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David Prado Oct. 8 2012. Antarctic Sea Ice: 1972-1975 John N. Rayner and David A. Howarth 1979.

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Presentation on theme: "David Prado Oct. 8 2012. Antarctic Sea Ice: 1972-1975 John N. Rayner and David A. Howarth 1979."— Presentation transcript:

1 David Prado Oct

2 Antarctic Sea Ice: John N. Rayner and David A. Howarth 1979

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4  The use of Nimbus V (launch Dec. 11, 1972) to determine sea ice extent and variability. Important because Nimbus V is the first continuous monitoring polar orbiting satellite.

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6  Determine Minimum latitude/highest ice extent (MINL) and Maximum latitude/lowest extent (MAXL).  Based on 155K brightness isotherm (NASA measurements used to validate) is assumed to be 15% sea ice concentration.  15.5 mm emissivity values: ◦ Old ice – 0.8 ◦ First year ice – 0.95 ◦ Sea water – 0.4  All results are based on the extremes (Feb and Sept).

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9  Based changes on a harmonic wave fit to the data (average outer boundary at o S yielding approximately 12.5 million km 2 ).  First harmonic fits 70% of the winter change in sea ice.

10 > 70% of variance

11  Based changes on a harmonic wave fit to the data (average outer boundary at o S yielding approximately 12.5 million km 2 ).  First harmonic fits 70% of the winter change in sea ice.  Smooth varying of MAXL at 68 o to 69 o S and MINL at 60 o S.  Found pack ice to vary from ~3 to ~20 million km 2.

12  Transition from cold temperature (ice growth) to warm temperature (ice loss) is asymmetrical which is attributed to polynyas.  Very rapid ice edge retreat when polynyas form (up to 330 km/day).  MINL is reached at different times (clockwise pattern around pole).  General trends expected to be persistent from year to year (i.e., asymmetrical grow/decay cycle).

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19 ICESat measurements of sea ice freeboard and estimates of sea ice thickness in the Weddell Sea Zwally, H.J., Yi, D., Kwok, R., and Zhao, Y. 2008

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21  Determine F (freeboard – total surface elevation above local sea level) from ICESat measurements.

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23  Estimate sea ice thickness from F, densities (snow, water, sea ice), and snow depth (AMSR-E).  Compare distribution and velocity (AMSR-E) of sea ice for spatial/temporal patterns.

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25  Compute local sea level from ICESat. ◦ 20 km running average along track.

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27  Compute local sea level from ICESat. ◦ 20 km running average along track.  Compare local sea level areas (minimum elevations) to Envisat images.

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29  Compute local sea level from ICESat. ◦ 20 km running average along track.  Compare local sea level areas (minimum elevations) to Envisat images.  Calculate Freeboard (surface elevation about local sea level) for ICESat track.  Determine sea ice thickness based on density equation.

30 P w = kg m -3 P s = 300 kg m -3 P I = kg m -3 F = Freeboard height T s = Snow depth T I = Ice thickness

31  Compute local sea level from ICESat. ◦ 20 km running average along track.  Compare local sea level areas (minimum elevations) to Envisat images.  Calculate Freeboard (surface elevation about local sea level) for ICESat track.  Determine sea ice thickness based on density equation.  Create snow/ice property maps and histograms.

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33  Freeboard distribution shows similar pattern to sea ice thickness distribution (modified by snow depth). ◦ Very limited observations

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35  Freeboard distribution shows similar pattern to sea ice thickness distribution (modified by snow depth). ◦ Very limited observations  Thickness estimates show similar results to previous field observations in May-June but are less than field measurements in Oct-Nov.

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37  Freeboard distribution shows similar pattern to sea ice thickness distribution (modified by snow depth). ◦ Very limited observations  Thickness estimates show similar results to previous field observations in May-June but are less than field measurements in Oct-Nov.  Estimated deviation from geoid (EGM 96) showed a similar patterns for different years and seasons. ◦ Attribute deviation to uncertainties in static geoid.

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39  AMSR-E derived sea ice motion shows clockwise rotation during the study time period. ◦ This causes a “piling up” of thicker sea ice along the southern portion of the Antarctic Peninsula which is observed in all four periods. ◦ Thicker ice in the northern Weddell sea is multi- year ice being pushed away from the Peninsula by the clockwise movement.

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42  Laser echo energy reduction by clouds.

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44  Averaging over footprint (70m).  Ocean swell effects on pack ice field.  Snow properties (dielectric constant/density).

45  Satellite sensors from 1972/1975 to 2004/2005 ◦ Nimbus V (ESMR)  Spatial resolution: km (50 o s) to 31.5 km (pole)  Spectral resolution: to GHz ◦ ICESat (GLAS)  Spatial resolution: 70 m footprint 172 m along track spacing  Vertical error: 2 cm

46  Satellites have become highly specialized with improved precision.  Nimbus V was the first satellite to allow for study of Antarctic sea ice with near daily resolution.  Rayner and Howarth described general patterns and trends in the distribution of sea ice both spatially and temporally and calculated maximum and minimum sea ice area.  Zwally et al. demonstrated the ability of ICESat (laser altimeter) to estimate freeboard and sea ice thickness on a year round scale with greatly improved spatial coverage.


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