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At least 541 records · Page 30
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Explorations of electric current system in solar active regions. I - Empirical inferences of the current flows

Techniques to identify sources of electric current systems and their channels of flow in solar active regions are explored. Measured photospheric vector magnetic fields together with high-resolution white-light and H-alpha filtergrams provide the data base to derive the current systems in the photosphere and chromosphere. As an example, the techniques are then applied to infer current systems in AR 2372 in early April 1980.

Ding, Y. J.↗
NASA NTRS1989

Design of the polarimeter for the Solar Activity Measurements Experiments (SAMEX) vector magnetograph

A design concept developed for a polarimeter on the vector magnetograph of the SAMEX satellite that would be very sensitive to solar vector magnetic fields is described. A description of the Poincare sphere is presented, along with the instrument scientific requirements, to provide an understanding of how the polarimeter design has been selected. It is shown that the design goal of a polarimetric sensitivity of 0.0001 can be achieved in the linear measurements using a hybrid analyzer. It is also noted that the systematic errors that produce linear crosstalk into the circular measurement will require the use of the redundant polarization measurements for in-flight calibrations and corrections of the data.

West, E. A.↗
NASA NTRS1989

The formation flare loops by magnetic reconnection and chromospheric ablation

Noncoplanar compressible reconnection theory is combined here with simple scaling arguments for ablation and radiative cooling to predict average properties of hot and cool flare loops as a function of the coronal vector magnetic field. For a coronal field strength of 100 G, the temperature of the hot flare loops decreases from 1.2 x 10 to the 7th K to 4.0 x 10 to the 6th K as the component of the coronal magnetic field perpendicular to the plane of the loops increases from 0 percent to 86 percent of the total field. When the perpendicular component exceeds 86 percent of the total field or when the altitude of the reconnection site exceeds 10 to the 6th km, flare loops no longer occur. Shock-enhanced radiative cooling triggers the formation of cool H-alpha flare loops with predicted densities of roughly 10 to the 13th/cu cm, and a small gap of roughly 1000 km is predicted to exist between the footpoints of the cool flare loops and the inner edges of the flare ribbons.

Forbes, T. G.↗
NASA NTRS1989

Evaluation of magnetic shear in off-disk center active regions

The changes that projection effects produce in the evaluation of magnetic shear in off-disk center active regions by comparing angular shear calculated in image plane and heliographic coordinates are analyzed, and the procedure for properly evaluating magnetic shear by transforming the observed vector magnetic field into the heliographic system is described. This procedure is then used to evaluate magnetic shear along the magnetic neutral line in an active region that was observed on April 24, 1984 at a longitude offset of -45 deg. In particular, the number of 'critically sheared' pixels along an east-west directed segment of the neutral line in the leader sunspot group changes from 16 in the image plane magnetogram to 14 in the heliographic magnetogram. The critical shear as calculated in the image plane served as a good predictor for the location of flaring activity since the flare ribbons of the great flare of April 24 bracketed the inversion line where the critical shear was located. These results indicate that for this particular region, projection effects did not significantly affect the evaluation of critical shear.

Venkatakrishnan, P.↗
NASA NTRS1991

Polarimetry of extreme ultraviolet lines in solar astronomy

Ways are suggested in which recent advancements in the fabrication of ultrasmooth, low scatter flow-polished mirror substrates and high-quality multilayer and interference film coatings can be used to create novel optical instruments for observing linear-polarization effects in the outer solar atmosphere. Attention is given to the observational parameters of all-reflective FUV/EUV imaging polarimeters; such a coronagraph/polarimeter, operating at Ly-alpha, could yield the first measurements of coronal vector magnetic fields.

Fineschi, Silvano↗
NASA NTRS1992

Neutral winds in the lower thermosphere from Dynamics Explorer 2

Doppler line profile measurements of the OI lambda 557.7 nm 'green line' emission, made by the Fabry-Perot interferometer on Dynamics Explorer 2, have provided altitude profiles of the meridional component of the lower thermospheric neutral wind. The wind inversion technique of Nardi has been used to extract the neutral wind profiles from the line-of-sight measurements. Individual lambda 557.7 nm Doppler line profiles and inverted volume-emission-rate and neutral-wind profiles are presented. Neutral wind measurements from the about 120 km altitude level, obtained on multiple orbital passes over the summer hemisphere polar region, have been merged to produce a synthesized averaged 'vector' wind field in geomagnetic coordinates. The wind pattern exhibits a region of anticyclonic vorticity in the daytime sector of the magnetic polar cap. Averaged winds of about 300 m/sec in the equatorial direction are observed in the early morning sector. The satellite winds are in reasonable agreement with the predictions of the NCAR and UCL thermosphere general circulation models, with significant regional discrepancies evident in both magnitude and direction.

