An investigation of the thermal response to meteorological forcing in a hydrodynamic model of Lake Superior

Lake Superior, the largest lake in the world by surface area and third largest by volume, features strong spatiotemporal thermal variability due to its immense size and complex bathymetry. The objectives of this study are to document our recent modeling experiences on the simulation of the lake thermal structure and to explore underlying dynamic explanations of the observed modeling success. In this study, we use a three‐dimensional hydrodynamic model (FVCOM—Finite Volume Community Ocean Model) and an assimilative weather forecasting model (WRF—Weather Research and Forecasting Model) to study the annual heating and cooling cycle of Lake Superior. Model experiments are carried out with meteorological forcing based on interpolation of surface weather observations, on WRF and on Climate Forecast System Reanalysis (CFSR) reanalysis data, respectively. Model performance is assessed through comparison with satellite products and in situ measurements. Accurate simulations of the lake thermal structure are achieved through (1) adapting the COARE algorithm in the hydrodynamic model to derive instantaneous estimates of latent/sensible heat fluxes and upward longwave radiation based on prognostic surface water temperature simulated within the model as opposed to precomputing them with an assumed surface water temperature; (2) estimating incoming solar radiation and downward longwave radiation based on meteorological measurements as opposed to meteorological model‐based estimates; (3) using the weather forecasting model to provide high‐resolution dynamically constrained wind fields as opposed to wind fields interpolated from station observations. Analysis reveals that the key to the modeling success is to resolve the lake‐atmosphere interactions and apply appropriate representations of different meteorological forcing fields, based on the nature of their spatiotemporal variability. The close agreement between model simulation and observations also suggests that the 3‐D hydrodynamic model can provide reliable spatiotemporal estimates of heat budgets over Lake Superior and similar systems. Although there have been previous studies which analyzed the impact of the spatiotemporal variability of overwater wind fields on lake circulation, we believe this is the first detailed analysis of the importance of spatiotemporal variability of heat flux components on hydrodynamic simulation of 3‐D thermal structure in a lake.Key Points:Thermal response to meteorological forcing of Lake Superior is examinedKey to the modeling success is to resolve the lake‐air interactionsSpatiotemporal variability of surface meteorological components is importantPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/113112/1/jgrc21314.pd

Multiple Salinity Equilibria and Resilience of Persian/Arabian Gulf Basin Salinity to Brine Discharge

The Persian/Arabian Gulf is the most important region for seawater desalination. Surrounding countries produce about 50% of global desalinated seawater. If Gulf salinity significantly rises because of desalination effluent (brine), marine ecosystems and the water supply for many population centers will be threatened. In order to quantify current and future impacts of seawater desalination on Gulf salinity and avoid costly environmental problems, it is vital to first examine the present Gulf salinity state and its response to salinity perturbation (i.e., determine its stability). Here, using a coupled Gulf-Atmosphere numerical climate model, we test the hypothesis that the Gulf has a single stable equilibrium state under the current climate. Simulations with different initializations under identical external forcing show that the natural coupled Gulf-Atmosphere system may exhibit a mixture of unstable and stable equilibrium salinity states. When continuous salinity perturbation is added to the simulations, results show that the present Gulf equilibrium state, characterized by annual mean basin-average salinity of about 40.5 g/kg, is stable. We conclude that Gulf basin salinity is resilient to present brine discharge activities under the current climate

Static test rig development and application for an airliner’s hyperstatic aero-engine pylon structure

A set of test system, which is suitable for static test of a hyperstatic aero-engine pylon structure of a certain aircraft, was designed according to the requirements of static structure test. This test technology solved some key problems such as support stiffness simulation of hyperstatic engine pylon and aero-engine loading simulation. Based on these experimental techniques, the static test on a hyperstatic aero-engine pylon of a certain aircraft has been completed in the paper. The test results testified to the stable and reliable working performance of the test system. And the aero-engine pylon, the test specimen, didn’t produce any crack or harmful large deformation under all work conditions, indicating that it has met the design requirements on both static strength and stiffness. The test technology can be applied in static tests of similar hyperstatic test specimen. The test data can serve as a basis for structural static strength and stiffness property evaluation of the aero-engine pylon

Improving Scene Text Image Super-resolution via Dual Prior Modulation Network

Scene text image super-resolution (STISR) aims to simultaneously increase the resolution and legibility of the text images, and the resulting images will significantly affect the performance of downstream tasks. Although numerous progress has been made, existing approaches raise two crucial issues: (1) They neglect the global structure of the text, which bounds the semantic determinism of the scene text. (2) The priors, e.g., text prior or stroke prior, employed in existing works, are extracted from pre-trained text recognizers. That said, such priors suffer from the domain gap including low resolution and blurriness caused by poor imaging conditions, leading to incorrect guidance. Our work addresses these gaps and proposes a plug-and-play module dubbed Dual Prior Modulation Network (DPMN), which leverages dual image-level priors to bring performance gain over existing approaches. Specifically, two types of prior-guided refinement modules, each using the text mask or graphic recognition result of the low-quality SR image from the preceding layer, are designed to improve the structural clarity and semantic accuracy of the text, respectively. The following attention mechanism hence modulates two quality-enhanced images to attain a superior SR result. Extensive experiments validate that our method improves the image quality and boosts the performance of downstream tasks over five typical approaches on the benchmark. Substantial visualizations and ablation studies demonstrate the advantages of the proposed DPMN. Code is available at: https://github.com/jdfxzzy/DPMN.Comment: Accepted by AAAI-202

Observing system simulation experiments with ensemble Kalman filters in Nantucket Sound, Massachusetts

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 116 (2011): C01011, doi:10.1029/2010JC006428.Observing system simulation experiments (OSSEs) were performed for Nantucket Sound, Massachusetts, as a pilot study for the design of optimal monitoring networks in the coastal ocean. Experiments were carried out using the ensemble Kalman filter (EnKF) for data assimilation with ensemble transform Kalman filter (EnTKF) and proper orthogonal decomposition (POD) for selecting the optimal monitoring sites. The singular evolutive interpolated Kalman filter (SEIK) was compared with EnKF for the data assimilation efficiency. Running the unstructured grid Finite-Volume Community Ocean Model (FVCOM) with perturbed initial fields of currents, water temperature, and salinity show that in this shallow coastal system, the velocity and surface elevation are able to restore themselves back to the true state over an inertial time scale after perturbation without data assimilation, while the water temperature and salinity are not. This suggests that in this vertically well mixed region with strong tidal influence, monitoring should be targeted at water properties rather than velocities. By placing measurement sites at an entrance or exit or a location with the maximum signal variance (EnTKF) or at extrema of the dominant EOF spatial modes (POD), we evaluated the capability of EnTKF and POD in designing the optimal monitoring site for the forecast model system in this region. The results suggest that understanding the multiscale dynamical nature of the system is essential in designing an optimal monitoring network since “optimal” sites suggested by an assimilation method may only represent a local-scale feature that has little influence on a region-wide system. Comparing EnKF and SEIK simulations shows that SEIK can significantly improve the data assimilation efficiency by reducing the ensemble number and increasing the convergence rate.This publication is the result of research sponsored by the MIT Sea Grant College Program under NOAA grant NA06OAR4170019; MIT SG projects 2006‐RC‐103, 2006‐R/RC‐102, 2006‐R/RC‐107, and 2008‐R/RC‐107; NERACOOS; and MWRA funds as well as U.S. GLOBEC Northwest Atlantic/Georges Bank Program NSF grants (OCE‐0234545, OCE‐0227679, OCE‐0606928, OCE‐ 0712903, OCE‐0732084, and OCE‐0726851)