Recent measurements of middle atmospheric electric fields and related parameters

In 1989, two series of rocket measurements were carried out to investigate middle atmosphere electric fields. The measurements were taken both in the Northern Hemisphere on Heiss Island (80°37′N and 58°03′E) and in the Southern Hemisphere in the Indian Ocean (40–60°S and ~45°E) on board the research vessel ‘Akademik Shirshov’. Along with the vertical electric fields, aerosol content and positive ion density were also measured. Some of the rocket launches were made during the extremely strong solar proton events (SPE) of October 1989. The experiments showed the strong variability of the electric fields in the middle atmosphere at polar and high middle latitudes. In all the measurements the maximum of the vertical electric field height profile in the lower mesosphere was observed to be more than ~ 1 V/m. The electric field strength and the field direction at maximum varied considerably among the launches. A maximum value of + 12 V/m was detected at a height of about 58 km at 58°30′S on 21 October 1989 during the SPE. The simultaneous measurements of the electric field strength, positive ion density and aerosols point out both an ion -aerosol interaction and a connection between the mesospheric electric fields and aerosol content.     

Equatorial spread-F by electric fields and atmospheric gravity waves generated by thunderstorms

It is assumed that atmospheric gravity waves, resulting in travelling ionospheric disturbances (TIDs), and electric fields, generated by convective thunderstorms, have a reasonable influence on the large-scale structure of premidnight equatorial spread-F irregularities. The responsible mechanisms, viz the superposition of thunderstorm generated electric fields on the ionospheric electric fields being the determining factor for irregularity generation and the steepening of TID structures due to spatial resonance, are briefly outlined. It is recalled that convective activity is most pronounced in the intertropical convergence zone over the African and South American continents. A model based on the typical features of seasonal and geographical variation of tropical convection generating the TIDs is presented which can explain seasonal and geographical variations of premidnight equatorial spread-F occurrence.     

A spectral approach for studying middle and upper atmospheric phenomena

We report on the application of a newly developed spectral code to the study of the middle/upper atmosphere. The spectral approach offers conceptual and practical convenience for analyzing the generation and interaction of different components of atmospheric activity through the decomposition of the dynamical fields into components with different zonal wave numbers (m). As examples and tests, we obtain solutions for the m = 0 (the mean circulation) and 1 (the diurnal tides) components separately (no mutual interactions), as well as the m = 1 component under the influence of the mean circulation. By simulating gravity wave effects with Rayleigh friction and eddy diffusion peaking near 90 km altitude, the mean circulation thus generated can reproduce the observed mesospheric temperature anomaly under solstice conditions. The computed diurnal tides are in good agreement with results obtained earlier by other authors. The large temperature gradient (associated with the m = 0 component) set up by the mesospheric temperature anomaly under solstice conditions creates a condition favorable for the development of baroclinic instabilities in the mesopause layer, especially near the summer pole. In our time dependent calculation, waves with approximately 4-day period are generated in the m = 1 component, superimposing with the 1-day period tides.     

The generation of electric fields by aerosol particle flow in the middle atmosphere

The generation mechanism of electric fields in the middle atmosphere based on the interaction between charged aerosol particles and an updrafting air flow is considered. Due to the gravity force there occurs a relative motion of air and aerosol particles which excites electric space charge waves. The mechanism is analogous to that of the resistive beam-plasma instability. It is shown that the most favourable conditions for the instability are realized at heights of 80–90 km in regions where the electron density is relatively low and heavy ions are predominant. Estimates are given for the aerosol component parameters which are necessary for the instability to be switched on.     

A quasi-DC model of electric fields in the ionosphere-ground region due to electrified clouds

The penetration of the quasi-DC electric fields, E due to electrified clouds, into the middle- and high-latitude ionosphere is theoretically studied during the initial stage of cloud charge separation. The electrification process is characterized by a source function S(t), whose variations are on the time scale of the relaxation process in the cloud. A first-order approximation solution for the time variation of E is obtained as an explicit function of the electric field in the steady-state case. Some features of the time variations of E at different altitudes (in the ionosphere and also in the atmosphere) are investigated, depending on the source function and the relaxation time constants. This result can also be applied for slowly electrifying clouds which do not produce lightning.     

Travelling atmospheric disturbances as a possible explanation for daytime positive storm effects of moderate duration at middle latitudes

Using N-h profiles, critical frequency data, and the AE index, we find that daytime positive storm effects at middle latitudes are caused by uplifting of ionization and lag the onset of substorm activity by about 2.5 h. Since the increase in electron concentration lags the increase in layer height by about one hour, the perturbation responsible for positive storm effects should propagate with a high velocity (~500 m/s) from high to lower latitudes. Travelling atmospheric disturbances are offered as a possible explanation for short and medium duration events. A model calculation of the ionospheric response to such a perturbation supports our hypothesis.     

A test of the Hines dispersion equation for atmospheric gravity waves

Simultaneous observations of an ionospheric wave by two incoherent scatter facilities and three Faraday-rotation polarimeters have provided measurements of the frequency, vertical wavelength, horizontal wavelength and direction of propagation of the wave. These measured values confirm the Hines dispersion equation for atmospheric gravity waves.     

Foil chaff clouds as a tool for in-situ measurements of atmospheric motions in the middle atmosphere: their flight behaviour and implications for radar tracking

The aerodynamic behaviour of foil chaff (rectangular plates) used for in-situ measurements of atmospheric motions in the middle atmosphere (up to 100 km altitude) can be described by Stokes' Law in which the corrections are applied to the coefficient of viscosity. The results obtained with this approximation are in good agreement with observations and allow us to explain in detail certain peculiarities occasionally seen in the tracking of chaff clouds by radar.     

A model passive probe for free atmosphere electric field measurements

A model of a passive probe for determination of electric field strength in the free atmosphere is developed. This model shows that the same probe can be used to determine mean monosigned ion conductivity and also conduction current density. Simulation of typical experimental conditions is used to derive the response to small altitude-dependent conductivity fluctuations. Results from a passive probe sounding indicate that conduction current density was nondivergent to (at least) 26 km and that small-scale conductivity fluctuations were only around ± 3% of the mean value.     

A search for a solar cycle-temperature relationship in the middle atmosphere over Volgograd

The variation of temperature in the middle atmosphere (15–80 km) at Volgograd (49°N, 44°E) during an 11-year solar cycle (1971–1982) has been studied. The temperature of the stratosphere did not show any significant influence of the sunspot cycle, but the temperatures of the mesosphere showed a strong in-phase relationship with the solar cycle. Computed correlation and regression coefficients were positive and highly significant in this region. At 60 and 70km the temperature variations were almost linearly related to the sunspot number. Seasonal studies indicated that solar activity has a much stronger influence on temperature during the winter than during the summer.     

元代山水画探源

元代山水画是中国古代山水画发展到较高阶段的表现。画家的创作,都是从自然界直接感受中获得了有用的题材,对于山水自然的理解更为深刻。     

A Further Proposal for the Hull Lines of the Madrague de Giens Ship (c.70 BC)

A review of studies carried out since 1978 on the Madrague de Giens ship remains have enabled a reassessment of the vessel's shell‐first construction process. Hypotheses concerning moulding criteria are developed, with the profile (sheer plan), main cross section (body plan), and active sections and reference planks used to mould the hulll proposed and evaluated. These are compared to the Marsala (3rd century BC), and Yass?ada 2 (4th century AD) ships, which have similar wine‐glass‐shaped bottoms. Some aspects of these moulding criteria appear common to those used in the Mediterranean during the Middle Ages and the Renaissance.