On Modeling of Extreme Rainfall Processes over a Wide Range of Time Scales

Statistical models based on the scale-invariance (or scaling) concept has increasingly become an essential tool for modeling extreme rainfall processes over a wide range of time scales. In particular, in the context of climate change these scaling models can be used to describe the linkages between the distributions of sub-daily extreme rainfalls (ERs) and the distribution of daily ERs that is commonly provided by global or regional climate simulations. Furthermore, the Generalized Logistic distribution (GLO) has been recommended in UK for modeling of extreme hydrologic variables. Therefore, the main objective of the present study is to propose a scaling GLO model for modeling ER processes over different time scales. The feasibility and accuracy of this model were assessed using ER data from a network of 21 raingages located in Ontario, Canada. Results of this assessment based on different statistical criteria have indicated the comparable performance of the proposed scaling GLO model as compared to other popular models in practice. Furthermore, an illustrative application of the proposed model for evaluating the climate change impacts on the ERs in Ontario using the available NASA downscaled regional climate simulations has demonstrated the accuracy and robustness of the GLO model.

Download Full-text

FRATs: Searching for fast radio transient in real-time with LOFAR

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312023733 ◽

2012 ◽

Vol 8 (S291) ◽

pp. 233-233

Author(s):

Heino Falcke ◽

Keyword(s):

Time Scales ◽

Search Space ◽

Large Field ◽

New Radio ◽

Wide Range ◽

Imaging Observation ◽

Previous Decade ◽

First Results ◽

Single Radio ◽

Radio Transients

AbstractLOFAR is an innovative new radio interferometer operating at low radio frequencies from 10 to 270 MHz. It combines a large field-of-view, high fractional bandwidth, rapid response, and a wide range of baselines from tens of meters to thousand kilometers. Its use of phased-array technology and its digital nature make LOFAR an extremely versatile instrument to search for transient radio phenomena on all time scales. Here we discuss in particular the search for fast radio transients (FRATs) at sub-second time scales. In fact, at these time scales the radio sky is rather dynamic due to coherent emission processes. Objects like pulsars, flaring stars, or planets like Jupiter are able to produce bright short flares. For pulsars, most previous detection strategies made use of the rotation of pulsars to detect them, using Fourier techniques, but it is also possible to detect pulsars and other objects through their single pulses. Such surveys have, e.g., led in the previous decade to the detection of Rapid Radio Transients (RRATS), but the unprobed search space is still rather large. LOFAR is now conducting a rather unique survey over the entire northern sky, searching for bright dispersed single radio pulses. This FRATs survey makes use of the LOFAR transient buffer boards (TBBs), which had initially been used to detect nanosecond radio pulses from cosmic rays. The TBBs store the radio data from each single receiver element of LOFAR and allow one to look back in time. A trigger system that runs parallel to normal imaging observation allows one to detect single pulses in an incoherent beam of all LOFAR stations, covering several tens to hundred square degrees at once. Once triggered, the data can be used to localize the pulse and to discriminate cosmic sources from terrestrial interference through 3D localization. The system has been successfully tested with known pulsars and first results of the ongoing survey will be presented.

Download Full-text

A comparative survey of the impacts of extreme rainfall in two international case studies

10.5194/nhess-2017-125 ◽

2017 ◽

Author(s):

Matthieu Spekkers ◽

Viktor Rözer ◽

Annegret Thieken ◽

Marie-Claire ten Veldhuis ◽

Heidi Kreibich

Keyword(s):

Case Studies ◽

Online Survey ◽

Residential Buildings ◽

Age Groups ◽

Extreme Rainfall ◽

Water Levels ◽

Economic Losses ◽

Biased Sampling ◽

Wide Range ◽

Damage Data

Abstract. Flooding is assessed as the most important natural hazard in Europe, causing thousands of deaths, affecting millions of people and accounting for large economic losses in the past decade. Little is known about the damage processes associated with extreme rainfall in cities, due to a lack of accurate, comparable and consistent damage data. The objective of this study is to investigate the impacts of extreme rainfall on residential buildings and how affected households coped with these impacts in terms of precautionary and emergency actions. Analyses are based on a unique dataset of damage characteristics and a wide range of potential damage explaining variables at the household level, collected through computer-aided telephone interviews (CATI) and an online survey. Exploratory data analyses based on a total of 859 completed questionnaires in the cities of Münster (Germany) and Amsterdam (the Netherlands) revealed that the uptake of emergency measures is related to characteristics of the hazardous event. In case of high water levels, more efforts are made to reduce damage, while emergency response that aims to prevent damage is less likely to be effective. The difference in magnitude of the events in Münster and Amsterdam in terms of rainfall intensity and water depth, is probably also the most important cause for the differences between the cities in terms of the suffered financial losses. Factors that significantly contributed to damage in at least one of the case studies are water contamination, the presence of a basement in the building and people's awareness of the upcoming event. Moreover, this study confirms conclusions by previous studies that people's experience with damaging events positively correlates with precautionary behaviour. For improving future damage data acquisition, we recommend to include cell-phones in a CATI survey to avoid biased sampling towards certain age groups.

