27-day Component Research Articles

Intensity of 27-day variations in solar emission and ionospheric electron content

The rotation of the Sun modulates solar emission with 27-day variations. Large-scale structures in the solar atmosphere, like sunspots and plages, rotate with the Sun and emit at extreme ultraviolet (EUV) and microwaves that produce the varying part of the emission. As EUV emission is the main driver of ionization in the Earth ionosphere, its variations are reflected in the electron content. In this paper, we analyze wide range of data from radio emission in 245–17000 MHz range and the entire EUV spectrum to total and global electron contents (TEC and GEC, respectively) in the ionosphere to find out where the 27-day variations are most prominent. We show that the relative contribution of 27-day variations to radio emission is maximal at 1000 MHz and decreases at 245 and 17000 MHz. The variations are pronounced throughout the EUV spectrum, their intensity vary at different spectral lines and, on average, is higher than in radio emission. The distribution of the variations in global ionospheric maps (GIM) shows an intensification of 27-day variations in TEC in the North America region, which can be related to the winter anomaly as it is also more significant in this region. Temporal variations of the 27-day component of emission are similar in shape for radio and EUV emission, as well as for GEC, and have a high correlation, up to 0.8. Cycle-averaged temporal variations imply that the 27-day component weakens significantly during solar minimum but can intensify during the remaining phases of the solar cycle. We also find that the flux at 1000 MHz, which originate from free-free emission in contrast to F10.7, can be used as a proxy index of solar activity because it has the highest intensity of 27-day variations and has been observed since 1956.

Recurrent Large Sunspot Structures and 27-Day Component of Solar Activity as Proxies to Axis-Nonsymmetry

The purpose of this paper is to design tools that quantify the structure of the nonsymmetrical component of the solar magnetic field. With the Fourier transform and the machine learning identification of recurrent objects, we define the 27-day component of solar proxies and recurrent large sunspot structures (ReLaSS), respectively. These two closely related characteristics are established to represent different components of the asymmetry of the solar magnetic field. We derive that the 27-day component and ReLaSS have anticorrelated since 1970 after dozens of years of a strong correlation. The persistence of the correlation sign during few solar cycles reflects yet unknown regularities of solar activity. The contribution of both proxies to the nonsymmetry of solar activity is shown to be lower in 1990–2010 than ∼100 years earlier. This property may be the trace of the asymmetry at the scales that are longer than the centennial Gleissberg cycle.

Method for estimation of solar, geomagnetic, and atmospheric contributions to 27-day component of peak electron density

Abstract The study suggests a new method for estimation of the solar, geomagnetic, and atmospheric contributions to 27-day component of peak electron density. For our analysis, we calculated complex amplitudes of 27-day components filtered from the data sets of peak electron density and indices of solar and geomagnetic activity. The use of complex amplitudes takes into account both the amplitude ratios and phase shifts (time delays between the 27-day components) within linear regressions. In this study we use the coefficients of determination for linear regressions to estimate the solar and geomagnetic contributions to the ionospheric variations. The coefficient of determination represents the proportion of the total variation in the dependent variable (ionospheric variations) that is explained by the independent variables (variations in solar and geomagnetic indices). Comparison with other studies showed that, apparently, the contribution estimation strongly depends on the filter bandwidth and the method for calculating the correlation coefficient. The choice of the optimal method and the filter bandwidth is open to question.

Near-transyear in solar magnetism

Daily data on solar magnetism, available from May 1975 to April 2002, were analyzed by linear-nonlinear rhythmometry, with particular focus on the near-transyear, slightly longer than the calendar year. The time structure of solar magnetism is compared to that of solar activity, gauged by Wolf numbers. An about 27-day component corresponding to the solar rotation period, is common to both variables but differs in harmonic content. About 10-year component characterizes solar activity but not solar magnetism. A near-transyear with a period of about 1.05 years is detected in solar magnetism. In solar activity, a near-transyear is also found but its period of about 1.10 years is longer than that characterizing solar magnetism, and it may be paired with an about 0.9-year component to correspond to an about 10-year modulation in amplitude or phase of an about-yearly component.