Killeen, T. L.↗
NASA NTRS1991

An overview of gravitational physiology

The focus of this review is on the response of humans and animals to the effects of the near weightless condition occurring aboard orbiting spacecraft. Gravity is an omnipresent force that has been a constant part of our lives and of the evolution of all living species. Emphasis is placed on the general mechanisms of adaptation to altered gravitational fields and vectors, i.e., both hypo- and hypergravity. A broad literature review of gravitational biology was conducted and the general state of our knowledge in this area is discussed. The review is specifically targeted at newcomers to the exciting and relatively new area of space and gravitational biology.

Miquel, Jaime↗
NASA NTRS1990

Electrodynamics of the Middle Atmosphere: Superpressure Balloon Program

This project called Electrodynamics of the Middle Atmosphere (EMA): Superpressure Balloon Program was begun by the PI at the Aerospace Corporation in Los Angeles under joint NSF and NASA funding originally combined in one grant ATM80-17071 and has continued at the University of Washington under grants ATM8212283, ATM84-11326 and ATM86-15628 and NASA grants NAGW-724 and NAGS-635. In the EMA experiment a comprehensive set of electrical parameters was measured during eight long-duration balloon flights in the Southern Hemisphere stratosphere. These flights resulted in the largest vector electric field data set ever collected from the stratosphere which has been a treasure-trove of new phenomena. Since the stratosphere has never been electrodynamically sampled in this systematic manner before, it is perhaps not surprising that several new discoveries have been made and reported. Another way to measure the success of this first EMA project is to note that all together the total data rate was about 1 bit/sec/payload amounting to 12 MBytes (1/3 of 1 standard 1600 BPI magnetic tape) which nevertheless has resulted in 14 papers and 2 masters theses (so far! . Ten of these papers and one masters thesis specifically acknowledge the support by NASA grant NAGS-635 are discussed herein.

Holzworth, Robert H.↗
NASA NTRS1992

The Stratospheric Wind Ingrared Limb Sounder: Investigation of atmospheric dynamics and transport from Eos

The Stratospheric Wind Infrared Limb Sounder (SWIRLS) is one of the instruments in the atmospheric sounder package to be flown by NASA on the Earth Observing System (EOS) B platform in the late 1990's. SWIRLS is designed to measure the horizontal vector wind field, atmospheric temperature, and the abundances and distributions of ozone and nitrous oxide in the middle atmosphere. These measurements will constitute a dynamical climatology of the stratosphere covering time scales ranging from diurnal to interannual. In addition, the SWIRLS investigation will quantify the physical mechanisms responsible for the structure and variations of stratospheric circulation and temperature fields, including the transport of species, particularly ozone, heat and momentum. Existing data sets lack the combination of accuracy, global and temporal coverage, spatial resoultion and simultaneity required to distinguish unambiguosly between the roles of dynamical and chemical processes in determining the current distribution of ozone and its evolution in the future. The measurement objectives, measurement approach, and instrumentation of SWIRLS is described.

Mccleese, D. J.↗
NASA NTRS1995

Vorticity and divergence in the solar photosphere

We have studied an outstanding sequence of continuum images of the solar granulation from Pic du Midi Observatory. We have calculated the horizontal vector flow field using a correlation tracking algorithm, and from this determined three scalar field: the vertical component of the curl; the horizontal divergence; and the horizontal flow speed. The divergence field has substantially longer coherence time and more power than does the curl field. Statistically, curl is better correlated with regions of negative divergence - that is, the vertical vorticity is higher in downflow regions, suggesting excess vorticity in intergranular lanes. The average value of the divergence is largest (i.e., outflow is largest) where the horizontal speed is large; we associate these regions with exploding granules. A numerical simulation of general convection also shows similar statistical differences between curl and divergence. Some individual small bright points in the granulation pattern show large local vorticities.

Wang, YI↗
NASA NTRS1996

A Real-Time Position-Locating Algorithm for CCD-Based Sunspot Tracking

NASA Marshall Space Flight Center's (MSFC) EXperimental Vector Magnetograph (EXVM) polarimeter measures the sun's vector magnetic field. These measurements are taken to improve understanding of the sun's magnetic field in the hopes to better predict solar flares. Part of the procedure for the EXVM requires image motion stabilization over a period of a few minutes. A high speed tracker can be used to reduce image motion produced by wind loading on the EXVM, fluctuations in the atmosphere and other vibrations. The tracker consists of two elements, an image motion detector and a control system. The image motion detector determines the image movement from one frame to the next and sends an error signal to the control system. For the ground based application to reduce image motion due to atmospheric fluctuations requires an error determination at the rate of at least 100 hz. It would be desirable to have an error determination rate of 1 kHz to assure that higher rate image motion is reduced and to increase the control system stability. Two algorithms are presented that are typically used for tracking. These algorithms are examined for their applicability for tracking sunspots, specifically their accuracy if only one column and one row of CCD pixels are used. To examine the accuracy of this method two techniques are used. One involves moving a sunspot image a known distance with computer software, then applying the particular algorithm to see how accurately it determines this movement. The second technique involves using a rate table to control the object motion, then applying the algorithms to see how accurately each determines the actual motion. Results from these two techniques are presented.

