Recent results on the Venus atmosphere from pioneer Venus radio occultations

Radio occultation measurements of the temperature structure of the Venus atmosphere have been obtained during seven occultation “seasons” extending from December 1978 to December 1983. Approximately 123 vertical profiles of temperature from about 40 km to about 85 km altitudes have been derived. Since these measurements cover latitudes from both poles to the equator, they have shown the latitudinal dependence of thermal structure. There is a smooth transition from the troposphere to the mesosphere at latitudes below about 45°, with the tropopause at about 56 km. The troposphere then rises to about 62 km in the “collar cloud” region between about 60° and 80° latitude, where a strong temperature inversion (up to 30 K) is present. In the polar areas, 80°–90°, the mesosphere becomes isothermal and there is no inversion. This latitudinal behavior is related to the persistent circulation pattern, in which a predominantly zonal retrograde motion at latitudes below 45° gradually changes to a circumpolar vortex at the “collar cloud” latitudes. Indeed, the radio occultation data have been used in a cyclostrophic balance model to derive zonal winds in the Venus atmosphere, which showed a mid-latitude (50°–55°) jet with a speed of about 120–140 ms^?1 at about 70 km altitude /1,2/. The observations obtained in 1983 and 1984 have shown that above the tropopause there is considerable temporal variability in the detailed thermal structure, suggesting that the persistent circulation pattern is subject to weather-like variability.     

Magnetic cloud and magnetosphere — Ionosphere response to the 6 November 1997 CME

In the present work we analyse the magnetic cloud (MC) at 1 AU on 9 November 1997. The appearance of a hotter and dense part (dense filament), with radial extent 10⁶ km, immediately behind the frontal part of the MC, is a distinctive feature of the event. The INTERBALL - Aurora] Probe had a chance to observe field-aligned currents in the mid - altitude magnetosphere during the substorm expansion phase intensification related to the dense filament. We emphasise the appearance of unusual “N”- shape magnetic structure, duration 3 min, amplitude 50 nT between field-aligned current region 1 and the magnetosphere lobe in the late evening hours. To explain some of the MC features we refer to a model scenario of the 6 November 1997 coronal mass ejection.     

Orbital barium CRRES injection — Effective source of ionospheric wavelike disturbances

Spectral analysis of artificial wavelike disturbances (WD) in ionospheric parameters is presented. The sources of WD are barium clouds injections in CRRES perigee experiments. Plasma concentration pulsations are found in the ionospheric F2 layer maximum over Havana (Cuba) at distances 1500–2500 km from the barium injection. It was found that for the spectral component with 10 min period, the delay (relative to injection moment) corresponded to WD propagation velocity in 323–390 m/s band and depended on the specific injection conditions. It was shown that in every experiment the WD effective propagation velocity in the terminator region correlated with the sunlit part of the trajectory from the injection point to Havana. When comparing this WD type with WD's of other origins (from earthquakes, high-altitude explosions and solar terminator), it was shown that purposeful injection in the ionosphere of even a small barium quantity with orbital velocity in terminator region might be the effective means for generation or amplification of natural WD.     

Remote monitoring of aerosols from space

Using the four-channel teleradiometer “Micron” aboard the Orbital Stations “Salyut-4” and “Salyut-6” the brightness profiles were determined in the near-infrared spectral region up to the height of 60 km (in case of noctilucent clouds up to 80–85 km). Proceeding from the data above we obtained information on the global and vertical distributions of atmospheric aerosol, water vapour concentration and the optical properties of the noctilucent clouds.     

