Applied Physics LaboratoryUniversity of WashingtonSeattle

Washington, United States

Applied Physics LaboratoryUniversity of WashingtonSeattle

Washington, United States
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Zhang J.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Kelly K.A.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

Seasonal and interannual-to-decadal variations of large-scale altimetric sea surface height (SSH) owing to surface heating and wind forcing in the presence of topography are investigated using simplified models. The dominant forcing mechanisms are time scale dependent. On the seasonal time scale, locally forced thermosteric height explains most of the SSH variance north of 18°N. First-mode linear long baroclinic Rossby waves forced by changes in the winds and eastern boundary conditions explain most of the variance between 10°N and 15°N and are also important east of Greenland. On interannual-to-decadal time scales, local thermosteric height remains important at several locations in the middle and high latitudes. A topographic Sverdrup response explains interannual-to-decadal SSH between 53°N and 63°N east of Greenland. Farther south, the linear Rossby wave model explains SSH variations on interannual-to-decadal time scales between 30°N and 50°N from mid-basin to the eastern boundary. Propagation of the eastern boundary condition into the interior dominates the interannual-to-decadal SSH signals south of 30°N. The effect from NAO-related heat flux on SSH is small, but forcing the topographic Sverdrup models with NAO-regressed winds gives slightly better agreement with the observed SSH in the subpolar gyre on interannual-to-decadal time scales than using the full winds. © 2016. American Geophysical Union. All Rights Reserved.


Shao A.E.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Mecking S.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Sonnerup R.E.,Joint Institute for the Study of the Atmosphere and OceansUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

An offline tracer transport model transport is used to simulate chlorofluorocarbon (CFCs), sulfur hexafluoride (SF6), oxygen, ideal age, and model transit time distributions (TTDs) to evaluate how well tracers can be used to constrain both the mean state and variability of oceanic ventilation. Using climatological transports, the two-parameter 1-D inverse Gaussian approximation of the model TTD is found to be an adequate representation of ventilation pathways within the parts of the subtropical gyres with simple ventilation dynamics, but a poor approximation for regions with large gradients in ideal age (i.e., near the base of the thermocline and the continental boundaries). TTDs inferred from CFC-12 and SF6 using a Peclet number-based lookup table approach yield poor representations of the model TTD with a consistent bias toward ventilation being strongly dominated by along-isopycnal diffusion. In a run with variable circulation, ideal age is used to track changes in thermocline ventilation. Variability in both apparent oxygen utilization (AOU) and tracer-inferred TTD mean ages inferred using CFC-12 (assuming fixed Peclet number) and dual tracers (SF6 and CFC-12) are well-correlated to ideal age variability in most of the thermocline. Changes in AOU are correlated with ideal age variability in even more regions compared to the TTD ages both horizontally and vertically down to intermediate depths. Generally, when changes in TTD mean age and AOU agreed in sign, correlations of both with ideal age changes were positive indicating the usefulness of tracers in diagnosing ventilation changes. © 2016. American Geophysical Union.


Zhang J.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

Early ice retreat and ocean warming are changing various facets of the Arctic marine ecosystem, including the biogeographic distribution of marine organisms. Here an endemic copepod species, Calanus glacialis, was used as a model organism, to understand how and why Arctic marine environmental changes may induce biogeographic boundary shifts. A copepod individual-based model was coupled to an ice-ocean-ecosystem model to simulate temperature- and food-dependent copepod life history development. Numerical experiments were conducted for two contrasting years: a relatively cold and normal sea ice year (2001) and a well-known warm year with early ice retreat (2007). Model results agreed with commonly known biogeographic distributions of C. glacialis, which is a shelf/slope species and cannot colonize the vast majority of the central Arctic basins. Individuals along the northern boundaries of this species' distribution were most susceptible to reproduction timing and early food availability (released sea ice algae). In the Beaufort, Chukchi, East Siberian, and Laptev Seas where severe ocean warming and loss of sea ice occurred in summer 2007, relatively early ice retreat, elevated ocean temperature (about 1-2°C higher than 2001), increased phytoplankton food, and prolonged growth season created favorable conditions for C. glacialis development and caused a remarkable poleward expansion of its distribution. From a pan-Arctic perspective, despite the great heterogeneity in the temperature and food regimes, common biogeographic zones were identified from model simulations, thus allowing a better characterization of habitats and prediction of potential future biogeographic boundary shifts. © 2016. American Geophysical Union. All Rights Reserved.


