Solar abundance determination from ultraviolet emission lines

Extensive observations of left and right circularly polarized emission were carried out with the 120 ft Haystack antenna, which at 3.8 cm has a HPBW of 4.4'. During a very quiet period, September 22-26, 1974, two regions were observed in the southern hemisphere of the Sun with brightness temperatures approximately 10 % below the surrounding solar disk temperature. Hot photographs show that the main region was associated with a long filament. The separation between the center of the radio depression and the filament increased as the filament advanced toward the limb, with the depression finally disappearing when the filament was at a radial distance >0.8 R o from the center of the solar disk. These observations are in agreement with a filament model consisting of a thin, tall and exceedingly long sheet of enhanced density encaged in a large and equally long tunnellike cavity of lower density. The electron density at the 3.8 cm emission level which occurs immediately below the transition zone was estimated to be lower inside the cavity than outside by a factor of 2. The origin of the other depression remains unclear because no relation to any Ha or magnetic feature could be found. A possible association with a coronal hole could not be established because no pertinent EUV or X-ray data were available. It would be of interest to investigate in future observations if a secondary depression is normally associated with the primary depression region over a long filament.

Section: Analysis Of the Datamentioning

confidence: 99%

Study of a filament with a circularly polarized beam at 3.8 cm

Straka¹,

Papagiannis

Kogut

1975

“…0 Equation ( 2 0 ) may t h e r e f o r e be w r i t t e n 2 2 FdF = n T f ( T ) dT . 0 0 I n t e g r a t i o n of e q u a t i o n ( 2 5 ) from TZF t o T 0 g i v e s ZF which shows t h a t f o r c o n s t a n t To and TZF9 Fo i s approximately prop o r t i o n a l t o n 0 " 3.2 COMPARISON OF THE MOD& WITH XW-RESONANCE-LINE DATA 3.2.1 O b s e r v a t i o n a l Evidence f o r a P l a n a r Constant-Heat-Flux Region The a n a l y s e s of Athay (1966) and Dupree and Goldberg (1967) of t h e emission of XW resonance l i n e s from a p l a n a r t r a n s i t i o n region, i n c o n j u n c t i o n w i t h t h e observed energy f l u x e s of s e v e r a l XW resonance l i n e s , p r o v i d e t h e e m p i r i c a l evidence f o r a p l a n a r c o n s t a n t -h e a t -f l u x region i n t h e temperature range 1 0 ' K t o 10 6 K. I n these a n a l y s e s t h e energy f l u x 5 l a t e d t o t h e s t r u c t u r e of t h e t r a n s i t i o n r e g i o n by observed a t t h e e a r t h i n an XW resonance l i n e i s re-…”

Section: K / H F Dt I S P O S I T I V E Due T O T H E F a C T T H A Tmentioning

confidence: 94%

“…r e g i o n from about 2,000 km t o about 10,000 k m above t h e photosphere (Athay, 1969, Dupree andGoldberg, 1967). Observed energy f l u x e s of extreme u l t r a v i o l e t resonance l i n e s e m i t t e d from t h e o u t e r s o l a r atmosphere imply (see S e c t i o n 3.2.1) t h a t above t h e lo5 K l e v e l t h e atmosp h e r e i s approximately p l a n a r , and t h a t t h e f l u x of h e a t flowing from t h e corona down t o t h e chromosphere remains roughly c o n s t a n t from t h e 10 K l e v e l down t o t h e 10 K l e v e l .…”

Section: T O About 10 K ( T Y P I C a L Temperature Of T H E Lower C mentioning

confidence: 99%

Structure of the chromosphere-corona transition region

Moore

Fung

1972

J a n u a r y 1971 I n s t i t u t e f o r Plasma Research S t a n f o r d U n i v e r s i t y S t a n f o r d , C a l i f o r n i a N a t i o n a l Aeronautics and Space A d m i n i s t r a t i o n Grant P ABSTRACTThe s t r u c t u r e and energy balance of t h e chromosphere-corona t r a ns i t i o n r e g i o n i s i n v e s t i g a t e d by means of a s t a t i c , p l a n a r model which i s compared w i t h t h e r e s u l t s of XW-resonance-line o b s e r v a t i o n s . I n t h i s model, t h e t r a n s i t i o n r e g i o n i s h e a t e d by thermal conduction from t h e corona and cooled by r a d i a t i v e l o s s e s . Comparison of t h e model w i t h o b s e r v a t i o n a l r e s u l t s i m p l i e s t h a t t h i s i s t h e dominant p r o c e s s i n t h e energy b a l a n c e of t h e t r a n s i t i o n region, and t h a t t h e base of t h e t r a n s i t i o n r e g i o n i s i n h e r e n t l y n o n -s t a t i c and/or non-planar. T h e model e x p l a i n s t h e o b s e r v a t i o n a l f i n d i n g of Noyes e t . a l . (1970) t h a t t h enumber d e n s i t y and t h e downward h e a t f l u x both i n c r e a s e by t h e same f a c t o r from q u i e t r e g i o n s t o a c t i v e r e g i o n s . The i m p l i c a t i o n s of t h e s e r e s u l t s a r e d i s c u s s e d w i t h r e g a r d t o s p i c u l e s .iii c

“…Equation (16) chromosphere up to a height of 2400 km above the photosphere, and it is then connected using the method described by Withbroe (1970) to a Dupree-Goldberg (1967) model for the transition zone and the lower corona. It is possible, of course, to start with a somewhat different profile for N and T and obtain the corresponding G-diagram based on this profile.…”

Section: The G Diagrammentioning

confidence: 99%

A simple derivation of microwave solar brightness temperatures and polarizations from thermal regions

Papagiannis

Kogut

1976

Using the full magnetoionic theory in the microwave region along a ray-path through the solar chromosphere and corona we have obtained a convenient expression, and from it a simple diagram which permits the direct computation of the brightness temperature and circular polarization from a thermal source, for any combination of the physical parameters which enter in their computation. IntroductionThe study of solar active regions at cm and mm wavelengths has provided considerable insight into the electron densities, temperatures and magnetic fields in these areas. High resolution microwave observations by Kundu et al. (1974) have shown that active regions consist of one or more extremely hot cores, only a few arc seconds in diameter, surrounded by an extended halo, which is not as hot. The high brightness temperatures and often high degrees of circular polarization observed in the cores are due to gyroresonance effects. The brightness temperature and polarizations of the halos on the other hand, where the magnetic fields are weaker, are due to free-free absorption produced by enhanced electron densities (5-10 times normal) over the entire active region.A complete understanding of the physics of active regions before, during, and after flare events (Alissandrakis and Kundu, 1975;Lang, 1974) is of utmost importance and this will necessitate the detailed study of the changes which occur not only in the hot cores but also in the large halos which surround them. The method developed in this paper can be applied in the study of the halos from high resolution maps of active regions as well as in the analysis of other thermal regions such as plage areas without sunspots, decaying active regions, and the cooler regions which surround solar filaments (Straka et al., 1975). Fitting a physical model to the observed values of left (Tz) and right (Tr) circularly polarized brightness temperatures is a rather complicated problem, primarily because of the several variable parameters involved. One possible simplification is to use a constant effective magnetic field for the emission region under consideration. This approach is suggested by the fact that the thermal emission in the microwave domain originates in a rather narrow layer in the upper chromosphere. Figure 1 shows the contribution to the brightness temperature (ATb/zlh) in the emission layer at 3.8cm for different models of the solar atmosphere.