Solar Daily Variation Research Articles

Lunar and solar daily variations of the geomagnetic field at Italian stations

Mean hourly values of magnetic declination D, horizontal intensity H and vertical intensity Z observed at Italian stations have been analyzed to determine solar and luni-solar diurnal components, together with the corresponding terms O 1 and N 2 of the lunar tidal potential. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. Differences between the dependence of S and L on season and sunspot number are considered and tentative explanations offered. The oceanic tidal effect has been determined and it is apparent that this is more likely to show the influence of the Atlantic Ocean rather than the Mediterranean Sea.

Seasonal dependence of lunar daily geomagnetic variations in different regions of the world.

Essential characteristics of the lunar daily geomagnetic variations L at three Japanese stations are presented along with those at 23 other stations in the world. The focus latitudes of L current system and the oceanic dynamo effect on L are examined with respect to the annual mean L. The focus latitudes of L current system estimated from daygraphs are lower than those of the current system of the solar daily geomagnetic variation S. On the other hand, the oceanic dynamo effect on L is remarkable for the vertical intensity Z and the complex features of the observed L (Z) are explained by this effect. In the seasonal mean L, the amplitude of L is not always minimum in local winter, in contrast to S. The data of all three Japanese stations shows the minimum amplitude in equinoctial months, and this anomalous seasonal change is a feature peculiar to the western North Pacific region. The seasonal variation of L shows a longitudinal inequality over the world. Possible causes of the inequality of the seasonal change are discussed, and it is suggested that the lunar tidal movements in the ionosphere may be the most plausible cause. The dependence of L on the sunspot number and magnetic activity is too complex to draw any definitive conclusion.

Solar and lunar daily variations of the geomagnetic field at Lunping

Summary Mean hourly values of geomagnetic declination, horizontal intensity and vertical intensity observed at Lunping have been analysed by the Chapman-Miller method to determine their solar and luni-solar diurnal components. Data obtained from 1966 to 1976 have been used. First the data are analysed as a whole, then reanalysed aftcr subdivision according to season, month and solar activity. The lunar semi-diurnal variations are separated into parts of ionospheric and oceanic dynamo origin. The results are tabulated, discussed and compared with other observatories.

Solar cycle and seasonal variations of the solar and lunar daily variations of total electron content at Lunping

The solar and lunar daily variations of the ionospheric total electron content observed at Lunping, which lies close to the crest zone of the so‐called equatorial anomaly, were analyzed by Chapman‐Miller method. The lunisolar diurnal variation L1 and lunar semidiurnal variation L2 were found to have significant seasonal variations, with amplitude increasing steadily from summer to winter. The hours for L1 and L2 variations to attain their respective maximum values also increase steadily from summer to winter. The seasonal variation of the semidiurnal variation L2 was found to be explainable by the additional fountain effect caused by the similar seasonal variation of the lunar semidiurnal electric field induced at the equatorial region. However, the seasonal variation of the lunisolar variation L1 was found not to be explainable by the additional fountain effect. Seasonal variations for the harmonic components of the solar daily variation were found to be different from those of lunar daily variation. Solar cycle variations of the harmonic components of the solar and lunar daily variations were found and described.

The lunar and solar daily geomagnetic variations at Sabhawala and Hyderabad

Summary. The first four harmonics of the lunar, L, and the solar, S, daily geomagnetic variations in the H, D and Z elements are determined for the observatories at Sabhawala and Hyderabad. Also included are similar results for Alibag with the main lunar terms separated into parts of oceanic and ionospheric origin. The data used are the alternate hourly mean values of H, D and Z for locally selected quiet days during the IQSY period, 1964-66. The predominances of the first lunar harmonic of H at Sabhawala and Alibag, and of the second solar harmonic at Sabhawala, are pointed out and discussed. The ratios of the seasonal ranges of both L and S to the respective annual mean ranges are found relatively enhanced in two of the seasons, in comparison with. the average global values for these latitudes for the IGY/C (sunspot maximum) period. This would indicate an inverse relationship of these ratios with solar activity.

