Geomagnetic Index Ap Research Articles

Dependence of the aurora borealis occurrences on the solar-terrestrial parameters

The recent measurements made by satellites of the aurorae in connection with solar phenomena have increased interest in auroral research. In the present investigation, we establish that, for the 20th solar cycle, the occurrence of visual discrete aurorae A, deduced from a complete set of data, is significantly related to the sunspot numbers R z, the number of flares F (of importance ⩾ 1) the solar wind streams derived from solar coronal holes H, and the geomagnetic index A p. By employing the theory of residues it has been found that A correlates significantly well with the above indices. Accuracies of the order of 75–94% were found for geomagnetic latitudes in the range of 54 ‡–63 ‡ N. The A-R zrelationship was investigated in particular for the period 1897–1951. For this period spectrum analysis of A annual values revealed the existence of 3–4 yr and 8–10 yr periodicities of significances 95% and 99%; respectively.

Cosmic ray modulations related to the interplanetary magnetic field intensity

Data covering a complete solar cycle (1965–1976) have been analyzed in a comprehensive investigation of the nature of transient modulations of relativistic galactic cosmic rays associated with interplanetary magnetic field intensity excursions in the vicinity of the earth. It had been recognized earlier that the correlation coefficient between the cosmic ray intensity and the IMF magnitude is small. In fact, it remains less than 0.5 throughout the solar cycle. In order to understand the nature of field‐related modulations and to minimize the complications arising from the effects of other features of solar plasma, the data are here analyzed by the method of superposed epochs. Following newly developed procedures for evaluating the statistical significance of the results obtained with this type of analysis, it is demonstrated that, while the days characterized by high IMF magnitude B are associated with intensity decreases, the IMF rarefactions (low B) cause an increase in the flux. In contrast to the case of geomagnetic disturbances, which respond more rapidly, maximum cosmic ray intensity variations associated with both high and low B occur 1 day after the key days characterized by field departures from average values. This indicates that the modulation mechanism becomes efficient only when the plasma engulfment of the earth extends at least a gyroradius beyond 1 AU. Finally, while the geomagnetic index Ap follows the interplanetary magnetic field changes rather closely, the polar nucleonic intensity shows a prolonged recovery time (7–10 days) following magnetic enhancements as well as rarefactions. These results suggest that, on average, interplanetary magnetic field intensity variations which are presumably related to disturbances traveling from the sun are effective transient modulators of the relativistic particles and that the corotation of the modulating region plays a significant role in the recovery of the cosmic ray intensity. An investigation of the spectra of the cosmic ray intensity variations produced by interplanetary magnetic field enhancements and rarefactions, respectively, over the rigidity range covered by ground‐based nucleonic intensity detectors has revealed that a power law of the form Kp−1 fits the data in both cases. This result is relevant to further theoretical studies of cosmic ray modulation processes.

Possible heating effect in the mesospheric 51 to 70 km altitude region over Thumba (8° N, 77° E) following geomagnetic activity

The variation in equatorial mesospheric temperatures at altitudes of 51 to 70 km during geomagnetically-active periods has been studied. A correlation analysis of rocketsonde temperature data obtained from the M-100 sounding rocket launchings at Thumba (8 deg. N, 77 deg. E) and the daily planetary geomagnetic index Ap has been carried out for a one-year period (December 1970 to December 1971).
 The results of the analysis reveal a highly significant in-phase relationship between the temperatures and Ap . The 51 to 70 km layer average temperature changes in-phase, around 3 to 4 days after the Ap increase. The temperature change has been quantified by (DELTA)T/(DELTA)Ap = 0.36° K (approx.) for a four-day lag between the time of Ap increase and the subsequent temperature increase.
 This heating effect in the 51 to 70 km altitude region around 3 to 4 days after variations in geo-magnetic activity, appears to be a part of the phenomenon of solar/geomagnetic activity induced perturbations in the equatorial neutral atmosphere over Thumba, observed by Raja Rao et al. (1978). Such results would form useful inputs for modelling the neutral atmosphere over India.

Association of corotating magnetic sector structure with Jupiter's decameter‐wave radio emission

Chree (superposed epoch) analyses of Jupiter's decameter‐wave radio emission taken from the new Thieman (1979) catalog show highly significant correlation with solar activity, indicated by the geomagnetic Ap index. The correlation effects can be explained in terms of corotating interplanetary magnetic sector features. At times when the solar wind velocity is relatively low, about 300 to 350 km/s, a sector boundary can encounter the earth and Jupiter almost simultaneously during the period immediately before opposition. After opposition this will not normally occur, as the solar wind velocities necessary are too low. The correlation effects are much enhanced for the three apparitions of 1962–1964, during which a relatively stable and long‐lived sector pattern was present. Chree analyses for this period indicate periodicities, equal to approximately half the solar rotation period, in the Jupiter data.

