Olga Kleptsova - Academia.edu (original) (raw)

Papers by Olga Kleptsova

Research paper thumbnail of OKleptsova/TC-Caribbean

Scripts for plotting/analysing the processed model output from "Impacts of 2017 Tropical Cyc... more Scripts for plotting/analysing the processed model output from "Impacts of 2017 Tropical Cyclones on the Caribbean under sea level and climate conditions for 2100"

Research paper thumbnail of Comparison of the ensemble Kalman filter and a modified representer method for sensitivity to prior data

In closed-loop reservoir management, data assimilation algorithms or automated history matching m... more In closed-loop reservoir management, data assimilation algorithms or automated history matching methods can be used to support decision-making tools. Due to prior information, which the user has to supply to the data assimilation procedure, it can never be fully automatic. For example, a statistical description of the reservoir properties must be formulated, as well as the uncertainty of the measurements. In a synthetic numerical experiment these weighting factors are known; in a field application they are not. One could say that there are not only uncertainties in the data and the reservoir properties, but there is also "uncertainty in the uncertainty". In this article the robustness of the Ensemble (Square Root) Kalman Filter and a gradient-based algorithm using Representer Expansions are compared with respect to prior input data. Some algorithm dependent settings are explored to try to make the filter reproduce the results of the Representer Method: the ensemble size, the initialization method and the Kalman update. The concept of assimilating data more then once with dampened weighting factors (added uncertainty) is introduced. First the equations that underlie the Ensemble Filter and the Representer Method are given. Then numerical experiments are presented and two measures of quantifying the success of the methods are introduced. According to one such measure, the Representer Method performed better for all numerical examples considered. The parameters of the filter can be chosen such that the filter with the correct input data is equally successful as the Representer Method, using the second measure. When the methods are fed with the wrong prior input, the second measure also favours the Representer Method, so for the examples considered in this article the Representer Method is less sensitive to "wrong" user input that the Kalman Filter.

Research paper thumbnail of Unstructured Orthogonal Meshes for Modeling Coastal and Ocean Flows

In this thesis a z?layer unstructured C-grid finite volume hydrostatic model is presented. An eff... more In this thesis a z?layer unstructured C-grid finite volume hydrostatic model is presented. An efficient and highly scalable implicit technique for the solution of the free surface equation is combined with an Eulerian approach for the advection of momentum. A consistent velocity reconstruc- tion procedure which not only satisfies the continuity law but also guarantees the discrete kinetic energy conservation is presented. It is shown that an ac- curate velocity reconstruction procedure is of crucial importance not only for discretization of the Coriolis term, but also for the correct advection of mo- mentum, especially in the multilayer case. Unlike other z?layer models the method presented here ensures that the staircase representation of bathymetry and free surface has no influence on the vertical structure of the flow. The method is therefore guaranteed to be strictly momentum conservative, also in the layers containing the free surface and bed. A number of test cases are present...

Research paper thumbnail of A tsunami generated by a strike-slip event: constraints from GPS and SAR data on the 2018 Palu earthquake

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 M w = 7.5 Palu earthqu... more A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 M w = 7.5 Palu earthquake (Sulawesi, Indonesia). With a predominantly strike-slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake-induced landslides. In this study we examine the tsunami potential of the co-seismic deformation. To this end, we present a novel geodetic data set of Global Positioning System and multiple Synthetic Aperture Radar-derived displacement fields to estimate a 3D co-seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co-seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co-seismic uplift (>2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co-seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video-derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co-seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic data set constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike-slip faults in transtensional basins. Plain Language Summary The 28 September Palu earthquake ruptured the Palu-Koro fault in NW Sulawesi, Indonesia, and was followed by a devastating tsunami in Palu Bay. As the Palu-Koro fault accommodates mostly horizontal motion, many studies proposed that submarine landslides, rather than the earthquake itself, triggered the tsunami. This study focuses on the contribution of the earthquake to sea floor displacements. We present a unique geodetic data set and estimate a high-resolution 3D displacement field. The rupture is not a straight feature in the landscape, but rather contains bends. It is near those bends that significant vertical displacements occurred. From the onshore geodetic data we infer another fault bend below Palu Bay. Estimations of fault slip for several scenarios of offshore fault geometries point to a few meters of sea floor uplift. We use these slip models as input for tsunami models, and can qualitatively explain the observations of tsunami runup heights and video-based tsunami arrival times around Palu Bay. Only at a few locations our models cannot explain tsunami observations, which leaves open the contribution of other possible sources to the tsunami locally. The Palu case underlines the potential importance of fault bends to tsunami generation for similar tectonic settings around the world. SIMONS ET AL.

