Sunrise Effect Research Articles

Regular and seasonal behaviour of atmospheric radio noise field strength (ARNFS) over low latitude station calcutta

The electromagnetic radiation of cloud discharge known as atmospheric radio noise field strength (ARNFS) shows a gradual fall from a frequency of 9 kHz to 81 kHz as studied over a period of two years at Calcutta, very close to Bay of Bengal. The main characteristic features of ARNFS at Calcutta are that-(i) ARNFS shows that midday median value is smaller than midnight median value in all months, (ii) level of daily minimum is higher in February and monsoon compared to other seasons, (iii) ‘sunrise effect’ and ‘sunset effect’ are well correlated with local sunrise and sunset times, (iv) the magnitude of ‘sunrise fade’ and ‘sunrise fade rate’ are maximum in April and lowest during winter period, (v) the magnitude of sunset fade is higher in premonsoon and postmonsoon while it is lowest in monsoon, (vi) number of occurrence of both sunrise effect and sunset effect is remark-ably smaller in monsoon. The positions of the sun and of atmospheric sources are jointly the causes of seasonal and diurnal variations. The missing of ‘sunrise effect’ and ‘sunset effect’ are due to local cloud activity and variation of electron density during geomagnetic storms.

A comparative study of the sunrise and sunset effects on the integrated field intensity of VLF atmospherics

Abstract. A comparative study is made of the stepped structure of atmospherics during sunrise and sunset hours at three harmonically related frequencies in the VLF band, observed at the coast of the Bay of Bengal. The occurrences of the steps, their duration, time sequence and amplitudes are critically examined. Our analysis reveals that the start times of the third and second steps of the sunrise effect are always before ground sunrise, while the start of the main step is distributed on both sides of it. During sunset hours, the onset time of the main step is before the local ground sunset, but for the second and third steps, the onset times are after that. The results are interpreted by considering the multi-hop propagation as well as the distributed noise sources surrounding the observing site.

Sunrise and range distribution of meteors

The influence of the sunrise effect on the ionization of the meteor zone has been found from the comparison of meteor echo range distributions obtained by the meteor radars at Springhill (120 000 echoes) and Budrio (7000 echoes) during the activity of the Geminids meteor shower. The position of the maximum of the echo range distribution corresponding to the motion of the shower radiant was found to be shifted to larger distances, as expected from the sunrise effect, independently of different antenna systems of the two equipments.

Sunrise effect on dayside Pc pulsations at the dip equator

A flux gate magnetometer with an amplitude resolution of 6 pT/LSB was installed at Huancayo, Peru (12°S, 750°W in geographic coordinates, 0.8°N, 335.6° in geomagnetic coordinates) in December 1985 and recorded field variations for 1 year with 3‐s sampling intervals. Horizontal field variations of Pc 3‐4 pulsations (periods from 150 to 30 s) were studied and it was found that the oscillations were observed predominantly in the H component (magnetic north‐south), though oscillations in the D component (magnetic east‐west) are superimposed temporarily at local sunrise. The D component signals, which last for ≈2 hours after local sunrise, bring about a large tilt of the polarization azimuth angles in the H‐D plane without a significant change in the ellipticity. The azimuth at sunrise lies in the NW‐SE quadrant during local summer (November to January), while it lies in the NE‐SW quadrant for local winter (March to September). On the basis of the observed seasonal change of the azimuth angles, we present a model of the ionospheric current system setup by the incident Pc 3‐4 pulsations in the dayside region of the dawn terminator at the dip‐equator.

Measurements of ionospheric and thermospheric temperatures and densities with the middle and upper atmosphere radar

The first incoherent scatter radar local time/seasonal/solar cycle averages of F region electron, ion, and neutral temperatures for Asian longitudes are presented. These measurements were made with the four‐pulse experiment by the middle and upper atmosphere (MU) radar in Japan over the period August 1986 to April 1990. The neutral temperature and density results are compared with MSIS‐86 model predictions. We divide our data into low and high solar activity levels, four seasons, and 24 one‐hour times bins. While the seasonal and solar activity behavior of the ionospheric density, and of the anticorrelation of the electron temperature with this density, shows many aspects in common with those at other locations, a few particular differences are evident. At low solar activity the height of the F layer varies from 240 km during the day to 320 km at night, regardless of season. At high solar activity the maximum density of the F layer varies little with season. These facts seem to indicate little seasonal change in F region neutral atmospheric composition at this geographic location. At solar maximum the F layer is established at a higher altitude than at low solar activity, and the summer F layer in particular is formed at such a high altitude that its decay at night is very slow, its diurnal variation is hence weak, and the density remains so high at sunrise that little sunrise effect in the electron temperature is produced. The neutral temperatures in the F region have the same basic diurnal pattern as does the MSIS‐1986 model temperatures, but the radar temperatures are consistently lower by an amount ranging up to 160 K for summer conditions at high solar activity. The measured and model temperatures are closest in the autumn and winter. The neutral density results are of low quality and do not provide any evidence of need to modify the MSIS model densities.

