Nadia A. KudryavtsevaTallinn University of Technology | TTU · Department of Cybernetics
Nadia A. Kudryavtseva
PhD
About
67
Publications
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Citations since 2017
Introduction
Additional affiliations
September 2016 - present
September 2015 - September 2016
December 2010 - June 2014
Education
June 2005 - October 2008
September 1997 - June 2002
Publications
Publications (67)
We present a complete cross-validation of Significant Wave Heights (SWH) extracted from altimetry data from all ten existing satellites with available in situ (buoy and echosounder) wave measurements for the Baltic Sea basin. The main purpose is to select an adequate altimetry data subset for a subsequent evaluation of the wave climate. The satelli...
The main properties of the climate of waves in the seasonally ice-covered Baltic Sea and its decadal changes since 1990 are estimated from satellite altimetry data. The data set of significant wave heights (SWH) from all existing ten satellites is cleaned and cross-validated against in situ buoy and echosounder measurements. Even though several sat...
The core properties of the wave climate and its changes in the Caspian Sea are established in terms of the annual mean significant wave height and its regional changes in 2002–2013 based on the outcome of the satellite altimetry mission JASON-1. Remotely estimated wave heights are validated against properties of the empirical distribution of instru...
Abstract. Analysis and prediction of water level extremes in the eastern Baltic Sea is a difficult task because of the contribution of various drivers to the water level, the presence of outliers in time series and possibly non-stationarity of the extremes owing to the changes in the atmospheric forcing. Non-stationary modelling of extremes was per...
An accurate assessment of the joint probability of water levels and waves is crucial to establish appropriate mitigation and adaptation strategies for possible flooding and coastal erosion in countries with extensive low-lying nearshore areas. The simultaneous occurrence of large waves and high still water levels can significantly increase the risk...
Najafzadeh F., Kudryavtseva N., Soomere T. & Giudici A. 2022: Effect of ice cover on wave statistics and wave-driven processes in the northern Baltic Sea. Boreal Env. Res. 27: 97-116. We explore the effect of sea ice on wind wave statistics and wave-driven hydrodynamic loads in a seasonally ice-covered sea. We compare the results of hypothetical ic...
Wave heights in the Baltic Sea in the period 1992–2015 have mainly increased in the sea’s western parts. The linear trends in the winter wave heights exhibit a prominent meridional pattern. Using the technique of Empirical Orthogonal Functions (EOF) applied to multi-mission satellite altimetry data, we explain a large part of this increase with the...
Wave heights in the Baltic Sea in 1992–2015 have predominantly increased in the sea's western parts. The linear trends in the winter wave heights exhibit a prominent meridional pattern. Using the technique of Empirical Orthogonal Functions (EOF) applied to the multi-mission satellite altimetry data, we link a large part of this increase in the wave...
The phenomenon of wave set-up may substantially contribute to the formation of devastating coastal flooding in certain coastal areas. We study the appearance and properties of empirical probability density distributions of the occurrence of different set-up heights on an approximately 80 km long section of coastline near Tallinn in the Gulf of Finl...
The core properties of the wave climate and its changes in the Caspian Sea are established in terms of the annual mean significant wave height and its regional changes in 2002-2013 based on the outcome of the satellite altimetry mission JASON-1. Remotely estimated wave heights are validated against properties of the empirical distribution of instru...
Understanding the wave climate and its variability is crucial in coastal planning for minimizing future coastal hazards and economic loss. In fetch-limited and semi-enclosed basins like the Baltic Sea, small changes in the wind direction can lead to complex behaviour of the wave climate. Prominent advances in satellite altimetry make it feasible to...
The Baltic Sea, a semi-enclosed and seasonally ice-covered water body, is located in the northern part of Europe where the changes in the wind direction can lead to significant spatial and temporal variations in the wave climate. Variability in waves has a substantial impact on shipping, coastal infrastructure and coastal population. Therefore, und...
We analyse a two-step mechanism for the formation of extremely high water levels in a semi-enclosed sub-basin of the Baltic Sea with the pumping of large amounts of water first into this sea and then into the Gulf of Riga. The analysis is based on hourly water level recordings at two observations sites in the gulf (Pärnu and Daugavgriva) and at one...
Understanding of the wave climate is of high importance for the safety of navigation, coastal protection and quantifying coastal erosion. The existing studies of the Baltic Sea wave climate have revealed that it is a complex phenomenon with highly variable patterns (in both space and time) of wave properties. However, the exact driving mechanisms b...
The classic approach to extreme water levels and their return periods relies on the choice of a convenient extreme value distribution and the subsequent evaluation of its parameters. However, there is increasing evidence that these parameters vary with time owing to climate change. A novel non-stationary modeling of parameters of a generalized extr...
