An ionospheric origin for Pi 1 micropulsations     

J.S. Reid 《Planetary and Space Science》1976,24(7):705-710

Cosmic noise absorption pulsation events observed with fast response riometers at Macquarie Island in the southern auroral zone have almost always been accompanied by Pi 1 micropulsations. A cross-spectral analysis of fast response riometer data and vertical component induction magnetometer data for one such event showed that, after the low frequency components are removed, the absorption A(t) is better correlated with the absolute value of the field Z(t) than with the recorded quantity $\text{d}\text{Z}\text{dt}$. The peaks in Z(t) lag those in A(t) by one second while A(t) lags $\text{d}\text{Z}\text{d}\text{t}$ by abou second. Furthermore, many of the pulsations in Z(t) show a similar time asymmetry to that commonly observed in c.n.a. pulsations, viz. a more rapid onset time than decay time.These results are taken as evidence that the Pi 1 micropulsations observed from the ground during the recovery phase of an auroral substorm are brought about by fluctuations in the ionospheric currents which give rise to the magnetic bay, these fluctuations being due to conductivity changes resulting from particle precipitation. The lag between A(t) and Z > (t) is attributed to the self-inductance of the electrojet.  相似文献   

Development of an auroral absorption substorm: Studies of substorm related absorption events in the afternoon-early evening sector     

A. Ranta  H. Ranta  T.J. Rosenberg  U. Wedeken  P. Stauning 《Planetary and Space Science》1983,31(12):1415-1434

We discuss the effects in ionospheric absorption of particle precipitation observed in the afternoon-early evening sector during substorms with onset in the midnight sector. All events considered here occurred during magnetically disturbed periods, K_p > 3. For many of the substorm events a smooth southward moving absorption bay is seen in the midnight and evening sectors about 1 h preceeding the onset. The magnetic pulsation activity is low during this preceding bay.

After substorm onset near magnetic midnight the precipitation region may expand with a sharp onset at the front towards the West in spatially confined regions at high and low L-values separately with about equal velocities. The observations are consistent with a model of westward expansion of the energetic electron precipitation in two regions, aligned parallel to the auroral oval, at high and low L-values of about L 6 and L 4.8.

The westward expanding absorption activity correlates well with local magnetic variations. In magnetic pulsations PiB events are seen at high latitudes simultaneously with the westward moving onsets while at low latitudes IPDP pulsations are observed during the active part of the absorption events. Later in the substorm event a slowly varying absorption event (SVA) is sometimes observed at the lower L-values, L 3–4.  相似文献   

Post-storm mid-latitude green aurora and electron precipitation     

J. Oksman  C.U. Wagner  K. Kaila  E.-A. Lauter 《Planetary and Space Science》1981,29(4):405-413

Unusual auroral emission at mid-latitudes, showing nearly exclusively the green oxygen line (557.7 nm) and occurring during the early part of the recovery phase after strong magnetic storms is described. The emission has a life-time of up to several hours, consists of cloud-like patches and appears quite isolated at medium latitudes with no simultaneous aurorae at higher latitudes. The name “post-storm mid-latitude green aurora” is proposed for this emission. For the event observed during the night of 29–30 August 1978, additional ionospheric measurements from heights below the mid-latitude aurora ($\text{?}{}_{\min }$, A3-LF data) are available from nearby observations. Our investigation shows that the emission was observed just at the beginning of a post-storm effect (PSE) in ionospheric absorption. The optical and absorption data have been used to extract information on precipitating high-energy electrons, assumed to be the cause of both the optical emisson and the excessive absorption. During the night in question precipitating electrons with fluxes above the quiet-time level and energies upto at least 200 keV were found in a region extended in latitude (2.7 < L < 3.3) and probably even more extended in longitude. Latitudinally narrow bands, elongated along shells of constant L, with extremely high fluxes of 10–20keV electrons (according to our estimates at least 5. 10⁷ el cm^?2s^?1) were embedded within this region.  相似文献   