Preliminary results concerning atmospheric gravity waves deduced from f0 F2 large-scale oscillations

Measurements of quasi-periodic variations ("oscillations") of the ionospheric critical frequency f0F2 made at the ionospheric station at Rome and other surrounding European stations are analysed by introducing as their hourly amplitude the difference between any hourly value and the symmetrical 3-h running mean. These oscillations are local ionospheric effects of systematic atmospheric gravity waves (AGWs) whose characteristics are briefly discussed. In particular, the existence of daily waves which are excited by sunrise effects is pointed out. The interference among these waves and other AGWs from meteorological activity (short period) and magnetospheric activity (long period) produces a variety of wave-like patterns.

Sunrise and sunset effects as observed on microwave propagation over a line-of-sight path

Microwave signal propagation provides an effective measure of studying the variable nature of the atmosphere. Sunrise and sunset periods are characterized by the dissolution and formation of nighttime temperature inversions. Signal amplitude recordings at 6.7 GHz over DumDum-Andul line-of-sight (LOS) communication link during post-sunrise period are characterized by the appearance of an enhancement in signal strength (as high as 20 dB). The sunset effect or the evening transition is observed as an enhancement in signal amplitude of about 10- 12 dB over the link. The signal characteristics observed during transition periods over the 6.7 GHz DumDum-Andul link are studied herein.

On: “Ionospheric induced very low frequency electric field wavetilt changes” by D. V. Thiel and I. J. Chant (GEOPHYSICS, January, 1982, p. 60–62)

The paper by Thiel and Chant reports the well‐known sunrise and sunset effect which in micropulsation studies is referred to as the dawn and dusk “chorus.” However, we disagree with the interpretation of these authors. Their choice of wavetilt as the diagnostic function is slightly misleading since they are essentially measuring at the surface of the earth despite the unfortunate location of their magnetic sensor at a height of 4 m and presumably in a building. In this case the wavetilt [Formula: see text] according to their equation (1) is equivalent to [Formula: see text] where [Formula: see text] is the impedance of the earth and [Formula: see text] is the impedance of free space. This result is independent of the mode of propagation but certainly at their distance of 4000 km is predominantly the sky wave except during the dawn and dusk periods. The turbulence due to the formation or breakup of the D‐layer in the ionosphere virtually destroys the ionospheric reflected component which is the dominant contributor to the field incident on the earth. We suggest that during most of the day the authors are measuring the impedance of the earth scaled by a numerical constant.

Sunrise effect on atmospherics and its relation to the direction of the night noise source

Нa основе ре улярноŭ сезонноŭ вaрuaцuu моменmов эффекma восхо¶rt;a Солнцa нa amмосферuкaх был рaзрaбоmaн новыŭ меmо¶rt;, коmорыŭ оnре¶rt;еляеm нanрaвленuе uсmочнuков, uз коmорых nрuхо¶rt;um во время восхо¶rt;a Солнцa в nрuемную сmaнцuю ночноŭ amмосферныŭ шум. Меmо¶rt; был nрuменен к нaблю¶rt;енuям amмосферuков нa ¶rt;вух сmaнцuях с рaзным ео рaфuческuм nоложенuем (Уnuце, Чехословaкuя, 27 кГц, u Вumошa, Бол aрuя, 29 кГц) в mеченuе 1967–1970 . Меmо¶rt; nре¶rt;осmaвляеm ¶rt;вa решенuя, но uз aнaлuзa выmекaеm, чmо nре¶rt;nочmенuе нa¶rt;о оm¶rt;amь нanрaвленuю орuенmuровaнному блuже к эквamору, u чmо uсmочнuкu рaзмещены верояmнее все о в mроnuкaх. О¶rt;нuм uз резульmamов aнaлuзa есmь maкже оnuсaнuе мо¶rt;елu nолно о явленuя эффекma восхо¶rt;a Солнa. Нanрaвленuя uзменяюmся нa обеuх сmaнцuях в mеченuе о¶rt;a ре улярно меж¶rt;у южнымu u ю о-зana¶rt;нымu нanрaвленuямu. Обосновaнuе ¶rt;aнно о решенuя nо¶rt;¶rt;ержuвaеm aнaлuз эффекmов восхо¶rt;a u зaхо¶rt;a Солнцa нa amмосферuкaх нaблю¶rt;енных в южноŭ nолусфере [15]. Верояmно, чmо в mеченuе о¶rt;a uмееm месmо некоmорыŭ кaнaльныŭ эффекm в рaсnросmрaненuu ¶rt;лuнных рa¶rt;uоволн, коmорыŭ связaн с зaвuсuмосmью условuŭ ¶rt;ля рaсnросmрaненuя рa¶rt;uоволн в ночноŭ uоносфере оm ео рaфuческоŭ ¶rt;ол оmы (uлu лучше оm месmно о временu), u коmорaя можеm обьяснumь нaблю¶rt;енную ре улярносmь сезонноŭ вaрuaцuu в нanрaвленuu amмосферuков nрuхо¶rt;ящuх к нaблю¶rt;amелю ¶rt;о восхо¶rt;a Солнцa.

