230 research outputs found
Design and operation of automated ice-tethered profilers for real-time seawater observations in the polar oceans
An automated, easily-deployed Ice-Tethered Profiler (ITP) has been developed for deployment on perennial sea ice in polar oceans to
measure changes in upper ocean temperature and salinity in all seasons. The ITP system consists of three components: a surface
instrument that sits atop an ice floe, a weighted, plastic-jacketed wire-rope tether of arbitrary length (up to 800 m) suspended from the
surface instrument, and an instrumented underwater unit that profiles up and down the wire tether. The profiling underwater unit is
similar in shape and dimension to an ARGO float except that the float's variable-buoyancy system is replaced with a traction drive unit.
Deployment of ITPs may be conducted either from ice caps or icebreakers, utilizing a self contained tripod/winch system that requires no
power. Careful selection of an appropriate multiyear ice floe is needed to prolong the lifetime of the system (up to 3 years depending on
the profiling schedule). Shortly after deployment, each ITP begins profiling the water column at its programmed sampling interval. After
each acquired temperature and salinity profile, the underwater unit (PROCON) transfers the data and engineering files using an inductive
modem to the surface controller (SURFCON). SURFCON also accumulates battery voltages, buoy temperature, and locations from GPS at
specified intervals in status files, and queues that information for transmission at the start of each new day. At frequent intervals, an
Iridium satellite transceiver in the surface package calls and transmits queued status and CTD data files onto a WHOI logger computer,
which are subsequently processed and displayed in near-real time at http://www.whoi.edu/itp. In 2004 and 2005, three ITP prototypes
were deployed in the Arctic Ocean. Each system was programmed with accelerated sampling schedules of multiple one-way traverses per
day between 10 and 750-760 m depth in order to quickly evaluate endurance and component fatigue. Two of the ITPs are continuing to
function after more than 10 months and 1200 profiles. Larger motor currents are observed at times of fast ice floe motion when larger
wire angles develop and drag forces on the profiler are increased. The CTD profile data so far obtained document interesting spatial
variations in the major water masses of the Beaufort Gyre, show the double-diffusive thermohaline staircase that lies above the warm,
salty Atlantic layer, and many mesoscale eddys. Deployed together with CRREL Ice Mass Balance (IMB) buoys, these ITP systems also
operate as part of an Ice Based Observatory (IBO). Data returned from an array of IBOs within an Arctic Observing Network will provide
valuable real time observations, support studies of ocean processes, and facilitate numerical model initialization and validation.Funding was provided by the National Science Foundation under Contract Nos. OCE-0324233 and ARC-0519899
On the state dependency of fast feedback processes in (palaeo) climate sensitivity
Palaeo data have been frequently used to determine the equilibrium (Charney)
climate sensitivity , and - if slow feedback processes (e.g. land
ice-albedo) are adequately taken into account - they indicate a similar range
as estimates based on instrumental data and climate model results. Most studies
implicitly assume the (fast) feedback processes to be independent of the
background climate state, e.g., equally strong during warm and cold periods.
Here we assess the dependency of the fast feedback processes on the background
climate state using data of the last 800 kyr and a conceptual climate model for
interpretation. Applying a new method to account for background state
dependency, we find K(Wm) using the latest LGM
temperature reconstruction and significantly lower climate sensitivity during
glacial climates. Due to uncertainties in reconstructing the LGM temperature
anomaly, is estimated in the range K(Wm).Comment: submitted to Geophysical Research Letter
Judging distance across texture discontinuities
Sinai et al (1998 Nature 395 497 - 500) showed that less distance is perceived along a ground surface that spans two differently textured regions than along a surface that is uniformly textured. We examined the effect of texture continuity on judged distance using computer-generated displays of simulated surfaces in five experiments. Discontinuities were produced by using different textures, the same texture reversed in contrast, or the same texture shifted horizontally. The simulated surface was either a ground plane or a frontoparallel plane. For all textures and both orientations, less distance was judged in the discontinuous conditions than in continuous conditions. We propose that when a surface contains a texture discontinuity, a small area adjacent to the perceived boundary is excluded from judged distances
At Sea Test 2 deployment cruise : cruise 475 on board R/V Oceanus September 22 – 26, 2011 Woods Hole –Woods Hole, MA
The R/V Oceanus, on Cruise 475, carried out the deployment of three moorings for the
Coastal and Global Scale Nodes (CGSN) Implementing Organization of the NSF Ocean
Observatories Initiative. These three moorings are prototypes of the moorings to be used
by CGSN at the Pioneer, Endurance, and Global Arrays. Oceanus departed from Woods
Hole, Massachusetts on September 22, 2011 and steamed south to the location of the
mooring deployments on the shelf break. Over three days, September 23-25, Oceanus
surveyed the bottom at the planned mooring sites, deployed the moorings, and carried out
on site verification of the functioning of the moorings and moored hardware. Oceanus
returned to Woods Hole on September 26, 2011.Funding was provided by the National Science Foundation
through the Consortium for Ocean Leadershi
Acoustic and oceanographic observations and configuration information for the WHOI moorings from the SW06 experiment
This document describes data, sensors, and other useful information pertaining to the moorings that were