The solar wind-magnetosphere energy coupling and magnetospheric disturbances     

S.-I. Akasofu 《Planetary and Space Science》1980,28(5):495-509

The recent finding of the solar wind-magnetosphere energy coupling function ε has advanced significantly our understanding of magnetospheric disturbances. It is shown that the magnetosphere-ionosphere coupling system responds somewhat differently to three different input energy flux levels of ε. As ε increases from < 10¹⁷ erg s^?1 to > 0¹⁹ erg s^?1, typical responses of the magnetosphere-ionosphere coupling system are:ε < 10¹⁷ erg s^?1: an enhancement of the S_q^p, etc,ε ≈ 10¹⁸ erg s^?1: substorm onset,10¹⁸ erg s^?1 < ε < 10¹⁹ erg s^?1f: a typical substorm,ε >10¹⁹ erg s^?1: an abnormal growth of the ring current belt, resulting in a magnetospheric storm.It is stressed that the magnetospheric substorm results as a direct response of the magnetosphere to a rise and fall of ε above ≈ 10¹⁸ erg s^?1, so that it is not caused by a sudden conversion of magnetic energy accumulated prior to substorm onset. The variety of the development of the main phase of geomagnetic storms is also primarily controlled by ε.  相似文献   

A simultaneous observation of large-scale periodic TIDs in both hemispheres following an onset of auroral disturbances     

《Planetary and Space Science》1987,35(6):785-791

A study has been undertaken on the position of the auroral sources of large-scale TIDs (LS TIDs) in both hemispheres. A selected case study, herewith presented, refers to an onset of an auroral substorm at the equatorward edges of the southern and northern auroral zones which preceded the occurrence of periodic variations in virtual height (h′F) of the F-region in the Southern and Northern Hemispheres. The variations in h′F had characteristics typical of large-scale TIDs propagating equatorwards with a velocity of about 800 m s⁻¹, and with a constant period of 135 min in both hemispheres. The horizontal wavefront of LS TIDs was observed in mid-latitudes to be in excess of 7000 km. The LS TIDs were found to be in phase at the stations which are equidistant from the auroral sources. From this it was concluded that the periodic LS TIDs were likely to produce a constructive interference effect at the points of their encounter near the equator.It was concluded that the sources of LS TIDs in both hemispheres were elongated along the L-shell with L-value between 4 and 5, and had a large longitudinal extent, exceeding 60°. The source locations were consistent with the positions of the belts of energetic particle precipitations as inferred from the standard riometer and magnetometer data. The large quasi-linear extent of the source is consistent with the wide horizontal wavefronts of LS TIDs as well as with a large distance of their propagation.  相似文献   

Temperature variation of the plasma sheet during substorms     

A.T.Y. Lui  C.-I. Meng  L.A. Frank  K.L. Ackerson  S.-I. Akasofu 《Planetary and Space Science》1981,29(8):837-842

The temperature and density of the plasma in the Earth's distant plasma sheet at the downstream distances of about 20–25 R_e are examined during a high geomagnetic disturbance period. It is shown that the plasma sheet cools when magnetospheric substorm expansion is indicated by the AE index. During cooling, the plasma sheet temperature, T, and the number density, N, are related by $\text{T ∝ N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ (adiabatic process) in some instances, while by T ∝ N^?1 (isobaric process) in other cases. The total plasma and magnetic pressure decreases when $\text{T ∝ N}{}^{\mathrm{<mtext>2</mtext><mtext>3</mtext>}}$ and increases when T ∝ N^?1. Observation also indicates that the dawn-dusk component of plasma flow is frequently large and comparable to the sunward-tailward flow component near the central plasma sheet during substorms.  相似文献   

Estimates of quasipolar absorption by methane in the atmosphere of Titan     

Kenneth Fox 《Icarus》1975,24(4):454-459

The basis for “quasipolar” absorption (QPA) by CH₄ is the existence of a small electric dipole moment in its ground state. The integrated intensity α_QPA at a temperature of 90K is calculated to be between 4.8 × 10^?5 and 1.9 × 10^?2 cm^?2 atm^?1. With an assumed mean pressure of 0.1 atm and a relative abundance of $\text{[}\text{CH}{}_4\text{]}\text{[}\text{H}{}_2\text{]}\text{= 1}$, it is estimated that the ratio of quasipolar to pressure-induced absorption (PIA) is 0.05 ? α_QPA/α_PIA ? 18 for the spectral range from 0 to 300 cm^?1. This result suggests that quasipolar absorption may contribute to a weak, CH₄-induced greenhouse in the atmosphere of Titan.  相似文献   

Average high latitude magnetic field: Variation with interplanetary sector and with season—I. Disturbed conditions     