Some features of the variability associated with solar and lunar daily variations

Summary. Long-term variability in solar and lunar daily variations, and its association with solar and magnetic activity, in the three geomagnetic ele- ments, H, D and 2, at Alibag is studied by an analysis of the data for each year separately during the period 1932-72. From year to year, consider- able change in amplitude, with very small change in phase, is noticed in the case of solar daily variation, whereas, for lunar daily variation, changes in both amplitude and phase are found to be large. Solar cycle influence on the solar daily variation is observed to be prominent, and a distinct influence on the lunar daily variations is also seen; the observed influence of magnetic activity on these variations appears to be merely a reflection of the strong association between solar and magnetic activities. Bartels (1932) describes a method of estimating the total variability of geomagnetic solar daily variation, S, by the use of harmonic dials. Analysing the daily data of Huancayo and Watheroo, by this method, he finds large variability in S and the assumption of normality in the distribution of the vector S to be valid. Gupta (1972) arrives at similar conclusions in his analysis of the geomagnetic data at Sodankyla. In this note, Bartels' method is applied to the harmonics of S and of lunar daily variation, L, in H, D and 2 at Alibag, computed (by B.R.A. and reported elsewhere) separately for each of the years during the 41-yr period, 1932-72. The relative contributions of the variations in solar and magnetic activities to the variability of S and L are calculated to ascertain which of the two is the larger contribu- ting factor. Harmonic dials and probable ellipses for each of the solar harmonics in each of the ele- ments are drawn (Fig. 1) by the procedure given by Bartels and also detailed by Chapman & Bartels (1940). In the case of L, only the fundamental harmonic, L2, is considered as it is generally large and well determined, especially in H. Of the 41 yearly values of L2 for each element, 30, 27 and 23 are significant in H, D and 2 respectively. A count of the points inside and outside of each of the ellipses has shown that they are nearly equal, indicating the validity of the assumption of Gaussian distribution of the cloud of points.

Upper-mantle conductivity determined by the geomagnetic lunar daily variation

The geomagnetic lunar daily variation, and the solar daily variation, have been recently analysed by Malin. The response measurements that he obtained are used here to investigate the radial distribution of electrical conductivity in the upper mantle. It is found that these observed response measurements require low conductivity in the mantle, at least as far down as 650 km from the surface. This result is compatible with the conductivity models determined by the quiet-day daily variation, and so justifies the use of these variation fields for geomagnetic deep sounding.

Worldwide distribution of geomagnetic tides

Geomagnetic lunar-daily variations result from the Moon’s tidal action on the ionosphere and oceans. They provide information that bears on the general large-scale dynamics of the atmosphere, and can also add to our understanding of ionospheric processes. For these reasons the variations, though small, are worth determining from geomagnetic data. The data for this study are hourly mean values of the geomagnetic elements from 100 observatories for the interval 1957.5 to 1960.0. These are analysed by the Chapman-Miller method to obtain parameters of the principal lunar harmonics. For each observatory, the contribution of the sea tidal dynamo to these parameters is empirically determined; this contribution has been ignored in previous worldwide studies, but is shown here to be an appreciable proportion of the total lunar effect, and worthy of study in its own right. After removal of the ocean dynamo effect, the remaining geomagnetic lunar daily variation, ascribed to the ionospheric dynamo and its associated induced currents, is represented by a series of spherical harmonic coefficients, and separated into parts of internal and external origin. (In this context, the relative merits of spherical harmonic analysis and the Price-Wilkins method of analysis are discussed.) Internal and external current systems associated with the ionospheric dynamo effect are deduced. Similar analyses, for the solar daily geomagnetic variation and for the lunar semidiurnal tide in the atmospheric pressure, are appended.

Seasonal Variations in the Solar and Lunar Daily Geomagnetic Variations

Summary Seasonal variations of the solar, S, and lunar, L, daily geomagnetic variations are discussed in terms of the ratio of seasonal range to annual mean range, for data based on hourly mean values from 100 observatories for the interval 1957.5 to 1960.0. It is shown that, for all elements, the greatest and least values of the ratio occur at high latitudes for both S and L. The conflicting views of previous workers on the difference between seasonal variations of L and S are discussed in the light of the present results and those from longer series of data from a few observatories.

Lunar and solar daily variations of the geomagnetic field at Toolangi

Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Toolangi during two ten year periods (1924–1933 and 1949–1958) have been analysed to determine their solar and luni-solar diurnal components. The results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed. It is shown that there are marked differences in the dependence ofS andL on the various parameters and a tentative explanation of this phenomenon is given.

