Lagerloef G.,Earth and Space Research
Eos | Year: 2012
Understanding the links between ocean circulation, the global water cycle, and climate variations requires knowledge of ocean surface salinity. NASA's Aquarius satellite mission (http://aquarius.nasa.gov), which monitors the global open ocean surface salinity field, embarked on its science operations phase after completing the in-orbit performance assessment on 1 December 2011. The data (Figure 1) are already showing new and interesting information. © 2012 American Geophysical Union. All Rights Reserved.
Lilly J.M.,Earth and Space Research |
Olhede S.C.,University College London
IEEE Transactions on Signal Processing | Year: 2010
The generalizations of instantaneous frequency and instantaneous bandwidth to a bivariate signal are derived. These are uniquely defined whether the signal is represented as a pair of real-valued signals or as one analytic and one anti-analytic signal. A nonstationary but oscillatory bivariate signal has a natural representation as an ellipse whose properties evolve in time, and this representation provides a simple geometric interpretation for the bivariate instantaneous moments. The bivariate bandwidth is shown to consist of three terms measuring the degree of instability of the time-varying ellipse: amplitude modulation with fixed eccentricity, eccentricity modulation, and orientation modulation or precession. An application to the analysis of data from a free-drifting oceanographic float is presented and discussed. Copyright © 2010 IEEE.
Fricker H.A.,University of California at San Diego |
Padman L.,Earth and Space Research
Journal of Geophysical Research: Oceans | Year: 2012
We use data acquired between 1978 and 2008 by four satellite radar altimeter missions (Seasat, ERS-1, ERS-2 and Envisat) to determine multidecadal elevation change rates (dhi/dt) for six major Antarctic Peninsula (AP) ice shelves. In areas covered by the Seasat orbit (to 72.16°S), regional-averaged 30-year trends were negative (surface lowering), with rates between-0.03 and-0.16 m a-1. Surface lowering preceded the start of near-continuous radar altimeter operations that began with ERS-1 in 1992. The average rate of lowering for the first 14 years of the period was typically smaller than the 30-year average; the exception was the southern Wilkins Ice Shelf, which experienced negligible lowering between 2000 and 2008, when a series of large calving events began. Analyses of the continuous ERS/Envisat time series (to 81.5°) for 1992-2008 reveal a period of strong negative dhi/dt on most ice shelves between 1992 and 1995. Based on prior studies of regional atmospheric and oceanic conditions, we hypothesize that the observed elevation changes on Larsen C Ice Shelf are driven primarily by firn compaction while the western AP ice shelves are responding to changes in both surface mass balance and basal melt rates. Our time series also show that large changes in dhi/dt can occur on interannual time scales, reinforcing the importance of long time series altimetry to separate long-term trends associated with climate change from interannual to interdecadal natural variability. Copyright 2012 by the American Geophysical Union.
Agency: NSF | Branch: Standard Grant | Program: | Phase: PHYSICAL OCEANOGRAPHY | Award Amount: 464.38K | Year: 2014
Overview: Sea ice extent around Antarctica has slowly increased over the satellite era (1979-present), against the general decline of other global cryosphere components and contrary to modern negative sea ice extent trends in global coupled climate models (CCMs). Previous hypotheses have focused on large-scale mechanisms that impact the sea ice mass balance: changes in wind stress fields due to stratospheric ozone depletion; a more energetic Southern Ocean hydrologic cycle; increased downwelling long wave radiation; and enhanced freshwater production under ice shelves. An additional hypothesis will be tested: Mesoscale ocean processes that are not resolved in CCMs play a significant role in controlling ice edge position and sea-ice characteristics in the marginal ice zone and that inter-annual variability and trends in ocean mesoscale activity can drive changes in sea ice extent that are not closely correlated with the annual-averaged Southern Ocean state such as position of Antarctic Circumpolar Current fronts.
Intellectual Merit: Daily satellite-derived sea-ice concentration fields will be analyzed to determine the effect of ocean mesoscale variability on sea-ice edge characteristics that influence true and satellite-measured sea-ice extent. Statistics will include the increase in ice-edge length due to mesoscale processes as a measure of increased exposure of the Marginal Ice Zone to open-ocean processes. Sea ice extent derived from different gridded datasets of sea-ice concentration will be compared to determine whether inter-annual variability and trends in sea ice extent are sensitive to measurement methodology and spatial resolution. If justified by prior work, near-contemporaneous Envisat ASAR high-resolution radar images will then be compared with sea-ice concentration fields from AMSR-E. A database of tracked eddies will also be analyzed to determine whether eddies generated by Antarctic Circumpolar Current frontal instabilities and interactions with topography contribute to ice-edge variability. These analyses will be performed on circum-Antarctic and regional scales, at annual resolution to resolve inter-annual variability and trends.
