Importance of electric field measurement over low latitudes at stratospheric heights by balloons

The vertical field in the stratosphere around 35 km is predominantly of atmospheric origin whereas the horizontal electric field at these altitude is mainly of ionospheric origin. The electrical coupling between ionosphere and atmosphere is not known for low latitudes. Balloon borne electric field measurements are planned from Hyderabad, India (geographic latitude 17.5° N) to understand this coupling. Measurement of stratospheric electric fields are also important from the point of view of the sun-weather relationship. It si suggested that the balloon borne electric field measurements are important to understand the electrodynamics of the middle atmosphere.     

New planetary atmosphere simulations: application to the organic aerosols of Titan.

The atmosphere of Titan partly consists of hazes and aerosol particles. Experimental simulation is one of the powerful approaches to study the processes which yield these particles, and their chemical composition. It provides laboratory analogues, sometimes called tholins. Development and optimization of experimental tools were undertaken in order to perform chemical and physical analyses of analogues under conditions free from contamination. A "Titan aerosol generator" was developed in the frame of the Cassini-Huygens mission, in order to produce Titan's aerosol analogues within conditions closer to those of the titanian atmosphere: cold plasma simulation system, low pressure and low temperature. The direct current (DC) glow discharge is produced by applying a DC voltage between two conductive electrodes inserted into the gas mixture-model of the studied atmosphere- at low pressure. A high-impedance power supply is used to provide the electrical field. All the system is installed in a glove box, which protect samples from any contamination. Finally the research program expected with this new material is presented.     

Variations of quasi-electrostatic fields and ionosphere potential above lightning discharge at equatorial latitudes

Lightning discharges by thunderstorms cause generation of electromagnetic pulses and of quasi-electrostatic fields (QESF) in the atmosphere above, which occur in different time-scales. QESF penetrate into the mesosphere and the lower ionosphere where they are big enough to generate considerable electric charge transfer there and, in some cases, to cause red sprites. These processes may have an important contribution to the global atmospheric electric circuit. Significant transient variations of the ionospheric potential above the thunderstorm take place as well. QESF depend on the atmospheric conductivity and in the ionosphere they are affected also by its anisotropy determined by geomagnetic field orientation. QESF after a lightning discharge are investigated theoretically in this work in the case of equatorial latitudes (by horizontal geomagnetic field), where thunderstorms are important contributors to the global circuit. Results for DC electric fields in the lower equatorial ionosphere above a thundercloud obtained by earlier models demonstrate some specific features of the spatial distribution of these fields, which appear due to geomagnetic field orientation. Thus, the electric fields can be shifted by tens or more kilometers to east of the cloud charge region; also their horizontal scale is much bigger than in the case of middle latitudes. Here, a presence of similar specific features of quasi-electrostatic field distributions and ionospheric potential variations caused by a lightning stroke is studied. A situation when no secondary ionization is generated is considered. A model based on the Maxwell equations for potential electric fields is proposed. Computations of QESF in the middle atmosphere and of the ionospheric potential variations are provided as dependent on conductivity and its anisotropy in D-region. The obtained results for the ionosphere show that the electric fields in the equatorial lower ionosphere are comparable to these formed in the case of middle latitudes. However, their horizontal scales are much bigger and depend on conductivity profiles. Similar features are valid also for the ionospheric potential variations and for their horizontal scales.     

The optical parameters of the atmosphere of Venus

This work is devoted to the derivation of the optical properties of the Venus atmosphere from “Venera-10” optical measurements. Within the framework of a two-layer model of Venus atmosphere it is found that in the spectral interval 0.52 – 0.85 μm the optical thickness of the upper cloud layer is ≈ 50 and the optical parameters of the lower layer are similar to the Rayleigh ones. Comparison is made between the measurements of radiation field within the atmosphere and the results of strict calculations. A preliminary conclusion is suggested that there are considerable numbers of aerosol particles with a radius ? 0.03 μm in the lower layer. The results of the upper boundary of the cloud layer is estimated to be ≈ 70 km.     

