Radio Emission of the Sun and Planets By V. V. Zheleznyakov. Translated By H. S. H. Massey. Edited By J. S. Hey. (International Series of Monographs in Natural Philosophy, Vol. 25.). Pp. xiv + 697. (Pergamon Press: Oxford, London and New York, February 1970.) 300s; $40.

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Solar Radio Astronomy

The record of flare incidence from January 1969 to October 1988 indicates that the north-south (N-S) distribution of large flares is periodic and approximately in phase with the 11-year sunspot cycle. These data are based on observations of the whole-disk Sun in continuum soft X-rays which commenced in early 1969 and have proceeded without interruption to the present time. The pattern of occurrence, observed for slightly less than two sunspot cycles, is that large flares concentrate in north heliographic latitudes soon after solar minimum and then migrate gradually southward as the cycle progresses. By the end of the cycle, most large flares occur in the south. The degree of N-S asymmetry apparently is a function of the intensity of the flare; the most intense flares show the largest amount of N-S asymmetry. The data suggest that sunspots and flares may be driven by distinctly different excitation mechanisms arising at different levels in the convection zone. This conjecture is supported by recent work of Bai (1987, 1988), who has discovered that the superactive regions producing the majority of flares rotate at a speed substantially different from the Carrington rate, which is based primarily on the observed motion of sunspots.

Evidence for Solar-Cycle Evolution of North-South Flare Asymmetry During Cycles 20 and 21

Mid-term quasi-periodicities in solar coronal mass ejections (CMEs) during the most recent solar maximum cycle 23 are reported here for the first time using the four-year data (February 5, 1999 to February 10, 2003) of the Large Angle Spectrometric Coronagraph (LASCO) onboard the Solar and Heliospheric Observatory (SOHO). In parallel, mid-term quasi-periodicities in solar X-ray flares (class >M5.0) from the Geosynchronous Operational Environment Satellites (GOES) and in daily averages of Ap index for geomagnetic disturbances from the World Data Center (WDC) at the International Association for Geomagnetism and Aeronomy (IAGA) are also examined for the same four-year time span. Several conceptual aspects of possible equatorially trapped Rossby-type waves at and beneath the solar photosphere are discussed.

Periodicities in Solar Coronal Mass Ejections

The mass distribution index of the Geminid, Quadrantid, Arietid, Eta Aquariid, Orionid and South Delta Aquariid meteor showers have been measured using data from 2007 to 2010 from the Canadian Meteor Orbit Radar (CMOR). Single-station data from the 29.85-MHz system were used to find mass index as a function of solar longitude, and to compare separate years of showers. The variation in mass index with solar longitude can provide information on the structure of the stream and how the structure changes with time. The Geminids and Quadrantids were the most prominent showers seen by CMOR, and had peak mass indices of 1.65 and 1.55, respectively. They had clear, strong peaks and little year-to-year variation. The other showers had slightly higher peak mass indices and a greater variability, even though a more sporadic contamination, which might have affected the results.

A meteoroid stream survey using the Canadian Meteor Orbit Radar – III. Mass distribution indices of six major meteor showers

Meteor complex of asteroid 3200 Phaethon: its features derived from theory and updated meteor data bases

We present statistical analysis of about 63000 soft X-ray flare (class≥C) observed by geostationary operational environmental satellite (GOES) during the period 1976–2008. Class wise occurrence of soft X-ray (SXR) flare is in declining trend since cycle 21. The distribution pattern of cycle 21 shows the transit of hemispheric dominance of flare activity from northern to southern hemisphere and remains there during cycle 22 and 23. During the three cycles, 0–100, 21–300 latitude belts in southern hemisphere (SH) and 31–400 latitude belt in northern hemisphere (NH) are mightier. The 11–200 latitude belt of both hemisphere is mightiest. Correlation coefficient between consecutive latitude appears to be increasing from equator to poleward in northern hemisphere whereas pole to equatorward in southern hemisphere. Slope of the regression line fitted with asymmetry time series of daily flare counts is negative in all three cycles for different classes of flares. The yearly asymmetry curve fitted by a sinusoidal function varies from 5.6 to 11 years period and depends upon the intensity of flare. Variation, of curve fitted with wings of butterfly diagram, from first to second order polynomial suggests that latitudinal migration of flare activity varies from cycle to cycle, northern to southern hemisphere. The variation in slope of the butterfly wing of different flare class indicates the non uniform migration of flare activity.