Taylor, Jaime R.↗
NASA NTRS1998

[MODIS Investigation]

The objective of the last six months were: (1) Continue analysis of Hawaii Ocean Time-series (HOT) bio-optical mooring data, and Southern Ocean bio-optical drifter data; (2) Complete development of documentation of MOCEAN algorithms and software for use by MOCEAN team and GLI team; (3) Deploy instrumentation during JGOFS cruises in the Southern Ocean; (4) Participate in test cruise for Fast Repetition Rate (FRR) fluorometer; (5) Continue chemostat experiments on the relationship of fluorescence quantum yield to environmental factors; and (6) Continue to develop and expand browser-based information system for in situ bio-optical data. We are continuing to analyze bio-optical data collected at the Hawaii Ocean Time Series mooring as well as data from bio-optical drifters that were deployed in the Southern Ocean. A draft manuscript has now been prepared and is being revised. A second manuscript is also in preparation that explores the vector wind fields derived from NSCAT measurements. The HOT bio-optical mooring was recovered in December 1997. After retrieving the data, the sensor package was serviced and redeployed. We have begun preliminary analysis of these data, but we have only had the data for 3 weeks. However, all of the data were recovered, and there were no obvious anomalies. We will add second sensor package to the mooring when it is serviced next spring. In addition, Ricardo Letelier is funded as part of the SeaWiFS calibration/validation effort (through a subcontract from the University of Hawaii, Dr. John Porter), and he will be collecting bio-optical and fluorescence data as part of the HOT activity. This will provide additional in situ measurements for MODIS validation. As noted in the previous quarterly report, we have been analyzing data from three bio-optical drifters that were deployed in the Southern Ocean in September 1996. We presented results on chlorophyll and drifter speed. For the 1998 Ocean Sciences meeting, a paper will be presented on this data set, focusing on the diel variations in fluorescence quantum yield. Briefly, there are systematic patterns in the apparent quantum yield of fluorescence (defined as the slope of the line relating fluorescence/chlorophyll and incoming solar radiation). These systematic variations appear to be related to changes in the circulation of the Antarctic Polar Front which force nutrients into the upper ocean. A more complete analysis will be provided in the next Quarterly report.

Abbott, Mark R.↗
NASA NTRS1999

Integrated Dual Imaging Detector

A new type of image detector was designed to simultaneously analyze the polarization of light at all picture elements in a scene. The integrated Dual Imaging detector (IDID) consists of a lenslet array and a polarizing beamsplitter bonded to a commercial charge coupled device (CCD). The IDID simplifies the design and operation of solar vector magnetographs and the imaging polarimeters and spectroscopic imagers used, for example, in atmosphere and solar research. When used in a solar telescope, the vector magnetic fields on the solar surface. Other applications include environmental monitoring, robot vision, and medical diagnoses (through the eye). Innovations in the IDID include (1) two interleaved imaging arrays (one for each polarization plane); (2) large dynamic range (well depth of 10(exp 5) electrons per pixel); (3) simultaneous readout and display of both images; and (4) laptop computer signal processing to produce polarization maps in field situations.

Rust, David M.↗
NASA NTRS1993

An Integrated Imaging Detector of Polarization and Spectral Content

A new type of image detector has been designed to simultaneously analyze the polarization of light at all picture elements in a scene. The Integrated Dual Imaging Detector (IDID) consists of a polarizing beamsplitter bonded to a charge-coupled device (CCD), with signal-analysis circuitry and analog-to-digital converters, all integrated on a silicon chip. It should be capable of 1:10(exp 4) polarization discrimination. The IDID should simplify the design and operation of imaging polarimeters and spectroscopic imagers used, for example, in atmospheric and solar research. Innovations in the IDID include (1) two interleaved 512 x 1024-pixel imaging arrays (one for each polarization plane); (2) large dynamic range (well depth of 10(exp 6) electrons per pixel); (3) simultaneous readout of both images at 10 million pixels per second each; (4) on-chip analog signal processing to produce polarization maps in real time; (5) on-chip 10-bit A/D conversion. When used with a lithium-niobate Fabry-Perot etalon or other color filter that can encode spectral information as polarization, the IDID can collect and analyze simultaneous images at two wavelengths. Precise photometric analysis of molecular or atomic concentrations in the atmosphere is one suggested application. When used in a solar telescope, the IDID will charge the polarization, which can then be converted to maps of the vector magnetic fields on the solar surface.