Research paper thumbnail of For a Z-Level Coordinate Models

© The Author(s) 2010. This article is published with open access at Springerlink.com Abstract In ... more © The Author(s) 2010. This article is published with open access at Springerlink.com Abstract In this paper, we focus on a conservative mo-mentum advection discretisation in the presence of z-layers. While in the 2D case conservation of momentum is achieved automatically for an Eulerian advection scheme, special attention is required in the multi-layer case. We show here that an artificial vertical structure of the flow can be introduced solely by the presence of the z-layers, which we refer to as the staircase problem. To avoid this staircase problem, the z-layers have to be remapped in a specific way. The remapping procedure also deals with the case of an uneven number of layers adjacent to a column side, thus allowing one to simulate flooding and drying phenomena in a 3D model.

Research paper thumbnail of Impacts of Tropical Cyclones on the Caribbean Under Future Climate Conditions

Journal of Geophysical Research: Oceans, 2021

Joint effects of the dynamic sea-level rise projected changes in the large-scale atmosphere/ ocea... more Joint effects of the dynamic sea-level rise projected changes in the large-scale atmosphere/ ocean circulation, and wave climate on hurricane-induced extreme water levels in the Caribbean region are assessed. We use the 2D-depth integrated ADCIRC + SWAN wave-ocean model, baroclinically coupled to an ocean-eddying version of the Community Earth System Model, to compare impacts of the September 2017 hurricanes with projected impacts of similar hypothetical tropical storms occurring in the future. The model predicts only minor changes in the hurricane-induced extreme water levels for those Caribbean islands which were severely devastated by the 2017 tropical storms (Irma and Maria). That is, provided that the hurricane intensity remains at the present-day level, the global mean sea-level rise is the main future coastal flood risk factor. Plain Language Summary The unique geophysical setting makes the Caribbean region extremely vulnerable to climatic changes experienced over the past few decades. The majority of the population and important infrastructures such as ports and airports are concentrated in the coastal zones which are at risk of permanent flooding as sea level continues to rise. The economy of the small Caribbean islands is heavily dependent on tourism and associated industries which are under pressure due to coral bleaching and coastal erosion. Additionally, the Caribbean region experiences intense and frequent extreme weather events which can potentially become more destructive in the future. As it is uncertain whether the hurricanes themselves will change, we investigate how the present-day tropical cyclones will impact the Caribbean in the future. Our results indicate that islands in the Northeast Caribbean will not be at higher risk of hurricane-induced flooding in the future if coastal infrastructure and ecosystems (coral reefs and seagrass meadows) can withstand the sea-level rise and continue to provide important coastal protection services. In contrast, the projected increase in wave height in the southern Caribbean can lead to more coastal flooding and beach erosion in these areas. KLEPTSOVA ET AL.

Research paper thumbnail of Ocean model resolution dependence of Caribbean sea-level projections

Scientific Reports, 2020

Sea-level rise poses severe threats to coastal and low-lying regions around the world, by exacerb... more Sea-level rise poses severe threats to coastal and low-lying regions around the world, by exacerbating coastal erosion and flooding. Adequate sea-level projections over the next decades are important for both decision making and for the development of successful adaptation strategies in these coastal and low-lying regions to climate change. Ocean components of climate models used in the most recent sea-level projections do not explicitly resolve ocean mesoscale processes. Only a few effects of these mesoscale processes are represented in these models, which leads to errors in the simulated properties of the ocean circulation that affect sea-level projections. Using the Caribbean Sea as an example region, we demonstrate a strong dependence of future sea-level change on ocean model resolution in simulations with a global climate model. The results indicate that, at least for the Caribbean Sea, adequate regional projections of sea-level change can only be obtained with ocean models whi...

