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Stammer D.,University of Hamburg | Cazenave A.,CNRS Geophysical Research and Oceanographic Laboratory | Ponte R.M.,Atmospheric and Environmental Research Inc. | Tamisiea M.E.,National Oceanographic Center
Annual Review of Marine Science | Year: 2013

Regional sea level changes can deviate substantially from those of the global mean, can vary on a broad range of timescales, and in some regions can even lead to a reversal of long-term global mean sea level trends. The underlying causes are associated with dynamic variations in the ocean circulation as part of climate modes of variability and with an isostatic adjustment of Earth's crust to past and ongoing changes in polar ice masses and continental water storage. Relative to the coastline, sea level is also affected by processes such as earthquakes and anthropogenically induced subsidence. Present-day regional sea level changes appear to be caused primarily by natural climate variability. However, the imprint of anthropogenic effects on regional sea level-whether due to changes in the atmospheric forcing or to mass variations in the system-will grow with time as climate change progresses, and toward the end of the twenty-first century, regional sea level patterns will be a superposition of climate variability modes and natural and anthropogenically induced static sea level patterns. Attribution and predictions of ongoing and future sea level changes require an expanded and sustained climate observing system. © 2013 by Annual Reviews. All rights reserved. Source

Piecuch C.G.,Atmospheric and Environmental Research Inc.
Journal of Geophysical Research: Oceans | Year: 2013

Ocean bottom pressure variability, derived from Release-05 Gravity Recovery and Climate Experiment time-variable gravity coefficients over the ocean, is investigated along the tropical North Pacific for the case of long time scales (>1 yr) and large space scales (>750 km). To interpret the observations, a linear model of the bottom pressure response to interior wind stress curl is derived on the basis of normal vertical modes; the adjustment comprises contributions from barotropic Sverdrup dynamics as well as first baroclinic mode Rossby waves. Model solutions are evaluated numerically using time-mean ocean stratification from the Ocean Comprehensible Atlas and time-varying surface wind stress from the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis. In the western tropical North Pacific, model and data compare favorably; simulated and observed time series are significantly correlated, and the model generally explains more than half of the data variance; the good correspondence between model and data speaks to the good quality of the satellite-derived fields. In the central and eastern tropical North Pacific, findings are more ambiguous; model and data time series are mostly not significantly correlated, and simulations generally explain less than half of the data variance; discrepancies between model and data could point to physics absent from the model, for example, signals generated at the eastern boundary. Results provide observational demonstration that baroclinic contributions to bottom pressure changes can be important at low latitudes and low frequencies; findings hint at a basin-scale influence of tropical climate modes on the ocean bottom pressure field. © 2013. American Geophysical Union. All Rights Reserved. Source

Ponte R.M.,Atmospheric and Environmental Research Inc.
Geophysical Research Letters | Year: 2012

An ocean state estimate constrained by most available data is explored to assess characteristics of variability in deep steric height-a mostly unobserved quantity, yet important for understanding the relation between sea level, heat content and other ocean climate parameters. Results are based on monthly-averaged steric height anomalies, vertically integrated over the "unobserved" deep ocean (below ∼1700 m). Excluding linear trends, variability in deep steric height is typically 10-20% of that in the upper ocean, with larger values seen in extensive regions. Enhanced deep variability, at monthly to interannual time scales, occurs in areas of strong eddy energy. Deep signals are mostly thermosteric in nature, with halosteric contributions tightly correlated and generally compensating in the Atlantic and Indian oceans and adding in the Pacific. Potential inference of deep signals from knowledge of the upper ocean is hampered by poor correlations, and regressions based on upper ocean steric height fail to represent the estimated deep variability. Monthly sampling at ∼2° scales would allow for best determination of deep variability and long term trends. Copyright 2012 by the American Geophysical Union. Source

Agency: NSF | Branch: Standard Grant | Program: | Phase: ATMOSPHERIC CHEMISTRY | Award Amount: 227.82K | Year: 2016

This research is focused on studying the aging of emissions from biomass burning. Small particles emitted from biomass combustion can react in the atmosphere, changing their size, number, and composition. These aging processes will be modeled and the model results will be tested against actual data from field campaigns.

The following questions will be investigated: (1) What are the chemical processes that, when combined with the dispersion and coagulation of biomass-burning emissions, capture the evolution of aerosol size and number concentrations seen in the laboratory and the field? (2) Are the secondary organic aerosol (SOA) formation rates and size-distribution changes measured in lab experiments consistent with the field measurements of aerosol aging? If they are not, can we determine why (e.g. lack of continuous dilution or wall losses in chamber experiments)? (3) What properties most strongly determine the aged biomass-burning aerosol size and number? E.g. total mass emission flux, fresh particle size, fuel type, modified combustion efficiency, wind speed, fire area, vertical mixing depth, sunlight. (4) Can the variability in aged biomass-burning aerosol size and number be captured by a simple parameterization that is a function of the most important of the above properties?

Agency: NSF | Branch: Standard Grant | Program: | Phase: CR, Earth System Models | Award Amount: 450.67K | Year: 2015

Devastating storm surges result from a combination of the characteristics of the storm itself; e.g. wind strength, direction of storm approach to the coast, storm duration; and from preconditioning due to rising sea level, such that the storm waves can overtop protective barriers that provided adequate defense when sea level was lower. Water added to the oceans from melting glacier, ice caps, and ice sheets is a significant cause of sea level rise. In particular, the Greenland Ice Sheet is projected to be a major contributor to sea level rise during the present century. Much of the recently observed contribution is a response to warming ocean temperatures around Greenland, which cause marine-terminating glaciers to melt and calve icebergs into the ocean. Models that are used to predict this anticipated sea level rise exhibit a broad spread in ocean temperatures around the Greenland Ice Sheet, for reasons that are not well understood. This project is designed to improve understanding of the physical processes responsible for this spread in projected ocean temperatures amongst models.

The lead principal investigator for this project, through his ongoing work with local and state governments, will ensure that the results are relevant to and transferred to planners and policy-makers. His parent company will assist in a similar information transfer to the private sector. The project will also contribute to workforce development through support for the training of a graduate student in state-of-the-art interdisciplinary science and through support of three early-career scientists during their formative years.

The detailed mechanistic understanding provided by this work will reveal: the physical processes underlying the spread in CMIP5 projections of near-Greenland ocean warming; the nature and location of the surface fluxes driving warming; and the linkages between warming at different depths and different locations around the ice sheet. It will also provide a physical basis for linkages between near-Greenland ocean warming and other related Arctic climate system processes (e.g. Northern Hemisphere sea ice and the Atlantic Meridional Overturning Circulation). These linkages are vital to understanding how climate-driven changes in Greenland?s mass balance are coupled to other processes such as the loss of sea ice and more general polar surface warming. A two-part strategy will be used to evaluate causal physical mechanisms underlying the spread in CMIP5 projections of ocean warming in an efficient and detailed manner. Statistical analysis of ocean temperature will cluster AOGCMs by their ocean warming patterns and their co-variability (across space and models) with surface fluxes and other climate processes. Numerical simulations, forced by surface fluxes from a representative subset of CMIP5 models, will then be used to develop detailed oceanic heat budgets. Targeted perturbation experiments will isolate the role of atmospheric and Greenland meltwater flux in the context of widely varying CMIP5 representations of the Arctic freshwater budget.

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