Pi 3 magnetic pulsations associated with substorms

Using magnetic data from the North American IMS network at high latitudes, Pi 3 pulsations are analysed for a period of $\text{4}\text{1}\text{2}$ continuously-disturbed days. The data were obtained from 13 stations in the Alaska and Fort Churchill meridional chains and in the east-west chain along the auroral zone. In the past, Pi 3 pulsations associated with substorms have been classified into two sub-categories, Pi p and Ps 6. However, we find that Pi 3's which have longer periods than Pi p and which are different from Ps 6 are more commonly observed than these two special types. Power spectra, coherence and phase differences are compared among the stations. Results show that noticeable differences for latitudinal dependence of period and amplitude exist among midnight, morning and late-evening Pi 3 pulsations. Results for Pi 3 occurring near midnight indicate that the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the center of the westward auroral electrojet. On the other hand, for Pi 3 pulsations occurring in the morning, the periods at which the power spectral density is a maximum are longest, and the amplitude largest, near the poleward edge of the westward electrojet. Furthermore, for Pi 3 pulsations occurring in the late evening, their periods are longer and their amplitudes larger near both the Harang discontinuity and the poleward edge of the westward electrojet than near its center. Correlations between pairs of adjoining stations are better in the polar cap than at auroral latitudes. It is also found from hodograms that the sense of polarization often varies from one station to another for the same event, and that the time duration in which the same rotational sense is maintained is shorter near midnight than in the morning and late evening. It is suggested that the source regions of the morning and late-evening Pi 3's lie on the electrojet boundaries; that is at the Harang discontinuity (in the evening) and at the poleward edge of the westward electrojet (in the morning and evening). The generation of midnight Pi 3 pulsations, centered at a location within the westward auroral electrojet appears to be associated directly with the generation of that electrojet.     

Field-aligned currents between 400 and 3000 km in auroral and polar latitudes

The polar orbiting magnetically stabilized satellite AZUR measured transverse magnetic variations in auroral and polar latitudes by means of a two component flux-gate magnetometer. Simultaneous measurements of $\text{λ2972}\text{A}\text{?}$ and $\text{λ3914}\text{A}\text{?}$ auroral emissions are related to low-energy zero-pitch-angle electron fluxes, which cause the transverse magnetic disturbances. Power spectra of the magnetic field variations are consistent with those of geomagnetic micropulsations.The sources of the field-aligned currents can be located in the Alfvén layer and in the magnetotail.     

A phase and amplitude study of auroral pulsations

To supplement a rocket investigation of the auroral green line, data from some auroral pulsations have been analyzed by direct integration of the time-dependent continuity equations for each of the sources now thought to contribute. It is shown that indirect processes are not incompatible with studies of auroral pulsations, and that a non-negligible contribution to the green-line intensity comes from dissociative recombination. Calculations using the theoretical O(¹S) lifetime show that the remaining green line must come from a direct or very fast process; however, if the O(¹S) lifetime can be reduced, significant portions of the green line can come from the transfer of energy from N₂(A³Σ_u⁺) to atomic oxygen.     

Long term modulation of cosmic rays and inferable electromagnetic state in solar modulating region

It is demonstrated that the long term variation in cosmic ray intensity I(t) can be described by an integral equation,

$\text{I(t)=I}{}_{\mathrm{\infty }}\text{?}\text{∫}\text{0}\text{∞}\text{f(τ)S(t?τ)}\text{d}\text{τ}$

, which is derived from a generalization of Simpson's coasting solar wind model. A source function S(t?τ) is given by some appropriate solar activity index at a time t?τ(τ ? 0) and the characteristic functionf(τ)(?0 forτ ? 0) expresses the time dependence of the efficiency of the intensity depression due to solar disturbances represented by S(t ?τ) when the disturbances generated at the solar surface propagate through the modulating region with the solar wind. It is demonstrated further that the equation can be derived from the general diffusion-convection theory on some assumptions, and as a result, the source and characteristic functions can be related to diffusion coefficient and its transition in space. Assuming the sunspot number R (or two activity indices including R) as the source function, the characteristic function f(τ) [or f(τ)'s] is obtained with data of the cosmic ray intensity extended over several decades. Based on the theory, one can obtain from f(τ) the following physical quantities in space, such as the transition and life time of solar disturbances, the boundary of the modulating region, and the radial and time dependences of the diffusion coefficient, radial density gradient and modulated intensity of cosmic rays. Results deduced from the present analysis are consistent with those obtained directly or indirectly by space observations.     