R. Langel 《Planetary and Space Science》1973,21(5):839-855

High latitude magnetic field data from 16 northern observatories are averaged during periods of magnetic disturbance level Kp = 2^? to 3⁺. Within this disturbance level, variations between interplanetary magnetic field sector (toward and away from the Sun) and geomagnetic season (dipole latitude of the Sun: > 10° = summer, < ? 10° = winter) are delineated. Variations between seasons are: (1) The positive bay and polar cap disturbance is a maximum in summer and a minimum in winter for both sectors. (2) The negative bay disturbance is a maximum in summer and a minimum in winter when the interplanetary field is toward the Sun and vice versa during away sectors. Variations between sectors are: (1) During summer and equinox the negative bay disturbance is greater for toward sectors than for away sectors. The reverse occurs during winter. (2) The positive bay disturbance is greater during toward sectors than during away sectors for all seasons. (3) All diiferences in disturbance level are greater at sunlit local times than in darkness. (4) Angular differences in the direction of the horizontal disturbance of up to 75° occur between sectors in the polar cap and dayside during all seasons. (5) The polar cap-auroral belt boundary location is different for the two sectors. Compared to data from away sectors, this boundary for toward sectors is shifted northward near dawn (5–8^h) and southward between 10 and 22^h. (6) Accompanying this boundary difference there is a change in the direction of the vertical disturbance in the region between 9 and 14^h at geomagnetic latitudes 77–88°. ΔZ in this region is negative during away sectors and positive during toward sectors. Differences between sectors are attributed to changes in the ionospheric electric field configuration and in the distribution of magnetic field aligned currents.Features unrelated to sector or season also occur: (1) A significant Y component is present in both the positive and negative bays. (2) The vertical disturbance $\text{(¦ΔZ¦)}$ to the north of the auroral belt is much larger than that to the south. (3) Two distinct regions of maximum activity are present in the ΔZ accompanying the positive bay disturbance.  相似文献   

A synoptic investigation of particle precipitation dynamics for 60 substorms in IQSY (1964–1965) and IASY (1969)     

F.T. Berkey  V.M. Driatskiy  K. Henriksen  B. Hultqvist  D.H. Jelly  T.I. Shchuka  A. Theander  J. Ylindemi 《Planetary and Space Science》1974,22(2):255-307

Sixty auroral absorption substorms (30 in IQSY and 30 in IASY) have been analysed on the basis of riometer-recordings taken at some 40 stations distributed over auroral, subauroral and polar cap latitudes. Synoptic maps showing isoabsorption curves have been produced every 15 min (sometimes every 5 min) of the 60 substorms; 705 maps altogether.Some of the results of the analysis are as follows.Initiation of a substorm most frequently occurs near midnight but may occur anywhere between early evening and late morning. The time of onset becomes earlier and the latitude of onset moves equatorward as the level of magnetic activity increases.The longitude expansion velocities are contained in the range 0.7–7 km/sec except for a few extreme values which exceed 20 km/sec.The auroral absorption eastward expansion velocity is smaller than the corresponding velocity of the boundary of the region of activation of the visual aurora after break up by a factor $\text{14}\text{?12}$.The expansion velocity corresponds, in general, to drift velocities of electrons of energies in the range 50–300 keV but, for the extreme speeds, electron energies around 1 MeV are needed.Expansion of the absorption in the westward direction was seen in about half of the substorms studied. In about half of these, expansion along the auroral oval could be indentified, but in almost all of these cases some expansion in the auroral zone latitudes was also seen. In about an equal number of events, expansion was confined primarily to the auroral zone.The velocity of the westward expansion was about 1 km/sec along the auroral oval (i.e. approximately equal with the speed of the westward travelling surge) but about 2 km/sec along the auroral zone.The meridional expansion velocities found agree well with those measured for visual aurora (? 1 km/sec).The variability of the behaviour of different substorms is very large. To illuminate this the following may be mentioned, in addition to what has been stated above about the statistics.Although the absorption maximum practically always moves eastward from the initiation region, exceptions have been seen in which the maximum started moving west and in a later phase went eastward.Sometimes the absorption maximum stays in the injection area or very close to it, although in most cases it moves eastward into the dayside. In extreme eases it has been found to move more than 270° in the eastward direction.There are auroral absorption substorms in which injection seems to take place in more than one area simultaneously.The observations cannot all be understood in terms of gradient and curvature drift of electrons from a small area of injection only. A broad intrusion of hot plasma from the tail into the inner magnetosphere seems to be needed.No strong dependence of particle precipitation on the illumination of the upper ionosphere by sunlight was seen. The results do, therefore, not support the hypothesis of Brice and Lucas (1971) that cold plasma density increases, originating in the ionosphere, significantly increase the precipitation rate of energetic trapped particles.  相似文献   