Large scientific releases

Mass-injection experiments in space plasmas have been conducted for the last twenty years. These injections trace or stain chemical or physical processes, facilitating diagnosis of the natural state of the space plasma; artificially perturb the space plasma away from equilibrium, isolating and controlling selected parameters; simulate natural or artificial states of space plasmas; and utilize the advantages of space as a laboratory to study fundamental plasma physics.We use the Lagopedo ionospheric-depletion experiments to illustrate the special operational aspects of active experiments, including weather, logistics, communications, and real-time diagnostics. The various objectives and techniques of mass-injection experiments are described by example. The CAMEO experiment, a thermite barium release from a satellite over the nightside polar cap, is an excellent example of the use of barium injections to trace upward ion acceleration. The Periquito Dos experiment provided a “snapshot” view of convection electric fields in the dayside polar cusp region. Project Waterhole, an artificial depletion of the topside auroral ionosphere, attempted to modify the equilibrium character of the field-aligned currents and apparently shut off the aurora in a small space-time volume. The Trigger experiment is another example of an active perturbation experiment, wherein the auroral ionospheric transverse conductivities were modified via a cesium injection. The Buaro experiment, a shaped-charged barium injection perpendicular to the local geomagnetic field, resulted in an ion-beam/background-plasma system being displaced from equilibrium, permitting diagnostics of collisionless coupling of the ion beam to the background plasma.     

Measurements of the artificially stimulated precipitation of electrons from the inner radiation belt in the experiment “SPOLOKH-2”

Evidence for an enhancement of the electron flux associated with a barium chaped charge release from “SPOLOKH-2” rocket payload, launched from Volgograd (L = 2.2) on June 29, 1978, will be presented. There is also evidence for a periodic train of particle bursts occurring with about 11 second period during more than 100 seconds after the release. The observed phenomena is interpreted as a “trigger-effect”.     

电子环束流对航天器表面电位和等离子体鞘层的影响

采用二维三分量静电粒子模拟程序研究了电子环束流对低轨道磁化等离子体中运行的航天器表面电位和等离子体鞘层结构的影响.当有电子束流平行磁场入射时,航天器表面所带负电位的绝对值将增大.电子束流的速度和密度的增加将使航天器表面负电位绝对值增加很快.与此同时等离子体鞘层的尺度也将增大,形状将由向尾部延伸的“泪滴”状变成向两侧展开的“机翼”状.当电子环束流以相对于磁场成一定角度斜入射时,由于磁场的约束作用,航天器表面负电位的绝对值将随入射角增大而减小.      

Solar flare proton release from coronal magnetic traps and strong Alfvén turbulence in the corona

Drift instabilities arising when accelerated protons are trapped by coronal magnetic fields of active regions are investigated theoretically. If β, the ratio of total (plasma + energetic particles) pressure and magnetic field pressure is larger than some value, $\text{β?0.1}\text{to}\text{0.3}$, the magnetic trap is destructed and protons are released into interplanetary space. If $\text{β < β}{}^1$, the trapped protons excite gradient instability due to magnetic drift resonance. This “universal” instability results in rapid development of strong Alfvén wave turbulence with small wavelengths transverse to the magnetic field. Particle diffusion due to the waves has a rather complicated character and appears to be weak as compared to quasilinear diffusion. The role of Alfvén waves may consist in additional heating of the corona in the regions of closed magnetic field lines.     

Mass motions in a quiescent filament

The “disparition brusque” (DB) of a filament (N20, E35) has been observed above an active region with the Multichannel Subtractive Double Pass (MSDP) spectrograph operating on the Meudon Solar Tower, from 10h45 UT to 13h30 UT on June 22, 1981.Velocity fields and intensity fluctuations are measured in the Hα line. The DB doesn't take place simultaneously in all parts of the filament : thin threads (thickness <3 arc seconds) with upward radial velocities reaching about 50 km/s are successively observed inside the prominence from S to N regions. These motions correspond likely to the rise of material along magnetic loops closely related to the prominence structure. The dynamics inside such a magnetic loop is investigated : a high speed flow (supersonic, likely superalfvénic) strongly accelerated is evidenced and a deformation of the flux tube, probably due to the centrifugal forces exerted by the flow on the magnetic lines, is suggested.These results are compared with some theoretical works on dynamics inside magnetic loops, especially to siphon flow models. However, as in the case of the prominence support problem, better theoretical models are still needed.     