Ring current simulation in connection with interplanetary space conditions

A ring current model has been obtained which permits calculations ofD_st variations on the Earth's surface during magnetic storms. The changes in D_st are described by the equation

$\text{d}\text{d}\text{t}\text{D}{}_{\mathrm{sto}}\text{= F(EM)?}\text{D}{}_{\mathrm{sto}}\text{tau;}$

where $\text{D}{}_{\mathrm{sto}}\text{= D}{}_{\mathrm{st}}\text{-bp}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{+~tc}$; p = mnv² is solar wind pressure; F(EM) is the function, controlled by the electromagnetic parameters of interplanetary medium, of injection into ring current ; τ is the constant of ring current decay. $\text{C}\text{= C}\text{u}\text{τ?=18}\text{nT}$, where C is the level of the D_st-variation field measurements; ? is the injection function characterizing the quasisteady-state injection of energy into the ring-current region. The constant Ç is determined from the condition that the change of the ring current energy from magnetic storm commencement to end should equal the difference between the injected and dissipated energy throughout the storm. The values of the factors b and τ were found by the method of minimizing the sum of the quadratic deviations of the calculated D_st from the values observed throughout the storm : b = 0.23 nT/(eV cm^?3)^{$\text{1}\text{2}$}, τ = 8.2 h at D_st? ? 55 nT and τ = 5.8 h at -120 ? D_st ? — 55 nT. The injection function F(EM) is of the form F(EM) = d(E_y? A) at the values of the azimuthal component of the solar wind electric field E_y ? A, and F(EM) =0 at A?E_y.d = ? 1.2 × 10^?3 Ts^?1 (mV/m)^?1 and A = ? 0.9 mV m^?1 . Thus, the injection to ring current is possible at the northward B_z component of the IMF.     

Use of equivalency in estimating the historical size distribution of impact craters

A previous analysis of a stochastic model of lunar-type impact cratering is extended to utilize geological age data by defining a more general statistic $\text{Ω}{}_{\mathrm{i}}\text{(t)}$ to be the number of equivalent whole craters of original diameter d_i and age ≤t in an observational area A; each crater is taken to be equivalent to the fraction of its rim (or area) that is in A and not occluded by later craters. By integration of a new gain-loss differential equation, a generalization of the previous basic equation is obtained that relates the expected value $\text{ω}{}_{\mathrm{i}}\text{(t) = E[Ω}{}_{\mathrm{i}}\text{(t)]}$ to the process functions specifying the size distribution and flux of craters (primary or secondary) as they form. The results are specialized to the plausible case in which the cratered body can be subdivided into geological provinces of increasing ages t₁, t₂, …, t_i … and the size probability distribution can be approximated as constant within each of the periods t_i+1 - t_i. It is shown that use of the $\text{Ω}{}_{\mathrm{i}}$ permits, in principle, a reconstruction of the historical values of the process functions and correctly compensates for the effect of overlap by removing the false bias favoring large craters that results from the usual method of crater counting. Possible generalizations of the gain-loss equation are indicated.     

Interplanetary energy flux associated with magnetospheric substorms

It is shown that the interplanetary quantity ε(t), obtained by Perreault and Akasofu (1978), for intense geomagnetic storms, also correlates well with individual magnetospheric substonns. This quantity is given by $\text{ε(t) = VB}{}^2\text{sin}{}^4\text{(}\text{θ}\text{2}\text{)l}{}_{\mathrm{o}}{}^2$, where V and B denote the solar wind speed and the magnitude of the interplanetary magnetic field (IMF), respectively, and θ denotes the polar angle of the IMF; l_o is a constant ? 7 Earth radii. The AE index is used in this correlation study. The correlation is good enough to predict both the occurrence and intensity of magnetospheric substonns observed in the auroral zone, by monitoring the quantity ε(t) upstream of the solar wind.     

Auroral implications of recent measurements on O(1S) and O(1S) formation in the reaction of N+ with O2

Recent flowing afterglow measurements have shown that the reaction of N⁺ with O₂ produces 70 ± 30% of the oxygen atom product as $\text{O}\text{(}{}^1\text{D}\text{)}$ and < 0.1% as $\text{O}\text{(}{}^1\text{S}\text{)}$. These results indicate that this reaction does not contribute to the auroral green line emission (5577 Å), but can account for ～10% of the observed red line (6300 Å) auroral emission.     

