A Convective Model for the Weddell Polynya

Martinson, Douglas G.; Killworth, Peter D.; Gordon, Arnold L.

doi:10.1175/1520-0485(1981)011<0466:acmftw>2.0.co;2

Cited by 184 publications

(171 citation statements)

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“…In contrast to mechanisms discussed by Martinson et al (1981); Lemke (1987); Lemke et al (1990) or Timmermann et al (1999), preconditioning of the water column for polynya formation in our experiments is not associated with a shallow mixed layer. In their models, with reduced ocean dynamics, the creation of static instability through salt enrichment in a shallow mixed layer is the only mechanism that can lead to enhanced vertical mixing and increased heat transfer.…”

Section: Summary and Discussioncontrasting

confidence: 99%

“…± Atmospheric wind and temperature anomalies: while the e ect of ice export due to a divergent wind ®eld was found to be insu cient (Martinson et al 1981), the advection of anomalously warm air was recently suggested to be a contributing factor (van den Broeke 2000); ± Oceanic mixed-layer thickness and temperature anomalies: an unusually shallow mixed layer, related to localized upwelling, has been considered as a possible mechanism for triggering deep convection (Martinson et al 1981). Large warm subsurface eddies that were dected by Gordon and Huber (1984) support this idea.…”

Section: Introductionmentioning

confidence: 99%

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The effect of flow at Maud Rise on the sea-ice cover numerical experiments

Beckmann¹,

Timmermann²,

Pereira³

et al. 2001

Ocean Dynamics

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The role of seamounts in the formation and evolution of sea ice is investigated in a series of numerical experiments with a coupled sea ice±ocean model. Bottom topography, strati®cation and forcing are con®gured for the Maud Rise region in the Weddell Sea. The speci®c¯ow regime that develops at the seamount as the combined response to steady and tidal forcing consists of free and trapped waves and a vortex cap, which is caused by mean¯ow and tidal¯ow recti®cation. The enhanced variability through tidal motion in particular modi®es the mixed layer above the seamount enough to delay and reduce sea-ice formation throughout the winter. The induced sea-ice anomaly spreads and moves westward and a ects an area of several 100 000 km 2 . Process studies reveal the complex interaction between wind, steady and periodic ocean currents: all three are required in the process of generation of the sea ice and mixed layer anomalies (mainly through tidal¯ow), their detachment from the topography (caused by steady oceanic¯ow) and the westward translation of the sea-ice anomaly (driven by the timemean wind).

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Section: Summary and Discussioncontrasting

confidence: 99%

Section: Introductionmentioning

confidence: 99%

The effect of flow at Maud Rise on the sea-ice cover numerical experiments

Beckmann¹,

Timmermann²,

Pereira³

et al. 2001

Ocean Dynamics

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“…In the Antarctic, September is a period when the intriguing Weddell Sea polynya was prominently seen in early passive microwave satellite data during [1974][1975][1976] and to a lesser degree in 1973 (Martinson et al, 1981). Polynyas are semipersistent areas of open water within the ice pack driven either by persistent winds pushing ice away from a barrier such as land, fast ice, or an ice shelf (latent heat), or by upwelling ocean heat (sensible heat) (Morales Maqueda, et al, 2004).…”

Section: Nimbus I Satellite Datamentioning

confidence: 99%

New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

2013

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Abstract. Visible satellite imagery from the 1964 Nimbus I satellite has been recovered, digitized, and processed to estimate Arctic and Antarctic sea ice extent for September 1964. September is the month when the Arctic sea ice reaches its minimum annual extent and the Antarctic sea ice reaches its maximum. Images from a three-week period were manually analyzed to estimate the location of the ice edge and then composited to obtain a hemispheric estimate. Uncertainties were based on limitations in the image analysis and the variation of the ice cover over the three-week period. The 1964 Antarctic extent is higher than estimates from the 1979-present passive microwave record, but is in accord with previous indications of higher extents during the 1960s. The Arctic 1964 extent is near the 1979-2000 average from the passive microwave record, suggesting relatively stable summer extents during the 1960s and 1970s preceding the downward trend since 1979 and particularly the large decrease in the last decade. These early satellite data put the recently observed record into a longer-term context.

