175 research outputs found
A topographically controlled upwelling center off southern Vancouver Island
From January 1979 to June 1981 an oceanographic experiment off the west coast of Canada provided a unique view of a large annual upwelling event. The upwelling is driven by an interaction between the large scale coastal current systems and a narrow canyon that cuts the continental shelf. This interaction allows water to be raised from depths much greater than those normally expected from the classical wind-driven upwelling mechanisms...
Correlation scales, objective mapping and a statistical test of geostrophy over the continental shelf
We have constructed spatial structure functions for oceanographic variables, collected during 15 cruises off the coast of Vancouver Island, Canada over a 3 year period (1979–81), to determine the appropriate correlation function and unresolved noise level for objective mapping according to the Gauss-Markov theorem. The assumption of quasigeostrophic flow has been tested by comparing the longitudinal and transverse velocity shear structure functions derived from geopotential height fields with those derived from 6 current meter moorings. In addition objective maps of geopotential height imply current shears similar to the directly observed shear vectors, as would be expected under geostrophic control. Structure functions of geopotential height, temperature, salinity, and log-transformed phytoplankton chlorophyll a pigment concentration all have a broad maximum near a separation of 30 km, consistent with a dominant eddy wavelength of ≃60 km, also the estimated wavelength of the most unstable baroclinic disturbance. The sensitivity of the objective maps generated using the Gauss-Markov theorem to different correlation functions, length scales and noise levels was tested: where the sampling was well distributed, the patterns changed little.Temporal structure functions (for data from 25 cruises) of geopotential height, temperature and salinity are roughly cyclic with minima at time lags of 1 and 2 years. The structure functions increase monotonically with lags up to at least 90 days indicating that temporal changes during a ship survey (several days) are sufficiently small that the maps can be regarded as synoptic. Finally, a composite kinetic energy spectrum from a long term (≃3 years) current meter mooring at the edge of the continental shelf has well defined peaks in a band with 10–50 day periods (which we believe represents the mesoscale eddies with ≃60km wavelength), and at the annual and the major tidal and inertial periods
Solid Rocket Booster (SRB) - Evolution and Lessons Learned During the Shuttle Program
The Solid Rocket Booster (SRB) element integrates all the subsystems needed for ascent flight, entry, and recovery of the combined Booster and Motor system. These include the structures, avionics, thrust vector control, pyrotechnic, range safety, deceleration, thermal protection, and retrieval systems. This represents the only human-rated, recoverable and refurbishable solid rocket ever developed and flown. Challenges included subsystem integration, thermal environments and severe loads (including water impact), sometimes resulting in hardware attrition. Several of the subsystems evolved during the program through design changes. These included the thermal protection system, range safety system, parachute/recovery system, and others. Obsolescence issues occasionally required component recertification. Because the system was recovered, the SRB was ideal for data and imagery acquisition, which proved essential for understanding loads and system response. The three main parachutes that lower the SRBs to the ocean are the largest parachutes ever designed, and the SRBs are the largest structures ever to be lowered by parachutes. SRB recovery from the ocean was a unique process and represented a significant operational challenge; requiring personnel, facilities, transportation, and ground support equipment. The SRB element achieved reliability via extensive system testing and checkout, redundancy management, and a thorough postflight assessment process. Assembly and integration of the booster subsystems was a unique process and acceptance testing of reused hardware components was required for each build. Extensive testing was done to assure hardware functionality at each level of stage integration. Because the booster element is recoverable, subsystems were available for inspection and testing postflight, unique to the Shuttle launch vehicle. Problems were noted and corrective actions were implemented as needed. The postflight assessment process was quite detailed and a significant portion of flight operations. The SRBs provided fully redundant critical systems including thrust vector control, mission critical pyrotechnics, avionics, and parachute recovery system. The design intent was to lift off with full redundancy. On occasion, the redundancy management scheme was needed during flight operations. This paper describes some of the design challenges, how the design evolved with time, and key areas where hardware reusability contributed to improved system level understanding
Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere
A method for the full three-dimensional (3-D) reconstruction of the
trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations
Observatory (STEREO) data is presented. Four CMEs that were simultaneously
observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and
Behind STEREO satellites were analysed. These observations were used to derive
CME trajectories in 3-D out to ~15Rsun. The reconstructions using COR1/2 data
support a radial propagation model. Assuming pseudo-radial propagation at large
distances from the Sun (15-240Rsun), the CME positions were extrapolated into
the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in
the different fields-of-view. It was found that CMEs slower than the solar wind
were accelerated, while CMEs faster than the solar wind were decelerated, with
both tending to the solar wind velocity.Comment: 17 pages, 10 figures, 1 appendi
Evolution of microflares associated with bright points in coronal holes and in quiet regions
We aim to find similarities and differences between microflares at coronal
bright points found in quiet regions and coronal holes, and to study their
relationship with large scale flares. Coronal bright points in quiet regions
and in coronal holes were observed with Hinode/EIS using the same sequence.
