Engineering topics

Michels, D. J.

Publications and source records attributed to Michels, D. J..

At least 19 records

NASA NTRS1997

White-light coronal mass ejections: A new perspective from LASCO

More than 275 coronal mass ejections (CMEs) were recorded by the large angle spectroscopic coronagraph (LASCO) from January 1996 through August 1997. Some of the characteristics of 65 of these CMEs, occurring during a three month period (May to July 1997) were quantified. During this time the rate of CME detection was about 0.7 CMEs per day; the distribution of apparent latitudes was clustererd near the equator with an average latitude of 3 deg N; the average width of the CMEs was 49 deg; and the average speed was 324 km/s. The statistical measures and the distributions for these CMEs agree with the existing literature. One new result was the high fraction (plus or minus 35 deg) of CMEs with at least one concave-outward morphological feature, which was considered a possible signature of magnetic disconnection. A new small-scale phenomenon that appears to be the white light counterpart of the extreme ultraviolet microjets detected in the polar coronal holes is described.

St.Cyr, O. C.↗

NASA NTRS1997

Solar energetic particle events and coronal mass ejections: New insights from SOHO

The scientific payload of SOHO, launched in December 1995, enables comprehensive studies of the sun from its interior, to the outer corona and solar wind. In its halo orbit around the Lagrangian point of the sun-earth system, the comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic partiles in the energy range 44 keV/particle to greater than 53 MeV/n. Although solar activity was at minimum, COSTEP detected from mid December 1995 until the end of July 1997, 30 solar energetic particle (SEP) events, including both gradual and implusive type SEPs. These minimum phase SEP events are unique in the sense that their associated solar source phenomena can be investigated in detail without interference by other simultaneous solar events as is usually the case at times around solar activity maximum. Simultaneous observations of the solar corona are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). From the correlated SOHO observations, a one to one correspondence of SEP events with coronal mass ejections (CMEs) was found. Most of the SEP events were associated with west-limb CMEs, some with halo CMEs that later passed the SOHO spacecraft and with Moreton-like disturbances in the lower solar atmosphere as observed by the EIT. Many SEP events were detected at sector boundaries of the interplanetary magnetic field (IMF) suggesting a magnetic connection to coronal streamers at the sun as supported by LASCO observations of mass ejections at the base of helmet streamers. Energetic particle and LASCO white-light observations yield evidence that CMEs often lead to large-scale disturbances of the sun's corona, probably affecting at times areas all around the sun.

Bothmer, V.↗

NASA NTRS1997

Fluxes of MeV particles at Earth's orbit and their relationship with the global structure of the solar corona: Observations from SOHO

The SOHO satellite, launched on 2 December 1995, combines a unique set of instruments which allow comparative studies of the interior of the sun, the outer corona and solar to be carried out. In its halo orbit around the L1 Lagrangian point of the sun-earth system, SOHO's comprehensive suprathermal and energetic particle analyzer (COSTEP) measures in situ energetic particles in the energy range of 44 keV/particle to greater than 53 MeV/n. The MeV proton, electron and helium nuclei measurements from the COSTEP electron proton helium instrument (EPHIN) were used to investigate the relationships of intensity increases of these particle species with the large-scale structures of the solar corona and heliosphere, including temporal variations. Coronal observatons are provided by the large angle spectroscopic coronagraph (LASCO) and the extreme ultraviolet imaging telescope (EIT). It was found that during times of minimum solar activity, intensity increases of the particles have two well defined sources: corotating interaction regions (CIRs) in the heliosphere related to coronal holes at the sun and coronal mass ejections.

Posner, A.↗

NASA NTRS1997

The solar minimum X2.6/1B flare and CME of 9 July 1996: Solar data - Pt. 1

The solar observations from GOES-8, the Solar and Heliospheric Observatory (SOHO), and the Yohkoh satellite concerning the events of the X-class flare are discussed. The Michelson Doppler imager (MDI) magnetometer shows a new region of magnetic activity in AR 7978. The rapid development and evolution of this region is shown by the MDI and the extreme-ultraviolet Doppler telescope (EDT) data. The coronal mass ejections (CMEs) observed using coronagraphs are presented. The possible association between the CME and the X-flare is considered.

Andrews, M. D.↗

NASA NTRS1997

The solar minimum X2.6/1B flare and CME of 9 July 1996: Propagation - Pt 2

The interplanetary propagation aspects of the first X-class solar flare and coronal mass ejection are discussed. The solar data relevant to this event are summarized. Data from WIND and charge element and isotope analysis system (CELIAS) show solar wind plasma and interplanetary magnetic field disturbances early on 12 July 1996. It was observed that the extrapolation of the coronal mass ejection back to the flare time suggests a close association between them. Moreover, the coronal mass ejection speed is similar to the type two shock's speed. The results suggest that the coronal mass ejection is intimately related to the shock itself.