Temporal evolution analysis of storm-enhanced density during an intense magnetic storm on March 2015

An intense Storm Enhancement Density (SED) event with the magnetic storm occurred on 17–24 March 2015 has been investigated. The morphological character of the SED during different phase of the magnetic storm is examined and compared with the non-storm time. Three intensity indexes, i.e., “general” SED index, “heavy” SED index and “severe” SED index, are defined to represent the intensity of SED respectively represented by the numbers of the ionospheric total electron content (TEC) grids with TEC > 60 TECu, TEC > 80 TECu and TEC > 100 TECu. The temporal evolution of the SED intensity indexes during a time span covering the non-storm time and the magnetic storm time have also been investigated. The SED exhibits a shape with two parallel slender troughs in the middle and low latitudes during the non-storm time and then gradually develops into an ellipse structure as the development of magnetic storm. The intensity of SED and the fluctuation of the TEC evolution are generally corresponding to the fluctuation of Dst index. The analyzing results enrich our understanding of the temporal and spatial evolution of the ionospheric SED.     

Infrared spectrometry of Venus from “Venera-15” and “Venera-16”

Fourier spectrometers for the investigation of infrared spectra of Venus were installed on the recent Soviet orbiters “Venera-15” and “Venera-16”. Many spectra with reliable absolute calibration were obtained in the 280–1500 cm^?1 region with a spectral resolution of 5 cm^?1 (ground based processing) and about 7 cm^?1 (preoprocessed on board) and a spatial resolution of about 100 km at the Venusian cloud top level. Bands of CO₂, H₂O, H₂SO₄ and SO₂ are identified. The 15 μm-CO₂- fundamental band was used for retrieval of altitude dependent temperature profiles. There are significant differences in the cloud structure above 60 km for distinct regions of Venus, demonstrated by differences in the spectra.     

The collective gyration of a heavy ion cloud in a magnetized plasma

In both the ionospheric barium injection experiments CRIT I and CRIT II, a long-duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomenon which was proposed for the CRIT 1 experiment is here compared to the results from CRIT II which made a much more complete set of measurements. The model follows the motion of a low-β ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v_i but slightly tilted towards the self-polarization direction E_P = −v_ixB. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic-field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents give a perturbation of the magnetic field related to the electric field perturbation by ΔE/ΔB ≈ V_a. The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT II. The possibility to extend the model to the active region, where the ions are produced in this type of self-ionizing injection experiments, is discussed.     

Experiments with injection of powerful plasma jet into the ionosphere

This paper describes two rocket experiments “Aelita” with high power lithium plasma injection. The results of onboard magnetometer, massspectrometer, photometer, plasma, corpuscular and ground radar measurements are given. Dynamics and structure of plasma formation are discussed.     

Tropical storm structure revealed by stereoscopic photographs from Skylab

A stereo pair of photographs taken by Skylab astronauts over Hurricane Ellen, September 19, 1973, resulted in the first stereo analysis over tropical storms. This pair is also the first evidence to indicate the existence of “supercell” convection in developing tropical storms. The photos are analyzed to determine the cloud top structure of the intense convection occurring in one quadrant of the storm. This type of supercell convection in tropical storms has recently been correlated with subsequent rapid deepening. The stereo analysis revealed that a circular cloud feature over the storm center was a dome which protruded 3–4 km above the undisturbed cirrus clouds. The center of the dome was capped by smaller scale convective turrets which protruded another 1–2 km above the dome. The existence of shear induced waves in the cloud tops is shown with wave amplitude ranging from 150–300 m and wave lengths ranging from 2–4 km. The existence of gravity waves at the cloud tops is also shown with wave amplitudes of 500–600 m and wavelengths of 10–12 km.     

The observation of the galactic anticenter region by the balloon borne gamma-ray telescope Natalya-I

This paper presents the results of measurements of gamma radiation with energies above 5 MeV, from the galactic anticenter region. The balloon-borne gamma ray telescope “Natalya-I”, was launched on 6 November, 1980 from the Tata Institute of Fundamental Research's Balloon Facility (Hyderabad, India) and reached ceiling altitude of 35 km. The results on the accelerator calibration of the telescope, using a “tagged” gamma ray beam are also presented.     

