The NTHMP Tsunameter Network

A tsunameter (soo-NAHM-etter) network has been established in the Pacific by the National Oceanic and Atmospheric Administration. Named by analogy with seismometers, the NOAA tsunameters provide early detection and real-time measurements of deep-ocean tsunamis as they propagate toward coastal communities, enabling the rapid assessment of their destructive potential. Development and maintenance of this network supports a State-driven, high-priority goal of the U.S. National Tsunami Hazard Mitigation Program to improve the speed and reliability of tsunami warnings. The network is now operational, with excellent reliability and data quality, and has proven its worth to warning center decision-makers during potentially tsunamigenic earthquake events; the data have helped avoid issuance of a tsunami warning or have led to cancellation of a tsunami warning, thus averting potentially costly and hazardous evacuations. Optimizing the operational value of the network requires implementation of real-time tsunami forecasting capabilities that integrate tsunameter data with numerical modeling technology. Expansion to a global tsunameter network is needed to accelerate advances in tsunami research and hazard mitigation, and will require a cooperative and coordinated international effort.     

A mixed finite element approach for viscoelastic wave propagation

In this paper, we are interested in the modeling of wave propagation in viscoelastic media. We present a family of models which generalize the Zeners model. We achieve its mathematical analysis: existence and uniqueness of solutions, energy decay and propagation with finite speed. For the numerical resolution, we extend a mixed finite element method proposed in [8]. This method combines mass lumping with a centered explicit scheme for time discretization. For the resulting scheme, we prove a discrete energy decay result and provide a sufficient stability condition. For the numerical simulation in open domains we adapt the perfectly matched layers techniques to viscoelastic waves [23]. Various numerical results are presented.     

Sixty six day periodicity of polar coronal holes

Fourier analysis of the coronal hole size distribution shows sixty six day periodicity in respect of the time of advancement of solar cycle which is presumed to be due to the differential rotation of solar envelope.     

Disappearence of equatorial Es, associated with magnetic field depressions

The phenomenon of the sudden disappearance of equatorial sporadic E at two stations, namely, Trivandrum and Kodaikanal is studied. It is established that whenever there is a sudden disappearance of E_s, there is a depression in the horizontal magnetic field (H) range. Electron velocities during the presence and absence of sporadic E have been estimated. These results show that the irregularities responsible for sporadic E are present even when the electron velocities are less than the ion thermal velocity.     

Database of Comet Polarimetry: Analysis and Some Results

We present the electronic database (EAR-C-COMPIL-5-DB-COMET-POLARIMETRY-V1.0, NASA Planetary Data System) involving published and some unpublished results of cometary polarimetry. The database contains more than 2600 measurements of linear and circular polarization for 64 comets since 1940s. The narrow-band and wide-band measurements within the spectral region 0.3–2.2 micron are presented. The ranges of phase angles, helio- and geocentric distances of comets are 0.4–122°, 0.6–4.8 AU, 0.03–4.9 AU, respectively. We have comprised more than 60 references to the published papers and unpublished sources. The data we included are presented in a tabular format in the ASCII codes. The database can be used as the observational basis for detailed theoretical modeling, interpretation of the phase-angle and spectral dependence of polarization, classification of comets, laboratory simulating, and for selecting future space-mission targets. Analysis of the available data allowed us to summarize some observed characteristics of linearly and circularly polarized light and their phase-angle, heliocentric, spectral, and spatial dependencies.     

Standard cumulative semivariograms of stationary stochastic processes and regional correlation

The standard cumulative semivariograms (SCS), obtained analytically from the currently employed stationary stochastic processes, provide a basis for the model identification and its parameter as well as regional correlation estimations. The analytical solutions for different stationary stochastic processes such as independent (IP), moving average (MA), autoregressive (AR), and autoregressive integrated moving average ARIMA (1,0,1) processes give rise to different types of SCSs which can be expressed in terms of the autocorrelation structure parameters only. The SCSs of independent and MA processes appear as linear trends whereas other type of processes have SCSs which are nonlinear for short distances but become linear at large distances. Irrespective of the stationary stochastic process type the linear portions of SCSs have unit slopes. The vertical distance between these linear portions and that of the IP cumulative semivariogram (CS), provide an indicator for measuring the regional correlation. In the case of stationary processes, the straight line portions of any CS are parallel to each other. Hence, it is possible to identify the model from the sample CS. Finally, necessary procedures are provided for the model parameters estimation. The methodology developed, herein, is applied to some hydrochemical ions in the groundwater of the Wasia aquifer in central part of Kingdom of Saudi Arabia.     

Gradient coupling within the terrestrial ionospheric plasma

The gradient coupling within the ionospheric plasma in the presence of local variation of atmospheric heating and other modifications during high power radio wave propagation has been studied. The appropriate form of coupled equations for the modified situation is obtained. The electromagnetic and acoustic modes of wave propagation have been separated and solved, by the WKB method. Field quantities may be used to explore different properties of the medium under the modified condition.