Latitude gradients in the natural variance in stratospheric conductivity – Implications for studies of long-term changes

Stratospheric electrical conductivity measurements have been made from high altitude research balloons at various locations around the world for more than 40 years. In the stratosphere, conductivity changes may indicate changes in aerosol or water vapor content. In this paper, we will compare the short term variation amplitude in data taken at several latitudes from equatorial to polar cap. Short term variations that occur on time scales of weeks to months (10⁵–10⁷ s) can be attributed to Forbush decreases, geomagnetic storms, aerosol injections by volcanos and forest fires, etc. Variations with time scales of minutes to days (10³–10⁵ s) can have amplitudes of a factor of ∼2 or more at high magnetic latitude. The variance at equatorial latitude is much smaller. The sources of these fluctuations and the latitude gradient remain unknown. Variations of all origins completely obscure any long-term climatic trend in the data taken in the previous four decades at both mid and high latitude.     

磁化等离子体中斜传播的离子孤波

近几年卫星空间电场测量经常证认出局地非线性离子静电波,它们可能与极光粒子加速有直接关系。这些静电波被认为或者是离子声波模的演化,或者是静电离子逥旋波模的演化结果。本文研究了磁场中斜传播小振幅离子非线性波的演化,得到非线性Schrodinger方程。结果表明离子声孤波和离子迴旋孤波都是可能的。计算结果与卫星S(3-3)电场测量比较,可以很好说明部分测量结果。      

Atmospheric electrical conductivity measurements and modeling for application to air pollution studies

The experimentally measured ground level atmospheric electrical conductivity is validated from a simplified ion–aerosol model for which the inputs are ionization rate from surface radioactivity, aerosol density and meteorological parameters. Also estimated from the model is the reduction in conductivity for assumed aerosol levels. It is seen that for an increase of ambient aerosols by threefold the percent reduction in conductivity is 7% and it is 10% for an increase by sixfold. Thus, the variations in the measured ground level conductivity can be used to examine the atmospheric pollution, if any.     

由电离层电位所建立的大气电状态

本文在已知电离层电位分布下, 解析地计算了大气电位, 电场和电流强度的全球分布.结果表明, 在大气导电率随高度呈指数增加的情况下, 100km高度上的电离层电位, 几乎无衰减地扫到25km以下.大气电场较强的区域主要在20km以下的低层大气区, 其垂直分量比水平分量大4个数量级.而中高层大气电场较弱, 且两分量量级相当.本文还提出了一种考虑地面形状对大气电场影响的解析方法.      

The detection of energetic cometary and solar particles by the EPONA instrument on the Giotto mission

EPONA is an energetic particle detector system incorporating totally depleted silicon surface barrier layer detectors. Active and passive background shielding will be employed and, by applying various techniques, particles of different species, including electrons, protons, alpha particles and pick-up ions of cometary origin may be detected over a wide spectrum of energies extending from the tens of KeV into the MeV range.

The instrument can operate in two modes namely (a) in a cruise phase or storage mode and (b) in a real time mode. During the real time mode, observations at high spatial (octosectoring) and temporal (0.5s) resolution in the cometary environment permit studies to be made of accelerated particles at the bow shock and/or in the tail of the comet. In conjunction with magnetic field measurements on board Giotto, observations of energetic electrons and their anisotropies can determine whether the magnetic field lines in the cometary tail are open or closed. Further, the absorption of low energy solar particles in the cometary atmosphere can be measured and such data would provide an integral value of the pertaining gas and dust distribution. Solar particle background measurements during encounter may also be used to correct the measurements of other spacecraft borne instruments potentially vulnerable to such radiation.

Solar particle flux measurements, obtained during the cruise phase will, when combined with simultaneous observations made by other spacecraft at different heliographic longitudes, provide information concerning solar particle propagation in the corona and in interplanetary space.     