The wind induced coastal upwelling process often contains a mid-phase that involves coherent long-living cross-shore surface jets of cooler water. These jets extend to 40–45 km from the coast and tend to start from particular coastal locations. We develop a simple method for evaluating the depth in the water column from where the upwelled water ori...
Type III solar radio bursts are the Sun's most intense and frequent nonthermal radio emissions. They involve two critical problems in astrophysics, plasma physics, and space physics: how collective processes produce nonthermal radiation and how magnetic reconnection occurs and changes magnetic energy into kinetic energy. Here magnetic reconnection...
The main properties of the climate of waves in the seasonally ice-covered Baltic Sea and its decadal changes since 1990 are estimated from satellite altimetry data. The data set of significant wave heights (SWHs) from all existing nine satellites, cleaned and cross-validated against in situ measurements, shows overall a very consistent picture. A c...
The main properties of the climate of waves in the seasonally ice-covered Baltic Sea and its decadal changes since 1990 are estimated from satellite altimetry data. The data set of significant wave heights (SWH) from all existing nine satellites, cleaned and cross-validated against in situ measurements, shows overall a very consistent picture. A co...
The closure depth indicates the depth down to which storm waves maintain a universal shape of the coastal profile. It is thus a key parameter of the coastal zones for a variety of engineering and ecosystem applications. Its values are commonly estimated with respect to the long-term mean water level. The present study re-evaluates closure depths fo...
Many astronomical sources produce transient phenomena at radio frequencies, but the transient sky at low frequencies (<300 MHz) remains relatively unexplored. Blind surveys with new widefield radio instruments are setting increasingly stringent limits on the transient surface density on various timescales. Although many of these instruments are lim...
Currently, three sources of wave data are available for the research community, namely, buoys, modelling, and satellite altimetry. The buoy measurements provide high-quality time series of wave properties but they are deployed only in a few locations. Wave modelling covers large domains and provides good results for the open sea conditions. However...
Due to the complex geometry and relatively small size of the Baltic Sea, the global studies of wave climatology do not cover the interior of the Baltic Sea. The existing studies have revealed highly variable patterns (in both space and time) of wave properties and equally complicated patterns of long-term changes in the wave climate. Moreover, diff...
In this paper we present observations, simulations, and analysis demonstrating the direct connection between the location of foreground emission on the sky and its location in cosmological power spectra from interferometric redshifted 21 cm experiments. We begin with a heuristic formalism for understanding the mapping of sky coordinates into the cy...
We present observations of high-amplitude rapid (2 s) variability toward two
bright, compact extragalactic radio sources out of several hundred of the
brightest radio sources in one of the 30x30 deg MWA Epoch of Reionization
fields using the Murchison Widefield Array (MWA) at 155 MHz. After rejecting
intrinsic, instrumental, and ionospheric origins...
We compare first order (refractive) ionospheric effects seen by the Murchison
Widefield Array (MWA) with the ionosphere as inferred from Global Positioning
System (GPS) data. The first order ionosphere manifests itself as a bulk
position shift of the observed sources across an MWA field of view. These
effects can be computed from global ionosphere...
Low-frequency, wide field-of-view (FoV) radio telescopes such as the
Murchison Widefield Array (MWA) enable the ionosphere to be sampled at high
spatial completeness. We present the results of the first power spectrum
analysis of ionospheric fluctuations in MWA data, where we examined the
position offsets of radio sources appearing in two datasets....
Low-frequency, wide-field radio telescopes such as the Murchison Widefield Array (MWA) enable the dense spatial sampling of the ionosphere and plasmasphere on regional scales. For a physically compact array such as the MWA, the refractive shifts in the positions of celestial sources in the synthesised radio images are proportional to spatial gradie...
The Murchison Widefield Array (MWA) is a Square Kilometre Array (SKA)
Precursor. The telescope is located at the Murchison Radio--astronomy
Observatory (MRO) in Western Australia (WA). The MWA consists of 4096 dipoles
arranged into 128 dual polarisation aperture arrays forming a connected element
interferometer that cross-correlates signals from al...
We present new low-frequency observations of the nearby radio galaxy Fornax A at 154 MHz with the Murchison Widefield Array,
microwave flux-density measurements obtained from WMAP and Planck data, and γ-ray flux densities obtained from Fermi data. We also compile a comprehensive list of previously published images and flux-density measurements at r...
We present the results of an approximately 6,100 square degree 104--196MHz
radio sky survey performed with the Murchison Widefield Array during instrument
commissioning between 2012 September and 2012 December: the Murchison Widefield
Array Commissioning Survey (MWACS). The data were taken as meridian drift scans
with two different 32-antenna sub-a...
The Murchison Widefield Array (MWA) is a new low frequency interferometric
radio telescope, operating in the remote Murchison Radio Observatory in Western
Australia. In this paper we present the first MWA observations of the well
known radio relics in Abell 3667 (A3667) between 120 and 226 MHz. We clearly
detect the radio relics in A3667 and presen...
