Arctic Field Projects

Project Title: Arctic Floats: A Pilot Effort for Arctic Argo (Award# 1643339)

PI: Nguyen, An T (
Phone: (512) 471.4207 
Institute/Department: U of Texas, Austin, Institute for Computational Engineering and Science (ICES) 
IPY Project?
Funding Agency: US\Federal\NSF\GEO\OPP\ARC\AON
Program Manager: Dr. William Ambrose (
Discipline(s): | Data Management |

Project Web Site(s):

Science Summary:
The Arctic Ocean plays an important role in regulating the world ocean's heat, and freshwater, and its nutrient cycles. Understanding, monitoring, and predicting how the Arctic Ocean changes as climate changes are thus imperative, but can only be achieved with a comprehensive observation network. The exceedingly successful global Argo program, which consists of roughly 3000 autonomous instruments distributed throughout the world ocean measuring physical properties of the upper 2000 m of the water column, has demonstrated how such a monitoring system can be maintained using low-cost autonomous profiling floats. Technological advancement has made it possible to deploy Argo-type floats in the deep Arctic basin, but sea ice reduces the floats’ ability to surface at regular intervals to determine their position and to transmit data to satellites. Using simulations, we will investigate uncertainties associated with extended "silent times" during which floats are unable to surface. We will determine the reduced accuracies in temperature and salinity measurements as a function of a float’s initial position and length of silent times. Use of auxiliary information to estimate the float's movements during silent times will also be explored. These simulations will help establish the likelihood that floats will report their positions after residing 1-5 years under ice and the number of floats that are needed to reduce the uncertainty in the measurement of water mass properties, helping us design a plan for using Arctic floats in the near future. This work leverages much of the high latitude satellite and in situ observations and the use of the Arctic Sub-polar gyre state estimate (ASTE) to extract as much information as possible on: (a) the uncertainty associated with operating near-future float technology, and (b) the geographic distribution of where new observations would have the most impact on better understanding the hydrographic changes occurring in the Arctic. We will quantify several metrics, related to the likelihood of a float’s surfacing-time as a function of time-mean and time-varying sea ice state, the float's associated position uncertainties, and the implied hydrographic uncertainties. The use of the observations and the state estimate are complementary in that ASTE can inform the initial design of the float deployment, and in turn future float data will be used to further constrain and improve ASTE.

Logistics Summary:
The project’s overarching goal is to assess the value of hydrographic measurements from Argo-type floats in the Arctic, given the constraint of reduced surfacing frequency in the presence of sea ice. With increasing time between two consecutive surfacing position un- certainty of intermediate partial profiling of the water column increases, which translates into increased inferred hydrographic uncertainties. Our goal is to quantify estimate the expected surfacing period as a function of position and sea ice coverage and the implied hydrographic uncertainties of profiles taken without surfacing. The project had five main thrusts: (1) develop a methodology to track synthetic Argo- type float trajectories under ice, (2) develop metrics to quantify accumulated error in float positions and implied hydrographic measurement uncertainties under ice, (3) quantify 3D geographic maps of uncertainty in hydrographic measurements, (4) quantify 2D map of likelihood of float surfacing frequency, (5) initial scientific analyses. No fieldwork is associated with this project.

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