Coronal interconnection of two active regions observed in 3.5–8.0 keV X-rays

Using HXIS data, we have studied the further development of the coronal arch extending towards the SE above active region No. 17255 in November 1980. The arch, studied originally by vestka (1984) disappeared on 10 November (after pronounced revival), but since 9 November HXIS revealed another arch-like structure towards the SW. We have studied the development of this new structure which appeared to be most likely an arch interconnecting AR 17255 with AR 17251, located nearly 30° to the west. This interconnection revived many times during the following days with intensity varying with the activity in both active regions. We have estimated the physical characteristics in this coronal structure and compared them with observations of interconnecting loops made at lower energies by Skylab in 1973. The temperature (maximum values 7.5–14 × 10⁶ K) and the density (1.1–5.0 × 10⁹ cm^–3) are found to be higher than in the Skylab loops (a result that could be expected because the HXIS energy range was harder than that of Skylab) and similar to the values deduced for the earlier arch system extending to the SE. However, much shorter decay times of the brightness variations indicate the presence of conduction in contrast to the SE arch in which conduction was clearly inhibited. This supports the assumption that the SE and SW coronal structures were two different phenomena.Presently at Delft Institute of Technology, Landbergstraat 3, 2628 CE Delft, The Netherlands.     

Large-Scale Active Coronal Phenomena in YOHKOH SXT Images. III. Enhanced Post-Flare Streamer

We demonstrate several events where an eruptive flare close to the limb gave rise to a transient coronal streamer visible in X-rays in Yohkoh SXT images, and analyze one of these events, on 28–29 October 1992, in detail. A coronal helmet streamer began to appear 2 hours after the flare, high above rising post-flare loops; the streamer became progressively narrower, reaching its minimum width 7–12 hours after the flare, and widened again thereafter, until it eventually disappeared. Several other events behaved in a similar way. We suggest that the minimum width indicates the time when the streamer became fully developed. All the time the temperature in the helmet streamer structure was decreasing, which can explain the subsequent fictitious widening of the X-ray streamer. It is suggested that we may see here two systems of reconnection on widely different altitudes, one giving rise to the post-flare loops while the other creates (or re-forms) the coronal helmet streamer. A similar interpretation was suggested in 1990 by Kopp and Polettofor post-flare giant arches observed on board the SMM; indeed, there are some similarities between these post-flare helmet streamers and giant arches and, with the low spatial resolution of SMM instruments, it is possible that some helmet streamers could have been considered to be a kind of a giant arch.     

Stereoscopic measurements of flares from PHOBOS and GOES

A unique approach to observing the Sun stereoscopically in soft X-rays was afforded by the PHOBOS mission to Mars during 1989. Concurrent measurements of two flares from two widely separated spacecraft allowed us to obtain estimates of each flare's height above the solar surface. The requirement was that the flare had to be over the limb as observed by one spacecraft and on the visible disk as viewed by the other. The first flare occurred on March 4, when the active region was beyond the east limb as observed by GOES (at Earth), but on the disk as viewed by PHOBOS (at Mars). The second flare, on March 15, was on the disk for GOES, but beyond the west limb for PHOBOS. We believe that the same extraordinary active region, 5395, was responsible for both events. Soft X-ray photometers on each spacecraft contained two broad-band channels. The two-channel data were used to computeflare (assumed isothermal) plasma temperatures. The sharply peaked flare on March 4 indicated essentially identical maximum electron temperatures ( 13 Mk) at both spacecraft, confirming that the hottest plasma was indeed concentrated at the highest (unocculted) part of the loop. However, in the case of the long-duration March 15 flare, whose loop was in apparent upwards motion, the partially occulted flare indicated substantially cooler temperatures. This finding suggests that the hot core of this flare may have been below the limb, or that the partially occulted flux originated not from post-flare loops but from an independent, higher X-ray arch. The PHOBOS and GOES X-ray photometers were intercompared in July 1988, soon after the PHOBOS launch, to establish relative calibration parameters.     