Dryer, M.↗

NASA NTRS1992

The Large Angle Spectroscopic Coronagraph (LASCO): Visible light coronal imaging and spectroscopy

The Large Angle Spectroscopic Coronagraph (LASCO) is a triple coronagraph being jointly developed for the Solar and Heliospheric Observatory (SOHO) mission. LASCO comprises three nested coronagraphs (C1, C2, and C3) that image the solar corona for 1.1 to 30 solar radii (C1: 1.1 to 3 solar radii, C2: 1.5 to 6 solar radii, and C3: 3 to 30.0 solar radii). The inner coronagraph (C1) is a newly developed mirror version of the classic Lyot coronagraph without an external occultor, while the middle coronagraph (C2) and the outer coronagraph (C3) are externally occulted instruments. High resolution coronal spectroscopy from 1.1 to 3 R solar radii can be performed by using a Fabry-Perot interferometer, which is part of C1. High volume memories and a high speed microprocessor enable extensive onboard image processing. Image compression by factors of 10 to 20 will result in the transmission of 10 to 20 full images per hour.

Brueckner, Guenter E.↗

NASA NTRS1989

The extreme ultraviolet imaging telescope on board SOHO

The design of the multibandpass Extreme-Ultraviolet Imaging Telescope designed for 1996 launch on board the Solar Heliospheric Observatory is described. The telescope will observe simultaneously distinct temperature ranges in the solar corona, defined by well chosen emission lines. Images in four narrow bandpasses at wavelengths ranging from 17 to 31 nm will be obtained using normal-incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. Results are presented on the performances measured on a 2/3 scale mock-up. The bandpasses could be adjusted to better than 1 percent in wavelength.

Delaboudiniere, J. P.↗

NASA NTRS1988

EIT: Solar corona synoptic observations from SOHO with an Extreme-ultraviolet Imaging Telescope

The Extreme-ultraviolet Imaging Telescope (EIT) of SOHO (solar and heliospheric observatory) will provide full disk images in emission lines formed at temperatures that map solar structures ranging from the chromospheric network to the hot magnetically confined plasma in the corona. Images in four narrow bandpasses will be obtained using normal incidence multilayered optics deposited on quadrants of a Ritchey-Chretien telescope. The EIT is capable of providing a uniform one arc second resolution over its entire 50 by 50 arc min field of view. Data from the EIT will be extremely valuable for identifying and interpreting the spatial and temperature fine structures of the solar atmosphere. Temporal analysis will provide information on the stability of these structures and identify dynamical processes. EIT images, issued daily, will provide the global corona context for aid in unifying the investigations and in forming the observing plans for SOHO coronal instruments.

Delaboudiniere, J. P.↗

NASA NTRS1986

Properties of metre-wavelength solar bursts associated with coronal mass ejections

An investigation is made to determine the relationship between a coronal mass ejection (CME) and the characteristics of associated metre-wave activity. It is found that (1) the CME width and leading edge velocity can be highly influential in determining the intensity, spectral complexity and frequency coverage of both type II and continuum burst; (2) the presence of a CME is possibly a necessary condition for the production of a metric continuum event and (3) metric continuum bursts as well as intense, complex type II events are preferentially associated with strong, long lasting soft X-ray events.

Robinson, R. D.↗

NASA NTRS1986

Solwind observations of coronal mass ejections during 1979-1985

Coronal observations have been processed for parts of each year during the interval 1979-1985. Around sunspot maximum, coronal mass ejections (CMEs) occurred at the rate of approximately 2 per day, and had a wide range of physical and morphological properties. During the recent years of relatively low sunspot number, CMEs occurred at the rate of only 0.2 per day, and were dominated by the class of so-called streamer blowout. These special CMEs maintained a nearly constant occurrence rate of roughly 0.1 per day during the entire interval.

Sheeley, N. R., Jr.↗

NASA NTRS1985

Coronal mass ejections - 1979-1981

An overview of observations of coronal mass ejections (CMEs) during the interval March 28, 1979 through December 31, 1981 is presented. An introduction is first provided to the instrument used in the observations, the method of identifying CMEs, the concepts of CME structural classes, CME importance categories, and the distribution of mass ejections among these classes and categories. The properties of CMEs are given for all mass ejections regardless of their structural classes or importance categories, and then for each class and category. After a brief discussion of the instrument duty cycle, the occurrence rate is presented for all CMEs and for major CMEs, for fast CMEs only, and finally for equatorial CMEs only. The results are compared to those obtained previously.

Howard, R. A.↗

NASA NTRS1985

White-light and radio sounding observations of coronal transients

A concerted search for coronal transients was conducted with the 'Solwind' coronagraph during the solar occultations of the two Helios spacecraft in October/November 1979. The polarization angle and bandwidth of the linearly polarized S-band downlink signal were monitored at the three 64-m tracking stations of the NASA Deep Space Network to determine coronal Faraday rotation and spectral broadening. A one-to-one correspondence could be established between abrupt disturbances in the two signal parameters and the passage of a white-light transient through the signal ray path from spacecraft to earth. The white-light morphology and the additional information provided by the radio sounding coverage are presented for each of the five distinct events recorded. Although no specific example could be observed in sufficient detail in both white light and Faraday rotation to derive the small-scale magnetic structure, some qualitative descriptions of the orientation and rough estimates of the magnitude of the transient magnetic field could be made.

