Some aspects of mid-latitude spread-Es, and its relationship with spread-F

After discussing some examples of mid-latitude spread-E_s this paper presents distributions showing the diurnal, annual and sunspot-cycle variations of this phenomenon. The variations are very similar to those found for mid-latitude spread-F. Also, a superposed-epoch analysis involving an investigation of spread-F occurrence relative to controls consisting of nights of high spread-E_s occurrence showed a relationship of high significance. A similar analysis using spread-F occurrence relative to daytime spread-E_s controls also suggested a relationship between these parameters. The results presented in this paper together with results from previous work suggest strongly that the two phenomena (spread-E_s and spread-F) are produced by the same or similar disturbances. Also it seems likely that the disturbances responsible for spread-F during night hours are also present during daylight hours.     

Disappearence of equatorial Es, associated with magnetic field depressions

The phenomenon of the sudden disappearance of equatorial sporadic E at two stations, namely, Trivandrum and Kodaikanal is studied. It is established that whenever there is a sudden disappearance of E_s, there is a depression in the horizontal magnetic field (H) range. Electron velocities during the presence and absence of sporadic E have been estimated. These results show that the irregularities responsible for sporadic E are present even when the electron velocities are less than the ion thermal velocity.     

Is Te equal to Tnm at the heights of 100 to 120 km?

Low and mid-latitude lower E-region electron temperature profiles which were obtained by means of an insitu probe were collected. Profiles which are discussed here cover the heights of 90–120 km and measurement reliability at these heights is discussed mainly in terms of electrode contamination and aerodynamical heating.Although measurement errors might exist in some of the electron temperature profiles, it is conclusively described that daytime electron temperature is very often much higher than the possible neutral temperature and T_e ≈ T_n is rarely seen.     

A dynamical effect in the ionospheric f1 layer

Incoherent scatter observations of the ionospheric F₁ layer above Saint-Santin (44.6°N) are analyzed after correction of a systematic error at 165 and 180 km altitude. The daytime valley observed around 200 km during summer for low solar activity conditions is explained in terms of a downward ionization drift which reaches ?30 m s^?1 around 180 km. Experimental determinations of the ion drift confirm the theoretical characteristics required for the summer daytime valley as well as for the winter behaviour without a valley. The computations require an effective dissociative recombination rate of $\text{2.3 × 10}{}^{\mathrm{?7}}\text{(}\text{300/}\text{T}{}_{\mathrm{e}}\text{)}{}^{0.7}\text{(}\text{cm}{}^3\text{s}{}^{\mathrm{?1}}\text{)}$ and ionizing fluxes compatible with solar activity conditions at the time when the valley is observed.     

On determining magnetohydrodynamic shock parameters θBn and MA

In a collisionless plasma, the magnetohydrodynamic shock structure, the associated waves and turbulence depend strongly on the shock parameters θ_Bn and M_A, where θ_Bn is the angle between the upstream magnetic field and the shock normal and M_A is the upstream Alfvén Mach-number. A method is given to determine θ_Bn and M_A and their estimated errors for all types of shocks without knowing the shock normals. The only measured quantities needed to determine θ_Bn and M_A are the plasma density and magnetic field on both sides of the shock. The estimated error of θ_Bn using our method can be obtained in a straightforward manner and is more reliable than that based on the calculated shock normal and the upstream magnetic field. Its simplicity and ability to handle parallel shocks as well as perpendicular and oblique shocks are illustrated by examples. This method should be useful for characterizing the types of shocks from analyzing the copious amount of data on magnetohydrodynamic (MHD) shocks found in space.     

