Local relief and the height of Mount Olympus

A three‐dimensional assessment of the net volume of rock differentially eroded from below mountain tops to form valleys yields a range‐wide constraint on feedback between valley development and the height of mountain peaks. The ‘superelevation’ of mountain peaks potentially attributable to differential removal of material from below peaks in the Olympic Mountains, Washington, was constrained by fitting a smoothed surface to the highest elevation points on a 30 m grid digital elevation model of the range. High elevation areas separate into two primary areas: one centred on Mount Olympus in the core of the range and the other at the eastern end of the range. The largest valleys, and hence areas with the greatest volume of differentially eroded material, surround Mount Olympus. In contrast, the highest mean elevations concentrate in the eastern end of the range. Calculation of the isostatic rebound at Mount Olympus attributable to valley development ranges from 500 to 750 m (21 to 32 per cent of its height) for a 5 to 10 km effective elastic thickness of the crust. Comparison of cross‐range trends in mean and maximum elevation reveals that this calculated rebound for Mount Olympus corresponds well with its ‘superelevation’ above the general cross‐range trend in mean elevation. It therefore appears that the location of the highest peak in the Olympics is controlled by the deep valleys excavated in the centre of the range. Copyright © 2000 John Wiley & Sons, Ltd.     

On the form of noctilucent clouds

Summary the possibility of the fine structure wave form of noctilucent clouds being due solely to variations in the dust density arising from the wave motions of the dust particles is discussed, with the conclusion that this state of affairs is unlikely.     

Coordinated optical and radar image measurements of noctilucent clouds and polar mesospheric summer echoes

Novel coincident 3-D radar, lidar and optical image measurements of dynamical structures in polar mesosphere summer echoes (PMSE) and noctilucent clouds (NLC) are presented. Common volume mesospheric measurements were made over central Alaska using the new Poker Flat Incoherent Scatter Radar (PFISR), a co-located Rayleigh lidar and remote, two-station digital image observations, enabling the first detailed investigation of the horizontal and vertical structures of NLC and PMSE. Coincident measurements were made of an unusual NLC display recorded on 10–11 August 2007, characterized by a broad luminous band that contained several prominent wave forms. Concurrent lidar and image measurements established the presence of NLC within the radar volume from ～09:00 UT (01:00 LT), when the solar depression angle was 10.4°, until dawn. Strong but intermittent PMSE were detected by PFISR, with distinct patchy structures that exhibited a similar southward motion as the NLC. Detailed comparison of the 3-D PMSE structures and the NLC lidar and image data have revealed striking similarities when account was taken of the NLC layer altitude, suggesting a direct link between their small-scale spatial signatures (within the current resolution of the radar measurements). At the same time, the lidar detected a sustained increase in the backscatter signal, while the imagers revealed the development of copious short horizontal wavelength (4.9 km) billow waves. We conclude that strong wind shears associated with the Kelvin–Helmholtz billow instabilities played a key role in the development of a neutral turbulence layer in close proximity to the NLC layer resulting in the strong but intermittent PMSE detected at 450 MHz on this occasion.     

On mixing processes in cumulus clouds

An examination is made of the hypothesis that internal cloud properties are determined by the mixing of dry air from above the cloud top and cloud base air in such a way that the mixture is neutrally buoyant with respect to the clear air environment at each level. It is concluded that the resulting mixture is much drier than is actually observed. Comments are made about observed cloud properties which need to be taken into account in any model of the mixing process.     

Multiple levels of magma storage during the 1980 summer eruptions of Mount St. Helens, WA