Bird, M. K.↗

NASA NTRS1985

The frequency of long-duration solar X-ray events

The rate of occurrence of coronal and interplanetary phenomena during the solar sunspot cycle was studied based on nearly continuous satellite data for long-duration events in the period 1969-1982. The data were obtained using the NRL SOLRAD and the NOAA GOES spacecraft for each year in the interval. The duration of the X-ray events was defined as the time for the logarithm of the 1-8 A flux to return to approximately 10 percent of the pre-event level. The total number of X-ray events is plotted next to the annual sunspot number for the interval 1969-1982. It is shown that the long duration of X-ray events was not related to the sunspot cycle, particularly events of 6 hr or more.

Koomen, M. J.↗

NASA NTRS1985

A comparison of solar helium-3-rich events with type II bursts and coronal mass ejections

The acceleration process for energetic particles in He-3-rich events and for particles in normal-abundance events are compared. A list of 66 He-3-rich events observed with the Goddard Space Flight Center particle detector on ISEE 3 is presented, and it is shown that these events are not statistically associated with either of the two common signatures of normal-abundance events, metric type II and coronal mass ejections. This result indicates that enhanced abundance events may be produced only in the impulsive phases of flares, while normal abundance events are produced in subsequent flare shock waves.

Kahler, S.↗

NASA NTRS1985

Doppler scintillation observations of interplanetary shocks within 0.3 AU

It is pointed out that more definitive shock velocity observations near the sun are needed for an improved determination of the extent of shock deceleration from the sun to earth. Woo and Armstrong (1981) have demonstrated the use of radio scattering and scintillation observations, using spacecraft signals, for measuring interplanetary shock waves near the sun. Woo and Armstrong provided the first near-sun profiles of solar wind speed and electron density fluctuation for a shock wave produced by a solar flare. The present investigation has the objective to demonstrate the use of Doppler or phase scintillations for monitoring and observing interplanetary shocks. It is also shown that Doppler noise, a parameter which is routinely observed and recorded by the NASA Deep Space Network, is essentially a measure of Doppler scintillations.

Woo, R.↗

NASA NTRS1985

Coronal mass ejections and interplanetary shocks

A comparison between Solwind observations of coronal mass ejections (CME's) and Helios 1 observations of interplanetary shocks during 1979-1982 indicates that 72 percent of the shocks were associated with large, low-latitude mass ejections on the nearby limb. Most of the associated CME's had speeds in excess of 500 km/s, but some of them had speeds in the range 200-400 km/s. An additional 26 percent of the shocks may have been associated with CME's, but we were less confident of these associations because the sizes and locations of the CME's did not seem appreciably different from those of the numerous CME's without Helios shocks. Only 2 percent of the shocks clearly lacked CME's. As the average level of sunspot activity declined during 1982, the shock frequency also declined, but the observed shocks and some of their associated CME's had unusually high speeds well in excess of 1000 km/s.

Sheeley, N. R., Jr.↗

NASA NTRS1985

Characteristics of coronal mass ejections associated with solar frontside and backside metric Type II bursts

Fast velocities of 500 km/s or greater coronal mass ejections (CME's) are compared with reported metric type II bursts to study the properties of CME's associated with coronal shocks. An earlier report of fast frontside CME's with no associated metric type II bursts is confirmed, and it is calculated that 33 + or - 15 percent of all fast frontside CME's are not associated with such bursts. Faster CME's are more likely to be associated with type II bursts, as expected from the hypothesis of piston-driven shocks. However, CME brightness and associated peak 3-cm burst intensity are also important factors, as might be inferred from the Wagner and MacQueen (1983) view of type II shocks decoupled from associated CME's. The equal visibility of solar frontside and backside CME's is used to deduce the observability of backside type II bursts. It is calculated that 23 + or - 7 percent of all backside type II bursts associated with fast CME's can be observed at the earth and that 13 + or - 4 percent of all type II bursts originate in backside flares. CME speed again is the most important factor in the obervability of backside type II bursts.

Kahler, S. W.↗

NASA NTRS1984

Associations between coronal mass ejections and solar energetic proton events

A comparison between proton events and coronal mass ejections (CMEs) based on nearly three years of observations around the recent maximum of solar activity is presented. Peak proton fluxes are found to correlate with both the speeds and the angular sizes of the associated CMEs. It is shown that CME speeds do not significantly correlate with CME angular sizes, so that peak proton fluxes are correlated with two independent CME parameters. With larger angular sizes, CMEs are more likely to be loops and fans rather than jets and spikes and are more likely to intersect the ecliptic.

Kahler, S. W.↗