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Sea-ice mechanical weakening by ocean currents and winds: �Observations and statistics

Earth Observation and Climate Processes (EOCP)

S. Willmes, G. Heinemann, F. Schnaase

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Sea-ice mechanical weakening by ocean currents and winds: �Observations and statistics

Earth Observation and Climate Processes (EOCP)

S. Willmes, G. Heinemann, F. Schnaase

Sea-ice leads: When, where and WHY?

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Arctic sea ice

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2022 March 29

Source: meereisportal.de Sensor: AMSR2

Source: NASA EOSIDS worldview Sensor: MODIS

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Arctic sea ice: leads

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Source: meereisportal.de Sensor: AMSR2

2022 March 29

LeadScore, Reiser et al. (2020)

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Arctic sea ice: leads

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Source: meereisportal.de Sensor: AMSR2

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Arctic sea ice: leads

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Source: meereisportal.de Sensor: AMSR2

2022 March 29

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Arctic sea ice: leads

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Source: meereisportal.de Sensor: AMSR2

LeadMap, Reiser et al. (2020)

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Arctic sea ice: leads

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SIC, Reiser et al. (2020)

Source: meereisportal.de Sensor: AMSR2

2022 March 29

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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ArcLeads daily maps

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  • Daily binary lead maps (1 km²)
  • NOV-APR, 2002/03-2021/22
  • Cloud gaps
  • Pixel-based retrieval uncertainty

​

LEAD =

a significant, positive, local surface temperature anomaly (1x1 km²) in the cold winter sea ice

​

​

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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ArcLeads daily maps

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Lead Map 1x1 km²

Lead Fraction 5x5 km²

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Lead climatology overview

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Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Lead climatology overview

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No significant inter-annual trends!

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Trends for individual months?

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Regional monthly trends:

​

CA (NOV) +

LS (NOV) +!

ES (NOV) +

BS (APR) +

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BS (FEB) -

BK (MAR) -

CN (JAN) -!

CN (FEB) –

​

p<0.1

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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ArcLeads climatology

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IBCAO V4.0

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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ArcLeads climatology

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IBCAO V4.0

What drives these patterns?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Leads climatology

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Current velocity (cm/s)

What drives these patterns?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Leads climatology

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EKE (cm²/s²)

What drives these patterns?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Barents Sea

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Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Laptev Sea

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IICWG Oslo, 21-23 March 2023

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Chuckchi Sea

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IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Good metrics ... ?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Good metrics ... ?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Good metrics ... ?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Good metrics ... ?

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Coincident Percentile Exceedance (CPE)

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IICWG Oslo, 21-23 March 2023

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Ocean shaping lead dynamics

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Coincident Percentile Exceedance (CPE)

High frequencies in lead occurrence in regions of strong currents / current gradients along bathymetric features

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Winds shaping lead dynamics

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  • Wind speed has no influence on average lead frequency

​

  • Wind field divergence maximum coincides with Beaufort Sea lead area
  • Is the wind field more important in the short-term (days to weeks?)

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  • Does the ocean prime the sea-ice stability for break-up during strong wind events?

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IICWG Oslo, 21-23 March 2023

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Wind divergence and leads

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IICWG Oslo, 21-23 March 2023

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Wind divergence and leads

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IICWG Oslo, 21-23 March 2023

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Conclusions and discussion

  • Does the ocean act as a primer for sea-ice stability?
  • What‘s the individual role of ocean and atmosphere?
  • Does the ocean only react to local atmospheric forcing?
  • What is the individual contribution of dynamic vs. thermodynamic weakening?
  • Is this valuable information for forecasting and a description of mechanistic processes?

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  • Lead hot spots follow bathymetric features and associated current gradients
  • The temporal variability of the wind field divergence correlates with lead dynamics on the local scale (Beaufort Sea and Fram Strait)

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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TC paper

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https://tc.copernicus.org/preprints/tc-2023-22/

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IICWG Oslo, 21-23 March 2023

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Antarctic: PADOS project

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Patterns and Drivers of Sea-Ice Dynamics in the Southern Ocean

Current velocity

NEMO-LIM2 ocean-sea ice model, (Patara et al., GEOMAR)

Bathymetry; IBCSO

Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023

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Summary

Daily pan-Arctic lead data and climatologies, 2002-2022 NOV-APR

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Local drivers of lead dynamics:

  • Ocean processes determine „background activity“ (long-term influence) through currents. Tides yet to be analysed.
  • Atmosphere impacts short-term dynamics, mostly through wind divergence

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  • In-depth analysis pending, also for Antarctic sea ice (PADOS).
  • Comments welcome!

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Willmes et al., Patterns of Arctic sea-ice leads

IICWG Oslo, 21-23 March 2023