Research paper thumbnail of On a momentum conservative z-layer unstructured C-grid ocean model with flooding

Ocean Modelling, 2012

ABSTRACT We present a z-layer unstructured C-grid finite volume hydrostatic model. An efficient a... more ABSTRACT We present a z-layer unstructured C-grid finite volume hydrostatic model. An efficient and highly scalable implicit technique for solution of the free surface equation is combined with an Eulerian approach for the advection of momentum. We show that an accurate velocity reconstruction procedure is of crucial importance not only for discretization of the Coriolis term, but also for the correct advection of momentum, especially in the multilayer case. Unlike other z-layer models the method presented here ensures that the staircase representation of bathymetry and free surface has no influence on the vertical structure of the flow. The method is therefore guaranteed to be strictly momentum conservative, also in the layers containing the free surface and bed. A number of test cases are presented to show that the model is able to accurately simulate Coriolis dominated flows and flooding and drying processes both in the depth-averaged case and in the presence of multiple z-layers. We use a simulation of 2004 Indian Ocean tsunami to evaluate the ability of the method to simulate fast propagating tsunami waves and detailed inundation processes. Results obtained using two different rupture models are compared to the tide gauge arrival times, satellite altimetry data and the inundation observations in the Banda Aceh area. The comparison is used not only to assess the quality of the underlying rupture models but also to determine the value of the available data sources for such an assessment.

Research paper thumbnail of On the accurate and stable reconstruction of tangential velocities in C-grid ocean models

Ocean Modelling, 2009

The Arakawa C-grid is in widespread use in structured grid atmospheric and oceanic models. It now... more The Arakawa C-grid is in widespread use in structured grid atmospheric and oceanic models. It now forms the grid of choice for a number of efficient and compact unstructured grid codes. In order to calculate the Coriolis terms, the C-grid requires the interpolation of the tangential velocities. In the case of a finite volume and or finite difference C-grid model, the tangential velocities have to be reconstructed from the cell normal velocities. This has to be handled with care otherwise the calculated Coriolis terms can be inaccurate, and even lead to instabilities. The interpolation matrix used to calculate the tangential velocities has to be skew-symmetric otherwise it can be shown to be unstable. Moreover, we show that the velocity reconstruction should be consistent with the discretized flow equations. Here a number of reconstructions for the tangential velocity components are described. We show that one has superior properties in the case of variable topography. Furthermore, we show that it is applicable for both structured and unstructured grids consisting of any cyclic polygons. We believe the result is therefore of general applicability to both structured and unstructured grid modellers who employ a classic Arakawa Cgrid.

Research paper thumbnail of An accurate momentum advection scheme for a z-level coordinate models

Ocean Dynamics, 2010

In this paper, we focus on a conservative momentum advection discretisation in the presence of zl... more In this paper, we focus on a conservative momentum advection discretisation in the presence of zlayers. While in the 2D case conservation of momentum is achieved automatically for an Eulerian advection scheme, special attention is required in the multi-layer case. We show here that an artificial vertical structure of the flow can be introduced solely by the presence of the z-layers, which we refer to as the staircase problem. To avoid this staircase problem, the z-layers have to be remapped in a specific way. The remapping procedure also deals with the case of an uneven number of layers adjacent to a column side, thus allowing one to simulate flooding and drying phenomena in a 3D model.

