Periods Of Sun Research Articles

Importance of Intermittent Shade to the Ecophysiology of Subalpine Herbs

We report here on the importance of intermittent shade periods for improving water relations and, thus, daily carbon gain in two subalpine understorey herbs. Data on carbon assimilation and plant water status during intermittent sun/shade periods and continuous full sun periods are presented for Arnica latifolia and its congener, Arnica cordifolia. The apparent importance of natural shade periods to the physiological performance and differences in small-scale distribution patterns between the two congeners is discussed

Effects of solar transit in Ku-band VSAT systems

Behavior of networks of very small aperture satellite terminals (VSATs) operating at Ku band during the solar transit period, is compared to more traditional C or Ku-band satellite networks. Based on analyses and experiments, it is explained why solar transit outages are rarer in Ku-band VSAT systems than conventional satellite communications systems. In many cases, Ku-band VSAT systems will operate through periods of Sun transits without any significant increase in transmission error rates or incidences of link outages. >

Solar microbursts at meter-dekameter wavelengths

Microbursts are low-brightness temperature bursts observed by the Clark Lake radioheliograph. The bursts occur several times per hour during quiet Sun periods and are seen at the observing frequencies from 30 to 70 MHz. They are stationary at a given frequency, have short rise times, and durations of 2-10 s. Observations of the bursts are presented and given an interpretation in terms of plasma emmission. The burst properties suggest that they are weak type III bursts. The observations imply that energy releases on the Sun continue to be impulsive, with nonthermal electron distributions, for small releases of energy. The relation of the bursts to type III bursts and hard X-ray bursts are discussed.

Site Microenvironment and Seedling Survival of Shasta Red Fir

ABSTRACT: Distribution of established red fir (Abies magnifica A. Murr.) seedlings in intact stands is generally patchy on a scale of 10-50 m2. We investigated the relationship between site microenvironment and seedling distribution in summer 1982. At each of six sites in the northern California Coast Range, we established two adjoining 36-M2 study plots: a survival (S) plot with germinants and 1to 5-year-old seedlings, and a nonsurvival (NS) plot with germinants only. We examined the plots for differences in soil characteristics, litter depth and composition, soil moisture, insolation patterns and substrate temperatures. We also monitored survival of the 1982 cohort biweekly from emergence in late June until mid-September, and once more in July 1983. Solar tracks superimposed on hemispherical photographs of the canopies revealed that S plots had fewer hours with full sun irradiance throughout the summer. NS plots had long periods of midday sun and significantly higher midday surface temperatures from July to late August. Other microenvironmental factors were not significantly different between plots. The major effect of high surface temperature was probably increased drought stress. Twice the proportion of 1982 seedlings died of desiccation on NS plots as on S plots during the summer drought. This differential mortality maintained the preemergence patchiness. Seedling survival (68 70) was also significantly greater on three -iM2 artificially shaded plots than on three similar plots left exposed to the sun (44 %o).

Modelling of the lower thermosphere: contributions of incoherent scatter observations

The various topics described in this review show the important contribution of Incoherent Scatter soundings to the description, understanding and modelling of the lower thermosphere structure and variations. Indeed the large amount of data gathered since 1965 at the various Incoherent Scatter observatories has permitted major progress in the description and then the modelling of the characteristics of propagating and in situ generated tides in the lower thermosphere; estimates of the amount of energy dissipated by gravity waves have been given from observations of their propagation in the E- and F-region. The vertical distribution and the long-term variations of temperature and concentration of molecular nitrogen have been observed and modelled; an indication has been given that molecular oxygen may be in diffusive equilibrium between 120 and 200 km under lower solar activity conditions but this does not appear to be the case during active sun periods. Finally, theoretical computations of the eddy diffusion coefficient from the modelled temperature and density profiles in the lower thermosphere have revealed a large seasonal variation of this parameter around a mean value of a few 10 6cm 2 s −1.

Short-term temperature variation in needles of Pinussilvestris L.

