Kilometers In Altitude Research Articles

Research Spotlight: Explaining strange features of sprite lightning

A sprite is an electrical discharge similar to lightning, but it occurs in the upper atmosphere (at altitudes of 50–90 kilometers), above large thunderstorms. These large flashes of light, which are triggered in almost all cases by a rare lightning form in which positive charge is held at the top of clouds rather than the ground, can span tens of kilometers of altitude.

Experimental and Numerical Simulation of the Mechanical Behavior of Stratospheric Balloons Materials

The school of aerospace of Tsinghua University has started a project to develop new kind of stratospheric balloons for earth observation. These balloons will be designed to stand in the same position during a few days at 20 kilometers of altitude. To reach this goal, the first step is to select adapted materials for the balloon envelope. The materials for stratospheric balloons application should have specific properties adapted to the environment such as mechanical, thermo-optical, and permeability properties. Thus, we have asked a material manufacture company to develop and manufacture a material adapted to our application. In this paper, we will present the first results concerning the mechanical properties of the material. Experimental facilities have been developed to test the mechanical behavior of the materials at room and low temperature. The future development of the project will be to identify behavior law adapted to our material that fits with the experimental results.

Anticipating the next decade of Sun‐Earth system variations

Approximately every decade, the Sun enters a new phase when its magnetic activity increases from quiescent conditions to peak values about 3–5 years later. This intensified solar activity gradually reduces over the next 6–7 years, returning the system to “quiet” conditions. The near‐periodic 11‐year solar cycle is manifested by the regular presence of large sunspots during high solar activity (solar maximum) and few, if any, sunspots during quiet periods (solar minimum).This cycle, in turn, creates significant observable effects on Earth and its surrounding environment. During times of peak solar activity, Earth's atmosphere warms globally. In the past decade, the Sun's increased brightness at solar maximum warmed the Earth's atmosphere by about 0.1 degree Kelvin (0.1 K) in the 10 kilometers nearest to the surface (the troposphere), 1 K near 50 kilometers in altitude (at the top of the stratosphere), and 400 K at an altitude of 500 kilometers in the thermosphere. During this time, total ozone concentration increased by a few percent, offsetting for a while the overall decline associated with chlorofluorocarbon (CFC) pollution. Electron densities in the ionosphere and neutral densities in the thermosphere increased by 1–2 orders of magnitude, altering the propagation of radio waves that enable communication and increasing the drag on spacecraft in low‐Earth orbits.

High‐resolution radar measurements of turbulent structure in the equatorial electrojet

Observations of the equatorial electrojet were made with unprecedented altitude resolution at the Jicamarca Radio Observatory in January 1990. We obtained high‐quality Doppler spectra with 250‐m and sometimes better altitude resolution at heights from 95 to 120 km during the daytime and early evening with the large 50‐MHz radar. This resolution and coverage revealed a richness of dynamics and structure not previously appreciated, a structure that is sometimes reminiscent of VHF radar maps of equatorial spread F, albeit at smaller primary scale sizes. Individual scattering centers sometimes appear to drift in large swirls over many kilometers in altitude, maintaining their identity for times occasionally as long as a minute or two. On the other hand, we also see rapid variations with altitude (a kilometer or less) and time (a few seconds or less) in the Doppler spectra and signal power.

Nonlinear evolution of the auroral electron beam

The nonlinear spatial evolution of the auroral electron beam and beam‐generated electrostatic whistler noise is followed from source to atmosphere. Changes in beam parameters are determined by using the equations of conservation of total particle and wave energy and momentum flux density. Wave power fluxes are calculated by numerically integrating the wave kinetic equation. Levels of beam generated noise are quantified by using thermal levels of Cerenkov radiation as a source. Wave refraction and source geometry as well as beam recoil and thermalization influence beam generated power flux spectra. Beam parameters evolve on ionospheric scale lengths, and their positive slope feature in velocity space is maintained over thousands of kilometers of altitude even though they can generate wave energy density fluxes sufficient to modify the ionospheric density profile. For a beam source at 7000 km altitude, peak fluxes of electrostatic whistler noise as high as 10−10 W/m² Hz can be generated in the altitude region between 3000 and 5000 km. Beams with densities large enough to be unstable at the source altitude generate sufficient wave noise at the plasma frequency to disrupt the source structure.

The ski accident in the last 15 years. Correlations with equipment

In the region of Davos/Klosters an extensive epidemiological study has been performed on winter sports-accidents, especially from alpine skiing during the last 15 years. The ski-accidents have been related to the skiers activity, measured by the kilometers of altitude (vertical drop) in downhill-skiing. The injuries are still mainly located on the extremities, fractures of the lower leg have significantly decreased but serious ligamentous injuries of the knee have replaced them in high numbers. The severity of the injuries has been evaluated considering multiple factors and a decrease could be noted. Permanent disability does occur but fortunately only rarely. The incidence of ski-accidents as well as the high costs of treatment highly demand continuation of research activities for the benefit of the safety of the skiers.