Localized auroral disturbance in the morning sector of topside ionosphere as a standing electromagnetic wave

An intense, localized auroral disturbance observed by Intercosmos-Bulgaria-1300 satellite in the morning sector at the altitude 850 km is analyzed in detail. The disturbance is characterized by strong “jumps” of electric and magnetic fields reaching ～ 80 mV/m and ～ 100 nT, fluctuations of ion density (Δn/n ～ 70%) and bursts of downward and upward energetic electron fluxes. Electric and magnetic disturbances display a distinct spatial-temporal relationship typical for the standing quasi-monochromatic wave ($\text{? ～ 1}\text{Hz}\text{, λ}{}_{\mathrm{x}}\text{～ 10}\text{km}$). The ratio of amplitudes of electric and magnetic fluctuations is equal to Alfvén velocity (ΔE/ΔB ～ v_A/c). However, a strong parallel component of the electric field (～ 30 mV/m) and large ion density fluctuations indicate significant changes of plasma properties (the effects of anomalous resistivity are possible).     

The roles of the north-south component of the interplanetary magnetic field on large-scale auroral dynamics observed by the DMSP satellite

An extensive study of DMSP photographs and the simultaneous interplanetary magnetic field data suggests that the quantity defined by

$\text{S=∫}{}^{\mathrm{\tau }}{}_0\text{(Ф}{}_{\mathrm{D}}\text{? Ф}{}_{\mathrm{N}}\text{)dt}$

has a fundamental importance in substorm processes, where Φ_D and Φ_N denote the production rate of merged (or open) field lines along the dayside X-line and of reconnected (or closed) field lines along the nightside X-line, respectively; t = 0 is measured from the time when the B_z component begins to decrease after a prolonged period of a large positive B_z value. It is shown, first of all, that substorms occur so long as S > 0, regardless of the sign of the B_z component and its changes (namely, the southward and northward turnings) and of its time derivative as well. Secondly, the intensity of substorms is proportional to S². By introducing the quantity S, the recent confusion of the problem of the roles of the north-south component of the interplanetary magnetic field on substorm processes can be removed.Since S is equal to the amount of the open magnetic fluxes at a time reckoned from t = 0, it is proportional to (A₁ ? A₀), where A₀ denotes the minimum polar cap area (namely, the area bounded by the minimum auroral oval) and A₁ the polar cap area at an arbitrary time t. Therefore, substorms can occur whenever the auroral oval is larger than its minimum size. Further, an intense substorm tends to occur along a large oval.The quantity S can also be considered as an excess flux, and thus the substorm can be considered as a process by which the magnetosphere tends to remove sporadically the excess energy associated with S.     

Substorm energy

It is shown that the area A_k(× 10⁶km²) covered by brightest auroras and the area A_q bounded by the auroral oval have a simple relation given by

$\text{A}{}_{\mathrm{k}}\text{= 0.05(A}{}_{\mathrm{q}}\text{? A}{}_0\text{)}{}^2$

, where A₀ denotes the area of the minimum size oval and the quantity (A_q ? A₀)² is proportional to the energy ε_q which is stored in the magnetotail and is available for substorms. Following the definition of the intensity of solar flares, A_k may be chosen as a measure of the intensity of substorms. It is also found that the joule heat energy produced by the auroral electrojet is also proportional to (A_q ? A₀)². Thus, it may be concluded that the intensity of substorms is proportional to the energy ε_q stored in the magnetotail.     

Comment on the group velocity of surface waves on the plasma sheet boundary

In the recent estimation by Maltsev and Lyatsky (1984) of the group velocity of surface waves on the inner boundary of the plasma sheet, the effect of the curvature of the field lines of the ambient magnetic field of the Earth on the spectrum has been assessed. The authors have not accounted for the fact, however, that the group velocity of the compressional surface magnetohydrodynamic waves itself is nonzero transverse to the magnetic field—a characteristic which has been omitted in the spectrum of Chen and Hasegawa (1974), being used by Maltsev and Lyatsky.This characteristic of compressional surface MHD waves is inherent for the spectrum $\text{ω = (}\text{k}{}_6\text{k}\text{)V}{}_{\mathrm{A}}\text{(k}{}^2{}_6\text{+ 2k}{}^2{}_{\mathrm{\perp }}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$, obtained by Nenovski (1978) in the cold plasma limit V_A ? V_S(V_A is Alfvén velocity, and V_S, sound velocity). A comment has been made on the restrictions, proceeding from the approximation, used by Maltsev and Lyatsky. The estimation of the velocities for movements of auroral riometer absorption bays have been reviewed.     