Long-term (50 years) measurements of cosmic ray fluxes in the atmosphere

Since the middle of 1957 till present time the group of researchers of P.N. Lebedev Physical Institute of the Russian Academy of Sciences has carried out the regular balloon borne measurements of charged particle fluxes in the atmosphere. The measurements are performed at polar (northern and southern) and middle latitudes and cover the interval of heights from the ground level up to 30–35 km. Standard detectors of particles (gas-discharged counters) have been used. More than 80,000 measurements of cosmic ray fluxes in the atmosphere have been performed to the present time. In the data analysis the geomagnetic field and the Earth’s atmosphere are used as cosmic ray spectrometers.     

New insights into Titan's organic chemistry in the gas and aerosol phases.

Titan, the largest satellite of Saturn, with a dense atmosphere very rich in organics, and many couplings in the various parts of its "geofluid", is a reference for studying prebiotic chemistry on a planetary scale. New data have been obtained from experiments simulating this organic chemistry (gas and aerosol phases), within the right ranges of temperature and a careful avoiding of any chemical contamination. They show a very good agreement with the observational data, demonstrating for the first time the formation of all the organic species already detected in Titan atmosphere including, at last, C4N2, together with many other species not yet detected in Titan. This strongly suggests the presence of more complex organics in Titan's atmosphere and surface, including high molecular weight polyynes and cyanopolyynes. The NASA-ESA Cassini-Huygens mission has been successfully launched in October 1997. The Cassini spacecraft will reach the Saturn system in 2004 and become an orbiter around Saturn, while the Huygens probe will penetrate into Titan's atmosphere. In situ measurements, in particular from Huygens GC-MS and ACP instruments, will provide a detailed analysis of the organics present in the air, aerosols, and surface. This very ambitious mission should yield much information of crucial importance for our knowledge of the complexity of Titan's chemistry, and, more generally for the field of exobiology.     

Solar cosmic rays in the near Earth space and the atmosphere

Solar energetic particles (SEPs) constitute a distinct population of energetic charged particles, which can be often observed in the near Earth space. SEP penetration into the Earth’s magnetosphere is a complicated process depending on particle magnetic rigidity and geomagnetic field structure. Particles in the several MeV energy range can only access to periphery of the magnetosphere and the polar cap regions, while the GeV particles can arrive at equatorial latitudes. Solar protons with energies higher than 100 MeV may be observed in the atmosphere above ∼30 km, and those with energies more than 1 GeV may be recorded even at the sea level. There are some observational evidences of SEP influence on atmospheric processes. Intruding into the atmosphere, SEPs affect middle atmosphere odd-nitrogen and ozone chemistry. Since spatial and temporal variations of SEP fluxes in the near Earth space are controlled by solar activity, SEPs may present an important link between solar activity and climate. The paper outlines dynamics of SEP fluxes in the near Earth space during the last decades. This can be useful for tracing relationship between SEPs and atmospheric processes.     

Analytical pyrolysis experiments of Titan aerosol analogues in preparation for the Cassini Huygens mission.

Comparative pyrolysis mass spectrometric data of Titan aerosol analogues, called "tholins", are presented. The Titan tholins were produced in the laboratory at Cornell by irradiation of simulated Titan atmospheres with high energy electrons in plasma discharge. Mass-spectrometry measurements were performed at FOM of the solid phase of various tholins by Curie-point pyrolysis Gas-Chromatography/Mass-Spectrometry (GCMS) and by temperature resolved in source Pyrolysis Mass-Spectrometry to reveal the composition and evolution temperature of the dissociation products. The results presented here are used to further define the ACP (Aerosol Collector Pyrolyser)-GCMS experiment and provide a basis for modelling of aerosol composition on Titan and for the interpretation of Titan atmosphere data from the Huygens probe in the future.     