Microflares associated with bright points are identified from the X-ray
lightcurve. The temporal variation of physical properties was traced in the
course of microflares. The lightcurves of microflares indicated an impulsive
peak at hot emission followed by an enhancement at cool emission, which is
compatible with the cooling model of flare loops. The density was found to
increase at the rise of the impulsive peak, supporting chromospheric
evaporation models. A notable difference is found in the surroundings of
microflares; diffuse coronal jets are produced above microflares in coronal
holes while coronal dimmings are formed in quiet regions. The microflares
associated with bright points share common characteristics to active region
flares. The difference in the surroundings of microflares are caused by open
and closed configurations of the pre-existing magnetic field.Comment: 9 pages, 11 figures, accepted for publication in A&
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Cold halocline in the northern California Current: an invasion of subarctic water
Subsurface upper ocean waters off Oregon and Vancouver Island were about 1° cooler in July 2002 than in July 2001. The anomalously cool layer coincides with the permanent halocline which has salinities of 32.2 to 33.8, suggesting an invasion of nutrient-rich Subarctic waters. The anomalously cool layer lies at 30–150 m. The cool anomaly is likely caused by stronger southward flow in the California Current and weaker northward flow in the Alaska and Davidson Currents during spring 2002. Other factors may include reduced coastal downwelling in late winter and early spring 2002, enhanced eastward flow in the Subarctic Current, and enhanced winder mixing offshore
Horizontal flow fields observed in Hinode G-band images II. Flow fields in the final stages of sunspot decay
We present a subset of multi-wavelengths observations obtained with the
Japanese Hinode mission, the Solar Dynamics Observatory (SDO), and the Vacuum
Tower Telescope (VTT) at Observatorio del Teide, Tenerife, Spain during the
time period from 2010 November 18-23. Horizontal proper motions were derived
from G-band and Ca II H images, whereas line-of-sight velocities were extracted
from VTT Echelle H-alpha 656.28 nm spectra and Fe I 630.25 nm spectral data of
the Hinode/Spectro-Polarimeter, which also provided three-dimensional magnetic
field information. The Helioseismic and Magnetic Imager on board SDO provided
continuum images and line-of-sight magnetograms as context for the
high-resolution observations for the entire disk passage of the active region.
We have performed a quantitative study of photospheric and chromospheric flow
fields in and around decaying sunspots. In one of the trailing sunspots of
active region NOAA 11126, we observed moat flow and moving magnetic features
(MMFs), even after its penumbra had decayed. We also noticed a superpenumbral
structure around this pore. MMFs follow well-defined, radial paths from the
spot all the way to the border of a supergranular cell surrounding the spot. In
contrast, flux emergence near the other sunspot prevented it from establishing
such well ordered flow patterns, which could even be observed around a tiny
pore of just 2 Mm diameter. After the disappearance of the sunspots/pores a
coherent patch of abnormal granulation remained at their location, which was
characterized by more uniform horizontal proper motions, low divergence values,
and diminished photospheric Doppler velocities. This region, thus, differs
significantly from granulation and other areas covered by G-band bright points.