Download Full-text

Secular evolution of close-in planets: the effects of general relativity

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa271 ◽

2020 ◽

Vol 493 (1) ◽

pp. 427-436

Author(s):

F Marzari ◽

M Nagasawa

Keyword(s):

General Relativity ◽

Numerical Integration ◽

Time Scales ◽

Initial Conditions ◽

Outer Planet ◽

Secular Perturbations ◽

Secular Evolution ◽

Eccentric Orbits ◽

Wide Range ◽

Comparable Time

ABSTRACT Pairs of planets in a system may end up close to their host star on eccentric orbits as a consequence of planet–planet scattering, Kozai, or secular migration. In this scenario, general relativity and secular perturbations have comparable time-scales and may interfere with each other with relevant effects on the eccentricity and pericenter evolution of the two planets. We explore, both analytically and via numerical integration, how the secular evolution is changed by general relativity for a wide range of different initial conditions. We find that when the faster secular frequency approaches the general relativity precession rate, which typically occurs when the outer planet moves away from the inner one, it relaxes to it and a significant damping of the proper eccentricity of the inner planet occurs. The proper eccentricity of the outer planet is reduced as well due to the changes in the secular interaction of the bodies. The lowering of the peak eccentricities of the two planets during their secular evolution has important implications on their stability. A significant number of two-planet systems, otherwise chaotic because of the mutual secular perturbations, are found stable when general relativity is included.

Download Full-text

Swift/XRT, Chandra, and XMM–Newton observations of IGR J17091–3624 as it returns into quiescence

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2009 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1115-1126

Author(s):

M Pereyra ◽

D Altamirano ◽

J M C Court ◽

N Degenaar ◽

R Wijnands ◽

...

Keyword(s):

Black Hole ◽

Neutron Star ◽

Time Scales ◽

Strong Evidence ◽

Spectral Properties ◽

X Ray ◽

Term Evolution ◽

Wide Range ◽

Low Mass

ABSTRACT IGR J17091–3624 is a low-mass X-ray binary (LMXB), which received wide attention from the community thanks to its similarities with the bright black hole system GRS 1915+105. Both systems exhibit a wide range of highly structured X-ray variability during outburst, with time-scales from few seconds to tens of minutes, which make them unique in the study of mass accretion in LMXBs. In this work, we present a general overview into the long-term evolution of IGR J17091–3624, using Swift/XRT observations from the onset of the 2011–2013 outburst in 2011 February till the end of the last bright outburst in 2016 November. We found four re-flares during the decay of the 2011 outburst, but no similar re-flares appear to be present in the latter one. We studied, in detail, the period with the lowest flux observed in the last 10 yr, just at the tail end of the 2011–2013 outburst, using Chandra and XMM-Newton observations. We observed changes in flux as high as a factor of 10 during this period of relative quiescence, without strong evidence of softening in the spectra. This result suggests that the source has not been observed at its true quiescence so far. By comparing the spectral properties at low luminosities of IGR J17091–3624 and those observed for a well-studied population of LMXBs, we concluded that IGR J17091–3624 is most likely to host a black hole as a compact companion rather than a neutron star.

Download Full-text

Mobility characteristics of debris slides and flows triggered by Hurricane Maria in Puerto Rico

Landslides ◽

10.1007/s10346-020-01445-z ◽

2020 ◽

Vol 17 (12) ◽

pp. 2795-2809 ◽

Cited By ~ 1

Author(s):

Erin K. Bessette-Kirton ◽

Jeffrey A. Coe ◽

William H. Schulz ◽

Corina Cerovski-Darriau ◽

Mason M. Einbund

Keyword(s):

Puerto Rico ◽

Debris Flows ◽

Extreme Rainfall ◽

Source Areas ◽

Tropical Environments ◽

Digital Elevation ◽

Wide Range ◽

Hazard And Risk ◽

Elevation Model ◽

Landslides And Debris Flows

Abstract Mobility is an important element of landslide hazard and risk assessments yet has been seldom studied for shallow landslides and debris flows in tropical environments. In September 2017, Hurricane Maria triggered > 70,000 landslides across Puerto Rico. Using aerial imagery and a lidar digital elevation model (DEM), we mapped and characterized the mobility of debris slides and flows in four different geologic materials: (1) mudstone, siltstone, and sandstone; (2) submarine basalt and chert; (3) marine volcaniclastics; and (4) granodiorite. We used the ratio of landslide-fall height (H) to travel length (L), H/L, to assess the mobility of landslides in each material. Additionally, we differentiated between landslides with single and multiple source areas and landslides that either did or did not enter drainages. Overall, extreme rainfall contributed to the mobility of landslides during Hurricane Maria, and our results showed that the mobility of debris slides and flows in Puerto Rico increased linearly as a function of the number of source areas that coalesced. Additionally, landslides that entered drainages were more mobile than those that did not. We found that landslides in soils developed on marine volcaniclastics were the most mobile and landslides in soils on submarine basalt and chert were the least mobile. While landslides were generally small (< 100 m2) and displayed a wide range of H/L values (0.1–2), coalescence increased the mobility of landslides that transitioned to debris flows. The high but variable mobility of landslides that occurred during Hurricane Maria and the associated hazards highlight the importance of characterizing and understanding the factors influencing landslide mobility in Puerto Rico and other tropical environments.

