Solar Maximum Mission Satellite Research Articles

Coronal Observations from the Solar Maximum Mission Satellite

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Spatial and temporal evolution of soft and hard X-ray emission in a solar flare

We study the spatial and temporal characteristics of the 3.5 to 30.0 keV emission in a solar flare on April 10, 1980. The data were obtained by the Hard X-ray Imaging Spectrometer aboard the Solar Maximum Mission Satellite. It is complemented in our analysis with data from other instruments on the same spacecraft, in particular that of the Hard X-ray Burst Spectrometer. Key results of our investigation are: (a) Continuous energy release is needed to substain the increase of the emission through the rising phase of the flare, before and after the impulsive phase in hard X-rays. The energy release is characterized by the production of hot (5 × 107 ≲ T ≲ 1.5 × 108 K) thermal regions within the flare loop structures. (b) The observational parameters characterizing the impulsive burst show that it is most likely associated with non-thermal processes (particle acceleration). (c) The continuous energy release is associated with strong chromospheric evaporation, as evidenced in the spectral line behavior determined from the Bent Crystal Spectrometer data. Both processes seem to stop just before flare maximum, and the subsequent evolution is most likely governed by the radiative cooling of the flare plasma.

Solar energy shortage?

According to the results of a recent study by the Jet Propulsion Laboratory (JPL), there has been a decrease of a tenth of a percent in the total amount of solar energy reaching the earth over the 18‐month period from February 1980 to August 1981. This conclusion is based on data obtained from the Active Cavity Radiometer Irradiance Monitor (ACRIM) that is incorporated onto the Solar Maximum Mission satellite. The results are significant for studies of the physics and geophysics of the sun and could have implications for short‐ and long‐term weather patterns on the earth's surface.The ACRIM has a precision of better than 10 4, whereas the uncertainties in the best earth‐based observations are on the order of 1% to 2%. The JPL group conducting the study suggests that the decrease in the sun's energy may even have been a factor in this year's unusually harsh winter.

The impulsive and gradual phases of a solar limb flare as observed from the solar maximum mission satellite

Simultaneous observations of a solar limb flare in the X-ray and ultraviolet regions of the spectrum are presented. Temporal and spectral X-ray observations were obtained for the 25–300 keV range while temporal, spectral, and spatial X-ray observations were obtained for the 30–0.3 keV range. The ultraviolet observations were images with a 10″ spatial resolution in the lines of O v (Te ∼ 2.5 × 105 K) and Fe xxi (Te ∼ 1.1 × 107 K). The hard X-ray and O v data indicate that the impulsive phase began in the photosphere or chromosphere and continued for several minutes as material was ejected into the corona. Impulsive excitation was observed up to 30 000 km above the solar surface at specific points in the flare loop. The Fe xxi observations indicate a preheating before the impulsive phase and showed the formation of hot post-flare loops. This later formation was confirmed by soft X-ray observations. These observations provide limitations for current flare models and will provide the data needed for initial conditions in modeling the concurrent coronal transient.

Solar irradiance variations due to active regions

Questions regarding changes in solar irradiance due to activity are important, since such changes may have a significant effect on the earth's climate. Solar irradiance measurements conducted outside the earth's atmosphere and, therefore, not affected by it have become possible by utilizing for such measurements satellites, such as the Nimbus 7 and the Solar Maximum Mission satellite (ACRIM experiment). The present investigation has the objective to show that a combination of sunspots and faculae is capable of representing the observed variations in the values of ACRIM data to a satisfactory degree, given the current level of uncertainties in the ground-based data.

Comparison of observed Ca xix and Ca xviii relative line intensities with current theory

A comparison is made between Ca xix and Ca xviii line ratios observed in solar flares with the Bent Crystal Spectrometer (BCS) on the Solar Maximum Mission (SMM) satellite and currently available atomic data. Close agreement is found with the excitation rates recently published by Pradhan et al. (1981). The observations show little dependence of line ratios on electron temperature, supporting a further conclusion that cascade contributions to the 23P and 23S levels are not significant.