Transitions in eruptive style—explosive to effusive, sustained to pulsatory—are a common aspect of volcanic activity and present a major challenge to volcano monitoring efforts. A classic example of such transitions is provided by the activity of Mount St. Helens, WA, during 1980, where a climactic Plinian event on May 18 was followed by subplinian and vulcanian eruptions that became increasing pulsatory with time throughout the summer, finally progressing to episodic growth of a lava dome. Here we use variations in the textures, glass compositions and volatile contents of melt inclusions preserved in pyroclasts produced by the summer 1980 eruptions to determine conditions of magma ascent and storage that may have led to observed changes in eruptive activity. Five different pyroclast types identified in pyroclastic flow and fall deposits produced by eruptions in June 12, July 22 and August 7, 1980, provide evidence for multiple levels of magma storage prior to each event. Highly vesicular clasts have H₂O-rich (4.5–5.5 wt%) melt inclusions and lack groundmass microlites or hornblende reaction rims, characteristics that require magma storage at P≥160 MPa until shortly prior to eruption. All other clast types have groundmass microlites; P_H20 estimated from both H₂O-bearing melt inclusions and textural constraints provided by decompression experiments suggest pre-eruptive storage pressures of ∼75, 40, and 10 MPa. The distribution of pyroclast types within and between eruptive deposits can be used to place important constraints on eruption mechanisms. Fall and flow deposits from June 12, 1980, lack highly vesicular, microlite-free pyroclasts. This eruption was also preceded by a shallow intrusion on June 3, as evidenced by a seismic crisis and enhanced SO₂ emissions. Our constraints suggest that magma intruded to a depth of ≤4 km beneath the crater floor fed the June eruption. In contrast, eruptions of July and August, although shorter in duration and smaller in volume, erupted deep volatile-rich magma. If modeled as a simple cylinder, these data require a step-wise decrease in effective conduit diameter from 40–50 m in May and June to 8–12 m in July and August. The abundance of vesicular (intermediate to deep) clast types in July and August further suggests that this change was effected by narrowing the shallower part of the conduit, perhaps in response to solidification of intruded magma remaining in the shallow system after the June eruption. Eruptions from July to October were distinctly pulsatory, transitioning between subplinian and vulcanian in character. As originally suggested by Scandone and Malone (1985), a growing mismatch between the rate of magma ascent and magma disruption explains the increasingly pulsatory nature of the eruptions through time. Recent fragmentation experiments Spieler et al. (2004) suggest this mismatch may have been aided by the multiple levels at which magma was stored (and degassed) prior to these events.Editorial responsibility: J Stix     

On the interaction between cumulus clouds and the larger-scale environment

This article briefly reviews the published and unpublished work carried out by the author and his colleagues during the past few years on the interaction between cumulus clouds and the larger-scale environment. This work has been directed toward: (a) identifying favorable large-scale environments for generation of an organized meso disturbance and (b) investigating the feedback effect of a cumulus ensemble on the large-scale environment. Feedback includes the redistribution of heat and moisture by cumulus clouds in the large-scale atmosphere once a large number of different sized cumuli have developed. Both cumulus clouds over the continental United States and over the tropical oceans are considered in this article and some differences between them are discussed. A number of unsolved questions which the author feels are of importance are raised.     

On the question of cold air production beneath thunderstorm clouds

Studia Geophysica et Geodaetica - При помощи простой модели...     

On the influence of microphysics parametrization on the rainfall rates in numerical models of clouds

Accuracy of formulas for growth by accretion and evaporation of rain in bulk parametrization of these processes for the case of light and moderate precipitation is investigated. It is done by comparison of results from two simple models: with bulk approach and with exact calculations of growth or evaporation of drops in each size bin separately. Growth by accretion is accurately represented in bulk parametrization but rain evaporation is overpredicted. Corrected formula for rain evaporation is suggested.     

Evolution of the Olympus Mons Caldera,Mars

Synoptic images of the Martian volcano Olympus Mons are of a quality and quantity that are unique for mars and, somewhat surprisingly, are appreciably better than image data that exist for many volcanoes on Earth. Useful information about the evolution of shield volcanoes on Earth can thus be derived from the investigation of this extraterrestrial example. We have used shadow-length measurements and photoclinometrically derived profiles to supplement and refine the topographic map of the Olympus Mons caldera. As much as 2.5 km of collapse took place within the 80×65 km diameter caldera and the elevation of the caldera rim varies by almost 2.0 km (low around the oldest collapse events, high around the youngest). An eight-stage evolutionary sequence for the caldera of Olympus Mons is identified which shows that caldera subsidence was a longterm process rather than the near-instantaneous event that has been interpreted from comparable terrestrial examples. Tectonic features on the caldera floor indicate a transition from an extensional environment (graben formation) around the perimeter of the caldera to compression (ridge formation) towards the caldera center. This transition from a compressional to extensional environment is surprisingly sudden, occurs at a radial distance of 17 km from the caldera center, and is import because it can be used to infer that the magma chamber was relatively shallow (thought to be at a depth of <16 km beneath the caldera floor; Zuber and Mouginis-Mark 1990). Ample evidence is also found within the Olympus Mons caldera for solidified lava lakes more than 30 km in width, and for the localzed overturning and/or withdrawal of lava within these lakes.     

