Yuliya Troitskaya

Pan Eurasian Experiment (PEEX) - A research initiative meeting the grand challenges of the changing environment of the Northern Pan-Eurasian Arctic-Boreal areas

The Pan-Eurasian Experiment (PEEX) is a new multidisciplinary, global change research initiative focusing on understanding biosphere-ocean-cryosphere-climate interactions and feedbacks in Arctic and boreal regions in the Northern Eurasian geographical domain. PEEX operates in an integrative way and it aims at solving the major scientific and society relevant questions in many scales using tools from natural and social sciences and economics. The research agenda identifies the most urgent large scale research questions and topics of the land-atmosphere-aquatic-anthropogenic systems and interactions and feedbacks between the systems for the next decades. Furthermore PEEX actively develops and designs a coordinated and coherent ground station network from Europe via Siberia to China and the coastal line of the Arctic Ocean together with a PEEX-modeling platform. PEEX launches a program for educating the next generation of multidisciplinary researcher and technical experts. This expedites the utilization of the new scientific knowledge for producing a more reliable climate change scenarios in regional and global scales, and enables mitigation and adaptation planning of the Northern societies. PEEX gathers together leading European, Russian and Chinese research groups. With a bottom-up approach, over 40 institutes and universities have contributed the PEEX Science Plan from 18 countries. In 2014 the PEEX community prepared Science Plan and initiated conceptual design of the PEEX land-atmosphere observation network and modeling platform. Here we present the PEEX approach as a whole with the specific attention to research agenda and preliminary design of the PEEX research infrastructure.

Adaptive retracking of Jason-1 altimetry data for inland waters: the example of the Gorky Reservoir

Standard altimetry data processing developed for open ocean conditions can be inapplicable for the case of inland waters, especially for narrow, elongated waterbodies and rivers, where the distance between shores is less than 10 km (while the eliminated area within the gain of the radar antenna for Jason-1,2 is about 50 km). These conditions are typical, for example, of the majority of reservoirs of the Volga River cascade (with one exception: the Rybinskoe Reservoir). Under these conditions only a few telemetric impulses fit the validity criteria, which causes a severe loss of data. Besides, errors in the water level retrieved from the altimetric measurements are enormous, as was demonstrated on the basis of comparison of in situ measurements at hydro-gauging stations for the water level of the Gorky Reservoir of the Volga River and all that is available along track 10 Hz TOPEX/Poseidon altimetry data and 20 Hz Jason altimetry data over the reservoir area. The problem of minimization of the errors can be resolved by retracking. For justification of the optimal retracking algorithm, the average impulse response of the statistically inhomogeneous surface was calculated theoretically, based on the works of Brown (1977) and Barrick and Lipa (1985) for the model of the terrain in the vicinity of the Gorky Reservoir. The model represents the main typical features of the waveform examples (e.g. high peaks or irregular complex shape), and the modelled waveforms are in good agreement with the Jason-1,2 waveforms for the same area. It was shown that for the Gorky Reservoir significant wave height (SWH) did not exceed 0.5 m (corresponding to the width of the leading edge less than 1 telemetric gate). Under these conditions the retracking algorithm based on the detection of the beginning of the leading edge of telemetric impulses is preferable for a correct assessment of variations in the water level in the Gorky Reservoir. A comparison of the data with in situ measurements at the hydro-gauging stations for the water level of the Gorky Reservoir shows that retracking dramatically increases the number of data involved in monitoring and significantly improves the accuracy of the measurement of the water level. The retracked data of water level have also been validated by comparing them with Jason-2 and Jason-1 after carrying out measurements for the Gorky Reservoir. The general principles of retracking algorithms for complex areas (land, coastal zone, inland waters, etc.), based on calculations of the waveform and taking into account statistical inhomogeneity of the reflecting surface adjusted to a certain geographic region, are discussed.

Atmospheric boundary layer over steep surface waves

Turbulent air-sea interactions coupled with the surface wave dynamics remain a challenging problem. The needs to include this kind of interaction into the coupled environmental, weather and climate models motivate the development of a simplified approximation of the complex and strongly nonlinear interaction processes. This study proposes a quasi-linear model of wind-wave coupling. It formulates the approach and derives the model equations. The model is verified through a set of laboratory (direct measurements of an airflow by the particle image velocimetry (PIV) technique) and numerical (a direct numerical simulation (DNS) technique) experiments. The experiments support the central model assumption that the flow velocity field averaged over an ensemble of turbulent fluctuations is smooth and does not demonstrate flow separation from the crests of the waves. The proposed quasi-linear model correctly recovers the measured characteristics of the turbulent boundary layer over the waved water surface.