Lunar and solar daily variations of the geomagnetic field at Watheroo, Western Australia

Mean hourly values of magnetic declination, horizontal intensity and vertical intensity observed at Watheroo (1919–1958) have been analysed to determine their solar and luni-solar diurnal components. Results, showing the variations of the first four harmonic components with season, degree of magnetic activity and annual sunspot number, are tabulated and discussed.

The solar and lunar daily geomagnetic variation of declination at Trevandrum, 1853?1869

The eye readings of easterly declination at Trevandrum observatory have been analysed to determine solar and lunar daily vatiations. Hourly readings during February 1853 to February 1865 are analysed by Chapman-Miller method. The 8 values read at unequidistant day-time hours during March 1865 to December 1869 are analysed to compute the amplitude and phase of the semimonthly wave at each of the hours separately. The semi-monthly lunar wave obtained from the hourly readings shows a considerable night-time variation. A brief discussion of the results is also given.

Ionospheric and magnetic observations during the annular solar eclipse of November 23, 1965

Vertical-incidence (VI) ionograms, magnetograms, and relative VI signal-amplitude (7-MHz) data were obtained in Bangkok, Thailand, during the annular solar eclipse on 23 November 1965. A maximum of 86% obscuration of the solar disk was observed at about 1007 local time (0307 GMT) in Bangkok, which was approximately 290 km from the center of the eclipse path. Marked changes in F2-layer virtual height and considerable stratification of the F layer, including formation of an F1.5 layer, were observed. Magnetograms indicate a large (approximately 25%) diminution in ionospheric current relative to normal solar daily (Sq) variations.

The lunar and solar semidiurnal variations of barometric pressure at Copenhagen, 1884–1949 (66 years)

AbstractSixty‐six years of bihourly barometric data for Copenhagen (55°·7N) are used to determine the lunar atmospheric tide there, L2 (p), and also the harmonic components Sn of the solar daily barometric variation S (p), for n = 1, 2, 3, 4, For L2 (p) seasonal means are given as well as the annual mean; for S2 (p) monthly, seasonal and annual mean values are given. The determinations are made for groups of days with different upper limits of range, 6·0 microbars (μb) and 8·7 ph, as well as for all days. It is shown that it is advantageous to exclude the days of larger range from the determination of L2 (p). Days of larger range are most frequent in winter. At that season, for days of smaller range, the mean pressure is higher than in summer.The 66‐year mean annual value of L2 (p) is 10·3 sin (2r + 87°·3) μb, with probable error 2·5 μb; for S2 (p) it is 225 sin (2t + 130°·8), with probable error 2·8 μb; here r and t denote respectively lunar and solar mean local time. Thus, in amplitude, S2 is 21·9 times L2, and in phase S2 exceeds L2 by 43°·5; L2 and S2 at Copenhagen vary seasonally in different ways; in both cases these variations are similar to those observed elsewhere in northern Europe. The corresponding amplitudes for Oslo (59°·9N), found by Haurwitz and Cowley (1967), are somewhat smaller, as might be expected.

Lunar daily harmonic geomagnetic variation as indicated by spectral analysis

Two series of hourly magnetic data, one from 54 observatories, have been analyzed spectrally and also, in some cases, harmonically. The main series is for the sunspot maximum 1957–1959, the other for the preceding minimum, 1953–1955. In all, 210 annual sets of hourly values, chiefly for the horizontal component H, were used. Prominent peaks appear in the spectra for the harmonics S n (with frequencies n cycles/day) of the solar daily variation S, for n up to 4, and in a few cases even up to 11. Lower peaks are shown for the components L n of the lunar daily variation L, up to 4, caused by the dynamo action, in the ionosphere, of the main term M 2 in the lunar atmospheric tide; the term T 1 possibly includes a significant part caused by the next main lunar tidal term, O 1 (diurnal). Other peaks appear less prominently, that may be identifiable with the L harmonics corresponding to dynamo action of minor lunar tidal terms; the indications of these peaks should be checked by harmonic analysis of longer series of data. For some of the data sets the amplitudes inferred from the spectral analysis are compared with those derived by harmonic analysis. The latter are systematically smaller, but for the solar harmonics S n the difference is slight. It is large, however, for the main lunar harmonics derived from high latitude data, which show much irregular disturbance.