Periodicities in energy dissipation rates in the auroral mesosphere/lower thermosphere

Abstract. It is possible for medium-frequency (MF) radar systems to estimate kinetic energy dissipation rates by measuring signal fading times. Here, we present approximately 5 years of such results from Tromsø (69° N, 19° E) and in particular, investigate the periodicities present at different altitudes in the regime 80 to 100 km. We detect the known annual variation in the mesosphere and the semiannual variation on the lower thermosphere. In addition, other features are observed including terannual and ~ 27-day components in the lower thermosphere.Key words. Meteorology and atmospheric dynamics (climatology; middle atmosphere dynamics; turbulence)

Mid-latitude summer response of the middle atmosphere to short-term solar UV changes

Abstract. Temperature and wind data obtained with Rayleigh lidar since 1979 and Russian rockets since 1964 are analyzed to deduce the summer response of the middle atmosphere to short-term solar UV changes. The equivalent width of the 1083 nm He I line is used as a proxy to monitor the short-term UV flux changes. Spectral analyses are performed on 108-day windows to extract the 27-day component from temperature, wind and solar data sets. Linear regressions between these spectral harmonics show some significant correlations around 45 km at mid-latitudes. For large 27-day solar cycles, amplitudes of 2 K and 6 m s-1 are calculated for temperature data series over the south of France (44°N), and on wind data series over Volgograd (49°N), respectively. Cross-spectrum analyses have indicated correlations between these atmospheric parameters and the solar proxy with a phase lag of less than 2 days. These statistically correlative results, which provide good qualitative agreement with numerical simulations, are both obtained at mid-latitude. However, the observed amplitudes are larger than expected, with numerical models suggesting that dynamical processes such as equatorial or gravity waves may be responsible.

Comparison of the correlation of incoherent scatter and ionosonde measurements of temperature with calcium plage and 2800-megahertz intensities

The variation in the diurnal thermospheric neutral temperatures has been studied. Minimum and maximum temperatures were calculated from 20 sets of diurnal incoherent scatter measurements taken at Arecibo, Puerto Rico, which corresponded to a range of 2800-MHz intensity of 120 to 167×10−22watt m−2 sec−1. Minimum temperatures were also derived from 850 reduced ionosonde records obtained from Ramey, Puerto Rico, for which the 2800-MHz intensity varied between 74 and 252×10−22 watt m−2 sec−1. Both sets of measurements were seasonally distributed. Various combinations of the monthly mean and daily values of the 2800-MHz and Ca II solar indices were fitted to the data. A formula incorporating the difference between the daily and monthly average Ca II index and the monthly average 2800-MHz index provided a better fit to all the data than did formulas incorporating only the Ca II index or the 2800-MHz index alone. The phase and amplitude of the semiannual component and the term dependenton Kp were found to remain almost the same for the maximum and minimum temperature. The term dependent on the 27-day component of the solar activity was found to be about 4 times as large for the diurnal maximum as for the minimum.

A high resolution spectral analysis of daily relative sunspot number and 10·7 cm. Solar flux

Auto and cross-spectra of relative sunspot number and slowly varying component of solar radiation at 10·7 cm. have been computed for a 52-month period beginning September 1, 1958. Significant features of the spectra are relatively high variance at periods corresponding to one, three and four solar rotations. Statistically significant spectral peaks have been observed at three other frequencies and are ascribed to amplitude modulation of the 27-day component. The cross-spectral analysis indicates that during the period under investigation the solar 10·7 cm. flux leads the sunspot number for periods in excess of about 27·7 days; for shorter periods the flux lags behind the sunspot number. The coherence between the two time series, after an initial decrease from unity at zero frequency, assumes a maximum value of 0·985 at 27·7 days. The phase and coherence indicate that long-lived radio emission regions and spots appeared to co-rotate during 1958–62 with a period of 27·7 days.

On the possible existence of a 29-day period in the sunspot number series 1940-1964

The possibility that the geomagnetic activity is subject to a lunar influence has been recently examined by Bell and Defouw [1966] and Guez [1966]. This influence was inferred from the presence of a peak in the spectral distribution of geomagnetic data in the 29-day band [Shapiro and Ward, 1966; Benoit and Guez, 1966]. The possibility that this 29-day peak could be caused by an amplitude modulation of a 27-day component by a modulating function whose period is one year was suggested by Coleman and Smith [1966]. The influence of this annual modulation was also examined by Benoit and Guez [1966] who separated its contribution to the 29-day peak from that of the lunar-orbit modulation.

An interpretation of the subsidiary peaks at periods near 27 days in the power spectra ofCiandKp

Subsidiary peaks in power spectra of Ci and Kp /magnetic indices/ attributed to amplitude modulation of 27-day components

The 24-Hrs Averages of Cosmic Ray Intensity in Stockholm 1947–48 and 1954

Curves are given showing the variation of the 24-hrs averages of the C.R. intensity as measured by means of directional counter telescopes during two registration periods separated by six years. During both periods the maximum deviations were 2–3 per cent. In accordance with the view expressed by SIMPSON (1954) the periods of maximum are to be regarded as recurrent rather than being a harmonic function of time. There are some traces of a 27-day component having an amplitude of ± 0.4 per cent. The C.R. intensity as a function of time is compared to the solar cycles, the relative sun-spot number, the sun-spot area and the Kp-index.