Arndt, Stefanie

Haas, Christian

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Stefanie Arndt, Christian HaasSpatial variability and temporal trends of snowmelt processes on Antarctic sea ice observed by satellite scatterometersAlfred Wegener Institute Helmholtz Center for Polar and Marine ResearchTemporal evolution of surface propertiesocean  Antarctic snow ice ice	ocean	snow	 lead	atmosphere	melt	pond	Ice	and	snow	transport	(dri3)	Lateral	mel6ng	Bo9om		mel6ng/	freezing	Internal	mel6ng	Ice	thickness	Snow	depth	Snowfall	Flooding	Snow-ice	forma2on	Internal	snowmelt	Superimposed			ice	forma2on	snow	ice	Internal	ice	layers	Year-round snow cover Seasonal changes in snow properties dominated by ‣ Diurnal thawing and refreezing ‣ Internal snowmeltwinter spring summer autumn winterTemporal evolution of surface propertiesocean  Antarctic snow ice ice	ocean	snow	 lead	atmosphere	melt	pond	Ice	and	snow	transport	(dri3)	Lateral	mel6ng	Bo9om		mel6ng/	freezing	Internal	mel6ng	Ice	thickness	Snow	depth	Snowfall	Flooding	Snow-ice	forma2on	Internal	snowmelt	Superimposed			ice	forma2on	snow	ice	Internal	ice	layers	Year-round snow cover Seasonal changes in snow properties dominated by ‣ Diurnal thawing and refreezing ‣ Internal snowmeltwinter spring summer autumn winterObjective Deriving onset dates of seasonal snowmelt processes on Antarctic-wide scales and its inter-annual variabilitySnowmelt patterns from passive microwave observationsMethod: Analysis of diurnal variations in brightness temperature (passive microwave, 37 GHz, vert. pol.)Temporary Snowmelt Onset (TeSMO)Arndt et al., 2016 (JGR)Snowmelt patterns from passive microwave observationsMethod: Analysis of diurnal variations in brightness temperature (passive microwave, 37 GHz, vert. pol.)Key points Temporary snowmelt shows a latitudinal dependence Continuous snowmelt is usually 17 days after temporary snowmelt onset observed  Results indicate four characteristic melt typesTemporary Snowmelt Onset (TeSMO)Arndt et al., 2016 (JGR)Temporal evolution of radar backscatterERS QSCAT ASCATBased on Haas, 2001Temporal evolution of radar backscatterERS QSCAT ASCATwinter pre-meltsnowmelt autumn/winterTemporal evolution of radar backscatterERS QSCAT ASCATwinter pre-meltsnowmelt autumn/winterTemporal evolution of radar backscatterERS QSCAT ASCATSpatial variability of snowmelt onset datesFrom scatterometer dataFrom passive microwave observationsRegion Pre-melt Onset Snowmelt Onset Diurnal thawing-refreezing OnsetTemporary Snowmelt Onset (TeSMO)Southern Weddell Sea 27 Nov ± 25 days 16 Dec ± 19 days 19 Dec ± 13 days 21 Dec ± 11 daysNorthern Weddell Sea 24 Nov ± 16 days 06 Dec ± 16 days 09 Dec ± 9 days 13 Dec ± 11 daysBellingshausen Sea 01 Dec ± 29 days 04 Dec ± 27 days 19 Oct ± 20 days 19 Oct ± 28 daysAmundsen Sea 24 Nov ± 23 days 06 Dec ± 18 days 02 Dec ± 10 days 05 Dec ± 16 daysRoss Sea 11 Dec ± 18 days 15 Dec ± 17 days 13 Dec ± 8 days 16 Dec ± 10 daysAll regions 29 Nov ± 10 days 10 Dec ± 12 days 09 Dec ± 5 days 12 Dec ± 8 daysLatitudinal gradient in snowmelt onset dates ‣ North: warm-air advection  ‣ South: diminished warm-air advection and stronger heat loss at the snow surfaceMean snowmelt onset dates.Differences between Ku- and C-bandC-band: ‣ ERS and ASCAT scatterometers ‣ Frequency: 5.6 GHz Ku-band: ‣ QSCAT scatterometer ‣ Frequency: 13.4 GHzKu-band derived pre-melt and snowmelt onset dates are earlier by 25 and 11 daysERS QSCAT ASCATTime series of snowmelt onset datesNo significant trend in snowmelt onset dates but large inter-annual variabilityOnset dates from different sensorsEarlier from scatterometerLater from scatterometerScatterometer observations: ‣ Frequency: 5.6 and 13.4 GHz ‣ higher penetration depth  Passive microwave observations: ‣ Frequency: 37 GHz ‣ smaller penetration depth Snowmelt onset dates from scatterometers are earlier by 13 and 5 days than those from passive microwave observationsOnset dates from different sensorsEarlier from scatterometerLater from scatterometerScatterometer observations: ‣ Frequency: 5.6 and 13.4 GHz ‣ higher penetration depth  Passive microwave observations: ‣ Frequency: 37 GHz ‣ smaller penetration depth Snowmelt onset dates from scatterometers are earlier by 13 and 5 days than those from passive microwave observationsz z z zT (°C)0-15T (°C)0-15T (°C)0-15T (°C)0-15Pre-melt from scatterometersSnowmelt from Ku-band Snowmelt from Ku- and C-band Snowmelt from scatterometer and PMW observationsSnowmelt from scatterometer observationsSnowmelt from PMW observationsOnset dates from different sensorsHypothesis:  Different sensors respond to snow melt processes in different depths within the snow coverz z z zT (°C)0-15T (°C)0-15T (°C)0-15T (°C)0-15Pre-melt from scatterometersSnowmelt from Ku-band Snowmelt from Ku- and C-band Snowmelt from scatterometer and PMW observationstimeSummary➡ Retrieved snowmelt onset dates show a latitudinal dependence ➡ Correcting for sensor differences between Ku- and C-band scatterometers allows to compile a backscatter time series ➡ Snowmelt onset dates show no significant trend but a large inter-annual variability for the study period ➡ Using satellite remote sensing sensors with different signal frequencies might allow to describe snowmelt processes in different snow layers  ➡ Improvement of energy and mass budget calculations for the ice-covered Southern Ocean ➡ Knowledge gain on uncertainties and spatial variability of space-borne retrievals of sea-ice concentration, sea-ice thickness and snow depth z z z zT (°C)0-15T (°C)0-15T (°C)0-15T (°C)0-15Pre-melt from scatterometersSnowmelt from Ku-band Snowmelt from Ku- and C-band Snowmelt from scatterometer and PMW observations

Spatial variability and temporal trends of snowmelt processes on Antarctic sea ice observed by scatterometer observations

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