Excitation of O(1S) and emission of 5577 Å radiation in aurora

The results of recent laboratory experiments suggest that the reaction N⁺ + O₂ → NO⁺ + O(¹S) is the principal source of O(¹S) in aurora. A negligible time delay between auroral ionization and O(¹S) production is associated with this indirect process, which is a necessary condition for a viable mechanism. The $\text{5577}\text{A}\text{?}\text{3914}\text{A}\text{?}$ volume emission rate ratio associated with this production source remains constant with altitude. The problems encountered by the currently accepted source of O(¹S), the reaction of N₂(A³Σ) molecules with atomic oxygen are explored, and the contributions of this and other reactions to the auroral green line emission are reevaluated.     

On fourier-analysis of geomagnetic pulsations pc-1, “two-fold” and “three-fold” pulsations pc-1 and fundamental frequencies of the magnetospheric cavity—I

The paper gives the results of detailed studies of the frequency spectra $\text{S}{}_{\mathrm{s}}\text{(?)}$ of the chain of the wave packets F_s(t) of geomagnetic pulsations PC-1 recorded at the Novolazarevskaya station. The bulk of the energy of F_s(t) is concentrated in the vicinity of the central frequencies $\text{?}{}_{\mathrm{s0}}$ of spectra—the carrier frequencies of the signals. The velocity $\text{V}{}_0\text{≌ 6.10}{}^3\text{km s}{}^{\mathrm{?1}}$ of the flux of protons generating these signals correspond to them. The spectra of the signals have oscillations—“satellites” irregularly distributed in frequency. These satellites, as the authors believe, testify to the presence of the individual groups of protons of low concentration whose velocities vary within 10³–10⁴ km s^?1.Their energy is only of the order of 10^?2–10^?3 of the energy of the main proton flux. Clearly pronounced maxima on double and triple frequencies $\text{? = 2?}{}_{\mathrm{s0}}\text{and}\text{3?}{}_{\mathrm{s0}}$ are detected. They show that the generation of pulsations PC-1 is accompanied by the generation on the overtones of wave packets called in this paper “two-fold” and “three-fold” pulsations PC-1. Intensive symmetrical satellites of a modulation character have been discovered on frequencies $\text{?}{}^{\mathrm{\pm }}{}_{\mathrm{sK}}$. Frequency differences $\text{Δ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{=}\text{¦?}{}_{\mathrm{s0}}\text{? ?}{}_{\mathrm{sK}}{}^{\mathrm{\pm }}\text{¦}\text{= (0.011,0.022}\text{and}\text{0.035)}\text{Hz}$ correspond to them. The authors believe that the values of Δ?^±_sK are resonance frequencies of the magnetospheric cavity in which geomagnetic pulsations PC-1 are generated. It is established that the values of Δ?^±_sK coincide closely with the carrier frequencies of geomagnetic pulsations PC-3 and PC-4 generated in the magnetosphere. This leads to the conclusion that the resonance oscillations of the magnetospheric cavity are their source. Thus, the generation of geomagnetic pulsations of different types and resonance oscillations in the magnetosphere are integrated into a unified process. The importance of the results obtained and the necessity to check further their trustworthiness and universality, using experimental data gathered in different conditions, is stressed.     

A discussion of the energy transfer from N2(A3Σu+) to O(1S) in pulsating aurora

In a recent paper, Brekke and Pettersen (1972) have introduced a method for estimating any indirect process in the production of the $\text{O}\text{(}{}^1\text{S}$) atoms in pulsating aurora; for 38 per cent of their data they found that the decay time for the indirect mechanism was shorter than the effective lifetime of the ${}^1\text{S}$ state. These data are related to the energy transfer from the N₂(A³Σ) molecules to the $\text{O}\text{(}{}^1\text{S)}$ state, and evidence is found for this process to contribute in the altitude range below 125 km.     

A note on the asymptotic density-potential relation of a spiral galaxy with a finite thickness