Diurnal and seasonal variations of space charge, electric field and cloud condensation nuclei in the lowest layer of the atmosphere

Diurnal and seasonal variations of space charge, vertical electric field and cloud condensation nuclei in the lowest layers of the atmosphere during winter, pre-monsoon, monsoon and post-monsoon seasons were studied. The curve showing the diurnal variation of space charge exhibited a double oscillation corresponding to that of the electric field during winter and pre-monsoon seasons. Similar features are absent during monsoon and post-monsoon seasons. During pre-monsoon the semi-diurnal components of space charge and electric field are in phase while in winter the semi-diurnal component of space charge occurs 1 h ahead of the electric field component. The mean values and diurnal ranges of both space charge and electric field are high during winter/pre-monsoon and are low during monsoon/post-monsoon seasons. The diurnal range of temperature and concentration of cloud condensation nuclei are positively correlated with space charge and the electric field. The pre-sunrise minimum in the electric field is associated with the characteristics of the F-region of the ionosphere rather than with the ground sunrise time. The variations in the F 2 layer critical frequency ( f 0 F 2 ) are reflected in the diurnal and ter-diurnal components of the surface electric field. The results of the present study support the hypothesis that the increase in the electrosphere potential could be the source of the atmospheric electric sunrise effect (Muir, 1975). DOI: 10.1111/j.2153-3490.1980.tb00950.x

On the sunrise effect in atmospheric electricity

Data are presented which suggest that the sunrise effect on the atmospheric electric potential or its gradient (and conduction current) close to the surface is caused by processes in the upper atmosphere, while at the same time other processes of local origin also appear to partake in this phenomenon. The sunrise effect on the atmospheric electric potential gradient has been shown to be related to an electrode effect. Simultaneous records of the atmospheric electric potential and conduction current reveal that the rise in both of these parameters commences before ground sunrise. However the current rise lags behind the potential gradient rise which has been tentatively explained.

Diurnal and seasonal variations of space charge, electric field and cloud condensation nuclei in the lowest layer of the atmosphere

Diurnal and seasonal variations of space charge, vertical electric field and cloud condensation nuclei in the lowest layers of the atmosphere during winter, pre-monsoon, monsoon and post-monsoon seasons were studied. The curve showing the diurnal variation of space charge exhibited a double oscillation corresponding to that of the electric field during winter and pre-monsoon seasons. Similar features are absent during monsoon and post-monsoon seasons. During pre-monsoon the semi-diurnal components of space charge and electric field are in phase while in winter the semi-diurnal component of space charge occurs 1 h ahead of the electric field component. The mean values and diurnal ranges of both space charge and electric field are high during winter/pre-monsoon and are low during monsoon/post-monsoon seasons. The diurnal range of temperature and concentration of cloud condensation nuclei are positively correlated with space charge and the electric field. The pre-sunrise minimum in the electric field is associated with the characteristics of the F-region of the ionosphere rather than with the ground sunrise time. The variations in the F 2 layer critical frequency ( f 0 F 2 ) are reflected in the diurnal and ter-diurnal components of the surface electric field. The results of the present study support the hypothesis that the increase in the electrosphere potential could be the source of the atmospheric electric sunrise effect (Muir, 1975). DOI: 10.1111/j.2153-3490.1980.tb00950.x

The potential gradient sunrise effect in atmospheric electricity

Experimental results are produced which show that the early part of the sunrise effect is apparently not related to variations in the temperature or humidity of the lower atmosphere. An electrode effect space charge layer tends to obscure rather than enhance the effect. The expected seasonal variation in the sunrise effect was not found. Two possible explanations of this are suggested.

