The simplest solar microbursts flux and circular polarization at 22 GHz

The simplest solar microwave microbursts detected with high sensitivity may be the response to the simpler energetic burst injections. Seventeen events from this category were identified in a series of more than 150 bursts recorded in 21–26 November, 1982. This first systematic study suggest that microbursts e-folding rise times concentrate into two classes of time scales, 0.05 s < t 1 s and 0.5 s t 2 s. Microbursts circular polarization present a dominant steady or slowly varying component that sets in before maximum emission. In some cases a faster component of polarization was found superimposed, which is not always well correlated in time with flux.     

Time variations of the solar neutrino flux

The Fourier analysis of the argon-37 production rate for runs 18–80 observed in Davis's well-known solar neutrino experiment is presented. The method of Fourier analysis with the unequally-spaced data of Davis and associates is described and the discovered periods are compared with recently published results for the analysis of the data of runs 18–69. The harmonic analysis of the data of runs 18–80 shows time variations of the solar neutrino flux with periods =8.33, 5.26, 2.13, 1.56, 0.83, 0.64, 0.54, and 0.50 yr, respectively, which confirms earlier computations.     

BoxCox multi-output linear regression for 10.7 cm solar radio flux prediction

We consider the problem of predicting the mid-term daily 10.7 cm solar radio flux(F10.7),a widely-used solar activity index.A novel approach is proposed for this task,in which BoxCox transformation with a proper parameter is first applied to make the data satisfy the property of homoscedasticity that is a basic assumption of regression models,and then a multi-output linear regression model is used to predict future F10.7 values.The experiment shows that the BoxCox transformation significantly improves the predictive performance and our new approach works substantially better than the prediction from the US Airforce and other alternative methods like Auto-regressive Model,Multi-layer Perceptron,and Support Vector Regression.     

Observations of solar filaments at 8, 15, 22 and 43 GHz

On April 3, 4, 6, and 8, 1978, solar observations were made using the Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. H filtergrams obtained at the Sacramento Peak Observatory on the same days showed an average of more than 30 filaments or filament fragments (per day) on the disk. Most of these appeared as depressions in brightness temperature at 15 and 22 GHz. Because of the relatively low spatial resolution at 8 GHz, only a few appeared at that frequency, and presumably because of lower opacity in filaments at higher frequencies, few depressions were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than H filaments, but virtually all the radio depressions overlay magnetic neutral lines. Taking the data sets for each day as independent samples, we found that at 22 GHz, 46 of the 77 radio depressions were associated with H filaments; at 15 GHz the correlation was smaller; only 27 out of 48 being associated with the H filaments. The data imply that the microwave depression features are the result of absorption by filaments and perhaps also the result of other effects of the associated filament channel, but not necessarily coronal depletion. The effects of filament absorption are, statistically, about twice as effective as other phenomena (such as absorption by material invisible in H, for example) in creating the radio depression. A center-to-limb study of a single large filament clearly showed that at 15 and 22 GHz the absorption by cool hydrogen supported above the neutral line was the predominant factor in producing the observed depression at radio frequencies.     

Active region evolution and solar flux variations

The goal of this study is to relate the changes in the solar radiative output to the growth and decay of magnetic active regions. We will test the assumption that each index of radiation variability is a convolution of an active-region magnetic driving function and a response function. The first step has been to identify the appropriate driving function. This driving function was assumed to have been data from the magnetic active regions derived from the Mount Wilson daily magnetograms (Howard, 1989). The daily magnetic reports were sorted to give active-region sequences. To estimate the magnetic flux of active regions outside the observing window, (i.e., behind the limb) we fit the data to a growing-and-decaying exponential function, which permits independent growth and decay. This double exponential gives reasonable fats to the observed temporal evolution of active-region magnetic flux.     

Observations of hysteresis in solar cycle variations among seven solar activity indicators

We show that smoothed time series of 7 indices of solar activity exhibit significant solar cycle dependent differences in their relative variations during the past 20 years. In some cases these observed hysteresis patterns start to repeat over more than one solar cycle, giving evidence that this is a normal feature of solar variability. Among the indices we study, we find that the hysteresis effects are approximately simple phase shifts, and we quantify these phase shifts in terms of lag times behind the leading index, the International Sunspot Number. Our measured lag times range from less than one month to greater than four months and can be much larger than lag times estimated from short-term variations of these same activity indices during the emergence and decay of major active regions. We argue that hysteresis represents a real delay in the onset and decline of solar activity and is an important clue in the search for physical processes responsible for changing solar emission at various wavelengths. The High Altitude Observatory is sponsored by the National Science Foundation.     

A coronal hole observed at 10.7 GHz with a large single dish

On July 24, 1973, a coronal hole was observed at 10.69 GHz (2.8 cm) with the Bonn 100-m telescope. The difference of the brightness temperature between outside and inside the hole was about 400 to 500 K. It is shown that this lack of emission can be explained by usually adopted values of the electron density at the bottom of the corona.     

