401 research outputs found
A statistical study of the performance of the Hakamada-Akasofu-Fry version 2 numerical model in predicting solar shock arrival times at Earth during different phases of solar cycle 23
The performance of the Hakamada
Akasofu-Fry, version 2 (HAFv.2) numerical model, which provides predictions
of solar shock arrival times at Earth, was subjected to a statistical study
to investigate those solar/interplanetary circumstances under which the
model performed well/poorly during key phases (rise/maximum/decay) of solar
cycle 23. In addition to analyzing elements of the overall data set (584
selected events) associated with particular cycle phases, subsets were
formed such that those events making up a particular sub-set showed common
characteristics. The statistical significance of the results obtained using the
various sets/subsets was generally very low and these results were not significant
as compared with the hit by chance rate (50%). This implies a low level
of confidence in the predictions of the model with no compelling
result encouraging its use. However, the data
suggested that the success rates of HAFv.2 were higher when the background
solar wind speed at the time of shock initiation was relatively fast. Thus,
in scenarios where the background solar wind speed is elevated and the
calculated success rate significantly exceeds the rate by chance, the
forecasts could provide potential value to the customer.
With the composite statistics available for solar cycle 23,
the calculated success rate at high solar wind speed, although clearly above
50%, was indicative rather than conclusive. The RMS error
estimated for shock arrival times for every cycle phase and for the
composite sample was in each case significantly better than would be
expected for a random data set. Also, the parameter "Probability of
Detection, yes" (PODy) which presents the Proportion of Yes observations
that were correctly forecast (i.e. the ratio between the shocks correctly
predicted and all the shocks observed), yielded values for the
rise/maximum/decay phases of the cycle and using the composite sample of
0.85, 0.64, 0.79 and 0.77, respectively. The statistical results obtained
through detailed analysis of the available data provided insights into how
changing circumstances on the Sun and in interplanetary space can affect the
performance of the model. Since shock arrival predictions are widely
utilized in making commercially significant decisions re. protecting space
assets, the present detailed archival studies can be useful in future
operational decision making during solar cycle 24. It would be of added
value in this context to use Briggs-Rupert methodology to estimate the cost
to an operator of acting on an incorrect forecast
Gaia CCDs: charge transfer inefficiency measurements between five years of flight
The European Space Agencyâs Gaia spacecraft was launched in December 2013 and has been in orbit at the Earth-Sun Lagrange point 2 (L2) for over 6 years. The spacecraft measures the positions, distances, space motions and many other physical characteristics of around one billion stars in the Milky Way and beyond. It has a focal plane of 106 Charge-Coupled Devices (CCDs) which have all been performing well but have been measuring a small but quantifiable degradation in performance in time due to Non-Ionizing Energy Loss (NIEL) damage from interstellar radiation. This NIEL damage produces trap defects which can capture charge from signals and reduces the quality of the data. Gaiaâs original mission lifetime was planned to be around 5 years and the pre-flight testing and radiation damage analysis was tailored around those timescales as well as with the projected solar activity before launch. Closer to the time of launch and during Gaiaâs years of orbit, it has been noted that the solar activity was lower than what was initially predicted. From the previous analysis of in-flight data in 2016, it was calculated that Gaia was experiencing an order of magnitude less radiation damage than was predicted. This paper describes the analysis of charge calibration data and corresponding Charge Transfer Inefficiency (CTI) measurements from the in-flight CCDs, both near the beginning of the mission and after more than 5 years in orbit to quantify the radiation damage impact. These sets of results can be compared with those from the pre-flight tests which can be used to evaluate and understand the differences between the on-ground and in-flight results
Relationship between solar energetic oxygen flux and MHD shock Mach number