High resolution measurements of nightside ion troughs at venus: Evidence of electrodynamic perturbations

The Bennett rf ion mass spectrometer (OIMS) on the Pioneer Venus Orbiter was particularly designed to provide variable temporal resolution for measurements of thermal ion composition and density. An Explore-Adapt mode is used to obtain priority for measurement of most prominent ion species, and in a 2/16 configuration, the two dominant ions within the available range of 16 species are selectively sampled at the highest rate of 0.2 sec/sample. The high resolution measurements are combined with independent observations from the magnetic field (OMAG), neutral mass spectrometer (ONMS), and electron temperature (OETP) experiments to investigate sharply structured troughs in the low altitude nightside ion concentrations. The results indicate a close correlation between the structure in the ion distributions and the structured configuration of the magnetic field which is draped about the planet. In the regions of the ion depletions, sharp fluctuations in electron temperature and anomalous increases in the density of neutral gases indicate that the ion depletion may be associated either with dynamic perturbation in the ion and neutral flows, and/or local joule heating. The configuration of the ion flow/magnetic field draping and consequent electric fields for these events must be analyzed in detail to understand the relationships.     

Microgravity particle research on the space station: the Gas-Grain Simulation Facility.

In the gravitational field on Earth, the large settling rate of micron-sized particles and the effects of gravity-induced convection prohibit many interesting studies of phenomena such as coagulation, collisions, and mutual interactions of droplets, dust grains and other particles. Examples of exobiology experiments involving these phenomena are the simulation of organic aerosol formation in Titan's atmosphere, studies of the role of comets in prebiotic chemical evolution, and simulations of carbon grain interactions in various astrophysical environments. The Gas-Grain Simulation Facility (GGSF) is a proposed Earth-orbital laboratory that will allow present ground-based experimental programs which study processes involving small particles and weak interactions to be extended to a new domain. Physics issues that scientists wishing to propose GGSF experiments must consider are reviewed in this paper. Specifically, coagulation, motion in gases and vacua, and wall deposition of particles in a microgravity environment are discussed.     

Comparison of ground reflectance measurement with satellite derived atmospherically corrected reflectance: A case study over semi-arid landscape

Atmospheric corrections to satellite data are important for comparing multitemporal data sets over tropical regions with variable aerosol loading. In this study, we evaluated the potential of 6S radiative transfer model for atmospheric corrections of IRS-P6 AWiFS satellite data sets, in a semi-arid landscape. Ground measurements of surface reflectance representing different land use/land cover categories were conducted to relate IRS-P6 AWiFS top of atmospheric reflectance. The 6S radiative transfer model was calibrated for local conditions using ground measurements for aerosol optical depth, water vapor and ozone with a sun photometer. Surface reflectance retrieved from 6S code was compared with top of atmosphere (TOA) reflectance and ground based spectroradiometer measurements. Accurate parameterization of the 6S model using measurements of aerosol optical depth, water vapor and ozone plays an important role while comparing ground and satellite derived reflectance measurements.     

Direct radiative forcing from black carbon aerosols over urban environment

There is growing evidence that the earth’s climate is changing and will likely continue to change in the future. It is still debated whether these changes are due to natural variability of the climate system or a result of increases in the concentration of greenhouse gases in the atmosphere. Black carbon (BC) has become the subject of interest for a variety of reasons. BC aerosol may cause environmental as well as harmful health effects in densely inhabited regions. BC is a strong absorber of radiation in the visible and near-infrared part of the spectrum, where most of the solar energy is distributed. Black carbon is emitted into the atmosphere as a byproduct of all combustion processes, viz., vegetation burning, industrial effluents and motor vehicle exhausts, etc. In this paper, we present results from our measurements on black carbon aerosols, total aerosol mass concentration and aerosol optical depth over an urban environment namely Hyderabad during January to May, 2003. Diurnal variations of BC indicate high BC concentrations during 6:00–9:00 and 19:00–23:00 h. Weekday variations of BC concentrations increase gradually from Monday to Wednesday and gradually decrease from Thursday to Sunday. Analysis of traffic density along with meteorological parameters suggests that the primary determinant for BC concentration levels and patterns is traffic density. Seasonal variations of BC suggest that the BC concentrations are high during dry season compared to rainy season due to the scavenging by air. The fraction of BC to total mass concentration has been observed to be 7% during January to May. BC showed positive correlation with total mass concentration and aerosol optical depth at 500 nm. Radiative transfer calculations suggests that during January to May, diurnal averaged aerosol forcing at the surface is −33 Wm² and at the top of the atmosphere (TOA) above 100 km it is observed to be +9 Wm⁻². The results have been discussed in detail in the paper.     