Limits to the accuracy of the 10.7 cm flux

The 10.7 cm flux data, which are widely used as an index of solar activity, are actually spot measurements of the solar flux density at 10.7 cm wavelength, made three times each day, usually at 17:00, 20:00, and 23:00 UT. These values, or the 20:00 UT determination alone, are frequently used as the average flux for that day. Since each spot measurement takes about one hour to make, and the Sun's emissions at that wavelength can vary over time scales shorter than the intervals between the measurements, the data are unavoidably undersampled. Radio emissions from transient events, such as flares, are defined as contaminants of the flux, and largely-empirical procedures have evolved which are used to filter them from the data. The utility of theF _10.7 index over more than 40 years suggests that the consequences of the under-sampling and the use of largely-empirical data filters are not serious. However, as new applications of the flux data appear, and existing ones become more quantitative, we need to better understand the accuracy of data as estimates of the 10.7 cm flux index, and to know how much precision we can reasonably expect to attain. In this paper we describe part of a study aimed at estimating how good the spot measurements are as estimators of the ‘daily-average’ flux. By a combination of measurement and modelling, the contributions to the flux monitor output truly due to the Sun are separated from the non-solar signals. We then derive the daily average 10.7 cm flux values and compare them with the spot measurements. We find that in general, the spot measurements are usually within a percent or so of the daily-average fluxes.     

The solar radius at 35 GHz

The solar radius at 35 GHz has been determined from solar radio maps made with a pencil beam antenna of half-power beam width 2.8 arcmin at the La Posta Astrogeophysical Observatory during 1973 and 1974. The 35 GHz radius was found to be 2.57% ±0.88% larger than the photospheric radius. The sensitivity of the result to the method of determination is discussed.     

On the long-period variations and magnitude of the solar neutrino flux

We analyze the solar neutrino flux fluctuations using data from the Homestake, GALLEX, GNO, SAGE, and Super Kamiokande experiments. Spectral analysis and direct quantitative estimations show that the quasi-five-year periodicity is the most stable neutrino flux variation. Revised mean solar neutrino fluxes are presented. These are used to estimate the observed pp flux of the solar electron neutrinos near the Earth. We consider two alternative explanations for the origin of the variable component of the solar neutrino deficit.     

Atmospheric temperature response to solar cycle UV flux variations

A radiative-convective climate model was used to explore the response of the mean global vertical temperature structure to a variation in the solar UV flux over the solar cycle. The model predicted a cooling of the troposphere and a warming of the stratosphere from solar minimum to solar maximum. The response of the atmospheric temperature to solar UV variations was found to be moderated by a concomitant change in the mean global stratospheric ozone content.     

Observations of extragalactic radio sources at 36 GHz

The observations of 34 extragalactic radio sources with the 22-m Crimean Astrophysical Observatory radio telescope at 36 GHz in 1985–1994 are presented. Intensity variations were detected in 27 objects, which may result from the appearance of new components in their cores.     

Effect of Coulomb collisions on time variations of the solar neutrino flux

We consider the processes that might suppress the time variations in the solar neutrino flux produced by the radial motion of the Earth through the neutrino interference pattern. We calculate these time variations and the extent to which they are suppressed by Coulomb collisions of the neutrino-emitting nuclei. This is done for both the 0.862-MeV ⁷Be neutrino line and the continuous neutrino spectrum, assuming a Gaussian energy response function of the neutrino detector. We find that the collisional decoherence averages out the time variations for neutrino masses A simple and clear physical picture of the time-dependent solar neutrino problem is presented and qualitative coherence criteria are discussed.     

Solar flux variations at 175 and 304 Å and their relation to solar wind parameters

Variations of solar emission in the spectral ranges corresponding to the transition region (304 Å) and corona (175 Å) and their relation to solar wind parameters are investigated for the maximum and declining phase of solar cycle 23 (2001–2004) based on the CORONAS-F/SPIRIT data. It is shown that the variations of solar flux in both ranges are similar and demonstrate a high correlation for long data series. Meanwhile, some time intervals were registered when the intensity variations at 304 Å are delayed with respect to those in 175 Å by, on average, two days. For long periods, the spectra of the full-disk flux at 175 Å and of the solar wind density are close to each other; the same is true for the solar flux spectrum in the 304-Å range and the spectrum of the solar wind velocity. The assumption is made that active processes in the lower corona mainly affect long-period density variations, while the velocity characterizes the kinetics of the total stream of the outflowing matter and its long-term variations are considerably related to the physics of processes occurring deeper in the Sun.     

Circular polarization of solar bursts at 22 GHz

The circular polarization of complex solar bursts was measured at short microwaves (22 GHz, × 1.35 cm) with high sensitivity (0.03 s.f.u. r.m.s.) and high time resolution (5 ms). The polarization shows up as soon as an excess burst emission is measured. Two components are found in the time development of the degree of circular polarization: (1) a steady level, sometime changing smoothly with time; (2) superimposed faster polarization time structures, small compared to the basic steady degree of polarization, and often not clearly related to the burst flux time structures. The observed degrees may range from 10% to more than 85%.In memoriam (1942–1981).     

Pencilbeam observation of solar bursts at 36 GHz

From a burst survey at 36 GHz, the diameter of the burst core was always found less than 1′. Several limb bursts with a remarkable flash intensity have been observed. Comparison of corresponding bursts on the disk exhibit in general a recognizable post-increase phase which seems to become faint at the solar limb. This work was performed at the Stockert Radio Observatory, near Bonn, Germany.     

Unpolarized impulsive solar bursts observed at 7 GHz

The occurrence of very faintly polarized, or unpolarized impulsive bursts observed at 7 GHz is discussed. It appears that some of them show a peculiar spectral peak somewhere between 5 GHz and 7 GHz. Possible interpretations are suggested, emphasizing the need to associate to the burst the state of polarization of the S-component in which it occurred.