Fluctuations In Length Of Day Research Articles

Element Cycling in Taiga Forests: State-Factor Control

ronment characterized by drastic seasonal fluctuations in day length and temperature, a short growing season, low soil temperatures, and permafrost (Van Cleve and Alexander 1981). The taiga is part of the circumpolar forest region near the latitudinal limit of tree growth. The taiga occupies large areas of Alaska, Canada, Scandinavia, and the Soviet Union (Van Cleve and Alexander 1981). With changing climate, ecological relationships within the taiga could assume global importance, because this region contains 20% of the world's stored carbon and is a large but unexplored source of methane and carbon dioxide, two gases implicated in causing climate change (Billings 1987, McBeath 1984, Reeburgh 1990). Flux rates of these gases are expected to change An understanding of taiga ecosystem controls is important for predicting global responses to climate change

A spectral analysis of the Earth's angular momentum budget

Changes in the circulation of the earth's atmosphere cause fluctuations in the length of day (LOD) by exchanging angular momentum with the surface of the earth. In this paper we examine the earth's polar angular momentum budget using earth rotation data from optical astrometry and lunar laser ranging together with simultaneous estimates of the atmospheric angular momentum Matm derived from meteorological data. The atmospheric excitation can explain most of the observed LOD fluctuations at periods between 700 and 40 days. The observed Matm spectral power is proportional to the inverse frequency squared for periods between 1 year and 3 days and flattens out at higher frequencies. The LOD and Matm spectra are very similar except at periods of <40 days, where the LOD measurement noise dominates. The Matm ‐ LOD coherence is highly significant between periods of 700 and 40 days. There is no evidence for phase shifts between the Matm and LOD data at periods between 600 and 40 days. A broad peak is clearly evident at periods of 40–60 days in the spectra of all three time series. The LOD data have a long‐term drift, not matched by the Matm data, that is probably the result of a core‐mantle angular momentum exchange. There are significant imbalances in the angular momentum budget. Most of the seasonal imbalance can be attributed to the effects of systematic errors in the meteorological data, but some of this discrepancy may be caused by exchanges of angular momentum with the oceans. The semiannual, monthly, and fortnightly tidal variations in the earth rotation were detected, and the observed amplitudes of these variations are consistent with theoretical estimates.

Spectral line similarity in the geomagnetic dipole field variations and length of day fluctuations

Power spectral density analysis using Burg's maximum entropy method (MEM) was applied to the geomagnetic dipole field and its rate of change for the years 1901-1969. Both spectra indicate relative maxima at 0.015 cycle/yr and its harmonics. These maxima correspond approximately to 66-, 33-, 22-, 17-, 13-, 11-, and 9-year spectral lines. The application of the same analysis techniques to the length of day (l.o.d.) fluctuations for the period 1865-1961 reveals similar spectral characteristics. The existence of the common spectral peaks with periods of 66 and 33 years in the l.o.d. fluctuations and the geomagnetic dipole field is clearly established. The existence of the higher harmonics is somewhat uncertain because of the line-splitting problem in the MEM spectral analysis. It is suggested that the spectral line similarity in the l.o.d. fluctuations and the dipole field variations is related to the motion within the earth's fluid core during the past 100 years.

Seasonal changes in reproductive productivity, growth rate, and food intake in mice exposed to different regimes of day length and environmental temperature.

Groups of mice were maintained in three different environments: (1) constant day length and constant temperature; (2) seasonal fluctuations in day length and constant temperature; (3) seasonal fluctuations in day length and seasonal fluctua-tions in temperature.