The output from an eddy-permitting three-dimensional regional ocean model with coupled sea ice or a data-constrained ocean state model (Southern Ocean State Estimate) will be analyzed to investigate how well these models represent the ocean mesoscale contribution to ice-edge perturbations. The investigators will also develop their own idealized models of ocean/ice/atmosphere interactions at the ice edge to investigate mechanisms for generation of ice-edge fronts whose instabilities may be significant contributors to the ice-edge mesoscale field.
Broader Impacts: This study will elucidate the mechanisms coupling the highly energetic Southern Ocean mesoscale field with sea ice. Antarctic sea ice has a profound effect on albedo, ocean/atmosphere heat and moisture fluxes and gas exchange, and so is an important component of the global coupled climate system. The concurrent analyses of existing data and eddy-permitting ocean/sea-ice models will inform interpretation of sea-ice variability in modern CCMs, and so identify critical developments needed to improve their representation of sea ice. Careful examination of the marginal ice zone will help inform the interpretation of satellite retrievals of ice-edge position. The investigators will continue their participation in local outreach activities including presentations at Pacific Science Center (Seattle) and the Robinson Center for Young Scholars at the University of Washington, public talks in Oregon and frequent contributions on Climate Science to the Corvallis newspaper Opinion Page, development of a project web page targeted at a general audience, and updating their outreach web site including polar photo server.
Agency: NSF | Branch: Standard Grant | Program: | Phase: PHYSICAL OCEANOGRAPHY | Award Amount: 130.93K | Year: 2010
Wind-forced inertial oscillations of the surface mixed layer generate propagating near-inertial waves, which eventually break and drive small-scale mixing in the ocean interior. The importance of such small-scale mixing for the large-scale circulation is becoming increasingly apparent. However, based on the current range of estimates, the flux of energy from the mixed layer to propagating near-inertial waves may either play a major role in the oceans power budget, comparable to the tidal input, or may be entirely negligible - a fundamental uncertainty.
This study uses data analyses, supplemented by numerical modeling, to assess the role of eddies in shaping the global character of mixed layer oscillations. The primary goal is a more accurate estimate of the global contribution of wind forcing to the near-inertial wave field. The strategy is built around accessing and interpreting the dynamical information contained in a recently enhanced dataset - the Global Drifter Program network of surface buoys, now available with approximately hourly resolution since 2005. The use of a new set of mathematical tools will capture the time-varying properties of inertial oscillations in the mixed layer, and simultaneously, those of the mesoscale eddies expected to modulate the inertial environment.
Intellectual Merit: This process-oriented study will be an important step in the larger goal of understanding and quantifying the mechanical energy budget of the ocean. It will have a direct benefit to the representation of the oceans response to wind forcing in general circulation models, and consequently, to our ability to accurately predict climate-scale variability. Furthermore, the approach which brings together advances and expertise in data collection, analysis, and numerical process modeling will make optimal use of newly available resources and will identify outstanding areas for future research.
Broader Impacts: A primary societal benefit of this work is its potential impact on our ability to predict long-term climate variability. Funds are included to support a postdoctoral researcher, who will gain exposure to novel datasets, data analysis techniques, and numerical studies. The project will benefit other investigators by supporting and promoting the use of the high-resolution drifter dataset as a new window on ocean dynamics. Analysis algorithms developed in this work will be freely distributed to the greater scientific community, by inclusion in JLAB, J. M. Lillys open-source software package for Matlab. The project will also fund two early career scientists.
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 30.00K | Year: 2011
Southern Ocean uptake of anthropogenic CO2 is currently estimated to be responsible for about 40% of the global oceanic CO2 uptake. Fluxes of CO2 into the ocean are driven by the differences in the partial pressure (pCO2) between the atmosphere and the surface ocean layer. As the surface ocean layers increase their pCO2 values, the uptake rate of the Southern Ocean should slow, unless other process (e.g. deep advection, surface cooling?) counteract this. Measurements of Southern Ocean pCO2 values over the past several decades have indicated a warming of the massive Antarctic Circumpolar Current (ACC) system, also leading to increasing surface pCO2. Upwelled water south of the various ACC fronts further brings increased (respired) pCO2 levels to the surface, but may be offset by poleward shifts in the strong westerly wind systems south of the fronts which encircle the Antarctic. Such shifts in the westerlies serve to reduce the area of the ocean over which pCO2 exchange can take place. The interplay of these different yet interacting physical factors is a useful diagnostic for the success of the next generation of climate-earth systems models in predicting future atmospheric CO2 concentrations, and the skill brought to future climate projections.