Research paper thumbnail of OKleptsova/TC-Caribbean

Scripts for plotting/analysing the processed model output from "Impacts of 2017 Tropical Cyc... more Scripts for plotting/analysing the processed model output from "Impacts of 2017 Tropical Cyclones on the Caribbean under sea level and climate conditions for 2100"

Research paper thumbnail of Comparison of the ensemble Kalman filter and a modified representer method for sensitivity to prior data

In closed-loop reservoir management, data assimilation algorithms or automated history matching m... more In closed-loop reservoir management, data assimilation algorithms or automated history matching methods can be used to support decision-making tools. Due to prior information, which the user has to supply to the data assimilation procedure, it can never be fully automatic. For example, a statistical description of the reservoir properties must be formulated, as well as the uncertainty of the measurements. In a synthetic numerical experiment these weighting factors are known; in a field application they are not. One could say that there are not only uncertainties in the data and the reservoir properties, but there is also "uncertainty in the uncertainty". In this article the robustness of the Ensemble (Square Root) Kalman Filter and a gradient-based algorithm using Representer Expansions are compared with respect to prior input data. Some algorithm dependent settings are explored to try to make the filter reproduce the results of the Representer Method: the ensemble size, the initialization method and the Kalman update. The concept of assimilating data more then once with dampened weighting factors (added uncertainty) is introduced. First the equations that underlie the Ensemble Filter and the Representer Method are given. Then numerical experiments are presented and two measures of quantifying the success of the methods are introduced. According to one such measure, the Representer Method performed better for all numerical examples considered. The parameters of the filter can be chosen such that the filter with the correct input data is equally successful as the Representer Method, using the second measure. When the methods are fed with the wrong prior input, the second measure also favours the Representer Method, so for the examples considered in this article the Representer Method is less sensitive to "wrong" user input that the Kalman Filter.

Research paper thumbnail of Unstructured Orthogonal Meshes for Modeling Coastal and Ocean Flows

In this thesis a z?layer unstructured C-grid finite volume hydrostatic model is presented. An eff... more In this thesis a z?layer unstructured C-grid finite volume hydrostatic model is presented. An efficient and highly scalable implicit technique for the solution of the free surface equation is combined with an Eulerian approach for the advection of momentum. A consistent velocity reconstruc- tion procedure which not only satisfies the continuity law but also guarantees the discrete kinetic energy conservation is presented. It is shown that an ac- curate velocity reconstruction procedure is of crucial importance not only for discretization of the Coriolis term, but also for the correct advection of mo- mentum, especially in the multilayer case. Unlike other z?layer models the method presented here ensures that the staircase representation of bathymetry and free surface has no influence on the vertical structure of the flow. The method is therefore guaranteed to be strictly momentum conservative, also in the layers containing the free surface and bed. A number of test cases are present...

Research paper thumbnail of A tsunami generated by a strike-slip event: constraints from GPS and SAR data on the 2018 Palu earthquake

A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 M w = 7.5 Palu earthqu... more A devastating tsunami struck Palu Bay in the wake of the 28 September 2018 M w = 7.5 Palu earthquake (Sulawesi, Indonesia). With a predominantly strike-slip mechanism, the question remains whether this unexpected tsunami was generated by the earthquake itself, or rather by earthquake-induced landslides. In this study we examine the tsunami potential of the co-seismic deformation. To this end, we present a novel geodetic data set of Global Positioning System and multiple Synthetic Aperture Radar-derived displacement fields to estimate a 3D co-seismic surface deformation field. The data reveal a number of fault bends, conforming to our interpretation of the tectonic setting as a transtensional basin. Using a Bayesian framework, we provide robust finite fault solutions of the co-seismic slip distribution, incorporating several scenarios of tectonically feasible fault orientations below the bay. These finite fault scenarios involve large co-seismic uplift (>2 m) below the bay due to thrusting on a restraining fault bend that connects the offshore continuation of two parallel onshore fault segments. With the co-seismic displacement estimates as input we simulate a number of tsunami cases. For most locations for which video-derived tsunami waveforms are available our models provide a qualitative fit to leading wave arrival times and polarity. The modeled tsunamis explain most of the observed runup. We conclude that co-seismic deformation was the main driver behind the tsunami that followed the Palu earthquake. Our unique geodetic data set constrains vertical motions of the sea floor, and sheds new light on the tsunamigenesis of strike-slip faults in transtensional basins. Plain Language Summary The 28 September Palu earthquake ruptured the Palu-Koro fault in NW Sulawesi, Indonesia, and was followed by a devastating tsunami in Palu Bay. As the Palu-Koro fault accommodates mostly horizontal motion, many studies proposed that submarine landslides, rather than the earthquake itself, triggered the tsunami. This study focuses on the contribution of the earthquake to sea floor displacements. We present a unique geodetic data set and estimate a high-resolution 3D displacement field. The rupture is not a straight feature in the landscape, but rather contains bends. It is near those bends that significant vertical displacements occurred. From the onshore geodetic data we infer another fault bend below Palu Bay. Estimations of fault slip for several scenarios of offshore fault geometries point to a few meters of sea floor uplift. We use these slip models as input for tsunami models, and can qualitatively explain the observations of tsunami runup heights and video-based tsunami arrival times around Palu Bay. Only at a few locations our models cannot explain tsunami observations, which leaves open the contribution of other possible sources to the tsunami locally. The Palu case underlines the potential importance of fault bends to tsunami generation for similar tectonic settings around the world. SIMONS ET AL.

