ALBERT

Beschreibung: Measurements of velocity fluctuations u (axial) and v (radial) and temperature fluctuations θ averaged over the turbulent zone have been made in a turbulent heated jet with a co-flowing stream and compared with the conventionally averaged results. The zone-averaged mean temperature and temperature fluctuation intensity appear to be nearly homogeneously distributed in the outer, intermittent region of the jet. This homogeneity does not apply to the u and v fluctuations. The flatness factor of the temperature within the turbulent part of the flow is remarkably constant throughout the intermittent region. Although the skewness of the turbulent θ fluctuations is non-zero, it is smaller than the skewness of the turbulent u and v fluctuations. The average [Formula ommited] of the heat flux over the turbulent zone increases in the intermittent region whereas the zone-averaged momentum flux [Formula ommited] and zone-averaged heat flux [Formula ommited] continuously decrease. This leads to the Prandtl number of the turbulent fluid being smaller than the conventional Prandtl number in the outer part of the flow. A budget for the square of the temperature fluctuations within the turbulent part of the flow indicates a constant distribution of temperature dissipation. The transport of heat by the large-scale structure of the flow is briefly discussed in the light of available experimental information on other turbulent shear flows. © 1975, Cambridge University Press. All rights reserved.

Beschreibung: The net surface snow accumulation on the Antarctic ice sheet is determined by a combination of precipitation, sublimation and wind redistribution. We present a 1 year record of hourly snow-height measurements that shows its seasonal variability. The measurements were made with an ultrasonic sensor mounted on an automatic weather station (AWS) installed at LGB69, Princess Elizabeth Land, Antarctica (70.835˚S, 77.075˚E; 1850 ma.s.l.). The average accumulation at this site is approximately 0.70 m snow a–1. Throughout the winter, between April and September, there was little change in surface snow height. The strongest accumulation occurred during the period October–March, with four episodic increases occurring during 2002. These episodic events coincided with obvious humidity ‘pulses’ and decreases of incoming solar radiation as recorded by the AWS. Observations of the total cloud amount at Davis station, 160 km north-northeast of LGB69, showed good correlation with major accumulation events recorded at LGB69. There was an obvious anticorrelation between the lowest cloud height at Davis and the daily accumulation rate at LGB69. Although there was no correlation over the total year between wind speed and accumulation at LGB69, large individual accumulation events are associated with episodes of strong wind. Strong accumulation events at LGB69 are associated with major storms in the region and inland transport of moist air masses from the coast.

Beschreibung: Early auroral observations recorded in various oriental histories are examined in order to search for examples of strictly simultaneous and indisputably independent observations of the aurora borealis from spatially separated sites in East Asia. In the period up to ad 1700, only five examples have been found of two or more oriental auroral observations from separate sites on the same night. These occurred during the nights of ad 1101 January 31, ad 1138 October 6, ad 1363 July 30, ad 1582 March 8 and ad 1653 March 2. The independent historical evidence describing observations of mid-latitude auroral displays at more than one site in East Asia on the same night provides virtually incontrovertible proof that auroral displays actually occurred on these five special occasions. This conclusion is corroborated by the good level of agreement between the detailed auroral descriptions recorded in the different oriental histories, which furnish essentially compatible information on both the colour (or colours) of each auroral display and its approximate position in the sky. In addition, the occurrence of auroral displays in Europe within two days of auroral displays in East Asia, on two (possibly three) out of these five special occasions, suggests that a substantial number of the mid-latitude auroral displays recorded in the oriental histories are associated with intense geomagnetic storms.Key words. Magnetospheric physics (auroral phenomena; storms and substorms)

Beschreibung: The earliest known drawing of sunspots appears in The Chronicle of John of Worcester, which was compiled in the first half of the twelfth century. In this medieval chronicle, the Latin text describing the sunspots is accompanied by a colourful drawing, albeit idealised, which shows the apparent positions and sizes of two sunspots on the solar disk. The date of this observation of sunspots from Worcester, England is firmly established as AD 1128 December 8. Assuming that the drawing was prepared fairly carefully, the angular diameters of the two sunspots are at least about 3 arcmin and 2 arcmin in the northern and southern hemispheres, respectively. Similarly, the heliographic latitudes of both sunspots are within the approximate range of 25°–35°. About five days after this observation of sunspots on the solar disk, on the night of AD 1128 December 13, a red auroral display was observed from Songdo, Korea (the modern city of Kaesong). This auroral observation was recorded in the Koryo-sa, the official Korean chronicle of the period. In addition, five Chinese and five Korean descriptions of auroral displays were recorded in various East-Asian histories between the middle of AD 1127 and the middle of AD 1129. The ten oriental auroral records in this particular interval correspond to six distinct auroral events, which provide evidence for recurrent, though possibly intermittent, auroral activity on a timescale almost exactly equal to the synodic-solar-rotation period (approximately 27 days). The six distinct auroral events were apparently associated with two series of recurrent geomagnetic storms, both of which were sufficiently intense to produce mid-latitude auroral displays in East Asia. These ancient solar and auroral observations are interpreted in terms of present-day understanding of solar-terrestrial physics. Con-temporary ground-based and satellite measurements during the last few decades have indicated that recurrent geomagnetic storms are usually a feature of the declining phase of the solar cycle. In addition, the strength of such recurrent geomagnetic storms has been classified as moderate rather than intense. The recurrent geomagnetic storms occurring during the interval AD 1127–1129 must have been sufficiently intense to produce mid-latitude auroral displays over China and Korea, some of which appeared or extended south of the observing site. This last statement remains true even after proper allowance is made for the fact that during the twelfth century, the north geomagnetic pole was probably situated at the usual high geographic latitude, but in the same geographic longitude range as East Asia. Therefore, it may be inferred that the two series of intense recurrent geomagnetic storms occurred near a medieval maximum in the "eleven-year" solar cycle. Moreover, the overall level of solar activity appears to have been especially high at the end of the second decade of the twelfth century.b〉Key words. Magnetospheric physics (auroral phenomena; storms and substorms) – Solar physics, astrophysics and astronomy (photosphere and chromosphere)