deployed from the R/V Knorr from July 24th to August 4th, 2006 in support of the SW06 experiment. The
SW06 experiment was a large, multi-disciplinary effort performed 100 miles east of the New Jersey coast. A
total of 62 acoustic and oceanographic moorings were deployed and recovered. The moorings were deployed in
a “T” geometry to create an along-shelf path along the 80 meter isobath and an across-shelf path starting at 600
meters depth and going shoreward to a depth of 60 meters. A cluster of moorings was placed at the
intersection of the two paths to create a dense sensor-populated area to measure a 3-dimensional physical
oceanography. Environmental moorings were deployed along both along-shelf and across-shelf paths to
measure the physical oceanography along those paths. Moorings with acoustic sources were placed at the outer
ends of the “T” to propagate various signals along these paths. Five single hydrophone receivers were
positioned on the across shelf path and a vertical and horizontal hydrophone array was positioned at the
intersection of the “T” to get receptions from all the acoustics assets that were used during SW06.Funding was provided by the Office of Naval Research under Contract
No. N00014-04-1014
Comparison of Early Model Forecasts With Satellite Data
The evaluation of hurricane forecast skill requires ensembles of historical forecasts. The purpose of this article is not to undertake such an evaluation, but rather to demon strate the current status of satellite physical retrievals and their potential to provide valu able information for such evaluations and contribute to model improvements. Predictions The hurricane in the ECMWF forecast, though, deviates by two to three degrees east of the best track, and makes landfall between Ala bama and Florida about 12 hours late. These differences in the hurricane track and accu mulated precipitation may reflect inadequa cies in the large-scale circulation provided in the initial conditions, or imperfect model physical parameterizations, but also may be due to the system's lack of predictability. Developments in Hurricane Forecasts Advances in spaceborne observations and numerical weather prediction (NWP) models provide new opportunities for improving hurricane forecasts. Apart from their impor tance for NWR global atmospheric models of hurricanes and their forecasts represent an important and unique test bed of model formulations. Recent developments that include moving from synoptic-scale-resolving to mesoscaleresolving global models show some very encouraging results. In addition to increasing resolution and including more physically based parameterizations on mesoscale effects in conventional general circulation models, cloud-scale-resolving global models-in which the cloud dynamics and mesoscale processes are explicitly resolved-also are being devel oped and could be used as a parallel approach to more realistically simulate hurricanes in global models in the future. Better resolution of the hurricane struc ture and larger-scale steering circulation, along with improved initial conditions pro vided by high-resolution satellite data and sophisticated data assimilation systems, could lead to better detection, monitoring, under standing, and prediction of the genesis and development of hurricanes that have such a devastating impact on society
Computational neural models of figure-ground segregation
Accepted manuscript2022-01-1
Middle Miocene Tectonic Boundary Conditions for Use in Climate Models
Utilizing general circulation models (GCMs) for paleoclimate study requires the construction of appropriate model boundary conditions. We present a middle Miocene paleotopographic and paleobathymetric reconstruction geographically constrained at 15 Ma for use in GCMs. Paleotopography and paleogeography are reconstructed using a published global plate rotation model and published geological data. Paleobathymetry is reconstructed through application of an age-depth relationship to a middle Miocene global digital isochron map, followed by the overlay of reconstructed sediment thickness and large igneous provinces. Adjustments are subsequently made to ensure our reconstruction may be utilized in GCMs
Evaluation of Arctic warming in mid-Pliocene climate simulations
Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2).
The PlioMIP2 ensemble simulates Arctic (60–90∘ N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 ∘C compared to the pre-industrial period, with a multi-model mean (MMM) increase of 7.2 ∘C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to −10.4×10^{6} km^{2}, with a MMM anomaly of −5.6×10^{6} km^{2}, which constitutes a decrease of 53 % compared to the pre-industrial period. The majority (11 out of 16) of models simulate summer sea-ice-free conditions (≤1×10^{6} km^{2}) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions, although the degree of underestimation varies strongly between the simulations. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regard to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that while reducing uncertainties in the reconstructions could decrease the SAT data–model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification than CMIP5 future climate simulations and an increase instead of a decrease in Atlantic Meridional Overturning Circulation (AMOC) strength compared to pre-industrial period. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change
A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2
The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and there is a clear pattern of polar amplification with warming polewards of 60° N and 60° S exceeding the global mean warming by a factor of 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, there is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (Equilibrium Climate Sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble earth system response to doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports
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