Iwasaki S.,Research Institute for Applied Mechanics | Lien R.-C.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

The response of the subpolar front in the Sea of Japan (also known as the East Sea) to winter cyclones is investigated based on quantitative analyses of gridded and satellite data sets. Cyclone passages affecting the sea are detected using time series of spatially averaged surface turbulent heat fluxes. As the cyclones develop, there are strong cold-air outbreaks that produce twice the normal heat loss over the sea. After removal of sea surface temperature (SST) seasonal trends, we found that cyclone passage (hence, cooling) mainly occurred over 3 days, with maximum SST reduction of -0.4°C. The greatest reduction was found along the subpolar front, where frontal sharpness (i.e., SST gradient) increased by 0.1°C (100 km)-1. Results of a mixed-layer model were consistent with both temperature and frontal sharpness, and localized surface cooling along the subpolar front resulted from both horizontal heat advection and turbulent heat fluxes at the sea surface. Further analyses show that this localized cooling from horizontal heat advection is caused by the cross-frontal Ekman flow (vertically averaged over the mixed layer) and strong northwesterly winds associated with the cold-air outbreak during cyclone passage. © 2016. American Geophysical Union.


Light B.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Carns R.C.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

The ice-albedo feedback mechanism likely contributed to global glaciation during the Snowball Earth events of the Neoproterozoic era (1 Ga to 544 Ma). This feedback results from the albedo contrast between sea ice and open ocean. Little is known about the optical properties of some of the possible surface types that may have been present, including sea ice that is both snow-free and cold enough for salts to precipitate within brine inclusions. A proxy surface for such ice was grown in a freezer laboratory using the single salt NaCl and kept below the eutectic temperature (-21.2°C) of the NaCl-H2O binary system. The resulting ice cover was composed of ice and precipitated hydrohalite crystals (NaCl · 2H2O). As the cold ice sublimated, a thin lag-deposit of salt formed on the surface. To hasten its growth in the laboratory, the deposit was augmented by addition of a salt-enriched surface crust. Measurements of the spectral albedo of this surface were carried out over 90 days as the hydrohalite crust thickened due to sublimation of ice, and subsequently over several hours as the crust warmed and dissolved, finally resulting in a surface with puddled liquid brine. The all-wave solar albedo of the subeutectic crust is 0.93 (in contrast to 0.83 for fresh snow and 0.67 for melting bare sea ice). Incorporation of these processes into a climate model of Snowball Earth will result in a positive salt-albedo feedback operating between -21°C and -36°C. © 2016. American Geophysical Union. All Rights Reserved.


Light B.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Dickinson S.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Perovich D.K.,Cold Regions Research and Engineering LaboratoryHanover | Holland M.M.,U.S. National Center for Atmospheric Research
Journal of Geophysical Research C: Oceans | Year: 2015

The albedo of Arctic sea ice is calculated from summertime output of twentieth century Community Climate System Model v.4 (CCSM4) simulations. This is compared with an empirical record based on the generalized observations of the summer albedo progression along with melt onset dates determined from remote sensing. Only the contributions to albedo from ice, snow, and ponds are analyzed; fractional ice area is not considered in this assessment. Key factors dictating summer albedo evolution are the timing and extent of ponding and accumulation of snow. The CCSM4 summer sea ice albedo decline was found, on average, to be less pronounced than either the empirical record or the CLARA-SAL satellite record. The modeled ice albedo does not go as low as the empirical record, nor does the low summer albedo last as long. In the model, certain summers were found to retain snow on sea ice, thus inhibiting ice surface melt and the formation or retention of melt ponds. These "frozen" summers were generally not the summers with the largest spring snow accumulation, but were instead summers that received at least trace snowfall in June or July. When these frozen summers are omitted from the comparison, the model and empirical records are in much better agreement. This suggests that the representation of summer Arctic snowfall events and/or their influence on the sea ice conditions are not well represented in CCSM4 integrations, providing a target for future model development work. © 2014. American Geophysical Union.


Drushka K.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Asher W.E.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Ward B.,National University of Ireland | Walesby K.,National University of Ireland
Journal of Geophysical Research: Oceans | Year: 2016

Rain falling on the ocean produces a layer of buoyant fresher surface water, or "fresh lens." Fresh lenses can have significant impacts on satellite-in situ salinity comparisons and on exchanges between the surface and the bulk mixed layer. However, because these are small, transient features, relatively few observations of fresh lenses have been made. Here the Generalized Ocean Turbulence Model (GOTM) is used to explore the response of the upper few meters of the ocean to rain events. Comparisons with observations from several platforms demonstrate that GOTM can reproduce the main characteristics of rain-formed fresh lenses. Idealized sensitivity tests show that the near-surface vertical salinity gradient within fresh lenses has a linear dependence on rain rate and an inverse dependence on wind speed. Yearlong simulations forced with satellite rainfall and reanalysis atmospheric parameters demonstrate that the mean salinity difference between 0.01 and 5 m, equivalent to the measurement depths of satellite radiometers and Argo floats, is -0.04 psu when averaged over the 20°S-20°N tropical band. However, when averaged regionally, the mean vertical salinity difference exceeds -0.15 psu in the Indo-Pacific warm pool, in the Pacific and Atlantic intertropical convergence zone, and in the South Pacific convergence zone. In most of these regions, salinities measured by the Aquarius satellite instrument have a fresh bias relative to Argo measurements at 5 m depth. These results demonstrate that the fresh bias in Aquarius salinities in rainy, low-wind regions may be caused by the presence of rain-produced fresh lenses. © 2016. American Geophysical Union.