We present the first Murchison Widefield Array observations of the well-known cluster of galaxies Abell 3667 (A3667) between
105 and 241 MHz. A3667 is one of the best known examples of a galaxy cluster hosting a double radio relic and has been reported
to contain a faint radio halo and bridge. The origin of radio haloes, relics and bridges is still...
Astronomical widefield imaging of interferometric radio data is
computationally expensive, especially for the large data volumes created by
modern non-coplanar many-element arrays. We present a new widefield
interferometric imager that uses the w-stacking algorithm and can make use of
the w-snapshot algorithm. The performance dependencies of CASA's...
An international consortium is presently constructing a beamformer for the
Atacama Large Millimeter/submillimeter Array (ALMA) in Chile that will be
available as a facility instrument. The beamformer will aggregate the entire
collecting area of the array into a single, very large aperture. The
extraordinary sensitivity of phased ALMA, combined with...
The Murchison Widefield Array (MWA) is a new low frequency interferomeric
radio telescope. The MWA is the low frequency precursor to the Square Kilometre
Array (SKA) and is the first of three SKA precursors to be operational,
supporting a varied science mission ranging from the attempted detection of the
Epoch of Reionisation to the monitoring of s...
The Murchison Widefield Array (MWA) is one of three Square Kilometre Array Precursor telescopes and is located at the Murchison Radio-astronomy Observatory in the Murchison Shire of the mid-west of Western Australia, a location chosen for its extremely low levels of radio frequency interference. The MWA operates at low radio frequencies, 80-300 MHz...
We discuss the opacity in the core regions of active galactic nuclei observed
with Very Long Baseline Interferometry (VLBI), and describe a new method for
deriving the frequency-dependent shifts of the VLBI core from the
frequency-dependent time lags of flares observed with single-dish observations.
Application of the method to the core shifts of t...
We present the results of a multi-frequency analysis of the enigmatic BL Lac object S4 0954+658. We have analyzed three epochs of dense VLBA observations with full polarization at 22 GHz and 8 GHz and one epoch at four frequencies 5 GHz, 8 GHz, 15 GHz, and 22 GHz taken in 1996-1998. We found that the jet is of a prominent helical shape and that the...
The quasar B0605-085 (OH 010) shows a hint for probable periodical variability in the radio total flux-density light curves. We study the possible periodicity of B0605-085 in the total flux-density, spectra and opacity changes in order to compare it with jet kinematics on parsec scales. We have analyzed archival total flux-density variability at te...
We present a kinematic analysis of jet component motion in the VLBI jet of the BL Lac object S5 1803+784, which does not reveal long-term outward motion for most of the components. Understanding the complex kinematic phenomena can possibly provide insights into the differences between quasars and BL Lac objects. The blazar S5 1803+784 has been stud...
We discuss a new approach for measuring flaring activity cycles of blazars and quasars. The activity cycles of 21 active galactic nuclei were estimated using the radio total flux-densities at five frequencies (5 GHz–37 GHz) and high resolution long-term very long-baseline interferometry (VLBI) observations (1.6 GHz–43 GHz). We define the activity c...
We present a new method to fit the variations of both coordinates of a VLBI
component as a function of time, assuming that the nucleus of the radio source
contains a binary black hole system (BBH system). The presence of a BBH system
produces 2 perturbations of the trajectory of the ejected VLBI components. By
using only the VLBI coordinates, the p...
We analyse the radio light curves of the blazars 1308+326, 2223−052 and 2251+158 using University of Michigan Radio Observatory
and Metsähovi Radio Observatory multifrequency monitoring data combined with high-resolution very long baseline interferometry
(VLBI) observations in order to extract the properties of prominent outbursts. The outbursts ar...
During the period 1966.5–2006.2 the 15 GHz and 8 GHz light curves of 3C 454.3 (z = 0.859) show a quasi-periodicity of ~12.8 yr (~6.9 yr in the rest frame of the source) with a double-bump structure. This periodic behaviour is interpreted in terms of a rotating double-jet model in which the two jets are created from the black holes of a binary syste...
The combined data of the University of Michigan Radio Astronomy Observatory and Metsähovi Radio Observatory provide us with radio light curves for active galactic nuclei monitored by both observatories from 4.8 to 37 GHz covering time-intervals up to ∼25 yr. We consider here such composite light curves for four gamma-ray blazars that have been near...
We present the results of a multi-frequency analysis of the structural variability in the parsec-scale jet of the blazar S5 1803+784. More than 90 epochs of observations at 6 frequencies from 1.6 GHz up to 22 GHz have been combined and analyzed. We discuss an alternative jet model for the source. In contrast to previously discussed motion scenarios...