We conclude that this peculiar flow pattern is a signature of sunspot decay and
the dispersal of magnetic flux.Comment: 13 pages, 11 figures, accepted for publication in Astronomy and
Astrophysic
The Impact of New EUV Diagnostics on CME-Related Kinematics
We present the application of novel diagnostics to the spectroscopic
observation of a Coronal Mass Ejection (CME) on disk by the Extreme Ultraviolet
Imaging Spectrometer (EIS) on the Hinode spacecraft. We apply a recently
developed line profile asymmetry analysis to the spectroscopic observation of
NOAA AR 10930 on 14-15 December 2006 to three raster observations before and
during the eruption of a 1000km/s CME. We see the impact that the observer's
line-of-sight and magnetic field geometry have on the diagnostics used.
Further, and more importantly, we identify the on-disk signature of a
high-speed outflow behind the CME in the dimming region arising as a result of
the eruption. Supported by recent coronal observations of the STEREO
spacecraft, we speculate about the momentum flux resulting from this outflow as
a secondary momentum source to the CME. The results presented highlight the
importance of spectroscopic measurements in relation to CME kinematics, and the
need for full-disk synoptic spectroscopic observations of the coronal and
chromospheric plasmas to capture the signature of such explosive energy release
as a way of providing better constraints of CME propagation times to L1, or any
other point of interest in the heliosphere.Comment: Accepted to appear in Solar Physics Topical Issue titled "Remote
Sensing of the Inner Heliosphere". Manuscript has 14 pages, 5 color figures.
Movies supporting the figures can be found in
http://download.hao.ucar.edu/pub/mscott/papers/Weathe
Modeling the Longitudinal Asymmetry in Sunspot Emergence -- the Role of the Wilson Depression
The distributions of sunspot longitude at first appearance and at
disappearance display an east-west asymmetry that results from a reduction in
visibility as one moves from disk centre to the limb. To first order, this is
explicable in terms of simple geometrical foreshortening. However, the
centre-to-limb visibility variation is much larger than that predicted by
foreshortening. Sunspot visibility is also known to be affected by the Wilson
effect: the apparent dish shape of the sunspot photosphere caused by the
temperature-dependent variation of the geometrical position of the tau=1 layer.
In this article we investigate the role of the Wilson effect on the sunspot
appearance distributions, deducing a mean depth for the umbral tau=1 layer of
500 to 1500 km. This is based on the comparison of observations of sunspot
longitude distribution and Monte Carlo simulations of sunspot appearance using
different models for spot growth rate, growth time and depth of Wilson
depression.Comment: 18 pages, 10 figures, in press (Solar Physics
2D and 3D Polar Plume Analysis from the Three Vantage Positions of STEREO/EUVI A, B, and SOHO/EIT
Polar plumes are seen as elongated objects starting at the solar polar
regions. Here, we analyze these objects from a sequence of images taken
simultaneously by the three spacecraft telescopes STEREO/EUVI A and B, and
SOHO/EIT. We establish a method capable of automatically identifying plumes in
solar EUV images close to the limb at 1.01 - 1.39 R in order to study their
temporal evolution. This plume-identification method is based on a multiscale
Hough-wavelet analysis. Then two methods to determined their 3D localization
and structure are discussed: First, tomography using the filtered
back-projection and including the differential rotation of the Sun and,
secondly, conventional stereoscopic triangulation. We show that tomography and
stereoscopy are complementary to study polar plumes. We also show that this
systematic 2D identification and the proposed methods of 3D reconstruction are
well suited, on one hand, to identify plumes individually and on the other
hand, to analyze the distribution of plumes and inter-plume regions. Finally,
the results are discussed focusing on the plume position with their
cross-section area.Comment: 22 pages, 10 figures, Solar Physics articl
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