Rust, D. M.↗
NASA NTRS1997

Interferometric estimation of ice sheet motion and topography

With ERS-1/2 satellite radar interferometry, it is possible to make measurements of glacier motion with high accuracy and fine spatial resolution. Interferometric techniques were applied to map velocity and topography for several outlet glaciers in Greenland. For the Humboldt and Petermann glaciers, data from several adjacent tracks were combined to make a wide-area map that includes the enhanced flow regions of both glaciers. The discharge flux of the Petermann glacier upstream of the grounding line was estimated, thereby establishing the potential use of ERS-1/2 interferometric data for monitoring ice-sheet discharge. Interferograms collected along a single track are sensitive to only one component of motion. By utilizing data from ascending and descending passes and by making a surface-parallel flow assumption, it is possible to measure the full three-dimensional vector flow field. The application of this technique for an area on the Ryder glacier is demonstrated. Finally, ERS-1/2 interferograms were used to observe a mini-surge on the Ryder glacier that occurred in autumn of 1995.

Joughlin, Ian↗
NASA NTRS2000

The Solar-B Mission

The Solar-B mission is a joint enterprise between Japan, the United States of America and the United Kingdom. The collaboration is led by ISAS, the Japanese Institute for Space and Astronautical Science (ISAS), NASA and PPARC (Particle Physics and Astrophysics Research Council) play supporting roles in the development of the scientific objectives and provision of the scientific instruments. The mission's primary objective is to conduct a systems study of the solar atmosphere through the acquisition of coordinated measurements of the photosphere, the transition region/low corona and the upper corona using three instruments: an optical telescope, an extreme ultraviolet imaging spectrometer and a soft x-ray telescope. Drs. Saku Tsuneta (NAOJ) and Alan Title (LMSAL) lead the optical imaging team. The optical telescope is a 50-cm aperture, diffraction limited, Gregorian. The focal plane package will record high resolution images, Dopplergrams, and vector magnetic fields on spatial scales dominated by elemental photospheric flux tubes, and over a field of view large enough to contain small active regions. Drs. Tetsuya Watanabe, Len Culhane (MSSL) and George Doschek (NRL) led the EUV imaging and spectroscopy team. The EUV telescope has a 15-cm primary mirror feeding a toroidal grating. The optics have multiplayer coatings which select two wavebands between 180-204 A and 250-290 A. Drs. Kiyoto Shibasaki (NAOJ) and Leon Golub (SAO) lead the X-ray imaging team. The x-ray telescope will provide full disk, soft x-ray images with twice the spatial resolution of the Yohkoh SXT and enhanced sensitivity to longer (>40 A) wavelengths. The launch of Solar-B, into a sun-synchronous orbit, is scheduled for August 2004. Solar-B is the second mission in the Sun-Earth Connection, Solar-Terrestrial Probe Program which is managed by the Goddard Space Flight Center. The Science Directorate of the Marshall Space Flight Center manages the Solar-B Project for the ST Probe Project Office. This paper discusses the objectives, specifications, and design of the scientific instruments as presented at the Preliminary Design Review held at MSFC in May 2000.

Davis, John M.↗
NASA NTRS2000

Prediction of Coronal Mass Ejections from Vector Magnetograms: Results from More Active Regions

In a previous pilot study of four predominantly bipolar active regions observed by the MSFC vector magnetograph in 1991-92, we found that two quantitative measures of the global nonpotentiality of an active region were promising predictors of whether the active region produced coronal mass ejections (CMES) during its rotation across the Sun. The two quantitative measures are 1) the length (L(sub ss)) of the segments along the active region's main neutral line on which the vector magnetic field is both strong and strongly sheared, and 2) the global net current (I(sub N) flowing up one side of the bipole and down the other. Two of the active regions had large measured global nonpotentiality (L(sub ss) approximately >10(exp 5) km and I(sub N) approximately >4x 10(exp 12) Amp) and produced three CMEs each. The other two active regions had much smaller measured global nonpotentiality and produced no CMES. We have now expanded our sample of active regions by a factor of 3 with active regions from 1991 to the present. We have calibrated the line-of-sight magnetic field by comparing it to the line-of-sight field measured by Kitt Peak and/or SOHO/MDI. We have resolved the 180 deg. ambiguity in the transverse field by using three different methods, and compared the resulting global net currents. We will compare the two measures of global nonpotentiality to each other and to the CME productivity of each active i-eolon in our expanded set. We will examine the extent to which these results from the expanded set confirm or modify the tentative rule for CME prediction that we found in our pilot study.

Falconer, D. A.↗