It is shown that the asymptotic σ₁(r) and ψ₁(r) relations can be derived very simply by using the method of double series expansion, where σ₁, ψ₁(r,0) and ψ₁ are the surface density perturbation, the gravitational potential perturbation at the symmetric plane Z=0 and the average potential perturbation respectively. The results are accurate to the order of both m²(kr)^?2 and k〈∣z∣〉, where m is the number of spiral arms, k is the radial wave number, r is the distance from the centre of the galaxy, and 〈∣z∣〉 is the average vertical distance of a star from the Symmetrie plane Z=0. Such an accuracy is usually sufficient for the discussion of spiral modes in a spiral galaxy of small but finite disk thickness. It is pointed out that ψ₁(r,0)～(σ₁(r) relation can be expressed in a unified form for different vertical density profiles if 〈∣z∣〉 is adopted as the thickness scale, and that ψ₁(r,0)～(σ₁(r) can be expressed in a unified form for different vertical density profiles if 〈∣z?z∣〉 the average vertical separation between two stars, is adopted as the thickness scale. Only the value of the ratio $\text{〈|z?z′|〉z}\text{〈|z|〉}$ is a functional of the vertical density profile. However, for the usual physically meaningful profiles, these values are very close to each other: It is $\text{2}$ for the Gaussian profile, $\text{1}\text{Ln}\text{2}\text{= 1.443}$ for the $\text{rmsech}{}^2\text{(}\text{z}\text{z}{}_1\text{(r)}\text{)}$ profile, and 1.5 for the $\text{exp}\text{[}\text{?|z|}\text{z}{}_1\text{(r)}\text{]}$ profile.     

Investigation of shock waves and tangential discontinuities of the cosmic plasma by the radio interference technique

The possibility of investigation of the cosmic plasma dynamics by the radio interference technique based on a finite time of radio wave propagation between the sounding and responding stations is shown. By locating the sounding station on a spacecraft the greatest contribution to the phase difference ΔΦ(t)or the phase difference growth rate $\text{Δ?}$ between the sounding and response signals are caused by disturbances in close proximity to the spacecraft. This method permits interplanetary shock waves and tangential discontinuities to be registered and the velocities and plasma density changes on their fronts to be determined. By using experimental data of ΔΦ(t) or $\text{Δ?(t)}$ one can also obtain information about plasma concentration jump, location and motion of bow shock wave and magnetopause and plasmapause. Available experimental data about different disturbances of cosmic plasma were analysed and the requirements on frequency stability of spacecraft-borne and groundbased radio equipment were estimated to register those disturbances. In most cases relative stability 10^?11–10^?13 provided by present atomic frequency standards is sufficient.     

Correlations between ground observations of Pi 2 geomagnetic pulsations and satellite plasma density observations

Ground observations of Pi 2 geomagnetic pulsations are correlated with satellite measurements of plasma density for three time intervals. The pulsations were recorded using the IGS network of magnetometer stations and the plasma density measurements were made on board GEOS-1 and ISEE-1. Using the technique of complex demodulation, the amplitude, phase and polarisation characteristics of the Pi 2 pulsations are observed along two meridional profiles; one from Eidar, Iceland (L = 6.7) to Cambridge, U.K. (L = 2.5) and the other from Tromso, Norway (tL = 6.2) to Nurmijarvi, Finland (L = 3.3). The observed characteristics of the Pi 2 pulsations are then compared with the plasma density measurements. Close relationships between the plasmapause position and the position of an ellipticity reversal and a variation in H component phase are observed. A small, secondary amplitude maximum is observed on the U.K./Iceland meridian well inside the position of the projection of the equatorial plasmapause. The primary maxima on the two meridians, in general occur close to the estimated position of the equatorward edge of a westward electrojet. Using the plasma density measurements, the periods of surface waves at the plasmapause for two intervals are estimated and found to be in good agreement with the dominant spectral peaks observed at the ground stations near the plasmapause latitude and within the plasmasphere. The polarisation reversal, together with phase characteristics, spectral evidence and the agreement between the theoretical and observed periods leads to the suggestion that on occasions a surface wave is excited on the plasmapause as an intermediate stage in the propagation of Pi 2 pulsations from the auroral zone to lower latitudes.     

The DH ratio in the atmosphere of Uranus: Detection of the R5(1) line of HD

Observations of Uranus during the 1975, 1976, and 1978 apparitions reveal a weak absorption at the wavelength of the R₅(1) line of HD with equivalent width $\text{1.0 ± 0.4}\text{m}\text{A}\text{?}$. The $\text{D}\text{H}$ ratio in Uranus' atmosphere implied by this line and other published spectra is (4.8 ± 1.5) × 10^?5, and may not be significantly different from that in the atmospheres of Jupiter and Saturn. In addition, the spectra exhibit two weak absorption at $\text{6044.76 ± 0.02}\text{and}\text{6045.54 ± 0.02}\text{A}\text{?}$ which we were unable to identify. No trace of absorption is visible near these wavelengths or near the HD wavelength in a laboratory spectrum of 4.92 km-am CH₄ which we obtained in an attempt to identify these absorption features and to verify that the HD feature does not arise from CH₄.