy for dynamic pressure fluctuations and magnetopause perturbations. Our results demonstrate that other explanations besides a nonstationary magnetopause—such as the inability to detect FMR in the presence of other ULF wave modes with large amplitudes—are required to explain the rarity of FMR observations in the outer magnetosphere. Key Points Typical magnetopause motion does not affect fast mode resonance occurrence Magnetopause motion cannot explain why FMR is rarely observed Selection criteria and non‐FMR wave activity affect FMR occurrence ratePeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109612/1/2014JA020401readme.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109612/2/Auxiliary_Material_fs01.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109612/3/Auxiliary_Material_fs02.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109612/4/jgra51354.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/109612/5/Auxiliary_Material_fs03.pd

Sparkling extreme-ultraviolet bright dots observed with Hi-C

Observing the Sun at high time and spatial scales is a step toward understanding the finest and fundamental scales of heating events in the solar corona. The high-resolution coronal (Hi-C) instrument has provided the highest spatial and temporal resolution images of the solar corona in the EUV wavelength range to date. Hi-C observed an active region on 2012 July 11 that exhibits several interesting features in the EUV line at 193 Å. One of them is the existence of short, small brightenings "sparkling" at the edge of the active region; we call these EUV bright dots (EBDs). Individual EBDs have a characteristic duration of 25 s with a characteristic length of 680 km. These brightenings are not fully resolved by the SDO/AIA instrument at the same wavelength; however, they can be identified with respect to the Hi-C location of the EBDs. In addition, EBDs are seen in other chromospheric/coronal channels of SDO/AIA, which suggests a temperature between 0.5 and 1.5 MK. Based on their frequency in the Hi-C time series, we define four different categories of EBDs: single peak, double peak, long duration, and bursty. Based on a potential field extrapolation from an SDO/HMI magnetogram, the EBDs appear at the footpoints of large-scale, trans-equatorial coronal loops. The Hi-C observations provide the first evidence of small-scale EUV heating events at the base of these coronal loops, which have a free magnetic energy of the order of 1026 erg. © 2014. The American Astronomical Society. All rights reserved

Neutrophil extracellular traps in stored canine red blood cell units

BackgroundNeutrophil extracellular traps (NETs), webs of DNA and citrullinated histones extruded from activated neutrophils cause transfusion‐related acute lung injury. Supernatants of stored red blood cell (RBC) units might promote NETosis in neutrophils from the units or from transfusion recipients.Hypotheses(1) NETs form during storage of canine RBC, (2) leukoreduction (LR) before storage of RBC reduces NETosis, and (3) supernatant from stored, nonleukoreduced (NLR) RBC units induces NETosis in healthy canine neutrophils modeling transfusion recipients.AnimalsSix healthy purpose‐bred research dogs were utilized for blood donation.MethodsProspective controlled study. RBC units were collected from each dog, aseptically divided into 2 equal subunits, 1 of which was leukoreduced, and stored for 42 days. Stored units were sampled biweekly for quantification of NET markers citrullinated histone H3 (Western blot) and cell‐free DNA (cfDNA) (DNA dye binding). Unit supernatants were applied ex vivo to canine neutrophils and extracellular DNA release representing NETosis was assessed.ResultsMarkers of NETs increased during RBC storage (cfDNA P < .0001 and citrullinated H3 P = .0002) and were higher in NLR than LR units (day 42 LR cfDNA 0.34 ± 0.82 ng/mL vs day 42 NLR 1361.07 ± 741.00 ng/mL, P < .0001; day 42 LR citrullinated H3 0.19 ± 0.13 AU vs NLR 0.57 ± 0.34 AU, P = .007). Isolated neutrophils did not form NETs when exposed to stored canine RBC supernatant.Conclusions and Clinical ImportanceNETosis occurs in stored canine NLR RBC units, and is attenuated by LR before storage. NETs might be mediators of transfusion reactions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/162806/3/jvim15876-sup-0001-supinfo.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162806/2/jvim15876_am.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/162806/1/jvim15876.pd