Neutron and electromagnetic emissions during the 1990 May 24 solar flare

In this paper, we are primarily concerned with the solar neutron emission during the 1990 May 24 flare, utilizing the counting rate of the Climax neutron monitor and the time profiles of hard X-rays and γ-rays obtained with the GRANAT satellite (Pelaezet al., 1992; Talonet al., 1993; Terekhovet al., 1993). We compare the derived neutron injection function with macroscopic parameters of the flare region as obtained from theHα and microwave observations made at the Big Bear Solar Observatory and the Owens Valley Radio Observatory, respectively. Our results are summarized as follows: (1) to explain the neutron monitor counting rate and 57.5–110 MeV and 2.2 MeV γ-ray time profiles, we consider a two-component neutron injection function,Q(E, t), with the form $$Q(E,t) = N_f {\text{ exp[}} - E/E_f - t/T_f ] + N_s {\text{ exp[}} - E/E_s - t/T_s ],$$ whereN _f(s),E _f(s), andT _f(s) denote number, energy, and decay time of the fast (slow) injection component, respectively. By comparing the calculated neutron counting rate with the observations from the Climax neutron monitor we derive the best-fit parameters asT _f ≈ 20 s,E _f ≈ 310 MeV,T _s ≈ 260 s,E _s ≈ 80 MeV, andN _f (E > 100 MeV)/N _s (E > 100 MeV) ≈ 0.2. (2) From the Hα observations, we find a relatively small loop of length ≈ 2 × 10⁴ km, which may be regarded as the source for the fast-decaying component of γ-rays (57.5–110 MeV) and for the fast component of neutron emission. From microwave visibility and the microwave total power spectrum we postulate the presence of a rather big loop (≈ 2 × 10⁵ km), which we regard as being responsible for the slow-decaying component of the high-energy emission. We show how the neutron and γ-ray emission data can be explained in terms of the macroscopic parameters derived from the Hα and microwave observations. (3) The Hα observations also reveal the presence of a fast mode MHD shock (the Moreton wave) which precedes the microwave peak by 20–30 s and the peak of γ-ray intensity by 40–50 s. From this relative timing and the single-pulsed time profiles of both radiations, we can attribute the whole event as due to a prompt acceleration of both electrons and protons by the shock and subsequent deceleration of the trapped particles while they propagate inside the magnetic loops.     

The semiannual variation in the magnetic activity indices Aa and Ap

The technique of Complex Demodulation is used to examine the long-term modulation of the semiannual variation in planetary magnetic activity as characterised by the A_a index for 1868–1980 and the A_p index for 1932–1980. From the phase results, strong support is found for an “equinoctial” mechanism for the semiannual variation. The amplitude shows a quasi 11 -year modulation for most of the period of analysis and a pronounced increase over the years 1938–1966 approximately. Comparison of the long-term modulation of the semiannual variation in activity, with that of the occurrence of stormy days suggests that the semiannual modulation is energy dependent, being more effective with increasing energy.     

Formation of blanketing sporadic E-layers at the magnetic equator due to horizontal wind shears

A careful survey of quarter-hourly ionograms for the year 1969 has shown that blanketing layer type ionization irregularities occur on many occasions in the E-region of the ionosphere over Trivandrum (dip ～ 0.6°S). It is shown that horizontal shears of horizontal neutral winds are the most likely sources of such layer type irregularities at the magnetic equator. The horizontal wind shears of required magnitude are shown to be provided by internal gravity waves of short period. The rarity of E_s-layer occurrence is attributed to the stringent requirements on the amplitude and wave vector orientation of the relevant gravity waves generating the E_s-layers.     

Thinning of the near-earth (10∼15 RE) plasma sheet preceding the substorm expansion phase

The timing of the plasma-sheet thinning relative to the onset of the expansion phase of substorms is examined by the analysis of the OGO 5 electron (79 ± 23 keV) and proton (100～150 keV) data with the aid of simultaneous magnetic field observations. It is found that the timing of the thinning is significantly dependent on the distance. At $\text{x}{}^2\text{+ y}{}^2\text{? 15 R}{}_{\mathrm{E}}$ the thinning often starts before the onset, while at $\text{x}{}^2\text{+ y}{}^2\text{? 15 R}{}_{\mathrm{E}}$ it tends to occur after the onset, where x and y refer to solar magnetospheric coordinates. The thinning that precedes the expansion-phase onset has been found to reduce the thickness to ～1 R_E, and further thinning may occur in a spatially limited region. Hence it is conceivable that the formation of the neutral line characterizing the substorm expansion phase is the consequence of the thinning of the plasma sheet in the near-Earth region.     