4u 0115+63 is one of the most active and best studied Be/X-ray transients. Previous studies of 4u0115+63 have led to the suggestion that it undergoes relatively fast quasi-cyclic activity. However, due to the lack of good coverage of the observations, the variability time scales are uncertain. Our objective is to investigate the long-term behaviour...
4U 0115+63 is one of the most active and best studied Be/X-ray transients. Previous studies of 4U 0115+63 have led to the suggestion that 4U 0115+63 undergoes relatively fast quasi-cyclic activity. However, due to the lack of good coverage of the observations, the variability time scales are uncertain. Our objective is to investigate the long-term...
Our earlier joint analysis of light curves for the blazar 0059+581 at 4.8, 8, 14.5, 22, and 37 GHz with high-resolution VLBI
images led us to suggest that the activity in this source develops in cycles, or periods, with a duration of about four years,
with a “typical scenario” for the development of the source’s activity taking place over a cycle....
We present the results of a multi-frequency analysis of the structural variability in the parsec-scale jet of the blazar S5 1803+784. More than 90 epochs of observations at 6 frequencies from 1.6 GHz up to 22 GHz have been combined and analyzed. We discuss an alternative jet model for the source. In contrast to previously discussed motion scenarios...
Frequency-dependent time lags for strong outbursts in four
γ-blazars are determined. The time lags for two adjacent outbursts
in 2230+114 are correlated with the outburst amplitudes. There is
evidence that bright outbursts in 2230+114 appear with a quasi-period
of (8.0±0.3) yr.
We present an analysis of multifrequency light curves of the sources 2223-052 (3C 446), 2230+114 (CTA 102), and 2251+158 (3C 454.3), which had shown evidence of quasi-periodic activity. The analysis made use of data from the University of Michican Radio Astronomy Observatory (USA) at 4.8, 8, and 14.5 GHz, as well as the Metsahovi Radio Astronomy Ob...
We performed the optical BVRI observations of BL Lac with a CCD photometer of the AI SPbSU equipped with an ST-7 camera attached to the 20-cm (1999) and 70-cm (2000-2001) telescopes at the Crimean Astrophysical Observatory. We carried out the infrared (JHK) observations with the 1.1-m Pulkovo Astronomical Observatory (Russian Academy of Sciences) t...
BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by theWEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have be...
We present the results of our multicolor observations of BL Lac in the period 1999–2001. We show that the spectral energy
distribution of the variable component in the range from K to B had remained unchanged for three years. The power-law spectrum is indicative of its synchrotron nature.
![Fig. 11.-BeppoSAX LECS [0.7-2] keV (top panel) and contemporaneous...](profile/Roberto-Nesci/publication/27276884/figure/fig5/AS:667785373941779@1536223848887/BeppoSAX-LECS-07-2-keV-top-panel-and-contemporaneous-R-band-bottom-panel-light_Q320.jpg)
BL Lacertae (BL Lac) was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. Simultaneous or quasi-simultaneous observations were taken at radio (University of Michigan Radio Astronomy Observatory and Metsähovi Radio Telescope) and optical (Whole Earth Blazar Telescope [WEBT] collaboration) frequencies, in X-r...
The Whole Earth Blazar Telescope (WEBT) is an international consortium
of about 30 optical observatories and 2 radio observatories devoted to
blazar monitoring during optical and multifrequency campaigns. The
dispersion in longitude of the WEBT members allows them to obtain dense
and quasi-continuous light curves, minimizing gaps due to Earth
rotat...
The first light curve of likely magnetic system SDSS J015543.40 +002807.2 is presented. The object has the light curve with an unusual deep minimum: approx 5.98 mag.
We present $UBVRI$ light curves of BL Lacertae from May 2000 to January 2001, obtained by 24 telescopes in 11 countries. More than 15 000 observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July–August 2000. The exceptional sampling reached allows one to foll...
We present R-band light curves of BL Lacertae from May 2000 to January 2001, obtained by 22 telescopes in 11 countries. More than 15000 UBVRI observations were performed in that period, which was the extension of the Whole Earth Blazar Telescope (WEBT) campaign originally planned for July-August 2000. The exceptional sampling reached allows one to...
Questions
Questions (4)
I am looking for in-situ measurements of wave heights for the Caspian Sea. I see that people published a comparison of wave modeling results with the in-situ data, so there are data from at least a few stations available, like Anzali, Neka, Amirabad, Fort-Shevchenko, Neftyanye Kamni, Kochubey, Astrakhan, Makhachkala, but simple googling does not show any downloadable data. Do you know where can I get the data, whom to ask and how open they are?
Many thanks!
Do you convert the binary output files to GRIB or netCDF formats or use some other tools to analyze the WAM model output?
I am working in a different research area, in astrophysics and working with radio astronomical data, but I really think that the climate change research is extremely important for all of us and willing to spend a few hours per week to help. I wonder, can I join some research project?