Computer Controlled Operation of Ultraviolet Spectrometer and Polarimeter on Solar Maximum Mission Satellite

Covers advancements in spacecraft and tactical and strategic missile systems, including subsystem design and application, mission design and analysis, materials and structures, developments in space sciences, space processing and manufacturing, space operations, and applications of space technologies to other fields.

Fluorescent excitation of photospheric Fe K-α emission during solar flares

The Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite provides high spectral and temporal resolution observations of the Fe Kα lines. We have analysed spectra from almost 50 solar flares that occurred during 1980. These data strongly support fluorescent excitation of photospheric iron by photons of E > 7.11 keV emitted by the hot coronal plasma produced during the flare. After comparison of the data with a model, we discuss the observed Kα line widths, estimates of the size of the emitting region, the height of the coronal source and the photospheric iron abundance.

SMM detects new reactions in solar flares

A gamma ray and neutron spectrometer instrument built at the University of New Hampshire under direction of Edward L. Chupp has detected several important new kinds of emissions from solar flares. The instrument was launched Feb. 14, 1980 on the Solar Maximum Mission satellite. Chupp reports that during a major flare on June 21, 1980, his experiment made the first clear observations of neutrons reaching the earth from a solar flare.Neutrons are neutral subatomic particles created in nuclear reactions with flares. Free neutrons decay spontaneously into protons and electrons in about 15 minutes, so only very high speed neutrons can reach the earth at all, as light takes about 8 minutes to reach the earth from the sun. In the June 21 flare an intense burst of gamma rays, lasting about 1 minute, was followed by a 20‐min stream of neutrons. This particular flare was probably the most intense to occur during this solar cycle.

Steady flows in the solar transition region observed with SMM

Steady flows in the quiet solar transition region have been observed with the Ultraviolet Spectrometer and Polarimeter experiment on the Solar Maximum Mission (SMM) satellite. The persistent vertical motions seen at disk center have spatial rms amplitudes of 1.4 km/s in the C II line, 3.9 km/s in Si IV, and 4.2 km/s in C IV. The amplitudes of the more horizontal flows seen toward the limb tend to be somewhat higher. Plots of steady vertical velocity versus intensity seen at disk center in Si IV and C IV show two distinct branches.

Observations of transitions of hydrogen-like Fe XXVI in solar flare spectra

Observations of solar flare spectra over the wavelength range 1.769-1.796 A with the Bent Crystal Spectrometer on the NASA Solar Maximum Mission satellite are presented. The 2P3/2, 2P1/2 and associated satellite transitions of Fe XXVI are identified, their intensities and widths estimated and the results compared with theoretical predictions. For two spectra, which include the isolated n = 2 satellite features, the observations can be reproduced by plasma temperatures of 24,000,000 and 28,400,000 K. Linewidth measurements show evidence for nonthermal velocities of up to 150 km/s. Emission measures derived from the Fe XXVI observations are compared with those from lower temperature Ca XIX and Fe XXV measurements and an emission measure decreasing with temperature is found.

Optical alignment of an x-ray collimator

The hard x-ray imaging spectrometer (HXIS) is one of the instruments aboard the NASA Solar Maximum Mission satellite. For the imaging of solar flares in hard x rays HXIS employs a grid collimator with an 8-sec of arc FWHM angular resolution. The collimator consists of ten grid plates in a sequence. The position accuracy of the grids in their planes must be better than a few microns. This paper describes a simple optical alignment method developed to perform measurements of the grid positions with a precision of 1 microm.

The surface preparation of beryl crystals for X-ray spectroscopy

One of the few crystals available for X-ray spectroscopy in the 1.0 to 1.5 nm band is natural beryl. This report describes work carried out to measure and improve the X-ray characteristics of four samples of the pink form of beryl (morganite) to establish the suitability of its use in the X-ray polychromator (XRP) instrument flown in the NASA Solar Maximum Mission satellite. Surface preparation of beryl crystals by etching in hydrofluoric acid followed by polishing in X-30 syton is shown to bring the rocking curve widths (FWHM) as measured on a two-crystal spectrometer to the near perfect values of 5 arc sec at Cu K alpha (0.154 nm) and 3.3 arc min at Cu L alpha (1.331 nm). In addition the crystals peak reflectivity can be enhanced by a factor eight times that of flat and ground but otherwise untreated crystals.