Research paper thumbnail of For a Z-Level Coordinate Models

© The Author(s) 2010. This article is published with open access at Springerlink.com Abstract In ... more © The Author(s) 2010. This article is published with open access at Springerlink.com Abstract In this paper, we focus on a conservative mo-mentum advection discretisation in the presence of z-layers. While in the 2D case conservation of momentum is achieved automatically for an Eulerian advection scheme, special attention is required in the multi-layer case. We show here that an artificial vertical structure of the flow can be introduced solely by the presence of the z-layers, which we refer to as the staircase problem. To avoid this staircase problem, the z-layers have to be remapped in a specific way. The remapping procedure also deals with the case of an uneven number of layers adjacent to a column side, thus allowing one to simulate flooding and drying phenomena in a 3D model.

Research paper thumbnail of Impacts of Tropical Cyclones on the Caribbean Under Future Climate Conditions

Journal of Geophysical Research: Oceans, 2021

Joint effects of the dynamic sea-level rise projected changes in the large-scale atmosphere/ ocea... more Joint effects of the dynamic sea-level rise projected changes in the large-scale atmosphere/ ocean circulation, and wave climate on hurricane-induced extreme water levels in the Caribbean region are assessed. We use the 2D-depth integrated ADCIRC + SWAN wave-ocean model, baroclinically coupled to an ocean-eddying version of the Community Earth System Model, to compare impacts of the September 2017 hurricanes with projected impacts of similar hypothetical tropical storms occurring in the future. The model predicts only minor changes in the hurricane-induced extreme water levels for those Caribbean islands which were severely devastated by the 2017 tropical storms (Irma and Maria). That is, provided that the hurricane intensity remains at the present-day level, the global mean sea-level rise is the main future coastal flood risk factor. Plain Language Summary The unique geophysical setting makes the Caribbean region extremely vulnerable to climatic changes experienced over the past few decades. The majority of the population and important infrastructures such as ports and airports are concentrated in the coastal zones which are at risk of permanent flooding as sea level continues to rise. The economy of the small Caribbean islands is heavily dependent on tourism and associated industries which are under pressure due to coral bleaching and coastal erosion. Additionally, the Caribbean region experiences intense and frequent extreme weather events which can potentially become more destructive in the future. As it is uncertain whether the hurricanes themselves will change, we investigate how the present-day tropical cyclones will impact the Caribbean in the future. Our results indicate that islands in the Northeast Caribbean will not be at higher risk of hurricane-induced flooding in the future if coastal infrastructure and ecosystems (coral reefs and seagrass meadows) can withstand the sea-level rise and continue to provide important coastal protection services. In contrast, the projected increase in wave height in the southern Caribbean can lead to more coastal flooding and beach erosion in these areas. KLEPTSOVA ET AL.