The temperatures of needles of 10- to 15-year-old trees of Pinussilvestris L. growing in a frost hollow in Sweden were measured with an ultraminiature thermocouple. The measurements were made in the spring of 1977, during days of variable cloudiness. During periods of full sun and very low wind speed the temperature of the needles exceeded that of the surrounding air by 12 to 15 °C.

Time Constants for Thermal Equilibration of Leaf, Canopy, and Soil Surfaces with Change in Insolation1

AbstractExperiments were conducted to determine the time constant for thermal equilibration of a cotton (Gossypium hirsutum L.) plant leaf, the plant canopy, and a soil surface with a change in incident solar radiation (insolation). The time course of surface temperatures sensed by portable radiation thermometers during periods of full sun and artificial shading were the data obtained. The plant leaf and the canopy equilibrated in 40 seconds to 1 minute, but the soil required more than 10 minutes. These results have important implications in interpreting airborne thermal scanner data obtained under partly cloudy sky conditions.

THE ANNUAL VARIATION OF TOTAL OZONE IN THE SOUTHERN HEMISPHERE1

A summary of Southern Hemisphere total ozone measurements made during the quiet sun period of 1960-1965 showed no pronounced changes from the annual variation pattern observed during the preceding active-sun years. Nor was any difference found during 1960-1965 between the annual variation of total ozone in the South Pacific area and the annual trend at other longitudes in the Southern Hemisphere. The present analysis does reemphasize that dissimilarities in the development pattern of the springtime ozone maxima in the Southern and Northern Hemispheres require that the ozone general circulation models be different in the two hemispheres. Following the International Geophysical Year (19571958), several hemispheric and worldwide summaries of the annual and latitudinal variation of to tal ozone mere published. Godson (1960), London (1962), and MacDonald (1963) constructed mean distribution diagrams for the Northern Hemisphere while a month-by-month variation for both hemispheres during the IGY was given by Ramanathan (1961). Kulkarni (1962) studied the distribution of total ozone in the Southern Hemisphere from IGY and pre-IGY observations and compared its pattern to that in the Northern Hemisphere. Dobson (1966) has pointed out the contrasts in the annual variations of ozone between the Arctic and Antarctic Regions as revealed by the intensive observations during the International Quiet Sun Years (1964-1965). The present study is an analysis of the Southern Hem

SYNOPTIC ANALYSES OF THE 5-, 2-, AND 0.4-MILLIBAR SURFACES FOR THE IQSY PERIOD

Rocket data from the Meteorological Rocket Network and other sources, in addition to high-level rawinsonde observations, are being employed to analyze a series of 5-, 2-, and 0.4-mb. charts. The broadscale analyses are being constructed for each week of the International Years of the Quiet Sun period, and primarily cover the North American and adjacent ocean areas. Methods employed for processing the various types of data as well as the analysis procedure are described. Analyses completed thus far confirm the existence of large-scale systems, such as the wintertime polar cyclone, and the Aleutian anticyclone, to at least the level of the stratopause. In addition there is evidence of large-scale periodic oscillations in the heights of upper-stratospheric constant-pressure surfaces during autumn and early winter. Furthermore, a significant tidal component is apparent in summertime rocketsonde winds, for which adjustment must be made in order to obtain consistent quasi-synoptic patterns.

Magnetic damping of rotation as a factor in stellar evolution.