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“…This convective feature or`chimneya was believed related to recurrent polynyas observed from satellites in late winter during the mid-70s (Zwally et al, 1983). This discovery led to intensive observational and modelling work to describe deep convection and conditions necessary for polynya formation (Killworth, 1979;Martinson et al, 1981;Martinson, 1990;Gordon and Huber, 1990;Lemke et al, 1991). We shall examine conditions representative of the Weddell Sea.…”

Section: The Weddell Seamentioning

confidence: 99%

On the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice-covered mixed layer in winter

Rudels¹,

Friedrich

Hainbucher

et al. 1999

Deep Sea Research Part II: Topical Studies in Oceanography

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In high-latitude oceans with seasonal ice cover, the ice and the low-salinity mixed layer form an interacting barrier for the heat #ux from the ocean to the atmosphere. The presence of a less dense surface layer allows ice to form, and the ice cover reduces the heat loss to the atmosphere. The ice formation weakens the stability at the base of the mixed layer, leading to stronger entrainment and larger heat #ux from below. This heat transport retards, and perhaps stops, the growth of the ice cover. As much heat is then entrained from below as is lost to the atmosphere. This heat loss further reduces the stability, and unless a net ice melt occurs, the mixed layer convects. Two possibilities exist: (1) A net ice melt, su$cient to retain the stability, will always occur and convection will not take place until all ice is removed. The deep convection will then be thermal, deepening the mixed layer. (2) The ice remains until the stability at the base of the mixed layer disappears. The mixed layer then convects, through haline convection, into the deep ocean. Warm water rises towards the surface and the ice starts to melt, and a new mixed layer is reformed. The present work discusses the interactions between ice cover and entrainment during winter, when heat loss to the atmosphere is present. One crucial hypothesis is introduced:`When ice is present and the ocean loses sensible heat to the atmosphere and to ice melt, the buoyancy input at the sea surface due to ice melt is at a minimuma. Using a onedimensional energy-balance model, applied to the arti"cial situation, where ice melts directly on warmer water, it is found that this corresponds to a constant fraction of the heat loss going to ice melt. It is postulated that this partitioning holds for the ice cover and the mixed layer in the high-latitude ocean. When a constant fraction of heat goes to ice melt, at least one deep 0967-0645/99/$ -see front matter 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 7 -0 6 4 5 ( 9 9 ) 0 0 0 2 8 -4 convection event occurs, before the ice cover can be removed by heat entrained from below. After one or several convection events the ice normally disappears and a deep-reaching thermal convection is established. Conditions appropriate for the Weddell Sea and the Greenland Sea are examined and compared with "eld observations. With realistic initial conditions no convection occurs in the warm regime of the Weddell Sea. A balance between entrained heat and atmospheric heat loss is established and the ice cover remains throughout the winter. At Maud Rise convection may occur, but late in winter and normally no polynya can form before the summer ice melt. In the central Greenland Sea the mixed layer generally convects early in winter and the ice is removed by melting from below as early as February or March. This is in agreement with existing observations.

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A Convective Model for the Weddell Polynya

Cited by 184 publications

References 0 publications

The effect of flow at Maud Rise on the sea-ice cover numerical experiments

The effect of flow at Maud Rise on the sea-ice cover numerical experiments

New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

On the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice-covered mixed layer in winter

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A Convective Model for the Weddell Polynya

Cited by 184 publications

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The effect of flow at Maud Rise on the sea-ice cover  numerical experiments

The effect of flow at Maud Rise on the sea-ice cover  numerical experiments

New estimates of Arctic and Antarctic sea ice extent during September 1964 from recovered Nimbus I satellite imagery

On the parameterisation of oceanic sensible heat loss to the atmosphere and to ice in an ice-covered mixed layer in winter

Contact Info

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The effect of flow at Maud Rise on the sea-ice cover numerical experiments

The effect of flow at Maud Rise on the sea-ice cover numerical experiments