On the potential for climate change impacts on marine anthropogenic radioactivity in the Arctic regions

Current predictions as to the impacts of climate change in general and Arctic climate change in particular are such that a wide range of processes relevant to Arctic contaminants are potentially vulnerable. Of these, radioactive contaminants and the processes that govern their transport and fate may be particularly susceptible to the effects of a changing Arctic climate. This paper explores the potential changes in the physical system of the Arctic climate system as they are deducible from present day knowledge and model projections. As a contribution to a better preparedness regarding Arctic marine contamination with radioactivity we present and discuss how a changing marine physical environment may play a role in altering the current understanding pertaining to behavior of contaminant radionuclides in the marine environment of the Arctic region.     

Systematic measurement of the radioactivity of atmospheric precipitation and evaluation of the artificial radioactivity of the atmosphere

Резюме В статье приводится описание методики измерений искусственной радиоактивности осадков. В результате измерений более 90 образцов бЫло доказано, что здесь мЫ имеем дело с искусственной радиоактивностью, вЫзЫваемой наличием продуктов распада образующихся в результате опЫтов с атомнЫм оружием. Доказательством этого служит прежде всего убЫвание активности испарений с временем. Абсолютная оценка показала, что здесь речь идет об активности порядка 10⁻¹⁰–10⁻⁹ кюру/л. в воде осадков. ПроведеннЫе работЫ показали, насколько важнЫми могут бЫть подобнЫе измерения для метеорологических целей, но в особенности для фпзики облаков и осадков.

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Address: Vojenská lékařská akademie J. Ev. Purkynê, Hradec Králové.

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Address: Geofysikální ústav ĈSAV, odd. meteorologie, Hradec Králové 8.     

Influence of natural radioactivity on creep rate

Steady-state creep in the earth's mantle is controlled by the diffusion coefficient and by the distances traveled by defects between sources and sinks. In this paper, we investigate the role played by additional vacancies created by natural radioactivity. According to recent studies, bombardment of solids by energetic particles can act as a perturbation. The resulting strain rate is proportional to the rate of vacancy creation and, contrary to ordinary creep mechanisms, is only weakly dependent on the temperature and the energy necessary to create those vacancies; it is independent of the grain size. The strain rate is of the same order of magnitude as the diffusion mechanism but smaller than the dislocation-climb rate by two to three orders of magnitude. Consequently, the strain rate produced by natural radioactivity does not play a major role in the observed rate of deformation, although it could constitute a lower limit to the creep rate and act as a regulatory mechanism. Furthermore, being less strongly affected by temperature and the vacancy-formation energy than are the other mechanisms, it is also less strongly affected by depth.     

The lobes of lava flows on Earth and Olympus Mons,Mars

The lobate distal margins of lava flows provide a useful source of morphological information on the rheology of the lava if the lobes are assumed to represent the arrest of free-flowing isothermal Bingham fluids on a slope. The widths of lobes are a more useful practical index than lobe thicknesses because they are about an order of magnitude larger and can be more accurately measured from aerial photographs and other remote images. Lobes do not suffer from the changes in morphology that channels undergo during the course of eruptions. A terrestrial data set of flow lobe and ancillary measurements from lavas throughout the range alkali olivine basalt to rhyolite shows some features that are predicted by the isothermal Bingham fluid model. These are correlation of width and thickness over more than two orders of magnitude and essentially no correlation of aspect ratio with slope. There is a positive correlation of lobe width with silica content of the lava. From a data set of measurements on lava flow lobes from the Martian volcano Olympus Mons the mean value of aspect ratio (0.07) was found to be significantly less than that for the terrestrial data set (0.19). Higher general levels of effusion rate on Olympus Mons are probably the factor responsible. After normalisation, lobe widths on Olympus Mons are found to be largely equivalent to those expected for terrestrial flows with andesitic/basaltic silica contents.     

Spectral properties of clouds

Summary In the shortwave region the variations of the spectral properties of clouds are due only to the variations of optical characteristics of water. It results in small variations in the scattering pattern. In the longwave region scattering and absorption are of essentially diffraction character. Results of computation for a typical cloud drop are given; the accuracy of «the layer of precipitated water» method is analysed; thicknesses of cloud layers are investigated when the flux incoming into a cloud gradually deforms into the blackbody radiation flux.

