Retrieving earthquake signature in grace gravity solutions

The GRACE satellites have been orbiting the Earth since 2002, monitoring the time variable gravity field. Some of the observed fluctuations are due to geodynamic causes, but they are often hidden in the complex signal, composed of hydrology, ocean, atmosphere, and geodynamics, the signal of geodynamic origin being usually the smallest. In addition, dealiasing residuals and noise make the separation of the signal from the different causes more difficult. We proposed a method based on the Empirical Orthogonal Function decomposition to extract the signal of physical origin, under the hypothesis that the physical signal is spatially more consistent than the noise and aliasing incomplete correction. We used synthetic geoid variations associated with earthquakes located at nearly 2000 positions at the Earth surface, based on several examples of large actual subduction events. We show that, with the present day accuracy, we can retrieve the geoid variations associated with more than 98 per cent of the earthquakes of magnitude 9 or above, around 60 per cent for magnitude 8.8, 40 per cent for magnitude 8.6 and 33 per cent for magnitude 8.3. Some events, with the right properties and location, can be detected with magnitude as low as 8. We then applied the method to the GRACE solutions, and retrieved the Hokkaido event (2003) and the Sumatra event (2004), which is in agreement with the retrieval rates mentioned here above.     

Regularities in sea level rise impact on the hydrological regime and morphological structure of river deltas

The problem of assessment of sea level rise impact on the hydrological regime and morphological structure of river deltas is discussed. Studies of the response of river deltas, which are among the most vulnerable natural objects, to the sea level rise has become urgent because of the global climate warming and the associated acceleration of the World Ocean level rise. Methods are described that can be used for the analysis, calculation, and prediction of sea level rise impact on submergence of deltas, propagation of backwater from the sea tides, surges, and salt seawater intrusion. Special emphasis is given to channel processes in delta branches, which accompany sea level rise, as well as to delta coastline erosion and flow redistribution among branches. In the course of research, due consideration was taken of the experience gained in studying the response of river deltas on the Caspian Sea coasts to the recent considerable level rise in this water body.     

Filter-based differential hygroscopicity analyzer of aerosol particles

We describe a new differential analyzer implementing a technique for studying the hygroscopic properties of filter-precipitated aerosol particles based on a katharometric measurement of the amount of water vapor absorbed by an aerosol sample. The instrument has been tested on particles of sodium chloride and ammonium sulphate. A comparison of our data with the results of analogous measurements described in literature shows that the suggested technique has several important advantages, i.e., (1) higher sensitivity, which allows the measurement of particles of no more than 0.1 mg in mass; (2) a wide range of relative humidity variations (up to 99% at an accuracy of 0.06% RH at the upper-range value); (3) the absence of intermediate measurement steps connected with the need to account for water absorption by elements of a measurement system; and (4) the absence of restrictions to the size and shape of particles studied. In addition, the measurement technique rules out the possibility of errors caused by the kinetic effects of mass transport in the aerosol-water vapor system.     

Hazardous hydrological processes in the dutch delta and measures for mitigation of their adverse effect on the population,economy, and ecosystems: 2. Experience in the mitigation of the adverse effect of hazardous hydrological processes on the population,economy, and ecosystems

Experience in mitigating the hazard of hydrological processes in the joint mouth area of the Rhine, Meuse, and Scheldt rivers is discussed. This experience is of use for the creation and implementation of regional programs for reducing the social, economic, and environmental losses under other natural conditions.     

Morphology of NmF2 nighttime increases in the Eurasian sector

A statistical analysis of two peaks (pre-midnight and post-midnight) occurrence in NmF2 daily variations was made on a latitudinal chain of four ionosonde stations in the Eurasian longitudinal sector. Overall 6182 cases of the first and 5600 cases of the second peak occurrence were analyzed using all available foF2 observations for the years of solar maximum and minimum. Well-pronounced and systematic variations with season and solar activity were revealed in the occurrence probability of the peaks, their amplitude and timing. The pattern of both peaks occurrence is similar during winter and equinoxes for midlatitude stations implying one and the same mechanism of their formation. The pre-midnight summer peak shows specific variations in particular during solar maximum pointing to a different mechanism controlling its appearance. Possible mechanisms of both peaks formation are discussed.     

Extreme flood on the Danube River in 2006

Causes and features of an extreme flood on the Danube River in spring and summer 2006 are considered. The water levels at some gauge stations on the Middle Danube and at most gauge stations on the Lower Danube exceeded maxima observed during previous 100–130 years. The flood on the Lower Danube lasted from March to July and led to widespread inundations and damage. The flood was caused by melt of large amounts of snow accumulated in the river basin during winter, very warm spring, and abundant rains. In recent decades, the occurrence frequency of extreme hydrological events on the Danube River (large spring-summer floods and catastrophic rainfall freshets) has increased.     

Spectra of atmospheric waves in the dynamo region of the ionosphere at Kamchatka

A spectral analysis of the diurnal variations in the geomagnetic field horizontal component, observed at Kamchatka and Barrow polar observatory in September–October 1999, has been performed. The complete set of oscillations of thermal tidal atmospheric waves with T = 24, 12, 8, and 4 h has been detected in the variation spectral power (Sq) at Kamchatka, and only the fundamental harmonic with T = 24 h has been distinguished at Barrow. The above periods vary in both directions relative to stable maximums during strong geomagnetic disturbances. The relative spectral intensity at subharmonics also vary toward the fundamental harmonic with a period of 24 h. In the frequency band 0.5–3 h (IGW periods), the maximal intensity in the background spectra is observed at T ～ 2 h and increases by an order of magnitude with increasing geomagnetic activity at both Kamchatka and Barrow. A day before earthquakes, the intensity of this maximum is below the rms background values, and the spectra widen toward the region of periods shorter than 2 h. A similar effect was previously observed in the power spectra of the diurnal variations in the quasistatic electric field and VLF noise, simultaneously measured in September–October 1999.     

Mapping the sun with the RTF-32 radio telescopes

The possibilities of using the RTF-32 radio telescopes of the interferometric QUASAR network for solar observations are investigated. A technique of solar radio mapping with the RTF-32 telescopes is presented. The software developed at the Institute of Applied Astronomy, Russian Academy of Sciences, for reducing such observations is described. The maps of the Sun at 1.35 cm, derived from observations at the Zelenchukskaya observatory November 4–14, 2004, are presented.