Manifestations of the Indian Ocean tsunami of 2004 in satellite nadir-viewing radar backscatter variations

This paper reports on the first experimental evidence for space‐observed manifestations of the open ocean tsunami in the microwave radar backscatter (in the C and Ku bands; electromagnetic wavelengths of 6 and 2 cm, respectively). Significant (a few dB) variations of the radar cross section synchronous with the sea level anomaly were found in the geophysical data record of the altimetry satellite Jason‐1 for the track that crossed the head wave of the catastrophic tsunami of 26 December 2004. The simultaneous analysis of the available complementary data provided by the satellite three‐channel radiometer enabled us to exclude meteorological factors as possible causes of the observed signal modulation. A possible physical mechanism of modulation of short wind waves due to transformation of the thin boundary layer in the air by a tsunami wave is discussed. The results open new possibilities of monitoring tsunamis from space, for example by support to warning systems based on fixed moorings and coastal stations.

Air-sea Interaction under Hurricane Wind Conditions

where U10 -the wind velocity at a standard meteorological height 〉10=10 m. which relate this coefficient to U10 are obtained either by generalizing empirical data (Garratt, 1977; Large & Pond, 1981, Taylor & Yelland, 2002; Fairall et al., 2003) or by numerical models (see, for example, Janssen, 1989; Janssen, 1991, Makin et.al, 1994; Hara & Belcher, 2004). Numerous field measurements give increasing dependencies of CD on wind speed, which relates to increasing of wave heights with the wind. The aerodynamic drag coefficient of the sea surface is a critical parameter in the theory of tropical hurricanes (Emanuel, 1995). To illustrate it we consider here the ideas of theory of energy balance in a tropical cyclone suggested by (Emanuel, 1986; Emanuel, 1995, Emanuel, 2003). According to this theory the mature tropical cyclone may be idealized as a steady, axisymmetric flow whose energy cycle is very similar to that of an ideal Carnot engine,

Adjusting of Wind Input Source Term in WAVEWATCH III Model for the Middle-Sized Water Body on the Basis of the Field Experiment

Adjusting of wind input source term in numerical model WAVEWATCH III for the middle-sized water body is reported. For this purpose, the field experiment on Gorky Reservoir is carried out. Surface waves are measured along with the parameters of the airflow. The measurement of wind speed in close proximity to the water surface is performed. On the basis of the experimental results, the parameterization of the drag coefficient depending on the 10 m wind speed is proposed. This parameterization is used in WAVEWATCH III for the adjusting of the wind input source term within WAM 3 and Tolman and Chalikov parameterizations. The simulation of the surface wind waves within tuned to the conditions of the middle-sized water body WAVEWATCH III is performed using three built-in parameterizations (WAM 3, Tolman and Chalikov, and WAM 4) and adjusted wind input source term parameterizations. Verification of the applicability of the model to the middle-sized reservoir is performed by comparing the simulated data with the results of the field experiment. It is shown that the use of the proposed parameterization improves the agreement in the significant wave height from the field experiment and from the numerical simulation.

Perturbation Theory for the Compound Soliton of the Gardner’s Equation; Their Interaction and Evolution in a Media with Variable Parameters

This paper is a brief review of the results of an approximate description of the evolution and interaction of composite solitons, obtained by the authors in 2001–2016. As one of the applications of the theory, the features of the evolution of intense internal waves in the shelf zone of the ocean are analyzed.

Surface Manifestations of Internal Waves Induced by a Subsurface Buoyant Jet (Experiment and Theory)

In this contribution we summarized the main results of the work on internal waves generated by vertical turbulent plumes in stratified fluids, including the mechanisms of internal wave generation, the structure of internal waves, and their surface manifestations Particular attention is focused on the major series of experiments performed in the Large Thermally Stratified Tank of the Institute of Applied Physics of the Russian Academy of Sciences, Nizhny Novgorod, Russia. The majority of results are applicable for the monitoring of the coastal zone of the oceans. The other potential implications include buoyant plumes generated by subglacial discharge in Greenland fjords.

Laboratory Experiment on Wave Induced Turbulence

A laboratory experiment was conducted inside a wind wave tank to investigate the wave induced turbulence. In this experiment, the wave surface elevation and velocity beneath the water surface were measured simultaneously to investigate the relation between the wave status and wave induced turbulence. The profile of the turbulent dissipation rate and Reynolds stress were calculated using experimental data. The effect of the wave status on turbulence is investigated with regard to the wind wave, swell, and mixed wave conditions. It was depicted that the turbulence decreased with increasing depth from the water surface and that the turbulence that was induced by a wave with larger wavelength and wave height is much stronger for the same wave status. Finally, we observed that the wind wave is more effective in activating the wave induced turbulence.

X-band radar cross-section at GALE force winds: Towards cross-polarization GMF for retrieval of hurricane wind speed and surface stress

Based on laboratory experiments, the logarithmic dependence of X-band cross-polarized NRCS on wind friction velocity was found for high wind conditions. Using this dependency, surface drag parameterizations at hurricane wind and available collocated field data on radar backscattering and wind speed, the geophysical model function (GMF) as NRCS via 10-m wind speed is derived. The GMP is applicable for wind speed retrieval at stormy and hurricane conditions.