Fundamental energy relations in the theory of compensation of non-equilibrium states in the earth's atmosphere

Summary The paper presents, in a condensed form, the fundamentals of global atmospheric energetics that have a bearing on the linear theory of compensation of non-equilibrium states in the Earth's atmosphere. The author introduces a new coordinate system with the vertical coordinate *=Z*/T*, which suits global atmospheric energetice.The relation between the energetics of the atmospheric system as a whole and the mean energetics level (MEL) is shown. Contrary to what has been assumed so far, it is proved that this level is neither an isopycnic level nor a physical surface, where */t=0 applies everywhere.List of Symbols Used x, y, z space coordinates in thez-system - x, y, space coordinates in the -system - t time - p, T, pressure, thermodynamic temperature and air density - p*, T*, pressure, temperature, density and geopotential on the mean energy level - g acceleration of the Earth's gravity - c _p ,c _v ,R specific temperature under constant pressure, volume and specific gas constant - = c _p /c _v Poisson's constant - E _k ,E _v ,E _p kinetic, internal and potential energies of the atmospheric system - r'(x,y) correction function to inhomogeneous atmosphere - v, v _n magnitude of motion velocity, magnitude of the normal component of velocity - O, S, S ₀ volume of the whole atmospheric system, surface limiting volumeO and the Earth's surface - Z _S height of surfaceS - arbitrary scalar quantity - _H , horizontal differential operators in thez- andp-systems Dedicated to Corresponding Member Vojtch Vítek, Director of the Institute of Physics of the Atmosphere of the Czechoslovak Academy of Sciences, at the occasion of his sixtieth birthday.     

Seismic response of weakly laterally inhomogeneous structure

Summary The seismic response (the transfer properties) of a model consisting of two layers above a homogeneous halfspace, with curved interfaces and continuously laterally varying velocity within the layers is investigated assuming vertical plane SH-wave incidence from below. The frequency response and the synthetic seismograms are computed by the ray and matrix methods. The dependence of the seismic response on the prevailing frequencies of the incident wave, the role of the individual layers in forming the seismic response, as well as the effect of causal absorption are studied.

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aamuam ua au (n¶rt;am ma) ¶rt;u, m u n¶rt;mua ¶rt;¶rt; nnmam ¶rt; , uuuauau a¶rt;a u n u anau m mu , n¶rt;nuu mua na¶rt;a n SH-. amm auu u ummuu a auma u amu m¶rt;au. ¶rt;am auum u auu m na¶rt;a amm na¶rt;a , m¶rt; nu uauu u auu u ma m nu.

     

On the problem of quasi-electrostatic whistler mode waves: A possible interpretation of discrete plasmaspheric emissions

Summary In a number of VLF experiments with low-orbiting Intercosmos satellites, high-intensity, discrete VLF emissions at frequencies above the local LHR were observed predominantly between L=2.3 and 4.0. The frequency of their intensity maximum varies continuously with geomagnetic latitude, and approximately parallels the value of a quarter of the equatorial electron gyrofrequency. An attempt is made to interprete these emissions in terms of quasi-electrostatic whistler-mode waves, generated in the near-equatorial region and propagating downward in the quasi-resonance mode. The generating mechanism is supposed to be the kinetic instability connected with the loss-cone and temperature anisotropy of the distribution function of energetic electrons. Some features of the discrete plasmaspheric emissions are discussed on the basis of theoretical considerations.

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¶rt; num a umu nmua m a¶rt;au umu ¶rt;um -uu a amma, a amm , num ¶rt; L=2,3 u L=4. amma aua umumu mu uu um uuaum um u nuuum aa mmu amuauamm m. ¶rt;numa nnma umnmuam mu uu mua aummamuu um , ¶rt;a nuamua amu u anmau u au-a u. ¶rt;naam, m mu uu ¶rt;am mam umu mumu an¶rt;u u m, aumnu mnam u nm u uu an¶rt;u. n mmu aau ¶rt;am m mu ¶rt;umm na uu.

     

Observations visuelles des aurores en tchécoslovaquie pendant l'agi et la CGI 1957–1959

Резюме Общее число полярных сияний, наблюденных в Чехословакии в течение МГГ и МГК, достигает 28, в том числе 4—большой интенсивности. 27-дневная повторяемость отчетливо наблюдается в период 14–18 дней магнитного вращения в течение 30-ти магнитных вращений.

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En l'honneru du 80^me anniversaire du Prof. Dr Bedřich Šalamon

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Adresse: Budečská 6, Praha 12.