Latitudinal distribution of soft X-ray flares and dispairty in butterfly diagram

Abstract The meteoroid ablation is an important source of upper atmosphere metal atoms. Many meteoroids ablate between 70 - 110 km and form an ionized plasma trail which is detected by radar technique. It is also known that the ablation heights of the meteors depend on various factors such as velocity, mass, and its composition, etc. The meteor ablation height provides new opportunities to gather information on the neutral atmosphere in the Mesosphere and Lower Thermosphere (MLT) region. In this study, we analysed the 11 years of meteor radar data (2005 - 2015), i.e., descending phase of solar cycle 23, and ascending phase of solar cycle 24, detected by all sky meteor radar at Thumba. We found that the solar activity influences the meteor ablation height, here, during the solar maxima meteor peak detection height rise to few hundred meters higher altitudes. We also examined the long term pattern of the meteor count rate which shows a decreasing trend and has good agreement with the sunspot number (SSN).

Variation of the meteor count rate and echo height during solar cycle 23 and 24

In this paper, we attempt to identify the driving forces responsible for the generation of low-latitude E-region field-aligned irregularities (FAIs). It is evident that the low-latitude E-region FAIs occur both during the day and night with preferential occurrence being most during local sunrise period. Simultaneous measurements are made with Gadanki radar and nearby located Ionosonde for understanding the low-latitude Es–FAIs relationship. The observations suggest that the occurrence and SNR of FAIs have a close relationship with ftEs−−fbEs. Finally, using the past electron density profiles and reasonable values of electric field, we have shown that it is generally difficult with the gradient drift instability to explain low-latitude E-region FAIs when electric field alone is considered as driving agency. We hypothesize that neutral winds play important role for the generation of irregularities at low latitudes outside the electrojet belt either by forming sharp Es layers or by enhancing the differential drift of electrons and ions or by both.

Low latitude E-region irregularities studied using Gadanki radar, ionosonde and in situ measured electron density

Geminid Meteor shower activity 2003–2005 as observed by Gadanki radar

The pulse-integrated signal to noise ratio as a function of time known as radar meteor light curve (analogous to optical light curve), is an indicative of ablation processes during meteoroid flight in the atmosphere. In this study, we present and discuss few examples of light curves of long duration specular overdense meteor echoes detected with 53 MHz Gadanki ($13.5^{\circ}N$, $79.2^{\circ}E$) MST radar. These echoes are of several seconds duration, where pulsation in amplitude is about ten cycles within few seconds. This means the fluctuations in amplitude are much slower than typical Fresnel oscillations of underdense as well as the head echo fluctuations. These light curves reveal several features unreported previously in the radar meteor returns that are consistent with meteoroid fragmentation. Some of them provide the strong observational evidence of a sub-millimeter-sized meteoroid, breaking apart into two distinct fragments. The pulsations in light curves are interpreted as being due to interference from two distinct scattering centers. Some other meteor events such as meteoroids undergoing quasi-continuous disintegration are also discussed.

G. Yellaiah

Papers

Latitudinal distribution of soft X-ray flares and dispairty in butterfly diagram

Variation of the meteor count rate and echo height during solar cycle 23 and 24

Low latitude E-region irregularities studied using Gadanki radar, ionosonde and in situ measured electron density

Geminid Meteor shower activity 2003–2005 as observed by Gadanki radar

Fragmentation of specular overdense meteor trail echoes observed with Gadanki MST radar