On the possibility of inferring the inter-planetary sector structure from daily variations of geomagnetic ap indices

The linear Bartels ap indices, which by definition should have no average U.T. variations, show in fact two different average U.T. variations if the data is divided into two groups according to the two Interplanetary Magnetic Field (IMF) polarities. These differences are found to be similar for all seasons and activity ranges. Correlating the ap variations of individual days to the average ap variations for days with interplanetary away and toward polarities, a simple but objective precept of calculations is given to infer the IMF sector structure with a success rate of 73% of the days for the years 1963–1973. The same method is employed to infer the IMF sector structure since 1932, and the results are compared to the sector structure inferred from polar cap magnetograms. Some known features of solar sector fields, e.g. the heliographic latitude dependence of the dominant polarity, are also found in the polarity classification based on ap variations, whereas the significant higher geomagnetic activity during intervals of toward polarity before 1963, which was found in the sector structure inferred from polar cap magnetograms, is not observed.

Correlations between solar, interplanetary, geomagnetic, ionospheric, atmospheric circulation and microseismic phenomena

Abstract Long‐period (1948–1967) correlations have been statistically determined for the frequency of occurrence of solar flares associated with type IV radio bursts, negative variation of cosmic ray level, geomagnetic indices AP, lower ionospheric absorption, polar vortex activity in the circumpolar pressure field pattern and long‐term microseismic activity, expressed in statistical variations of amplitudes and periods of meteorological microseisms down to latitudes of about 35° N. All of the characteristics mentioned exhibit the same type of changes even in the time position of secondary maxima while only a rough similarity was observed with respect to the correlation of sunspot numbers and A= 10.7 cm solar radio flux. As a whole this represents a wide scale of interactions between the space‐solar phenomena and physical fields of the earth.

Predominance of even Ap indices

A study of the frequency distribution of geomagnetic activity Ap indices shows that there is a tendency for more of the indices to be even than are odd. We identify the probable source of the bias, i.e., the use of a particular rounding rule in the derivation of the Ap values, and we suggest two methods for eliminating the tendency to even values.

Increased influx of stratospheric air into the lower troposphere after solar Hα and X ray flares

Evidence is presented of increase in the frequency of influxes of stratospheric air masses down to 3 km above sea level after the occurrence of Hα and/or X ray flares. A significant maximum of 7Be and 32P concentrations in air was found at our measuring station (Zugspitze peak, 3 km above sea level, Bavarian Alps) on the second or third day after the flare event. Both radionuclides are by far preponderantly generated in the lower stratosphere. The concentration maximums coincide in time with maximums of solar wind velocity and geomagnetic index Ap. Elucidation of the chain of causation between solar event and injection of stratospheric air down to ground level is subject to thorough and protracted investigation. So much can be said now that use of this statistically evident solar-terrestrial relationship would be in order in the practical forecasting of influxes of stratospheric air into the biosphere.

The effect of the field of a permanent magnet on the germination and growth of white mustard (BRASSICA ALBA L.) seeds

During 1968 samples of white mustard seeds were grown for a series of 4-day periods under conditions designed to test whether growth was affected by the presence of a stationary magnetic field. In one experiment the seedlings were rotated in the magnetic field, in the other they were stationary. The results show that the seedlings rotating in the magnetic field made more growth than a rotating or stationary control outside it, while the seedlings stationary under a magnet made less growth than those of a control sample. The differences in growth between the samples under a magnet and those not under it and between those stationary and those rotating were correlated with temperature and the Ap geomagnetic index and a possible explanation of these correlations suggested.

Some statistics on Pc 1 geomagnetic micropulsation occurrence at middle latitudes: Inverse relation with sunspot cycle and semi-annual period

The monthly rate of occurrence at California stations of hydromagnetic (hm) emissions, which are the predominant micropulsations in the Pc 1 category, was analyzed for the 12-year interval January 1955 through December 1966. The over-all approximate inverse relation between the hm emission occurrence rates and the sunspot cycle, first suggested by H. Benioff (1960), was confirmed. However, there were some significant departures from the strict inverse relation during the interval of the observations. In particular, there was a secondary peak of hm emission activity during 1960, when the rate of decrease of sunspot numbers was at its maximum, and there was some evidence for smaller peaks when the rate of increase of sunspot numbers was also a maximum. Furthermore, the cycle of hm emission occurrences appeared to precede the sunspot cycle by close to a year. There was some similarity in structure between the hm emission cycle and the smoothed variation of the Ap geomagnetic index over the same interval, even though the over-all Ap cycle varied with, or a little behind, the sunspot cycle and therefore differed considerably, on this basis, from the hm emission cycle. The California cycle of hm emission occurrences and the cycle observed at stations in the USSR are compared. There are a number of differences between the two cycles, the most striking of which is the absence of a maximum in the USSR data close to the sunspot minimum of 1964. The hm emission occurrences in California over the 12-year interval had a semiannual period, with a marked peak of activity during April and a smaller peak during September and October. There were minima of activity during January and June. The annual variation is similar to that shown by the Ci and Ap geomagnetic indices.