RAPID funding support will allow the examination of the variations, over decadal time sales, of the Southern Ocean pCO2 fields in the next variants of the Intergovernmental Panel on Climate Change (IPCC) coupled carbon/ climate models (earth system models) being produced as part of the next IPCC Assessment Report (IPCC AR5). Intercomparisons of Southern Ocean pCO2 trends over time, as revealed by in IPCC AR5 EaSMs, provides a way of assessing the skill of best available climate model predictions.
RAPID support is appropriate due to the short time window between the arrival of the model output in a publicly accessible archive and the deadline for papers analyzing the model output to be accepted for publication. AR5 chapter authors are prohibited from citing research which has not been accepted for publication in a peer-reviewed journal, and papers must be accepted by August 2012 in order to be referenced in the AR5.
Agency: NSF | Branch: Standard Grant | Program: | Phase: ANTARCTIC OCEAN & ATMOSPH SCI | Award Amount: 629.64K | Year: 2015
The Ross Ice Shelf is the largest existing ice shelf in Antarctica, and is currently stabilizing significant portions of the land ice atop the Antarctic continent. An ice shelf begins where the land ice goes afloat on the ocean, and as such, the Ross Ice Shelf interacts with the ocean and seafloor below, and the land ice behind. Currently, the Ross Ice Shelf slows down, or buttresses, the fast flowing ice streams of the West Antarctic Ice Sheet (WAIS), a marine-based ice sheet, which if melted, would raise global sea level by 3-4 meters. The Ross Ice Shelf average ice thickness is approximately 350 meters, and it covers approximately 487,000 square kilometers, an area slightly larger than the state of California. The Ross Ice Shelf has disappeared during prior interglacial periods, suggesting in the future it may disappear again. Understanding the dynamics, stability and future of the West Antarctic Ice Sheet therefore requires in-depth knowledge of the Ross Ice Shelf. The ROSETTA-ICE project brings together scientists from 4 US institutions and from the Institute of Geological and Nuclear Sciences Limited, known as GNS Science, New Zealand. The ROSETTA-ICE data on the ice shelf, the water beneath the ice shelf, and the underlying rocks, will allow better predictions of how the Ross Ice Shelf will respond to changing climate, and therefore how the WAIS will behave in the future. The interdisciplinary ROSETTA-ICE team will train undergraduate and high school students in cutting edge research techniques, and will also work to educate the public via a series of vignettes integrating ROSETTA-ICE science with the scientific and human history of Antarctic research.
The ROSETTA-ICE survey will acquire gravity and magnetics data to determine the water depth beneath the ice shelf. Radar, LIDAR and imagery systems will be used to map the Ross Ice Shelf thickness and fine structure, crevasses, channels, debris, surface accumulation and distribution of marine ice. The high resolution aerogeophysical data over the Ross Ice Shelf region in Antarctica will be acquired using the IcePod sensor suite mounted externally on an LC-130 aircraft operating from McMurdo Station, Antarctica. Field activities will include ~36 flights on LC-130 aircraft over two field seasons in Antarctica. The IcePod instrument suite leverages the unique experience of the New York Air National Guard operating in Antarctica for NSF scientific research as well as infrastructure and logistics. The project will answer questions about the stability of the Ross Ice Shelf in future climate, and the geotectonic evolution of the Ross Ice Shelf Region, a key component of the West Antarctic Rift system. The comprehensive benchmark data sets acquired will enable broad, interdisciplinary analyses and modeling, which will also be performed as part of the project. ROSETTA-ICE will illuminate Ross ice sheet-ice shelf-ocean dynamics as the system nears a critical juncture but still is intact. Through interacting with an online data visualization tool, and comparing the ROSETTA-ICE data and results from earlier studies, we will engage students and young investigators, equipping them with new capabilities for the study of critical earth systems that influence global climate.