The $\text{D}\text{H}$ ratio in the atmosphere of Uranus: Detection of the R₅(1) line of HD     

L. Trafton  D.A. Ramsay 《Icarus》1980,41(3):423-429

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.  相似文献   

Laboratory measurements of the microwave opacity and vapor pressure of sulfuric acid vapor under simulated conditions for the middle atmosphere of Venus     

Paul G. Steffes 《Icarus》1985,64(3):576-585

Microwave absorption observed in the 35- to 48-km-altitude region of the Venus atmosphere has been attributed to the presence of gaseous sulfuric acid (H₂SO₄) in that region. This has motivated the laboratory measurement of the microwave absorption at 13.4- and 3.6-cm wavelengths from gaseous H₂SO₄ in a CO₂ atmosphere under simulated conditions for that region. As part of the same experiments, upper limits on the saturation vapor pressure of gaseous H₂SO₄ have also been determined. The measurements for microwave absorption have been made in the 1- to 6-atm pressure range, with temperatures in the 500 to 575°K range. Using a theoretically derived temperature dependence, the best-fit expression for absorption from gaseous H₂SO₄ in a CO₂ atmosphere at the 13.4-cm wavelength is $\text{9.0 × 10}{}^9\text{q(P)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{T}{}^{\mathrm{?3}}\text{(}\text{dB km}{}^{\mathrm{?1}}\text{),}\text{where}\text{q}$ is the H₂SO₄ number mixing ratio, P is the pressure in atmospheres, and T is the temperature in degrees Kelvins. The best-fit expression for absorption at the 3.6-cm wavelength is 4.52 × 10¹⁰q(P)^0.85T^?3 (dB km^?1). The inferred H₂SO₄ vapor pressure above liquid H₂SO₄ corresponds to ln p = 8.84 ? 7220/t where p is the H₂SO₄ vapor pressure (in atm) and T is the temperature in degrees Kelvins. These results suggest that abundances of gaseous H₂SO₄ on the order of 15 to 30 ppm could account for the microwave absorption observed by radio occultation experiments at 13.3- and 3.6-cm wavelengths. They also suggest that such abundances would correspond to saturation vapor pressure existing at or above the 46- to 48-km range, which correlates with the observed cloud base. It is suggested that future measurements of absorption in the 1- to 3-cm wavelength range will provide additional tools for monitoring variations in H₂SO₄ abundance via radio occultation and radio astronomical observations.  相似文献   

Impact fragmentation experiments of basalts and pyrophyllites     

Yasuhiko Takagi  Hitoshi Mizutani  Shin-Ichi Kawakami 《Icarus》1984,59(3):462-477

Results of impact fragmentation experiments for basalts and pyrophyllites are reported. Aluminum cylindrical projectiles were impacted on cubic basalt and pyrophyllite targets at velocities of 70 to 990 m/sec. The targets and projectiles were 20 g to 3.3 kg and 2 to 20 g in weight respectively. Weights of the fragments produced by impacts were measured and the size distributions of fragments were examined. Data of the largest fragment mass (m_L) normalized to the original target mass (M_t), m_L/M_t, correlate better with the nondimensional impact stress, P_I, a new scaling parameter introduced by H. Mizutani, Y. Takagi, and S. Kawakami (1984, in preparation) than the conventional projectile's kinetic energy per unit target mass, E/M_t, used in the previous studies. All the m_L/M_t data for basalts obtained in the present study are summarized by m_L/M_t = 2.95 × 10^?2P_I^?1 where P_I = P₀L³/YR³, P₀ = peak shock pressure, L = projectile size, R = target size and Y = material strength of target. For aluminum targets, however, the m_L/M_t is 2.5 orders of magnitude larger than that for brittle targets at impacts with the same P_I. Size distributions of fragments expressed in a log N - log (m/M_t) diagram divided into three regimes bounded by two inflection points. In each regime the curve is expressed by $\text{N (>}\text{m}\text{M}{}_{\mathrm{t}}\text{) = A (}\text{m}\text{M}{}_{\mathrm{t}}\text{)}{}^{\mathrm{?a}}$. The slopes, a, of the log $\text{N -}\text{log}\text{(}\text{m}\text{M}{}_{\mathrm{t}}\text{)}$ curves in the regimes of a large and a medium size range are positively correlated with the nondimensional impact stress, P_I, and expressed as a = C₃ + a₃log P_I. The slopes, a, in the smallest size range are, on the other hand, nearly constant and have values of $\text{0.5}\text{to}\text{0.7 (}\text{1}\text{2}\text{?}\text{2}\text{3}\text{)}$. Present results indicate that the impact fragmentation is scaled well by the new scaling parameter, P_I, of Mizutani, Takagi, and Kawakami and that the present experimental data may shed new light on planetary impact processes.  相似文献   