view Abstract Citations (3) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Magnetic damping of rotation as a factor in stellar evolution. Wilson, Raymond H., Jr. Abstract A thin ring of conducting matter rotating in a magnetic field about an axis in its plane experiences a braking couple given by a well-known function of the area of the ring, its inductance, resistance, and angular velocity, and the effective strength of the magnetic field. Integrating this as an element of a conducting sphere leads to the approximate formula for its angular velocity co as function of time tin seconds: ~p1H2 log5-~1 = (I - to). p Here j (cgs, EMU) is the conductivity of the sphere, p its magnetic permeability, and p its density, while H is the external magnetic field strength in gauss. Such magnetic damping would tend to reduce rotation of all celestial objects in a magnetic field. As explained by Chandrasekhar and Fermi (1953) all present evidence indicates a magnetic field of 7 X 10-6 gauss in the sun's galactic region, due to motions of the ionized galactic plasma. The action of this field on a star like the sun depends partly on its conductivity. A reasonable estimate of the effective conductivity of the sun would be the logarithmic' mean between center and photosphere: (T = 10-6 cgs EMU (Spitzer 1954). Then by the above formula we may derive the sun's period of rotation at, say, 1o = 5 X I& yr. = 1.6 X 1017 sec. ago. Its mean density in this interval could be estimated as perhaps half that at present = 0.7. Assuming the galactic field to have remained constant, the effective component would be about 4 X 10-6 gauss. The result is that loge (coo/ii') = 3.7 so that the rotation period at to would have been 25/40 day = 15 hours. This is on the order of rotational velocities of young stars of early main- sequence type, from which, presumably, the sun and other similar stars have evolved (Struve 1950). Since the conductivity of a star with increasing depth below the photosphere seems to increase more rapidly than its density, the rotation of the interior would be slowed down more rapidly than that of its surface. A result for a fluid or partly fluid sphere would be turbulence, and more rapid rotation at the equator, such as is observed on the sun and the planet Jupiter. In planetary systems and double stars the action of any magnetic fields belonging to the separate members would add its effect to that of the general galactic field. For instance, in the case of close spectroscopic binary stars (Struve 1950), the total effective field might be on the order of 10-i gauss. Assuming other data as above, except the conductivity like that of the solar photosphere, I0-~ cgs EMU, the time required for reduction of rotation by a factor of 100 turns out to be I0~ years. This is the age estimated for such early-type stars (Struve 1950). Thus the theory of magnetic damping alone could possibly explain the abnormally slow rotation of such binary stars compared to that of single stars of the same age. Struve, 0. 1950, Stellar Evolution (Princeton Univ. Press), pp. 130, 83, 244. Chandrasekhar, S. and Fermi, E. 1953, Ap. J. ii8, 113. Spitzer, L. 1954, Smithsonian Physical Tables, p. 502. Naval Research Laboratory, Washington, D. C. Publication: The Astronomical Journal Pub Date: May 1956 DOI: 10.1086/107420 Bibcode: 1956AJ.....61R.193W full text sources ADS |

THE PRESENTATION OF POLLEN IN CERTAIN ANGIO‐SPERMS AND ITS COLLECTION BY APIS MELLIFERA

While investigating the pollen income of a hive of honey bees (Apis mellifera) it was found that some pollen types were collected in abundance, while others were collected rarely or not at all. Moreover, different pollens were collected at different times of the day, and the peak periods in the collection from different species varied strikingly. The first evidence that pollen production and pollen collection were connected was advanced by Synge (I947). The present work is a continuation of the author's previous studies (Percival, I950, I95I). Methods. A small number of plants or, in the case of trees and shrubs, branches was selected. Every flower opening thereon was observed, so that each day a population of flowers in all stages of anthesis was available for examination. The plants were observed throughout the whole, or major part, of their flowering, if this was possible. In some cases the observations were continued in successive seasons. The species usually revealed its rhythm of pollen presentation within a couple of days, but the observations were continued to obtain information on the effect of weather conditions upon it. The unit observed was the 'flower form', whether inflorescence or single flower, but the distinction broke down occasionally, e.g. the inflorescence of Prunus laurocerasus might be taken as the flower form, but observations were also made on the separate flowers. Counts of stamens presenting pollen were taken at hourly intervals if possible. Certain crops (e.g. the Legumes) present their pollen in the bud, so the number of flowers reaching a stage of opening at which the bee could exploit them was noted instead. The opening and closing of the flowers was noted if it occurred within the period of foraging. The data of pollen collection by the bees was taken at the hive or on the crops. All the crops grew near the hives, so any effect of distance on collection could be discounted. Temperature and relative humidity were measured by means of a whirling hygrometer. Periods of sun, rain or overcast were recorded, but air movement was not. Time of presentation of pollen. Most of the species so far studied produce pollen throughout the period 7 a.m.-5 p.m., but the peak period of pollen presentation differs widely (Table i). The longest period of presentation is seen in Helleborus abchasicus, where it is continuous day and night. Aesculus hippocastanum, Pyrus communis, Prunus laurocerasus and