Solar flare plasmas

The solar flare is discussed in terms of its three phases: energy storage, energy release, and dissipation. Some of the problems associated with theoretical modelling are considered, together with the limitations imposed by current observations. New measurements to be made by the N.A.S.A. Solar Maximum Mission satellite are expected to advance significantly our understanding of the flare mechanism.

Observations with the SMM gamma-ray spectrometer - The impulsive solar flares of 1980 March 29

Gamma-ray continuum emission from 0.3 to 1 MeV was observed with the gamma-ray spectrometer on the Solar Maximum Mission satellite during two impulsive solar flares on 1980 March 29, from active region 2363 at 0918 UT and from active region 2357 at 0955 UT. Evidence is presented for a hardening of the spectrum during the impulsive phase of the flares. The photon intensity greater than 100 keV appears to decay at a slower rate than that at lower energies. Time-integrated photon spectra for both flares are incompatible with a single-temperature thermal-bremsstrahlung model. Upper limits for prompt and delayed gamma-ray lines are presented.

Observation of the 2.223 MeV gamma-ray line on the SMM satellite - The event of 1980 June 7

The Gamma-Ray Spectrometer on the Solar Maximum Mission satellite observed ..gamma..-ray lines during the 0312 UT solar flare on 1980 June 7. The impulsive X- and ..gamma..-ray event lasted for or approx. =50 MeV, produced during a approx.40 s interval overlapping the impulsive photon emission time interval. A total production of 4 x 10/sup 29/ neutrons is required, if they were produced isotropically.

Observations of Solar Irradiance Variability

High-precision measurements of total solar irradiance, made by the active cavity radiometer irradiance monitor on the Solar Maximum Mission satellite, show the irradiance to have been variable throughout the first 153 days of observations. The corrected data resolve orbit-to-orbit variations with uncertainties as small as 0.001 percent. Irradiance fluctuations are typical of a band-limited noise spectrum with high-frequency cutoff near 0.15 day(-1) their amplitudes about the mean value of 1368.31 watts per square meter approach +/- 0.05 percent. Two large decreases in irrradiance of up to 0.2 percent lasting about 1 week are highly correlated with the development of sunspot groups. The magnitude and time scale of the irradiance variability suggest that considerable energy storage occurs within the convection zone in solar active regions.

The Solar Maximum Year and related space experiments

The Solar Maximum Year is a world-wide cooperative project to gain more insight in certain aspects of solar flares. It consists of three sub-programs: The Flare Build-up Study (FBS), the Study of Energy Release from Flares (SERF), and the Study of Travelling Interplanetary Phenomena (STIP). These programs are described. We also describe space observations to be performed during SMY, particularly the Solar Maximum Mission Satellite.

The High Altitude Observatory Coronagraph/Polarimeter on the Solar Maximum Mission

The High Altitude Observatory Coronagraph/Polarimeter, to be flown on the National Aeronautics and Space Administration's Solar Maximum Mission satellite, is designed to produce images of the solar corona in seven wavelength bands in the visible spectral range. The spectral bands have been chosen to specifically exclude or include ‘chromospheric’ spectral lines, so as to allow discrimination between ejecta at high (coronal) and low (chromospheric) temperatures, respectively. In addition, the instrument features spectral filters designed to permit an accurate color separation of the F and K coronal components, and a narrow band (5.5 A) filter to observe the radiance and polarization of the Fe xiv 5303 A line. The effective system resolution is better than 10 arc sec and the instrument images a selected quadrant (or smaller field) on an SEC vidicon detector. The total height range that may be recorded encompasses 1.6 to more than 6.0R ⊙ (from Sun center). The instrument is pointed independently of the SMM spacecraft, and its functions are controlled through the use of a program resident within the onboard spacecraft computer. Major experimental goals include: (a) Observation of the role of the corona in the flare process and of the ejecta from the flare site and the overlying corona; (b) the study of the direction of magnetic fields in stable coronal forms, and, perhaps, ejecta; and (c) examination of the evolution of the solar corona near the period of solar maximum activity.