Electric fields and potential patterns in the high-latitude ionosphere for different situations in interplanetary space     

Y.I. Feldstein  A.E. Levitin  D.S. Faermark  R.G. Afonina  B.A. Belov  V.Y. Gaidukov 《Planetary and Space Science》1984,32(7):907-923

The potential ? of the electric field at high latitudes has been obtained by solving numerically the second order differential equation in spherical coordinates: , where θ is colatitude, λ is longitude, σ^H and σ^P are the height-integrated Hall and Perdersen ionospheric conductivities, r = sinθ, and ψ is the current function. The boundary condition is ? = 0 on the geomagnetic parallel θ = 34°. Values of ψ are determined from geomagnetic field variations at the Earth's surface from geomagnetic field variations at the Earth's surface for various conditions in interplanetary space. σ^P and σ^H are taken to vary with season, local time, tilt of the geomagnetic dipole axis (UT), and intensity of corpuscular precipitation (the model proposed by Wallis and Budzinski, 1981). The model distributions of ?^M and E^M = -▽?^m so obtained are compared with observational results. The feasibility has been demonstrated of interpreting the statistical results and individual measurement data in terms of a unified dynamic model of ionospheric electric fields. The model makes allowance for the changes of electromagnetic “weather” in interplanetary space.  相似文献   

Conjugate effects in the generation of travelling ionospheric disturbances (TIDs) in the F-region     

L.A. Hajkowicz 《Planetary and Space Science》1983,31(12):1409-1413

A rapid onset of auroral absorptions was simultaneously recorded by a chain of standard riometers, situated in the northern and southern magneto-conjugate areas, during a period of pronounced substorm activity. The first absorption peak was followed by sequential disturbance patterns in the occurrence of the F-region parameters, virtual height (h′F) and spread - F, as deduced from the standard ionosonde data obtained over a wide range of latitudes in both hemispheres. The disturbances were consistent with the simultaneous occurrences of separate trains of large-scale ionospheric disturbances (TIDs), propagating equatorwards from the southern and northern auroral zones. It is suggested that TIDs were generated by an impulse-like increase in the conjugate particle precipitations, inferred from the riometer records. The precipitation pattern was limited to a high-latitude shell whose equatorwards edge was contained between L-values 5.0 and 5.3. The auroral sources of TIDs appeared to have large linear dimensions, extending at least 17 degrees in longitude.  相似文献   

The morphology of n and no in auroral substorms     

M.H. Rees  R.G. Roble 《Planetary and Space Science》1979,27(4):453-462

The effects of a typical auroral electron precipitation substorm sequence on odd nitrogen species in the thermosphere have been investigated. The analysis makes use of the time dependent model of the aurora developed by Roble and Rees (1977), which couples the thermal properties to the ionospheric chemistry and transport self-consistently and includes diffusive transport of NO, N(²D) and N(⁴S). A substantial increase in the E-region density of NO or of N(⁴S) is predicted, with the result depending on the production ratio of N(²D) to N(⁴S) in the aurorally dominant source mechanism, electron impact dissociation of N₂. A production ratio that favors N(²D) by a factor of one half or larger leads to enhancement of NO, while a ratio of $\text{1}\text{4}\text{N}\text{(}{}^2\text{D}\text{)+}\text{3}\text{4}\text{N}\text{(}{}^4\text{S}\text{)}$ results in a buildup of N(⁴S). The cyclical behaviour of the substorm, i.e. alternate intervals of electron precipitation and quiet periods, accentuates the scavenging effect of the initially dominant odd nitrogen species upon the less abundant one.  相似文献   