Research paper thumbnail of Ocean model resolution dependence of Caribbean sea-level projections

Scientific Reports, 2020

Sea-level rise poses severe threats to coastal and low-lying regions around the world, by exacerb... more Sea-level rise poses severe threats to coastal and low-lying regions around the world, by exacerbating coastal erosion and flooding. Adequate sea-level projections over the next decades are important for both decision making and for the development of successful adaptation strategies in these coastal and low-lying regions to climate change. Ocean components of climate models used in the most recent sea-level projections do not explicitly resolve ocean mesoscale processes. Only a few effects of these mesoscale processes are represented in these models, which leads to errors in the simulated properties of the ocean circulation that affect sea-level projections. Using the Caribbean Sea as an example region, we demonstrate a strong dependence of future sea-level change on ocean model resolution in simulations with a global climate model. The results indicate that, at least for the Caribbean Sea, adequate regional projections of sea-level change can only be obtained with ocean models whi...

Research paper thumbnail of On a momentum conservative z-layer unstructured C-grid ocean model with flooding

Ocean Modelling, 2012

ABSTRACT We present a z-layer unstructured C-grid finite volume hydrostatic model. An efficient a... more ABSTRACT We present a z-layer unstructured C-grid finite volume hydrostatic model. An efficient and highly scalable implicit technique for solution of the free surface equation is combined with an Eulerian approach for the advection of momentum. We show that an accurate velocity reconstruction procedure is of crucial importance not only for discretization of the Coriolis term, but also for the correct advection of momentum, especially in the multilayer case. Unlike other z-layer models the method presented here ensures that the staircase representation of bathymetry and free surface has no influence on the vertical structure of the flow. The method is therefore guaranteed to be strictly momentum conservative, also in the layers containing the free surface and bed. A number of test cases are presented to show that the model is able to accurately simulate Coriolis dominated flows and flooding and drying processes both in the depth-averaged case and in the presence of multiple z-layers. We use a simulation of 2004 Indian Ocean tsunami to evaluate the ability of the method to simulate fast propagating tsunami waves and detailed inundation processes. Results obtained using two different rupture models are compared to the tide gauge arrival times, satellite altimetry data and the inundation observations in the Banda Aceh area. The comparison is used not only to assess the quality of the underlying rupture models but also to determine the value of the available data sources for such an assessment.

Research paper thumbnail of On the accurate and stable reconstruction of tangential velocities in C-grid ocean models

Ocean Modelling, 2009

The Arakawa C-grid is in widespread use in structured grid atmospheric and oceanic models. It now... more The Arakawa C-grid is in widespread use in structured grid atmospheric and oceanic models. It now forms the grid of choice for a number of efficient and compact unstructured grid codes. In order to calculate the Coriolis terms, the C-grid requires the interpolation of the tangential velocities. In the case of a finite volume and or finite difference C-grid model, the tangential velocities have to be reconstructed from the cell normal velocities. This has to be handled with care otherwise the calculated Coriolis terms can be inaccurate, and even lead to instabilities. The interpolation matrix used to calculate the tangential velocities has to be skew-symmetric otherwise it can be shown to be unstable. Moreover, we show that the velocity reconstruction should be consistent with the discretized flow equations. Here a number of reconstructions for the tangential velocity components are described. We show that one has superior properties in the case of variable topography. Furthermore, we show that it is applicable for both structured and unstructured grids consisting of any cyclic polygons. We believe the result is therefore of general applicability to both structured and unstructured grid modellers who employ a classic Arakawa Cgrid.

Research paper thumbnail of An accurate momentum advection scheme for a z-level coordinate models

Ocean Dynamics, 2010

In this paper, we focus on a conservative momentum advection discretisation in the presence of zl... more In this paper, we focus on a conservative momentum advection discretisation in the presence of zlayers. While in the 2D case conservation of momentum is achieved automatically for an Eulerian advection scheme, special attention is required in the multi-layer case. We show here that an artificial vertical structure of the flow can be introduced solely by the presence of the z-layers, which we refer to as the staircase problem. To avoid this staircase problem, the z-layers have to be remapped in a specific way. The remapping procedure also deals with the case of an uneven number of layers adjacent to a column side, thus allowing one to simulate flooding and drying phenomena in a 3D model.