Analysis of decade-long time series of GPS-based polar motion estimates at 15-min temporal resolution

We present results from the generation of 10-year-long continuous time series of the Earth’s polar motion at 15-min temporal resolution using Global Positioning System ground data. From our results, we infer an overall noise level in our high-rate polar motion time series of 60 \(\upmu \hbox {as}\) (RMS). However, a spectral decomposition of our estimates indicates a noise floor of 4 \(\upmu \hbox {as}\) at periods shorter than 2 days, which enables recovery of diurnal and semidiurnal tidally induced polar motion. We deliberately place no constraints on retrograde diurnal polar motion despite its inherent ambiguity with long-period nutation. With this approach, we are able to resolve damped manifestations of the effects of the diurnal ocean tides on retrograde polar motion. As such, our approach is at least capable of discriminating between a historical background nutation model that excludes the effects of the diurnal ocean tides and modern models that include those effects. To assess the quality of our polar motion solution outside of the retrograde diurnal frequency band, we focus on its capability to recover tidally driven and non-tidal variations manifesting at the ultra-rapid (intra-daily) and rapid (characterized by periods ranging from 2 to 20 days) periods. We find that our best estimates of diurnal and semidiurnal tidally induced polar motion result from an approach that adopts, at the observation level, a reasonable background model of these effects. We also demonstrate that our high-rate polar motion estimates yield similar results to daily-resolved polar motion estimates, and therefore do not compromise the ability to resolve polar motion at periods of 2–20 days.     

A meteorological 80-m tower near Rotterdam

Construction, observation site and instrumentation are described of an 80-m meteorological observation tower, erected in Vlaardingen, The Netherlands, for studies in connection with air pollution problems along the Nieuwe Waterweg. From measurements made regularly in the period April 1967–April 1968 summaries are given of wind profile parameters and gustiness averages. Case histories are presented of an air pollution episode lasting several days, and of an hourly average wind direction difference of 120 ° over 70 m.     

A Technique of Rainfall Assimilation for Dynamic Extended Range Monsoon Prediction

Summary ?A methodology has been developed to assimilate satellite-measured rainfall during the initial phase of model integration for extended range monsoon prediction. The vertical profiles of latent heating corresponding to different rain rates have been derived from the model statistics. These heating rates have been assimilated through nudging in the thermodynamics equation of the model. This procedure of assimilating observed heating has corrected the simulation of heating location in the model and consequently removed the anomalous sinking motion over Indian landmass. With the correction of vertical circulation, both mean July rainfall over India and the distribution have improved. Interannual variability has been brought out for the years 1987 and 1988. In view of the availability of rainfall profile from Tropical Rain Measuring Mission (TRMM) there is a scope of adopting this method of assimilating observed rainfall, for extended range monsoon prediction. Received February 12, 1999/Revised May 4, 1999     

Modeling Forest Emissivity at L-Band and a Comparison With Multitemporal Measurements

This letter describes recent advances in modeling forest emissivity at L-band. The formulation is based on a previously developed discrete model and includes a new representation of forest litter. Comparisons with multitemporal radiometric data collected in the framework of the ldquoBray 2004rdquo experiment, which was carried out within Les Landes forest, are shown and discussed. Input variables are given by using detailed ground measurements. In general, the model reproduces both absolute values and temporal variations of measured brightness temperature. The contribution of the litter to overall emission was found to be important.     

Boron incorporation into mullite

Summary Boron-doped mullites were synthesized using aluminium nitrate-nonahydrate, tetraethoxysilane and boric acid in a sol–gel process with subsequent annealing at 950 and 1300 °C for five hours. Two different bulk compositions with constant Al₂O₃ contents (60 and 70 mol%, respectively) and varying SiO₂ plus B₂O₃ contents were investigated. X-ray powder diffraction analyses yielded a linear decrease of the lattice parameters with increasing bulk B₂O₃ content, which was interpreted as to be due to boron incorporation. Related to the increasing boron content, corresponding infrared spectra revealed a slight and continuous shift for most of the absorption bands. These data show that mullite is able to incorporate large amounts of boron into its structure (up to about 20 mol% B₂O₃ depending on the bulk composition of the starting materials). Infrared analyses suggest that boron is incorporated into the mullite structure in form of planar three-fold coordinated BO₃ groups. Author’s address: A. Beran, Institut für Mineralogie und Kristallographie, Universit?t Wien-Geozentrum, Althanstra?e 14, 1090 Wien, Austria     

Chandra measurements of the X-ray core and cluster of 3C 220.1

We report results of an 18-ks exposure with the ACIS instrument on Chandra of the powerful z =0.62 radio galaxy 3C 220.1. The X-ray emission separates into cluster gas of emission-weighted kT ∼5 keV , 0.7–12 keV luminosity (to a radius of 45 arcsec) of 5.6×10⁴⁴ erg s⁻¹ and unresolved emission (coincident with the radio core). While the extended X-ray emission is clearly thermal in nature, a straightforward cooling-flow model, even in conjunction with a point-source component, is a poor fit to the radial profile of the X-ray emission. This is despite the fact that the measured properties of the gas suggest a massive cooling flow of ∼130 M_⊙ yr⁻¹, and the data show weak evidence for a temperature gradient. The central unresolved X-ray emission has a power-law spectral energy index α ∼0.7 and 0.7–12 keV luminosity of 10⁴⁵ erg s⁻¹, and any intrinsic absorption is relatively small. The two-point spectrum of the core emission between radio and X-ray energies has α _rx=0.75 . Since this is a flatter spectrum than seen in other sources where the X-ray emission is presumed to be radio-related, regions close to the active galactic nucleus (AGN) in this source may dominate the central X-ray output, as is believed to be the case for lobe-dominated quasars. Simple unification models would be challenged if this were found to be the case for a large fraction of high-power radio galaxies.     

Turbulent flows over mountainous terrain modelled by the Reynolds equations

A numerical model based upon fundamental principles, a standard (k, ) turbulence closure and a finite element integration technique, is applied to separated flows over hills. Predictions are compared to experimental data from a wind tunnel. Although few-equation turbulence closures have been shown to have obvious deficiencies with respect to comparable flows, the model predicts remarkably accurately, without coefficient adjustments of any kind. Even the turbulent intensity is predicted quite realistically.