Damping of geomagnetic pulsations by the ionosphere     

R.S. Newton  D.J. Southwood  W.J. Hughes 《Planetary and Space Science》1978,26(3):201-209

A significant sink of geomagnetic pulsation energy is due to Joule dissipation in the ionosphere. To investigate this we have computed the damping experienced by standing Alfvén waves in a dipole magnetic field. Both the uncoupled poloidal and toroidal modes are considered with Joule dissipation being introduced through a boundary condition which relates the electric and magnetic field strengths at the ionosphere, viz: $\text{4πΣ}{}_{\mathrm{p}}\text{E}\text{c}\text{= b,}\text{where}\text{Σ}{}_{\mathrm{p}}$ is the height integrated Pederson conductivity. The damping rates are strongly dependent on the ionospheric conductivity and we find that typically the normalized damping rate, $\text{γ}\text{ω}\text{,}\text{is}\text{～0.1}$ for nightside values of conductivity and ～0.01 for the dayside. This would account for the observed scale of bandwidths in pulsation signals. Away from regions of extreme damping we find γ ∝ L^?1Σ_p^?1.  相似文献   

On the photodissociation of water vapour in the mesosphere     

Marcel Nicolet 《Planetary and Space Science》1984,32(7):871-880

The photodissociation of water vapour in the mesosphere depends on the absorption of solar radiation in the region (175–200 nm) of the O₂ Schumann-Runge band system and also at H-Lyman alpha. The photodissociation products are OH + H, OH + H, O + 2H and H₂ + O at Lyman alpha; the percentages for these four channels are 70, 8, 12 and 10%, respectively, but OH + H is the only channel between 175 and 200 nm. Such proportions lead to a production of H atoms corresponding to practically the total photodissociation of H₂O, while the production of H₂ molecules is only 10% of the H₂O photodissociation by Lyman alpha.The photodissociation frequency (s^?1) at Lyman alpha can be expressed by a simple formula where F_{10.7 cm} is the solar radioflux at 10.7 cm and N the total number of O₂ molecules (cm^?2), and when the following conventional value is accepted for the Lyman alpha solar irradiance at the top of the Earth's atmosphere ($\text{Δλ = 3.5}\text{A}\text{?}$) q_Lyα,∞ = 3 × 10¹¹ photons cm^?2 s^1?.The photodissociation frequency for the Schumann-Runge band region is also given for mesospheric conditions by a simple formula where J_SRB,∞(H₂O) = 1.2 × 10^?6 and 1.4 × 10^?6 s^?1 for quiet and active sun conditions, respectively.The precision of both formulae is good, with an uncertainty less than 10%, but their accuracy depends on the accuracy of observational and experimental parameters such as the absolute solar irradiances, the variable transmittance of O₂ and the H₂O effective absorption cross sections. The various uncertainties are discussed. As an example, the absolute values deduced from the above formulae could be decreased by about 25-20% if the possible minimum values of the solar irradiances were used.  相似文献   

On the origin and initial temperature of Jupiter and Saturn     

V.S. Safronov  E.L. Ruskol 《Icarus》1982,49(2):284-296

A two-stage growth of the giant planets, Jupiter and Saturn, is considered, which is different from the model of contraction of large gaseous protoplanets. In the first stage, within a time of ～3 × 10⁷ years in Jupiter's zone and ～2 × 10⁸ years in Saturn's zone, a nucleus forms from condensed (solid) material having the mass, ～10²⁸ g, necessary for the beginning of acceleration. The second stage may gravitating body, and a relatively slow accretion begins until the mass of the planet reaches ～10 m_⊕. Then a rapid accretion begins with the critical radius less than the radius of the Hill lobe, so that the classical formulae for the rate of accretion may be applied. At a mass m > m₁ ≈ 50 m_⊕ accretion proceeds slower than it would according to these formulae. When the planet sweeps out all the gas from its nearest zone of feeding (m = m₂ ≈ 130 m_⊕), the width of the exhausted zone being $\text{～}\text{built1}\text{3}$ of the whole zone of the planet) growth is provided the slow diffusion of gas from the rest of the zone (time scale increases to 10⁵?10⁶ years and more). The process is terminated by the dissipation of the remnants of gas. In Saturn's zone m₁ > m₂ ≈ 30 m_⊕. The initial mass of the gas in Jupiter's zone is estimated. Before the beginning of the rapid accretion about 90% of the gas should have been lost from the solar system, and in the planet's zone less than two Jupiter masses remain. The highest temperature of Jupiter's surface, ≈5000°K, is reached at the stage of rapid accretion, m < 100 m_⊕, when the luminosity of the planet reaches 3 × 10^?3 L_⊙. This favors an effective heating of the inner parts of the accretionary disk and the dissipation of gas from the disk. The accretion of Saturn produced a temperature rise up to 2000?2400° K (at m ≈ 20?25 m_⊕) and a luminosity up to 10^?4 L_⊙.  相似文献   