Thunderstorms: An Important Mechanism in the Transport of Air Pollutants

Acid deposition and photochemical smog are urban air pollution problems, and they remain localized as long as the sulfur, nitrogen, and hydrocarbon pollutants are confined to the lower troposphere (below about 1-kilometer altitude) where they are short-lived. If, however, the contaminants are rapidly transported to the upper troposphere, then their atmospheric residence times grow and their range of influence expands dramatically. Although this vertical transport ameliorates some of the effects of acid rain by diluting atmospheric acids, it exacerbates global tropospheric ozone production by redistributing the necessary nitrogen catalysts. Results of recent computer simulations suggest that thunderstorms are one means of rapid vertical transport. To test this hypothesis, several research aircraft near a midwestern thunderstrom measured carbon monoxide, hydrocarbons, ozone, and reactive nitrogen compounds. Their concentrations were much greater in the outflow region of the storm, up to 11 kilometers in altitude, than in surrounding air. Trace gas measurements can thus be used to track the motion of air in and around a cloud. Thunderstorms may transform local air pollution problems into regional or global atmospheric chemistry problems.

Observations of Lyman-α Emissions of Hydrogen and Deuterium

A spectrophotometer was flown on Spacelab 1 to study various mechanisms of Lyman-α emission in the upper atmosphere. The use of absorption cells filled with H 2 and D 2 gases allowed us to discriminate a number of weak Lyman-α emissions heretofore masked by the strong H geocoronal emission due to resonance scattering of solar photons. Preliminary results are presented on three topics: the first optical detection of the deuterium Lyman-α emission at 110 kilometers, with an intensity of 330 rayleighs indicating an eddy diffusion coefficient of 1.3 × 10 6 square centimeters per second; auroral proton precipitations seen on both the night and the day side; and an emission located above 250 kilometers of altitude, interpreted as the result of charge exchange of magnetospheric protons with geocoronal atoms.

Interferometer studies of equatorial F region irregularities and drifts

A radar interferometer technique developed at Jicamarca, Peru and first used to study electrojet irregularities has now been used successfully to study plasma turbulence in the equatorial F region. Our first results have shown that the most ‘turbulent’ echoes appear to come from a region that extends for tens of kilometers in altitude but for only a kilometer or less in the east‐west direction. This slab may very well be the wall of a depleted region, a plasma ‘bubble’. Sometimes the irregularities can be tracked as they move eastward or westward. Velocity profiles for the evening period obtained in this way show a strong shear, with westward velocities at the lowest altitudes observed and eastward velocities above. A plausible explanation for this shear is that the westward drifts are driven by electric fields produced by westward E region winds and mapped up along magnetic field lines, while at higher heights, where the electron density is greater, the drifts are controlled by the F region dynamo driven by eastward winds.

Variability of EHF air refractivity with respect to temperature, pressure, and frequency

EHF transfer properties of air are expressed by a complex refractivity N , yielding phase dispersion and attenuation due to the microwave spectrum of oxygen. Based upon an experimetally verified theory (Rosenkranz band shape), the variability of N with respect to temperature, pressure, and frequency variations is analyzed across the 40 to 140 GHz band for atmospheric conditions up to 40 kilometers in altitude ( 300-200\deg K, 760-5 torr). The discussion centers on the usefulness of such information when treating problems of possible propagation limitations imposed by turbulent air and of remote sensing atmospheric states.

Atomic hydrogen escape rate due to charge exchange with hot plasmaspheric ions

Data on ion and electron temperatures and concentrations to several thousand kilometers of altitude were obtained from the Atmosphere Explorer C satellite for 1974 and to 850 km from Arecibo incoherent scatter radar measurements. These data were used to normalize diffusive equilibrium profiles. From these profiles and by using the neutral atmospheric model of Jacchia (1971) and a new hydrogen model, the charge-exchange-induced neutral hydrogen escape fluxes for equatorial and middle latitudes were calculated. The data confirm earlier estimates that the charge exchange loss is more important than Jeans escape for the earth. It is also found that inside the plasmapause this charge exchange process with hot plasmapheric ions is the major production and loss process for the satellite population in the hydrogen geocorona.

