Observations of hysteresis in solar cycle variations among seven solar activity indicators

We show that smoothed time series of 7 indices of solar activity exhibit significant solar cycle dependent differences in their relative variations during the past 20 years. In some cases these observed hysteresis patterns start to repeat over more than one solar cycle, giving evidence that this is a normal feature of solar variability. Among the indices we study, we find that the hysteresis effects are approximately simple phase shifts, and we quantify these phase shifts in terms of lag times behind the leading index, the International Sunspot Number. Our measured lag times range from less than one month to greater than four months and can be much larger than lag times estimated from short-term variations of these same activity indices during the emergence and decay of major active regions. We argue that hysteresis represents a real delay in the onset and decline of solar activity and is an important clue in the search for physical processes responsible for changing solar emission at various wavelengths. The High Altitude Observatory is sponsored by the National Science Foundation.     

PSF-fitting techniques for crowded field 3D spectroscopy

From a historical point of view, it was only through the advent of the CCD as a linear, high dynamic range panoramic detector that it became possible to overcome the source confusion problem for stellar photometry, e.g., in star clusters or nearby galaxies. The ability of accurately sampling the point-spread-function (PSF) in two dimensions and to use it as a template for fitting severely overlapping stellar images is of fundamental importance for crowded-field photometry, and has thus become the foundation for the determination of accurate color-magnitude diagrams of globular clusters and the study of resolved stellar populations in nearby galaxies. Analogous to CCDs, the introduction of integral field spectrographs has opened a new avenue for crowded-field 3D spectroscopy, which benefits in the same way from PSF-fitting techniques as CCD photometry does. This paper presents first experience with sampling the PSF in 3D spectroscopy, reviews the effects of atmospheric refraction, discusses background subtraction problems, and presents several science applications as obtained from observations with the PMAS instrument at Calar Alto Observatory.     

The last Scandinavian Ice Sheet in northwestern Russia: ice flow patterns and decay dynamics

Advance of the Late Weichselian (Valdaian) Scandinavian Ice Sheet (SIS) in northwestern Russia took place after a period of periglacial conditions. Till of the last SIS, Bobrovo till, overlies glacial deposits from the previous Barents and Kara Sea ice sheets and marine deposits of the Last Interglacial. The till is identified by its contents of Scandinavian erratics and it has directional properties of westerly provenance. Above the deglaciation sediments, and extra marginally, it is replaced by glaciofluvial and glaciolacustrine deposits. At its maximum extent, the last SIS was more restricted in Russia than previously outlined and the time of termination at 18-16 cal. kyr BP was almost 10 kyr delayed compared to the southwestern part of the ice sheet. We argue that the lithology of the ice sheets' substrate, and especially the location of former proglacial lake basins, influenced the dynamics of the ice sheet and guided the direction of flow. We advocate that, while reaching the maximum extent, lobe-shaped glaciers protruded eastward from SIS and moved along the path of water-filled lowland basins. Ice-sheet collapse and deglaciation in the region commenced when ice lobes were detached from the main ice sheet. During the Lateglacial warming, disintegration and melting took place in a 200-600 km wide zone along the northeastern rim of SIS associated with thick Quaternary accumulations. Deglaciation occurred through aerial downwasting within large fields of dead ice developed during successively detached ice lobes. Deglaciation led to the development of hummocky moraine landscapes with scattered periglacial and ice-dammed lakes, while a sub-arctic flora invaded the region.     

The Earth's rotation and atmospheric circulation, from 1963 to 1973

Summary. The zonal angular momentum of the atmospheric circulation has been evaluated month-by-month and compared with astronomical observations of the length-of-day for the 10 years from 1963 May to 1973 April. The reason for undertaking this study is to enable the astronomical observations to be 'corrected' for the zonal wind effect and to investigate the residual excitation function for solid-Earth contributions. The principal conclusions reached are the following: (i) The annual change in length-of-day is almost entirely due to the seasonal changes in the zonal circulation with tidal, oceanographic and hydrologic phenomena contributing together at most 10 per cent of the total excitation, (ii) The semi-annual term is predominantly due to the zonal wind and the body tide, with oceanic and hydrologic terms contributing about 10 per cent, (iii) The atmospheric circulation plays a dominant role in length-of-day changes in the period range from 1 to about 4 yr. This is partly associated with the quasi-biennial oscillation and its harmonics. Both the period and amplitude of these fluctuations are very variable, (iv) At longer periods the atmosphere may still contribute to the total excitation but other excitation functions begin to rise above the spectrum of the meteorological excitation, (v) At periods less than about 1 yr the atmospheric excitation is dominant, and while the presence of other excitation functions cannot be excluded, they cannot exceed 20 per cent of the wind excitation. On the basis of these results the astronomical record from 1962 to 1978 has been 'corrected' for the meteorological 'noise'. The residual excitation exhibits only fluctuations on a time-scale of about 5 yr and longer and it is this result that must be attributed to core-mantle interactions or to other solid-Earth excitation functions.