Upper atmospheric response to transient heating

The response of the upper atmosphere to various forms of time-dependent heating is calculated by use of approximate analytic solutions of the heat conduction equation. Time lags of maximum temperature and density behind peak heating are distinctly different and, for short-duration heating events, are strongly altitude dependent. The time and space characteristics of a one-dimensional heat source that produces a density change consistent with the observed drag on satellites during a geomagnetic disturbance are identified. The desired model for polar substorm heating maximizes in the 140- to 160-km altitude region with an average duration of 4 to 5 hours. The relationship between the amount of heat injected per unit column during a disturbance of maximum geomagnetic index ap is q ∝ (ap)1/2. This simple relationship suggests a common heating mechanism that is present at all levels of activity.

Short-Term Correlations of Decameter Radio Emission from Jupiter and Solar Activity.

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Short-Term Correlations of Decameter Radio Emission from Jupiter and Solar Activity. Sastry, Ch. V. Abstract An analysis of decameter radio emission from Jupiter and solar activity over the past 10 yr by the Chree method of superposed epochs showed that there is a significant increase in the radio emission from Jupiter following enhanced solar activity during the past sunspot maximum. The indices used to represent solar activity are (1) geomagnetic planetary index Ap, (2) solar radio flux at centimeter wavelengths. It is pointed out that due to the directivity of the source on Jupiter, the effect of the satellite lo and the observing procedures the Jupiter data contain periodicities which are not inherent in the source. These periodicities are estimated in the following way. A two-dimensional histogram giving the occurrence probability as a function of LCM (system III) and the position of the satellite lo is calculated using all the available data. For an assumed 4 h observing function each day the theoretical probability of ohserving Jupiter based on the two-dimensional histogram is calculated for a number of days. A power spectrum analysis of these theoretical probabilities showed that there can be a number of periodicities in Jupiter data with periods ranging from 2 to 30 days. It is well known that solar data exhibit similar periodicities. The observed correlations may be due to the existence of similar periodicities in both time series. To test this hypothesis the probability of observing Jupiter for each day, for which observing times are available, during the period 1957 through 1961 is calculated using the two-dimensional histogram. These theoretical probabilities are correlated with the solar indices for the same period. The correlation curves thus obtained are similar to the correlation curves obtained by using the days on which Jupiter emission is detected. On the basis of these results it is suggested that there is no conclusive evidence that decameter radio emission from Jupiter and solar activity are related. Publication: The Astronomical Journal Pub Date: February 1966 DOI: 10.1086/110086 Bibcode: 1966AJ.....71R.179S full text sources ADS |

Solar plasma velocity, exospheric temperature, and geomagnetic activity

Ondoh and Hakura [1964] have pointed out that if solar plasma velocities are computed for the time interval between a flare and the corresponding geomagnetic disturbance, and then linearly correlated to the geomagnetic indices Kp and Ap, the resulting regression lines do not agree in slope with the corresponding regression lines derived from solar wind data supplied by Mariner 2 [Snyder et al., 1963]. The Mariner 2 velocities refer mostly to quiet or mildly disturbed days (0 < Kp < 6), whereas the velocities determined by Ondoh and Hakura come from magnetic storms (3 < Kp < 9). If Kp is taken to be the independent variable, the Mariner (‘wind’) slope is smaller than the storm slope; if Ap is the independent variable, the situation is reversed. Also, the Mariner velocities correlate better with Kp, and the storm velocities show a better correlation with Ap.

Atmospheric Heating in the Auroral Zones

ALL the data on atmospheric perturbations related to geomagnetic disturbances1–7 have so far been derived from the drag analysis of artificial satellites with perigees located in low or moderate latitudes. The amplitudes of these perturbations can be accounted for4 by assuming that the heating of the atmosphere above the height of 350 km is proportional to the 3-hourly geomagnetic index ap. A study of 46 atmospheric drag perturbations of Explorer IX (Satellite 1961 δ1, inclination 38.8°) during a 283-day interval in the year 1961 has yielded7 for the atmospheric heating the relation c= ΔT/Δap= 1.0° (temperature T in °K). A plot of the observed data is given in Fig. 1. If allowance is made for the limited resolution of the drag determinations, the value of the coefficient c must be increased to 1.2°.

太陽活動とオゾン層について

A statistical investigation of the variation of total ozone amount as measured by the deviation of ten-day running means to find out the influence of intense solar flares or of an intense solar corpuscular bombardment was carried out, each concerning with varying latitudinal belt.The method of calculation was the key day test or the superposed epoch method to see the variation from three-days before through ten-days after the key day. The ozone data used were those of twenty-two stations of the world namely, of Japan (5), America (5), Australia (3), Italy (3), Iceland (1), India (4) and of Switzerland (1), covering the period from January 1958 to March 1959.Key days were defined in two ways, namely the day when geomagnetic Ap index was greater than 45 and the day when the flare index, as defined by this author basing on the world wide flare data, was greater than 1500.According to the results of calculation ozone increased on the third or forth day after the flare key day except in the zone of lowest latitude. The statistical test did not show in general a property so much remarkable as to exceed the 5% confidence limit except the increase of ozone on the third day in the zone of 20∼30° latitude.In the case of geomagnetic key day generally none of the variation exceeded the 5% confidence limit except the case of 8 th day at the highest latitudinal belt. Also at the same zone it showed the tendency to decrease on the third day which is to be noted when compared with the increase of temperature at 100mb in the auroral zone that was reported by Ward.