Formation of turions, the vegetative perennation organs, plays an important role in the survival strategy of Spirodela polyrhiza (L.) Schleiden. Turion formation [quantified as number of turions formed per frond; specific turion yield (SY)] was investigated in 27 clones collected from a wide geographical range. The Pearson correlation was tested with (1) duration of growing season (monthly average temperature of ≥10°C), (2) relative growth rate of the fronds, (3) longitude and latitude, and (4) several climatic parameters, in all possible single and multiple regressions. All single coefficients of determination were below 0.10. The highest correlation (R(2) = 0.61; adjusted for the number of explaining variables 0.54) was found in a multiple linear regression with the following five parameters: average temperatures over the year and during the growing season, duration of the growing season and precipitation over the year and during the growth period. All these parameters were shown to have significant contributions. This equation was used successfully to predict the SY of five newly isolated clones. Finally, on the basis of all 32 clones the following conclusions were drawn: The mean annual temperature has the highest impact. It is suggested that lower temperatures decrease the survival rate of turions and that adaptation refers to increasing SY. The different levels of SY in the clones (ranging from SY = 0.22 to 5.9) were detected even after several years of in vitro cultivation. It is therefore assumed that these adaptations to the climatic conditions are genetically determined.

S U M M A R YThe length of day and the geomagnetic field are clearly correlated over decadal periods (10-100 yr). Provided the electrical conductivity of the lower mantle is sufficiently high, a considerable part of this correlation can be explained by electromagnetic core-mantle coupling. Investigating the associated core-mantle coupling torque and fluid velocity fields near the core surface, as well as the interpretation of the observed time lag between length of day and geomagnetic field variations requires the calculation of the temporally variable magnetic field near both sides of and on the core-mantle boundary by solving the magnetic induction equation. Such a solution presents a downward field continuation that has a non-harmonic character if the electrical conductivity is accounted for.In this paper the Earth's mantle is assumed to be a two-layer spherical shell, whose inner layer is electrically conductive. We only consider the poloidal part of the magnetic field with boundary values that are conventionally given by a spherical harmonic expansion of the observed geomagnetic potential field at the Earth's surface. Thus, we are concerned with a one-side-data supported problem, analogous to the inverse heat conduction problem (or sideways heat equation problem), well-known as an ill-posed inverse boundary value problem for a parabolic partial differential equation (diffusion equation).We develop a several-step solution procedure for this inverse problem in its integral form and use a special regularization method for the final solution. The capabilities of this downward continuation method (which includes varying the mantle conductivity model, quality of data approximation in the regularization and two different depths) are presented and discussed in comparison with the perturbation approach and the usual harmonic downward continuation. The data series used are the single magnetic field components (Gauss coefficients) of the spherical harmonic field expansion (Bloxham & Jackson 1992, J. geophys. Res., 97, 19 537-19 563) beginning from the year 1840 to 1990. In addition, to investigate the spectral effects (changing amplitudes, phase shifting), an artificial data series is used.The main result is the downward continuation of the radial component of a global (8,8) field onto the core-mantle boundary, produced using the different methods and for the two epochs, 1910 and 1960. Comparing the results with the perturbation solution reveals temporally and locally variable differences up to the order of 5000 nT, while the difference to the harmonic downward continuation amounts to 15000 nT.

[1] The inner core wobble (ICW) is a normal mode of rotation of the inner core relative to the mantle predicted theoretically. While many papers have been devoted to its theoretical formulation, no attempt of its detection has been published in the literature. In this work, we first give a preliminary formulation for the variations of gravity and geopotential coefficients associated with the ICW that complements the formulation for the polar motion. The results show that the ICW is most likely detectable using polar motion data. Then we attempt to detect the ICW by comparing the spectrum of an Earth orientation parameter time series with that of the sum of an oceanic angular momentum time series and an atmospheric angular momentum time series. We found no firm evidence of the ICW using our approach to a resolvability of a few milliarc seconds. At such a low amplitude in polar motion, the ICW is far below the current detectability of the variations of gravity measured by absolute and superconducting gravimeters and of the variations of the geopotential coefficients obtained from the Gravity Recovery and Climate Experiment (GRACE).Citation: Guo, J. Y., H. Greiner-Mai, and L. Ballani (2005), A spectral search for the inner core wobble in Earth's polar motion,

Abstract.It is well known that two close spectral peaks with comparable amplitudes exist in the Chandler wobble (CW) band in the observed polar motion spectrum during the first half of the past century. However, it is not generally accepted that the CW is an oscillation with two closely lying frequencies, and some authors attribute the appearance of these two peaks to some unusual phase variation (180• shift) of the CW during 1920s-1930s. In this note, the phase variation of the CW is explored using the longest Earth orientation parameter (EOP) time series currently available-the International Earth Rotation and Reference System Service (IERS) EOP-C01 from 1846 to 2003. The observation time series mainly containing the CW obtained by removing the annual wobble (AW) from the original EOP time series is compared with a synthetic double frequency CW times series constructed using the frequencies, amplitudes and initial phases of the two peaks precisely determined using spectral analysis. The result shows reasonable agreement between their peak times, a feature not shown before. This feature is in agreement with the hypothesis of a double frequency CW. While the result shown here is inconclusive that the CW really has two frequencies, this note is expected to serve as a reminder for its renewed interest.

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