Venus: Vertical Structure of Stratospheric Hazes from Mariner 10 Pictures

Abstract High-resolution pictures of the limb of Venus taken by the Mariner 10 television camera indicate the presence of tenuous haze layers high in the stratosphere. At least two distinct layers separated by a few kilometers in altitude appear in pictures taken in both orange and ultraviolet light and extend laterally for several thousand kilometers from the equator to high latitudes. Photometric profiles of these hazes have been analyzed to determine their vertical distribution. An “optical barometer” technique for determining the altitudes of the hazes is presented wherein the Rayleigh-scattering component is derived by comparing orange and UV brightness profiles for nearby picture pairs. This technique appears to work very well for the orange/UV pairs which were studied. The derived scale height for CO2gas is 4.2 km, corresponding to a temperature of 200 K, in good agreement with radio occultation data. The optical barometer yields a pressure of 4 mb for the level at which the stint path optical dept...

Evolution with solar activity of the atomic hydrogen density at 100 kilometers of altitude

This note clarifies an important point of the Vidal-Madjar et al. (1973) paper. In fact, some of the results presented in that paper are sensitive to the choice of the exospheric temperature. Because Vidal-Madjar et al. used a rough estimation of that parameter, neglecting the geomagnetic heating, systematic differences appeared in their results. The use of a more precise representation of the exospheric temperature here allows us to present in particular a better evaluation of the atomic hydrogen density evolution at 100-km altitude. This density variation seems to be rather large and at least a factor of 3 between 2 × 107 and 6 × 107 atoms cm−3. Furthermore, all the densities of atomic hydrogen at 500-km altitude, recalculated with the use of a better representation of the exospheric temperature parameter, are listed here for 3 consecutive years (1969, 1970, and 1971).

EQUATORIAL WESTERLIES OVER EAST AFRICA AND THEIR CLIMATOLOGICAL SIGNIFICANCE

It has been believed that the climate of East Africa is basically controlled by the two “monsoons” which are prevalent over the region. But, in addition, frequent appearances of westerlies and their rain bringing character have long been known empirically. The hitherto reports, however, contain some contradictory remarks regarding the season of frequent appearance, the spatial distribution, their origin and their association with weather. The author has attempted to make a full use of all the available data of meteorological observations to investigate the time and spatial distribution of the westerlies, and to discuss their origins and the relation with weather. The pilot balloon and radio-sonde observations clearly show that there is a distinct seasonality in the frequency of appearance. With the two minima in April and in November, which are common to most of the stations in East Africa, the westerlies during January-March are distinguished from those during May-October (Fig. 2). The horizontal and vertical distributions of the westerlies are entirely different between the two seasons. The westerlies during January-March are most frequent over southern Tanzania, steadily decreasing toward the north, and they are equally frequent at least up to 5 kilometers in altitude. By contrast, the westerlies during May to October, particularly in July and August, are most frequent over the eastern half of East Africa, with a large meridional extention from southern Tanzania across the equator at least to central Kenya. The wester-lies of this season characteristically appear at the 3-4 kilometer levels overlying the SE mon-soon (Fig. 3). Emphasis has been put in this paper upon the May-October westerlies, because of the insufficient data concerning the January-March westerlies. The May-October westerlies over Nairobi are by no means cool nor unstable compared with the easterlies. Rather, it must be noticed that a stable layer is repeatedly recognized between the westerlies and the underlying monsoon (Fig. 4). The moisture content is signifi-cantly greater in the westerlies than in the easterlies (Table 1). In addition, the time section analysis suggests the possibility of wave-like perturbations in the westerlies (Fig. 5), A drastic change demarcates the termination of the westerlies season (Fig. 6). According to the daily 500mb charts, a low pressure, which is different from the equatorial trough, is formed over the continent at about 15- S in the period January-March, and the westerlies are observed on the northern side of the low (Fig. 7). On the contrary, the May-October westerlies seems to be associated with the passages of troughs extending from the higher latitudes in the southern hemisphere, which are likely to develop over the eastern coast (Fig. 8). It is considered that the relationship between the westerlies and weather differs from region to region, for the reason that there is a great discrepancy between the spatial distributions of the westerlies and the weather. Even under the probable control of the westerlies, the Kenya Highlands experience frequent afternoon showers, while the Nairobi district is characterized by extensive stratified clouds but with only insignificant rainfall. An extreme dry condition prevails just east of the East African Highlands in northern Kenya, and also in the most parts of Tanzania. In spite of the common belief that the equatorial westerlies tend to produce rain, the author has shown that all of those regional differences of weather are related to the westerlies, and that they can be explained without much difficulty. The dryness in the east of the High-lands is possibly due to the subsidence of the westerlies on the lee side. The difference between the Nairobi district and northern Kenya may be attributed to the regional differences of character of the SE monsoon.