Reference
Arndt, S.; Willmes, S.; Dierking, W.; Nicolaus, N. (submi=ed, JGR): Timing and regional pa=erns of snowmelt on AntarcEc sea ice from passive microwave satellite observaEons.
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Regional pa2erns of snowmelt on Antarc:c sea ice based on passive microwave data
1 Alfred-Wegener-InsEtut Helmholtz-Zentrum für Polar- und Meeresforschung Bremerhaven, Germany
2 Universität Bremen, Germany
3 Universität Trier, Germany
* stefanie.arndt@awi.de
Stefanie Arndt1,2*, Sascha Willmes3, Wolfgang Dierking1, Marcel Nicolaus1
The be=er understanding of temporal variability and regional distribuEon of surface melt on Antarc:c sea ice is crucial for the understanding of atmosphere-ocean interacEons and the determinaEon of mass and energy budgets of sea ice. Since large regions of AntarcEc sea ice are covered with snow during most of the year, observed inter-annual and regional variaEons of surface melt mainly represent melt processes in the snow. In
this study we combine two approaches for observing both surface and volume snowmelt by means of passive microwave satellite data. The former is achieved by analyzing diurnal differences of the brightness temperature TB at 37 GHz, the la=er by analyzing the raEo TB(19GHz)/TB(37GHz). Moreover, we use both melt onset proxies to divide the AntarcEc sea ice cover into regions of characteris:c surface melt pa2erns.
Introduc:on
less
> 30/33 days ConEnuous Eme series of SIC > 70%
during melt season, 01 Oct to 31 Jan
Sea-ice
concentra:on SIC
> 70%
Diurnal varia:ons dTB in brightness temperature TB,37V
Diurnal varia*ons of 37 GHz ver*cal polarized brightness temperature (dTB) for one exemplary grid cell.
Threshold criteria
Threshold criteria
Melt transi:on retrieval
Spa:al and decadal variability of snowmelt pa2erns Conclusion and Summary Outlook
Classifica:on of dTB histograms into
MulE- modal
Uni- modal
DeterminaEon of
individual transiEon threshold as local minimum between first two modes
No significant diurnal surface variaEons
Melt onset detec:on
The date of melt onset is the first day of dTB/ XPGR exceeding the
respecEve
threshold for at least three
consecuEve days
Characteris:c surface types
(upper) Temporary and (lower) con*nuous
snowmelt onset detected from microwave
brightness temperature for the melt transi*on 2004/05. White areas indicate the maximal sea- ice-covered area of the previous year.
Classifica*on of Antarc*c sea ice into four characteris*c surface types from dTB and XPGR.
XPGR ≥ 1 Cross-polarized gradient ra:o XPGR
Cross-polarized gradient ra*o (XPGR) for one exemplary grid cell.
XPGR = TB(19GHz, H) TB(37GHz, V)
SensiEve to deeper snow melt
(leQ) Penguins and (right) autonomous snow depth buoys driQing with Antarc*c sea ice.
The regional pa=erns of dominant snow
processes and melt onset dates may be applied to improve:
§ EsEmates of AntarcEc-wide mass and energy budgets in the seasonal cycle
§ Seasonal analysis of habitat condi:ons for ice-associated organism
§ Retrieval of sea-ice thickness and associated ice volume from radar alEmetry
§ Results reveal four regimes with substan:al differences in their surface characterisEcs
§ Improvement of exis:ng snowmelt onset algorithms by
§ Individual dTB-thresholds
§ CombinaEon of different frequencies and polariza:ons of TB to allow for addiEonal descripEon of subsurface melt
§ Ongoing AntarcEc sea-ice advance triggered less by surface melt but rather by lateral/bo=om melt and dynamical atmospheric
variaEons
(a) Spa*al mean (solid line) and its standard devia*on (crosses) of the Temporary (TeSMO) and Con*nuous Snowmelt Onset (SMO), and (b) trend of accumulated days indica*ng temporary and (c) con*nuous melt from 1988/89 to 2014/15.
§ No significant trend in snowmelt onset from 1988/89 to 2014/15
§ Increase in
accumulated days
indicaEng conEnuous snowmelt in areas of increasing sea-ice
extent and vice versa
