Joan T. Schmelz

Coronal magnetic structures observing campaign. IV - Multiwaveband observations of sunspot and plage-associated coronal emission

Results of simultaneous observations of an active region located near the central meridian obtained on December 18, 1987, are presented. An asymmetric looplike structure connects the strong leading sunspot with a nearby region of opposite polarity. Both 6- and 20-cm emission lie along this structure, rather than over the sunspot, with higher frequency emission originating closer to the footpoint inside the sunspot. The 20-cm emission is due to a superposition of second- and third-harmonic gyroemission, where the field strength is 160-300 G, while the 6-cm emission is due to third-harmonic gyroemission from a region where the magnetic field strength ranges from 547 to 583 G. X-ray data associated with an area of trailing plage are used to predict the brightness temperature structure due to thermal bremsstrahlung emission in the 6- and 20-cm wavebands.

Microwave polarization inversion observed

An inversion of solar active region microwave polarization was observed during the Coronal Magnetic Structures Observing Campaign (CoMStOC) [Brosius et al., 1992; Nitta, 1991; Schmelz and Holman, 1991; Schmelz, 1991; Schmelz et al., 1988]. This campaign, carried out in November and December 1987, was intended to improve our understanding of active region coronal plasmas and magnetic fields. The intensity and polarization of solar active region microwave emission provides probes of the coronal magnetic field. When combined with simultaneous x-ray and photospheric magnetic field observations, they form a powerful data set that can be used to deduce the physical properties of the plasma and the magnetic field in the active region corona. This article describes some results from a highly successful campaign.

Multi-wave band SMM-VLA observations of an M2 flare and an associated coronal mass ejection

An M2 flare and an associated coronal mass ejection (CME) were observed by instruments on the Solar Maximum Mission as well as by the Very Large Array and other ground-based observatories on 1988 September 30 as part of the International Solar Month campaign. The multi-wave band data show a gradual, slowly changing event which lasted several hours. The microwave burst emission originates in compact (θ=10″-30″), moderately circularly polarized (ρ c ≤60%) sources (T b =0.5-20×10 6 K) located near the sites of bright Hα and soft X-ray emission. These data were combined with estimates of electron temperature (T e =1.5×10 7 K) and emission measure (EM≃2.0×10 49 cm −3 ) obtained from CA XIX and Fe XXV spectra to show that the microwave emission can be attributed to thermal gyrosynchrotron radiation in regions where the magnetic field strength is H=425-650 G.

International Solar Month–September 1988

Solar Maximum Mission (SMM) scientists plan to participate in a worldwide campaign to observe the Sun in September 1988. It is hoped that solar physicists from the Soviet Union and several European countries with experiments on the Soviet spacecraft PHOBOS (a mission to Mars which will carry solar instruments) will also be involved. PHOBOS will be launched in July; the TEREK instruments (a soft X ray imager, and ultrasoft X ray imager and a white light coronograph) will image the Sun twice every 5 days. Other instruments will obtain nonimaging solar data much more frequently. Now that the rapid rise phase of the new solar cycle is well under way, such joint observations of the Sun should be particularly fruitful.