Outline of a theory of solar wind interaction with the magnetosphere

Some new ideas on the interaction of the solar wind with the magnetosphere are brought forward. The mechanism of reflection of charged particles at the magnetopause is examined. It is shown that in general the reflection is not specular but that a component of momentum of the particle parallel to the magnetopause changes. A critical angle is derived such that particles whose trajectories make an angle less than it with the magnetopause enter the magnetosphere freely, so transferring their forward momentum to it. Spatially or temporally non-uniform entry of charged particles into the magnetosphere causes electric fields parallel to the magnetopause which either allow the free passage of solar wind across it or vacuum reconnection to the interplanetary magnetic field depending on the direction of the latter. These electric fields can be discharged in the ionosphere and so account qualitatively for the dayside agitation of the geomagnetic field observed on the polar caps. The solar wind wind plasma which enters the magnetosphere creates (1) a dawn-dusk electric field across the tail (2) enough force to account for the geomagnetic tail and (3) enough current during disturbed times to account for the auroral electrojets. The entry of solar wind plasma across the magnetosphere and connection of the geomagnetic to interplanetary field can be assisted by wind generated electric field in the ionosphere transferred by the good conductivity along the geomagnetic field to the magnetopause. This may account for some of the observed correlations between phenomena in the lower atmosphere and a component of magnetic disturbance.     

Petrographic and trace element analysis of uranium-rich tufa calcite, middle Miocene Barstow Formation, California, USA

An integrated petrographic and spectroscopic (X‐ray diffraction, phosphor imaging and synchrotron X‐ray absorption spectroscopy) study of tufas from the Miocene Barstow Formation, California, relates sample morphology, mineralogy and geochemical composition. The tufas, composed mainly of calcite that formed at the interface between an ancient alkaline lake and ground or spring waters, have textures similar to those of microbially mediated terrestrial stromatolites and travertines. The tufas have elevated concentrations of a number of trace elements including Mn, Fe, Sr and U. Synchrotron X‐ray fluorescence analyses show that U concentrations can exceed 500 p.p.m. X‐ray absorption spectroscopy indicates that the U in these samples is incorporated as U(IV). It is suggested here that alkaline lake waters had a high U/Ca ratio and tufa calcite formed where groundwater or (possibly epithermal) springs brought in Ca and trace elements such as Sr. The rapid, and possibly microbially mediated, precipitation of calcite allowed for incorporation of high concentrations of trace metals as either structural substitutes or extremely fine‐scale inclusions.     

Long-term temperature trends of the Hudson River: A study of the historical data

Water temperature data from the Hudson River at Poughkeepsie from 1908 to the present were acquired. This long-term data set contains (with a few gaps) daily water temperatures at a constant location for the 82-yr period. We hypothesized that water temperatures, because of the dampened variability as compared to air temperatures, would provide a useful record of long-term temperature change. The data were analyzed for statistically significant trends, both annually and monthly for long-term and 10-yr blocks; both warming and cooling trends within all categories were found. The longest significant trend was a 0.12°C per decade increase from about 1920 to 1990. This increase, which was statistically significant for both simple regression and time-series analysis, is within the limits of the suggested rates of change on the global scale. On the other hand, there was no significant trend from the beginning of the record (1908) to the present, due to an apparent dramatic cooling from 1908 to about 1920.     

Holocene variations in the Asian monsoon inferred from the geochemistry of lake sediments in central Tibet

We present a record of monsoon variations for the early and middle Holocene that is inferred from the geochemistry of sediment cores from Ahung Co, a lake in central Tibet. The resolution of this record is better than 50 yr and the age model is derived from radiocarbon ages of terrestrial charcoal, which eliminates errors associated with the lake hard-water effect. We made down-core geochemical measurements of % carbonate, % organic carbon, C/N and δ¹³C of bulk organic matter, δ¹³C and δ¹⁸O of carbonate, and % dolomite. Proxy calibration and modern water-balance reconstruction show that these are proxies for lake depth and the amount of monsoon precipitation. We find that lake level and monsoon precipitation have been decreasing at Ahung Co since the early Holocene (∼7500 cal yr B.P.). Superimposed on this trend are rapid declines in monsoon rainfall at 7000-7500 and 4700 cal yr B.P. and seven century-scale wet-dry oscillations. The cores do not contain sediment from the last ∼4000 yr. Surface sediments from the lake accumulated during the 20th century, however. From this, we argue that lake levels have risen again recently following a late Holocene dry period.