Accuracy assessment of global barotropic ocean tide models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109077/1/rog_stammeretal_tidereviewpaper_2014.pd

Large-scale impact of Saharan dust on the North Atlantic Ocean circulation

The potential for a dynamical impact of Saharan mineral dust on the North Atlantic Ocean large-scale circulation is investigated. To this end, an ocean general circulation model forced by atmospheric fluxes is perturbed by an idealized, seasonally varying, net shortwave flux anomaly, as it results from remote sensing observations of aerosol optical thickness representing Saharan dust load in the atmosphere. The dust dynamical impact on the circulation is assessed through a comparison between perturbed and an unperturbed run. Results suggest that, following the dust-induced shortwave irradiance anomaly, a buoyancy anomaly is created in the Atlantic offshore the African coast, which over the course of the time propagates westward into the interior Atlantic while progressively subducting. Changes in the large-scale barotropic and overturning circulations are significant after 3 years, which coincides with the elapsed time required by the bulk of the buoyancy perturbation to reach the western boundary of the North Atlantic. Although small in amplitude, the changes in the meridional overturning are of the same order as interannual-to-decadal variability. Variations in the amplitude of the forcing lead to changes in the amplitude of the response, which is almost linear during the first 3 years. In addition, a fast, but dynamically insignificant, response can be observed to propagate poleward along the eastern boundary of the North Atlantic, which contributes to a nonlinear response in the subpolar region north of 40°N

The Global ocean circulation during 1992-1997, estimated from ocean observations and a general circulation model

We discuss the three-dimensional oceanic state estimated for the period 1992- 1997 as it results from bringing together large-scale ocean data sets with a general circulation model. To bring the model into close agreement with ocean data, its initial temperature and salinity conditions where changed as well as the time-dependent surface fluxes of momentum, heat and freshwater. Resulting changes of those control fields are largely consistent with accepted uncertainties in the hydrographic climatology and meteorological analyses. Our results show that the assimilation procedure is able to correct for the traditional shortcomings of the flow field by changing the surface boundary conditions. Changes of the resulting flow field are predominantly on the gyre scale and affect many features which are often poorly simulated in traditional numerical simulations, such as the strengths of the Gulf Stream and its extension, the Azores Current and the anticyclonic circulation associated with the Labrador Sea. A detailed test of the results and their consistency with prior error assumptions shows that the constrained model has moved considerably closer to those observations which have been imposed as constraints, but also to independent data from the World Ocean Circulation Experiment not used in the assimilation procedure. In some regions where the comparisons remain indeterminate, not enough ocean observations are available. And in such situations, it is difficult to ascribe the residuals to either the model or the observations. We conclude from this experiment that we can find an acceptable solution to the global time-dependent ocean state estimation problem. As the estimates improve through the evolution of numerical models, computer power increases, and better assimilation schemes, improved and routine estimates will become possible

Science directions in a post-COP21-world of transient climate change: enabling regional to local predictions in support of reliable climate information

During recent decades, through theoretical considerations and analyses of observations andmodel simulations, the scientific community has fundamentally advanced our understanding of thecoupled climate system, thereby establishing that humans affect the Earth’s climate. Resulting from thisremarkable accomplishment, the COP21 agreement marks a historic turning point for climate research bycalling for actionable regional climate change information on time scales from seasonal to centuries for thebenefit of humanity, as well as living and nonliving elements of the Earth environment. Out of the underlyingUnited National Framework Convention on climate Change process, improving seamless regional climateforecast capabilities emerges as a key challenge for the international research community. Addressing itrequires a multiscale approach to climate predictions. Here we offer a vision that emphasizes enhancedscientific understanding of regional to local climate processes as the foundation for progress. The scientificchallenge is extreme due to the rich complexity of interactions and feedbacks between regional andglobal processes, each of which affects the global climate trajectory. To gain the necessary scientific insightand to turn it into actionable climate information require technical development, international coordination,and a close interaction between the science and stakeholder communities

Volume, heat, and freshwater transports of the global ocean circulation 1993-2000, estimated from a general circulation model constrained by World Ocean Circulation Experiment (WOCE) data.