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Effect of remote clouds on surface UV irradiance

Clouds affect local surface UV irradiance, even if the horizontal distance from the radiation observation site amounts to several kilometers. In order to investigate this effect, which we call remote clouds effect, a 3-dimensional radiative transfer model is applied. Assuming the atmosphere is subdivided into a quadratic based sector and its surrounding, we quantify the influence of changing cloud coverage within this surrounding from 0% to 100% on surface UV irradiance at the sector center. To work out this remote clouds influence as a function of sector base size, we made some calculations for different sizes between 10 km × 10 km and 100 km × 100 km. It appears that in the case of small sectors (base size 20 km × 20 km) the remote clouds effect is highly variable: Depending on cloud structure, solar zenith angle and wavelength, the surface UV irradiance may be enhanced up to 15% as well as reduced by more than 50%. In contrast, for larger sectors it is always the case that enhancements become smaller by 5% if sector base size exceeds 60 km × 60 km. However, these values are upper estimates of the remote cloud effects and they are found only for special cloud structures. Since these structures might occur but cannot be regarded as typical, different satellite observed cloud formations (horizontal resolution about 1 km × 1 km) have also been investigated. For these more common cloud distributions we find remote cloud effects to be distinctly smaller than the corresponding upper estimates, e.g., for a sector with base size of 25 km × 25 km the surface UV irradiance error due to ignoring the actual remote clouds and replacing their influence with periodic horizontal boundary conditions is less than 3%, whereas the upper estimate of remote clouds effect would suggest an error close to 10%.     

Identification of eruption clouds with the landsat satellites

Landsat satellite images were selected for the analysis of a tephraladen eruption cloud and a volcanic fume cloud. A 35 km long eruption plume from Sakurazima Volcano, Kyushu, Japan was viewed by the satellite on December 2, 1972. Multispectral Scanner (MSS) band 4 was density sliced into eight levels. Grey levels over the tephra-laden cumulus, which had formed at the terminus of the eruption plume, were distinct from most of the nearby cumulus clouds. MSS band 4 is the key band for identifying eruption clouds in overcast volcanic regions. A lume cloud from Stromboli, Italy was studied in the same manner. It is easily identified over land areas and for 8 km over water in areas of clear sky, but cannot be distinguished from banks of cumulus clouds.     

The electrical conductivity of clouds

Summary A modified Gerdien cell was designed, evaluated, and built for measurement of the polar conductivities in clouds. This conductivity dropsonde was attached to a U.S. Weather Bureau, 1680 mHz, radiosonde for telemetry and to measure pressure, temperature, and relative humidity profiles. The combined instruments were ejected from aircraft, and others were released from balloons into the region of interest.Eight flights were made during the 1967 thunderstorm season. Three of these drops were successful in measuring conductivity inside of electrically active clouds. Two fair-weather profiles were measured for comparison purposes, and three of the drops were faulty.These very preliminary results tend to indicate considerable electrical conductivity in thunderclouds. The data are too few to support a strong statement in favor of increased conductivity, but the instruments were sufficiently reliable to prove that the conductivity was not reduced, as is normally assumed, in the clouds investigated.This research was supported by the Atmospheric Sciences Section, National Science Foundation under Grant GA-701.     

Jet stream clouds in the Middle East

Summary A time cross-section was constructed for Cairo during the period 10–31 Dec. 57. The outstanding feature of this cross-section is the periodic existence of high wind maxima associated with high cloud formation. A method was suggested for the location of high wind centers from the thermal field only. Moreover, the climatological means of high clouds showed quick changes in the period of the Jet Stream migration. This has been taken as an evidence of the relation between the subtropical Jet Stream and high cloud formation in the region.Presented by Prof.M. G. El-Fandy     

Nuclear technique in tracing the cumuli clouds

Summary Within the scopes of Mount Olympus Cumulus Project (sponsored by NATO) which is currently in progress on the summit of Mount Olympus (Hellas), a new method has been applied, with non radioactive tracers, which would become radioactive afterwards by neutron irradiation at the Democritus (Athens) nuclear reactor.To this effect the solution of the tracers (various chemical compounds) was injected into the cumuli clouds by spraying it in the form of small droplets by means of an agricultural sprayer airblast nozzle type. After tracing, samples of the cloud were taken by means of a filter paper connected with a high volume air sampler.