Steele M.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Dickinson S.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research: Oceans | Year: 2016

In this work, we explore the seasonal relationships (i.e., the phenology) between sea ice retreat, sea surface temperature (SST), and atmospheric heat fluxes in the Pacific Sector of the Arctic Ocean, using satellite and reanalysis data. We find that where ice retreats early in most years, maximum summertime SSTs are usually warmer, relative to areas with later retreat. For any particular year, we find that anomalously early ice retreat generally leads to anomalously warm SSTs. However, this relationship is weak in the Chukchi Sea, where ocean advection plays a large role. It is also weak where retreat in a particular year happens earlier than usual, but still relatively late in the season, primarily because atmospheric heat fluxes are weak at that time. This result helps to explain the very different ocean warming responses found in two recent years with extreme ice retreat, 2007 and 2012. We also find that the timing of ice retreat impacts the date of maximum SST, owing to a change in the ocean surface buoyancy and momentum forcing that occurs in early August that we term the Late Summer Transition (LST). After the LST, enhanced mixing of the upper ocean leads to cooling of the ocean surface even while atmospheric heat fluxes are still weakly downward. Our results indicate that in the near-term, earlier ice retreat is likely to cause enhanced ocean surface warming in much of the Arctic Ocean, although not where ice retreat still occurs late in the season. © 2016. The Authors.


Steele M.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Dickinson S.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Zhang J.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Lindsay R.W.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research C: Oceans | Year: 2015

The seasonal evolution of sea ice loss in the Beaufort Sea during 1979-2012 is examined, focusing on differences between eastern and western sectors. Two stages in ice loss are identified: the Day of Opening (DOO) is defined as the spring decrease in ice concentration from its winter maximum below a value of 0.8 areal concentration; the Day of Retreat (DOR) is the summer decrease below 0.15 concentration. We consider three aspects of the subject, i.e., (i) the long-term mean, (ii) long-term linear trends, and (iii) interannual variability. We find that in the mean, DOO occurs earliest in the eastern Beaufort Sea (EBS) owing to easterly winds which act to thin the ice there, relative to the western Beaufort Sea (WBS) where ice has been generally thicker. There is no significant long-term trend in EBS DOO, although WBS DOO is in fact trending toward earlier dates. This means that spatial differences in DOO across the Beaufort Sea have been shrinking over the past 33 years, i.e., these dates are becoming more synchronous, a situation which may impact human and marine mammal activity in the area. Retreat dates are also becoming more synchronous, although with no statistical significance over the studied time period. Finally, we find that in any given year, an increase in monthly mean easterly winds of ∼1 m/s during spring is associated with earlier summer DOR of 6-15 days, offering predictive capability with 2-4 months lead time. © 2015. American Geophysical Union. All Rights Reserved.


Alkire M.B.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Morison J.,Applied Physics LaboratoryUniversity of WashingtonSeattle | Andersen R.,Applied Physics LaboratoryUniversity of WashingtonSeattle
Journal of Geophysical Research C: Oceans | Year: 2015

Fourteen years (2000-2014) of bottle chemistry data collected during the North Pole Environmental Observatory were compiled to examine variations in the composition of freshwater (meteoric water, net sea-ice meltwater, and Pacific water) over mixed layer of the Central Arctic Ocean. In addition to significant spatial and interannual variability, there was a general decrease in meteoric water (MW) fractions at the majority of stations reoccupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea-ice melt (SIM FW) between 2000 and 2012. Inventories (0-120 m) of MW and SIM FW computed using available data between 2005 and 2012 exhibited similar variations over the study area, allowing for first-order estimates of the mean annual changes in MW (-389±194 km3 yr-1) and SIM FW (292±97 km3 yr-1) for the Central Arctic region. These mean annual changes were attributed to the diversion of Siberian river runoff to the Beaufort Gyre and the overall reduction of sea ice volume across the Arctic, respectively. In addition to this lower-frequency variability, spatial gradients and interannual variations in MW, SIM FW, and Pacific water contributions to specific locations were attributed to shifts in the Transpolar Drift that advects waters of eastern and western Arctic origin through the study area. © 2015. American Geophysical Union.

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