Electric field measurements at a southern mid-latitude station obtained using an HF digital ionosonde

It is important to understand the convection of the inner magnetosphere to fully describe the response of the low- to mid-latitude thermosphere-ionosphere system to geomagnetic storms. Realistic numerical simulations of mid-latitude electric fields suffer from limited knowledge of lower thermospheric winds and ionospheric conductivity on a global scale. Even empirical models of mid-latitude electric fields suffer from the paucity of measurements made by the handful of incoherent scatter radars concentrated in the American-European sector, and the intermittent satellite measurements made in other regions. Thus it would be very useful to show the extent to which Doppler velocity measurements made with the numerous digital ionosondes deployed around the globe can be used to infer F-region electric fields. The monthly average diurnal variation of Doppler velocity measured by a recently commissioned Digisonde at Bundoora (145.1°E, 37.7°S, geographic; 49°S magnetic) is seen to resemble the average diurnal variation of ion drift measured by the incoherent scatter radar at Millstone Hill (71.5°W 42.6°N; 57°N). Moreover, the Bundoora measurements exhibit the nighttime westward perturbation drifts found in Dynamics Explorer-2 ion drift measurements.     

Consequences of the application of the streamer fluid model to the study of the sprite inception mechanism

We present the results of a streamer-fluid model used to investigate the electrodynamical coupling between the troposphere and upper atmosphere due to the penetration of lightning electric fields into the mesosphere and the lower ionosphere, generating sprites. The model solves the continuity equation for electrons and ions coupled to Poisson equation. The dominant physical response of the atmosphere is the formation of a screening-ionization wave. The wave shields the atmosphere above it from the action of the lightning field and, together with the conductivity reduction below it due to attachment, the wave amplifies the total field below it, allowing for the penetration of intense electric fields in the mesosphere as it propagates downwards into regions of higher density that compress the wave. This is the key physical mechanism for sprite inception. We evaluated the effects of the thundercloud charge geometry, lightning current waveshape, atmospheric conductivity, via different electron density profiles, and the effect of ionization, attachment and electron mobility coefficients in the electrical breakdown process, related to halo production, and sprite streamer initiation. The results showed that electrons with higher mobility are more efficient in shielding the lightning electric field before breakdown, causing delay, and they contribute to the formation of the streamer seed after breakdown, anticipating the sprite streamer inception. Similarly, a higher effective ionization rate, produced by modifications in the attachment and ionization coefficients, anticipates sprite inception. The simulations with 6 different electron density profiles, and therefore conductivities, spanning 4 orders of magnitude, showed that the altitude of breakdown and sprite initiation, as well as their time delays from the lightning discharge are directly related to atmospheric conductivity: higher conductivities produce halo and sprite inception at lower altitudes with longer delays and may hinder sprite formation. We document that variations of 30 times in the lightning current leads to sprite initiation altitudes in the range 66.0–73.5 km, with delays between 1.550 and 34.500 ms, while variations of 4 orders of magnitude in the conductivity profile lead to initiation altitudes 61.0–70.6 km, with delays in the range 3.825–9.825 ms. Consequently, we suggest that lightning characteristics dominate over atmospheric parameters in determining sprites’ initiation altitude and delay. The simulation of a −CG, with a constant current of 30 kA, did not produce a sprite seed, confirming an asymmetry in the response of the atmosphere to positive and negative lightning. This is due to the free electron drift direction that is away from the screening ionization wave, preventing the formation of the streamer seed for the great majority of −CGs. The same does not apply to halos, which depend on the occurrence of breakdown and can be produced by discharges of both polarities.