The solar semidiurnal variation of cosmic-ray intensity 70 m.w.e. underground

Cosmic-ray intensity measurements have been carried out during the last year at a depth of 70 m.w.e. in the Monte dei Cappuccini laboratory in Torino, using solid vertical semicubical scintillator telescopes with a total area of 2 m2. Hourly data for 245 days corrected for barometric changes have been analyzed for the solar, apparent sidereal, and antisidereal daily variations whose harmonics are as follows:[Formula: see text]The true sidereal diurnal variation is estimated to have an amplitude of 0.019% with a time of maximum at 1720 h local sidereal time. The solar diurnal variation at different depths underground follows the energy dependence calculated with Axford's theory. The solar semidiurnal variation shows instead a fairly constant value at different μ energies. Its order of magnitude agrees with that expected as a result of Fermi acceleration in collisions of primaries moving in roughly solar and antisolar directions with solar wind inhomogeneities.

East/west directional measurements of the cosmic-ray solar daily variation at an equatorial station

Two large scintillator telescopes of cubical geometry, tilted at an angle of 45° to the vertical, were set up pointing in the east and west directions at the equatorial station Makerere. Data from these telescopes are available from July 1964 onwards. During the initial year of observation the solar diurnal variation in both telescopes, after pressure correction, had an amplitude of about 0.2%, but the absence of any appreciable phase difference between the east and west directions suggests that in the intermediate range of rigidities (say 50–150 GV) there was no appreciable primary anisotropy during the last solar minimum. This conclusion is in agreement with that drawn from similar measurements made at Chacaltaya. The large amplitude of the Makerere diurnal variation, however, suggests that there is a substantial "local" source of the diurnal variation which is significantly different from that observed at Chacaltaya. The possible origin of this "local" source is briefly discussed.

Directional measurements of the cosmic-ray daily variation at a vertical depth of 60 m.w.e. in London

Semicubical telescopes pointing in the vertical direction and inclined cubical telescopes pointing in the east and north directions have been employed to measure the cosmic-ray daily variation at an underground site in London. Although the statistical accuracy of the measured daily variations is not very high, there are strong indications that during 1965, which was the year of maximum cosmic-ray flux associated with the last solar minimum, tire upper limiting rigidity of the corotation anisotropy (with time of maximum at 1800 h) was reduced to such low values that a Compton–Getting effect due to the motion of the earth around the sun became observable. Also, the atmospheric contribution to the measured solar daily variations appears to be very small. There is no evidence for an enhancement of the observable sidereal daily variation associated with the lowering of the upper limiting rigidity of the corotation anisotropy.

Quiet and disturbed solar-daily variations of magnetic field at high latitudes during the IGY

Quiet solar-daily variations S q in high latitudes on very calm days of the IGY winter are closely connected with S q in middle and low latitudes. In summer in the polar cap region additional variations - S q p appear. The current system of magnetic variations for five international quiet days in high latitudes of the northern hemisphere in summer as well as the single vortex current system S q p with the focus at ? ?80° at the 15 hour meridian, are given and discussed. The distribution of the disturbed vector in winter in high latitudes of the northern and southern hemispheres shows that polar electrojet with westward current is located at ? ?65° at midnight and ? ?76° at midday, that is approximately within the latitudes of the aurora oval-shaped zone. The eastward electrojet is not return currents from westward one and represent an important feature of DP disturbances in high latitudes. The corresponding current system is given. In summer the disturbed vector in high latitudes consists of the field of west and east electrojets and the field ( S q p ) d —modified field S q p · S D current system for the summer without S q p is given. DOI: 10.1111/j.2153-3490.1968.tb00376.x

The electrical conductivity in the region from 105 to 125km

During the last year a successful attempt was made by Hines to deduce the diurnal tide from rocket-release measurements. These data together with the results of the meteor-trail-method have been used to determine the tides in 52°N. The height-integrated electrical conductivity Σ 3′ for the region from 105 to 125 km and 52°N. latitude has been calculated using the theory of the symmetric dynamo, the tide data, and the solar daily quiet geomagnetic variations deduced from the records of the magnetic observatory Potsdam-Seddin-Niemegk. A first approximation of the annual variation, the variation during the sunspot cycle, and some values for the daily variation of Σ 3′ have been deduced. A comparison with data deduced from some rocket measurements gives a satisfactory agreement.