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 544.22K | Year: 2012
Funds are provided to develop understanding of the mechanisms and magnitude of heat transport upward from the Atlantic Water (AW) in the eastern (>30oE) Eurasian Basin (EB), to the point where accurate projections can be made for varying lateral input of AW under different scenarios of large-scale climate variability. Specific objectives are:
O1. To evaluate and improve parameterizations of heat and salt fluxes due to double-diffusive convection (DDC) including the sensitivity of DDC heat fluxes to added velocity shear (e.g., mean flow, tides);
O2. To map the spatial distribution of DDC parameters using all available eastern Arctic microstructure, Ice-Tethered Profiler (ITP) and Conductivity-Temperature-Depth (CTD) data for 2007 and 2009;
O3. To estimate the spatial distribution of velocity shear using a 3D baroclinic, coupled ocean/sea-ice model including tide forcing;
O4. To evaluate the relative roles of turbulent mixing and DDC processes in shaping EB upward fluxes;
O5. To estimate impact of DDC and feedbacks with stratification and shear on the hydrographic structure of the EB (via modeling); and
O6. To estimate the lateral intrusive heat fluxes, assessing their role in ventilating the ocean interior.
The PIs propose advanced analyses of a suite of existing hydrographic data with fine vertical resolution ? microstructure, CTD, ITP and MacLane moored profilers ? taking advantage of the unique EB dataset collected over the recent decade by the international community. A high-resolution 3D regional ocean model with active sea ice will be used to quantify upper ocean shear from mean flow, eddies and tides, and provide a tool for investigating sensitivity of modeled fluxes to parameterizations of DDC, shear-induced turbulence, and DDC/shear coupling.
Agency: NSF | Branch: Standard Grant | Program: | Phase: | Award Amount: 70.09K | Year: 2012
Funds are provided for a numerical modeling study of ocean circulation and ocean-ice interaction in Nares Strait, a 500-km long channel that separates northwest Greenland from Ellesmere Island at the northern end of Baffin Bay. The research addresses both Arctic/sub-Arctic sea-ice and freshwater exchange through Nares Strait. The project is motivated by the observation that Nares Strait is a major conduit of freshwater and sea-ice exchange between the Arctic and sub-Arctic oceans. The PIs will combine a high-resolution regional numerical ocean circulation and sea-ice model, forced by output from a high-resolution regional atmospheric model, to study the ocean and sea-ice dynamics and circulation in Nares Strait. A key element of this study is the availability of a high-quality, multi-year observational data set for model evaluation and for inverse modeling that will allow development of an optimized circulation estimate for the entire strait. With this model they will test the sensitivity of Nares Strait throughflow (freshwater, sea ice, and Atlantic Intermediate Water) to projected changes in larger-scale climate factors.
Although Fram Strait, the opening between Greenland and Svalbard, is often assumed to provide the dominant exchange pathway between the Arctic and Atlantic Oceans, the narrower passages through the Canadian Archipelago provide a second pathway for flow from the Arctic to the Atlantic Ocean. This study will provide insight on the processes controlling the magnitude of these exchanges, which are believed to influence the formation of dense water in the Labrador Sea that then enters the Atlantic Ocean, contributes to the large scale circulation, and modulates climate.
Agency: NSF | Branch: Standard Grant | Program: | Phase: ANTARCTIC OCEAN & ATMOSPH SCI | Award Amount: 135.00K | Year: 2014
CMIP5, the Coupled Model Intercomparison Project (Phase 5) promotes a standard set of earth system model climate simulations in order to: i) evaluate how realistic our models are in simulating climate of the recent past, ii) provide projections of future climate change on two time scales, one near term (out to about 2035) and one long term (out to 2100 and beyond), and iii) understand some of the factors responsible for differences in model projections, including quantifying some key feedbacks such as those involving clouds and the carbon cycle. This project aims to analyse CMIP5 model output to assess the impacts of physical processes in the Southern Ocean that influences surface water pCO2 variation, and air-sea CO2 uptake.
Systematic model intercomparisons will be carried out to tackle three main questions: 1) How significant are the zonal variations
in surface ocean pCO2 throughout the entire Southern Ocean, hence, how representative are conditions in Drake Passage of ESMs in other areas of the Southern Ocean? 2) Does the rate of pCO2 increase in the surface waters of the Southern Ocean concur with the increase of total Dissolved Inorganic Carbon (DIC) upwelled to the ocean surface south of the fronts? 3) What physical processes can explain the excessive surface water pCO2 concentrations found near the Polar Front in half of the eight available ESMs?
Increased knowledge of future climate change is in the interest of the US.