Download Full-text

High-energy emission from transients

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2012.0279 ◽

2013 ◽

Vol 371 (1992) ◽

pp. 20120279 ◽

Cited By ~ 2

Author(s):

J. A. Hinton ◽

R. L. C. Starling

Keyword(s):

Particle Acceleration ◽

Time Scales ◽

Supernova Remnants ◽

Gamma Ray ◽

Experimental Situation ◽

High Energy ◽

Galactic Cosmic Rays ◽

Time Variable ◽

Wide Range ◽

Cosmic Explosions

Cosmic explosions dissipate energy into their surroundings on a very wide range of time scales: producing shock waves and associated particle acceleration. The historical culprits for the acceleration of the bulk of Galactic cosmic rays are supernova remnants: explosions on approximately 10 4 year time scales. Increasingly, however, time-variable emission points to rapid and efficient particle acceleration in a range of different astrophysical systems. Gamma-ray bursts have the shortest time scales, with inferred bulk Lorentz factors of approximately 1000 and photons emitted beyond 100 GeV, but active galaxies, pulsar wind nebulae and colliding stellar winds are all now associated with time-variable emission at approximately teraelectron volt energies. Cosmic photons and neutrinos at these energies offer a powerful probe of the underlying physical mechanisms of cosmic explosions, and a tool for exploring fundamental physics with these systems. Here, we discuss the motivations for high-energy observations of transients, the current experimental situation, and the prospects for the next decade, with particular reference to the major next-generation high-energy observatory, the Cherenkov Telescope Array.

Download Full-text

Sequential Diffusion Spectra as a Tool for Studying Time-Dependent Translational Molecular Dynamics: A Cement Hydration Study

Molecules ◽

10.3390/molecules25010068 ◽

2019 ◽

Vol 25 (1) ◽

pp. 68

Author(s):

Igor Serša

Keyword(s):

Molecular Dynamics ◽

Porous Structure ◽

Time Scales ◽

Cement Hydration ◽

Pulse Sequence ◽

Spin Echo ◽

Model Parameters ◽

Signal Attenuation ◽

Wide Range ◽

Novel Method

The translational molecular dynamics in porous materials are affected by the presence of the porous structure that presents an obstacle for diffusing molecules in longer time scales, but not as much in shorter time scales. The characteristic time scales have equivalent frequency ranges of molecular dynamics, where longer time scales correspond to lower frequencies while the shorter time scales correspond to higher frequencies of molecular dynamics. In this study, a novel method for direct measurement of diffusion at a given frequency of translational molecular dynamics is exploited to measure the diffusion spectra, i.e., distribution of diffusion in a wide range of frequencies. This method utilizes NMR modulated gradient spin-echo (MGSE) pulse sequence to measure the signal attenuation during the train of spin-echoes formed in the presence of a constant gradient. From attenuation, the diffusion coefficient at the frequency equal to the inverse double inter-echo time is calculated. The method was employed to study the white cement hydration process by the sequential acquisition of the diffusion spectra. The measured spectra were also analyzed by the diffusion spectra model to obtain the time-dependence of the best-fit model parameters. The presented method can also be applied to study other similar systems with the time evolution of porous structure.

Download Full-text

TT ARI–94: A Study of 1.6…60 Minute Variability

International Astronomical Union Colloquium ◽

10.1017/s025292110003815x ◽

1996 ◽

Vol 158 ◽

pp. 37-40

Author(s):

I. L. Andronov ◽

K. Arai ◽

L. L. Chinarova ◽

N. I. Dorokhov ◽

T. A. Dorokhov ◽

...

Keyword(s):

Power Spectrum ◽

Time Scales ◽

Cycle Length ◽

Cataclysmic Variables ◽

Optical Data ◽

Private Communication ◽

American Continent ◽

Frequency Range ◽

Wide Range ◽

Tt Ari

We report photometric results from 44 runs at 11 observatories during the international campaign ‘TT Ari–94’. No coherent oscillations in the frequency range 10… 900 cycle d−1 are found. The highest peaks in the power spectrum cover the wide range of 28… 139 cycle d−1. Variations occur at a few preferred time-scales rather than at one cycle length, with a possible secular decrease. In the frequency range 90… 900 cycle d−1 the power spectrum obeys a power law with slope γ ranging from 0.8 to 2.6 for different runs.TT Ari is one of the brightest cataclysmic variables and remains one of the most interesting objects of this class. It exhibits a variety of phenomena observed at time-scales from seconds to months. A recent detailed photometric study of this object and a bibliographical overview may be found in Tremko et al. (1996). Tremko et al. (1992, 1993, 1994) discuss aspects of the TT Ari–88 campaign. Our campaign TT Ari–94 was unprecedented, as the observations were longitude-dispersed, from Japan through Turkmenia, to Europe and the American continent. Moreover, our optical data on October 7 partially overlap with the HST observations obtained by Home & Welsh (1995, private communication). The numerical results of observations obtained during these nights are shown in Table 1.

Download Full-text