This study correlates the time-intensity profile of a magnetohydrodynamic (MHD) shock with the corresponding solar energetic oxygen for a coronal mass ejection (CME) event that occurred on October 28, 2003. The intensity of MHD shock, in terms of Mach number, is simulated using a 1.5D MHD code, whereas the solar energetic oxygen flux is observed by the Solar Isotope Spectrometer (SIS) on board the Advanced Composition Explorer (ACE) spacecraft. A good correlation (Pearson correlation coefficient: r = 0.70 â 0.84) is found between the forward fast-mode shock Mach number and the hourly-averaged, logarithmic oxygen differential energy flux for 7 energy channels (7.3 â 63.8 MeV). We suspect that the intensity-time profile of high energy SEP events is manifested by the strength (Mach number) of CME-driven propagation shocks. While further studies with more events are required to be more conclusive, this study result provides a direction for future studies or predictions of SEP fluxes
Accuracy and Precision of Age Estimates for Pallid Sturgeon from Pectoral Fin Rays
Accurate age information is critical to the biological understanding and management of most fish species, but particularly for species of concern, such as the pallid sturgeon Scaphirhynchus albus. The accuracy and precision of pallid sturgeon age estimates from pectoral fin ray sections has never been established, yet all accumulated age information for the species was collected using this technique. To examine the accuracy and precision of age estimates, 16 pectoral fin ray samples from age-6 pallid sturgeon were obtained from Gavins Point National Fish Hatchery, South Dakota. The fin rays were sectioned, mounted, and independently examined twice by each of two readers. Only 28.1% of the age estimates accurately reflected the known age of the fish. Multiple readings of the same sample by the same reader (within-reader precision) only agreed 25% of the time, differences being as great as 5 years between the two estimates. Between-reader agreement was 46.9%, the two readers\u27 estimates of the same fish differing by as much as 2 years. Because of low accuracy and precision, estimated ages from pallid sturgeon pectoral fin rays should be viewed with caution
Arrival times of Flare/Halo CME associated shocks at the Earth: comparison of the predictions of three numerical models with these observations
International audienceThe arrival times at L1 of eleven travelling shocks associated both with X-ray flaring and with halo CMEs recorded aboard SOHO/LASCO have been considered. Close to the Sun the velocities of these events were estimated using either Type II radio records or CME speeds. Close to the Earth the shocks were detected in the data of various solar wind plasma, interplanetary magnetic field (IMF) and energetic particle experiments aboard SOHO, ACE, WIND, INTERBALL-1 and IMP-8. The real-time shock arrival predictions of three numerical models, namely the Shock Time of Arrival Model (STOA), the Interplanetary Shock Propagation Model (ISPM) and the Hakamada-Akasofu-Fry Solar Wind Model (HAFv.2) were tested against these observations. This is the first time that energetic protons (tens of keV to a few MeV) have been used to complement plasma and IMF data in validating shock propagation models. The models were all generally successful in predicting shock arrivals. STOA provided the smallest values of the "predicted minus measured" arrival times and displayed a typical predictive precision better than about 8 h. The ratio of the calculated standard deviation of the transit times to Earth to the standard deviation of the measurements was estimated for each model (treating interacting events as composite shocks) and these ratios turned out to be 0.60, 1.15 and 1.02 for STOA, ISPM and HAFv.2, respectively. If an event in the sample for which the shock velocity was not well known is omitted from consideration, these ratios become 0.36, 0.76 and 0.81, respectively. Larger statistical samples should now be tested. The ratio of the in situ shock velocity and the "Sun to L1" transit velocity (Vsh /Vtr) was in the range of 0.7?0.9 for individual, non-interacting, shock events. HAFv.2 uniquely provided information on those changes in the COBpoint (the moving Connection point on the shock along the IMF to the OBserver) which directly influenced energetic particle rise times. This model also illustrated the non-uniform upstream conditions through which the various shocks propagated; furthermore it simulated shock deformation on a scale of fractions of an AU. On the spatial scale (300 RE ), where near-Earth spacecraft are located, the passing shocks, in conformity with the models, were found to be locally planar. The shocks also showed tilting relative to the Sun-Earth line, probably reflecting the inherent directionality associated with their solar origin. Key words. Interplanetary physics (energetic particles; interplanetary shocks; solar wind plasma
Flareâgenerated shock evolution and geomagnetic storms during the âHalloween 2003 epochâ: 29 October to 2 November
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95151/1/jgra17876.pd
AF17 Competes With AF9 for Binding to DOT1A to up-Regulate Transcription of Epithelial NA\u3csup\u3e+\u3c/sup\u3e Channel α