Energetic positive ions in the cometary “foreshock” region

Ions produced by ionization of the cometary neutrals interact with the solar wind protons to produce large amplitude oscillations of the ambient magnetic field. Such oscillations are convected towards the comet at the unperturbed solar wind speed far from the shock and at a lower speed closer to the shock (due to the solar wind mass loading); hence, they can energize the incoming ions by Fermi acceleration. The spatial extension of the acceleration region is of the order of 10⁶ km and the resulting energy spectrum is harder than in the Earth's bow shock case. The energization of cometary ions produces an additional deceleration of the solar wind. It is suggested that Comet Halley may be the most efficient “cosmic ray shock” in the solar system.     

Marangoni effects under electric fields

An electric field when applied across liquid-liquid interface was found to cause, due to different susceptibilities of the two phases, what the authors would term as Marangoni “type” of instabilities, that resulted in the generation of bubbles/drops and caused the movement of the interface countering gravity. Thus “mixing” of the two phases would occur and in systems involving mass transfer, enhanced rates of transfer could be expected.Equations for the bubble formation involving parameters such as electrostatic pressure, surface tension, gravity force have been derived.In the case of non-gravitational or weak-gravitational fields such as obtainable in space, the separation of two liquids one below the other, as obtaining on the earth, exhibiting an interface may well nearly be impossible. Under such conditions recourse may have to be taken to super-imposition of other fields as a tool for obtaining the necessary contacting/separation. The dynamics of bubble formation etc. under these contexts are theoretically analysed.     

The properties of the low altitude magnetic belt in the Venus ionosphere

When the solar wind dynamic pressure is high, the Venus ionosphere usually contains a belt of steady magnetic field at the very lowest altitudes to which Pioneer Venus probes. The current layer that flows on the high altitude side of this low altitude belt is centered at an altitude which ranges from 170 to 190 km with a most probable altitude of 182 km. This altitude is independent of solar zenith angle and hence the current system is flowing horizontally rather than vertically as proposed by Cloutier and co-workers. The lower edge of the magnetic belt was probed only on the lowest altitude passes of Pioneer Venus. This boundary is even more stable in location. The belt has decayed to 90% of its maximum strength usually by 162 km and to 50% of its maximum strength by 155 km. We interpret these data to indicate that the observed magnetic structure of the Venus ionosphere is a product of temporal evolution rather than of spacecraft motion through a spatially varying static structure.     

The magnetic fields of Jupiter and Saturn

Jupiter and Saturn are two of the more “exotic” planets in our solar system. The former possesses its own system with 15 satellites in orbit about the parent planet. Saturn has a uniquely well developed and distinctive ring system of particulate matter and also at least 11 satellites, including the largest one amongst all the planets, Titan, with a radius of 2900 km ± 100 km. In the decade of the 70's, the USA launched 4 unmanned spacecraft to probe these giant planets in-situ with a suite of highly advanced instrumentation. Four separate encounters have occurred at Jupiter: 1. Pioneer 10 in December 1973 2. Pioner 11 in December 1974 3. Voyager 1 in March 1979 4. Voyager 2 in July 1979 The characteristics of these trajectories is shown in Table I. Thus far, only a single encounter of Saturn has occurred, that by Pioneer 11 in September 1979. Future encounters of Saturn by Voyager spacecraft will occur in mid-November 1980 and late-August 1981. It is the purpose of this talk to summarize what is presently known about the magnetic fields of these planets and the characteristics of their magnetospheres, which are formed by interaction with the solar wind.     

Validation of nimbus-7 temperature-humidity infrared radiometer estimates of cloud type and amount

Estimates of clear and low, middle and high cloud amount in fixed geographical regions approximately (160km)² are being made routinely from 11.5μm radiance measurements of the Nimbus-7 Temperature-Humidity Infrared Radiometer (THIR). The purpose of validation is to determine the accuracy of the THIR cloud estimates. Validation requires that a comparison be made between the THIR estimates of cloudiness and the “true” cloudiness. The validation results reported in this paper use human analysis of concurrent but independent satellite images with surface meteorological and radiosonde observations to approximate the “true” cloudiness. Regression and error analyses are used to estimate the systematic and random errors of THIR derived clear amount.