Es-q layer at huancayo during the March 1970 geomagnetic storm

The paper describes a comparison of vertical electron drift in the F-region (V_z) measured by VHP incoherent scatter radar at Jicamarca with the corresponding variations of geomagnetic horizontal field (H) and the maximum frequency reflected from The E_s layer (E_s) at Huancayo during the geomagnetic storm period 7–9 March, 1970. The V_z is generally upward during the daytime at the equator, but during 7–9, March, 1970, V_z was negative for brief periods associated with negative bays in H. These periods of abnormally low or of downward V_z correspond closely with the period of complete disappearance of the q type of E_s layer. The magnetic bays associated with the intensification of ring current do not affect the equatorial E_s- q and it is only the negative bays in H at the equator due to the ionospheric current flowing westward, that cause sudden disappearance of E_s? q. It is suggested that the q type of E_s is due to cross-field instability created in the electrojet region due to interaction of northward magnetic field and vertical upward Hall polarization electric field when the plasma density gradient is upward. The sudden disappearances of E_s? q are due to the reversal of the horizontal electric field in the equatorial ionosphere and thereby due to the reversal of the equatorial electrojet currents. These reversals of electric field may be due to the imposition on the normal S_q field of another westward electric field.     

Does IMF By induce the cusp field-aligned currents?

A well established correlation exists between the IMF B_y and the cusp field-aligned and horizontal currents (Wilhjelm et al., 1978). The northern and southern cusp currents may be parts of one large scale current system (D'Angelo, 1980) flowing mainly at the magnetopause and driven by the z-component of the solar wind electric field. Primdahl and Spangslev (1981) suggested that the large scale current system seems to shield out the IMF B_y from the interior of the magnetosphere. This paper proposes that the currents are induced by the change of sign of B_y at the IMF sector boundary crossings, and argues that the time constant for decay of the currents may well be one week or larger. The percentage errors in inferring the IMF sector polarity from the Godhavn H magnetogram increases with increasing time since the last sector boundary crossing. This is in accordance with a steady decay of the induced currents. Finally experimental tests are proposed to demonstrate the feasability of and possibly distinguish between the mechanisms.     

Liquid water on Mars: An energy balance climate model for CO2/H2O atmospheres

Geologic evidence of the prior existence of liquid water on Mars suggests surface temperatures T_s were once considerably warmer than at present; and that such a condition may have arisen from a larger atmospheric greenhouse. Here we develop a simple climate model for a CO₂/H₂O Mars atmosphere including water vapor-longwave opacity feedback in the atmosphere and temperature-albedo feedback at surface icecaps, under the assumption that once the Martian surface pressure was p_s ≥ 1 atm CO₂. Longwave flux to space is computed as a function of T_s and p_s using band-absorption models for the effect of the 15-μm fundamental, and the 10- and 15-μm hot bands, of the CO₂ molecule; as well as the pure rotation bands and e continuum of H₂O. The derived global radiative balance predicts a global mean surface temperature of 283°K at 1 atm CO₂. When the emission model is coupled to a latitudinally resolved energy balance climate model, including the effect of poleward heat transfer by atmospheric baroclinic eddies, the solutions vary, depending on p_s. We considered two cases: (1) the present Mars (p_s ? 0.007 atm) with pressure-buffering by solid CO₂ icecaps, and limited poleward heat flux by the atmosphere; and (2) a hypothetical “hot Mars” (p_s ? 1.0 atm), whose much higher CO₂ amount augmented by H₂O evaporative feedback yields a theoretical T_s distribution with latitude admitting liquid water over 95% of the surface, water icecaps at the poles, and a diminished equator-to-pole temperature gradient relative to the present.     

Observed characteristics of polar cleft Hα and OI emissions

Observations at Godhavn, Greenland show that the intersection of the polar cleft with the ionosphere can be recognized by simultaneous occurrence of hydrogen emissions (H_α, H_β>) and enhanced OI 6300 Å emission. The H_α-line reveals a characteristic narrow and symmetric Doppler profile which is interpreted as indicating that the solar wind protons retain their typical flux and energy spectrum all the way down to the ionosphere. The cleft intersection seems to cover the sector 04:00–22:00 geomagnetic time.     