We previously reported that Dot1a*AF9 complex represses transcription of the epithelial Na+ channel subunit α (α-ENaC) gene in mouse inner medullary collecting duct mIMCD3 cells and mouse kidney. Aldosterone relieves this repression by down-regulating the complex through various mechanisms. Whether these mechanisms are sufficient and conserved in human cells or can be applied to other aldosterone-regulated genes remains largely unknown. Here we demonstrate that human embryonic kidney 293T cells express the three ENaC subunits and all of the ENaC transcriptional regulators examined. These cells respond to aldosterone and display benzamil-sensitive Na+ currents, as measured by whole-cell patch clamping. We also show that AF17 and AF9 competitively bind to the same domain of Dot1a in multiple assays and have antagonistic effects on expression of an α-ENaC promoter-luciferase construct. Overexpression of Dot1a or AF9 decreased mRNA expression of the ENaC subunits and their transcriptional regulators and reduced benzamil-sensitive Na+ currents. AF17 over-expression caused the opposite effects, accompanied by redirection of Dot1a from the nucleus to the cytoplasm and reduction in histone H3 K79 methylation. The nuclear export inhibitor leptomycin B blocked the effect of AF17 overexpression on H3 K79 hypomethylation. RNAi-mediated knockdown of AF17 yielded nuclear enrichment of Dot1a and histone H3 K79 hypermethylation. As with AF9, AF17 displays nuclear and cytoplasmic co-localization with Sgk1. Therefore, AF17 competes with AF9 to bind Dot1a, decreases Dot1a nuclear expression by possibly facilitating its nuclear export, and relieves Dot1a*AF9-mediated repression of α-ENaC and other target genes
Spectral Analysis of the Chandra Comet Survey
We present results of the analysis of cometary X-ray spectra with an extended
version of our charge exchange emission model (Bodewits et al. 2006). We have
applied this model to the sample of 8 comets thus far observed with the Chandra
X-ray observatory and ACIS spectrometer in the 300-1000 eV range. The surveyed
comets are C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), C/2000 WM1
(LINEAR), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), C/2001 Q4 (NEAT), 9P/2005
(Tempel 1) and 73P/2006-B (Schwassmann-Wachmann 3) and the observations include
a broad variety of comets, solar wind environments and observational
conditions. The interaction model is based on state selective, velocity
dependent charge exchange cross sections and is used to explore how cometary
X-ray emission depend on cometary, observational and solar wind
characteristics. It is further demonstrated that cometary X-ray spectra mainly
reflect the state of the local solar wind. The current sample of Chandra
observations was fit using the constrains of the charge exchange model, and
relative solar wind abundances were derived from the X-ray spectra. Our
analysis showed that spectral differences can be ascribed to different solar
wind states, as such identifying comets interacting with (I) fast, cold wind,
(II), slow, warm wind and (III) disturbed, fast, hot winds associated with
interplanetary coronal mass ejections. We furthermore predict the existence of
a fourth spectral class, associated with the cool, fast high latitude wind.Comment: 16 pages, 16 figures, and 7 Tables; accepted A&A (Due to space
limits, this version has lower resolution jpeg images.
Direct observations of submarine melt and subsurface geometry at a tidewater glacier
Ice loss from the worldâs glaciers and ice sheets contributes to sea level rise, influences
ocean circulation, and affects ecosystem productivity. Ongoing changes in glaciers and
ice sheets are driven by submarine melting and iceberg calving from tidewater glacier
margins.Ice loss from the worldâs glaciers and ice sheets contributes to sea level rise, influences
ocean circulation, and affects ecosystem productivity. Ongoing changes in glaciers and
ice sheets are driven by submarine melting and iceberg calving from tidewater glacier
margins. However, predictions of glacier change largely rest on unconstrained theory for
submarine melting. Here, we use repeat multibeam sonar surveys to image a subsurface
tidewater glacier face and document a time-variable, three-dimensional geometry linked
to melting and calving patterns. Submarine melt rates are high across the entire ice face over
both seasons surveyed and increase from spring to summer. The observed melt rates are up
to two orders of magnitude greater than predicted by theory, challenging current simulations of
ice loss from tidewater glaciers.Department of Earth Sciences, University of Oregon,
Eugene, OR 97403, USA. 2
College of Earth, Ocean, and
Atmospheric Sciences, Oregon State University, Corvallis, OR
97331, USA. 3
Department of Natural Sciences, University of
Alaska Southeast, Juneau, AK 99801, USA. 4
Institute for
Geophysics, University of Texas at Austin, Austin, TX 78758,
USA. 5
Department of Marine Sciences, University of North
Carolina, Chapel Hill, NC 27599, USA. 6
Geophysical Institute,
University of Alaska Fairbanks, Fairbanks, AK 99775, USA.
*Corresponding author. Email: [email protected]
â Present address: Department of Marine and Coastal Sciences,
Rutgers University, New Brunswick, NJ 08901, USA.Ye
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