An analysis of ocean volume, heat and freshwater transports from a fully con-strained general circulation model is described. Output from a data synthesis, or state estimation, method is used by which the model was forced to a large-scale, time varying global ocean data set over six years. Time-mean fluxes estimated from this fully time-dependent circulation have converged with independent time-independent estimates from box inversions over most parts of the world ocean but especially in the southern hemisphere. However, heat transport estimates differ substantially in the North Atlantic where our estimates result in only 1/2 previous heat transports. The estimated mean circulation around Australia involves a net volume flux of 14 Sv through the Indonesian Through flow and the Mozambique Channel. In addition we show that this flow regime exist on all time scales above one month rendering the variability in the South Pacific strongly coupled to the Indian Ocean. Moreover, the dynamically consistent variations in the model show temporal variability of oceanic heat fluxes, heat storage and atmospheric exchanges that are complex and with a strong dependence upon location, depth, and time-scale. Results presented demonstrate the great potential of an ocean /state estimation system to provide a dynamical description of the time-dependent observed heat transport and heat content changes and their relation to air-sea interactions

Global ocean modeling and state estimation in support of climate research

During the last decade it has become obvious that the ocean circulation shows vigorous variability on a wide range of time and space scales and that the concept of a "sluggish" and slowly varying circulation is rather elusive. Increasing emphasis has to be put, therefore, on observing the rapidly changing ocean state on time scales ranging from weeks to decades and beyond, and on understanding the ocean's response to changing atmospheric forcing conditions. As outlined in various strategy and implementation documents (e.g., the implementation plans of WOCE, AMS, CLIVAR, and GODAE) a combination of the global ocean data sets with a state-of-the-art numerical circulation model is required to interpret the various diverse data sets and to produce the best possible estimates of the time-varying ocean circulation. The mechanism of ocean state estimates is a powerful tool for such a "synthesis" of observations, obtained on very complex space-time pattern, into one dynamically consistent picture of the global time-evolving ocean circulation. This process has much in common with ongoing analysis and reanalysis activities in the atmospheric community. But because the ocean is, and will remain for the foreseeable future, substantially under-sampled, the burden put on the modeling and estimations components is substantially larger than in the atmosphere. Moreover, the smaller dynamical eddy scales which need to be properly parameterized or resolved in ocean model simulations, put stringent requirements on computational resources for ongoing and participated climate research

Fast Ensemble Smoothing

Smoothing is essential to many oceanographic, meteorological and hydrological applications. The interval smoothing problem updates all desired states within a time interval using all available observations. The fixed-lag smoothing problem updates only a fixed number of states prior to the observation at current time. The fixed-lag smoothing problem is, in general, thought to be computationally faster than a fixed-interval smoother, and can be an appropriate approximation for long interval-smoothing problems. In this paper, we use an ensemble-based approach to fixed-interval and fixed-lag smoothing, and synthesize two algorithms. The first algorithm produces a linear time solution to the interval smoothing problem with a fixed factor, and the second one produces a fixed-lag solution that is independent of the lag length. Identical-twin experiments conducted with the Lorenz-95 model show that for lag lengths approximately equal to the error doubling time, or for long intervals the proposed methods can provide significant computational savings. These results suggest that ensemble methods yield both fixed-interval and fixed-lag smoothing solutions that cost little additional effort over filtering and model propagation, in the sense that in practical ensemble application the additional increment is a small fraction of either filtering or model propagation costs. We also show that fixed-interval smoothing can perform as fast as fixed-lag smoothing and may be advantageous when memory is not an issue

The Science of Reading

Those who teach children to read are continually seeking answers to several questions that will improve their approaches to helping children learn

Античные и средневековые городища на дне Иссык-Куля

В статье дается обзор результатов многолетних подводных археологических разведок на озере Иссык-Куль. Приводятся данные по местоположению некоторых затопленных городищ античности и средних веков (Тору-Айгыр, Кара-ой, Чигу). Описываются наиболее интересные артефакты, найденные на дне озера.В статті дається огляд результатів багаторічних підводних археологічних розвідок на озері Іссик-Куль. Наводяться дані про місцезнаходження деяких затоплених городищ античності і середньовіччя (Тору-Айгир, Кара-ой, Чігу). Описуються найцікавіші артефакти, знайдені на дні озера.The article is a review of the results of many years’ underwater archaeological researches at lake Issik Kul. Data about the place of location of some Ancient and Medieval towns (Toru-Aygir, Kara-oy, Chigu) are given. Most interesting artefacts found at the bottom of the lake are described