Ground-based observations of O2 (b1Σ+g−X3Σ−g) atmospheric bands in high latitude auroras

Analysis of observed spectrograms is based on comparison with synthetic spectra. The O₂(b¹Σ⁺_g?X³Σ^?_g Atm. (1,1) band in high latitude auroras observed from the ground is found to be the strongest in the Δv = 0 sequence. It is enhanced with altitude relative to the N₂ 1P(2, 0)and N⁺₂ M(2,0) bands, but the O₂ Atm. (2, 2) band has an unexpected low intensity. The range of rotational temperatures of the O₂ Atm. bands varies from approx. 200 to above 500 K which indicates that the altitude of the centroid of the emission region varies from about 100 km to the F-region. The highest temperature is found in the midday aurora associated with the magnetospheric cusp. Conspicuous relative variations between the intensities of N₂ and O₂ spectra are documented, but a satisfactory explanation of the variety is not given. Deviations of the observed O₂ Atm. band intensities from the vibrational intensity distribution predicted by Franck-Condor factors indicate that the excitation of the O₂ Atm. bands in aurora is not mainly due to particle impact on O₂, and the contribution due to energy transfer from hot O(¹D) atoms has to be found in future research.     

Terrestrial low-frequency bursts: Escape paths of radio waves through the bow shock

From the analysis of 119 low-frequency (LF) burst spectra observed onboard the Wind spacecraft, we propose an interpretation of the frequency-time characteristics including the low frequency cutoff of the LF burst spectra, and we use these characteristics to sound the bow shock structure at large tailward distances from Earth. When observed from within the solar wind, LF bursts appear to be made of two spectral components. The high frequency one is bursty and observed above twice the solar wind plasma frequency f_psw. The low frequency one is diffuse (ITKR) and its spectrum extends from about 2f_psw to a cutoff frequency f_c not much higher than f_psw; its onset time δt(f) increases as the frequency f decreases. For each of the 119 events observed from near the Lagrange point L1, the solar wind density variations were measured and the variations of the density jump across the shock calculated from plasma data all along a shock model over more than 2000R_E. But, except for a few events, neither the solar wind overdensities nor the shock density barrier can prevent waves with frequencies below f_c from reaching the spacecraft. Scattering on plasma density inhomogeneities was then introduced to account for the propagation of the LF burst waves in the magnetosheath, from near Earth to their escape point through the bow shock at a frequency-dependent distance |X_esc(f)| (GSE), and then in the solar wind to the spacecraft. In such media, at frequencies between 2f_psw and f_psw, the bulk speed of the scattered waves decreases rapidly as f decreases, and this accounts for the observed variations of the onset time δt(f). Angular scattering can also account for the observed cutoff at f_c if the distance |X_esc(f)| increases exponentially when f/f_psw decreases. As the shock model we used meets that requirement, we consider that this model is valid, which implies that the bow shock still exists beyond 1000R_E from the Earth. The observed decrease of the average spectral intensity of the LF burst between about 1.5f_psw and 2f_psw can also be explained by the scattering in the solar wind if we take into account the angular distribution of the rays when they leave the bow shock.     

Low latitude E-region irregularities studied using Gadanki radar,ionosonde and in situ measured electron density

In this paper, we attempt to identify the driving forces responsible for the generation of low-latitude E-region field-aligned irregularities (FAIs). It is evident that the low-latitude E-region FAIs occur both during the day and night with preferential occurrence being most during local sunrise period. Simultaneous measurements are made with Gadanki radar and nearby located Ionosonde for understanding the low-latitude Es–FAIs relationship. The observations suggest that the occurrence and SNR of FAIs have a close relationship with f _t E _s −−f _b E _s . Finally, using the past electron density profiles and reasonable values of electric field, we have shown that it is generally difficult with the gradient drift instability to explain low-latitude E-region FAIs when electric field alone is considered as driving agency. We hypothesize that neutral winds play important role for the generation of irregularities at low latitudes outside the electrojet belt either by forming sharp Es layers or by enhancing the differential drift of electrons and ions or by both.     