Magnetospheric chorus: Occurrence patterns and normalized frequency     

W.J. Burtis  R.A. Helliwell 《Planetary and Space Science》1976,24(11):1007-1024

New characteristics of VLF chorus in the outer magnetosphere are reported. The study is based on more than 400 hours of broadband (0.3–12.5 kHz) data collected by the Stanford University/Stanford Research Institute VLF experiment on OGO 3 during 1966–1967. Bandlimited emissions constitute the dominant form of whistler-mode radiation in the region $\text{4? L? 10}$. Magnetospheric chorus occurs mainly from 0300 to 1500 LT, at higher L at noon than at dawn, and moves to lower L during geomagnetic disturbance, in accord with ground observations of VLF chorus. Occurrence is moderate near the equator, lower near 15°, and maximum at high latitudes (far down the field lines). The centre frequency ? of the chorus band varies as L^?3> and at low latitudes is closely related to the electron gyrofrequency on the dipole field line through the satellite. Based on the measured local gyrofrequency $\text{?}{}_{\mathrm{H}}$, the normalized frequency distribution of chorus observed within 10° of the dipole equator shows two peaks, at $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.53}$ and $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.34}$. This bimodal distribution is a persistent statistical feature of near equatorial chorus, independent of L, LT and K_p. However there is considerable variability in individual events, with chorus often observed above, below, and between these statistical peaks; in particular, it is not unusual for single emissions to cross $\text{?}\text{?}{}_{\mathrm{H}}\text{= 0.50}$. When two bands are simultaneously present individual emission elements only rarely show one-to-one correlation between bands. For low K_p the median bandwidth of the upper band, gap and lower band are all ～16% of their centre frequencies, independent of L; for higher K_p the bandwidth of the lower band increases. Bandwidth also increases with latitude beyond ~10°. Starting frequencies of narrowband emissions range throughout the band. The majority of the emissions rise in frequency at a rate between 0.2 and 2.0 kHz/sec; this rate increases with K_p and decreases with L. Falling tones are rarely observed at dipole latitudes <2.5°. The observations are interpreted in terms of whistler-mode propagation theory and a gyroresonant feedback interaction model. An exact expression is derived for the critical frequency, $\text{?}\text{?}{}_{\mathrm{H}}\text{? 0.5}$, at which the curvature of the refractive index surface vanishes at zero wave normal angle. Near this frequency rays with initial wave normal angles between 0° and ?20° are focused along the initial field line for thousands of km, enhancing the phase-bunching of incoming gyroresonant electrons. The upper peak in the bimodal normalized frequency distribution is attributed to this enhancement near the critical frequency, at latitudes of ~5°. Slightly below the critical frequency interference between modes with different ray velocities may contribute to the dip in the bimodal distribution. The lower peak may reflect a corresponding peak in the resonant electron distribution, or guiding in field-aligned density irregularities. The observations are consistent with gyroresonant generation of emissions near the equator, followed by spreading of the radiation over a range of L shells farther down the field lines.  相似文献   

Cosmic ray ionization of the Jovian atmosphere     

Louis A. Capone  John Dubach  Robert C. Whitten  Sheo S. Prasad 《Icarus》1979,39(3):433-449

An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic ray-induced cascade may be especially importannt in ionizing the atmosphere at levels where the total number density exceeds 10¹⁹ cm^?3 (well below the ionospheric layers produced by solar euv). A model containing both positive and negative ion reactions has been employed to compute equilibrium electron and ion number densities. Peak electron number densities on the order of 10³ cm^?3 may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH₄⁺ and C_nH_m⁺ cluster ions, with n ? 2; it is suggested that the absorption of galactic cosmic ray energy at such relatively high pressures in the Jovian atmosphere $\text{(M ? 10}{}^{18}\text{to}\text{10}{}^{20}\text{cm}{}^{\mathrm{?3}}\text{)}$ and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.  相似文献