NOAA AR 8210: EVOLUTION AND FLARES FROM MULTIBAND DIAGNOSTICS

NOAA 8210 has been a region showing a remarkable level of activity well before solar maximum. Dominated by a large, rapidly rotating spot, it produced several intense flares during its disk passage at the end of April–beginning of May 1998. We examine the development of AR 8210 in H and white light (WL) and study the evolution of its complex magnetic topology. While the other principal flares are briefly reviewed, the great X1.1/3B flare of 2 May, which was observed at Kanzelhöhe Solar Observatory during a SOHO/UVCS ground support campaign, is studied in detail. This event has been documented in full-disk H and Na-D intensitygrams, Dopplergrams, and magnetograms, with a time cadence of one minute each. The flare was associated with a CME and produced significant geomagnetic effects. Furthermore, we point out the perspectives for our planned Flare Monitoring and Alerting System, since the two new instruments (Magneto-Optical Filter and Digital H camera), which made their first operational run with the campaign, are crucial components for this program.     

An instrument to measure solar magnetic fields by an atomic-beam method

Using the atomic-beam technique in absorption, a new kind of very narrow-passband filter is obtained, which may also be used as a high-resolution spectrograph and as a Babcock window for detecting solar magnetic fields without a spectrograph.     

Some developments of the magnetic beam absorption filter

In the present paper some experimental arrangements are shown which utilize the magnetic filter described by Cimino et al. (1968). For a single cell we have elaborated an elementary theory in the following cases: (i) absorption by an atomic beam in a uniform magnetic field (i.e. pure damping profile); (ii) atomic beam in a non-uniform magnetic field; (iii) vapours in a uniform magnetic field (i.e. gaussian distribution); (iv) vapours in a non-uniform magnetic field.     

An instrument to observe low-degree solar oscillations

We have constructed an instrument optimized to observe solar oscillations of low degree. The primary goal of this instrument, which we call LOWL, is to measure the frequency splitting of the low-degree modes in order to determine the rotation rate of the solar core. The LOWL is a Doppler imager based on a magneto-optical filter. It employs a two-beam technique to simultaneously observe solar images in opposite wings of the absorption line of potassium at 769.9 nm. This instrument is very stable against drifts in the wavelength zero-point, is insensitive to noise sources due to intensity fluctuations and image motion, and has a Doppler analyzer with no moving parts. The LOWL has been deployed at HAO's observing station on Mauna Loa, Hawaii and will operate for a period of at least two years.The National Center for Atmospheric Research is sponsored by the National Science Foundation.     

The stark effect as a calibration tool in helioseismology

In this paper we address the problem of the calibration for the Doppler signal obtained from resonant scattering spectrometers and magneto optical filters that are being used to measure solar oscillations. After discussing current methods of calibration, we suggest and study a new method based on the Stark effect. Our analysis and preliminary test confirm the capability and the advantages of the method.     

Analysis of two-decade meteorological and air quality trends in Rome (Italy)

Theoretical and Applied Climatology - The extreme temperature events are a concern in recent years due to climate variability particularly in India as there is an increase in the temperature...     

Magnetic Contamination and Correction in Sodium Dopplergrams

Recently a new version of a sodium double-band magneto-optical filter has been built in order to provide simultaneous Doppler and magnetograms using the same optical path (Cacciani, Moretti, and Rodgers, 1997; Cacciani et al., 1988, 1994). Two observing stations based on this instrument are being installed as part of the French network IRIS. One is already operational in Apple Valley, California, and the other one will be delivered shortly to Tashkent, Uzbekistan. The performance of the instrument is such as to detect the l = 0 mode of solar oscillations from resolved images with a signal-to-noise ratio that has never been achieved before (Cacciani and Moretti, 1994). The magnetic and velocity signals are corrected for the changes that occur in the solar D-line profile in active versus non-active regions. This kind of analysis will be performed by our group in conjunction with parallel analysis of GOLF and IRIS integrated data which use the same sodium lines.     

Abstracts of forthcoming papers

A new polarimeter is described which allows the simultaneous determination of the four Stokes parameters analysing the electric signal both in frequency and phase. The signal consists of two frequencies and 2 . From the 2 component the amount and the azimuth of linearly polarized light is obtained by using a two-phase lock-in amplifier (or two separate amplifiers). From the component the circular polarization is obtained. Instrumental and spurious effects, caused by rotating elements, are avoided. Magnetographic applications in solar physics and improvements as compared to previous magnetographs are suggested.     

The magneto-optical filter

In this paper we describe a filter which utilizes magneto-optical effects for velocity fields measurements. The working principle of the instrument is described and its transmission profiles are given. Velocitygrams are shown of the five minutes oscillations (FMO) and the results compared with the expected (theoretical) signal from the instrument. We found a V _rms of 400 m s^–1 for the FMO.