Some early results from the ATS‐6 Radio Beacon Experiment

The multifrequency satellite radio beacon enables the measurement of the columnar electron content of the ionosphere and plasmasphere along the ray path and its spatial and temporal structure. Measurements include modulation phase, Faraday rotation, and amplitude. The characteristics of the beacon transmitter and its design are presented together with the design of the Boulder receiver and antennas and the calibration procedures. A shape factor F is defined which depends on the electron density and geomagnetic field distributions. It is found that F varies by about 30% from day to night. It is shown that the ratio of the plasmaspheric content to total content varies from about 0.08 during the day to about 0.35 at night. Other examples which are presented to illustrate the uses of the radio beacon include sunrise effects, solar flare enhancements of total content, and the ionospheric storms of early July 1974.

The ionosphere as the source of the atmospheric electric sunrise effect

A number of mechanisms have been suggested to explain the increase in the fair weather potential gradient which occurs at about sunrise. These mechanisms have all been concerned with processes occurring in the lower atmosphere. In this paper it is suggested that an increase in the electrosphere potential could be the source of the sunrise effect. A mechanism is proposed which would account for the increase in electrosphere potential. This proposed mechanism would identify the electrosphere with a specific part of the ionosphere.

Sunrise Effects on the Latitudinal Variations of Topside Ionospheric Densities and Scale Heights

IONOSPHERIC sunrise represents the transition period between quasi-equilibrium conditions attained during the night and those attained during the day. The arrival of sunrise is manifested by a rapid increase in electron temperatures and a less rapid increase in ion temperatures at all altitudes1. In a plasma distribution that tends towards equilibrium, a sharp increase in particle temperature results in a redistribution of the plasma. In the topside ionosphere, this is manifested by a diffusive flux of ions and electrons.

Atmospheric electricity, turbulence and a pseudo-sunrise effect resulting from a solar eclipse

Recordings made of several atmospheric electric parameters at the Naval Research Laboratory, Waldorf, Md. observatory during the eclipse of 7 March 1970 showed variations similar in nature to classical descriptions of the so-called sunrise effect. The recording of space charge density was spectrally analyzed with the fast Fourier algorithm, and the resultant power spectra were fitted to a power law spectral decay model. Since the decay exponent in this model is related to the fractions of the space charge resident on large and small ions, it is then possible to follow time variations in small-to-large ion ratios through the period of the eclipse. It is shown that the variations in the recorded atmospheric electric variables and in the spectral decay exponent are consistent with a strong diminution of turbulence near the ground as the Sun is obscured and the establishment of a thin layer above the ground in which a higher than normal density of small ions is produced by surface radioactivity. The subsequent resumption of turbulent mixing carries these ions upward, producing the ‘sunrise effect’ variation pattern. The rapidity with which heating is restored is seen to be responsible for those differences in behavior which are observed. It is concluded that eclipse conditions provide a unique opportunity to investigate phenomena which are strongly influenced by atmospheric turbulence.

On very-low-frequency atmospherics at Roburent, Northern Italy

The diurnal and seasonal variation of the VLF sferics pulse rate recorded at Roburent, Northern Italy, on 27 kHz since 1966 is derived. By analyzing the sunrise effect, the minimum distance of the thunderstorm centers providing at that time an unperturbed behaviour of the sferics pulse rate is obtained: this distance varies in azimuth and with the seasons and lies between 600 and 1300 km. In the time of the equinoxes, however, it is more stable between 700 and 900 km. The role of the groundwave propagation, generated by thunderstorm center within a radius of less than 500 km, is emphasized.

Ozone screening heights deduced from sunrise effects at very low frequencies

During the period August–September of any year, the entire NAA-São Paulo path is illuminated almost simultaneously at sunrise, resulting in a sharp drop in the phase of the received signal. Using sunrise phase transitions and an assumed night-time reflection height of 90 km, an ozone screening height of 58 km was deduced. A calculation of the wavelength of the photo-detaching radiation, using this value of the screening height yielded a value of λ = 3015 A ̊ .

Effect of wind on diurnal and seasonal variations of atmospheric electric field

Diurnal and seasonal variations of atmospheric electric potential gradient and the effect of wind on them, have been studied, with the recordings over a period of 1 yr at this station. Negative potential gradients, observed in high wind speeds, are explained by arguing the dust particles to be negatively charged. Further, reasons are given in favour of free convection as a possible cause of sunrise effect.