1. David Prado Oct. 8 2012

2. Antarctic Sea Ice: 1972-1975 John N. Rayner and David A. Howarth 1979

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.

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).

9.  Based changes on a harmonic wave fit to the data (average outer boundary at 63.75 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 63.75 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).

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

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

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.

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

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

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 = 1023.9 kg m -3 P s = 300 kg m -3 P I = 915.1 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.

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

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.

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.

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.

42.  Laser echo energy reduction by clouds.

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: 28.05 km (50 o s) to 31.5 km (pole)  Spectral resolution: 19.225 to 19.457 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.