Improved accuracy in in-situ probe measurements of ionospheric ne and Te, using techniques requiring only low bandwidth telemetry channels

This paper presents the results of a recent rocket firing through a quiet, mid-day E-region in which measurements of ionospheric electron densities and electron temperatures were made using improved diagnostic techniques. Excellent agreement was found to exist between the in-situ measurements of electron density and those deduced from ionograms obtained during the flight using ground based equipment. Measurements of the contact potential difference existing between the two graphite coated grids forming the electron temperature probe demonstrated that serious errors can be introduced into the electron temperature measurements if not taken into account and showed further that appreciable changes in the contact potential difference can occur during a short flight. The results of the flight indicate that the modifications made to both experiments represent significant improvements and demonstrate that the data outputs of each experiment are in a convenient form to be electronically stored, read at a subsequent time compatible with the telemetry sampling and telemetred to ground using only a small number of low bandwidth channels.     

A possible current system associated with the Sqp variation

It is suggested that the quiet day daily magnetic variation in the polar cap region, S_q^p, results partly from the short-circuit effect of the magnetotail current by the polar ionosphere. This implies that there is an inward field-aligned current from the dawnside magnetopause to the forenoon sector of the auroral oval (positively charged) and an outward field-aligned current to the duskside magnetopause from the afternoon sector of the oval (negatively charged), together with the ionospheric (Pedersen and Hall) currents. The distribution of the magnetic field vectors of both combined current systems agrees with the observed S_q^pvector distribution. The space charges provide an electric field distribution which is similar to that which has been observed by polar orbiting satellites.     

On the MOND external field effect in the solar system

In the framework of the MOdified Newtonian Dynamics (MOND), the internal dynamics of a gravitating system s embedded in a larger one S is affected by the external background field E of S even if it is constant and uniform, thus implying a violation of the Strong Equivalence Principle: it is the so-called External Field Effect (EFE). In the case of the solar system, E would be A _cen≈10^?10 m?s^?2 because of its motion through the Milky Way: it is orders of magnitude smaller than the main Newtonian monopole terms for the planets. We address here the following questions in a purely phenomenological manner: are the Sun’s planets affected by an EFE as large as 10^?10 m?s^?2? Can it be assumed that its effect is negligible for them because of its relatively small size? Does E induce vanishing net orbital effects because of its constancy over typical solar system’s planetary orbital periods? It turns out that a constant and uniform acceleration, treated perturbatively, does induce non-vanishing long-period orbital effects on the longitude of the pericenter ? of a test particle. In the case of the inner planets of the solar system and with E≈10^?10 m?s^?2, they are 4–6 orders of magnitude larger than the present-day upper bounds on the non-standard perihelion precessions \(\Delta\dot{\varpi}\) recently obtained with by E.V. Pitjeva with the EPM ephemerides in the Solar System Barycentric frame. The upper limits on the components of E are E _x ≤1×10^?15 m?s^?2, E _y ≤2×10^?16 m?s^?2, E _z ≤3×10^?14 m?s^?2. This result is in agreement with the violation of the Strong Equivalence Principle by MOND. Our analysis also holds for any other exotic modification of the current laws of gravity yielding a constant and uniform extra-acceleration. If and when other corrections \(\Delta\dot{\varpi}\) to the usual perihelion precessions will be independently estimated with different ephemerides it will be possible to repeat such a test.     

Pilgrim dark energy in f(T,T G ) cosmology

We work on the reconstruction scenario of pilgrim dark energy (PDE) in f(T,T _G ). In PDE model it is assumed that a repulsive force that is accelerating the Universe is phantom type with (w _DE f(T,T _G ) models and correspondingly evaluate equation of state parameter for various choices of scale factor. Also, we assume polynomial form of f(T,T _G ) in terms of cosmic time and reconstruct H and w _DE in this manner. Through discussion, it is concluded that PDE shows aggressive phantom-like behavior for s=?2 in f(T,T _G ) gravity.